The Kynix Blog

IntroductionA printed circuit board (PCB) mechanically supports and electrically connects electrical or electronic components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. A PCB allows signals and power to be routed between physical devices.What are PCBs? How Do PCBs Work?CatalogIntroductionⅠ PCB Basics1.1 PCB MaterialsⅡ PCB Product CharacteristicsⅢ Common Sense of PCB ProcessⅠ PCB Basics1.1 PCB Materialsa. Copper Clad Laminate（referred to as CCL, or sheet material）Tg: Glass Transition Temperature, which is the temperature at which glassy substances are transformed between glassy and highly elastic (usually softened). In the PCB industry, this glassy substance is generally referred to as resin or dielectric layer composed of resin and glass fiber cloth. Tg is an important technical index reflecting the heat resistance of printed circuit board substrates. Generally, the higher the Tg value of printed circuit boards, the better the heat resistance. The Tg of general FR-4 copper-clad epoxy glass laminates for SMT printed circuit boards is 130 ～ 140℃, which can meet the requirements when using Sn-Pn solder. For lead-free solders with higher melting points, the Tg of the substrate can not withstand the high temperature of welding if the Tg ≤ 150 ° C. In special cases (high temperature use), the Tg can be greater than 170 ° C. However, excessive Tg will cause the hardness of the substrate to increase and the material to become brittle. Therefore, we cannot simply pursue high Tg. We should comprehensively consider the performance of the board and choose a suitable printed board substrate with a higher Tg, which is one of the requirements for lead-free welding.CTI: Comparative Tracking lndex (or comparative leakage index, tracking index). The highest voltage value that the surface of the material can withstand 50 drops of electrolyte (0.1% ammonium chloride aqueous solution) without the formation of leakage traces. The unit is V.CTE: Coefficient of thermal expansion. Generally, the sheet material performance of a PCB is measured by the linear expansion coefficient, which is defined as the ratio of the increase in length to the original length under a unit temperature change, such as Z-CTE. The lower the CTE value, the better the dimensional stability and vice versa.TD: Thermal decomposition temperature refers to the temperature at which the base material resin loses weight by 5%. It is a sign of delamination and performance degradation caused by the heat of the base material of printed circuit boards.CAF: Conductive Anodic Filament of printed boards is the phenomenon of electrochemical insulation damage on insulating substrates. It refers to the state where dendritic metals are precipitated between wires under the action of an electric field after a voltage is applied to parallel circuits on printed circuit boards. Or conductive anodic filament(CAF) occurs along the glass fiber surface of the substrate, thereby reducing the insulation between the wires.T288: It is a technical index that reflects the welding resistance of the printed circuit board substrate. It refers to the maximum time that the printed circuit board substrate can withstand the high temperature of welding at 288°C without blistering and delamination. The longer this time, the better it is for welding. For traditional Sn-Pb alloys with low welding temperature (220 ～ 230℃), when the thermal decomposition time of printed circuit board substrate is 260 ℃, T260≥30s can meet the requirements of SMT printed circuit board. For lead-free welding, the temperature is generally 250 ~ 260℃, the thermal decomposition temperature of the substrate of the printed circuit board will increase, and only T288≥300s at 288 ℃ can ensure that the substrate does not decompose and the performance is not damaged during welding.DK: dielectric constant.DF: Dissipation factor refers to the ratio of the energy that has been lost in the insulation sheet material of the signal line to the energy that still exists in the line.OZ: oz is the abbreviation of the symbol ounce, which is British measurement unit and also unit of weight. 1 OZ means the thickness of copper with a weight of 1 OZ evenly spread over an area of 1 square foot (FT2). It is the average thickness of copper foil expressed by the weight per unit area. It is expressed by a formula, that is, 1OZ = 28.35g / FT2. b. Copper FoilED Copper Foil: Electrodeposited copper, copper foil commonly used in PCB, cheap.RA Copper Foil: Rolled annealed copper, copper foil commonly used in FPC.Drum Side: smooth side of electrodeposited copper foilMatt Side: rough side of electrodeposited copper foilCopper: Elemental symbol Cu, atomic weight 63.5, density 8.89 g / cm3, and the electrochemical equivalent of Cu2 + is 1.186 g / Ah. c. Prepreg: referred to as PPEpoxy Resin: an organic polymer compound containing two or more epoxy groups in the resin molecule, which is a resin component used in prepregs that are currently commonly used.DICY: Dicyandiamide, a common hardenerR.C: resin contentR.F: resin flowG.T: gel timeV.C: volatile contentHarden: Under certain conditions (high temperature, high pressure or light), the epoxy resin and the hardener undergo cross-linking polymerization to form a polymer with a three-dimensional mesh structure. d. InkViscosity: Viscosity refers to the relative movement between adjacent fluid layers when fluid is flowing, and frictional resistance will be generated between the two fluid layers. Unit: Pascal. Seconds (pa.s).Hardness: The hardness of the ink after pre-baking is 2B, the hardness of the ink after exposure is 2H, and the hardness of the ink after finishing is 6H. Thixotropic: a property that the ink is gelatinous when it is left to stand, but its viscosity changes when it is touched. It is a physical property of a liquid, that is, its viscosity decreases under agitation, and it will return to its original viscosity soon after standing. By stirring, the thixotropic effect lasts for a long time and it is enough to reconstitute its internal structure. To achieve high-quality screen printing, the thixotropic of the ink is very important. In particular, during the squeegee process, the ink is agitated to make it liquid. This action speeds up the speed of ink passing through the mesh, and promotes the original ink with separate wires to be evenly integrated. Once the squeegee stops moving, the ink returns to a stationary state, and its viscosity quickly returns to the original required data. e. Dry Film· Structure of dry film Figure 1. Structure of Dry Film· Dry film consists of three parts and ingredients:   — Supporting film(Polyester)   — Photo-resist dry film   — Covering film(Polyethylene)· Main ingredients① Binder(film-forming resin) ②Monomer ③Photo-initiator ④Plasticiser ⑤Adhesion promoter ⑥Thermal polymerization inhibitor ⑦Dye ⑧Solvent· The types of dry film are divided into three types according to the different methods of developing and removing the dry film: solvent-based dry film, water-soluble dry film, and peel-off dry film; according to the purpose of dry film, it is divided into: dry resist film, masking dry film and solder mask dry film.· Photosensitivity: It refers to the amount of light energy required for the photoresist to react to form a polymer with a certain resistance under the irradiation of ultraviolet light. In the case of constant light source intensity and light distance, the sensing speed is expressed as the length of exposure time. Short exposure time means that the sensing speed is fast.· Resolution: refers to the number of lines (or intervals) that can be formed by the dry film resist within a distance of 1mm. The resolution can also be expressed by the absolute size of the lines (or intervals). f. Net YarnNet density:— T number \ mesh number: refers to the number of meshes within 1 cm. g. Drill bit· geometry structure name of drill bitFigure 2. Geometry Structure Name of Drill Bit· Point AngleThe point angle is composed of two narrow and long first point angle surfaces and two triangular hook-shaped second point angle surfaces. These four sides meet at the point angle, forming two short edges called chisel edges at the center of the joint. This is the place that the sheet material first touches. This chisel edge is first positioned under pressure and rotation to drill into the stack. A protruding square strip on each of the two outer sides of the first point angle surface is called a margin. This margin tends to spiral upward along with the drill body part, which is the contact part between the drill pin and the hole wall. The right angle at the intersection of the margin and the edge lip is very important to the quality of the hole wall. The point angle has a long edge between the first and second point angle surfaces. The point where the two long edges and the two chisel edges meet in the middle is the point angle. The angle formed by the two long edges is called the point angle. When the drilling paper is made of phenolic resin substrate, the drill point angle is about 90° ~ 110° due to less resistance. When drilling paper is FR4 glass fiber board, the point angle should be slightly blunt at 115° ~ 135°. The most common one is 130°. The angle between the first point angle surface and the horizontal plane of the long edge is about 15°, which is called primary face angle. The second point angle is about 30°, and the angle formed by the chisel edge and the edge lip is called a cheisel edge angle. · Types of drill bitFigure 3. Types of Drill Bit Ⅱ PCB Product Characteristics1) Impedance· The sum of resistance and reactance (capacitance, inductive reactance) on a vector. Common impedance types are characteristic impedance and differential impedance.2) Warpage· Maximum bow (Figure a) and twist (Figure b) of printed circuit boards using surface mount components should be less than or equal to 0.75%3) RoHSRoHS, the abbreviation of restriction of hazardous substances, is the restriction of the use of certain hazardous substances in electrical and electronic equipment. RoHS lists a total of six harmful substances, including: lead(Pb), cadmium(Cd), mercury(Hg), hexavalent chromium( Cr6+), polybrominated diphenyl ether(PBDE), polybrominated biphenyl(PBB).4) BacklightIt is an enlarged visual inspection method to check the integrity of the copper wall of the through hole. The method is to carefully thin the substrate outside the hole wall from a certain direction, and then use the principle of resin translucency to shoot light from the back. If the quality of the chemical copper hole wall is intact and there is no any holes or pinholes, the copper layer must be able to block light and be dark in the microscope. Once there are holes in the copper wall, light spots must appear and be observed , and can be enlarged as photographic evidence. The ground sample is about 4-6mm wide.Figure 5. Backlight Standard Diageam5) Anode Phosphor Copper Ball· Purity requirementsElementContent(%)ElementContent(%)Cu≥99.91Ni≤0.002P0.040-0.06Sb≤0.002Pb≤0.002As≤0.002Fe≤0.0025S≤0.002Sn≤0.002O≤0.002 · Features— A black (or brown-black) film forms on the surface of phosphor copper after power is applied.— Black (or brown-black) film is Cu3P, also called phosphor copper anode film.· Role of phosphor copper anode film— The anode film itself can catalyze and accelerate the (Cu+-E → Cu2+) reaction, thereby reducing the accumulation of CU+.— After the anode film is formed, it can inhibit the continuous generation of Cu+.— The electrical conductivity of the anode film is 1.5X104-1 cm-1, which has metal conductivity.— Phosphor copper is less anodized than pure copper (1A / DM2 P0.04-0.065%, phosphor copper is less anodized than oxygen-free copper, 50MV-80MV) and will not cause anode passivation.— Anode film will greatly reduce the phenomenon of tiny grains falling off the anode.— Anode film prevents the copper anode from dissolving too quickly.6) Method for Estimating Surface Area of Electroplated Copper Anode· Method for estimating surface area of round titanium basket copper anode: pDLF/2p = 3.14 D = diameter of titanium basket L = length of titanium basket F = factor· Method for estimating surface area of square titanium basket copper anode: 1.33LWFL = length of titanium basket W = width of titanium basket F = factor· F is related to the diameter of the copper ball:Diameter = 12 mm    F = 2.2Diameter = 15 mm    F = 2.0 Diameter = 25 mm    F = 1.7Diameter = 28 mm    F = 1.6 Diameter = 38 mm    F = 1.27) ICD IssuesInternal Connection Defects Ⅲ Common Sense of PCB Processa. Etching FactorThe index used to consider the amount of etching lateral erosion, because the amount of lateral erosion will be different for different copper thickness, so the etching factor is different from the total copper thickness.Calculation method:b. Lateral ErosionThe etching of the side wall of the wire under the resist pattern is called lateral erosion, and the degree of lateral erosion is expressed by the width of the side etching:· lateral erosion is related to the type, composition and etching process and equipment of the etching solution. c. Pool EffectDuring the etching process, the circuit board passes through the etching machine horizontally. Due to the gravity acting on it, the fresh medicine is blocked by the old one and cannot effectively react with the copper surface. d. Different Stages of ResinsA-stage resin: Some thermosetting resins are liquid in the early stages of manufacture or liquid when heated, and can still dissolve in some liquids at this time.B-stage resin: Some thermosetting resins can soften when heated in the middle stage of the reaction, but they cannot be completely dissolved or melted. At this time, they can swell or partially dissolve when contacted with some solvents.C-stage resin: The later stage of the reaction of some thermosetting resins, when it is practically insoluble or infusible. e. Font Color of SubstrateRed font: flame retardant grade, other fonts: non flame retardant grade. f. OthersMSDS: Material Safety Data Sheet provides a variety of information on safety, health and environmental protection for chemical substances and products, and can provide information on basic knowledge, protective measures and emergency actions of chemicals. In some countries, MSDS is also called SDS, and SDS terminology is used in ISO 11014.SGS: Societe Generale de Surveillance S.A. Founded in 1887, it is currently the world's largest and oldest non-governmental third party engaged in product quality control and technical certification of multinational companies. Headquartered in Geneva, it has 251 branches around the world, 256 professional laboratories and 27,000 professional and technical personnel, and carries out product quality inspection, monitoring and assurance activities in 142 countries.UL: UNDER WRITERS LABORATORIES INCIPC: The Institute for International and Packaging Electronic CircuitsISO: International Standards OrganizationMIL: Military StandardJPC: Japan Printed Circuit AssociationCOV: Coefficient of variationFR4: Abbreviation for Flame Retardant Type 4. It is the name of a flame-resistant printed circuit board material composed of a composite material of glass fiber and epoxy resin. It is the most widely used printed circuit board. g. pH ValueAlso known as the hydrogen ion concentration index and pH value, it is a scale of the hydrogen ion activity in a solution, which is a measure of the acidity and alkalinity of a solution in the usual sense. The concept was proposed by Danish biochemist Søren Peter Lauritz Sørensen in 1909. P stands for German Potenz, which means strength or concentration, and H stands for hydrogen ion (H +). Sometimes pH is also written in Latin as pondus hydrogenii.Under normal conditions (25°C, about 298K), when pH <7, the solution is