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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. 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

CatalogⅠ The Role of the FuseⅡ Working Principle of the FuseⅢ Classification of the FuseⅣ The Terminologies of the FuseⅤ Safety Standards and Signs for Fuse TubesⅥ Factors Affecting Fuse Life and Evaluation of Fuse Life6.1 Factors Affecting the Life of the Fuse6.2 Effect of the Use of the Fuse After Aging6.3 Test Evaluation of Fuse LifeⅦ Fuse Suitable CircuitⅧ Precautions for Using the Fuse TubeⅨ Selection of Fuse TubeⅩ FAQⅠ The Role of the Fuse• Under normal circumstances, the fuse acts as a connection circuit in the circuit.• In the case of abnormal (overload), the fuse acts as a safety protection element in the circuit, and safely cuts off and protects the circuit by blowing itself. Figure 1.Ⅱ Working Principle of the FuseWhen the fuse is energized, the heat converted by the electrical energy causes the temperature of the meltable item to rise. When the normal working current or the allowable overload current passes, the generated heat is radiated to the surrounding environment through the meltable body and the outer casing, and the heat generated by convection, conduction, etc. is gradually balanced with the generated heat. If the generated heat is greater than the amount of heat dissipated, the excess heat gradually accumulates on the meltable item, causing the temperature of it to rise; when the temperature reaches and exceeds the melting point of the meltable item, it will be melted, blown and the current will be cut off and plays a role as a safety protection circuit. Ⅲ Classification of the Fuse• According to the external size, it is divided into φ2, φ3, φ4, φ5, φ6 and others. • According to the blowing characteristics, it is divided into fast-blown type, medium time-delay blown type, and time-delay type. (it can also be divided into express, strong delay). • According to the breaking capacity, it is divided into low breaking type and high breaking type (it can also be divided into enhanced breaking type). • According to safety standards (or areas of use): UL/CSA (North America) specification, IEC (China, Europe, etc.) specification, MIT/KTL (Japan/Korea) specification, etc. • Other classifications. Ⅳ The Terminologies of the Fuse• Rated current: The nominal operating current of the fuse tube (the maximum current that the fuse maintains normal operation for a long time under normal conditions). • Rated voltage: The nominal working voltage of the fuse (the maximum voltage that can safely withstand when the fuse is disconnected). When a fuse is selected, the rated voltage of the selected fuse should be greater than the input voltage of the protected circuit. • Breaking capacity: When a large overload current (such as a strong short circuit) occurs in the circuit, the fuse can safely cut off (break) the maximum current of the circuit. It is the most important safety indicator for fuses. Safe breaking means that something endangers the surrounding elements, components and even personal safety such as splashing, burning, the explosion will not happen in the breaking circuit.  • Overload capability (load carrying capacity): The fuse can maintain the maximum overload current for working within the specified time. When the current flowing through the fuse exceeds the rated current, the temperature of the meltable item will gradually rise after a period of time and eventually be blown. The UL standard stipulates that the fuse remains in operation for more than 4 hours, and the maximum unblown current is 110% of the rated current (100% for the miniature fuse tube) The IEC standard stipulates that the fuse remains in operation for more than one hour, and the maximum unblown current is 150% of the rated current. • Fuse characteristics (I-T): The relationship between the load current applied to the fuse and the fuse blowing time. Blowing characteristic curve (I-T curve): A curve formed by the average blowing time coordinate point of the fuse under different load currents in a logarithmic coordinate system in which the load current is the X-axis and the blowing time is the Y coordinate. Each type of fuse has a corresponding curve that represents its blowing characteristics, which is a good indication of the fuse's overload performance and it is for reference when selecting the fuse. Blowing characteristics table: A table consisting of several specified representative load current values and corresponding blowing time ranges. All safety standards have clearly stated that this is the most important basis for the acceptance of fuses. For example, fast-blow type such as UL, CSA, MIT/KTLA, is specified as:In 100% 4 hours(minimum)In 135% 1 hour(maximum)In 200% 2 minutes(maximum) • Melting heat value (I2t): The nominal energy value that the cut-off current needed to melt and partially carburate the fuse, which