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IntroductionThe mass air flow sensor, also known as the air flow meters, is one of the important sensors of the electronic jet engine. It converts the inhaled air flow into electrical signals and sends them to the Electronic Control Unit (ECU). As one of the basic signals to determine fuel injection, it is a sensor to measure the inhaled air flow into the engine.      CatalogIntroductionCatalogⅠ OverviewⅡ Structural PrincipleⅢ The Structure of the Valve Type Air Flow SensorⅣ Karman Scroll Air Flow SensorⅤ Measuring RangeⅥ Detection PrincipleⅦ Ultrasonic Karman Vortex Air Flow SensorⅧ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionⅨ FAQⅠOverviewIn order to obtain the best concentration of the mixture under various operating conditions, the electronically controlled gasoline injection engine must accurately measure the amount of air inhaled into the engine at each moment, which is the main basis for the ECU to calculate (control) the amount of fuel injection.  If the air flow sensor or circuit fails and the ECU does not get the correct intake signal, it will not be able to control the fuel injection properly, which will cause the mixture to be too thick or too thin, and the engine will not operate properly. There are many types of air flow sensors in the electronic controlled gasoline injection system. According to their structure types, the common air flow sensors can be divided into blade (wing) type, core type, hot-wire type, hot film type, Karman vortex type, etc.                     Ⅱ Structural PrincipleIn the electronic controlled fuel injection device, the mass air flow sensor, which measures the amount of air absorbed by the engine, is one of the important components to determine the control precision of the system. When the control precision of the air-fuel ratio (A/F) of the air and mixture inhaled by the engine is specified as ±1.0, the allowable error of the system is ±6[%]~7[%]. When the allowable error is distributed to each component of the system, the allowable error of the air flow sensor is ±2[%]~3[%]. The ratio of the maximum value to the minimum value of the air flow rate inhaled by a gasoline engine is 40-50 in a natural intake system, and 60-70 in a supercharged system. In this range, the air flow rate of the sensor should be able to maintain a measurement accuracy of ±2~3[%]. The air flow sensor used in the electronic control fuel injection device should not only maintain the measurement accuracy over a wide measurement range, but also have excellent measurement response and can be measured. For pulsating air flow, the output signal processing should be simple. According to the different characteristics of the air flow sensor, the fuel control system is divided into L-type control for direct measurement of air intake volume and D-type control for indirect measurement of air intake volume (indirect measurement of air intake according to the negative pressure of the intake manifold and the engine speed).                                                           The microcomputer ROM in the D-type control mode stores in advance the intake air volume under various conditions based on the engine speed and the pressure in the intake pipe. The microcomputer is based on the measured operation. The intake pressure and speed in the state, referrring to the intake volume memorized by ROM, can calculate the fuel volume. The air flow meter used for L-type control is basically the same as the general industrial flow sensor, but it can adapt to the harsh environment of the car, but it is the response requirements for the rapid changes in the flow rate that occur during the throttle and the requirements for high-precision detection in the uneven airflow caused by the shape of the intake manifold before and after the sensor. The original electronic fuel injection control system did not use a microcomputer. It was an analog circuit. At that time, a valve-type air flow sensor was used, but several other air flow sensors emerged as microcomputers were used to control fuel injection.Ⅲ The Structure of the Valve Type Air Flow SensorThe valve type air flow sensor is mounted on the gasoline engine and installed between the air filter and the throttle. Its function is to detect the air intake of the engine and convert the detection results into electrical signals, which are then input into the microcomputer. The sensor is composed of an air flow meter and potentiometer. Look at the working process of the air flow sensor first. The air drawn in by the air filter rushes to the valve, and the valve turns to stop at the position where the intake is balanced by the return spring. In other words, the opening of the valve is proportional to the intake.  A potentiometer is also installed on the rotating shaft of the valve, and the sliding arm of the potentiometer rotates synchronously with the valve. The voltage drop of the sliding resistance is used to convert the opening of the measuring piece into an electrical signal, which is then input into the control circuit.Ⅳ Karman Scroll Air Flow SensorIn order to overcome the shortcomings of the valve type air flow sensor, that is, under the premise of ensuring measurement accuracy, expanding the measurement range and eliminating the sliding contact, a small and lightweight air flow sensor has been developed, namely the Karman Vortex Air Flow Sensor. The Karman vortex is a physical phenomenon. The vortex detection method and electronic control circuit have nothing to do with the detection accuracy. The air path area and the size change of the vortex column determine the detection accuracy. Because the output of such a sensor is an electronic signal (frequency), the AD converter can be eliminated when the signal is input to the control circuit of the system. Therefore, in essence, the Karman vortex air flow sensor is a signal suitable for microcomputer processing. This sensor has the following three advantages: high test precision, which can output linear signal and signal processing is simple; long-term use and performance will not change; because it detects volume flow, it does not need to correct temperature and atmospheric pressure.                                     The principle of flow detection of this air flow sensor is that when a Karman vortex is generated, it follows the change of speed and pressure. The basic principle of flow detection is to make use of the velocity change. The signal waveform output from the air flow sensor to the control module is shown in the figure. The signal is a square wave and a digital signal. The more air intake, the higher the frequency of the Karman vortex, and the higher the frequency of the output signal of the air flow sensor. The temperature and pressure compensation air flow sensor, mainly used for industrial pipeline flow measurement of medium fluid, such as gas, liquid, vapor and other media. It is characterized by small pressure loss, large range, high precision, and is almost unaffected by fluid density, pressure, temperature, viscosity and other parameters when measuring volume flow in working conditions.Features of the Karman Vortex Flow Meter                                There are no movable mechanical parts, so the reliability is high and the maintenance is small. The instrument parameters can be stable for a long time. This instrument adopts piezoelectric stress sensor, which has high reliability and can work in the working temperature range of -10℃~+300℃. There are analog standard signals and digital pulse signal outputs, which are easy to use with digital systems such as computers. It is a relatively advanced and ideal flow. The biggest advantage of the air flow sensor is that the meter coefficient is not affected by the physical properties of the measuring medium, and can be extended from a typical medium to other mediums. However, the frequency range is also very different because of the great difference between liquid and gas velocity ranges. In the amplifier circuit that processes the vortex signal, the passband of the filter is different, and the circuit parameters are also different. Therefore, the same circuit parameter cannot be used to measure different media.Ⅴ Measuring Range             Ⅵ Detection PrincipleOverhead power lines in the field whine when blown by the wind. The higher the wind speed is, the higher the sound frequency will be. This is because the air flows through the wire and forms a vortex. This phenomenon can occur in liquid, gas and other fluids, which can be used to make a vortex flow sensor. After the column is placed in the tube, two rows of vortices are formed, and the flow rate can be measured according to the frequency of occurrence of the vortices. Because the vortex turns into two parallel rows and alternates left and right, similar to the street lights on both sides of the street, it is called the vortex street. Because this phenomenon was first discovered by Karman, it is also called Karman Vortex Street.                                  Karman Vortex StreetⅦ Ultrasonic Karman Vortex Air Flow SensorThe ultrasonic air flow sensor is provided with two intake channels, the main channel and the side channel. The detection part of the intake flow is located on the main channel. The purpose of setting the side channel is to adjust the flow of the main channel so as to make the detection characteristics of the main channel present an ideal state. That is to say, for engines with different exhaust volume, one specification of air flow sensor can be used to cover a variety of engines by changing the cross-section size of the air flow sensor channel. The Karman vortex generator is composed of triangular columns and several vortex amplifiers on the main channel. On both sides of the place where the Karman vortex is generated, the ultrasonic transmitter and the ultrasonic receiver belonging to the electronic detection device are arranged oppositely. These two components can also be classified into the sensor. The electrical signal generated by the two electronic sensors is passed through the air. The control circuit (hybrid integrated circuit) of the flow sensor is shaped and amplified into an ideal waveform, and then input to the microcomputer. In order to detect vortices by ultrasound, sound-absorbing materials are glued to the inner wall of the vortex channel to prevent irregular reflections of ultrasonic waves.Ⅷ Karman Vortex Type Air Flow Sensor for Pressure Change DetectionThe vortex occurs alternately from both ends of the vortex generator, so the pressure at both ends of the vortex generator also alternately changes. This pressure change is guided to the mirror cavity through the pressure guide hole on the cone-shaped column on the downstream side of the vortex generator. In the mirror cavity, the mirror in the mirror cavity is tensioned with a very thin tension band, so distortion and vibration appear on the tension band. In addition, a leaf spring is used to apply appropriate tension to the tension band. Pressure changes other than vibration and scroll pressure are difficult to affect, so stable torsion and vibration can be obtained. The pressure formed by the vortex passes through the pressure guide hole to the reflector cavity, and the pressure changes synchronously with that in the reflector, and the reflector twists and vibrates in the tension band. The reflector is very lightweight and can operate even at low flow rates and very small pressure changes. On the upper part of the reflector, a light sensor composed of light-emitting diodes and phototransistors is correspondingly arranged. When the light emitted by the diode is reflected by the reflector and hits the phototransistor, it will become a current and output after the waveform circuit.Ⅸ FAQ1. What is the difference between the MAF sensor and the oxygen sensor?The MAF is the Mass Air Flow sensor and just as the name implies the sensor measures the mass of air going into the engine at the sensor (this is important because vacuum leaks or unmetered air is unaccounted for on the MAF sensor). Typically it uses a heated element and the air moving across the element cools it to "measure" the incoming air, however, vane style meters existed in the earlier days of electronic fuel injection. There are upstream and downstream oxygen sensors. The upstream sensor is responsible for checking the exhaust output of the engine. If there is too much fuel left in the exhaust the O2 sensor sends that information to the ECU and it will "trim" it out. If the O2 sensor samples the exhaust and there is too much oxygen in the exhaust stream then the sensor sends that info to the ECU and it will command more fuel. The downstream O2 sensor is present to monitor the condition of the catalytic converter(s). If it is out of range the ECU will flag it and the check engine light will illuminate. This is a very simple, quick, overview of the sensors but should give you a basic idea of their operation. 2. What are the symptoms of a bad mass airflow sensor?A faulty mass airflow sensor will cause problems similar to low compression or low vacuum, and will also show symptoms similar to when your vehicle has low fuel pressure from a faulty fuel pump. Here are some of the most common symptoms of a faulty mass airflow sensor:The engine is very hard to start or turn overThe engine stalls shortly after startingThe engine hesitates or drags while under load or idleHesitation and jerking during accelerationThe engine hiccupsExcessively rich or lean idling 3. How does a MAF sensor work?Installed in the intake pipe between the air filter housing and the intake manifold, most MAF sensors work on the hot wire principle. Put simply, a MAF has two sensing wires. One is heated by an electrical current, the other is not. As air flows across the heated wire, it cools down. When the temperature difference between the two sensing wires changes, the MAF sensor automatically increases or decreases the current to the heated wire to compensate. The current is then changed to a frequency or a voltage that is sent to the ECU and interpreted as airflow. The quantity of air entering the engine is adjusted accordingly. 4. Can a car run without a mass airflow sensor?Well, the answer to that is no. If you disconnect the mass airflow sensor, then the car should keep running and still be able to start normally. This means that if your mass airflow sensor dies completely, then your car will stay running and surprisingly the car might run better without the mass airflow sensor. 5. Why a MAF sensor needs to be replaced?If the sensor gets dirty, it won’t be able to read the airflow. When the MAF sensor doesn’t work, the engine may idle roughly, hesitate, and have difficulty starting. It may even stall on you while driving, which is no fun. The most common cause for the sensor to become dirty is an air filter that doesn’t get replaced when needed. When the air filter is clogged, it allows more dirt and debris to slip by and accumulate on the sensor. Routine maintenance and air filter replacement can extend the life of your MAF sensor and ensure it continues to work correctly. While the exact timing varies based on where and how much you drive, a good rule to follow is every 10,000 to 12,000 miles. 6. What will a bad mass airflow sensor do?A contaminated or failed mass air flow sensor cannot measure the amount of air flow correctly. This causes the engine computer to miscalculate the amount of injected fuel. As a result, a bad mass air flow sensor causes various driveability problems, including a no-start, stalling, lack of power and poor acceleration. 7. Will a bad mass airflow sensor cause a misfire?If an oxygen sensor or mass airflow sensor is failing, it could give incorrect data to your engine's computer, causing the misfire. When a vacuum line is broken, it can cause a fuel-injected motor to misfire. ... Replacing a vacuum line that's gone bad can potentially resolve the misfire. 8. How long does it take for the mass air flow sensor to reset?When you change a MAF sensor, you need to disconnect the battery for about 10 minutes so the computer forgets the learned parameters and resets to the factory parameters. Then it goes into learn mode and may take a little while before it learns all the parameters of the new MAF sensor. 9. How long can I drive with MAF unplugged?When you unplug the MAF, the computer goes to a default value stored in your memory. Your fuel economy will probably suffer a little bit, but no big issues. You're OK for a week or two, but replace the MAF with a proper TDI unit. The long-term effect is that the car does not operate to its full potential. 10. Can you bypass a MAF sensor?There is a sensor on the air intake called the mass air flow sensor. This sensor calculates how much air to mix with the fuel. You can bypass the MAF sensor, and allow the O2 sensor to calculate how much air is needed. 

