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Introduction When the reverse bias voltage applied to the PN junction increases to a certain value, the phenomenon that the reverse current density suddenly begins to increase rapidly is called PN junction breakdown. From the mechanism, it can be divided into three categories: avalanche breakdown, tunnel breakdown and thermoelectric breakdown. Among them, there are two physical mechanisms for forming reverse breakdown in PN junction: zener breakdown and avalanche breakdown. Generally, both breakdowns coexist. So what is the difference between them? Avalanche Breakdown and Zener Breakdown Effect Explained Catalog Introduction Ⅰ Basic Characteristics 1.1 Avalanche Effect 1.2 Zener Effect Ⅱ Zener Effect vs Avalanche Effect Ⅲ Transistor Secondary Breakdown and Protection 3.1 A Brief Description 3.2 Cause of Breakdown 3.3 Precaution 3.4 Snubber Circuit Examples Ⅳ FAQ Ⅰ Basic Characteristics 1.1 Avalanche Effect As the reverse voltage increases, the electric field in the space charge region strengthens, and the energy obtained by the carriers in the barrier region also increases. When the reverse voltage is close to the breakdown voltage, these carriers with higher energy meet the neutral atoms in the space charge region and cause collision ionization, generating new electron-hole pairs. These newly generated electrons and holes will regain energy under the action of the electric field, collide with other neutral atoms to ionize them, and generate more electron-hole pairs. With reaction continues, causing the number of carriers in the space charge region to increase sharply, just like an avalanche, what’s more, the reverse current also increase sharply, resulting in breakdown. So this breakdown is called avalanche breakdown (or avalanche effect).This breakdown generally occurs in PN junctions with lower doping concentration and higher applied voltage. Because a PN junction in this state has a wider space charge region and more opportunities for impact ionization. Figure 1. Zener Breakdown vs Avalanche Breakdown 1.2 Zener Effect When the reverse voltage increases to a certain value, a strong electric field can be established in the barrier region, which can directly pull out the valence electrons bound in the covalent bond, so that a large number of electron-holes are generated in the barrier region. Then a large reverse current is formed, resulting in breakdown. At this time, atoms in the barrier region are directly excited under the action of a strong electric field is called Zener effect/breakdown. It is caused by the tunneling effect in quantum mechanics. Giving a simple metaphor, the simple understanding is that the two lines are too close, and they pass through directly. At this time, the potential barrier loses its function of blocking electrons, and a breakdown occurs.Zener breakdown generally occurs in PN junctions with higher doping concentrations. This is because the PN junction under this situation has a large charge density and a narrow width in the space charge region. As the temperature increases, the energy gap decreases, and a breakdown can be resulted in with a small reverse voltage. Figure 2. PN Junction Ⅱ Zener Effect vs Avalanche Effect 1) Zener effect mainly depends on the maximum electric field in the space charge region, and in the collision ionization mechanism is related to both the field strength and the collision accumulation process of carriers. Obviously, the wider the space charge region, the more times of multiplication, so the avalanche breakdown is not only related to the electric field, but also related to the width of the space charge region, which requires the thickness of the PN junction.2) Because avalanche breakdown is the result of impact ionization. If we increase the electrons and holes in the space charge region by means of illumination or fast particle bombardment, they will also have a multiplier effect. However, the above external effects will not have a significant impact on the Zener breakdown.3) The breakdown voltage is determined by the tunnel effect, and its temperature coefficient is negative, that is, the breakdown voltage decreases with the increase of temperature, which is the result of the decrease of the forbidden band width with the increase of temperature. The breakdown voltage determined by avalanche multiplication decreases with the increase of temperature due to the impact ionization rate (the ionization rate represents the number of electron-hole pairs generated by a carrier drifting a unit distance under the action of an electric field), and its temperature coefficient is positive. That is, the breakdown voltage increases with temperature. Zener with voltage lower than 5-6V is mainly due to Zener breakdown; Zener with voltage higher than 5-6V is mainly due to avalanche breakdown. Zener diodes with a voltage between 5-6V have similar breakdown degrees and the best temperature coefficient, which is why many circuits use 5-6V Zener tubes. The principle of the Zener tube determines that its response speed is not very fast, so a tube reference voltage is used in occasions with high speed requirements.4) For the PN junction with higher doping concentration and thinner barrier, it is mainly Zener breakdown. The PN junction with lower doping and therefore wider potential barrier is mainly avalanche breakdown, and the breakdown voltage is relatively high.The PN junction breakdown is an important electrical property, and the breakdown voltage limits the working voltage of the circuit, so semiconductor devices have certain requirements for the breakdown voltage. However, a variety of devices such as Zener diodes, avalanche diodes, and tunnel diodes can be fabricated by using the breakdown phenomenon.Under normal circumstances, the avalanche breakdown and Zener breakdown are within a certain range of conditions (breakdown voltage, time), with the normal working conditions are restored, are reversible. If it is only for protection, the TVS voltage regulator tube is mainly used for voltage regulation. The smaller the current passing through, the better. When the instantaneous voltage exceeds the normal working voltage of the circuit, the TVS diode will avalanche, providing an ultra-low resistance path for the instantaneous current, which is diverted through the diode, avoiding the protected device. In additional, the protected circuit keeps the cut-off voltage until the voltage returns to normal value. When the instantaneous pulse ends, the TVS diode automatically returns to the high resistance state, and the entire circuit entering the normal voltage, the failure mode of the TVS tube is mainly short circuit. But when the overcurrent passed is too large, it may also cause the TVS tube to be burst and open. Figure 3. TVS Diode Ⅲ Transistor Secondary Breakdown and Protection 3.1 A Brief Description In most switching power supplies, power switching transistors work under high-voltage, high-current high-frequency pulses, and switching on and off under such conditions will cause a great impact on the transistors. Secondary breakdown is one of the important causes of transistor damage. To design a high-performance, high-reliability switching power supply, it is necessary to have a clear understanding of the secondary breakdown of transistors and avoidance measures. 3.2 Cause of Breakdown The secondary breakdown is mainly caused by the high local temperature in the device body. The temperature rise is caused by thermal imbalance when forward biased and avalanche breakdown when reverse biased.Because the thermal resistance of the transistor is unevenly distributed throughout the tube, in some weak areas, the temperature rise will be higher than other parts, forming a so-called "hot spot", and so on until a critical temperature, causing the breakdown of the tube. The secondary breakdown caused by the avalanche breakdown is a phenomenon in which the electric field distribution of the junction is changed due to the excessive current density at some points after the primary avalanche breakdown occurs, resulting in a negative resistance effect and the local temperature is too high. 3.3 Precaution Turn-on and turn-off losses are important factors that affect the normal operation of switching devices. In particular, the transistor is prone to secondary breakdown in the dynamic process, and this phenomenon is directly related to the switching loss. Therefore, reducing the switching loss of the self-shutdown device is a necessary measure for the correct use of the device. There are two ways to reduce losses:(1) Turn off the transistor at the lowest possible collector-emitter voltage (Vce).(2) When the transistor is turned off during the rise of the emitter voltage, the emitter current should be minimized. For example, introducing a buffer circuit is one of the ways to achieve the above purpose. 3.4 Snubber Circuit Examples The following snubber circuits can be used in the design of switching power supplies to ensure that the transistors operate within a safe area.1) The commonly one is an energy-consuming shutdown snubber circuit. Although it consumes more energy, this circuit is simple. Figure 4. Commonly Used Shutdown Snubber Circuit It consists of an RCD network connected in parallel with transistor switches. When the transistor is turned off, the load current charges the capacitor C through the diode D, so that the collector current of the tube gradually decreases. Because the voltage across the capacitor C cannot be abruptly changed, its collector voltage is restrained. The situation where the collector voltage and current reach their maximum values at the same time is avoided, so there is no maximum instantaneous power consumption spike. When the tube is turned on, the capacitor releases energy and dissipates it in the resistor.2) Two commonly used energy-consuming turn-on snubber circuits.a. An inductor-diode network is connected in series with the transistor collector to form a turn-on snubber circuit. When the tube is turned on, the inductance Ls controls the current rise rate di/dt during the collector voltage drop. When the tube is turned off, the energy stored in the inductor Ls 1/2 freewheels through the diode Ds, and its energy is dissipated in the resistance of Ds and the reactor. Figure 5. Open Snubber Loop with Unsaturated Reactance b. Turn-on snubber circuit with saturable reactor: The purpose of using turn-on snubber circuit is to make the collector voltage drop to 0 when the collector current of the transistor is small, so as to minimize the turn-on loss. Especially for inductive loads, the effect is more significant. The designed saturable reactor should be: in one hand, after the collector voltage drops to zero, the buffer reactor is in a saturated state; in the other hand, before saturation, the collector voltage drops to zero, the reactor presents a high resistance, and the magnetizing current flowing through the tube is small to achieve the purpose of reducing turn-on loss. Figure 6. Open Snubber Circuit with Saturable Reactance 3) In the figure, Co is a transfer capacitor, and Dc is a feedback diode. These two components feed back energy to the load. When the tube is turned off, the buffer capacitor Cs is charged to the power supply voltage Vcc, and when the tube is turned on next time, the load current is transferred from the freewheeling diode Df to the transistor. At the same time, the voltage on Cs resonates to Co. When the tube is turned off again, the Cs is charged again, the capacitor Co is discharged to the load, and the energy is fed back. Figure 7. Passive Feedback Shutdown Buffer Circuit 4) This circuit stores the magnetic field energy and feeds back to the power supply through the transformer. The transformer is wound with two wires, and its primary side has a certain inductance; the polarity of the width side is opposite to that of