acidic, when pH> 7, the solution is alkaline, and when pH = 7, the solution is neutral. h. Hull Cell TestHull designed Hull cell in 1939. The Hull cell test only requires a small amount of plating solution. After a short time test, the plating effect of the plating solution can be obtained in a wide range of current density. Because this test is sensitive to the composition and operating conditions of the plating solution, it is commonly used to determine the concentration and pH value of each component of the plating solution, and to determine the current density range for obtaining a good coating. The Hull cell has become an indispensable tool for electroplating research and electroplating process control.Hull cells are usually made of insulating materials such as plexiglass or rigid polyvinyl chloride. The bottom surface is trapezoidal, and the cathode and anode are placed on two sides that are not parallel. There are five types of capacity: 250ml, 267ml, 320ml, 534ml, and 1000ml. Generally, 250ml plating solution is often added to a 267ml test cell, which is convenient for converting the additives into how many grams per liter.Figure 8. Dimensions of Hull Celli. Current Density A / dm2A/dm2 — how many amperes per square decimeter area, 1A / dm2 — This is the current density of electroplating, which means that the current passes through the plating area of the workpiece per square decimeter is 1A and dm means decimeter. Generally, we use a 267ml Hull cell, place the test piece at the cathode and immerse it in the test solution. The area of the test piece is approximately 1dm2. j. TP: THROUGH POWERCalculation method:k. Replacement ReactionA replacement reaction is a chemical reaction in which a simple substance reacts with a compound to form another simple substance and a compound. Any replacement reaction is a metathesis reaction, including a reaction of metal and metal salt, the reaction of metal and acid, etc.; the replacement reaction must be a redox reaction, and the redox reaction is not necessarily a replacement reaction; the replacement reaction occurs according to the active list of metals. l. EDS：Energy Dispersive X-ray SpectroscopyThe surface of the sample being tested is irradiated with a condensed electron beam. Due to the interaction between the electron beam and the sample, various electrons or X-rays, photons, and other information are generated. Then, this information is collected and processed in different ways to display various characteristics of the sample (morphology, microstructure, composition, crystal plane, etc.) m. SEM：Scanning Electron MicroscopeAn electron beam with a diameter of 20 mm to 30 mm emitted from the cathode of the electron gun is accelerated by the voltage between the cathode and the anode, and is directed toward the lens barrel, and is condensed by the condenser lens and the objective lens, and is reduced into an electron probe with a diameter of about several nanometers. Under the action of the scanning coil on the upper part of the objective lens, the electron probe scans the surface of the sample in a raster pattern and excites a variety of electronic signals. These electronic signals are detected by corresponding detectors, amplified, converted into voltage signals, and finally sent to the grid of the picture tube and modulate the brightness of the picture tube. The electron beam in the picture tube is also raster scanned on the phosphor screen, and this scanning movement is strictly synchronized with the scanning movement of the electron beam on the sample surface, so that a scanning electron image corresponding to the contrast and the intensity of the received signal is obtained. The image reflects the topographical features of the sample surface. n. BONDINGBonding is a wiring method in the chip production process. It is generally used to connect the chip's internal circuit with gold or aluminum wires to the package pins or gold-plated copper foil on the circuit board before packaging. Ultrasonic waves from an ultrasonic generator (generally 40-140KHz), which generates high-frequency vibration through the transducer, are transmitted to the splitter through the horn. When the splitter is in contact with the lead wire and the welded part, under the action of pressure and vibration, the surfaces of the metal to be welded rub against each other, the oxide film is destroyed, and plastic deformation occurs, causing the two pure metal surfaces to closely contact each other to achieve the combination of atomic distance, and finally form a strong mechanical connection. After bonding (ie, after the circuit is connected to the pins), the chip is packaged with black glue. o. The Giovanni EffectIt means that due to the potential difference between two metals, an electric current is generated through the medium, and then an electrochemical reaction occurs, and the anode with a high potential is oxidized. p. Vacuum Degree; Degree of VacuumThe degree of thinness of the gas under vacuum is usually expressed by "high vacuum" and "low vacuum", high vacuum indicates "good" vacuum, and low vacuum indicates "poor" vacuum. If the pressure in the device under test is lower than atmospheric pressure, a vacuum gauge is required for pressure measurement. The value read from the vacuum gauge is called the degree of vacuum. The degree of vacuum is a value indicating that the actual value of the system pressure is lower than the atmospheric pressure, that is: the degree of vacuum = atmospheric pressure-absolute pressureThere are usually two ways to identify the degree of vacuum:   — First, it is marked with "absolute pressure" and "absolute vacuum degree" (that is, how much pressure is higher than "theoretical vacuum"); in actual cases, the absolute pressure value of the vacuum pump is between 0 and 101.325KPa. The absolute pressure value needs to be measured with an absolute pressure meter. The initial value of the gauge (absolute vacuum gauge) for measuring the vacuum degree at 20°C and the place where the altitude = 0 is 101.325KPa (ie, a standard atmospheric pressure).   — The second is to use "relative pressure" and "relative vacuum degree" (that is, how much pressure is lower than "atmospheric pressure") to identify. "Relative vacuum degree" refers to the difference between the pressure of the measured object and the atmospheric pressure at the measurement site and is measured with an ordinary vacuum gauge. In the absence of vacuum (that is, at atmospheric pressure), the initial value of the gauge is 0. When measuring vacuum, its value is between 0 and -101.325KPa (usually expressed as a negative number).Commonly used vacuum units are Pa, Kpa, Mpa, atmospheric pressure, kilogram (Kgf / cm2), mmHg, mbar, bar, PSI, etc. The approximate conversion relationship is as follows:   — 1MPa = 1000KPa   — 1KPa = 1000Pa   — 1 atmospheric pressure = 100KPa = 0.1MPa   — 1 atmospheric pressure = 1 kg (Kgf / cm2) = 760mmHg   — 1 atmospheric pressure = 14.5 PSI   — 1KPa = 10mbar   — 1bar = 1000mbar Frequently Asked Questions about PCB Basic1. What is PCB and types of PCB?A printed circuit board (PCB) is a thin board made from fiberglass, composite epoxy, or other laminate materials. PCBs are found in various electrical and electronic components such as beepers, radios, radars, computer systems, etc. Different types of PCBs are used based on the applications. 2. What is the basis of PCB?PCB is the acronym of Printed Circuit Board, a mechanical base that contains tracks and footprints reflecting the schematic of the design. Modern PCBs are typically made of a non-conductive substrate that is overlayed by copper layers. 3. What are the basic steps of PCB design?Here's the full list of PCB layout and design steps:Create the Schematic.Create a Blank PCB Layout.Schematic Capture: Linking to Your PCB.Designing Your PCB Stackup.Defining Design Rules and DFM Requirements.Place Components.Insert Drill Holes.Route Traces. 4. What are the common types of PCB?Common Types of Printed Circuit BoardsSingle Layer PCB. Single layer printed circuit boards are among some of the simplest to design and manufacture. ...Double Layer PCB.Multi-Layer PCB.High Density Interconnect (HDI) PCB.High Frequency PCB. 5. Which material is used in PCB?copper circuitryPrinted circuit boards (PCBs) are usually a flat laminated composite made from non-conductive substrate materials with layers of copper circuitry buried internally or on the external surfaces. They can be as simple as one or two layers of copper, or in high density applications they can have fifty layers or more.

Ⅰ IntroductionAn operational amplifier, or op-amp for short, is fundamentally a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. Learn more about the most common opamp basics, essential knowledge when selecting and using an op amp in electronics. We can conclude our section and look at Op Amp basics with the following properties and questions. Opamp Basics: Op-Amp CircuitsCatalogⅠ IntroductionⅡ Amplifier Figures of MeritⅢ Q & AⅣ Application: LM358 Classic CircuitsⅡ Amplifier Figures of MeritNegative FeedbackIt is a important technique to improve bandwidth and distortion and control gain.Open-loop GainIt refers to the ratio of the voltage change at the output of the amplifier to the voltage change at the input when the amplifier input and output are open. Common-mode Rejection Ratio (dB)It is the ratio of the amplifier's amplification factor of the differential voltage signal to the amplification factor of the common mode voltage signal.Input Current NoiseIt is the equivalent current noise applied in parallel with the input of the noiseless amplifier.Output CurrentIt refers to the current driven by the load at the output of the op amp. It is usually a function: input overdrive, correlation between output voltage and power supply, temperature, source, and drain characteristics will differ.Phase MarginIt is the phase shift between an output of the same frequency and an inverting input in an open-loop circuit.Voltage GainIt is the ratio of the change in output voltage to the change in input voltage.Programmable Gain BufferIt can set the gain resistance of the op amp (integrated on the template), and the gain can be set to +1, +2, or -1 through simple external connections.Saturation VoltageIt is the voltage between the collector and emitter of the transistor under saturation conditions. In the saturated state, the emitter-base and collector-base are forward biased, so that the voltage between the collector-emitter is very low.Rise TimeThis refers to the time required for the output voltage to change from 10% of its final value to 90% of its final value.Unity-gain BandwidthIt refers to the frequency at which the amplifier's open-loop gain is equal to one. If the op amp frequency response has a single-pole roll-off, the unity-gain bandwidth is equal to 1UGBW.Strobe “OFF” VoltageThe strobe “OFF” voltage is the minimum voltage at the strobe pulse and is guaranteed not to interfere with the comparator operation.Input Current IndexIt refers to the average of the current drawn from the two input pins. In addition, the input current is also commonly called bias current.Gain Bandwidth ProductIt refers to the product of the amplifier's bandwidth and the gain at which the bandwidth is measured.Large Signal Voltage GainIt refers to the ratio of the change in output voltage to the change in input voltage. This parameter is usually specified at a large output voltage, smaller than the maximum output voltage, which is the typical value under direct current conditions.Offset Voltage Temperature CoefficientIt refers to the average rate of change in offset voltage due to changes in junction temperature within a specified temperature range.Output High VoltageIt refers to the high DC output voltage of the comparator, which produces the high output current. And it is usually related to the totem pole or push-pull output of the comparator.Input Source CurrentIt refers to the maximum output positive current produced under the comparator's push-pull output state.Total Harmonic Distortion (THD)When a pure sinusoidal signal is input to the op amp as Vin (w) = Vpsin (wt):Input harmonic distortion: Vout(w)a1Vpsin(wt)+a2Vpsin(wt)+...+anVpsin(nwt)The expression of THD is: THD(%)=[sqrt(a2xa2+a3xa3+...+anxan)/a1]x100Common-Mode Input Impedance (RINCM)It refers to the ratio of the change in the common-mode input voltage to the change in the input current at the inverting or non-inverting terminal.Output Low VoltageIt refers to a low DC output voltage. The output drive is a low voltage sink current. This specification is usually related to the totem pole or push-pull output of the comparator.Using a CMOS op amp as the output driver, although the circuit works well, but requiring a 1m shielded cable, and the oscillation of the operational amplifier is about 1MHz when there is no input signal. If shorten the cable to 10cm, the oscillation is stable.Some op amps are not suitable for driving capacitive loads directly, such as long shielded cables, which is a capacitive load. In addition, coaxial cables have about 60-100pF capacitance per meter.Harmonic DistortionIt refers to the unwanted spurious signals generated at the amplifier output due to the non-linearity of the signal line. When the input is a sinusoidal signal, these spurious signals will appear as integer times of the input frequency (for example, second harmonic, third harmonic).Output Leakage Current (ILEAKAGE)It means that the current enters the comparator output (the output is driven high). It often appears at the output of open collector and open drain.Power Supply Rejection Ratio (PSRR)It refers to the ratio of the change in the input offset voltage to the change in the power supply voltage, PSRR (dB) = 20log10 (DVOS / DVS)Linear Phase DeviationIt refers to how a closed-loop phase response of an operational amplifier approaches and follows the linear relationship between phase change and frequency in a specific frequency band.