IntroductionA potentiometer is a three-terminal resistor with a sliding or rotating contact. It is an adjustable voltage divider with two static contacts and one moving contact. The moving terminal is a wiper that travels across the resistance element, usually in an arc controlled by a rotary knob. Rotating the knob gives a ratiometric division of the potential across the resistance element. Potentiometer generally used in speakers and receivers for volume control. In addition, it cannot directly control the motor because its power is too small. When potentiometer acting as a voltage divider, the absolute resistance of the potentiometer will not affect the output voltage, and its output voltage is proportional to the input voltage.Figure 1. Potentiometer StructureCatalogIntroductionⅠ Potentiometer WiringⅡ Potentiometer Symbol and Diagram DescriptionsⅢ Potentiometer Voltage Divider Circuit BasicsⅣ Potentiometer Resistance MeasuresⅠ Potentiometer WiringThe potentiometer can be used as a three-terminal component or a two-terminal component. The latter can be regarded as a rheostat. For a general potentiometer (three pins), the slider near the center which is a resistance wire. The two pins at both ends of the resistance wire are connected to the input and the ground (some are not connected), respectively. That is, one pin is connected to the input signal and the other pin is grounded. At this time, the resistance wire has a total resistance value on the two sections. You move the sliding piece to go across this resistance wire to get a variable resistance. If the input and output signals are reversed, the sliding direction of the slide is opposite to the resistance change.How to Wire a Potentiometer1) For a potentiometer (or a trimming resistors) with traditional pins (three pins), the resistance at both ends is fixed, and the resistance of the middle pin is variable. That is, the terminal on both sides of the potentiometer are total resistance, and the middle is changing. For example, the power supply is connect from any one contact on resistor sides and output from the middle contact, and the voltage changes with the rotation of the middle contact.Figure 2. Potentiometer Voltage Divider Output2) Although the resistance can vary with the slider, the total resistance value of pins is fixed. At this time, the potentiometer is equal to a current controller, and the selected current output terminals must be the sliding terminal. Commonly used potentiometers have poor resistance accuracy and poor temperature coefficient, but as long as the resistance of the potentiometer is uniform, so is the output voltage value.Figure 3. Potentiometer as Voltage Divider3) If a potentiometer used as a variable voltage divider, one contact connects to the input voltage, the middle contact connects to the output voltage, and the other contact can be grounded. When the rotary handle or sliding handle of the potentiometer take action, the movable contact slides on the resistor. At this time, an output voltage that has a certain relationship with the external voltage, wiper angle and travel stroke.4) If a potentiometer used as a variable resistor, one end connects to the input voltage, the middle end connects to the output, and the other end can be suspended or connected to the middle end to obtain a smooth and continuously changing resistance value.Figure 4. Potentiometer Connected as Variable Resistor As above mentioned, a potentiometer can be connected as a variable resistor, if you want to know more info, you can get it from The Differences Between Potentiometer and Adjustable Resistor. Ⅱ Potentiometer Symbol and Diagram DescriptionsNamePotentiometer SymbolDescriptionNormal PotentiometerUse RP (resistor potentiometer) to represent the potentiometer. The symbol in the figure mark the 3 pins of the potentiometer, indicating the chip pins.Potentiometer SwitchS1 is a switch attached to the RP, and S1 is controlled by the RP rotary handle. When you start to turn the handle, after the switch closes, this circuit is the same as a normal potentiometer. This kind of potentiometer is mainly used in volume control circuits with power switches.As a Variable ResistorThe potentiometer at this time can be regarded as a variable resistor.A Potentiometer with dual portDivide the 3 pins of the potentiometer into 4 ends to form a dual-port circuit. That is, terminals 1 and 2 input signals, terminals 3 and 4 output signals, and terminals 2 and 4 are common terminals, which usually connected to the ground of the line.Dual Gang PotentiometersIt has two single potentiometer circuit symbols, which are connected by a dotted line to indicate that the resistances of dual gang potentiometer are adjusted simultaneously, that is, their resistance values increase or decrease at the same time.Half Linear StrokeThis is a special dual gang potentiometer. Two potentiometer travel strokes are synchronized, but their resistance changes are not the same during adjustment. Only one mechanical stroke of this kind of potentiometer changes in resistance, and the resistance value of the silver zone is zero of another one. The silver zone with no resistance is indicated by shading in the circuit symbol. When the moving contact slides up from the middle, the moving piece RP-1 will enter the silver zone, and RP-2 will enter the varistor area; when the moving handle slides down from the middle position, the RP-2 will enter the silver zone, and RP-1 enters the varistor zone. This special potentiometer can be used in a stereo balance controller circuit (a control circuit in stereo equipment).With Central TapIt has one more pin than the ordinary potentiometer, that is, the tapping pin. The tapping pin is set at the middle resistance of the potentiometer, and the resistance between the tap and the two fixed contacts is equal. There are also potentiometers whose taps are not set in the middle position.Figure 5. Potentiometer CircuitsⅢ Potentiometer Voltage Divider Circuit Basics1) The resistor of the potentiometer is mostly made of polycarbonate synthetic resin. The following items should be avoided: ammonia, other amines, aqueous alkali solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, strong chemicals (excessive pH), etc., otherwise it will affect potentiometer performance.2) When soldering the potentiometer terminals, avoid using water-capacitive flux, which will cause metal oxidation and mold material. Using inferior flux, poor soldering may cause problems in soldering, resulting in poor contact or open circuit.3) If the soldering temperature of the terminal is too high or the soldering time is too long, it may cause damage to the potentiometer. The temperature range of the plug-in potentiometer is 235℃±5℃; the wire bonding type is 350℃±10℃, and the soldering point should be more than 1.5mm away from the potentiometer body. In addition, avoid heavy pressure on the terminals, otherwise it is easy to cause poor contact.4) During soldering, the height of the flux entering the printing machine board should be adjusted properly, and it should be avoided to affect the potentiometer. Because it will cause poor contact between the brush and the resistor, or result in noise.5) The potentiometer is better in the voltage adjustment structure.6) Avoid condensation or water droplets on the surface of the potentiometer, and avoid using potentiometer in a humid place to prevent insulation deterioration or short circuit.7) When fixing the screws of the rotary potentiometer, the strength should not be too strong to avoid poor rotation. For the direct-sliding potentiometer, avoid using too-long screws, otherwise it may hinder the movement of the sliding handle and even damage the potentiometer itself.8) In the process of putting the potentiometer on the knob, the pushing force should not be too large (don’t exceed the parameter index of the rated pushing and pulling force), otherwise it may cause damage to the potentiometer.9) The rotary force of the potentiometer will decrease as the temperature increases, and become smaller as the temperature decreases. If the potentiometer is used in a low temperature environment, it needs special low temperature resistant grease.Figure 6. Potentiometer Voltage Divider Circuit Connections10) If the shaft or sliding handle of the potentiometer is too long, it is easy to shake and cause the instability of the circuit signal.11) The carbon film of the potentiometer can withstand the ambient temperature of 70℃, and its function may be lost when the temperature is higher than 70℃.12) For a adjustable potentiometer, when the DC is allowed to pass through the movable contact, the problem of anodic oxidation may occur. In this case, it is best to connect the component with the negative end and connect the moving contact with the positive end.13) The load current of the adjustable potentiometer cannot be increased at will to keep circuit safety. And actual current measurement would be to put ammeter in series with the potentiometer in the active circuit.14) Do not exceed the rated power when using the adjustable potentiometer. For example, when the power dissipation exceeds the rated value, it will cause the potentiometer to overheat.15) A Potentiometer is sensitive if it is capable of measuring very small potential differences, and shows a significant change in balancing length for a small change in potential difference being measured.16) A DC potentiometer is created by dropping voltage across a set of resistors in series. Different resistors will produce different values. In AC potentiometer, one can use resistors or even inductors or capacitors as impedances which will drop voltages and provide a voltage less than applied voltage.17) If positioned the potentiometer wiper on the center of the resistor element then the voltage at the wiper is 50%; if the wiper is positioned 1/4 of the way from the negative node then the wiper voltage is 1/4th the entire voltage.18) Potentiometer nomenclature: It generally use the direct marking method. Letters and numbers are marked on the potentiometer shell to indicate their model, nominal power, resistance, and the relationship between resistance and rotation angle.If you have any interest, with a deep reading, you can get more info from What is the Voltage Divider Basic and Rule. Ⅳ Potentiometer Resistance MeasuresThe main checking requirements for the potentiometer are: ① The resistance value meets the circuit requirements. ② The connection between the center sliding end and the resistor is good, and the rotation is smooth. For potentiometer with switches, the switch action should be accurate, reliable and flexible. Therefore, the performance of the potentiometer must be checked before use.1) Resistance measurement: First, select the appropriate gear of the multimeter according to the resistance of the measured potentiometer. Whether the resistance between the two ends of the AC is consistent with the nominal resistance. Rotate the sliding contact, and its value should be fixed. If the resistance indicates infinite, the potentiometer is damaged.2) Then measure the contact between the center end and the resistor, that is, the resistance between the two ends of BC. The method is to set the ohm range of the multimeter in the appropriate range. During the measurement, slowly rotate the shaft and observe the reading of the multimeter. Normally, the reading changes steadily in one direction. If there is a jump, drop, or blockage, it means that the movable contact has failures.3) When the center end slides to the head or the end, the resistance value of the center end and the coincident end is 0 for an ideal state. In the actual measurement, there will be a certain value (generally determined by the nominal value, generally less than 5Ω), which is normal. Frequently Asked Questions about Potentiometer Voltage Divider1. How can a potentiometer be used as a voltage divider?Potentiometers can be used as voltage dividers. To use the potentiometer as a voltage divider, all the three pins are connected. One of the outer pins is connected to the GND, the other to Vcc and the middle pin is the voltage output. Basically, the voltage divider is used to turn a large voltage into a smaller one. 2. How does a potentiometer affect voltage?When the potentiometer resistance is decreased (the wiper moves downwards) the output voltage from pin 2 decreases producing a smaller voltage drop across R2. Likewise, when the potentiometer resistance is increased (the wiper moves upwards) the output voltage from pin 2 increases producing a larger voltage drop. 3. What is a dual gang potentiometer?It means two potentiometer combined on the same shaft, enabling the parallel setting of two channels. Most common are single turn potentiometers with equal resistance and taper. 4. How many volts can a potentiometer handle?100 voltsIf the potentiometer is rated at 1 Watt, you can only apply a maximum of 100 volts. I.e 10 mA. That applied to the voltage across the full 10000 ohms. That also means that you cannot pass more than 10 mA into the Wiper.