the primary side, and a reverse diode is connected. When the tube is turned on, the primary side bears all the power supply voltage, and the secondary side has no energized circuit. When the tube is turned off, the polarity of the induced voltage on the secondary side is reversed, and when its voltage is higher than the power supply voltage Vcc, energy is fed to the power supply. Figure 8. Passive Feedback Opens the Buffer Circuit 5) The turn-on snubber circuit and the turn-off snubber circuit are combined to form a composite snubber circuit, and the composite snubber circuit has a protective effect when the transistor is turned on and off. This kind of circuit is also divided into two types: energy consumption and energy feeding.a. When the tube is turned on, the snubber capacitor is discharged through the Cs, Rs, and Ls loops, which reduces the current rising rate that the tube bears. In addition, when the tube is turned on, the inductance Ls can also limit the reverse recovery current of the freewheeling diode Df. Figure 9. Energy-consuming Composite Buffer Circuit b. When the transistor is turned off, the capacitor Co and the inductor Ls operate in parallel to feed the stored energy to the load. When the capacitor Co is discharged, the voltage on the inductor Ls gradually decreases to 0, and the load current is conducted through the freewheeling diode Df during this period. Figure 10. Energy-feeding Compound Snubber Circuit The various snubber circuits mentioned above can be divided into two types, namely energy-consuming and energy-feeding. The energy-consuming circuit is simple but relatively consumes more energy, and is suitable for the use of low-power circuits. The energy-feeding circuit is complex, but in a high-power supply, if the energy dissipated by the snubber circuit is dissipated in the form of heat, it is bound to cause a lot of trouble, so the energy-feeding buffer circuit should be used.   Ⅳ FAQ 1. What is a zener breakdown voltage?A normal p-n junction diode allows electric current only in forward biased condition. ... This sudden rise in electric current causes a junction breakdown called zener or avalanche breakdown. The voltage at which zener breakdown occurs is called zener voltage and the sudden increase in current is called zener current. 2. Which breakdown occurs in Zener diode?avalanche breakdownIn Zener diodes, avalanche breakdown occurs. When the Vz is greater than 8 volts in a Zener diode, avalanche breakdown occurs because there is an isolation of electrons and holes. 3. What is difference between avalanche and zener breakdown?The main difference between Zener breakdown and avalanche breakdown is their mechanism of occurrence. Zener breakdown occurs because of the high electric field whereas, the avalanche breakdown occurs because of the collision of free electrons with atoms. Both these breakdowns can occur simultaneously. 4. How do you calculate Zener breakdown voltage?The reverse current that results after the breakdown, is called Zener current (Iz). At breakdown, increase of VI increases II by large amount, so that V0 = VI– RI II becomes constant. This constant value of V0 which is the reverse breakdown voltage, is called Zener voltage. 5. What is avalanche breakdown of diode?What is Avalanche Breakdown? The avalanche breakdown occurs when a high reverse voltage is applied across the diode. As we increase the applied reverse voltage, the electric field across the junction increases. This electric field exerts a force on the electrons at the junction and frees them from covalent bonds. 6. How does an avalanche breakdown take place?Avalanche breakdown usually occurs when a high reverse voltage is applied across the diode. So as we increase the applied reverse voltage, the electric field across the junction will keep increasing. This generated electric field exerts a force on the electrons at the junction and it frees them from covalent bonds. 7. What is avalanche effect of Zener diode?Avalanche breakdown involves minority carrier electrons in the transition region being accelerated, by the electric field, to energies sufficient for freeing electron-hole pairs via collisions with bound electrons. The Zener and the avalanche effect may occur simultaneously or independently of one another. 8. What do you mean by zener breakdown voltage?When reverse biased voltage applied to the zener diode reaches zener voltage, it starts allowing large amount of electric current. At this point, a small increase in reverse voltage will rapidly increases the electric current. Because of this sudden rise in electric current, breakdown occurs called zener breakdown. 9. Is Zener voltage the same as breakdown voltage?The breakdown voltage,commonly called the Zener voltage, is the reverse-biased voltage that causes the diode to conduct current. Breakdown voltages usually range from 2.4 V to hundreds of volts. 10. What is meant by Zener effect?The Zener effect is a type of electrical breakdown that occurs in a reverse-biased PN junction when the electric field enables tunnelling of electrons from the valence to the conduction band of a semiconductor, leading to a large number of free minority carriers which suddenly increase the reverse current. 11. Which factor is responsible for Zener effect?In effect, electrons from the p-side valence band are able to tunnel across the barrier into the empty states in the n-side conduction band when a small reverse bias is applied. The result is a strong current from n to p in the diode, causing zener breakdown. 12. What is valence breakdown?Avalanche breakdown (or “the avalanche effect”) is a phenomenon that can occur in both insulating and semiconducting materials. It is a form of electric current multiplication that can allow very large currents within materials which are otherwise good insulators. It is a type of electron avalanche.

Introduction RF power amplifier is an important part of various wireless transmitters. In the front-end circuit of the transmitter, the power of the RF signal generated by the modulation oscillator circuit is very small, and it needs to go through a series of amplification-buffer stage, intermediate amplification stage, and final power amplification stage to obtain enough RF power before feeding. In order to obtain a sufficiently large RF output power, a RF power amplifier must be used. RF Power Amplifier Design: The Basics Catalog Introduction Ⅰ Requirements of RF Power Amplifier Ⅱ Types of Power Amplifier in Use Ⅲ Parameters of RF Power Amplifier Design Ⅳ Key Feature: Non-Linearity 4.1 Nonlinear Characteristics 4.2 Influence of Nonlinear Characteristics Ⅴ FAQ Ⅰ Requirements of RF Power Amplifier With the vigorous development of modern digital mobile communication technology, users have more requirements on the performance of wireless communication equipment. To achieve stable and high-speed data transmission in various environments is one of the main goals of future mobile communication system researchers. The RF power amplifier is the last stage of the transmitter. It amplifies the modulated frequency band signal to the required power, ensuring that the receiver in the coverage area can receive a satisfactory signal level, but it cannot interfere too much with the communication of adjacent channels, and meanwhile try to keep the amplified high-power signal without distortion. The requirements of these different aspects make the users of power amplifiers have to consider many factors in all aspects. So you should get a full knowledge of RF power amplifiers. Figure 1. Classic RF Power Amplifier Circuit Ⅱ Types of Power Amplifier in Use What are the main types of RF amplifiers for such an important device?1) According to the operating frequency bandsAccording to the working frequency band, it can be divided into narrowband RF power amplifier and broadband RF power amplifier. The former generally uses frequency selective networks as load circuits, such as LC resonant circuits. The latter does not use the frequency selection network as the load loop, but employs the transmission line with a wide frequency response as the load.2) According to the network propertiesAccording to the nature of the matching network, power amplifiers can be divided into non-resonant power amplifiers and resonant power amplifiers. The matching network of the non-resonant power amplifier is a non-resonant system, such as high-frequency transformers, transmission line transformers and other non-resonant systems, and its load properties are purely resistive, where this is also called reactance properties.3) According to current conduction angleBased on it, RF power amplifiers can be divided into class A, AB, B, C, D, E and so on. The differences between these categories can be seen in the following table: Classification Conduction Angle Efficiency Linearity Application Class A Θ=360° ≤30% Very good Small Signal Low Power Amplification Class B Θ=180° ≤60% Lower than class A For High Power Class C Θ<180° About 60% Nonlinear amplifier For High Power Class AB 180°<Θ<360° 30%~60% Better than class B Small signal works in class A, large signal works in class B Class D Work in switch mode 80% Very good, only good for low frequencies Switch mode amplifier Class E Work in switch mode 90% Completely nonlinear amp Switch mode amplifier In the classification of amplifiers, we often talk about amplifiers of class A to E according to the conduction angle. Class A power amplifier is a linear amplifier, its response to the sine-wave  input is a sine-wave output, generally without distortion amplification, and the output frequency is the same as the input frequency. Since class A amplifiers do not require additional filtering circuitry, their packages can be small and cost less. The output of a class B amplifier is a half sine wave of the input, resulting in half-wave distortion, which produces many harmonics. The output power and efficiency of the class C working state are the highest among these working states, and most of the amplifiers used for radio frequency work in the class C. Figure 2. Class A Amplifier Load Curve   Ⅲ Parameters of RF Power Amplifier Design RF power amplifiers are electronic circuits that comprehensively consider issues such as output power, excitation level, power consumption, distortion, efficiency, size and weight. In the transmitting system, the output power of the RF power amplifier can be as small as mW and as large as several kW, but this refers to the output power of the final power amplifier. In order to achieve high power output, the last stage must have a sufficiently high excitation power level. At the same time, it has other important indicators, as follows:1) Operating FrequencyGenerally speaking, it refers to the linear operating frequency range of the amplifier. If the frequency starts at DC, the amplifier is considered to be a DC amplifier.2) GainThe working gain is the main indicator to measure the amplification ability of the amplifier. Here it is defined as the ratio of the power delivered to the load by the amplifier output port to the power actually delivered by the signal source to the amplifier input port.Gain flatness refers to the variation range of amplifier gain in the entire operating frequency band under a certain temperature, and is also a main indicator of the amplifier. Figure 3. Output Power and 1dB Compression Point (P1dB) Referring to the Figure 3, when the input power exceeds a certain amount, the gain of the transistor begins to decrease, and the end result is that the output power saturates. When the gain of the amplifier deviates from a constant or is 1dB lower than other small signal gains, this point is the famous 1dB compression point (P1dB). Generally speaking, the power capacity of an amplifier is expressed by the 1dB compression point.3) EfficientSince the power amplifier is a power component, it needs to consume the supply current. Therefore, the efficiency of the power amplifier is extremely important to the efficiency of the whole system. Power efficiency is the ratio of the RF output power of the amplifier to the DC power supplied to the transistors.