-3dbIt refers to the frequency when the value of the small signal output amplitude of the closed-loop amplifier decreases to 3dB.Common-mode Voltage RangeIt refers to the typical value of the voltage range at the input, which determines the performance of the amplifier.Specified Power Supply RangeIt describes the power supply voltage required for the operational amplifier to operate.Output Absorption CurrentIt refers to the highest output negative current of the comparator.Output Voltage SwingIt refers to the maximum peak-to-peak swing of the output voltage under a specific load and power supply voltage.Current FeedbackIt refers to a technology used in current feedback amplifiers whose output signal reflects the value of the current input to the inverting input (transimpedance gain function). In some aspects, this topology has operational advantages over traditional voltage feedback.Closed Loop BufferIt refers to an amplifier with high input impedance and low output impedance and a fixed gain of +1. Its typical applications are used for isolation, increased output drive, capacitive load, etc., in addition, there is no need to set the gain resistance.Closed-loop Gain It is the ratio of the change in the output voltage to the change in the input voltage after the feedback and input network added. Generally, this value is set using an external resistance.Common-mode RangeThe common-mode range, also known as the input voltage range, is a measure of the range of input voltages that the input pins of an op amp can accept. This specification is usually relative to the power supply amplitude.Output ImpedanceIt refers to the ideal series output impedance of the ideal operational amplifier when there is no impedance, which is the approximate output impedance of the op amp measured under AC  conditions.Transient ResponseIt refers to the step function response of the closed-loop system of the amplifier under the condition of small signal (usually less than 100mV).Slew RateWhen given a transition or square wave input, the amount of change in the amplifier's output from one level to another. Typical values are averages of values measured based on a change in total output voltage from 10% to 90%.Response TimeIt is the time interval when the input step function makes the output from the initial value to the logic threshold voltage.Unity Gain FrequencyIt refers to the frequency at which the gain of the voltage feedback op amp is 1 (0 dB). For an ideal operational amplifier, its gain-bandwidth product is equal.Intercept PointIt refers to the output power of the fundamental frequency, which is equal to the power value of the fundamental frequency in the specified distortion term (2nd, 3rd, or 3rd intermodulation).Input Offset CurrentIt refers to the current difference between the two inputs.Voltage OverdriveIt means that a certain amount of input step voltage exceeds the minimum drive input voltage required by the comparator to change from one logic level to the opposite logic level.Differential Gain & Differential PhaseDifferential gain refers to the change in the input and output of the gain, and differential phase refers to the phase change in the input stage. They are video measurements, and are a standard measurement in the broadcasting field to measure relative changes in the interpretation of video signal consistency.Voltage FeedbackA technique used in traditional operational amplifiers, where part of the output voltage is fed back to the input, and the voltage difference between the two inputs is amplified by the operational amplifier. Avol Open-loop Voltage Gain“A” is a sign of gain. The letter “V” written below indicates the gain of voltage, and the letter “ol” also written below is an abbreviation for open loop. Open-loop voltage gain refers to the gain (Vout / Vin) of the amplifier without feedback. Due to the existence of the bias voltage, these errors must be compensated.Logic Threshold VoltageIt refers to the voltage that causes the comparator output state to change when the input offset voltage is exceeded.Output ResistanceIt refers to the value of the series resistance at the output of an ideal op amp with zero output resistance, which measured under DC conditions.Gain FlatnessIt refers to the volume of gains “violently increasing” and “rapidly decreasing” in a given bandwidth range measured in decibels (dB), which affects the most important parameter specifications such as phase margin, gain margin, and closed-loop gain.Offset Current Temperature CoefficientIt refers to the average rate of change in deviation current due to changes in junction temperature within a specified temperature range.Input ImpedanceIt is the ratio of input AC voltage to input AC current.Input Voltage NoiseIt refers to the equivalent voltage noise in series with a noiseless amplifier.Input Offset VoltageIt is the product of the DC error voltage between the inputs and the closed-loop gain, because of the non-ideal balance between the input stage and the output is caused by the DC error voltage of the input terminals.Gain MarginOpen loop gain when the phase between the inverting input and output crosses zero at a certain frequency.Supply CurrentIt refers to the current required from the power supply to the unloaded amplifier and to the power supply at the output midpoint.Settling TimeIt refers to the time between the input step function initial value and the output voltage reaching the specified error band. The error band refers to the percentage of the total voltage change.Differential Input ResistanceIt is the ratio of the change in the input voltage to the change in the input current.Ⅲ Q & AQ1: What is the difference between a voltage feedback amplifier and a current feedback amplifier?A: The internal circuits of these two op amps are different. The voltage feedback op amp is restricted by the internal design, and it only has a very low input bias current, but there is no internal limit on the differential input voltage, because it is limited only when external feedback is required. In contrast, for a current feedback amplifier, its differential input voltage is subject to internal design, but it does not limit its input bias current, so it is limited only when external feedback is required.Q2: What is the difference between open and closed loops?A: The open loop gain is actually the internal gain of the op amp without feedback, and usually takes any value between 1,000 and 10,000. Closed loop gain is the gain of the entire circuit, which is equal to the open loop gain divided by 1 plus the loop gain (the improvement coefficient). In fact, the gain of the op amp when there is no feedback is the open loop gain, and the gain when feedback is considered is closed-loop gain.Q3: If the op amp has ideal AC characteristics, the Bode plot (gain-frequency response) is a unipolar system. What is the gain slip rate in dB / decade?A: In a unipolar system, the gain drops (or decreases) at 20dB / decade, which is 6dB / octave. This is responsive to any single pole, and it is also suitable for a simple RC filter or an ideal operational amplifier. However, because op amps have more high-frequency poles, the phase shift will begin to increase as the frequency approaches the unity gain frequency of the op amp.Q4: What is the difference between unity gain bandwidth, gain bandwidth product (GBP), and -3dB frequency?A: Many op amps have an open-loop gain reduction rate of -20db / decade when the frequency is stable. At any point during this descent phase, the GBW is a constant. If the unity-gain operation of the op amp is stable, then the unity-gain bandwidth, or the frequency at which the open-loop gain is 1, is usually equal to GBP. In addition, GBP is not equal to (usually higher than) the unity gain bandwidth. The -3dB frequency is a measure of the bandwidth of an operational amplifier when it is operating in a closed loop. The -3dB point is the frequency at which the gain of the overall closed-loop system drops by 3dB. The unity gain frequency for closed loop applications can be calculated using BW=GBP/Av. The -3dB frequency and unity-gain bandwidth applied depend on the feedback gain setting, output swing, load, and circuit layout.Q5: Why do some amplifiers oscillate with a capacitive load?A: The output impedance of the op amp and the capacitance of the capacitive load may form a resistance-capacitance oscillation. Also they form an R-C oscillation at the output stage, which causes additional phase lag in the feedback signal. CMOS amplifiers have a high output impedance which will cause the electrodes to be approached or lower the unity gain frequency of the op amp. The additional phase lag of the electrodes will weaken the phase margin of the op amp The total phase lag of the amplifier causes the phase angle of the unity gain frequency to increase by more than 180 degrees to cause the total feedback phase shift in unity gain to exceed 180. degree. In addition, the output impedance of a CMOS amplifier is between 100 and 500, causing a relatively low pole frequency. And meanwhile, the output impedance of the high-speed bipolar operational amplifier is in the range of 1 to 100, which causes the pole frequency to be much higher than that of the CMOS operational amplifier, so that the pole is far from the unity gain frequency of the device. The drive of a CMOS amplifier to a capacitive load can be improved by placing an output resistor at the output and an external positive feedback capacitor.Q6: If the output of the op amp stays close to the voltage rail, that is, the output rail, what is the reason?A: There are many ways for operational amplifiers to “rail”. The difficulty is keeping it away from the "rail". If the input exceeds the input voltage range, the output is usually near to a supply voltage rail. In theory, if the output exceeds the actual supply voltage, and a higher supply voltage is given, the op amp will go to rail output again. If there is no feedback or the polarity of the feedback is wrong, the op amp goes to rail output again. At the same time, if the non-inverting input is higher than the negative inverting input, the op amp also goes to rail output. The application of the operational amplifier should be analyzed to ensure that the power supply voltage used has a proper input and gain, so that in normal operation, its input voltage is within the rated value and the output voltage is within the normal range.Q7: What is the difference between the common-mode voltage and input voltage range of an op amp?A: Common mode voltage means that one voltage is applied to both inputs at the same time. Input voltage range is the range of voltages that can be accepted by the input pins. It is necessary to remember that the op amp should suppress the common-mode voltage, and amplify the difference between the two input pins only.Q8: The SPICE model of the bipolar operational amplifier works well, but the SPICE model of the CMOS operational amplifier does not work. Is there a need to set SPICE?A: To input the appropriate bias current to the model, the SPICE model applied on CMOS operational amplifier needs to set the default GMIN option to the largest SPICE package value.Q9: What is the difference between the amplifier's output current and short-circuit current?A: Short circuit current refers to the current generated by the device if the output is connected directly to the power line. This indicates that the output current is limited depending on the design of the device. However, the short-circuit current does not represent the true output of the drive capability of the output. Due to the impedance characteristics of the output stage, the maximum output current is determined by the swing of the output voltage under load. In facet, the smaller the load, the larger the output swing; the larger the load, the smaller the output swing.Q10: How to check the stability of an op amp circuit?A: Check the stability of the control loop, such as the pulse load and related changes in output voltage. The pulse load may be a load current with a pulse or step change, so that the output of the op amp circuit should be connected to a series R-C circuit. The greater the circuit swing or vibration, the worse the stability of the circuit.Q11: Are there any good ways to minimize noise when amplifying a low-level DC signal?A: To obtain a high signal-to-noise ratio, the circuit must be well designed. This includes choosing the best amplifier bandwidth and knowing the impedance of the input signal. If the input signal source has a fairly high impedance, it makes no sense to choose a low voltage noise amplifier, which has high current noise.Q12: How should design a low frequency (<1Hz) differentiator to minimize the output noise?A: The only reason that the output of the differentiator contains noise is because there is a lot of gain and the input is noisy. The traditional differentiator uses Rs-Cs in series at the input and the Rf-Cf in parallel near the operational amplifier. It is not necessary to try more Rs or Cf to minimize noise. The noise of the output come from the differentiator does not mean that it is harmful, because it also amplifies useful signals. In addition, if disconnect a loop, the differential output noise may be beneficial and will stabilize the loop. If the output of the differentiator is quite noisy or has too much input noise, analyze which are the real sources of them.Q13: How to protect the amplifier input from being higher or lower than the supply voltage?A: What must be done is either to clamp the input of the device, or to limit the input current of the device, or ideally, do both. The easiest way is to choose a current limiting resistor to limit this current. The selection is based on the fact that the current generated by the circuit input at the maximum input voltage is less than the maximum current rating of the input pin. Usually, a 1K to 100K resistor in series with this input pin is effective. However, since the signal is usually connected directly to a non-inverting input pin, a non-inverting amplifier may need a protective resistor connected to this pin. For high impedance circuits, a large resistor and or low leakage current diode can be used.Q14: What is the difference between a single-supply amplifier and a dual-supply amplifier?A: There is no difference in the actual circuit, layout, and characteristics of the amplifier. When an operational amplifier is designated as dual power supply, the output load is usually referenced to ground (GND), while a single power supply operational amplifier is usually referenced to the midpoint voltage of a single supply, and it is usually specified to operate on lower voltages, but this is not a necessary requirement. Therefore, whether the op amp is powered by a single 5V power supply and ground (GND), or powered by +2.5 and -2.5V, these is no different. Ⅳ Application: LM358 Classic CircuitsThis Video is Going to Show Top 5 Electronics Project Using OP-AMP LM358The LM358 includes two independent, high-gain, internal frequency-compensated dual operational amplifiers. It is suitable for single-supply operation with a wide range of power supply voltages. It is also suitable for dual-supply operation. LM358 applications include sensor amplifiers, DC gain modules and all other operational amplifiers that can be powered by a single power supply. The classic circuits of LM358 are as shown as following:Figure 1. Active DC-coupled Low Pass RC Filter Figure 2. LED Driver Figure 3. Transistor-Transistor-Logic (TTL) Drive Circuit Figure 4. Active RC Band Pass Filter Figure 5. Squareware Oscillator Figure 6. Hysteresis ComparatorFigure 7. Active Band Pass filter Figure 8. Lamp Driver Figure 9. Current Monitor Figure 10. Low Drift Peak Detector Figure 11. Voltage Follower Figure 12. Power Amplifier Peripheral CircuitFigure 13. Voltage Controlled Oscillator VCOFigure 14. Fixed Current Source Figure 15. Pulse Generator Figure 16. AC Coupled Non-inverting Amplifier Figure 17. AC Coupled Inverting Amplifier Figure 18. Adjustable Gain Instrumentation Amplifier Figure 19. DC Amplifier Figure 20. Pulse Generator Figure 21. Bridge Current Amplifier Figure 22. Introducing Differential Input Signal Figure 23. DC Differential Amplifier Frequently Asked Questions about Op Amps Basics1. What is an op amp basics for dummies?An op amp is a super-sensitive electronic amplifier circuit that's designed to amplify the difference of two input voltages. Thus, an op amp has two inputs and one output. ... Most op amps require both a positive and a negative voltage power supply, with voltages usually ranging from 6 V to 18 V. 2. What is the basic use of op amp?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 3. What is operational amplifier and its types?An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Op amps usually have three terminals: two high-impedance inputs and a low-impedance output port. 4. Which purpose the op amp is used?As the name suggests, the purpose of an amplifier or an op amp is to amplify or increase the input signal to produce an output signal which is much larger than that of the input, with a similar waveform as that of the input. The main change in the output signal will be the increase in the power level. 5. What does it mean when an op amp saturates?Originally Answered: What happens when an op-amp is saturated? that means the amplification or gain is so high as to make the output signal with a given input signal, so large as to exceed the compliance range of the power supply of the ope amp. More simply put, if you have an op amp supplied with +/-15V supply rails.