IntroductionDefinition: A ceramic capacitor is a capacitor that has a ceramic dielectric as its dielectric material. Multi-layer ceramic capacitors and ceramic disc capacitors are the two most common types. The dielectric in a ceramic capacitor is ceramic. Ceramics, a well-known insulator, is one of the first materials used in the manufacture of capacitors. Ceramic capacitors come in a variety of geometric forms, some of which have been phased out due to size, parasitic effects, or electrical characteristics, such as ceramic tubular capacitors and barrier layer capacitors. Multi-layer ceramic capacitor, also known as ceramic multi-layer chip capacitor (MLCC), and ceramic disc capacitor are the two types of ceramic capacitors most widely used in modern electronics.                                                                                                                                             Typical Multilayer Ceramic Capacitor With a production volume of about 1000 billion devices per year, MLCCs are the most widely used capacitors. Due to their small size, they are commonly used and manufactured using SMD (surface-mounted) technology. Ceramic capacitors are usually made with very small capacitance levels, ranging from 1nF to 1F, with a maximum capacitance of 100F. Ceramic capacitors are thin, and their maximum rated voltage is low. Since they lack polarity, they can be safely linked to AC electricity. Due to low parasitic effects including resistance and inductance, ceramic capacitors have excellent frequency response. Ceramic capacitors have the following advantages over other capacitors: small size, large capacity, good heat resistance, mass production suitability, and low price.CatalogIntroductionCatalogⅠThe Origin of Ceramic CapacitorsⅡ Classification of Ceramic Capacitors  2.1 Semiconductor Ceramic Capacitors  2.2 High Voltage Ceramic CapacitorsⅢ Characteristics  3.1 Precision and Tolerance  3.2 Size Advantages  3.3 High Voltage and High PowerⅣ Ceramic Dielectric TypesⅤ Construction and Properties of Ceramic Capacitors  5.1 Ceramic Disc Capacitors  5.2 Multi-layer Ceramic Capacitor (MLCC) Ⅵ Advantages and Disadvantages  6.1 Advantages  6.2 DisadvantagesⅦ Applications for Ceramic CapacitorsⅧ How to read ceramic capacitor value?Ⅸ How to Test Ceramic Disc CapacitorⅩ FAQⅠThe Origin of Ceramic CapacitorsLombardi from Italy invented ceramic dielectric capacitors in 1900. It was discovered in the late 1930s that by adding titanate to ceramics, the dielectric constant can be doubled, resulting in cheaper ceramic dielectric capacitors. Ceramic capacitors were first used in military electronic equipment around 1940, following the discovery of the insulation properties of BaTiO3 (Barium titanate), the primary raw material for today's ceramic capacitors. Around 1960, ceramic laminate capacitors became commercially available. It had become an essential part of electronic devices by 1970, thanks to the rapid growth of hybrid IC, computers, and portable electronic devices. Ceramic dielectric capacitors currently account for approximately 70% of the overall capacitor market.                                                                                                             Historic Ceramic CapacitorsⅡ Classification of Ceramic Capacitors2.1 Semiconductor Ceramic Capacitors(1)Surface Layer Ceramic CapacitorThe miniaturization of capacitors, that is, the capacitor obtains the largest possible capacity in the smallest possible volume, which is one of the development trends of capacitors. For the separation of capacitor components, there are two basic approaches to miniaturization: ①Make the dielectric constant of the dielectric material as high as possible; ②Make the thickness of the dielectric layer as thin as possible. Among ceramic materials, the dielectric constant of ferroelectric ceramics is very high, but when ferroelectric ceramics are used to manufacture ordinary ferroelectric ceramic capacitors, it is difficult to make the ceramic dielectric very thin. Firstly, due to the low strength of ferroelectric ceramics, it is difficult to carry out actual production operations because it is easy to fracture when it is thin. Secondly, when the ceramic medium is fragile, it is easy to cause various structural defects and the production process will be challenging.(2)Grain Boundary Layer Ceramic CapacitorThe surface of BaTiO3 semiconductor ceramics with sufficiently developed grains is coated with appropriate metal oxides (such as CuO or Cu2O, MnO2, Bi2O3, Tl2O3, etc.), and heat treatment is performed under oxidizing conditions at appropriate temperatures. Then the substance will form a low eutectic solution phase with BaTiO3, rapidly diffuse and penetrate into the ceramic along with the open pores and grain boundaries, forming a thin solid solution insulating layer on the grain boundaries. The resistivity of this thin solid solution insulating layer is very high (up to 1012~1013Ω·cm). Although the ceramic grain interior remains as semiconductor, the entire ceramic body is shown as the dielectric constant of 2×104 to 8×104 dielectric medium. Capacitors made with this kind of porcelain are called boundary layer ceramic capacitors, or BL capacitors for short.2.2 High Voltage Ceramic CapacitorsThe ceramic materials of high-voltage ceramic capacitors are barium titanate-based and strontium titanate-based. Barium titanate-based ceramic materials have the advantages of high dielectric coefficient and good AC withstand voltage characteristics, but also have the shortcomings of capacitance change rate with the increase of medium-temperature and decrease of insulation resistance. The Curie temperature of strontium titanate crystal is -250℃, and it is a cubic perovskite structure at room temperature.  It is a para-electric body, and there is no spontaneous polarization phenomenon. Under high voltage, the dielectric coefficient of strontium titanate ceramic material changes little. The dielectric loss tangent value (tgδ) and capacitance change rate are small, which makes it a high-voltage capacitor dielectric. 2.3 Multilayer Ceramic CapacitorsMultilayer ceramic capacitors are the most widely used type of electronic component. They are stacked alternately in parallel with the internal electrode material and ceramic body and fired into a whole, also known as chip monolithic capacitors. It has the characteristic of small size, high specific volume and high precision. It can be mounted on a printed circuit board (PCB) and hybrid integrated circuit (HIC) substrates. It can effectively reduce the volume and weight of electronic information terminal products (especially portable products), and also improve product reliability.                                                             Multilayer ceramic capacitors conform to the IT industry's development direction of miniaturization, lightweight, high performance, and multifunction. The outline of the national vision goal for 2010 clearly puts forward that new components such as surface-mounted components should be the development focus of the electronic industry. It is not only simple packaging, good sealing, and can effectively isolate the opposite electrode. MLCC can store charge, block DC, filter merge, distinguish different frequencies and tune the circuit in the electronic circuit.  It can partially replace organic film capacitors and electrolytic capacitors in high-frequency switching power supplies, computer network power supplies and mobile communication equipment. What's more, it can greatly improve the filtering performance and anti-interference performance of high-frequency switching power supplies.                                                Ⅲ Characteristics3.1 Precision and ToleranceCeramic capacitors are currently available in two classes: class 1 and class 2. When high stability and low losses are needed, Class 1 ceramic capacitors are used. They are extremely precise, and the capacitance value remains constant regardless of applied voltage, temperature, or frequency. Within a total temperature range of -55 to +125 °C, the capacitance thermal stability of the NP0 series of capacitors is 0.54%. The nominal capacitance value's tolerances can be as poor as 1%. Class 2 capacitors have a large capacitance per volume and are used in less sensitive applications. Their thermal stability in the operating temperature range is usually 15%, and nominal value tolerances are about 20%.3.2 Size AdvantagesMLCC devices outclass other capacitors when high component packing densities are needed, as is the case in most modern printed circuit boards (PCBs). The “0402 multi-layer ceramic capacitor package” measures just 0.4 mm x 0.2 mm to demonstrate this point. There are 500 or more ceramic and metal layers in such a box. As of 2010, the minimum ceramic thickness was on the order of 0.5 microns.3.3 High Voltage and High PowerCeramic capacitors that are physically bigger and can withstand even higher voltages are known as power ceramic capacitors. These are much larger than the ones used on PCBs, and they have specialized terminals for connecting to a high-voltage supply safely. Ceramic capacitors with a power specification of much more than 200 volt-amperes can withstand voltages ranging from 2 kV to 100 kV. Printed circuit boards use smaller MLCCs that are rated for voltages ranging from a few volts to several hundreds of volts, depending on the application.Ⅳ Ceramic Dielectric TypesUnlike other capacitor types such as tantalum capacitors and electrolytic capacitors, ceramic capacitors may use a variety of dielectrics. These various dielectrics give capacitors very different properties, so in addition to deciding on a ceramic capacitor, a second decision about the type of dielectric may be needed. Popular ceramic capacitor dielectrics, such as C0G, NP0, X7R, Y5V, Z5U, and many others, are frequently listed in distributors' lists. However, determining which form is best necessitates a little more study. Ceramic Capacitor Dielectric ClassesSome industry organizations have identified a range of ceramic dielectric application classes to make selecting capacitors with the appropriate dielectric easier. These application groups divide the various ceramic capacitor dielectrics into separate classes based on the anticipated application.     