is simply the minimum amount of heat required to blow the fuse. Total I2t=melted I2t+ arcing I2t The melting I2t (corresponding to the pre-arcing I2t in the IEC standard) refers to the energy required from the melting of the fuse to the moment of arcing; the arcing I2t refers to the energy required for the arcing from the moment it starts to the moment it eventually extinguishes. For low-voltage fuses, the arcing time is very short and often negligible. That is to say, the arcing I2t can be calculated as zero. Both UL and IEC do not require I2t, but I2t has some help with fuse selection. The I2t measurement of the fuse is calculated as I2t when the fuse's blowing time is less than 10ms (usually 8ms). • Voltage drop: The voltage difference across the fuse after thermal equilibrium underrated current conditions. • Temperature rise: Under a certain current condition, the difference between the surface temperature of the fuse and the initial temperature of the energization (which can be understood as the ambient temperature) after the heat balance is reached, that is, the temperature rise = the surface temperature of the fuse - the ambient temperature. Figure 2.Ⅴ Safety Standards and Signs for Fuse Tubes• UL, CSA standards: North American regional safety standards such as the United States, Canada; small current fuse tube standards are UL248-1/14, CSA248-1/14.Safety sign:--- UL/CSA LIST (Listing Sign), the product safety sign passed the test in accordance with UL/CSA248-1/14.--- UL/CSA RECOGNIZED (Approved Sign), the product safety mark passed the test partly in accordance with UL/CSA248-1/14. • JIS Standard: Japanese Electrical Safety Standard. The standard for small current fuse tubes is JIS C6575.Safety sign:--- T--- PSEBoth signs were valid before the end of 2006, after which only the “PSE” mark was valid. • KTL Standard: Korean Electrical Safety Standard.Safety sign:--- K • IEC standards: International Electrotechnical Commission standards and safety standards used in Europe and China. The standard for small current fuse tubes is IEC60 127, GB 9364 (China).Safety sign:CCC --- ChinaSEMKO --- SwedenVDE --- GermanyBSI --- UKIMQ --- Italy Ⅵ Factors Affecting Fuse Life and Evaluation of Fuse Life6.1 Factors Affecting the Life of the Fuse• Working environment temperature:Excessive ambient temperature is detrimental to the life of the fuse. Time-delay (slow-blow) fuses, such as tin ball type, begin to spread to the wire when the temperature is approximately 160℃ (150-170℃); the meltable item (wire) of the fast-blow fuse begins to violently oxidize at a temperature approximately equal to 200℃ (175 to 225℃). As the fuse is oxidized from the outside to the inside, multiple times of diffusion, thermal stress fatigue, etc., the life of the fuse will be gradually shortened. Therefore, it is recommended that the time-delay fuse should not work above 150℃ for a long time, and the fast-blow fuse should not work above 175~225℃ for a long time. • Pulse current:Constant pulse shock will cause thermal cycling, which will cause the diffusion, oxidation, thermal stress, etc. of the fuse to be generated and even accelerated. The fuse will age as the pulse energy and frequency increase. The impact resistance life of the fuse depends on the I2t of the pulse as a percentage of the fuse's own I2t; normally, it should be less than 20%, so that the fuse can withstand more than 100,000 times of impact. • Other:Such as the tube clamp in contact with the fuse, and the length and cross-sectional area of the connecting wire. The contact resistance between the fuse and the pipe clamp is large, which is detrimental to the service life. The UL standard specifies that the contact resistance between the fuse to the tube clamp is less than 3mΩ during the test. When the contact resistance is large, the tube clamp does not dissipate heat but generates heat and transmits it to the fuse. 6.2 Effect of the Use of the Fuse After AgingAfter the fuse has aged, the situation that the current should be cut off and the fuse is not blown will not happen. When the fuse ages, it is equivalent to a drop in the rated value (current) rather than a rise, so there is no safety problem in the circuit, but the circuit is cut off under a small overload current or pulse. 6.3 Test Evaluation of Fuse LifeThe "endurance test method" is specified in the IEC standard, and there is no similar regulation in the UL standard. The durability test in the IEC standard is the life test by using the DC power supply test at normal temperature:• The voltage drop is measured until the temperature is stable under the rated current;• 1.2 times of rated current for 1h, cut off current for 15min and circulate for 100 times;• Power on 1.5In for 1h and measure voltage drop;• Measure the voltage drop with method a. Requirements: The voltage drop change before and after the test should not exceed 10%, and the sign is still clear and identifiable, and the end cap solder joint does not show any deterioration. Figure 3.