Ⅰ IntroductionAs we all know, capacitors have always played a very important role in electronic circuits. They are responsible for the coupling of signals in electronic circuits, the differentiation of volt-ampere characteristics in RC circuits, such as integration, the "channel" in oscillating circuits, bypass and power filter, etc. Aluminum electrolytic capacitor is made of anodized aluminum foil, corroded cathode aluminum foil and electrolytic paper in the middle, then impregnated with working electrolyte and sealed in aluminum shell. CatalogⅠ IntroductionⅡ Common problems of electrolytic capacitor  2.1 Why can't an aluminum electrolyte capacitor withstand reverse voltage?  2.2 What are the similarities and differences between nonpolar capacitance and polar capacitance?  2.3 What will happen when a polar capacitor is reversed?  2.4 The reverse connection of the polar capacitor will explode. Does it mean that it can't be directly connected to the AC power supply?  2.5 If the polarity capacitor is reversed, why is it short-circuited?  2.6 Why does the resistivity of electrolytic capacitor become smaller when the positive and negative poles are reversed?  2.7 Why can we only use a nonpolar capacitor in a pure AC circuit?  2.8 What is electrolytic capacitance?  2.9 The characteristics of electrolytic capacitors are as follows  2.10 What are the similarities and differences that cannot be ignored between polar and nonpolar capacitors in performance, principle and structure?Ⅲ SummaryⅣ FAQ Ⅱ Common problems of electrolytic capacitor2.1 Why can't an aluminum electrolyte capacitor withstand reverse voltage?Due to the polarity of electrolytic capacitors, it is necessary to pay attention to the correct connection of positive and negative electrodes in use, otherwise, not only the capacitors can not play a role, but also the leakage current is very large. In a short time, the inside of the capacitors will heat up, damage the oxide film, and then damage.  As shown in the figure, the basic structure of the aluminum electrolytic capacitor is composed of an anode, aluminum layer attached to the insulating medium, cathode aluminum layer of the receiving electrode and the real cathode composed of electrolyte. The electrolyte is soaked in the paper between the two aluminum layers. Aluminum oxide layer is plated on the aluminum layer, which is very thin compared with the voltage applied on it, and it is easy to be broken down, leading to capacitor failure. The alumina layer can withstand the forward DC voltage. If it bears the reverse DC voltage, it is easy to fail in a few seconds. This phenomenon is called the "valve effect", which is why the aluminum electrolytic capacitor has polarity. If both electrodes of the electrolytic capacitor have an oxide layer, the non-polar capacitor will be formed.Many articles report the mechanism of the threshold phenomenon of the reverse voltage of the aluminum electrolytic capacitor, which is called the hydrogen ion theory. When the electrolytic capacitor bears the reverse DC voltage, that is, the cathode of the electrolyte bears the positive voltage while the oxide bears the negative voltage, The hydrogen ions gathered in the oxide layer will pass through the medium and reach the boundary between the medium and the metal layer, and then they will be converted into hydrogen. And the expansion force of the gas causes the oxide layer to fall off. Therefore, the current flows directly through the capacitor after breaking through the electrolyte, and the capacitor fails. This DC voltage is very small. Under the reverse DC voltage of 1 ~ 2V, the aluminum electrolytic capacitor will immediately fail due to the hydrogen ion effect in a few seconds. On the contrary, when the positive voltage is applied to the electrolytic capacitor, the negative ions are concentrated between the oxide layers. Because the diameter of the negative ions is very large, they can not break through the oxide layer, so they can withstand higher voltage.2.2 What are the similarities and differences between nonpolar capacitance and polar capacitance?Are nonpolar capacitors the same as nonpolar electrolytic capacitors? Most kinds of capacitors are nonpolar, only the electrolytic capacitors have polarity. Among them, there are very special nonpolar electrolytic capacitors. Compared with ordinary capacitors, electrolytic capacitors have a larger capacity, lower price and smaller volume than other capacitors, but electrolytic capacitors generally have polarity, and their working reliability, withstand voltage, temperature resistance, dielectric loss and other indicators are not as good as other capacitors.The so-called non-polar electrolytic capacitor is actually the back-to-back packaging of two identical electrolytic capacitors. This kind of capacitor has large loss, low reliability and low voltage withstand, which can only be used in a few occasions with low requirements.2.3 What will happen when a polar capacitor is reversed?If the capacitance capacity is very small, the withstand voltage is very high, and the working voltage is low, there will be nothing wrong with the reverse connection. If the capacity is slightly large (above 100uF) and the withstand voltage is close to the working voltage, the capacitance can just work for nearly 10 minutes, then it will bulge and burst.2.4 The reverse connection of the polar capacitor will explode. Does it mean that it can't be directly connected to the AC power supply?It can't be connected to the AC power supply, because the polar capacitor is designed to be used in the DC power supply for filtering, and there is special material inside the polar capacitor, which can not bear the backpressure. If it is connected to the AC power supply, it will breakdown reversely or explode.2.5 If the polarity capacitor is reversed, why is it short-circuited?The internal structure of the polar capacitor is divided into the positive electrode, a dielectric layer and the negative electrode. The dielectric layer has the property of unidirectional conduction. Of course, the dielectric layer of the product will not play the role of insulation after being connected reversely, and the capacitor will be short-circuited. 2.6 Why does the resistivity of electrolytic capacitor become smaller when the positive and negative poles are reversed?It involves the principle of electrolytic capacitor. When the positive electrode of the capacitor is connected positively, a very thin oxide film (alumina) will be formed as the dielectric. When the negative electrode of the capacitor is connected reversely, H2 will be produced without forming the oxide film, and the other electrode will not form the oxide film which can be used as the dielectric due to different materials. 2.7 Why can we only use a nonpolar capacitor in a pure AC circuit?In the circuit of DC voltage superposing AC signal, if we can ensure that the lowest voltage after superposing will not become negative, we can use a capacitor with polarity. In the case of the same capacity, the volume and cost of the polar capacitor are far less than that of the nonpolar capacitor, so when we need a larger capacity, the volume of the capacitor is a big contradiction. We usually replace non-polar capacitors with polar ones, which not only solves the volume problem but also reduces the cost. Large capacitance can filter the AC signal with a lower frequency and above, while small capacitance can only filter the signal with higher frequency and above. 2.8 What is electrolytic capacitance?Electrolytic capacitor is a kind of capacitor. Its medium is coated with electrolytes. It can be divided into positive and negative electrodes and cannot be connected wrongly. The capacitance is composed of two metal poles and the insulating material (medium) sandwiched between them.2.9 The characteristics of electrolytic capacitors are as follows①The capacitance per unit volume is dozens to hundreds of times larger than other kinds of capacitance.②Rated capacity can easily reach tens of thousands of μ for even several F, but it is not as good as double electric layer capacitance.③The price is much lower than other kinds because the components of electrolytic capacitors are ordinary industrial materials, such as aluminum. The equipment for manufacturing electrolytic capacitors is also common industrial equipment, which can be mass-produced at a relatively low cost. Electrolytic capacitors are usually made up of metal foil (aluminum/tantalum) as the positive electrode, and the insulating oxide layer (alumina/tantalum pentaoxide) of metal foil as the dielectric. The negative electrode of aluminum electrolytic capacitor is composed of thin paper/film or electrolyte polymer soaked in electrolyte, the negative electrode of the tantalum electrolytic capacitor is usually manganese dioxide. As both of them use electrolytes as the negative electrodes, the electrolytic capacitor gets its name. The polar electrolytic capacitor usually plays the role of power filter, decoupling, signal coupling, the time constant setting, DC isolation and so on in the power circuit or IF and LF circuits. It can't be used in an AC power circuit. When it is used as a filter capacitor in the DC power circuit, its anode (positive) should be connected with the positive end of the power voltage, and the cathode (negative) should be connected with the negative end of the power voltage. It can't be reversed, or it will be damaged. 2.10 What are the similarities and differences that cannot be ignored between polar and nonpolar capacitors in performance, principle and structure? Polar capacitance is a kind of electrolytic capacitance. It consists of two electrodes formed by the anode aluminum foil and the cathode electrolyte. A layer of aluminum oxide film produced on the anode aluminum foil is used as the dielectric of capacitance. As a result of this structure, it has polarity. When the capacitance is directly connected, the aluminum oxide film will remain stable due to the electrochemical reaction. When the reverse connection is made, the aluminum oxide layer will become thinner, which makes the capacitor easy to be broken down and damaged.  Therefore, we must pay attention to the polarity of the electrolytic capacitor in the circuit. Ordinary capacitors are nonpolar. We can also connect two anodes or cathodes of electrolytic capacitors in series to form nonpolar electrolytic capacitors. ①The same principleThey both store and release charges.The voltage on the plate shall not change suddenly. (voltage here refers to the electromotive force of charge accumulation) ②Different mediaWhat's the medium? It's the material between the two plates of the capacitor. Most of the polar capacitors use electrolytes as a dielectric material, and the capacity of the polar capacitor is larger than that of the same volume. In addition, the capacity of the same volume of polar capacitance produced by different electrolyte materials and processes will be different. The withstand voltage of the capacitor is closely related to the dielectric materials used. There are also many dielectric materials for non-polar capacitance, most of which are metal oxide film, polyester and so on. The reversibility or irreversibility of dielectric determines the use environment of polar and nonpolar capacitors. ③Different performance.Performance and maximization of requirements are the requirements for use. If a metal oxide film capacitor is used for filtering in the power supply part of the TV set, and the capacity and withstand voltage of the capacitor should meet the requirements of filtering, a power supply must be installed in the shell. For a filter, only the polar capacitance can be used, which is irreversible. The positive terminal must be connected to the high potential terminal and the negative terminal to the low potential terminal. Generally, when the electrolytic capacitance is more than 1 microfarad, it is used for coupling, decoupling, power filtering, etc. Most of the nonpolar capacitors are below 1 microfarad, which participates in resonance, coupling, frequency selection, current limiting, etc. Large capacity and high withstand voltage capacitors are usually used for reactive power compensation, motor phase-shifting and frequency conversion power supply phase-shifting. There are many kinds of nonpolar capacitors. ④Different capacityFor capacitors of the same volume, when the medium is different, the capacity is also different. ⑤Different structureWe can use capacitors of any shape without considering the tip discharge. The polar capacitance is usually round, and there are few polar capacitances of square type. There are many shapes of nonpolar capacitors, including tube type, deformed rectangle, sheet type, square type, circular type, combined square type and circular type, and of course there are intangible ones. Here intangible refers to distributed capacitance.The distributed capacitance in HF and IF devices should not be ignored. The function is the same. The main difference is their capacity. Due to the influence of material structure, the capacity of non-polar capacitance is relatively small, generally below 10uF, while the capacity of polar capacitance is usually large. When filtering the power supply, you have to use a polar capacitor of large capacity. Ⅲ SummaryOne of the basic principles of circuit design is to require the designer to fully understand and master the real components. The components used should be standard parts, general parts, and the most common models on the market (the better the versatility of components, the easier the procurement, the larger the supplier's output, and the lower the procurement cost). For the components used in the drawings, if the materials can only be obtained by customization, the cost is certainly not low. If you can't get the customized material, this design is wastepaper. In addition, large capacitance is suitable for filtering low-frequency signals and small capacitance for filtering high-frequency signals. However, decoupling is only one function of capacitance. Different kinds of capacitance have different characteristics and usages. This aspect has a lot to do with experience. It is impossible to achieve it quickly. It can only be accumulated through practice. Ⅳ FAQ1. Which capacitor gives a long-term service: ceramic capacitors or aluminum and tantalum electrolytic capacitors?Electrolytics have a limited lifetime, 10,000 hours at high temps.Tantalums are really good capacitors, until they short out, whenever they feel like it.Ceramics tend to live the longest. 2. Why is aluminum used in electrolytic capacitors?Aluminum has been found to be among ideal materials for electrolytic capacitors due to the following reasons—1) It easily forms a thin oxide layer with a high dielectric constant.2) This layer can be formed in a wide range of thicknesses to suit different applications.3) The aluminum oxide layer can be formed and can withstand high voltages exceeding 400 V. Other materials Tantalum/ Niobium can only take small voltages of below 25 V. 4) Aluminum can be made into foil/ plate / formed into shape. In yesteryears, it was common to use shapes of this metal mechanically formed into different shapes.5) These properties allow high capacitor values for low and high voltages in small size.6) Most amenable to convenient manufacturing processes like winding, punching, forming (oxidation).7) Most abundant material on earth, hence very cheap.There are hardly any other materials that have these properties. 3. What is the role of aluminum electrolytic capacitors?Aluminum electrolytic capacitors are polarized capacitors because of their anodization principle. They can only be operated with DC voltage applied with the correct polarity. Operating the capacitor with the wrong polarity or with AC voltage leads to a short circuit and can destroy the component. 4. What happens if the electrolytic capacitor backward?Electrolytic capacitors are polar by nature and have positive and negative terminals clearly marked. If the polarity is reversed while connecting, the dielectric in the form of an oxide layer is damaged. A heavy current flows, a large amount of heat is generated, and the capacitor is damaged. 5. How do you determine the polarity of the Aluminium electrolytic capacitor?If the case is insulated, you can try applying a small bias voltage (3-5V) to the capacitor in each direction (through a current-limiting resistor of 100K or so) and see which direction allows the least current; this will be the correct polarity of the capacitor. 6. What are aluminum electrolytic capacitors used for?Especially aluminum electrolytic capacitors are used in many applications as decoupling capacitors to filter or bypass undesired biased AC frequencies to the ground or for capacitive coupling of audio AC signals. Then the dielectric is used only for blocking DC. 7. How long do aluminum electrolytic capacitors last?Today's aluminum electrolytic capacitors have a longer shelf life, usually around 2 years, as compared to their predecessors. For aluminum electrolytic capacitors, the changes in ESR, capacitance, and leakage current are caused by the chemical reactions between the aluminum oxide film and the electrolyte. 8. How do you read an electrolytic aluminum capacitor?The value of the capacitor is denoted in picofarads for ceramic, film, and tantalum capacitors, but for aluminum electrolytic capacitors the value is denoted in microfarads. For small values the letter R is used to denote a decimal point, e.g. 0R5 is 0.5, 1R0 is 1.0 and 2R2 is 2.2, etc. 9. How are aluminum electrolytic capacitors made?Aluminum electrolytic capacitors are made by layering the electrolytic paper between the anode and cathode foils and then coiling the result. The process of preparing an electrode facing the etched anode foil surface is extremely difficult. Due to this process, the electrolyte essentially functions as the cathode. 10. What are aluminum capacitors used for?Aluminum electrolytic capacitors (electrolytic) are widely used in power supply applications requiring high capacitance in energy-dense, small-volume packages having very low equivalent series resistance (ESR). 