ηp=RF Output Power/DC Input Power4) Intermodulation Distortion (IMD)Intermodulation distortion refers to the mixed components of two or more input signals with different frequencies passing through a power amplifier. This is due to the nonlinear nature of the amplifier. Among them, because the third-order intermodulation product is very close to the fundamental signal, it has the greatest influence, so the third-order intermodulation is the most important consideration for the related products. The lower the third-order intermodulation product, the better.5) Third-order Intermodulation Cut-off Point (IP3)The intersection point of the extension line of the fundamental wave signal output power and the extension line of the third-order intermodulation in Fig is called the third-order intermodulation cut-off point, which is represented by the symbol IP3. It is also an important indicator of nonlinearity. When the output power is constant, the greater the output power of the third-order intermodulation cut-off point, the better the linearity of the power amplifier.6) Dynamic RangeThe dynamic range of a power amplifier generally refers to the difference between the minimum detectable signal and the maximum input power in the linear operating region. Naturally, this value must be as large as possible.7) Harmonic DistortionWhen the input signal increases to a certain level, the power amplifier will generate a series of harmonics due to its work in the nonlinear region. For high-power amplifier systems, filters are generally required to reduce harmonics below 60dBc.8) Input/Output VSWR (Voltage Standing Wave Ratio)This is also a very important indicator of how well the amplifier matches the overall system. The deterioration of the input-output ratio will lead to the deterioration of the gain fluctuation and group delay of the system. However, it is difficult to design a power amplifier with a high VSWR. In general systems, the input VSWR of the power amplifier is required to be lower than 2:1.The main technical indicators of RF power amplifiers are output power and efficiency. Therefore how to improve them is the core of the design goals of RF power amplifiers. Usually in the RF power amplifier, the fundamental frequency or a certain harmonic can be selected by the LC resonant circuit to achieve distortion-free amplification. In addition to this, the harmonic components in the output should be as small as possible to avoid interference with other channels. Figure 4. Increase the Power of the RF Input Signal Ⅳ Key Feature: Non-Linearity In an ideal amplifier, the output signal should faithfully reflect the input signal, that is, the waveform should be the same. But in fact, for many reasons, the input signal cannot be exactly the same waveform as the input signal, which is called amplifier distortion.Amplifier distortion mainly includes frequency distortion (linear distortion) and waveform distortion (non-linear distortion). The former mainly refers to the difference in gain and delay of the amplifier for different frequency components; the latter refers to the same frequency, the output signal and the input signal are not linear. Frequency distortion is represented by spectral changes in the frequency domain, while nonlinear distortion is represented by changes in the time-domain waveform. Non-linear distortion is different from frequency distortion mainly because a large number of new frequency components are generated. The nonlinear distortion of the power amplifier is mainly discussed here. 4.1 Nonlinear Characteristics From the small-signal model and input characteristic curve of an ideal transistor, it can be seen that the transistor amplifier itself is not an ideal linear device, and at the same time, due to the influence of parasitic parameters, the linearity is further reduced. But within a certain power range, the transistor can be regarded as linear amplification. For power amplifier designers, how to obtain higher output power and improve linearity is the key.For a transistor amplifier, its volt-ampere characteristics can be described as follows: A power series expansion can be used to describe the volt-ampere characteristics of the device: In the formula, an(n=0,1,2,3,…) is a coefficient related to the circuit characteristics. Usually, the larger the n, the smaller the value of the coefficient an. When the nonlinear device in the circuit is represented by a power series, the number of series terms taken depends entirely on the magnitude of the signal amplitude and the required precision. 4.2 Influence of Nonlinear Characteristics The influence of the nonlinear characteristics of the device on the amplifier can be discussed in two cases. One is when there is only one signal at the input end, and the other is when the input end has one to two other signals in addition to the useful signal.🔺Only one signal at the inputLet the signal at the input end be , and substitute it into formula 2, at this time there is When the amplitude of the input signal is large and the effect of the cubic term must be considered, the fundamental frequency signal obtained from formula 2 is: Figure 5. 1dB Compression Point (PA) A3 in formula 3 is usually a negative value, that is, y1(t) decreases as the input signal amplitude increases, a phenomenon called gain compression.The "1dB compression point" is often used in engineering to measure the linear performance of the device. The 1dB compression point is defined as the input signal power P1dB that reduces the gain by 1dB from the linear gain. As shown in Figure 5. According to the definition of 1dB compression point and formula 3, we can get 🔺Two signals at the input.The signal amplified at the input end of the amplifier is generally not a single tone signal, but a spectral signal composed of a certain bandwidth. Due to the nonlinearity of the device, a large number of combined interference frequency components other than the useful signal will be generated at the output end. In addition, the combined frequency components of two or more interfering signals may also cause interference to the useful signal. Have an assumption: Substitute into formula 1, where It can be seen from the above formula that the fundamental frequency components of ω1 and ω2 are generated by the first and third power terms: A total of multiple frequency components are generated: ω1 , ω2 , ω1 ± ω2, 2ω1 - ω2, 2ω2 - ω1 , 3ω1 - 2ω2, 3ω2 - 2ω1.The difference frequency 2ω1 - ω2, 2ω2 - ω1 in the combined frequency is generated by the cubic term. The combination of these two signal frequencies is just within the sideband range of the signal frequency, which may cause interference to adjacent channels, and is one of the main indicators of transmission signal. Figure 6. Intermodulation Signal Interference This interference is caused by the mutual modulation of the two signals, so it is called intermodulation interference. At the same time, it is generated by a cubic term, so it is also called third-order intermodulation interference in engineering.When the third-order intermodulation interference is an important indicator of the communication machine, it is often measured by the intermodulation distortion ratio IMR and the third-order intermodulation blocking point IP3 in engineering. IMR is defined as the ratio of the amplitude of the third-order intermodulation product to the amplitude of the fundamental signal at a certain input amplitude. Definition of IP3: When the third-order intermodulation component increases to be equal to the fundamental frequency component, the receiver cannot receive normally, so there is a . Figure 7. Third-order Intermodulation Blocking Point 🔺Sideband Signals Figure 8. Sideband Signals and the Spectrum In fact, most of the sideband signals are generated outside the bandwidth after the useful signals of different frequencies within the bandwidth are modulated with each other. That is, the sideband signal rises faster than the in-band signal, and the spectral mask in the above figure becomes more and more flat. The increase of sideband signals will cause interference to adjacent channels, so the IEEE 802.11 protocol has strict requirements on the spectrum template, as shown in the Figure 9. Figure 9. DSSS Signal Modulation Spectral Mask Figure 10. OFDM 20MHz Bandwidth Signal Spectral Mask For the power amplifier, its nonlinear characteristics will increase the sideband of the modulated signal, and the sideband amplitude is not easily suppressed by other networks such as filters, and it is easy to cause design difficulties. Therefore, when choosing a PA, not only should pay attention to the maximum linear output that it can achieve, but also whether it can meet the sideband spectrum requirements at this output power.🔺Other Effects of NonlinearityIn addition to the previously mentioned gain drop, which generates a large number of harmonic components, as well as third-order intermodulation and sidebands, nonlinearity can also cause signal and EVM to deteriorate, etc.   Ⅴ FAQ 1. What is RF power amplifier?A radio frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency signal into a higher power signal. 2. How does RF power amplifier work?An RF amplifier is actually a tuned amplifier that enables the input signal of broadcast or transmitted information to control an output signal. The RF amplifier uses frequency-determining networks to convert the input signal into an output signal that will provide the required response at a given frequency. 3. What is the most efficient class of RF power amplifier?Class C AmplifierThe Class C Amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers mentioned here. The previous classes, A, B and AB are considered linear amplifiers, as the output signals amplitude and phase are linearly related to the input signals amplitude and phase. 4. How do I choose an RF power amplifier?Considerations When Choosing An RF Power Amplifier:Gain.Operating Frequency.Output Power Level.Efficiency.Linearity.Mismatch Tolerance.Noise Level. 5. What are the advantages of RF amplifier?Following are the RF Amplifier advantages:The RF amplifier offers greater gain i.e. better sensitivity. It offers better selectivity and hence it has ability to select wanted signals from multiple input signals at the RF receiver. 6. What are the different types of RF amplifiers?Amplifier TypesBroadband AmplifiersGain Block AmplifiersLog AmplifiersVariable Gain AmplifiersLow Noise AmplifiersCoaxial and Waveguide Power AmplifiersLinear AmplifiersBi-Directional Amplifiers 7. What is RF amplifier circuit?A radio frequency power amplifier (RF power amplifier) is a type of electronic circuit that converts a low-power radio-frequency signal into a higher power signal. 8. Is Class D amplifier better than a class AB?The most common audio power amplifier operates in the Class-AB mode. It provides the greatest amount of output power with the least amount of distortion. ... Class-D amplifiers are switches that are more efficient and produce less heat than their Class-AB equivalents. 9. What are RF amplifiers used for?Whenever people need to magnify a radio frequency signal into a higher power signal, the RF amplifier plays a pivotal role. They are used in commercial and defense avionics, space and deep space, electronic warfare, naval applications, mobile internet, satellite communication, and wireless communications. 10. Which amplifier is used in RF amplifier?RF power amplifiers using LDMOS (laterally diffused MOSFET) are the most widely used power semiconductor devices in wireless telecommunication networks, particularly mobile networks. LDMOS-based RF power amplifiers are widely used in digital mobile networks such as 2G, 3G, and 4G.