International bodies such as the IEC (International Electrotechnical Commission) and the EIA (Electronic Industries Alliance) have standardized these ceramic capacitor classes.Ⅴ Construction and Properties of Ceramic Capacitors5.1 Ceramic Disc CapacitorsCeramic disc capacitors are made by coating a ceramic disc on both sides with silver contacts. These devices can be constructed from several layers to achieve higher capacitances. Ceramic disc capacitors are usually through-hole components that have lost popularity due to their large scale. If capacitance values allow, MLCCs are used instead. Ceramic disc capacitors have capacitance values ranging from 10pF to 100pF and voltage ratings ranging from 16 volts to 15 kV and beyond.                                                                    5.2 Multi-layer Ceramic Capacitor (MLCC)MLCCs are made by combining finely ground granules of paraelectric and ferroelectric materials and layering the mixture with metal contacts alternately. Following the layering, the device is heated to a high temperature and the mixture sintered, yielding a ceramic substance with the desired properties. The capacitance of the resulting capacitor is increased by connecting several smaller capacitors in parallel. MLCCs are made up of 500 layers or more, with a minimum layer thickness of 0.5 microns. As technology advances, layer thickness decreases, allowing for higher capacitances in the same volume.Ⅵ Advantages and Disadvantages6.1 AdvantagesThe following are some of the benefits of using a ceramic capacitor:• This capacitor's physical structure is very compact.• It is well suited for the application of AC signals due to its non-polarized nature.• Signal interference suppression, such as radiofrequency suppression and electromagnetic interference suppression, is improved with these capacitors.• This capacitor is reasonably priced, and it can withstand voltages of up to 100 volts.6.2 DisadvantagesThe following are the drawbacks of using these capacitors:• The capacitance value of these capacitors is less than one microfarad.• These components are also responsible for the Microphonic effect in circuits.• It is unable to withstand high voltages. Since it can easily impact the dielectric present in it. As a consequence, there is a breakdown.Ⅶ Applications for Ceramic CapacitorsGiven that MLCCs are the most commonly manufactured capacitor in the electronics industry, it should come as no surprise that they have a wide range of applications. A resonant circuit in transmitter stations is an interesting high-precision, high-power application. High-voltage laser power supplies, power circuit breakers, and induction furnaces all use Class 2 high-power capacitors. Small-form SMD (surface mount) capacitors are commonly used in printed circuit boards, and capacitors the size of a grain of sand are used in high-density applications. They're also used in DC-DC converters, where high frequencies and high levels of electrical noise put a lot of strain on the components. Since ceramic capacitors are non-polarized and come in a wide range of capacitances, voltage ratings, and sizes, they can be used as a general-purpose capacitor. Ceramic disc capacitors, which are used throughout brush DC motors to reduce RF noise, are familiar to many hobbyists, especially in the field of robotics.Ⅷ How to read ceramic capacitor value?Ceramic capacitors normally have three digits for their values, such as 102, 103, and 101, and the values are in Pico farads. The numbering scheme is simple to understand if you note that picofarads, not microfarads, are used.The worth of a ceramic capacitor with three digits – ABC is AB*10^C Pico Farad. The digit 104 means 10*104pF = 100000pF = 100nF = 0.1uF if ABC is 104. The first two digits of the printed code correspond to the first two digits of the capacitor value, while the third digit indicates the number of zeroes that must be applied to convert the capacitor value to Pico Farad. If we calculate in Nano Farad for values ending with 4, then the reading becomes easy like 104 is 100nF. If we calculate in Nano Farad for values ending with 3, then the reading becomes easy like 103 is 10nF.Some ceramic capacitors are polarized, meaning they have both positive and negative terminals. The capacitor can be identified by its tolerance in addition to its capacitance value. There is many tolerance marking schemes in use, with one and two alphabets being the most common. You don't need to recall them unless you're dealing with a precise circuit. We only looked at ceramic capacitors in direct current (DC) circuits with voltages ranging from 12V to near zero in this short article. Hobbyists are familiar with this collection. It is also useful to be familiar with the tolerance marking scheme for professional purposes. Ⅸ How to Test Ceramic Disc CapacitorCeramic disc capacitors are units used in the computer industry to control voltage for various dielectric functions. Ceramic layers aim to dissipate heat generated by high voltage while also protecting the environment — both internal and external — from damage. Volumetric efficiency is inversely proportional to stability and accuracy with these capacitors, making testing difficult.Step 1 Ceramic capacitors must be tested since they will short out if they are exposed to high voltage. Your monitor can blink or go blank if this happens. This issue can be resolved by removing all of the ceramic capacitors. Ceramic capacitors, on the other hand, can be tested if you have the right tools. Step 2To measure a ceramic capacitor, use a wireless multimeter. The capacitor works properly when the voltage is constant. However, you won't be able to accurately calculate it if the ohmmeter's output and digital capacitance don't match the capacitor's voltage, so the second option is preferable. Step 3To locate the short circuit or assess cases where optical capacitance meters fail to produce shortened readings, use an analog insulation tester. In order to obtain a 12-volt output, set the analog meter to 10 Kohm. This phase is needed for the ceramic capacitor to be tested. You may also use both methods to improve measurement precision if you do want to stop removing the capacitor and test it aboard.Related recommendation: How to Test a Start Capacitor?                                             How to Discharge a Capacitor? Ⅹ FAQ1. What is Ceramic Capacitor?A fixed value type of capacitor where the ceramic material within the capacitor acts as a dielectric is the Ceramic Capacitor. This capacitor consists of more alternating layers with ceramic and also a metal layer which acts as an electrode. The composition of this ceramic material in this capacitor tells about the electrical behavior along with its applications. We can define a ceramic capacitor as A fixed-value capacitor where the ceramic material acts as the dielectric. 2. What are the advantages of ceramic capacitors?Following are the advantages of ceramic capacitors:Manufacturing cost is lessHigh-frequency performance is exhibitedThe stability of the capacitor is dependent on the ceramic dielectric 3. What is the capacitance range for a ceramic capacitor?The typical capacitance range for a ceramic capacitor is 10 pF to 0.1 μF. 4. Can I replace all electrolytic capacitors with ceramic ones?If you can find ceramic capacitors of the correct value, you can certainly do this. Ceramic capacitors are more stable, have a longer useful lifetime, have higher voltage ratings and are not polarized. Be prepared to find that there will be a substantial size difference. 5. What are the differences between electrolytic, tantalum and ceramic capacitors?Ceramic capacitors don't have polarity, their terminals can be interchanged. They are suitable for both ac and dc. They don't have any chemical reaction involved in their work. They have a lesser capacity for the same given size. Electrolytic capacitors have polarity (i.e. they have fixed positive and negative terminal), Suitable for dc only. A chemical reaction involves the formation of aluminum oxide on the electrode. ( Consists of aluminum electrodes in a solution of Ammonium borate).Higher capacity. A tantalum electrolytic capacitor, a member of the family of electrolytic capacitors, is a polarized capacitor whose anode electrode (+) is made of tantalum on which a very thin insulating oxide layer is formed, which acts as the dielectric of the capacitor. A solid or liquid electrolyte that covers the surface of the oxide layer serves as the second electrode (cathode) (-) of the capacitor. 6. What is the time constant for the discharge of the capacitors in (figure 1)?figure 1The equivalent resistance:R= 2*1× 10∧3 = 2000 i©=> the time constant: T= R*C = 2000*1× 10∧-6 = 2×10∧-3s = 2ms 7. How do you read a ceramic capacitor value?The first two digits, in this case, the 10 give us the first part of the value. The third digit indicates the number of extra zeros, in this case, 3 extra zeros. So the value is 10 with 3 extra zeros, or 10,000. Ceramic disc capacitor codes are always measured in pico Farads or pF. 8. How can you tell if a ceramic capacitor is bad?Use the multimeter and read the voltage on the capacitor leads. The voltage should read near 9 volts. The voltage will discharge rapidly to 0V because the capacitor is discharging through the multimeter. If the capacitor will not retain that voltage, it is defective and should be replaced. 9. Do ceramic capacitors degrade over time?Among ceramic capacitors, the capacitance, especially of capacitors classified as a high dielectric constant (B/X5R, R/X7R characteristics), decreases over time. ... When the capacitor cools down below the Curie point, aging starts again. 10. How do you tell the positive and negative of a ceramic capacitor?In general, the ceramic capacitor has no positive and negative poles, and the capacity is generally small. It is often used for signal source filtering, and the polarity is only temporary behavior. This is a kind of non-polar electrolytic capacitor, so it is not polar. 