Ⅰ IntroductionLithium batteries are a type of battery that uses lithium metal or lithium alloy as the cathode material and use a non-aqueous electrolyte solution. Lithium battery is an ambiguous term. In 1912, lithium metal batteries were first proposed and studied by Gilbert N. Lewis. In the 1970s, M. S. Whittingham proposed and began researching lithium-ion batteries. Due to the very active chemical properties of lithium metal, the processing, storage, and use of lithium metal require very high environmental requirements. With the development of science and technology, lithium batteries (broadly speaking) have now become mainstream. CatalogⅠ IntroductionⅡ HistoryⅢ Li & Li-ion Battery Features3.1 Advantages3.2 DisadvantagesⅣ Lithium Battery VS Lithium Ion Battery4.1 Lithium Batteries4.2 Li-ion BatteryⅤ ApplicationⅥ Battery Security6.1 Battery Storage6.2 Charging Rules6.3 Battery ExplosionⅦ Development ProspectsⅧ One Question Related to lithium metal & lithium ion Battery and Going Further8.1 Question8.2 AnswerⅡ HistoryIn the 1970s, M.S. Whittingham used titanium sulfide as the positive electrode material and metallic lithium as the negative electrode material to make the first lithium battery.In 1980, J. Goodenough discovered that lithium cobaltate could be used as a cathode material for lithium-ion batteries.In 1982, R.R.Agarwal and J.R.Selman of the Illinois Institute of Technology discovered that lithium ions can be embedded into the graphite, which is fast and reversible. At that time, lithium batteries made of metal lithium have attracted much attention because of their safety issues. Therefore, people tried to embed lithium ions to graphite to make rechargeable batteries. Finally, first available lithium-ion graphite electrode was successfully trial-produced by Bell Labs.In 1983, M. Thackeray, J. Goodenough, and others found that manganese spinel is an excellent cathode material, which has good properties of low cost, stability, and excellent electrical and lithium conduction. Its decomposition temperature is high, and its oxidizing property is far lower than that of lithium cobaltate. Even if having a short circuit or overcharge, combustion and explosion can be avoided as far as possible.In 1989, A. Manthiram and J. Goodenough discovered that a positive electrode using a polymeric anion would generate a higher voltage.In 1991 Sony released the first commercial Li-ion battery. Subsequently, lithium-ion batteries revolutionized the development of consumer electronics. For example, the weight and volume of portable electronic devices such as mobile phones, notebooks, and calculators has greatly reduced.In 1996, Padhi and Goodenough discovered that phosphates with an olivine structure, such as lithium iron phosphate (LiFePO4), are more superior than traditional cathode materials, and  become the mainstream cathode materials gradually.Lithium batteries were first used in pacemakers. Lithium batteries have the advantages of low self-discharge rate and gentle discharge voltage, so that the pacemaker implanted in the human body can operate for a long time without recharging. Lithium batteries generally have a nominal voltage higher than 3.0V, making them more suitable as integrated circuit power supplies.To develop a new better lithium battery, various materials have been researched and tested. Ⅲ Li & Li-ion Battery Features3.1 Advantages1) High energy density. With high storage power density, it has reached 460-600Wh / kg, which is about 6-7 times that of lead-acid batteries. It is one of the major advantages of lithium ion battery technology. For example, high energy-dense 18650 cells can deliver over 3,000mAh and the costs have dropped further today.2) Long cycle life, the service life can reach more than 6 years. For example, the battery 1C (100% DOD) with lithium ferrous phosphate as the positive electrode is charged and discharged about 10,000 times.3) High rated voltage, a single battery working voltage is 3.7V or 3.2V, which is approximately equal to the series voltage of 3 Ni-Cad or Ni-MH rechargeable batteries, in addition, it is convenient to form a battery power pack. What’s more, lithium batteries can use a new type of voltage regulation technology to adjust the voltage to 3.0V to suit the use of small appliances.4) High power resistance capacity. For example, phosphate lithium-ion battery for electric vehicles can reach 15-30C charge and discharge capacity, which is convenient for high-intensity startup acceleration.5) Low self-discharge rate. It is one of the most outstanding performances of the battery, which can generally be less than 1% per month, and it is much lower than that of other rechargeable cells such as Ni-Cad and NiMH batteries.6) Light weight, about 1 / 6 to 1 / 5 of lead acid products under the same volume.7) Good performance at high and low temperature. For example, the battery can be used in the environment of -20 ℃ ~ 60 ℃, after processing, it can be used in the environment of -45 ℃.8) Less harm to environment. Regardless of production, use and scrap, it does not contain or produce any toxic and harmful heavy metal substances, such as lead, mercury, cadmium.9) There are several types available. It means that the right technology can be used for the special application required. 3.2 Disadvantages1) Lithium primary batteries have poor safety and risk of explosion.2) Li-ion batteries (lithium cobaltate) cannot be discharged at high currents.3) Li-ion batteries need protecting circuit to prevent the battery from being overcharged and over discharged.4) Li-ion batteries will only last two or three years from the date of manufacture whether you use them or not.5) High production requirements and costs.6) Limited use conditions, because they are extremely sensitive to temperature.7) As for air transportation/travel, many airlines limit the number of lithium ion batteries they take.Ⅳ Lithium Battery VS Lithium Ion Battery4.1 Lithium Batteries4.1.1 ChemistriesLithium batteries are primary batteries that have metallic lithium as an anode, and metallic lithium or other alloy metals used as cathode, regarded PP or PE film as the the separator.Note: Discharge reaction: Li+MnO2=LiMnO2They have low self-discharge rate, annual self-discharge can be ≤1%. The service life of fully sealed (metal welded, lazer seal) batteries up to 10 years, and semi-sealed batteries are generally 5 years.Lithium metal is used as the negative electrode, and the positive electrode and the electrolyte are thionyl chloride (sulfoxide). Cylindrical batteries have electricity after assembly. The voltage is 3.6V, which is one of the most stable types of batteries. It is suitable for use on electronic instruments and equipment that cannot be maintained frequently, providing subtle current. 4.1.2 Battery StructureLithium batteries usually come in two shapes: cylindrical and square. The inside of the battery is a spiral winding structure, and a very fine and highly permeable polyethylene film separator is used to separate the positive and negative electrodes. The positive electrode contains a current collector composed of lithium cobaltate (or nickel-cobalt lithium manganate, lithium manganate, lithium ferrous phosphate, etc.) and the aluminum foil. The negative electrode consists of a current collector composed of graphitized carbon material and the copper foil. The battery is filled with an organic electrolyte solution. It is also equipped with a safety valve and a PTC element (partially cylindrical) to protect the battery from damage during abnormal conditions and output short circuits. 4.1.3 Battery Material AnodeThere are many choices of anode materials, for example, LiFePO4 is mostly used as mainstream products.  Chemistry ReactionThe lithium ion is embedded when discharge, and de-embedded in the charge.On Charge：LiFePO4 → Li1-xFePO4 + xLi+ + xe-On Discharge：Li1-xFePO4 + xLi+ + xe- → LiFePO4 CathodeGraphite is commonly used, and new research has found that titanate may be a better material. Chemistry ReactionThe lithium ion is de-embedded when discharge, and embedded in the charge.On Charge：xLi+ + xe- + 6C → LixC6On Discharge：LixC6→ xLi+ + xe- + 6C Conductive CoatingThe conductive coating is also called pre-coating. In industry, it usually refers to a layer of conductive coating applied to the surface of the positive electrode current collector-aluminum foil. The earliest experiments on aluminum foil in batteries can be traced back to the 1970s. With the development of new energy industry, especially the development of LiFePO4 batteries, it has become a hot new technology in the industry.The conductive coating can effectively improve the adhesion of the pole pieces in the lithium battery, reduce the amount of binder used, and also significantly improve the battery's electrical performance:1) Contact resistance decreases 40%2) Adhesive reduces 50%3) Battery voltage increases 20%at the same magnification.Material and current collector adhesion increases 30%, and no delamination after long-term cycling.In addition, carbon coated aluminum foil is another coating which made of conductive carbon-based composite paste and high-purity electronic aluminum foil by transfer coating process. 4.1.4 Shell CharacteristicsTo improve safety and voltage, scientists have invented materials such as graphite and lithium cobaltate to store lithium atoms. The molecular structure of these materials forms nano-scale small storage lattices that can be used to storage. In this way, even if the battery case is broken and oxygen enters, the oxygen molecules will be too large to enter these small storage cells, so that lithium atoms will not react with the oxygen to avoid explosion.  4.2 Li-ion Battery4.2.1 TerminologyLithium-ion battery is a type of batteries with non-aqueous electrolyte that uses lithium alloy metal oxides as anode material, graphite as cathode material.Li-ion batteries currently include liquid lithium-ion batteries (LIB) and polymer lithium-ion batteries (PLB). Among them, the liquid lithium ion battery refers to a secondary battery whose Li + is compound. The positive electrode uses lithium cobaltate and lithium manganate, and the negative electrode uses a lithium-carbon interlayer compound. Li-ion batteries have advantages of high operating voltage, small size, light weight, high energy, no memory effect, no pollution, small self-discharge, and long cycle life. Note:Reaction on anode: LiCoO2==Li(1-x)CoO2+XLi++Xe-(electron)Reaction on cathode: 6C+XLi++Xe- = LixC6Total reaction: LiCoO2+6C = Li(1-x)CoO2+LixC6Its practicality has greatly reduced the weight and volume of portable electronic devices such as mobile phones and notebook computers, and the using time is greatly extended. Because lithium-ion batteries do not contain heavy metal cadmium, compared with nickel-cadmium batteries, the environmental pollution is greatly reduced. 4.2.2 Li-ion Battery Characteristics High energy densityThe weight of a Li-ion battery is half that of a nickel-cadmium or nickel-hydrogen battery of the same capacity, and the volume is 20-30% of a nickel-cadmium battery and 35-50% of a nickel-hydrogen battery. High voltageThe operating voltage of a lithium-ion battery cell is 3.7V (average value), which is equivalent to three nickel-cadmium or nickel-metal hydride batteries connected in series. Small pollutionLi-ion batteries do not contain harmful metal substances such as cadmium, lead, and mercury. No lithium metalLi-ion batteries do not contain metallic lithium, so they are not subject to the ban imposed by airlines of carrying lithium batteries in passenger aircraft. Long cycle lifeUnder normal conditions, the charge-discharge cycle of a lithium-ion battery can exceed 500 times, and a iron phosphate battery can reach 2000 times. No memory effectThe memory effect refers to the phenomenon that the capacity of the battery decreases during the charge and discharge cycle of the nickel-cadmium battery. Lithium-ion batteries do not have this effect. Quick chargeUsing a constant current & voltage charger with a rated voltage of 4.2V, the lithium-ion battery can be fully charged in 1.5 ~ 2.5 hours; and the newly developed lithium iron phosphate battery can be fully charged in 35 minutes. 4.2.3 Matters of UseKeeping lithium-ion batteries regularly charged and discharged can extend battery life. Lithium-ion battery power is maintained at 10% ~ 90% is better for the battery. This means that you don't need to reach 100% when charging batteries for digital products such as mobile phones and laptops. Under normal circumstances, 50% of the power is best for lithium-ion battery storage.When digital products equipped with lithium-ion batteries are exposed to sunlight or stored in hot cars, it is best to turn these products off because lithium-ion batteries will age faster if the operating temperature exceeds 60℃. 4.2.4 Li-ion Battery SelectionLi-ion batteries are divided into liquid lithium-ion batteries and polymer lithium-ion batteries. The electrolyte of a lithium-ion battery is fluid, so it is more unstable than a lithium polymer battery, and it may explode if it is hit by an external force or if a non-compliant charger is used. And now that the popularization of portable electronic products such as smart phones, e-books, tablets, and laptops uses batteries as a power source, battery hidden troubles will break out at any time. To prevent these, we must pay attention to the following:1) The capacity is clearly marked. Batteries without a clearly marked capacity (such as 1000mAh) are likely to be inferior or recycled.2) Standby time. It is the continuous use time from the time the battery is loaded to the next charge.3) Safety protection circuit board. Without it, the lithium battery is at risk of deformation, leakage, and explosion.Lithium Ion Vs Lithium Polymer BatteriesⅤ ApplicationWith the development of microelectronic technology, more and more miniaturized devices have been put forward, which places high requirements on power sources. Lithium batteries have subsequently entered a large-scale practical stage.The earliest application was lithium sub primary battery, used in pacemakers. Due to the low self-discharge rate and gentle the discharge voltage, this makes it possible to implant the pacemaker into the human body for long-term use.Lithium manganese batteries generally have a nominal voltage higher than 3.0V, which is more suitable for integrated circuit power supplies and is widely used in computers, calculators, and watches.Li-ion batteries are widely used in mobile phones, notebook computers, power tools, electric vehicles, street light backup power supplies, navigation lights, and small household appliances, which can be said to be the most popular type.Ⅵ Battery Security6.1 Battery Storage6.1.1 Lithium BatteryPrimary lithium battery can be discharged continuously or intermittently. Once the power is exhausted, it can no longer be used, and it is widely used in electronic products with low power consumption such as cameras. It has a low self-discharge rate and can be stored for up to 3 years. In addition, it is good to store lithium primary batteries in low temperature to get better storage.Note: Lithium primary batteries are different from lithium ion batteries, the former cannot be charged. 6.1.2 Li-ion BatteryAlso called secondary lithium battery. It can be stored for more than half a year at 20°C. This is due to its low self-discharge rate and most of its capacity can be recovered.The self-discharge phenomenon e4xists in lithium batteries. If the battery is stored below 3.6V for a long time, it will cause the battery to over-discharge and damage the internal structure of the battery, reducing the battery service life. Therefore, long-term storage of lithium batteries should be recharged every 3 to 6 months, that is, keeping the battery voltage at 3.8 ~ 3.9V, and it is appropriate to maintain the discharge depth at 40% ~ 60%. The battery should be stored in a dry environment at 4 ℃ ~ 35 ℃ or in a moisture-proof packaging. In addition, Keep away from heat sources and sunlight.Storage requirements: In the environment with a temperature of 20 ± 5℃ and a humidity of no more than 50%, the air and water vapor must be prevented from contacting the aluminum foil during transportation. 