Introduction IGBT and MOSFET are fully controlled devices and are voltage-driven, that is, the device is turned on or off by controlling the gate voltage. In fact, the structure of the IGBT is an NPN-type MOSFET plus a P-junction, that is, an NPNP structure, which is a P-type BJT driven by MOS in principle. So what is the difference between them? What is the specific connection of them? MOSFET BJT or IGBT - Brief Comparison Catalog Introduction Ⅰ MOSFET & IGBT Review Ⅱ Si IGBT vs SiC MOSFET Ⅲ Different Requirements for Si IGBT and SiC MOSFET 3.1 ON & OFF State 3.2 Short-Circuit Protection 3.3 Interference and Delay Ⅳ IGBT Working Principle by Analogy with MOSFET Ⅴ FAQ Ⅰ MOSFET & IGBT Review MOSFET is a metal-oxide-semiconductor field effect transistor, or metal-insulator-semiconductor. The source and drain of it can be swapped, and they are both N-type regions formed in the P-type backgate. In most cases, these two regions are the same, even if the two ends are reversed, it will not affect the performance of the device. Such devices are considered symmetrical. According to the polarity of its "channel" (working carrier), MOSFET can be divided into two types: N-type and P-type, usually also called NMOSFET and PMOSFET, abbreviations including NMOS, PMOS, etc.IGBT (insulated gate bipolar transistor), is a composite fully controlled voltage-driven power semiconductor device composed of BJT (bipolar transistor) and MOS. Have the advantages of high input impedance of MOSFET and the low on-voltage drop of the GTR. When the GTR saturation voltage is reduced, the current carrying density is large, but the driving current is large; the MOSFET driving power is small, the switching speed is fast, but the on-state voltage drop is large, and the current carrying density is small. The IGBT combines the advantages of the above two devices, and the driving power is small and the saturation voltage is reduced. In simple terms, an IGBT is equivalent to a thick base PNP transistor driven by a MOS. Figure 1. N-MOSFET Architecture Ⅱ Si IGBT vs SiC MOSFET Since the differences between IGBT and MOSFET in structure, working principle and application range are quite detailed, it is impossible to express clearly in one sentence. Next, we will compare the differences between silicon (Si) IGBTs and silicon carbide (SiC) MOSFETs in detail.The electrical parameters and characteristics of Si IGBT and SiC MOS drivers are quite different. The requirements for driving of SiC MOS are also different from those of traditional silicon devices. They have the characteristics of low on-resistance and small switching loss, which can reduce device loss and improve system efficiency, and more suitable for high frequency circuits. It is widely used in new energy vehicle motor controller, vehicle power supply, solar inverter, charging pile, UPS, PFC power supply and other fields.The difference between the two is mainly reflected in the GS turn-on voltage, GS turn-off voltage, short-circuit protection, signal delay and anti-interference, as follows: Characteristic Si IGBT SiC MOSFET Drive Requirements Switching Frequency Low, >30kHz High, 50~500kHz 1) Use high power gate resistors. 2) Optimize the cooling environment. 3) Improve the efficiency of the DC-DC conversion circuit and reduce the overall loss of driving power. Threshold Voltage 5V-6V 1.6V-4.5V Negative pressure shutdown/Miller clamp to prevent false turn-on Switching Time 300ns 50ns 1) Use digital isolation driver chip, the signal transmission delay can reach 50ns, and it has relatively high consistency, and the transmission jitter is less than 5ns. 2) the low transmission delay push-pull chip is selected. Switching-On Time 15V 15V~22V 1) Priority is given to stabilizing the negative voltage to ensure that the shutdown voltage is stable. 2) A negative voltage clamping circuit is added to ensure that it does not exceed the standard during shutdown. Switching-Off voltage -15V~-5V -5V~0V Short-Circuit Withstand Time <10μs 2~5μs A diode or a resistor string is used to detect short circuits, and the shortest short-circuit protection time is limited to about 1.5μs. CMTI 15kV/μs 100kV/μs 1) The common mode anti-interference ability reaches 100kV/μs to transmit the isolation chip for signal transmission. 2) The optimized isolation transformer design is adopted, and its primary side and the secondary side are shielded to reduce mutual crosstalk. 3) The Miller clamp is used to prevent the influence of the switch of the same bridge arm.   Ⅲ Different Requirements for Si IGBT and SiC MOSFET For a fully-controlled switching device, configuring an appropriate on-off voltage is of great significance for the safety and reliability of the device. Due to the difference between IGBT and MOSFET, the requirements for the two are also different.IGBT is a field-controlled device whose turn-on and turn-off are determined by the voltage between the gate(G) and the emitter(E). The working principle of MOS tube (enhancement mode NMOSFET) is to use VGS to control the amount of "induced charges" to change the condition of the conductive channel, and then to control the drain current. 3.1 ON & OFF State 1) Silicon IGBT: Silicon IGBTs of various manufacturers have the same turn-on and turn-off voltage requirements.· The typical turn-on voltage is required to be 15V.· The shutdown voltage value range is -5V~-15V, and customers can choose the appropriate value according to their needs. The common values are -8V, -10V, -15V.· Prioritize stable positive voltage to ensure stable turn-on.2) Silicon carbide MOSFET: Different manufacturers have different switching voltage requirements:· The turn-on voltage is required to be higher than 22V~15V.· The shutdown voltage is required to be higher -5V~-3V.· Prioritize negative voltage stabilization to ensure stable turn-off voltage.· Increase the negative voltage clamping circuit to ensure that it does not exceed the standard when it is turned off. 3.2 Short-Circuit Protection The switching device has the risk of short circuit during operation, and configuring a suitable short circuit protection circuit can effectively reduce the damage caused by the short circuit during the use of the switching device. Compared to Si IGBTs, SiC MOSFETs have shorter short-circuit withstand times.1) Silicon IGBTThe time of surrender and short-circuit of Si IGBT is generally less than 10μs. When designing the short-circuit protection circuit of it, set the detection delay and corresponding time of short-circuit protection to 5-8μs.2) SiC MOSFETGenerally, the short-circuit withstand capability of SiC MOSFET modules is less than 5μs, and short-circuit protection is required to work within 3μs. A diode or a resistor string is used to detect short circuits, and the protection time is limited to about 1.5μs. 3.3 Interference and Delay 1) The impact of high dv/dt and di/dt on the system.When the switching action is performed under the condition of high voltage and high current, the switching of the silicon carbide MOSFET device will generate high dv/dt and di/dt, which will affect the driver circuit. It is very important to improve the anti-interference ability of the driver circuit for the reliable operation of the system. the following way to achieve.· Add common mode choke coil and filter inductor to the input power supply, which reduce the interference of driver EMI to low voltage power supply.· A low-pass filter is added to the rectification part of the secondary side power supply, which reduce the interference of the driver to the high-voltage side.· Use an isolation chip with a common mode immunity of 100kV/μs for signal transmission.· Optimize the isolation transformer design, and use shielding layer on primary side and secondary side to reduce crosstalk between each other.· Use Miller clamp to prevent the influence of the switch of the same bridge arm. 2) Low transmission delayUsually, the application switching frequency of silicon IGBT is less than 40kHZ, and the recommended application switching frequency of SiC MOSFET is greater than 100kHz. The increase of application frequency makes MOS require the driver to provide lower signal delay time. The transmission delay of the SiC MOSFET drive signal should be less than 200ns, and the transmission delay jitter should be less than 20ns, which can be achieved by the following methods.· Using digital isolation driver chip, the signal transmission delay can reach 50ns, and it has relatively high consistency, and the transmission jitter is less than 5ns.· Select push-pull chips with low transmission delay and short rise & fall time. Due to the conductance modulation effect, the on-state specific resistance of high voltage SiC IGBTs is much lower than that of power SiC MOSs, and does not change much as the blocking voltage rating increases. When the conductance modulation effect is fully exerted, the on-state voltage drop of the IGBT drift region is only related to the bipolar diffusion coefficient and bipolar lifetime of the carriers, and will not change with the increase of the on-current. When the operating temperature changes, the on-state voltage drop of the SiC high voltage IGBT decreases with the increase of the junction temperature. This is mainly because the bipolar lifetime of the extra carriers in the SiC epitaxial layer will increase with the increase of temperature. Although the diffusion coefficient will shrink to some extent with the increase of temperature, the greater prolongation of lifetime will eventually make the the bipolar diffusion length increased, thereby reducing the on-state voltage drop. It is especially true in n-channel devices.This is in sharp contrast to the larger increase in the forward voltage drop of the power MOS at high temperature. Silicon carbide p-channel IGBTs have higher on-state voltage drop than n-channel IGBTs at the same current density due to their larger channel resistance, but their volt-ampere characteristics do not change much with temperature. As for the applications, this is undoubtedly an advantage. Figure 2. Comparison of characteristics between SiC IGBT and power MOS under the Same Condition of Withstand Voltage of 20kV. It is not difficult to calculate from the intersection of the equal power consumption curve in the figure and the on-state characteristic curves of these devices: corresponding to the same power consumption of 300W/cm2, the ratio of the on-state current of the silicon carbide IGBT to the silicon carbide power MOS versus p-channel devices and n-channel devices are different, they are 1.5 and 1.8 at room temperature, respectively, and increase to 2.7 and 3.5 at 225°C, indicating that high-voltage and high-current SiC IGBTs are more suitable for high-temperature applications.In a word, compared with Si IGBT, SiC MOSFET not only improves system efficiency, power density and operating temperature, but also puts forward higher requirements for the driver. In order to make silicon carbide MOSFET better in the system, it is necessary to give SiC MOSFET a appropriate driver.   