IntroductionIn electronics, what is clipper? A circuit which removes the peak of a waveform is known as a clipper. Clipper circuit is designed to prevent a signal from exceeding a predetermined reference voltage level. The clipper circuit can be designed by utilizing both the linear and nonlinear elements such as resistors, diodes, or transistors. The diode clipper, also known as a diode limiter, is a wave shaping circuit that limits positive or negative amplitude, or both. In electronics, diode clipper circuits are commonly used to process various signals. It is is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. Clipping changes the shape of the waveform and alters its spectral components.Clipper Circuits IntroductionCatalogIntroductionⅠ Clipper Circuit Types1.1 Positive Clipper Circuit1.2 Negative Clipper Circuit1.3 Combinational Limiter CircuitⅡ Clipper Circuits Analysis2.1 Clipper Circuit Structure2.2 Clipper Circuit ProblemsⅢ General Forms of Clipper Circuits3.1 Clipper Circuit Description3.2 Common Clipper Circuit ExamplesⅠ Clipper Circuit TypesDiode clipper is a limiting circuit which limits the output voltage. In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A basic diode limiter circuit is composed of a diode and a resistor. It is divided into three types: positive clipper circuit, negative clipper circuit and combinational clipper circuit. The positive clipper circuit produces a clipping effect when the input voltage is higher than a certain upper limit value; the negative clipper circuit produces a limit effect when the input voltage is lower than a certain lower limit value; the combinational clipper circuit produces a limit effect when the input voltage is too high or too low. In a positive clipper, the positive half cycles of the input voltage will be removed. During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. The clipper circuits are described as following.1.1 Positive Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the positive portions of the waveform. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. In following figure, when the input signal voltage is lower than a preset upper limit voltage, the output voltage will change with the input voltage, however, when the input voltage reaches or exceeds the upper limit, the output voltage will remain at a fixed value, so that the signal amplitude is limited at the output.1.2 Negative Clipper CircuitThe diode in clipper circuit is connected in series to the input signal and that attenuates the negative portions of the waveform, is termed as negative series clipper. For the figure below, the diode is series to the input and output. If the diode has ideal switching characteristics, when iu is lower than E, D will not conduct, ou=E; when ui is higher than E, D will conduct, ou=iu. The limiting characteristic of this limiter circuit is shown in the figure.1.3 Combinational Limiter CircuitThis kind of circuit combines the positive and negative limiters together which shows in the following figure. Ⅱ Clipper Circuits Analysis2.1 Clipper Circuit StructureIn the circuit, Al is an integrated circuit (a common component), VT1 and VT2 are transistors, Rl and R2 are resistors, and VDl to VD6 are diodes.Analyzing the effect of VD1 and VD2 in the circuit mainly explains the following points.1) It can be seen from the circuit that the circuit structure of the two groups of diodes are the same. Both play the same role in this circuit, so the working principle of them are the same.2) The pin ① is connected to the base of the transistor VT1 through a resistor Rl. Obviously Rl is a signal transmission resistor. The signal output on the pin ① is added to the base of VT1 through Rl (there is no DC blocking capacitor between pin ① and VT1). From this circuit structure, it can be judged that the pin ① is an output signal pin, and it outputs a composite signal of DC and AC. The purpose of determining that the pin ① is to figure out the specific function of the diode VD1 in the circuit.3) The DC voltage output by pin ① is not high enough to make the external diode in a conducting state. The analysis is: if the DC voltage output by the pin ① is high enough, then VD1, VD2 and VD3 conduct, and the internal resistance becomes small. This will shunt the AC signal output by the pin ① to the ground, so the signal will be attenuated. However, this circuit does not need such attenuation. Therefore, the conclusion drawn from this: VD1, VD2 and VD3 are not turned on by pin ① DC voltage output.4) The output from pin ① is the superimposed signal of DC and AC, which is added to the base of the transistor VT1 through the resistor Rl. VT1 is an NPN transistor. If the amplitude of the positive half-cycle AC signal added to the base of VT1 is very large, which may burn the VT1. When the negative half-cycle signal added to the base of VT1 is large, which has no effect on VT1, because the negative signal on the base of VT1 reduces current.Follow the above circuit analysis, it can be judged that VD1, VD2, and VD3 in the circuit has clipper function, to prevent VT1 from burning out. 2.2 Clipper Circuit ProblemsIn the figure, Ul is the DC voltage in the output of pin ①, U2 is the limiting voltage value.When the AC voltage in the output signal of pin ① is relatively small, the positive half cycle of the AC signal plus the DC output voltage does not make the VD1, VD2 and VD3 conduction. Therefore, all diodes are cut off, which has no effect on the AC signal output by pin ①. Assuming that the positive half-cycle output AC signal by pin ① is very large during a certain period, as shown in the signal waveform, at this time it plus the DC voltage can conduct VD1, VD2 and VD3. If the conduction voltage of each diode is 0.7V, then three diodes is 2.1V. Since the tube voltage drop after conduction is basically the same, that is, the maximum voltage of pin ① is 2.1V. So the excess part of the positive half cycle of the AC signal is limited by the resistor. When the DC and AC output signals at pin ① is less than 2.1V, diodes will not conduct and keep cutoff state, which has no clipping effect on the signal.For the specific details of clipper circuit, there are several explanations as follows.1) The negative half cycle large signal output by the pin ④ will not cause VT1 overcurrent, because it will decrease the base voltage of the NPN transistor and the base current, so there is no need to add the limiter circuit.2) The one-way limiter circuit mentioned above, it can only limit the large signal part of the positive or negative half of the signal, and does not limit the signal in the other half. The other is the combinational limiter circuit, which can limit the positive and negative half-cycle signals at the same time.3) There are many reasons for the abnormal increase of the signal amplitude. For example, the fluctuation of the power supply voltage cause it to increase a lot at a certain moment, and the large-scale interference pulse from the outside into the circuit also causes a certain increase.4) After the three diodes VD1, VD2 and VD3 conduct, the sum of the DC and AC voltages on pin ① is 2.1V. This voltage added to the base of VT1 through resistor Rl is maximum, so as to the current of VT1.5) Since the pin ① is the same as the external circuit of pin ②, the working principle of the limiter circuit is the same. So only one circuit needs to be analyzed when analyzing the circuit.6) According to the characteristics of the series circuit, the current in the series circuit is equal everywhere. It can be known that the three series diodes VD1, VD2 and VD3 are turned on at the same time, or they will be turned off at the same time. Therefore, in the series circuit, a diode is turned on and other diodes are turned on.Ⅲ General Forms of Clipper Circuits3.1 Clipper Circuit DescriptionThere are two types of clippers namely series and parallel. In series clipper, diode is connected in series with the load. In parallel clipper, diode is in parallel to the load.1) Series clippers: if the diode is connected in series with load resistanceUnbiased series clipper: in that case the circuit diode is connected in series with load resistance and no external voltage is applied to the circuit.+ve unbiased series clipper: if the +ve portion of output is clipped its called +ve unbiased series clipper.-ve unbiased series clipper: if the -ve portion of output is clipped its called +ve unbiased series clipper.Biased series clipper: if in the circuit, diode is connected in series with load resistance and external voltage is applied to the circuit+ve biased series clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve biased series clipper: if the -ve portion of output is clipped its called +ve biased series clipper.2) Parallel clippers: if the diode is connected in parallel with load resistanceUnbiased parallel clipper: in that case the circuit diode is connected in parallel with load resistance and no external voltage is applied to the circuit.+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve unbiased parallel clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve unbiased parallel clipper.Biased parallel clipper: if in the circuit, diode is connected in parallel with load resistance and external voltage is applied to the circuit+ve unbiased parallel clipper: if the +ve portion of output is clipped its called +ve biased series clipper.-ve unbiased parallel clipper: if the -ve portion of output is clipped its called +ve biased series clipper. 3.2 Common Clipper Circuit ExamplesIn general, clippers circuit are classified into two types: Series Clippers, Shunt Clippers, and Dual (Combination) Clippers.Series Clipper: The diode is connected in series with the load resistance. 👇Figure 1. Series Positive ClipperThe positive amplitude waveform is cut, and the negative amplitude waveform is retained, as follows:Figure 2. Series Positive Clipper with Positive BiasThe positive amplitude waveform is cut, and the offset positive voltage is retained on the negative amplitude waveform, as follows:Figure 3. Series Positive Clipper with Negative BiasThe waveform of positive amplitude is cut, and the negative voltage is shifted based on the waveform of negative amplitude, as follows:Figure 4. Series Negative ClipperThe negative amplitude waveform is cut, and the positive amplitude waveform is retained, as follows:Figure 5. Series Negative Clipper with Positive BiasThe negative amplitude waveform is cut, and the positive voltage is offset on the positive amplitude waveform, as follows:Figure 6. Series Negative Clipper with Negative BiasThe negative amplitude waveform is cut, and the negative voltage is offset on the positive amplitude waveform as follows: Shunt Clipper: Diode is in parallel with load resistance in circuit. 👇Figure 7. Shunt Positive ClipperFigure 8. Shunt Positive Clipper with Positive BiasFigure 9. Shunt Positive Clipper with Negative BiasFigure 10. Shunt Negative ClipperFigure 11. Shunt Negative Clipper with Positive BiasFigure 12. Shunt Negative Clipper with Negative Bias Dual (Combination) Clipper: It is desired to remove a small portion of both positive and negative half cycles. 👇Figure 13. Combination ClipperWhen the positive and negative waveforms must be limited, a combinational limiter circuit is required, as follows:Images Reference: Clipper Circuits - Series Clipper, Shunt Clipper, and Dual Clipper Frequently Asked Questions about Diode Limiter and Clipper Circuit1. What is Clipper and clamper?The major difference between clipper and clamper is that clipper is a limiting circuit which limits the output voltage while clamper is a circuit which shifts the DC level of output voltage. ... While clamper is used when we need multiples of the input voltage at the output terminal. 2. What is the function of clipper circuit?In electronics, a clipper is a circuit designed to prevent a signal from exceeding a predetermined reference voltage level. A clipper does not distort the remaining part of the applied waveform. 3. What is Clipper circuit and its types?A clipper is a device which limits, remove or prevents some portion of the wave form (input signal voltage) above or below a certain level, in other words, the circuit which limits positive or negative amplitude ,or both is called chipping circuit. The clipper circuits are of the following types. Series positive clipper. 4. What is the difference between a positive clipper and a negative Clipper?Positive Clipper and Negative Clipper. In a positive clipper, the positive half cycles of the input voltage will be removed. ... During the negative half cycle of the input, the diode is forward biased and so the negative half cycle appears across the output. 5. How does diode clipping work?The Diode Clipper, also known as a Diode Limiter, is a wave shaping circuit that takes an input waveform and clips or cuts off its top half, bottom half or both halves together. This clipping of the input signal produces an output waveform that resembles a flattened version of the input. 6. What is the main purpose of a diode limiter?The diode limiter also called Clipper as it is used to limit the input voltage. A basic diode limiter circuit is composed of a diode and a resistor. Depending upon the circuit configuration and bias, the circuit may clip or eliminate all or part of an input waveform. It limits the output voltage to a specific value. 7. What is the purpose of a clamping diode?The clamping circuit fixes the voltage lower limit to zero, that is, the start of the signal is 0 V. The positive clamping circuit blocks the input signal when the diode is forward biased. During the negative half cycle of an AC signal, the diode is forward biased and allows electric current through it. 8. What is a diode clamping circuit?A clamper circuit shifts the DC level or the reference level of the signal to the desired level without changing the shape of the waveform. The clamper circuit can be designed using the diode, resistor, and the capacitor.