Ⅶ Fuse Suitable Circuit• Very fast and fast-blow type fuse tubes: Suitable for circuits with relatively constant current, or circuits with low inrush current, and there are shock-resistant fragile components in the circuit. • Medium time-delay and time-delay blown fuse tubes: Suitable for circuits with normal inrush current, and there are no shock-resistant fragile components in the circuit. Lightning-resistant fuse tube for special circuits that need to withstand lightning strikes, such as telephones. • Breaking current fuse tube: Suitable for circuits where large short-circuit current may occur. • Oxygen resin package and plastic case type fuse tube: suitable for installation of dense components or circuits where contact short circuits may occur. • 350V, 300V fuse tube: suitable for electronic rectifiers and other products. Ⅷ Precautions for Using the Fuse Tube1. The rated voltage of the selected fuse should be greater than the input voltage of the protected circuit. 2. The rated current of the UL specification fuse is determined under laboratory conditions and should be used less than 75% of the nominal value in actual use. For example, the circuit operating current is 0.75A, we can select the fuse tube with a minimum rated current of 1A. 3. The rated current of the IEC specification fuse tube can be used at 90% or 100% of the nominal value in actual use. For example, the circuit operating current is 0.9A, and the fuse tube with a minimum rated current of 0.9A or 1A can be selected. 4. Under different operating environment temperatures, the working life of the fuse is different. The higher the temperature, the shorter the working life of the fuse. In actual selection, the rated current of the fuse should be increased according to the coefficient. 5. The breaking capacity of the fuse tube is proportional to its volume and inversely proportional to the rated voltage, that is, the larger the volume or the smaller the rated voltage, the larger the breaking capacity of the fuse tube; the smaller the volume or the larger the rated voltage, the smaller the breaking capacity of the fuse tube. Therefore, if a small-size fuse tube is used, it is necessary to determine that the short-circuit current that may occur in the protected circuit is not too large; if a large short-circuit current may occur in the protected circuit, a larger-size fuse tube with a larger breaking current must be selected. 6. The surge I2t of the protection circuit should be less than 20% of the rated I2t of the fuse tube. The fuse tube can withstand more than 100,000 surges in the protected circuit. Ⅸ Selection of Fuse Tube1. Determine the safety sign: According to the market requirements for the product to be sold, select the safety certification sign and safety standard (UL standard or IEC standard fuse tube) of the fuse tube. 2. Determine the dimensions of the fuse tube: Select the dimensions of the fuse tube according to the installation space and the defined safety certification sign and safety standards. 3. Determine the model number: Select the type of fuse tube based on the current characteristics of the circuit being protected. For example, if the current characteristic of the protected circuit is a constant current, the fast-blow type should be selected. 4. Determine the rated voltage: Determine the rated voltage of the fuse tube according to the input voltage of the protected circuit and the requirements for use. For example, if the input voltage of the protected circuit is 220V, the fuse tube with rated voltage above 220V should be selected, 250V, 300V, 350V, etc. can also be selected; but considering the cost factor, it is not necessary to use the rated voltage which is too high. 5. Determine the minimum rated current: According to the stable operating current of the protected circuit and the relevant use loss factor, the rated current of the fuse tube is initially determined. For example, the stabilized working current of the protected circuit is 1A, the UL standard time-delay fuse tube should be selected, and the working environment temperature is about 80℃. The minimum rated current of the fuse tube is selected as 1A × 1.25 ÷ 0.5 = 2.5A. 6. Determine the minimum I2t of the fuse tube: Determine the I2t of the fuse tube based on the surge I2t of the protected circuit. For example, the surge I2t of the protected circuit is 1 (A2S). To ensure that the fuse tube can withstand more than 100,000 times of impact, the I2t of the fuse tube should be greater than 1÷0.2=5 (A2S). 