Ⅳ IGBT Working Principle by Analogy with MOSFET IGBT is a Darlington pair composed of GTR and MOSFET: part of which is MOSFET driver, and the other part is thick-base PNP transistor. Figure 3. IGBT Architecture Its simplified equivalent circuit is shown in the figure below, and RN in the figure is the modulation resistance in the base area of the PNP transistor. It can be clearly seen from this circuit that the IGBT is a composite device of Darlington configuration composed of transistors and MOSFET, where the transistor in the figure is a PNP transistor, and the MOSFET is an N-channel field effect transistor, so the IGBT of this structure is called an N-channel IGBT, and its symbol is N-IGBT. Similarly there are P-channel IGBTs, namely P-IGBTs. Figure 4. Simplified Equivalent Circuit The electrical graphic symbols of the IGBT are shown in the figure. IGBT is a field-controlled device, and its turn-on and turn-off are determined by the voltage UGE between the gate and the emitter. When the gate-emitter voltage UCE is positive and greater than the turn-on voltage UCE (th), a channel is formed in the MOSFET and is a PNP. The N-type transistor provides the base current to turn on the IGBT. At this time, the holes (minority carriers) injected into the N- region from the P+ region modulate the conductance of the N- region, reduce the resistance RN of the N- region, and make the IGBT also has a small on-state voltage drop. When no signal or reverse voltage is applied between the gate and emitter, the channel in the MOSFET disappears, the base current of the PNP transistor is cut off, and the IGBT is turned off. It can be seen that the driving principle of IGBT is basically the same as that of MOSFET.① When UCE is negative: J3 junction is in reverse bias state, and the device is in reverse blocking state.② When UCE is positive: UC< UTH, the channel cannot be formed, and the device is in a forward blocking state; UG> UTH, an N-channel is formed under the insulating gate, and conductance is generated in the N- region due to the interaction of carriers modulation so that the device is conducting forward. Figure 5. Hybrid Switch Using Si IGBT and SiC MOSFET 1) ONThe structure of IGBT silicon is very similar to that of power MOSFET, and the main difference is that JGBT adds a P+ substrate and an N+ buffer layer, in terms of it, one MOS drives two bipolar devices (devices with two polarities). The application of the substrate creates a J junction between the P, and N+ regions of the tube. When the positive gate bias causes the inversion of the P base region under the gate, an N-channel is formed, and an electron flow occurs at the same time, and a current is generated exactly in the manner of a power MOSFET. If the voltage produced by this electron flow is in the range of 0.7V, J1 will be forward biased, some holes will be injected into the N- region, and the resistivity between N- and N+ will be adjusted, which reduces the power conduction the total loss of the pass and initiates a second charge flow. The end result is the temporary emergence of two different current topologies within the semiconductor layer: an electron flow (MOSFET current), and a hole current (bipolar). When UCE is greater than the turn-on voltage UCE(th), a channel is formed in the MOSFET to provide base current for the transistor, and the IGBT is turned on. 2) On-State Voltage DropThe conductance modulation effect reduces the resistance RN and reduces the on-state voltage drop. The so-called on-state voltage drop refers to the tube voltage drop UDS when the IGBT enters the on-state, and this voltage decreases with the rise of UCS. 3) Shut DownWhen a negative bias is applied to the gate or the gate voltage is lower than the threshold value, the channel is disabled and no holes are injected into the N-region. In any case, if the current of the MOSFET decreases rapidly during the switching phase, the collector current decreases gradually. This is because there are still minority carriers in the N layer after the commutation starts. This reduction in residual current value (wake) is entirely dependent on the charge density at turn-off, which in turn is related to several factors, such as the number and topology of dopants, layer thickness and temperature. The decay of minority carriers makes the collector current have a wake waveform. Collector current will cause increased power dissipation and cross-conduction problems, especially on devices that use freewheeling diodes.Considering that the wake is related to the recombination of minority carriers, the current value of the wake should be closely related to the Tc, IC of the chip, and has a close relationship with the mobility of holes. Therefore, depending on the temperature reached, it is feasible to reduce the undesirable effects of this current on the end equipment design. When a back pressure or no signal is applied between the gate and the emitter, the channel in the MOS disappears, the base current of the transistor is cut off, and the IGBT is turned off. 4) Reverse BlockingWhen a reverse voltage is applied to the collector, the junction is reverse biased and the depletion layer expands to the N-region. Because the thickness of this layer is reduced too much, an effective blocking ability will not be obtained, so this mechanism is very important. In addition, if the size of this region is increased too much, the voltage drop will continuously increase. 5) Forward BlockingWhen the gate and emitter are shorted and a positive voltage is applied at the collector terminal, the junction is controlled by the reverse voltage. At this time, the depletion layer of the N drift region is still subjected to the externally applied voltage. 6) LatchICBT has a parasitic PNPN thyristor between the collector and the emitter. Under special conditions, this parasitic device will turn on. This phenomenon increases the amount of current between the collector and the emitter, reduces the controllability of the equivalent MOSFET, and often causes device breakdown problems. The thyristor turn-on phenomenon is known as IGBT latch-up. Specifically, the causes of such defects vary, but are closely related to the state of the devices.   Ⅴ FAQ 1. Are there SiC IGBT?Along with the increasing maturity for the material and process of the wide bandgap semiconductor silicon carbide (SiC), the insulated gate bipolar transistor (IGBT) representing the top level of power devices could be fabricated by SiC successfully. 2. Where are SiC MOSFETs used?The primary automotive applications for SiC power MOSFETs, diodes, and modules are onboard electric vehicle (EV) chargers, DC/DC converters, and drivetrain inverters. Plug-in hybrid EVs and battery EVs (BEVs) use onboard chargers to “refuel” the vehicle battery either at home or at a public charging station. 3. What is SiC MOSFET?Silicon Carbide (SiC) MOSFETs exhibit higher blocking voltage, lower on state resistance and higher thermal conductivity than their silicon counterparts. SiC MOSFETs are designed and essentially processed the same way as silicon MOSFETs. 4. Can MOSFET replace IGBT?Due to the higher usable current density of IGBTs, it can usually handle two to three times more current than a typical MOSFET it replaces. This means that a single IGBT device can replace multiple MOSFETs in parallel operation or any of the super-large single power MOSFETs that are available today. 5. What are the advantages of silicon carbide?Silicon carbide MOSFETs have a critical breakdown strength that is 10x of silicon, and silicon carbide MOSFETs can operate at much higher temperatures, provide higher current density, experience reduced switching losses, and support higher switching frequencies. 6. What are the advantages of silicon carbide (SiC) over silicon (Si)?The advantage of SiC starts in the material itself having a 10x higher dielectric breakdown field strength, 2x higher electron saturation velocity, 3x higher energy bad gap and 3x higher thermal conductivity than Silicon. 7. What is the difference between silicon and silicon carbide?Silicon has a breakdown voltage of around 600V, while silicon carbide can withstand voltages 5-10 times higher. ... Silicon carbide can switch at nearly ten times the rate of silicon, which results in smaller control circuitry. 8. What is SiC in semiconductor?SiC (silicon carbide) is a compound semiconductor composed of silicon and carbide. SiC provides a number of advantages over silicon, including 10x the breakdown electric field strength, 3x the band gap, and enabling a wider range of p- and n-type control required for device construction. 9. Which is better MOSFET or IGBT?When compared to the IGBT, a power MOSFET has the advantages of higher commutation speed and greater efficiency during operation at low voltages. What's more, it can sustain a high blocking voltage and maintain a high current. ... The IGBT is also a three terminal (gate, collector, and emitter) full-controlled switch. 10. Why use an IGBT instead of a MOSFET?The main advantages of IGBT over a Power MOSFET and a BJT are: 1. It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. ... It canbe easily controlled as compared to current controlled devices (thyristor, BJT) in high voltage and high current applications. 11. Why is MOSFET preferred?Mosfet provides a very good isolation between the gate and the other two terminals compared to bjt. Mosfet can handle more power compared to BJT. The mosfet has a very low power loss and a high speed. Voltage signals can easily operate a mosfet, so it is used in many digital circuits. 12. Where are MOSFETs used?Power MOSFETs are commonly used in automotive electronics, particularly as switching devices in electronic control units, and as power converters in modern electric vehicles. The insulated-gate bipolar transistor (IGBT), a hybrid MOS-bipolar transistor, is also used for a wide variety of applications. 13. Why IGBT is very popular nowadays?With its lower on-state resistance and conduction losses as well as its ability to switch high voltages at high frequencies without damage makes the Insulated Gate Bipolar Transistor ideal for driving inductive loads such as coil windings, electromagnets and DC motors. 14. How many terminals are in a MOSFET?four terminalsThe MOSFET has four terminals: drain, source, gate, and body or substrate. 15. Why is IGBT bipolar?IGBTs is a bipolar device that utilizes two types of carriers, electrons and holes, resulting from the complex configuration that features a MOSFET structure at the input block and bipolar output, making it a transistor that can achieve low saturation voltage (similar to low ON resistance MOSFETs) with relatively fast. 16. How many types of IGBT are there?two typesInsulated Gate Bipolar Junction Transistor (IGBTs) are normally classified into two types. (ii) Punch Through [PT-IGBT]. These IGBTs are also referred to as symmetrical and asymmetrical IGBTs. These varieties of IGBT differ widely with regard to their fabrication technology, structural details etc. 17. What is full MOSFET?MOSFET stands for metal-oxide-semiconductor field-effect transistor. It is a field-effect transistor with a MOS structure. Typically, the MOSFET is a three-terminal device with gate (G), drain (D) and source (S) terminals. 18. How does an IGBT work as a switch?As defined by being a transistor, an IGBT is a semiconductor with three terminals which work as a switch for moving electrical current. Just as the word “gate” suggests, when voltage is applied to the gate, it opens or “turns on” and creates a path for current to flow between the layers. 19. Can I use transistor instead of MOSFET?It very much depends on the application. BJTs can be cheaper than FETs. This is especially true for high voltage switching where the much larger die area of FETs make them much more expensive. 20. Can IGBT conduct in reverse direction?No. The IGBT cannot conduct current in the reverse direction (from emitter to collector) even with a positive Vge applied to it, because it has a bipolar-type structure. ... However, the gate has no control over this reverse current flow; it is simply the forward biasing of the diode that allows it.