IntroductionIn-memory computing (IMC), a technique of future computing, stores data in RAM to run calculations entirely in computer memory. With the rise of the big data era, faster data processing capabilities are required. Computer memory and storage space are also growing exponentially to adapt to large-capacity data collection and complex data analysis, which promotes the development of AI (artificial intelligence), and then derives emerging stuff, that is, in-memory computing.In-memory Computing (IMC) ExplainedCatalogIntroductionⅠ Memory Wall: Processor /Memory Performance GapⅡ Developing RequirementⅢ What Is In-memory Computing?3.1 In-memory Computing Definition3.2 Four Realization MethodsⅣ Driving Force of In-memory Computing and Market Prospects4.1 In-memory Computing for AI4.2 In-memory Computing Product Outlook4.3 In-memory Computing Market and ProspectⅤ ConclusionⅠ Memory Wall: Processor / Memory Performance GapThe von Neumann architecture has occupied the dominant position in computer system when the computer invented. This kind of calculation method is to store the data in the main memory first, and then fetch the instructions from the main memory to execute them in order when running. We all know that if the connecting speed of the memory cannot keep up with the performance of the CPU, the computing will be limited. This is a memory wall. At the same time, in terms of efficiency, the von Neumann architecture also has obvious shortcomings. It consumes more energy to read and write data than to calculate once time.Figure 1. Von Neumann Architecture DiagramThe performance of computer processors has developed rapidly based on Moore's Law, and has been directly improved with the invention of transistors. The main memory of the computer uses the DRAM. It is a high-density storage solution based on capacitor charging and discharging. Its performance (speed) depends on two aspects, namely the reading/writing speed of the capacitor charging and discharging in the memory and the interface bandwidth between the devices. The read/write speed of capacitor charging and discharging has increased with Moore’s Law, but the speed is not as fast as the processor. In addition, the interface between DRAM and the processor is a mixed-signal circuit, and its bandwidth increasing speed is mainly restricted by the signal integrity of the traces on the PCB. This has also caused the performance improvement of DRAM to be much slower than that of the processor. At present, the performance of DRAM has become an huge bottleneck of overall computer performance, the so-called "memory wall".  It blocks the computing performance improvement.Figure 2. Moore's Law Effect Ⅱ Developing RequirementIn the current AI technology, with the increasing amount of data and calculations, the original von Neumann architecture is facing more and more challenges. Rely on expanding CPU, the hardware architecture can’t have a large amount of calculation. Also the larger storage capacity is heavily rely on the past architecture, it is also very unsuitable for AI. When the memory capacity is large to a certain extent, it can only show that certain technologies need innovation. In order to solve the "memory wall" problem, future computers are not based on computing memory, but the in-memory computing, thereby reducing the cost of data access in the calculation process.Figure 3. Conventional Computing vs In-memory Computing Ⅲ What Is In-memory Computing?3.1 In-memory Computing DefinitionIn-memory computing (or in-memory computation) is a technique based on RAM data storage and indexing, which proposed by the MIT research group, and its main purpose is to accelerate the convolution calculation. We know that convolution calculations can be expanded into weighted accumulation calculations. From another perspective, it is actually a weighted average of multiple numbers. Therefore, the circuit realizes the weighted average of the charge domain. The weight (1-bit) is stored in SRAM, and the input data (7-bit digital signal) becomes an analog signal through the DAC. According to the corresponding weight in the SRAM, the output is multiplied by 1 or -1 in the analog domain, which averaged in the analog domain, and finally read out by the ADC as a digital signal. Specifically, since the weight of the multiplication is 1-bit (1 or -1), it can be controlled by using a switch and a differential line simply. If the weight is 1, the capacitor on the side of the differential line is charged to the required output value. Otherwise, let the other side of the differential line be charged to this value. As for average, connect several differential lines together in the charge domain.Of course, there is more than one circuit for in-memory calculation, and the calculation accuracy is not limited to 1-bit. However, we can see the above examples that the core idea of in-memory calculations is generally to convert calculations into weighted calculations. Store the weights in the memory unit, then modifications on the core circuit of the memory (such as the readout circuit) are made. So that the process of reading is like a process in which the input data and weights are multiplied in the analog domain, that is, convolution. Because convolution is a core part of AI and other calculations, in-memory computing can be widely used in such applications. In-memory computing uses analog circuits for calculations, which is the difference compared with traditional digital logic calculations.In more traditional architectures, there are some multiply-accumulate circuits (MAC) for tensor math, especially the matrix multiplication. These architectures attempt to arrange the MAC in a way that moves weights and activations to the appropriate location. Activations are calculated from the previous neural network layer. Multiplication usually involves activations and weights, both must be moved to the place where multiplies them. In-memory computing makes use of it. Therefore, if the weights are stored in memory, the memory can access through activations to obtain multiplication and accumulation. The only difference from the actual memory is that the in-memory computing concatenates all word lines at once, instead of decoding the input to get one word line only.Figure 4. In-memory Computing Diagram3.2 Four Realization MethodsThe attempt is to enter the analog domain and treat the storage unit as an analog unit instead of a digital unit to reduce consumption. We have already got a way to use simulation on the front end of the inference engine. That is in-memory computing. Therefore, we take digital data, using a DAC to convert it to an analog value, and then driving a memory with these analog content to obtain an analog bit-line output, finally using an ADC to convert the result back to a digital format. However, the in-memory computing is still in the exploratory stage, and there are many specific implementation methods to study, currently there are three types: RRAM, Flash, SRAM, and DRAM.Based on RRAMRRAM is the most common method of doing this, because it is easy to use by applying Ohm's law to a series of resistors, but it still has the problem of relying on RRAM. The relationship between programming and resistance is non-linear, which requires more work to be done to make viable calculation circuits in RRAM memory for market. So it is just an idea, and the specific plan is still under study. Based on FlashNOR Flash memory has a more traditional word-line/bit-line structure. It is both resistive and capacitive. Generally, the memory cell is a transistor that is turned on or off. However, if it is partially conductive, it can be used as a resistor. The resistance depends on the amount of charge on the floating gate of the memory cell (capacitor). When running all the time, the cell will conduct to its maximum capacity. During this process, it does not conduct at all, however, it can be partially programmed. There is a problem is that you cannot precisely control the number of electrons. Moreover, the response to any number will vary with the process and temperature and other variables.Two companies are studying this method. Microchip owns their memBrain array, thanks to their acquisition of SST, and Mythic is a start-up company dedicated to an inference engine that uses in-memory computing with flash memory. Both companies said that they are using extensive calibration techniques to deal with this change.Another issue, flash cells will lose electrons over time. Electrons will flow around, which brings up an interesting topic: on this type of memory array, data retention and durability will be like.From the application point of view, it depends on whether it is to be used in cloud computing or edge inference engine. At the edge, it may perform certain fixed reasoning functions throughout the life cycle of the device. Therefore, if there are enough arrays, then you will load the weights for the first time and don't need to program it anymore (unless you do a update), because the flash memory is non-volatile. Although you still need to move activations, there is no need to move the weights, which will be stored permanently in the array. This would indicate that data durability (number of times the device can be programmed before cumulative damage accelerates electron leakages to an unacceptable level) does not matter, it only need to program once.In contrast, in cloud applications, the device is likely to be shared as a general-purpose computing resource, so this requires reprogramming for each new application. This means that battery life becomes more important in the cloud. Mythic claims to have a 10K write cycle, and has observed that even if it is reprogrammed every day, it will last for more than 10 years.If set an analog value for it and use an analog value in the cell, then in theory, each electron is important. However, if there is enough electron migration, you need to refresh the storage unit, or compensate for electrons change in some way. Because the same analog input today will produce different results than a year ago. The calibration circuit can also deal with some aging problems. However, for data retention, Mythic said they do perform regular updates of the weight values stored in flash memory. This will make persistence the main wear-out mechanism rather than data retention. Microchip stated that its data retention time is TBD, but it is likely to reprogram the device quarterly or annually to restore the unit.So they need a large number of high-quality ADCs and DACs to keep the signal-to-noise ratio (SNR) within a scope of accurate reasoning, which is the focus of designing work. Mythic claims that they provide a novel ADC, so that Microchip can share it to reduce the number required. Although ADC does consume energy, it also greatly reduces overall system consumption. Based on SRAMThis idea came from a lecture at Hot Chips at Princeton University. By definition, SRAM is a bistable unit. Therefore, it cannot be in an intermediate state, how should this be handled? And the DACs and ADCs that need to be corrected more over than the array in terms of area and power consumption.The point of this problem boils down to the question of how to simulate. They explained that this method uses more than one-bit line for calculation. Since the unit is still a digital value, it takes several bit lines to perform a calculation. The bit line can be split, and different groups perform different multiplications. The following figure illustrates it.Figure 5. Bit LineWith 8 inputs at a time, so the input vector is sliced and several consecutive multiplications are carried out to obtain the final results. The bit line charge is deposited on the capacitor. When ready to read, the charge is read out and sent to the ADC for conversion back to the digital domain. Their basic unit structure is as follows:Figure 6. Bit CellThese capacitors may affect chip size issues, but they said that the metal above the cell can be used. Of course, one cell is now 80% larger than the standard 6T SRAM cell (even without capacitors), but they say that their overall circuit is still much smaller than a required circuit based on standard digital implementation. In addition, since their basic array operations are still in digital form, they are less sensitive to noise and changes, which means their ADCs can be simpler and consume less power.Figure 7. Chip SizeBased on DRAMThis idea refers to not using a lot of power to obtain DRAM content, and in some way incorporate calculations into the CPU or other computing structures and directly run it on the DRAM die, which is what UPMEM does. A simple processor is built on the DRAM die, also the architecture will not compete with Xeon chips, they call this set "processing in memory" or PIM.Figure 8. PIM ChipInstead of bringing data to calculations, they bring calculations to data. The runtime is performed by the CPU in DRAM chip. That is, there is no need to move the data to any location outside of the DRAM chip, just send the calculating result back to the host system. Also, since ML calculations usually involve a lot of reduction, less data required for calculations. Although this does require some minor changes to the DRAM, they did not change the