7. Determine the rated current of the fuse tube: According to the minimum rated current and the minimum I2t value, check the corresponding model specifications, and take the primary rated current specification that is greater than the minimum rated current value and whose I2t value is also greater than the minimum I2t value as the rated current of the selected fuse tube. For example, based on the above minimum,(1) If the I2t of the rated current of 2.5A is 4.3A2S and the I2t of 3A is 5.4A2S, take 3A as the rated current of the selected fuse tube;(2) If the I2t of rated current of 2A is 5.3A2S and the I2t of 2.5A is 7.6A2S, take 2.5A as the rated current of the selected fuse tube. Ⅹ FAQ1. What is Fuse?A Fuse or an Electric Fuse is an Electrical / Electronic device that protects the circuit from different electrical faults like over-current and overload. Fuses can be considered sacrificial elements in the circuit as they act as a weak link in the entire circuit. 2. What is the working principle of fuse?An electric fuse is based on the principle of the heating effect of electric current. It is made up of thin metallic wire of non-combustible material. A fuse is always connected between the ends of the terminal in a series connection with the circuit. 3. What is the application of fuse?Used to protect transformers, motors and power systems from over-current conditions. In feeders, power transformers, and solar circuits. Electrical appliances and house distribution boards use fuse for domestic purposes. 4. What is the type of fuse?Fuses can be divided into two major categories, AC fuses, and DC fuses. The below block diagram illustrates the different types of fuse under each category.  5. Are fuses AC or DC?Generally, fuses have a DC voltage rating that is half of the maximum AC voltage rating. 6. Why fuse is not used in the neutral wire?Because the fuse can disconnect the circuit only when the excess current flows completely through the neutral. ... Since, neutral is not a live conductor coming from the source, disconnecting a neutral line can only open the current path through neutral. But, the live phase still carries the charge. 7. How do I choose a fuse size?In order to select the right amperage of the fuse, you first need to know the full-load steady-state current of the circuit at an ambient temperature of 25º C (68º F). Once the current value is determined, then a fuse rating should be selected to be 135% of this value (taken to the next standard value). 8. How do you use fuses in a circuit?Fuses should always be connected to the hot wire and should be placed before any other component in the circuit. In most projects, the fuse should be the first thing the hot wire connects to after it enters your project enclosure. 9. How long do fuses last?Fuses never need to be replaced unless they are tripped/activated by a failing component or any other even with the circuits of the car. They are encapsulated in plastic and are in a vacuum inside the piece. As long as the current limit isn't reached, that wire will not burn out. 10. Do fuses reduce voltage?The voltage rating of a fuse must be at least equal to or greater than the circuit voltage. It can be higher but never lower. ... If a fuse is used with a voltage rating lower than the circuit voltage, arc suppression will be impaired and, under some overcurrent conditions, the fuse may not clear the overcurrent safely. 

Ⅰ IntroductionWith the improvement of computer technology, the demand for non-volatile memory is increasing, their read and write speed requirements are getting faster and faster, and the power consumption  are becoming smaller and smaller as required by users. But the traditional non-volatile memory such as EEPROM , FLASH, etc. have been difficult to meet these needs.Traditional mainstream semiconductor memories can be divided into two categories: volatile and nonvolatile. Volatile memory includes static random access memory (SRAM) and dynamic random access memory (DRAM). Both SRAM and DRAM lose their saved data when power off. Although RAM is easy to use and performs well, a big disadvantage of it is data loss.Non-volatile memory does not lose stored data in the case of a power failure, because all mainstream non-volatile memories are derived from read-only memory (ROM) technology. ROM, what is called a read-only memory is definitely not easy to write, in fact, it cannot be written at all. All memories developed by ROM technology are difficult to write data, including EPROM, EEPROM and Flash. And these memories not only have a slow writing speed, but also can only be erased and written in a limited number of times.Based on improving semiconductor technologies, ferroelectric memory, a new type of memories, has some unique characteristics. Ferroelectric memory is compatible with all the functions of RAM, and it is a non-volatile memory like a ROM. In other words, ferroelectric memory bridges the gap between these two types of storage, a type of non-volatile RAM. Compared with traditional non-volatile memory, it has attracted much attention due to its advantages such as low power consumption, fast read and write speed, and strong anti-irradiation capability. CatalogⅠ IntroductionⅡ TerminologyⅢ Working PrincipleⅣ FRAM Material