Introduction As a power semiconductor device, IGBT(insulated-gate bipolar transistor) is widely used in the fields of rail transit, smart grid, industrial energy saving, electric vehicles and new energy equipment. It has the characteristics of energy saving, convenient installation and easy maintenance, and stable heat dissipation. It is the core device for energy conversion and transmission. A brief overview, IGBT can be said to be a combination of MOSFET(metal–oxide–semiconductor field-effect transistor) and BJT(bipolar junction transistor). That is, it combines the gate voltage control transistor (high input impedance) of the MOSFET, and uses the dual carriers of the BJT to achieve the purpose of large current (voltage-controlled bipolar device). So what is the internal structure of such a combination? This article will explain in detail with examples. What is IGBT and Its Applications Catalog Introduction Ⅰ IGBT Module Explained Ⅱ IGBT Internal Structure Ⅲ IGBT Internal Current Flow Ⅳ How to Disassemble IGBT Module? Ⅴ FAQ Ⅰ IGBT Module Explained The model of the IGBT module to be disassembled as an example is: FF1400R17IP4. The appearance and equivalent circuit of the module are shown in Figure 1. The length, width and height of this module are: 25cmx8.9cmx3.8cm. The module contains two IGBTs, which are what we often call half-bridge modules. The rated voltage and current of each IGBT are 1.7kV and 1.4kA. Figure 1. FF1400R17IP4 Part 8, 9, 10, 11, and 12 are power terminals and need to be connected to a power circuit.1, 2, 3, 4, and 5 are auxiliary control terminals, which need to be connected to the gate drive circuit.6 and 7 are NTC thermistors, used for temperature detection or over-temperature protection.After having a general understanding of its structure, what can we do with such a black module with this structure? Take an example around us: new electric vehicles, everyone should be familiar with it. Three such black modules can be used as a three-phase motor driver. If it is equipped with a battery, it can drive an electric bus. Of course, this module is also used in many other applications. Figure 2. IGBT in Electric Bus   Ⅱ IGBT Internal Structure After having a preliminary understanding of the external structure and application of the IGBT module, let us enter the subject of this article to see what the inside of this high-tech black module looks like. Figure 3 is the internal picture of the IGBT module with the black casing removed. It should be noted that the most common copper and aluminum are inside the IGBT module. Figure 3. IGBT Internal Structure Figure 4 is a cross-sectional view of the IGBT module. If the black casing and external connection terminals are removed, the IGBT module mainly contains 3 components, the heat dissipation substrate, the DBC substrate and the silicon chip (including the IGBT chip and the Diode chip), and the rest is mainly solder layers and interconnecting wires are used to connect IGBT chips, Diode chips, power terminals, control terminals and DBC(Direct Bond Copper). Below we will briefly introduce each part. Figure 4. IGBT Section View ① Heat Sink SubstrateThe bottom of the IGBT module is the heat dissipation substrate, the main purpose is to quickly transfer the heat generated by the IGBT switching process. Since copper has better thermal conductivity, the substrate is usually made of copper, and the thickness of it is 3-8mm. Of course, there are also substrates made of other materials, such as aluminum silicon carbide (AlSiC), both of which have their own advantages and disadvantages. ② DBCDBC (Direct Bond Copper) is a ceramic surface metallization technology, which contains 3 layers. Have a ceramic insulating layer in the middle and a copper clad layer above and below respectively, as shown in Figure 5(a). Simply put, it is to cover both sides of an insulating material with a copper layer, and then etch a pattern that can carry current on the front side, and the back side must be directly soldered to the heat sink substrate. Figure 5. BDC Base vs PCB The main function of DBC needs to ensure the electrical insulation capacity between the silicon chip and the heat dissipation substrate and good thermal conductivity, while also providing a certain current transmission capacity. The DBC substrate is similar to a 2-layer PCB circuit board. The insulating material in the middle of the PCB is generally FR4, while the commonly used ceramic insulating materials for DBC are aluminum oxide (Al2O3) and aluminum nitride (AlN).For the IGBT module analyzed in this article, there are 6 DBCs inside, and each has 4 IGBT chips and 2 Diode chips. Among them, 2 IGBT chips and 1 Diode chip are used as the upper tube, and the rest are used as the lower tube. As shown in Figure 6. Figure 6. DBC Diagram and Equivalent Circuit ③ IGBT ChipThe IGBT chip model used inside the module is: IGCT136T170. The manual can be downloaded from Infineon official website. Figure 7 shows the top view and basic parameters of the IGBT chip. The gate and emitter of the IGBT are above the chip (front side), and the collector is below (back side). The thickness of the chip is 200um. After the IGBT powers on, the current flows from bottom to top, so the IGBT of this structure can also be called a vertical device. Chip Type VCE ICn1) Die Size IGC136T170S8RH2 1700A 117.5A 17.72×7.7mm2 Figure 7. IGBT Chip Diagram If you make a vertical cut on the 200um chip, you can get the internal structure shown in Figure 8, which is a combination of P-type or N-type semiconductors with different doping. Figure 8 shows the well-known equivalent circuit of an IGBT, which is usually understood as a MOS-controlled PNP transistor. When start to learn about power electronics, you may feel that this picture is a bit strange. Why not draw the collector on the top and the emitter on the bottom? Until you understand that the IGBT current flows from bottom to top, it is not difficult to explain. Figure 8. IGBT Chip Structure and Equivalent Circuit Let’s have a general understanding of the electrical parameters of this IGBT chip. This chip can pass a DC current of 117.5A at 100°C. It can be seen from Figure 4 that a single IGBT device inside the module contains a total of 12 IGBT chips, so the total current is: 117.5*12=1412A, which is basically the same as the 1400A rated current in the IGBT module manual.In order to ensure the current sharing effect between IGBT chips, a 11.5Ω resistor has been integrated inside the gate of each chip. At the same time, considering the current sharing between the DBCs, the two chips on each DBC share a gate resistor externally, as shown in Figure 10. When measuring it with a multimeter, and the resistance is about 4.13Ω. You can calculate it in conjunction with Figure 9 to see if it is consistent with the 1.6Ω in the IGBT module manual. Of course, you can refer to the official manual for more detailed parameters of the IGBT chip. Figure 9. IGBT Equivalent Circuit ④ Diode ChipFigure 10 is a top view of the Diode chip, with the anode on the front and the cathode on the back. The current direction of the diode is from top to bottom, which is exactly the opposite of the current direction of the IGBT. The rated current of the diode chip is 235A, and each IGBT is composed of 6 diodes in parallel, and the total current can reach 1410A, which is basically the same as the 1400A in the module manual. The thickness of diode chip is the same as IGBT, it is also 200um. For more detailed parameters of the diode chip, please refer to the official manual. Chip Type VR IFn1) Die Size SIDC130D170H 1700A 235A 16.3×8mm2 Figure 10. Diode Diagram Such a thin semiconductor material can have kV voltage and hundreds of amperes of current on and off, it’s amazing. This is why the price of high-power semiconductor devices is so very expensive.The upper copper layer interconnection of IGBT chip, Diode chip and DBC is generally realized by bonding wires. Commonly used bonding wires are aluminum wire and copper wire. Among them, the aluminum wire bonding process is mature and the cost is low, but the electrical and thermodynamic properties of the aluminum wire bonding are poor, and the expansion coefficient mismatch is large, which affects the service life of the IGBT. The copper wire bonding process has the advantages of excellent electrical and thermodynamic properties, high reliability, and is suitable for modules with high power density and efficient heat dissipation.   Ⅲ IGBT Internal Current Flow After having a basic understanding of the internal structure of the IGBT module, let us go back and interconnect all the above components to see how the current flows inside the IGBT module. Here we take the upper tube IGBT in one of the DBCs as an example to illustrate the current flow. Red represents the current direction of the upper tube IGBT (S1 and S2), and blue represents the current direction of the diode D1. Figure 11(b) is a left cross-sectional view and a schematic diagram of the current direction of the module of Figure . Figure 11(a). IGBT Current Flow Figure 11(b). IGBT Current   Ⅳ How to Disassemble IGBT Module? Some friends may be curious about how to disassemble this module, but it is actually very simple. You only need to prepare two screwdrivers and a small hammer. Figure 12. IGBT Disassemble Step 1: Unscrew the 4 screws at the bottom of the IGBT module.Step 2: Use a flat-blade screwdriver to pry open all the terminals on the front of the IGBT module. This step is very important. It is necessary to ensure that all the terminals after being pried are vertical to the module substrate.Step 3: You need to fix the IGBT in one place, or use a flat-blade screwdriver to align any position of the connection between the plastic casing of the IGBT module and the substrate, hit the screwdriver with a hammer, and pry the casing from the substrate with the screwdriver. After prying open one position, place something on it, and then pry another position, repeat that, after slowly prying open, just pry open with your hands directly.   Ⅴ FAQ 1. What is IGBT module?An IGBT is a is power semiconductor die and is the short form of insulated-gate bipolar transistor. ... An IGBT power module functions as an electronic switching device. By alternate switching direct current (DC) can be transformed to alternating current (AC) and vice versa. 2. How does IGBT module work?The IGBT combines the simple gate-drive characteristics of power MOSFETs with the high-current and low-saturation-voltage capability of bipolar transistors. The IGBT combines an isolated-gate FET for the control input and a bipolar power transistor as a switch in a single device. 