manufacturing process. Under this case, a standard DRAM module will provide multiple opportunities for distributed computing. At the same time, it becomes complicated to use this function to write a program.They said that a server using PIM offload will consume twice as much power than a standard server connected to a DRAM module without PIM. However, with a throughput of 20 times, it still provides them with a 10 times energy efficiency advantage. In addition, this method can help defend against side-channel security attacks. Thus a group of computing threads originally contained in one or more CPUs flows to DRAM. Therefore, it is necessary to check all DRAMs and figure out where thread is in some way, but this will be a difficult task. Ⅳ Driving Force of In-memory Computing and Market Prospects4.1 In-memory Computing for AIPeople have recognized the problem of "memory wall" for a long time, but why is in-memory computing only raised in the past two years? So we have to analyze the boost behind its rise.The first motivation is the rise of AI based on neural networks, especially the hope that AI can be popularized in mobile and embedded devices. So that in-memory computing with a high energy efficiency ratio has attracted attention. In addition, neural networks have a high tolerance for errors in calculation accuracy. Therefore, errors introduced in simulation calculations of in-memory computing can often be accepted. That is to say in-memory computing and AI are good partners for each other.The second motivation is the new memory. For in-memory computing, the memory characteristics often determine the efficiency of in-memory computing. Therefore, new memories improvement will often drive the development of in-memory computing. For example, the recently popular ReRAM uses resistance modulation to store data, so the readout of each bit uses a current signal instead of a traditional charge signal. In this way, it is a very natural operation for current to accumulate (combining several currents directly to achieve the sum of currents, even without additional circuits). That is to say, ReRAM is very suitable for in-memory calculations. From the perspective of memory promotion, new memories are also willing to catch up with the AT trend. Therefore, new memory manufacturers are also happy to see in-memory computing based on their own memories to accelerate AI development, which will broaden the memory market. 4.2 In-memory Computing Product OutlookChip products for in-memory computing are expected to come in two forms. The first form is sold as a memory IP with computing functions. Such memory IP may be traditional SRAM, or new memory such as eFlash, ReRAM, MRAM, and PCM.The second form is to directly build AI acceleration chips based on in-memory calculations. For example, Mythic plans to make PCIe accelerator cards based on flash memory, that is, access data with the main CPU through the PCIe interface. The weight data is stored on the Mythic memory chip, so that when the data is sent to the Mythic IPU, the calculation can be directly read out. In this way, the action of reading the weights data is eliminated.Figure 9. Mythic is a Pcie Accelerator 4.3 In-memory Computing Market and ProspectWhat impact will in-memory computing have on the AI chip market? First of all, we see that in-memory computing uses analog calculations, so its accuracy will be affected by the low signal-to-noise ratio. Usually the upper limit of accuracy is about 8-bit, and it can only do fixed-point calculations not the floating-point calculations. So in-memory computing is not suitable for the AI training market that requires high calculation accuracy. In other words, the main battlefield of in-memory computing is the AI inference market. For example, it is more suitable for embedded artificial intelligence, which has high requirements for energy efficiency not the accuracy. In fact, in-memory computing is actually most suitable for occasions where large memory is needed. For instance, flash is inherently required in IoT and other scenarios, so if you can add the in-memory computing to flash, it is quite suitable. However, introducing in-memory computing in a large storage memory may not appropriate. Based on this analysis, we believe that in-memory computing may become an important part of embedded AI (such as smart IoT) in the future. Ⅴ ConclusionWith the rise of AI and new memories, in-memory computing has also become a new hot spot. Based on the unique characteristics of the memory, it combines with analog calculations in memory, thereby greatly reducing the memory read and write operations in AI. Although the accuracy of calculation in the memory is limited by analog calculation, it is also suitable for embedded AI applications that pursue energy efficiency most and can accept a certain loss of accuracy. Frequently Asked Questions about In-Memory Computing Technology1. Why do we need in memory computing?In-Memory Computing provides super-fast performance (thousands of times faster) and scale of never-ending quantities of data, and simplifies access to increasing numbers of data sources. 2. What does in memory mean?An in-memory database is a type of purpose-built database that relies primarily on memory for data storage, in contrast to databases that store data on disk or SSDs. ... Because all data is stored and managed exclusively in main memory, it is at risk of being lost upon a process or server failure. 3. How does in memory computing work?In-memory computing means using a type of middleware software that allows one to store data in RAM, across a cluster of computers, and process it in parallel. Consider operational datasets typically stored in a centralized database which you can now store in “connected” RAM across multiple computers. 4. What is in memory computing in SAP HANA?An In-Memory database means all the data from source system is stored in a RAM memory. In a conventional Database system, all data is stored in hard disk. It provides faster access of data to multicore CPUs for information processing and analysis. 5. How is data stored in memory?Normally memory is described as a storage facility where data can be stored and retrieved by the use of an address. This is accurate but incomplete. A computer memory is a mechanism whereby if you supply it with an address it delivers up for you the data that you previously stored using that address. 6. What is in memory data processing?In-memory processing is the practice of taking action on data entirely in computer memory (e.g., in RAM). ... Since the storage appears as one big, single allocation of RAM, large data sets can be processed all at once, versus processing data sets that only fit into the RAM of a single computer. 7. What is in memory database processing and what advantages does it provide?The major advantage of systems using in-memory databases vs traditional database systems is: its performance speed. ... Source data is loaded into the system memory in a compressed and format. Therefore, in-memory processing reduces disk seek time for accessing data and streamlining the work involved in processing queries. 8. What is big data computing?Big data computing is an emerging data science paradigm of multi dimensional information mining for scientific discovery and business analytics over large scale infrastructure. ... Big data is characterized by 5V's such as volume, velocity, variety, veracity, and value.

IntroductionAs we all know, the most basic passive linear components are resistors (R), capacitors (C) and inductive components (L). These components can be used to form 4 different circuits: RC circuit, RL circuit, LC circuit and RLC circuit. They have some important properties for analog electronics, and can be used as passive filters. In practice, capacitors (and RC circuits) are usually used instead of inductors to form filter circuits. This is because capacitors are easier to manufacture with smaller size. This article mainly introduces the RC Circuit in series and parallel state.RC circuit (resistor–capacitor circuit), also called RC filter or RC network, has a resistor and a capacitor in series connection. When connected to a DC voltage source, the capacitor charges exponentially in time. That is, a capacitor can store energy, and when a resistor placed in series with it will control the rate at which it charges or discharges. This produces a characteristic time dependence that turns out to be exponential.RC Circuits Basic ExplainedCatalogIntroductionⅠ RC Circuit Basics1.1 What is RC Circuit?1.2 RC Circuit CharacteristicsⅡ How to Calculate RC Circuit?Ⅲ RC Circuits Classification3.1 Series and Parallel Circuits3.2 Example: RC Low Pass FilterⅣ Visualizing Filter Response4.1 Frequency Response4.2 Low Pass Filter Phase Shift4.3 Second-order Low-pass FilterⅤ ConclusionⅠ RC Circuit Basics1.1 What is RC Circuit?For a RC circuit (resistor-capacitor circuit), the primary composes of a resistor and a capacitor. According to the arrangement of resistors and capacitors, it can be divided into a RC series circuit and a RC parallel circuit. In addition, simple RC parallel circuits cannot resonate, because resistor does not store energy. However, LC parallel circuits can resonate. RC circuits are widely used in analog circuits and pulse digital circuits. If a RC parallel circuit connected in series in the circuit, it can attenuate low-frequency signals, and if it connected in parallel in the circuit, it can attenuate high-frequency signals. That is filtering.RC circuit is common element in electronic devices. It also play an important role in the transmission of electrical signals in nerve cells. A capacitor can store energy and a resistor placed in series with it will control the rate at which it charges or discharges.Figure 1. Passive Low-pass RC Circuit1.2 RC Circuit CharacteristicsIn the analog circuit, the passive RC filter circuit can be divided into a low-pass filter circuit and a high-pass filter circuit according to the connection and size of the capacitor.The low-pass filter circuit is somewhat equal to the integrator circuit (capacitor C is in parallel at the output.), but both circuits are applied to different requirements. The integrator circuit mainly uses the integration effect of the capacitor C when it is charged. In the case of square wave input, periodic sawtooth wave (triangular wave) will generate, so the capacitor C and resistor R are selected according to the square wave. While the low-pass filter circuit bypasses the higher frequency signal (because XC=1/( 2πfC), when f is larger, XC is smaller, which is equivalent to a short circuit), so the value of capacitor C is determined by referring to the value of the low frequency. For the filter circuit of the power supply, theoretically the larger the value of C, the better.Figure 2. Low Pass Filter CircuitThe high-pass filter circuit has the same form as the differential circuit or the coupling circuit. In the pulse digital circuit, due to the different relationship between RC and pulse width, it is divided into a differential circuit and a coupling circuit. In an analog circuit, choosing an appropriate capacitance C value can pass higher frequency signals selectively, even block DC and low-frequency signals. For example, a capacitor connected in series with a tweeter, is to prevent the low pitch from entering the tweeter to avoid burnout. What’s more, in the multi-stage AC amplifier circuit, the high-pass filter circuit is also a coupling circuit.Figure 3. High Pass Filter CircuitⅡ How to Calculate RC Circuit?From a mathematical point of view, suppose that the RC circuit has been connected to a DC power supply with a voltage value of U0. The voltage on the capacitor is equal to the power supply’s, and at a certain moment t0 the left end S of the resistor is grounded, then the capacitor discharges. In the theoretical analysis, the time t0 is taken as the zero point of time.According to KVL's law, establish the circuit equation: The initial condition is .This is a first-order homogeneous differential equation, and its general solution is .After substituting into the original equation: The characteristic equation is .The characteristic root is .According to , get .Therefore, the required initial value of the differential equation is It can be seen that the voltage attenuation speed on the capacitor depends on the , and its size only depends on the circuit structure and component parameters.When the unit of resistance is Ω and the unit of capacitance is F, the unit of product RC is seconds (s), which is represented by τ, then the capacitor voltage can be written as .tτ2τ3τ4τ5τ...∞uc(t)Uo0.368Uo0.135Uo0.05Uo0.018Uo0.0067Uo...