FeaturesⅤ Circuit StructureⅥ Reading and Writing ProcessⅦ FRAM StructureⅧ Comparison of FRAM with Other Storage TechnologiesⅨ FRAM UsageⅩ SummaryⅪ One Question Related to FRAM and Going Further11.1 Question11.2 AnswerⅡ TerminologyFerroelectric Memory (FeRAM)Ferroelectric memory (FRAM), also known as F-RAM or FeRAM, is a type of random access memory with fast read and write speed, and the ability to retain data after power is turned off (such as read-only memory and flash memory) is combined, which is the most commonly used type of personal computer memory. Since it is not as dense as dynamic random access memory (DRAM) and static random access memory (SRAM), that is, it cannot store as much data as they do in the same space. In other words, it cannot replace DRAM and SRAM technologies. However, because it can store data quickly with very low power conditions, it is widely used in consumer’s small devices, such as personal digital assistants (PDA), mobile phones, power meters, smart cards, and security systems. FRAM’s read and write speed is faster than flash memory. In some applications, it may also replace electrically erasable read-only memory (EEPROM) and static random access memory (SRAM), and will become a key component of future wireless products. Ⅲ Working PrincipleFeRAM or ferroelectric RAM seems to indicate that an iron element exists within the memory this is not actually the case. A ferroelectric is a material containing a crystal that can spontaneously polarize. It has two states that can be reversed by an external electric field. When an electric field is applied to the ferroelectric crystal, the central atom moves in the crystal following the electric field direction. When an atom moving, it passes through an energy barrier, causing charge breakdown. Internal circuits react to the charge breakdown and set the memory. After the electric field is removed, the central atom remains polarization state, which makes the materials non-volatile, so the state of the memory is preserved. Because there is no atomic collision in the entire physical process, the ferroelectric memory has the characteristics of high read and write speed, ultra-low power consumption, and unlimited writes, making it very suitable to act as temporary storage memory in important systems to transfer various data between subsystems, for each subsystem to read and write frequently.Therefore, with an external electric field, the polarization characteristics of ferroelectric materials will change. When this electric field is removed, the data can still be saved. Without an external electric field, there are two stable states of polarization characteristics. Figure 1 is a hysteresis loop of a ferroelectric material capacitor, showing the different polarities of the ferroelectric capacitor under different applied electric fields. Among them, the two most important parameters are the degree of residual polarization Pr, and the coercive field Ec. In the absence of electric field effect, +/- Pr represents two states of “0” and “1”. To obtain these two states, the applied electric field must be greater than +/- Ec, at this time, the required threshold voltage is also determined.Figure 1. Ferroelectric Hysteresis LoopThe industry explores the use of ferroelectric materials for DRAM: using them as dielectric materials in DRAM capacitors. That is, ferroelectrics are used to replace high-K dielectric materials in standard logic devices, and finally non-volatile transistors are formed, which are FeFETs. The two stable polarization states of the ferroelectric gate oxide change the threshold voltage of the transistor, even when the supply voltage is removed. Therefore, the binary state is encoded in the threshold voltage of the transistor. The writing operation of the memory cell can be completed by applying a pulse on the gate of the transistor, which will change the polarization state of the ferroelectric material and affect the threshold voltage. For example, applying a positive pulse will reduce the threshold voltage, making the transistor in the “on” state. Reading is done by measuring the drain current. This memory mode is similar to the operating mode of a NAND flash: electrons are injected and drawn out of the floating gate, which adjusting the threshold voltage of the transistor.In contrast, the leakage current factor of ferroelectric capacitors is not as important as traditional non-volatile memories such as EEPROM and FLASH, because the information storage of FeRAM is realized by polarization, not free electrons. Ⅳ FRAM Material FeaturesIdeal ferroelectric materials need to meet the following characteristics:Small dielectric constantReasonable self-polarization degree (~ 5μC/ cm2)High Curie temperature (outside the storage and operating temperature range of the device)The thickness of ferroelectric materials should be thin (submicron) to make the coercive field EC smaller. Ferroelectric