3. What is the purpose of IGBT?The IGBT combines, in a single device, a control input with a MOS structure and a bipolar power transistor that acts as an output switch. IGBTs are suitable for high-voltage, high-current applications. They are designed to drive high-power applications with a low-power input. 4. How many layers are there in IGBT?Working of IGBTIGBT is constructed with 4 layers of semiconductor sandwiched together. The layer closer to the collector is the p+ substrate layer above that is the n- layer, another p layer is kept closer to the emitter and inside the p layer, we have the n+ layers. 5. Which are the terminals of IGBT?The three terminals of IGBT are Gate, Collector and Emitter. 6. How many terminals Mosfet has?four terminalsThe MOSFET has four terminals: drain, source, gate, and body or substrate. 7. What is the function of injecting layer in IGBT?The p+ substrate is also called injector layer because it injects holes into n- layer. The n- layer is called drift region. The next p layer is called the body of IGBT. The n- layer in between the p+ & p region serves to accommodate the depletion layer of pn- junction i.e. J2. 8. Can I replace IGBT with MOSFET?Due to the higher usable current density of IGBTs, it can usually handle two to three times more current than a typical MOSFET it replaces. This means that a single IGBT device can replace multiple MOSFETs in parallel operation or any of the super-large single power MOSFETs that are available today. 9. What are the three terminals of an IGBT and how does it function?The IGBT (insulated gate bipolar transistor) is a three-terminal electronic component, and these terminals are termed as emitter (E), collector(C) and gate(G). Two of its terminals namely collector and emitter are associated with a conductance path and the remaining terminal 'G' is associated with its control. 10. What is an IGBT describe its construction?IGBT – Working, Types, Structure, Operation & Applications. ... The IGBT (Insulated Gate Bipolar Transistor) takes the best parts of both BJT and MOSFET into a single transistor. It takes the input characteristics (high input impedance) of MOSFET (Insulated Gate) and the output characteristics of BJT (Bipolar nature). 11. How does IGBT convert DC to AC?The IGBT act as a switch (when a signal is applied to the gate, they turn on and then turn off when the signal is removed). By closing Q1 and Q4, a positive d.c. supply is applied to the load. Q2 and Q3 will result in a negative d.c. supply across the load. 12. What is the advantage of IGBT?The main advantages of IGBT over a Power MOSFET and a BJT are: It has a very low on-state voltage drop due to conductivity modulation and has superior on-state current density. So smaller chip size is possible and the cost can be reduced. 13. What is drift layer in IGBT?The drift region (electric field or movement of charge) of the IGBT works as a base of the PNP transistor . The current gain of the transistor depends upon the width and doping level of the transistor. 14. What is the structure of IGBT?The structure of IGBT is very much similar to that of PMOSFET, except one layer known as injection layer which is p+ unlike n+ substrate in PMOSFET. This injection layer is the key to the superior characteristics of IGBT. Other layers are called the drift and the body region. The two junctions are labeled J1 and J2. 15. What are the advantages of IGBTs?Advantages of IGBT:Simple drive circuitLow on-resistanceHigh voltage capacityFast switching speedEasy of driveLow switching lossLow on stage power dissipationLow gate drive requirement 16. Why IGBT is very popular nowadays?With its lower on-state resistance and conduction losses as well as its ability to switch high voltages at high frequencies without damage makes the Insulated Gate Bipolar Transistor ideal for driving inductive loads such as coil windings, electromagnets and DC motors. 17. Why diode is used in IGBT?We know that MOSFET or IGBT is a unidirectional device, they only conduct current in forward bias and block the current in reverse bias. ... For this reason, an external diode is connected across the MOSFET or IGBT or SCR to provide a path for reverse current.

Executive Summary: What is a Phototransistor?A phototransistor is a light-sensitive semiconductor device that converts incident light into electric current while providing internal gain amplification. Unlike simple photodiodes, phototransistors utilize a bipolar junction structure (NPN or PNP) to amplify the signal, making them highly effective for optical switching, object detection, and encoding systems in modern 2026 electronics.Ⅰ Introduction to PhototransistorsThe phototransistor is a specialized semiconductor device engineered to detect light levels and modulate the current flowing between the emitter and collector based on the photon intensity it receives.While both phototransistors and photodiodes serve as optical sensors, the phototransistor distinguishes itself through high sensitivity attributed to the internal gain of its bipolar transistor architecture. As of 2026, this intrinsic amplification makes phototransistors the preferred choice for applications requiring robust signal detection without complex external amplification circuitry.Ⅱ Video Tutorial: How Phototransistors WorkVisual learners can understand the practical operation of light detection in the following tutorial.Phototransistor Tutorial Phototransistor Video Description:A comprehensive tutorial demonstrating how to utilize phototransistors for precise light detection in circuit design.  Ⅲ What Is a Phototransistor?A phototransistor is an electronic switching and current amplification component that operates by converting photon energy into electrical signals. When light strikes the exposed base-collector junction, a reverse current flows proportional to the luminance intensity.Widely used to convert light pulses into digital electrical signals, these components are powered by light interactions rather than solely electrical bias at the base. They offer high gain and low cost, making them ubiquitous in 2026 consumer electronics. Figure 1: Phototransistor SymbolFunctionally, phototransistors share similarities with photoresistors (LDRs), but with a key distinction: phototransistors generate current and voltage through the photovoltaic effect and amplification, whereas LDRs only change resistance.Transistors with the base terminal exposed are chemically doped to maximize light sensitivity. Photons striking the depletion layer generate electron-hole pairs, activating the transistor just as a base current would in a standard BJT. Silicon-based photosensors typically respond to visible and near-infrared radiation (approx. 400nm to 1100nm). Ⅳ How are Phototransistors Constructed?The phototransistor's structure is specifically optimized for photo-applications by maximizing the area of the base-collector junction. While ordinary bipolar transistors exhibit some photosensitivity, phototransistors feature significantly larger base and collector areas to capture maximum light flux.Figure 2: Construction of a PhototransistorⅤ Semiconductor Material EvolutionHistorical phototransistors utilized a homo-junction structure, fabricated entirely from germanium or silicon. In contrast, modern 2026 phototransistors often employ type III-V semiconductor materials, such as gallium arsenide (GaAs), to target specific wavelengths and increase efficiency.Key structural variations include:NPN Topology: The most popular configuration due to the higher mobility of electrons compared to holes.Heterostructures: Utilizing different materials on either side of the PN junction to enhance conversion efficiency.Mesa Structure: A common physical layout for optimized light absorption.Schottky Junctions: Occasionally used for the collector to improve switching speeds.To ensure optimal sensitivity, the emitter contact is frequently offset, preventing it from blocking light from reaching the active region. Ⅵ How Does a Phototransistor Work?A phototransistor operates by using light to control the flow of current, effectively replacing the base current of a standard transistor with photon energy.Biasing: The collector is biased positively relative to the emitter (in NPN), creating a reverse-biased Base-Collector (B-C) junction.Injection: Light strikes the B-C junction, generating electron-hole pairs.Amplification: The movement of these carriers constitutes a base current, which the transistor amplifies by its gain factor (hFE).Typically, the physical base terminal is left unconnected (floating), as the device is controlled entirely by incident light. Ⅶ Key Electrical CharacteristicsSince phototransistors are essentially Bipolar NPN Transistors with an exposed junction, their V-I characteristics resemble a standard BJT family of curves, but with Light Intensity (mW/cm²) replacing Base Current (IB).Dark Current: When no light is present, a minuscule leakage current flows from collector to emitter. In high-precision applications, minimizing this Dark Current is crucial.Light Current: As light intensity increases, the base current rises, triggering the amplification process. Figure 3: Reverse Bias Configuration The collector current characteristics curve below demonstrates the linear relationship between light intensity and output current in the active region.Figure 4: Collector Current vs. Irradiance Ⅷ Selection Criteria & PropertiesWhen selecting a component for 2026 designs, engineers must evaluate specific properties to ensure the device matches the optical environment.Critical Datasheet Properties:Peak Wavelength: The specific color of light (e.g., 850nm IR vs. 560nm Visible) the device is most sensitive to.Linearity: How accurately the output follows the input light intensity.Sensitivity: The ratio of output current to incident light power.Response Time: The rise and fall time, which determines the maximum data rate (typically slower than photodiodes).Acceptance Angle: The field of view from which the sensor can detect light. Ⅸ Common Types: BJT vs. FETPhototransistors are primarily categorized by their internal transistor architecture:BJT Phototransistor: The standard type. In darkness, it leaks only ~100 nA. Under illumination, it can conduct up to 50mA. This high current handling capability distinguishes it from photodiodes.Photo-FET (Field Effect Transistor): Utilizes light to generate a gate voltage that controls the drain-source current. Photo-FETs offer extremely high input impedance and are more sensitive to weak light signals, though they are less common in general switching applications. Ⅹ Practical Circuit Examples (2026 Applications)The primary goal of phototransistor circuits is to generate a usable output voltage from light-induced current. Unlike photodiodes which often require Transimpedance Amplifiers (TIA), phototransistors have built-in gain, allowing for simpler circuit designs.Common Configurations:Common-Emitter (Inverting): Output voltage drops as light increases.Common-Collector (Non-Inverting): Output voltage rises as light increases.Figure 5: Basic Amplifier Configurations 10.1 Step-by-Step Circuit Implementations 1. Light Operated Relay (Automatic Day Switch)Mechanism: When light strikes phototransistor Q1, it conducts, supplying base current to the driver transistor Q2. Q2 then activates the mechanical relay, turning on the connected load. 2. Darkness Operated Relay (Night Light)Mechanism: By inverting the logic, the relay activates only when light is absent. In darkness, the phototransistor turns off (high resistance), allowing the bias resistor to trigger Q2. 