6.2 Charging Rules Charging voltageGenerally, the battery voltage of a mobile phone is 3.7V, but the voltage of a general charger is 5V, but it will not affect the use. Shallow charge and dischargeThis is more beneficial for lithium batteries. Only when the power module of the product is calibrated for lithium batteries, it is necessary to deepen and deep charge. Therefore, lithium-ion-powered products do not have to be constrained by the process. Overcharge and overdischargeThe rated voltage of a lithium-ion battery is generally 3.7V. Depending on different materials, the positive electrode of lithium iron phosphate is 3.2V. The international standard for termination charge voltage when fully charged is 4.2V, and iron phosphate is 3.6V. Overdischarge or self-discharge reaction at low voltage will cause decomposition and destruction of lithium active material, and may not be recovered. And any kind of overcharging of lithium-ion battery will cause severe damage to the battery performance and even cause explosion. Therefore, the lithium-ion battery must avoid overcharging during the charging process.6.3 Battery Explosion6.3.1 Explosions ExpressThe type of battery cell explosion can be summarized into three types: external short circuit, internal short circuit, and overcharge. Here, the “external” refers to the outside of the battery cell and includes short circuits caused by poor internal insulation design of the battery pack. When a short circuit occurs outside the battery cell and the electronic component fails to cut off the circuit loop, high heat will be generated inside the battery cell, causing some of the electrolyte to vaporize, which will expand the battery case.When the internal temperature of the battery reaches 135 degrees Celsius, a good quality separator paper will close the pores, the electrochemical reaction will be terminated almost, the current will drop suddenly, and the temperature will decrease slowly, avoiding the explosion. However, if the pore closing rate is too poor, or the separator paper with poor quality, the battery temperature will continue to increase, causing more electrolyte vaporize, and finally the battery case will be broken, even be exploded.The internal short circuit is mainly caused by piercing diaphragm by the burrs of copper foil and aluminum foil piercing the diaphragm, or dendritic crystals of lithium atoms.These tiny needle-like metals can cause micro-short circuits. The copper and aluminum foil burrs are caused during the production process, and the observed phenomenon is that the battery leaks too quickly, and most of them can be detected by the cell plant or assembly plant. Moreover, because the burr is small, it is sometimes blown out, which makes the battery return to normal. Therefore, this kind of explosion is less happened. Therefore, the explosion caused by the internal short circuit is mainly caused by overcharge.After overcharging, needle-shaped lithium metal crystals are everywhere on the pole pieces, piercing points are everywhere to make micro short circuits. Therefore, the temperature of the battery will gradually increase, and finally the electrolyte is vaporized at high temperature. In this case, whether the temperature is too high to damage electrode materials and the battery housing burns and explodes, both situations will cause an explosion.Based on the above types of explosions, we can focus on batteries protection in three aspects: overcharge, external short circuits, and improvement of battery safety.When designing a battery system, two electronic protections must be provided for overcharge, overdischarge, and overcurrent. Final protection method, the safety level of batteries, which can be roughly differentiated according to the ability to withstand short circuit and overcharge. In addition, before the battery explodes, if lithium atoms accumulate on the surface of the battery, the explosion power will be greater. Comparing the performance of aluminum shell cells with steel shell cells, aluminum shells have high safety advantages. Moreover, consumers use inferior chargers. Thus the ability of cells to resist overcharge is more important than the ability to withstand external short circuits. 6.3.2 Explosion Causes1) Large internal polarization2) The pole piece absorbs water and reacts with the electrolyte.3) The quality and performance of the electrolyte.4) The amount of injection does not meet the process requirements.5) Poor sealing performance during laser welding in assembly process.6) Manufacturing dust is easy to cause micro short circuit.7) The positive and negative plates are thicker according to technological requirements, and it is difficult to insert the case.8) Sealing problem of liquid injection, for example, poor sealing of steel ball causes air drum.9) The shell is too thick, and the deformation of the shell will affect the thickness.10) High external ambient temperature. 6.3.3 Protection MeasuresTo avoid over-discharging or over-charging due to improper use, a triple protection mechanism is provided in the single-cell lithium-ion battery. The first is the use of switching elements. When the temperature in the battery rises, its resistance value rises, if the temperature is too high, the power supply will automatically stop. The second is to choose an appropriate separator material. When the temperature rises to a certain value, micron-sized micropores on the separator will automatically dissolve, so that lithium ions cannot pass through, and the internal reaction of the battery stops. The third is to set a safety valve (that is, the vent hole on the top of the battery). When the internal pressure of the battery rises to a certain value, the safety valve will automatically open to ensure the safety of battery.Sometimes, although the battery itself has safety control measures, due to some reasons, for example, security control fails, or the lack of a safety valve, or the gas is too slowly to release through the safety valve, therefore, the internal pressure of the battery will rise sharply and cause an explosion.In general, the total energy stored in a lithium-ion battery is inversely proportional to its safety. As the battery capacity increases, the battery volume also increases, its heat dissipation performance becomes poor, and the possibility of accidents will increase significantly. For Li-ion batteries for mobile phones, the basic requirement is that the probability of a safety accident is less than one in a million. For large-capacity lithium-ion batteries, especially electric vehicles, the use of forced heat dissipation is particularly important.Choose a safer electrode material, for example lithium manganate material, to ensure that the molecular structure is fully charged, the lithium ions of the positive electrode have been completely embedded in the carbon pores of the negative electrode to avoid the generation of dendrites is fundamentally. At the same time, the stable structure of lithium manganate makes its oxidation performance much lower than that of lithium cobaltate, and the decomposition temperature exceeds 100 °C of lithium cobaltate. The danger of burning and explosion caused by the precipitation of metallic lithium is avoided when having short circuit or overcharge.After the lithium battery cell is overcharged to a voltage higher than 4.2V, side effects will begin to occur. The higher the overcharge voltage, the higher the danger. Because the number of lithium atoms remaining in the positive electrode material is less than half, at this time, the storage cell collapses, causing the battery capacity to permanently decrease. If you continue to charge, since the storage cell of the negative electrode is already filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the surface of the negative electrode toward the lithium ions. These lithium metal crystals will pass through the separator paper, making the positive and negative electrodes short-circuit. Sometimes the battery explodes before a short circuit occurs.When at a  overcharge process, materials such as the electrolyte will vaporize, which will cause the battery case or pressure valve to swell and rupture, allowing oxygen to enter and react with the lithium atoms accumulated on the negative electrode surface.Therefore, when charging a lithium battery, the upper limit of the voltage must be set to guarantee the battery life, capacity, and safety. The optimal charging voltage limit is 4.2V. There is also a lower voltage limit when the lithium battery is discharged. When the cell voltage is lower than 2.4V, some materials will start to be destroyed. In addition, when the lithium battery is discharged from 3.0V to 2.4V, the released energy accounts for only about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cutoff voltage. When charging and discharging, the limitation of current is also necessary. If the current is too large, lithium ions have no time to enter the storage cell, and will collect on the surface of the material, which will affect the battery performance.After these lithium ions have obtained electrons, lithium atom crystals will be generated on the surface of the material, which will cause danger, like overcharge. Therefore, the protection of lithium-ion batteries must include: the upper limit of the charging voltage, the lower limit of the discharge voltage, and the upper limit of the current. In general, except the lithium battery cell, there is a protective plate in the lithium battery pack.Ⅶ Development ProspectsTo develop more excellent batteries, various materials have been studied. For example, lithium sulfur dioxide batteries and lithium thionyl chloride batteries are very characteristic. Their positive electrode active materials are solvents for the electrolyte. This structure made only in non-aqueous electrochemical systems. Therefore, the research of lithium batteries has also promoted the development of electrochemical theory of non-aqueous systems. Except the use of various non-aqueous solvents, polymer thin film batteries has also been studied.Lithium batteries are widely used in energy storage systems such as hydropower, thermal power, wind power and solar power, telecommunications, electric vehicles, military equipment, aerospace and other fields.Lithium-ion batteries have been widely used in portable appliances such as laptop computers, video cameras, and mobile communications due to their unique performance advantages. With the shortage of energy and environmental protection, lithium battery is widely used in the electric vehicle industry, especially the emergence of lithium iron phosphate material batteries, which has promoted the development and application of the lithium battery industry. Ⅷ Questions Related to Lithium & Lithium-ion Batteries1. Is a lithium battery the same as a lithium ion battery?Lithium batteries feature primary cell construction. This means that they are single-use—or non-rechargeable. Ion batteries, on the other hand, feature secondary cell construction. This means that they can be recharged and used over and over again. 2. Do lithium-ion batteries need a special charger?Ultimately, using a battery charger with a specific Lithium charge algorithm is the best option for maximum performance and lifespan of any lithium battery. 3. Can you overcharge a lithium battery?In a lithium-ion battery, overcharging can create unstable conditions inside the battery, increase pressure, and cause thermal runaway. ... At best, this will lead to reduced capacity and shortened life cycle, and at worst this could cause thermal runaway. 4. Which is better lithium ion or lithium polymer battery?High powerBoth lithium-ion and lithium-poly batteries are suitable with high and robust power usages. However, lithium-ion batteries are more efficient and popular than lithium-polymer. They have higher energy levels and powers and are more suitable for heavy usages. 5. What is the difference between a lithium battery and a lithium-ion battery?Lithium batteries feature primary cell construction. This means that they are single-use—or non-rechargeable. Ion batteries, on the other hand, feature secondary cell construction. This means that they can be recharged and used over and over again.

Ⅰ IntroductionIn recent years, with the rapid development of the internet of things (IoT) and electronic technologies, embedded devices such as mobile phones, smartwatches, and sports bracelets have become important elements of cloud computing, IoT, and big data analytics. Embedded terminal devices become more usual in daily life. However, to meet the high storage requirements of these increasingly diverse applications, scientific research personnel face more challenges. Non-volatile memory is more and more popular in the market due to its advantages such as low energy consumption, non-volatile, high density, and low latency. The following is a basic introduction to new non-volatile memory with good future development prospects.The Future of Non-volatile MemoryCatalogⅠ IntroductionⅡ TerminologyⅢ Concept and ClassificationⅣ One Question Related to Non-volatile Memory and Going Further4.1 Question4.2 AnswerⅡ TerminologyMemory is an important part of computer systems. According to different positions in the storage system, memory can be simply divided into three types: on-chip memory, main memory, and hard disk. Correspondingly, static memory (SRAM), dynamic memory (DRAM), and magnetic disks have become the traditional technologies to realize these storage system. Over the past 40 years, these three technologies have achieved tremendous technical and commercial success. With the exception of magnetic disks, the manufacture of both static and dynamic memory relies on semiconductor integration technology. Although these two technologies are different, they also have a common characteristic: they both use the accumulation and release of charge on semiconductor devices to achieve data storage. For example, in a dynamic memory, the charge is used to represent a logic 1, and the discharge represents logic 0. In static memory, this process is achieved by charging and discharging the parasitic capacitance of the transistor. For example, solid-state storage, which widely used in flash memory, also stores data by capturing and releasing the charge on the floating gate of the transistor.With the improvement of manufacturing technologies, the size of semiconductor nano devices has continued to shrink, and the charges that can be stored on all of the above traditional memory devices has also decreased, which has brought serious reliability issues: First, more leakage current; second, a small perturbation of charges will have a relatively greater impact. In addition, the inherent limitations of the charge storage mechanism itself also can't be avoided, the processing of traditional mainstream memories at the nanoscale and the process disturbances are also very challenging.From the aspect of functions, static memory and dynamic memory both belong to the volatile memory category. Its characteristic is that when the power supply is off, the data stored in the memory will disappear and cannot be recovered. Especially in the design of dynamic memory, the charge on the capacitor will gradually leak out as the time increases. Therefore, the stored info need to be refreshed periodically. The static memory doesn't have this issue, but the area of the memory cell is usually large (about 20 times that of the dynamic memory cell), causing serious leakage current. Flash memory belongs to the non-volatile memory, and the data stored on it will be retained for a long time after the power off. In terms of performance, the first two types of memory read & write speed are on the level of nanoseconds, while the flash memory are on the level of hundreds of microseconds or even milliseconds. For the reading mode, the static memory and the dynamic memory can achieve random storage, for example, any one or several memory cells can be read and written at will. It different for Flash, although its storage density is high, the read operation must be performed in units of pages. Moreover, the