materials should stand a certain breakdown filed strength.Internal switching speed should be fast (nanosecond level)The ability to keep the data and the long-lasting ability will be good.If used by the military, it is also required to be able to resist radiation exposure. Good chemical stabilityGood processing uniformityEasy to integrate into CMOS processNo bad effect on the surrounding circuitsSmall pollution After years of research and development, there are currently two main types of mainstream ferroelectric materials: PZT and SBT.PZT is lead zirconate titanate PbZrxTil-xO3; SBT is strontium bismuth tantalate Sr1-yBi2 + xTa2O9. The structure of these two materials is shown in Figure 2. Figure 2. Schematic Diagram of PZT and SBT Material StructurePZT is the most studied and widely used. Its advantage is that it can be made at lower temperatures by sputtering and MOCVD. It has the advantages of large residual polarization, cheap raw materials, and low crystallization temperature.; its disadvantages are fatigue degradation problems, and lead pollution to the environment. Moreover, the film deposition process of these materials has proved to be very challenging. At the same time, the extremely high dielectric constant (about 300) of these materials is a big obstacle to their integration into transistors.In addition, scientists have discovered the presence of a ferroelectric phase in a less complex material, hafnium oxide (HfO2), which raise a new concept of storage concept. The researchers found that the ferroelectric phase) can be stabilized by doping silicon (Si) into HfO2. Compared with PZT, HfO2 has a lower dielectric constant and can deposit thin films in a conformal manner (ie, the atomic layer deposition (ALD) process). Most importantly, scientists are familiar with HfO2, because it is the HK gate oxide material in the logic device HKMG. By modifying this CMOS-compatible material, logic transistors can become non-volatile FeFET memory transistors.Functional verification of FeFETs has been implemented in a two-dimensional planar architecture. At the same time, the HfO2 conformal deposition process makes 3D stacking possible, for example, depositing ferroelectric materials on vertical “walls’ to stack transistors in a vertical direction.In terms of materials, 3D FeFETs can solve some of the challenges brought by 2D FeFET structures. One challenge is related to the polycrystalline nature of the HfO2. Scaling the thickness of the HfO2 film will significantly reduce the number of grains in this layer. Because not all the crystal grains have the same polarization direction, the reduction of crystal grains will affect the consistency of the transistor’s response to the external electric field, and eventually lead to large differences between the tubes. By 3D stacking, this drawback is overcome in physical filed. That is, HfO2 does not need to be compressed too thinly, thereby reducing tube-to-tube variation.These vertical FeFETs are expected to have more advantages than complex 3D NAND flash memory, including simple process, lower power consumption and faster speed. Compared to 3D NAND flash memory, vertical FeFET can be programmed at a lower voltage, which improves memory reliability and scalability.The biggest advantage of SBT is that it does not have the problem of fatigue degradation, and it does not contain lead, which meets EU environmental standards; however, its disadvantages are that the process temperature is higher, which makes the process integration difficult, and the degree of residual polarization is small. The comparison of the two materials is shown in Table 1.Table 1. Comparison between PZT and SBT  PZTSBTStructureABO3Layered structureDeposition technologySol-gel,MOCVDSol-gel,MOCVDProcess temperature450℃~700℃750℃~850℃Residual polarity3012Fatigue10101010Data hold85℃@10a- At present, from the perspective of environmental protection, PZT has been banned, but from the perspective of performance and process integration of ferroelectric memory and cost, SBT has no advantages compared to PZT. Therefore, the selection of ferroelectric materials is worth discussing. Ⅴ Circuit StructureThe circuit structure of the ferroelectric memory is mainly divided into the following three types: 2 transistors-2 capacitors (2T2C), 1 transistor-2 capacitors (1T2C), 1 transistor-1 capacitor (1T1C), as shown in Figure 3. The 2T2C structure has two opposite capacitors for each bit as a reference to each other, so the reliability is better, but occupies too much space, which is not suitable for high-density applications. The transistor / single capacitor structure can be used like a DRAM to provide a reference for each column of the memory array, compared with the existing 2T2C structure, they effectively reduce the required space of the memory cell by half. This design greatly improves the efficiency of ferroelectric memory and reduces the production cost of ferroelectric memory products. The 1T1C structure has a higher integration density (8F2), but its reliability is poor. And the 1T2C structure is a compromise between these two structures. Figure 3. Three FRAM StructuresAt present, in order to obtain a high-density memory, 1T1C structure is mostly used (as shown in Figure 4). In addition, a chain structure is also adopted, thus Chain FeRAM is made. This structure is similar to the NAND structure. Through this method, a higher storage density than 1T1C can be obtained, but this method will also greatly increase the access time. Chain FeRAM (CFeRAM) structure is shown in Figure 5. Figure 4. 