∞0The τ time constant is the time it takes for the capacitor voltage to drop to 1/e=36.8% of the initial value. Specifically, it is the time required to charge the capacitor, through the resistor, from an initial charge voltage of zero to approximately 63.2% of the value of an applied DC voltage, or to discharge the capacitor through the same resistor to approximately 36.8% of its initial charge voltage. When t=4t, the capacitor voltage is very small, and it is generally considered that the circuit enters a steady state, which is also called the zero input response of the RC first-order circuit. Ⅲ RC Circuits Classification3.1 Series and Parallel CircuitsRC Series CircuitIn circuit, the capacitor cannot flow DC current, and R & C have an obstructive effect on the current. So the total impedance is determined by the resistance and capacitive reactance, and it changes with frequency. RC series circuit has a turning frequency: f0=1/2πR1C1. When the input signal frequency is greater than f0, the total impedance is basically unchanged, and it is equal to R1.RC Parallel CircuitThe RC parallel circuit can pass both DC and AC signals. It has the same turning frequency as the RC series circuit: f0=1/2πR1C1. On the one hand, when the input signal frequency is less than f0, the total impedance of the circuit is equal to R1, on the other hand, when the input signal frequency is greater than f0, the capacitive reactance of C1 is relatively small, and the total impedance is the sum of resistance and capacitance. In addition, when the frequency is high to a certain level, the total impedance is zero.Introduction to Parallel RC CircuitWhat’s more, as frequency increases, the capacitor will act like a short circuit to high frequency current in its path. At low frequencies, the capacitor tends to block current flow.3.2 Example: RC Low Pass FilterCircuit AnalysisTo create a passive low-pass filter, we need to combine the resistor elements with the reactance elements. That is a circuit consisting of a resistor and a capacitor or an inductor. Theoretically speaking, the RL low-pass topology is equivalent to the RC low-pass topology in terms of filtering ability. However, in practice, RC circuits are more common.Figure 4. RC Low-pass FilterAs shown in the figure, connecting a resistor in series with the signal path and a capacitor in parallel with the load, an RC low-pass response can be generated. In the figure, the load is a single part, but in actual circuits, it may be more complicated, such as the input stage of an analog-to-digital converter, amplifier, or oscilloscope to measure the response of the filter.If a resistor and a capacitor form a frequency-dependent voltage divider circuit, we can intuitively analyze the filtering function of the RC low-pass circuit.Figure 5. Change RC Low-pass Filter into a Voltage DividerWhen the frequency of the input signal is low, the impedance of the capacitor is high than the resistor. Therefore, most of the input voltage will drop on the capacitor (and both ends of the load, which is in parallel with the capacitor). When the input frequency is higher, the impedance of the capacitor is lower than the impedance of the resistor, which means that the resistor voltage decreases and less voltage is transferred to the load. Therefore, low frequencies pass and high frequencies are blocked.Cutoff FrequencyWhere the filter does not cause significant attenuation for a frequency range is called the passband, and the opposite is called the stopband. Analog filters, such as RC low-pass filters, always gradually transit from the passband to the stopband. This means that it cannot be recognized that the filter stops passing the signal and starts blocking one frequency of the signal. This is why the cutoff frequency concept introduced.When checking the frequency response graph of the RC filter, the signal spectrum is "cut" into two halves of the image, one of which is retained and one is discarded. Because as the frequency moves from below the cutoff point to above the cutoff value, the attenuation gradually increases.The cut-off frequency of the RC low-pass filter is actually the frequency at which the input signal amplitude is reduced by 3dB (this value is chosen because a 3dB reduction is equal to a 50% reduction in power). Therefore, the cutoff frequency is also called -3dB frequency. The term bandwidth refers to the width of the passband of the filter. For a low-pass filter, its bandwidth is equal to the -3dB frequency (as shown in the figure below).Figure 6. Cutoff Frequency -3dBFilter Response CalculationWe can discuss the theoretical behavior of the low-pass filter by a typical voltage divider. The output of the resistor divider is expressed as following:The RC filter uses an equivalent structure, using a capacitor XC replace R2. Then we need to calculate the total impedance and place it in the denominator, so there is The reactance of a capacitor represents the opposite amount of current, but unlike resistance, the opposite amount depends on the frequency of the signal passing through the capacitor. Therefore, we must calculate the reactance at a specific frequency. The equation we use for this as follows: In the above design example: R≈160Ω and C=10nF. We assume that the magnitude of VIN is 1V, so we can simply remove VIN from the calculation. First, let's calculate the amplitude of VOUT with a sine wave frequency: While suppressing noise, the amplitude of the sine wave is basically unchanged. Because the cutoff frequency (100kHz) we chose is much higher than the sine wave frequency (5kHz).Let’s see how the filter successfully attenuates the noise component.The noise amplitude is only about 20% of its original value. Ⅳ Visualizing Filter Response4.1 Frequency ResponseThe most convenient way to assess the effect of a filter on a signal is to examine the frequency response graph. That is Bode plot, which has amplitude (in decibels) on the vertical axis and frequency on the horizontal axis; the horizontal axis usually has a logarithmic scale so that the physical distance between 1Hz and 10Hz is the same as 10Hz to 100Hz and 100Hz to 1kHz. This configuration allows us to quickly and accurately evaluate the behavior of the filter over a large frequency range.Figure 7. Bode PlotEach point on the curve represents the amplitude that the output signal is 1V and the frequency is equal to the corresponding value on the horizontal axis. For example, when the input frequency is 1MHz, the output amplitude (assuming the input amplitude is 1V) will be 0.1V (because -20dB corresponds to a tenfold reduction factor).The curve in the passband is almost completely flat, and then as the input frequency approaches the cutoff frequency, it starts to drop faster. Finally, the rate of change of attenuation becomes stable, that is, for every ten times the input frequency increases, the amplitude of the output signal decreases by 20dB. 4.2 Low Pass Filter Phase ShiftThe way in which the filter modifies the amplitude of various frequency components in the signal has been discussed above. However, in addition to amplitude effects, reactive circuit elements always involve phase shifts.The concept of phase refers to the value of the periodic signal at a specific moment in the cycle. Therefore, when we say that a circuit causes a phase shift, we mean that it creates a misalignment between the input signal and the output signal. That is the input and output signals no longer start and end their periods at the same time. The phase shift value, such as 45° or 90°, indicates how much misalignment has been created.Each reactance element in the circuit introduces a 90° phase shift, but this phase shift does not occur at the same time. The phase of the output signal is the same as the amplitude of the output signal, and it changes gradually as the input frequency increases. In the RC low-pass filter, we have a reactive element (capacitor), so the circuit will eventually introduce a 90° phase shift.As with the amplitude response, the phase response can be most easily evaluated by examining the graph on the horizontal axis which represents the logarithmic frequency. The following description is the general pattern.The phase shift is initially 0°, and it gradually increases until it reaches 45° at the cutoff frequency. During this part of the response, the rate of change is increasing. With time, the phase shift continues to increase, but the rate of change is decreasing. As the phase shift approaches 90°, the change of rate becomes very small.Figure 8. Phase Shift4.3 Second-order Low-pass FilterAs above mentioned, we have assumed that the RC low-pass filter consists of a resistor and a capacitor. This configuration is a first-order filter. The "order" of passive filters is determined by the number of reactive components (ie capacitors or inductors) in the circuit. Higher-order filters have more reactive components, which lead to more phase shift and steeper roll-off.Second-order filters are usually built a resonant circuit consisting of inductors and capacitors (this topology is called "RLC", or resistor-inductor-capacitor circuit). However, it is also possible to create a second-order RC filter. As shown in the figure below, all we need to do is to cascade two first-order RC filters.Figure 9. Second-order Filter CircuitAlthough this topology can produce a second-order response, it is not widely used. Because its frequency response is usually not as good as a second-order active filter or a second-order RLC filter.Frequency ResponseWe can try to create a second-order RC low-pass filter by designing a first-order filter based on the required cutoff frequency, that is connecting two first-order stages in series. This set has a similar overall frequency response, with a maximum roll-off of 40dB/decade instead of 20dB/decade.However, we cannot simply connect these two stages together and analyze the circuit as a second-order low-pass filter. In addition, even if we insert a buffer between the two stages so that the first RC stage and the second RC stage can be used as independent filters, the attenuation at the original cut-off frequency will be 6dB instead of 3dB. Because the two stages work independently.Figure 10. Frequency Response of RC-RC FilterA limitation of the second-order RC low-pass filter is that the designer cannot tune the conversion from passband to stopband by adjusting the Q factor (this parameter indicates the degree of damping of the frequency response.) of the filter. If two identical RC low-pass filters are cascaded, the overall transfer function corresponds to the second-order response, but the Q factor is always 0.5. When Q = 0.5, the filter is at the boundary of over-damping, which results in a "sag" frequency response in the transition region. While second-order active filters and second-order resonant filters do not have this limitation, designers can control the frequency response of the transition region. Ⅴ ConclusionAll electrical signals contain a mixture of requiring frequency and unwanted ones. Undesirable frequency components are usually caused by noise and interference, and in some cases they have a negative impact on the performance of the system.Filters are circuits that react to different parts of the signal spectrum in different ways. The low-pass filter is designed to pass low frequency components and block high frequency components. The output voltage of an RC low-pass filter can be calculated by considering the circuit as a voltage divider (frequency-independent) composed of resistance and reactance.The graph of amplitude (in dB, on the vertical axis) vs. log frequency (in Hz, on the horizontal axis) is a convenient and effective way to check the theoretical behavior of the filter. You can also use phase and log frequency graph determines the amount of phase shift that will be applied to the input signal.The second-order filter provides a steeper roll-off, and its response is useful when the signal cannot provide broadband separation between the desired frequency and the unwanted one. You can make a second-order RC low-pass filter by connecting two identical first-order RC low-pass filters, but the overall -3 dB frequency will be lower than expected.In RC filtering circuit, the capacitor can store energy, and the resistor placed in series with it can control the charge-discharge rate. And this produces a characteristic time dependence that turns out to be exponential. Frequently Asked Questions about RC Filter Circuit1. What does an RC filter do?RC circuits can be used to filter a signal by blocking certain frequencies and passing others. The two most common RC filters are the high-pass filters and low-pass filters; band-pass filters and band-stop filters usually require RLC filters, though crude ones can be made with RC filters. 2. What is RC filter in electronics?A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors. ... A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit. 3. How do you calculate RC circuit?The (real value) impedance is the real part of the complex impedance Z. For a series RC circuit, we get Z=√R2+(1ωC)2 Z = R 2 + ( 1 ω C ) 2 . We see that the amplitude of the current will be V/Z=V√R2+(1ωC)2 V / Z = V R 2 + ( 1 ω C ) 2. 4. What is RC circuit used for?The RC circuit has thousands of uses and is a very important circuit to study. Not only can it be used to time circuits, it can also be used to filter out unwanted frequencies in a circuit and used in power supplies, like the one for your computer, to help turn ac voltage to dc voltage. 5. What is RC series circuit?A circuit that contains pure resistance R ohms connected in series with a pure capacitor of capacitance C farads is known as RC Series Circuit. A sinusoidal voltage is applied and current I flows through the resistance (R) and the capacitance (C) of the circuit.