content update of the flash memory cannot be achieved by directly overwriting the original content, but must be written to a new erased page. In addition, the maximum times of read and write supported by flash memory is extremely limited, typically between thousands of and millions of times. Ⅲ Concept and ClassificationConcept: Non-volatile memory refers to the computer memory of the person whose stored data will not disappear when the power is turned off. It is characterized by non-volatile, byte-by-byte access, high storage density, low energy consumption, and fast read and write speed, but the read speed  far faster than write, in other words, they are asymmetric in a limited life.Classification: According to whether the data in the memory can be rewritten at any time, the traditional non-volatile memory can be divided into two categories: read-only memory (ROM) and Flash memory. New type non-volatile memory compared with traditional non-volatile memory, its device has greatly improved energy consumption, read and write speed, integration density, etc. At present, the newly developed new non-volatile memory mainly includes four types: dielectric memory (FRAM), magnetic medium memory (MRAM), Ovonic phase change memory (OUM), and polymer memory (PFRAM).The following highlights four new non-volatile memories.The technical limitations of traditional memories and the huge challenges brought by the light weight have prompted researchers to look for a new generation of memory devices. People want to find a memory with the following characteristics:1) Nano level read and write speed of static memory2) Integrated density with dynamic memory and even flash memory level3) Flash-like non-volatile memory featuresAlthough such a storage technology has not been fully realized at present, some very promising new storage devices have been developed, and some have even entered the production stage. The four newly developed non-volatile memories are very promising for data processing, because of the limitations of traditional non-volatile memories, it is very likely to replace flash memory in the future.Table 1. New Non-volatile Memories Basic SituationsItemPerformanceManufactureLimitationApplicationFerroelectric RAM(FRAM)1) low energy consumption 2) high read & write speed3) long storage time4) low power operation5) anti-radiationsmaller size1) limit read & write times2) low storage density3) low reliability1) RF IC card2) fast-start memory3) embedded cache4) aerospaceMagnetic RAM(MRAM)1) high read & write speed 2) unlimited read & write times3) low power operationsimple circuithigh cost1) storage2) industrial automation, 3) games 4) energy management 5) communication 6) transportation7) aerospace electronics8) sensor terminalsPhase Change Memory (OUM) 1) long service life2) safety 3) low energy consumption1) small capacity2) low cost1) lower read &write speed2) poor temperature characteristic1) wired and wireless communications2) consumer electronics 3) PC and embedded devicesPolymeric RAM1) good stability 2) low power operation1) 3D stack2) easy processing3) low cost1) limit read & write times, 2) destructiveness1) PC 2) digital camera 3) mobile phoneFRAMa. IntoductionFRAM is the non-volatile memory technology in the new generation. In terms of performance, it consumes low energy and can store data for a long time although there is power failure. It combines the characteristics of high read-write speed of RAM and long-term data storage of ROM. Embedded FRAM in the non-volatile memory situation of radiation-resistant and low-power has great significance. It can be embedded in the chip in a more direct way and has better performance than any other alternative chips. In terms of manufacturing and technology, FRAM is easier to reduce size than flash memory due to the advanced nodes (65 nm or smaller), and does not require the use of very thin oxides or high voltages. b. LimitationWhen FRAM reaches a certain times of read and write, FRAM cells will lose their durability, and the FRAM yield problem caused by array size restrictions and further improvements in storage density and reliability still need to be resolved.c. ApplicationFRAM is a non-volatile memory that combines the advantages of low power consumption, high speed, long service life, and anti-radiation. It is promising in RF 1C card, fast startup memory, and system chip of cache and aerospace.d. Commercial progressFrom the point of international respect, well-known American company Ramtorn, which developed the first 4K bit commercial ferroelectric memory in 1993; after 1998, Ramtorn focused on product research and development, and handed over all production to semiconductor manufacturers. With the time goes by, Ramtorn represents the highest level of PZT-based commercial ferroelectric memory. Many other countries started late in the field of ferroelectric research and mainly based on scientific research. For example, the main work of some countries is still the preparation of ferroelectric thin films. MRAMa. MRAM BasicsMRAM is a non-volatile memory. For the performance, the write speed of MRAM is extremely fast, almost 1000 times that of flash memory, and 20 times that of FRAM. And it has unlimited read and write times, also it can switch on and off instantly and extend the battery life of portable computers. In terms of manufacturing and technology, the circuit of MRAM is simpler than ordinary memories, and only one readout circuit is needed for chip access. In addition, MRAM is easier to integrate (only 5 photomask layers are needed in the entire process), and there is no need to redesign at the transistor level of flash memory. All other core technologies used in the design can remain the same and work consistently.From 1986 to 1988, Albert Fert and Peter Grünberg discovered that nano-multilayer films composed of alternating ferromagnetic and non-magnetic metal layers made of molecular beam epitaxy have a much larger size than AMR, which is named as giant magnetoresistance (GMR). GMR is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers, but it was difficult to put into practice. Soon, further research by Parkin team found that the (ferromagnetic / non-magnetic metal / ferromagnetic) three-layer film made by sputtering technology has a much larger giant magnetic resistance at room temperature than a single-layer ferromagnetic metal. For the spin valve, opened the way for practical use of GMR.The discovery and research of GMR had led to the realization of high-sensitivity read heads in high-density disks, and promoted the development of the entire modern hard disk industry. The earliest application of spin valve sensors in hard disk read heads was in the IBM Deskstar 16GP Titan, which was released in 1997 and has a storage capacity of 16.8GB. In 2007, Hitachi introduced the Deskstar 7K1000, the first 1TB hard drive.b. MRAM LimitationMRAM is much higher than flash memory in the production costs.c. MRAM ApplicationWith the advantages of low power consumption, high-speed reading, high integration, radiation resistance and unlimited rewrites, MRAM is used in storage, industrial automation, gaming, energy management, communications, consumption electronic,transportation and avionics fields. In addition, the IOT and big data analytics are gradually emerging,ubiquitous sensor terminals need to collect massive amounts of data, in order to save storage power consumption, MRAM and STT-MRAM have become the better choices for their relatively good performance.d. MRAM Commercial ProgressIn 2006, Freescale launched the world’s first commercial MRAM product with a capacity of 4Mb. Judging from the current product specifications and development status, the use of MRAM is still limited to some specific markets. From the perspective of cost and capacity, it cannot compete with NAND flash memory with a maximum capacity of 8Gb and DRAM with 512Mb capacity. However, with Samsung, Intel, TSMC and Global Foundry and other integrated circuit leaders strengthening investment in R & D and related production lines, STT-MRAM is gradually begin mass production, partially replacing SRAM and DRAM products and becoming one of the mainstream memories. OUMa. OUM BasicPhase change memory is a kind of memory that realizes information storage through material phase change. It is the non-volatile and large-capacity storage technology advocated by Intel, the world's number one semiconductor chip manufacturer. In terms of performance, it has a long read and write operation life and is easier to integrate than flash memory. OUM memory cells are extremely dense, and read operations is more safer than other memories. Low energy consumption, requiring very low power to operate. In addition, OUM unit can write about 1 billion times, which makes it an ideal alternative to large-capacity memory in portable devices. From the aspect of manufacturing process, compared with the integration of existing logic circuits, its storage unit is only 1/3 of MRAM and FRAM, and its production cost is lower than other new memories.Crystalline Phase and Amorphous Phase ChangeAlthough phase change memory is often categorized as “new memory”, the concept of “phase change” has introduced over 50 years. In 1962, the phase transition of As-Te glass was discovered. In 1968, Stanford Robert Ovshinsky described in an article that certain semiconductor materials can rapidly switch between two different states of resistance and conductivity under the action of an electric field (on the order of 10μs), he utilized chain structures, cross links, polymeric concepts, and divalent structural bonding with a huge number of unbonded lone pairs to achieve what is now referred to as the “Ovshinsky Effect”, an effect that turns special types of glassy, thin films into semiconductors upon application of low voltage. This discovery directly led to a large number of subsequent studies on the phase transition of thin films based on tellurium-arsenide-germanium-silicon alloy materials or sulfur-based glasses. In 1970, Nevill and Gordon Moore demonstrated the world’s first 256-bit phase change memory, and Moore was later known for putting forward the famous “Moore's Law” about the number of transistors in a dense integrated circuit doubles about every two years and served as the co-founder of Fairchild Semiconductor and CEO of Intel. After that, research on semiconductor memories based on phase change materials has gradually slowed down due to issues such as materials and power consumption, but phase change materials have been used very successfully in rewritable optical discs such as CD-RW / DVD-RW.   b. OUM LimitationThe read and write speed and frequency of OUM are not as good as FRAM and MRAM, and how to maintain its driving temperature stably is also a big technical problem.c. OUM ApplicationPhase change memory is suitable for wired and wireless communication equipment, consumer electronics, PC and other embedded applications due to its fast read and write speed, strong upgrade capabilities, and low power consumption. For example, it is used in the aerospace embedded system and used in smart meters to further integrate its storage architecture.d. OUM Commercial ProgressPhase change memory, as one of the most promising new memories, can be embedded at all levels of the memory architecture. Because of the similarity between phase change memory and dynamic memory, especially its lower power consumption and scalability, it has been considered as the best substitute for dynamic memory. But phase change memory also has disadvantages. The first is its limited times of erases and writes (usually only 107 to 108). If the number of erasing and writing exceeds this limit, the life of the memory cell will end, and the device can no longer be used. The second disadvantage is the limited write speed. The write speed of phase change memory is 6-10 times slower than dynamic memory. Write Operation of Phase Change Memory UnitNevertheless, phase change memory still has good applications in some fields. Several related studies have proposed various methods to overcome these shortcomings. For example, an architecture adjustment is used to compensate for the loss caused by the performance of writing, which can greatly reduce power consumption, thereby accelerating the commercialization of phase change memory as the main memory of a computer.In addition, the multi-level cell technology has been successfully implemented on phase change memory. In the design of a multi-level cell phase change memory, 2N resistive states are used to represent N digits, respectively, in other words, in a 2-bit multi-level cell phase change memory, 00, 01, 10, and 11 can be represented by four different resistance values, respectively. In the specific design, the resistance of the phase change material can be changed by adjusting the amplitude and time of the writing current / voltage. PFRAMa. PFRAM BasicsPFRAM is a plastic, polymer-based, and non-volatile memory. In terms of performance, PFRAM has advantages such as good stability and low power consumption. From manufacturing process, high density can be obtained through three-dimensional stacking technology, which is easy to make and has extremely low manufacturing costs, only about 10% of NOR-type flash memory.b. PFRAM LimitationPFRAM has a limited read and write operation life and its reads are destructive.c. PFRAM ApplicationThe final product of (PFRAM will be an all-organic storage system, which will be suitable for personal computers, handheld computers, digital cameras, mobile phones, handheld radios and communication devices, GPS systems, audio, video, game background program and other important fields.d. PFRAM Commercial ProgressPFRAM develops slowly in commercial use, and Intel is in a leading position. In 2014, Intel recruited JonKrueger (architecture and software engineer) to work for its polymer memory group and greatly promote the development of multi-layer plastic memory, finally their work is close to the software development stage, which indicates that this memory technology will accelerate to the market.Memory technology will continue to improve to meet different applications. On the one hand, The new type memories will create a new market and enter various application markets, on the other hand, it involves new materials and research concepts, it will be difficult to become the mainstream of the market in a long time. However, in the aerospace, industrial automation,  embedded cache of system chip and other sub-application areas, the new non-volatile memory will gradually transfer its technological breakthroughs to market penetration and achieve rapid development.With the advent of the 5G era, the development of application markets such as the IOT, artificial intelligence, and smart cities, and the urgent need for diverse memory requirements, coupled with traditional memory market change, new type memories will play an increasingly important role in the market. Ⅳ Questions Related to Non-volatile Memory and Going Further 1. Which memory is called non-volatile memory?Examples of non-volatile memory include read-only memory (see ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape and punched cards. 2. Which is non-volatile memory RAM or ROM?RAM, which stands for random access memory, and ROM, which stands for read-only memory, are both present in your computer. RAM is volatile memory that temporarily stores the files you are working on. ROM is non-volatile memory that permanently stores instructions for your computer. 3. What is another name for non-volatile memory?Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. 4. Which is the most non-volatile memory?NAND flash, the most common type used in data storage, includes several variants, such as single-level cells or one bit per multi-level cell or two bits per cell; three-level cells or three bits per cell and quad-level cells or four bits per cell, respectively. 5. What is non-volatile memory explain with example?NV or non-volatile memory is a term used to describe memory or storage that is saved regardless if the computer has power. ... An example of non-volatile memory and storage is a computer hard drive, flash memory, and ROM.