1T1C Layout Figure 5. Chain FeRAM (CFeRAM) Circuit StructureⅥ Reading and Writing ProcessAccording to the polarity of the electronic memory cell, a small charge amount is “0” and a large charge amount is “1”. This charge is converted into a reading voltage, which is “0” when it is less than the reference voltage and when it is greater than the reference voltage represents “1”. The stored information is read out as shown in Figure 6. Figure 6. Reading and Writing Process of FRAMDuring the reading process, the word line voltage is increased to turn on the MOS transistor, and then the drive line voltage is increased as VCC, so that different charges of the storage capacitor are distributed to the bit line parasitic capacitance, so different voltages appear on the BL to identify the data. During a writing process, the word line is raised to turn on the MOS transistor, and a pulse is applied to the drive line, so that different data on the bit line are stored in two different steady states of the ferroelectric capacitor.By adding a positive voltage or a negative voltage, these two voltages can make the capacitor into two different polarities. In this way, the information is written into the memory. Ⅶ FRAM StructureAt present, the most common device structures of ferroelectric memories are planar and stack structures. The difference between the two is the location of the dry ferroelectric capacitor and the way in which the capacitor is connected to the MOS tube. In the planar structure, the capacitor is placed above the field oxide, and the electrode of the capacitor is connected to the active area of the MOS tube through metal aluminum. The process is relatively simple, but the unit spacing is large. In the stack structure, the capacitor is placed in the source region, the lower electrode of the capacitor is connected to the source terminal of the MOS tube through a plug based on CMP process, which has a high integration density. In addition, the stack structure can adopt the method of making ferroelectric capacitors on metal wires, thereby reducing the mutual influence during the formation process. The following schematic diagrams of the two structures are shown in Figure 7 and Figure 8. Figure 7. Planar Structure Figure 8. Stack StructureThe process of the planar structure is relatively simple. The isolation uses the LOCOS structure, and the planarization does not require the CMP. The stacked structure has a high degree of integration based on advanced technique, and STI is used for isolation, in addition, CMP is required for planarization, and copper wires can be used.In addition, there is a structure that uses a ferroelectric material as the gate. Such a device can eliminate the destructive problem of data readout, and theoretically it is more space-saving and can make more greater integration. However, there are still serious problems with this structure, that is, the data storage capacity is very poor, only one month or less, so it is far from practical. Figure 9 is a schematic diagram of such a structure. Figure 9. FeFET Structure DiagramAt present, the ferroelectric memory generally adopts a planar structure with the line width more than 0.5 μm, and generally uses a stack structure when the line width is less than 0.5 μm. Ⅷ Comparison of FRAM with Other Storage TechnologiesAt present, Ramtron’s FRAM mainly includes two categories: serial FRAM and parallel FRAM. Among them, serial FRAM is divided into I2C two-line FM24×× series and SPI three-line FM25xx series. Serial FRAM is compatible with the traditional 24xx and 25xx E2PROM pins and timing, which can be directly replaced.FRAM products have the advantages of RAM and ROM, and fast read and write speed, in addition, they can be used as non-volatile memory. Due to the shortcoming of ferroelectric crystals, the number of accesses is limited, beyond which FRAM is no longer non-volatile. The maximum access times given is 10 billion, but it not means FRAM will be scrapped when over this upper limit. In the terms of it, FRAM is not non-volatile, but it can still be used as an ordinary RAM.FRAM vs E2PROMFRAM can be used as a second option for E2PROM. Except the performance of E2PROM, the FRAM access speed is much faster. When using FRAM, it must be determined that once there are 10 billion accesses is down to FRAM in the system, there is no damage.FRAM vs SRAMIn terms of speed, price, and convenience, SRAM is better than FRAM; but from the perspective of the entire design, FRAM has certain advantages. Non-volatile FRAM can hold startup programs and configuration information. If the maximum access speed of all the memories in the application is 70ns, one piece of FRAM can be used to complete the system, making the system structure more simpler.FRAM vs DRAMDRAM is suitable for applications where density and price are more important than access speed. For example, DRAM is the best choice for graphics display memory. There are a large number of pixels to be stored, and the recovery time is not very important. If you don’t need to save the last content at the next boot, use volatile DRAM memory. The role and cost of DRAM are reasonable compared with FRAM. In short, it turns out that DRAM cannot be replaced by FRAM totally.FRAM vs FlashAt present, the most commonly used program memory is Flash, which is more convenient and cheaper to use. The program memory must be non-volatile, and easier to rewrite, but the use of FRAM is limited by access times.Ⅸ FRAM UsageData collection and recordingFeRAM allows designers to write data faster and more frequently, and at a lower price than EEPROM.Typical applications: meters (electric meters, gas meters, water meters, flow meters), RF/ID instruments, car black boxes, air bags, GPS, power grid monitoring systems, and so on. Parameter setting and storageFeRAM helps designers solve the problem of data loss due to sudden power failure by storing data in real time. Parameter storage in the FeRAM is used to track the changes of the system in the past time. Its purpose includes restoring the system state or confirming a system error when the power is on.Typical applications: photocopiers, printers, industrial controls, set-top boxes, network equipment  and large household appliances. Non-volatile bufferFeRAM can quickly store data before it is stored in other memory, so that the data in the buffer will not be lost when having power failure.Typical applications: industrial systems, ATM teller machines, tax control machines, commercial settlement systems (POS), fax machines, non-volatile cache memory in hard disk, etc. Ⅹ SummaryFerroelectric memory is an emerging non-volatile memory. It started early and realized industrialization. Because of its advantages such as low power consumption, fast read and write speed, and strong anti-irradiation capabilities, there is a market for small-scale storage areas with low power consumption and radiation resistance. Having the characteristic of anti-radiation, in the case of electromagnetic waves or radiation, the data is still safe, so it has important applications in space science, medicine and other specific fields. However, the ferroelectric memory also has the disadvantages that it is difficult to improve the integration, the process is more contaminated, and it is difficult to be compatible with the CMOS technique. So that it needs further research and solution. Ⅺ One Question Related to FRAM and Going Further11.1 QuestionWhat is FRAM used for?11.2 AnswerFerroelectric RAM is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. It is one of a growing number of alternative non-volatile random-access memory technologies that offer the same functionality as flash memory. FRAM can be used in many fields, for example, with ultra-low power consumption, it is very suitable for intelligent water meters, gas meters and so on. Frequently Asked Questions about Ferroelectric RAM1. What is FRAM memory?Ferroelectric RAM (FeRAM, F-RAM or FRAM) is a random-access memory similar in construction to DRAM but using a ferroelectric layer instead of a dielectric layer to achieve non-volatility. 2. What is ferroelectric effect?Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. ... Thus, the prefix ferro, meaning iron, was used to describe the property despite the fact that most ferroelectric materials do not contain iron. 3. How does FRAM work?FRAM is a nonvolatile storage memory that retains its data even after the power is turned off. However, similar to commonly used DRAM (Dynamic Random Access Memory) found in personal computers, workstations, and non-handheld game-consoles, FRAM requires a memory restore after each read. 4. What are the unique characteristics of FRAM?FRAM has the characteristics of both ROM (Read Only Memory) and RAM (Random Access Memory), and features faster write, great read/write cycle endurance, and low power consumption. 5. Which enables the read and write operation in Feram?Write Operation in Ferroelectric Random Access Memory (FRAM)Similar to read operation, a pre-charge operation follows a write access. The circuit applies 'write' data to the Ferroelectric capacitors. If necessary, the new data simply switches the state of the ferroelectric crystals.