Ⅰ. Filter DefinitionIn electronics, a filter (signal processing) is a kind of devices or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal. Most often, this means removing some frequencies or frequency bands. However, filters do not exclusively act in the frequency domain; especially in the field of image processing many other targets for filtering exist. As is known to all, electronic filters remove unwanted frequency components from the applied signal, enhance wanted ones, or both.Introduction to Signal FilteringCatalogⅠ. Filter DefinitionⅡ. Type of Filters and Functions  2.1 Type of Filters  2.2 Filtering FunctionsⅢ. Filter TechnologiesⅣ. Main Characteristic Indexes of FilteringⅤ. Filter Classifications Analysis  5.1 Passive Filter & Active Filter  5.2 Digital Filter & Analog FiltersⅥ. One Question Related Filter and Going Further  6.1 Question  6.2 AnswerⅡ. Type of Filters and Functions2.1 Type of FiltersFilters have different effects on signals of different frequencies. According to this fact, the basic filter types can be classified into four categories: low-pass, high-pass, band-pass, and band-stop. Each of them has a specific application in DSP. One of the objectives may involve digital filters design in applications. Generally, the filter is designed based on the specifications primarily for the passband, stopband, and transition band of the filter frequency response. The filter passband is the frequency range with the amplitude gain of the filter response being approximately unity. The filter stopband refers to the frequency range over which the filter magnitude response is attenuated to eliminate the input signal whose frequency components are within that range. The transition band means the frequency range between the passband and the stopband.Figure 1. Filtering Out the Noise (signal processing)Because there are many different standards of classifying filters and these overlap in many different ways, there is no clearly distinctive classification. Filters may be:non-linear or linearanalog or digitaltime-variant or time-invariant , also known as shift invariance.discrete-time (sampled) or continuous-timepassive or active type of continuous-time filterinfinite impulse response (IIR) or finite impulse response (FIR) type2.2 Filtering FunctionsSeparate useful signals from noise to improve signal immunity and signal-to-noise ratio.Filter out unwanted frequency to improve signal analysis accuracy.Separate single frequency from complex frequencFigure 2. Electronic FilterⅢ. Filter TechnologiesFilters can be built in a number of different technologies. Before that, it is necessary to know some basics of it deeply.Center frequencyThe main parameters of the filter: the center frequency of the filter's pass-band f 0, generally f 0 = (f 1 + f 2) / 2, f 1 and f 2 are boundary frequencies of band-pass or band-stop filter, which decreased by 1dB or 3dB. In addition, narrowband filters often use the smallest point of insertion loss as the center frequency to calculate the pass-band bandwidth. Cutoff frequencyIt refers to the right frequency point of the pass-band of the low-pass filter and the left frequency point of the pass-band of the high-pass filter, and it is usually defined by relative loss points, 1dB or 3dB. The relative reference for the relative loss is: the low-pass is based on the insertion loss at DC, and the high-pass is based on the insertion loss at a high-pass frequency at which no parasitic stop-band occurs. Pass-band bandwidthThe bandwidth of the filter is simply the difference between the upper and lower cutoff frequencies, while passband bandwidth is the difference between the upper and lower cutoff frequencies of, for example, a band-pass filter, a communication channel, or a signal spectrum. Insertion lossIt refers to the loss of the original signal in the circuit due to the introduction of the filter. And it is characterized by the loss at the center or the cutoff frequency. If it is the full-band interpolation loss, it must be emphasized.Note: When adding a filter at the input end, the impedance of the filter should be mismatched with the impedance of the power supply. The more severe the mismatch, the more ideal the attenuation is, and the better the insertion loss characteristics. That is, if the internal resistance of the noise source is low impedance, the input impedance of the EMI filter connected to it should be high (such as a series inductor with a large amount of inductance); if the internal resistance of the noise source is high impedance, the input impedance of the EMI filter should be low (such as a large parallel capacitor). Due to the imbalance of the line impedance, the two components will convert to each other during transmission, and the situation becomes complicated. RippleIt refers to the peak-to-peak value of the insertion loss that fluctuates on the basis of the average loss curve with the frequency in the 1dB or 3dB bandwidth (cutoff frequency). Pass-band riplpeThe amount of change in insertion loss in the pass-band with frequency. For example, in a 1dB bandwidth, it is 1dB. Pass-band standing wave ratio (VSWR)An important indicator for measuring whether the signal in the filter pass-band is properly transferred. Ideal VSWR is 1: 1, when mismatched, VSWR> 1. For an actual filter, bandwidth satisfies VSWR <1.5: 1, which is generally less than 3dB, and the proportion when at 3dB is related to the filter order and insertion loss. Return lossThe decibels (dB) of the ratio of the port's signal input power to the reflected power, and it is also equal to | 20Log10ρ |, where ρ is the voltage reflection coefficient. In addition, when the input power is completely absorbed by the port, the return loss value is infinite. Stop band rejectionIt is a major index to measure the performance of filter selection. The higher the index, the better the suppression of out-of-band interference signals. There are usually two formulations: one is how much dB is required to suppress a given out-of-band frequency fs, and the calculation method is the attenuation fs=As-IL; another is to propose a characterizing filter whose amplitude-frequency response is close to the ideal rectangle index of degree-rectangular coefficient (KxdB> 1), KxdB = BWxdB / BW3dB, (x can be 40dB, 30dB, 20dB, etc.). The more the filter order, the higher the rectangularity, in other words, the closer the K is to the ideal value 1, the more difficult it is to make an ideal filter. Delay (Td)It refers to the time required for the signal to cross the filter. The value is the derivative of the diagonal frequency of the transmission phase function. In-band phase linearityThis indicator characterizes the phase distortion introduced by the filter on the transmission signal in the pass-band. The filter designed according to the linear phase response function, which has good phase linearity, but its frequency selectivity is very poor. It is only used to pulse or phase-modulate signal transmission system applications. Order (stage)For high-pass and low-pass filters, the order is the sum of all capacitors and inductors in the filter circuit. For a band-pass filter, the order is the total number of parallel resonators; for a band-stop filter, the order is the total number of series and parallel resonators. Absolute bandwidth / relative bandwidthThis indicator is usually used for band-pass filters, which characterize the frequency range of signals that can pass through the filter, and reflects the frequency selection of the filter. Relative bandwidth is the percentage of absolute bandwidth to center frequency. Standing waveIt indicates the impedance matching between the filter port and the required system, and also it indicates how much of the input signal failed to enter the filter and was reflected back to the input. LossIt represents the energy lost after the signal passes through the filter, that is, the energy consumed by the filter. Pass-band flatnessThe absolute value of the difference between the maximum loss and the minimum loss in the pass-band of the filter, which characterizes the difference in energy consumption of filters for different frequency signals. Out-of-band rejectionIt is the "attenuation" outside the pass-band frequency range of the filter, which characterizes the filter's ability to select unnecessary frequency signals. Absolute group delayThe time it taken for a signal to pass from the input port to the output port within the pass-band of the filter. Group delay fluctuationThe difference between the maximum and minimum absolute group delay in the pass-band of the filter, which characterizes the dispersion characteristics of a filter. Power capacityIt refers to the maximum power of the pass-band signal that can be input to the filter. Phase consistencyThe difference in the phase of the transmitted signal between different filters of the same index in the same batch, which characterizes the differences (consistency) between batch filters. Amplitude consistencyThe difference of transmission signal loss between different filters with the same index in the same batch, which represents the differences (consistency) between batch filters.Figure 3. Low-Pass Electrical FilterⅣ. Main Characteristic Indexes of FilteringCharacteristic frequency① The pass-band cutoff frequency fp = wp / (2p) is the frequency of the boundary point between the passband and the transition band, at which the signal gain decreases to the specified lower limit.② Stop-band cut-off frequency fr = wr / (2p) is the frequency of the boundary point between the stopband and the transition band, at which the signal attenuation (reciprocal of the gain) decreases to the specified lower limit.③ The corner frequency fc = wc / (2p) is the frequency when the signal power is attenuated to 1/2 (about 3dB). In many cases, fc is often used as the pass-band or stop-band cutoff frequency.④ Natural frequency f0 = w0 / (2p), when there is no loss in the circuit, it refers to the resonance frequency of the filter, and complex circuits often have multiple natural frequencies. Gain and attenuationThe gain of the filter in the pass-band is not constant.① For the low-pass filter pass-band gain Kp, for the ordinary filters, it refers to the gain at w = 0; for the high-pass, it refers to the gain at w → ∞; for the band pass, it refers to the gain at the center frequency.② For the band-stop filter, the stop-band attenuation should be given, and the attenuation is defined as the inverse of the gain.③ The change amount of the pass-band gain △ Kp, refers to the maximum change amount of the gain at each point in the pass-band. If △ Kp is in dB, it means the variation of the gain dB value. Damping coefficient and quality factorThe damping coefficient is a characterization of a filter’s damping effect on a signal with an angular frequency at w0, and is an indicator of energy loss in the filter.The reciprocal of the damping coefficient is called quality factor, and is an important indicator of the frequency selection characteristics of the valence band-pass and band-stop filters, Q = w0 / △ w, where △ w in the formula is the 3dB bandwidth of the band-pass or band-stop filter, w0 is the center frequency, and in many cases the center frequency is equal to the natural frequency. SensitivityThe filtering circuit is composed of many components, and changes of parameter values of each component will affect the performance of the filter. The sensitivity of a certain performance index y of the filter to the change of a certain component parameter x is recorded as Sxy, which is defined as: Sxy = (dy / y) / (dx / x).This sensitivity is not the same concept with the sensitivity of measuring instruments or circuit systems. The smaller the sensitivity, the stronger the fault tolerance of the circuit, and the higher the stability. Group delay functionWhen the filter's amplitude-frequency characteristics meet the design requirements, in order to ensure that the output signal distortion does not exceed the allowable range, certain requirements should be put forward for its phase-frequency characteristic ∮(w). In filter design, the closer the group delay function d∮ (w) / dw is to a constant, the smaller the signal phase distortion. Ⅴ. Filter Classifications Analysis5.1 Passive Filter & Active FilterPassive filterA passive filter is composed of passive components only. It is based on the principle that the reactance of the capacitive and inductive components changes with frequency. The advantages of this type of filter are: simple circuit, causal power supply, and high reliability. Also there are disadvantages: the signal in the pass-band has energy loss, the load effect is relatively obvious, and electromagnetic induction is easy to cause when using inductive components. When the inductance is large, the size and weight of the filter are relatively large, which is not applicable in the low frequency range.The passive filter circuit has a simple structure and is easy to design, but its pass-band magnification and cut-off frequency change with the load, so it is not suitable for occasions with large signal processing requirements. Passive filter circuits are usually used in power circuits, such as filtering after DC power rectification, or LC (inductance, capacitor) circuit filtering when high current loads are used. Active filterActive filters are composed of passive components and active devices. The advantages of this type of filter are that the signal in the pass-band has no energy loss, even be amplified; the load effect is not obvious, and the mutual influence is small when multi-levels are connected. The simple method of cascading is easy to form high-order filter, and the device is small, lightweight, and does not require magnetic shielding. Their disadvantages are that the pass-band range is limited by the bandwidth of the active device and requires a DC power supply; the reliability is not as high as that of a passive filter, and it is not suitable for high voltage, high frequency, and high power applications.The load of the active filter circuit does not affect the filtering characteristics, so it is often used in places with superior signal processing requirements. Active filter circuit is generally composed of an RC network and integrated operational amplifier, so it can only be used under the condition of suitable DC power supply, and it can also be amplified. However, the composition and design of the circuit are also more complicated. Active filter circuits are not suitable for high voltage and high current applications. 5.2 Digital Filter & Analog Filters5.2.1 TerminologyA digital filter is an algorithm or device consisting of a digital multiplier, an adder, and a delay unit. The function of the digital filter is to perform arithmetic processing on the digital code of the input discrete signal to achieve the purpose of changing the signal spectrum. Digital filters can be made by computer software or large-scale integrated digital hardware.There are active and passive analog filters. Active filters mainly consist of op amps, op amps,  resistors, and capacitors. They have problems such as voltage drift, temperature drift, and noise, while digital filters do not get these problems, so they can achieve high stability and accuracy. 5.2.2 Differences between Digital filter & Analog filtersDigital filters are used for discrete systems, analog filters are used in continuous-time systems, and they can also be used in discrete-time systems, such as SC (switched capacitor) filters.From the point of view of implementation, analog filters are generally built with analog devices such as capacitors and inductors. Digital filters can be implemented by software or digital chips. It is troublesome to replace the capacitor and inductor when the technique parameters of the analog filter are changed. If there is a need for replacement, it is necessary to modify the coefficients (such as when implemented in software).From the technical view, for example, it is very difficult for analog filters to reach -60dB, and digital filters can easily reach this.The biggest difference between analog and digital filters is that the digital filter on the Fs/2 frequency is flipped, that is, symmetrical, while analog filters are not. Therefore, a large number of interpolation filters are selected in the DAC, and the image frequency is placed at a far frequency point, and then the analog filter regarded as a sound meter is used to filter out the image frequency in the radio frequency band.The expression of analog filters is different from digital filters: analog filters are represented by H (S), and digital filters are represented by H (Z). Analog filter is based on the approximation of amplitude-frequency characteristics, while digital filters can achieve phase matching.Figure 4. EMI Filters ImageⅥ. One Question Related to Filter and Going Further6.1 QuestionHow to Select EMI Filters?6.2 AnswerSome people think that the higher the insertion loss of an EMI filter, the better, and the more stages of the filtering network, the better. In fact, this is not the right way to choose a EMI filter. In addition, the more stages of the filtering network, the more expensive, the larger the size and weight. In practice, the best way to select and evaluate an EMI filter is to install it on a device for testing. As is known to all, the performance of a filter depends largely on the load impedance of the device. It cannot be derived from one data of impedance insertion loss. Because it is a complex function of the filtering element impedance and the equipment impedance, and its magnitude and phase change within the frequency range. What's more, different performance levels of conducted radiation control (FCC, VDE) and sensitivity control required by the filter selection test are performed on the device. Frequently Asked Questions about Filter (Signal Processing) Basics1. What is filter in digital signal processing?In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal. 2. Why do we use filter in digital signal processing?Digital filters are used for two general purposes:(1) Separation of signals that have been combined(2) Restoration of signals that have been distorted in some way. Analog (electronic) filters can be used for these same tasks; however, digital filters can achieve far superior results. 3. What is filter response?In comparison, filters carried out by convolution are called Finite Impulse Response or FIR filters. As you know, the impulse response is the output of a system when the input is an impulse. In this same manner, the step response is the output when the input is a step (also called an edge, and an edge response). 4. Which filter is present in DSP system?An ideal bandpass filter and second-order approximations. With DSP software, there are two basic approaches to filter design: finite impulse response (FIR) and infinite impulse response (IIR). 5. What are the functions of filter in signal processing?In the field of signal processing, a filter is a device or process that, completely or partially, suppresses unwanted components or features from a signal. This usually means removing some frequencies to suppress interfering signals and to reduce background noise. 6. What is filter frequency?A frequency filter is an electrical circuit that alters the amplitude and sometimes phase of an electrical signal with respect to frequency. ... The frequency separating the attenuation band and the pass is called the cut-off frequency. 7. What is IIR filter in DSP?The infinite impulse response (IIR) filter is a recursive filter in that the output from the filter is computed by using the current and previous inputs and previous outputs. Because the filter uses previous values of the output, there is feedback of the output in the filter structure. 8. Where FIR filter is used?The term FIR abbreviation is “Finite Impulse Response” and it is one of two main types of digital filters used in DSP applications. Filters are signal conditioners and function of each filter is, it allows an AC components and blocks DC components. The best example of the filter is a phone line, which acts as a filter. 9. What are the most commonly used active filters?The most common and easily understood active filter is the Active Low Pass Filter. Its principle of operation and frequency response is exactly the same as those for the previously seen passive filter, the only difference this time is that it uses an op-amp for amplification and gain control. 10. Why IIR filter is unstable?So, for unstable filters, the impulse response is not absolutely summable. In another way, the impulse response never approaches zero. Again, for IIR filter, h continues to go on with n i.e. never goes to zero. So, IIR filters are supposed to be unstable. Recommended ReadingComplete Introduction and Classification of Filters and ApplicationsPrinciple and Function of the FilterCommon Applications of FilterClassification of Electronic Filters