3. Light Interruption Alarm (Security System)Mechanism: This circuit functions as a tripwire. Under normal conditions (laser/light hitting sensor), the phototransistor pulls the SCR gate LOW (off). When the beam is broken by an intruder, the gate voltage rises, latching the SCR and sounding the alarm until manually reset. Ⅺ Datasheet Specifications to WatchTo ensure system reliability, consult the following parameters in manufacturer datasheets:Collector Current (IC): Maximum current the device can handle (typically 1mA - 50mA).Dark Current (ID): Leakage current in total darkness (lower is better for precision).Peak Wavelength (λp): The wavelength of maximum sensitivity.VCE(sat): Collector-Emitter saturation voltage.Rise/Fall Time (tr/tf): Critical for optical data transmission applications.Power Dissipation (Ptot): Thermal limits of the package. ⅻ Pros and Cons AnalysisSelecting the right optical sensor requires balancing sensitivity, speed, and cost.AdvantagesDisadvantagesHigh Gain: Produces higher current output than photodiodes, reducing the need for external amplifiers.Limited Voltage: Cannot withstand high voltages compared to Thyristors or Triacs.Cost-Effective: Inexpensive to manufacture and integrate into ICs.Slower Speed: Slower response time (lower bandwidth) compared to PIN photodiodes.Simplicity: Can drive small relays or logic gates directly in simple circuits.Temperature Sensitivity: Dark current increases significantly with temperature fluctuations. XIII Modern Applications in 2026Due to their versatility, phototransistors are integral to many modern technologies:Optocouplers (Optoisolators): Protecting low-voltage logic circuits from high-voltage spikes in power supplies.Optical Encoders: Used in robotics and motors to detect position and speed.Object Detection: Proximity sensors in smartphones and automated manufacturing lines.Safety Systems: Smoke detectors and light curtain barriers for industrial machinery.Remote Control Receivers: IR detection for consumer electronics (though often integrated with demodulators). XIV Comparison: Photodiode vs. PhototransistorWhile both detect light, their use cases differ based on speed and sensitivity needs.FeaturePhotodiodePhototransistorOutputLow Current (µA)High Current (mA) - AmplifiedResponse SpeedVery Fast (Nanoseconds)Moderate (Microseconds)ApplicationsFiber Optics, High-Speed DataRemote Controls, Light Switches, EncodersNoiseLow NoiseHigher Noise levels XV Frequently Asked Questions1. What type of device is a phototransistor?A phototransistor is a bipolar semiconductor device. It functions as a transistor where the base current is generated by incident photons striking the exposed semiconductor junction, rather than an electrical connection.2. What is the main difference between a standard transistor and a phototransistor?Physically, the primary difference is the packaging. A phototransistor has a transparent lens or window to allow light to reach the junction, and it often lacks an external base pin. Electrically, it is controlled by light intensity rather than input current.3. Is a phototransistor considered a sensor?Yes, it is a discrete photosensor. It detects the presence and intensity of light and converts it into a measurable electrical signal.4. How do you test if a phototransistor is working?You can test it using a multimeter or a simple circuit:Connect the phototransistor in series with a resistor and LED to a power source (checking polarity).Expose the sensor to light; the LED should brighten.Cover the sensor; the LED should dim or turn off.5. Which is better: Photodiode or Phototransistor?Neither is universally "better"; it depends on the application. For high-speed data (like fiber optics), a photodiode is superior. For switching and sensing without extra amplifiers, a phototransistor is more efficient due to its internal gain.{ "@context": "https://schema.org", "@graph": [ { "@type": "Article", "headline": "Phototransistors: The Ultimate 2026 Guide", "datePublished": "2021-12-02", "dateModified": "2026-01-07", "description": "A comprehensive guide to phototransistors, covering construction, working principles, circuit diagrams, and 2026 applications.", "image": "https://www.kynix.com/editor_u/image/20211202/2021120216390176.jpg", "author": { "@type": "Organization", "name": "Kynix Electronics" } }, { "@type": "FAQPage", "mainEntity": [ { "@type": "Question", "name": "What type of device is a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "A phototransistor is a bipolar semiconductor device where the base current is generated by incident photons striking the exposed junction." } }, { "@type": "Question", "name": "What is the difference between a transistor and a phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "The main difference is that a phototransistor has an exposed optical window and is controlled by light intensity, whereas a standard transistor is controlled by electrical current at the base pin." } }, { "@type": "Question", "name": "Is a phototransistor a sensor?", "acceptedAnswer": { "@type": "Answer", "text": "Yes, a phototransistor is a discrete photosensor that converts light intensity into an electrical signal." } }, { "@type": "Question", "name": "Which is better: Photodiode or Phototransistor?", "acceptedAnswer": { "@type": "Answer", "text": "Photodiodes are better for high-speed data applications, while phototransistors are better for switching and sensing applications requiring higher sensitivity and gain." } } ] }, { "@type": "HowTo", "name": "How to Build a Simple Light Interruption Alarm", "step": [ { "@type": "HowToStep", "name": "Setup the Phototransistor", "text": "Connect the phototransistor to a pull-down resistor to create a voltage divider." }, { "@type": "HowToStep", "name": "Connect the SCR", "text": "Connect the output of the phototransistor junction to the Gate of an SCR (Silicon Controlled Rectifier)." }, { "@type": "HowToStep", "name": "Align the Light Source", "text": "Point a laser or light beam directly at the phototransistor. This keeps the SCR gate low (Off)." }, { "@type": "HowToStep", "name": "Trigger the Alarm", "text": "Interrupt the light beam. The phototransistor turns off, voltage spikes at the SCR gate, latching the alarm on." } ] } ]}

Introduction The transistor is a current-control device. For example, control the collector-emitter current by changing the base current. In a general voltage amplification occasion, this amplification effect comes from the use of resistors to convert current into voltage. In the small-signal model, the source of the base current is the ratio of the input voltage to the base-emitter dynamic resistance rbe, which is usually kΩ. So the base current is very small, and may only be a few tenths of mA. Through the amplification of the transistor, the base current is generated between the collector and the emitter by β times. This article will introduce how transistor works in the common-emitter amplifier circuit. Transistor Amplifiers Circuit Introduction Catalog Introduction Ⅰ Common-emitter Amplifier Circuit Formula Ⅱ Common-emitter Amplifier Circuit Design 2.1 Design Steps 2.2 Circuit Analysis 2.3 Common-emitter Circuit Design 2.4 Circuit Performance Parameters Ⅲ Common-emitter Amplifier Circuit Expansion 3.1 Increase Magnification 3.2 Low-voltage and Low-loss Circuit 3.3 Differential Output Circuit 3.4 Filter and Tuning Amplifier Circuit Ⅳ Summary Ⅴ FAQ Ⅰ Common-emitter Amplifier Circuit Formula Here, take the common emitter amplifier circuit as an example: Figure 1. Transistor Common-emitter Amplifier Circuit △Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbe△Vi/rbe=△ibThus, the collector generates a current of β times ib:△ie=β△ibFurthermore, the output voltage can be obtained by the relative positive power supply potential:△Vo=VCC-△ieRc=VCC-β△ibRc=VCC-△Vi·Rc/rbeThus, we can get an inverted amplified voltage signal by AC coupling and controlling the collector resistance Re. But generally the emitter will have a resistance to control the gain, so the above formula is not practical. When designing a circuit in non-extreme situations, we often hope that the circuit can work with most general-purpose transistors, avoiding the parameter that depends on component parameters such as rbe. At the same time, it is very cumbersome to consider the base current in the specific calculation. Therefore, in the general design process, the existence of the base current is ignored in an approximate calculation (In some circuits, although the base current is ignored, it is still necessary to give the base a certain current drive to make the circuit working normally). In addition, the calculation of gain is the external circuit resistance not the rbe.Among them, the base-emitter tube voltage drop VBE is also a very important parameter, which is generally equal to 0.6V (silicon tube). The parameters of the transistor circuit can all be obtained according to VBE=0.6V and Ohm's law.The cumbersome part of the transistor circuit lies in the setting of the static operating point. Usually, careless design will cause clipping and distortion of the output waveform. Therefore, the selected values of some experimental values can be used for reference. The overall design idea is: quantitatively determine the voltage and current to calculate the resistance.   Ⅱ Common-emitter Amplifier Circuit Design The common-emitter amplifier circuit is a typical inverting amplifier, which has a wide range of applications and stable effects. First show the overall design ideas, and then explain the purpose and principles of the design in steps. 2.1 Design Steps 1) Determine the supply voltage VCC, and determine the static emitter current IE according to the frequency curve/noise curve/others.2) Determine VE, where selects 1~2V to absorb temperature drift.3) According to VE and IE, calculate the emitter static resistance RE ( IE≈IC).4) Determine the magnification Av, and apply the relationship Av=RC/RE to calculate the static collector resistance RC. At this point, the static working point has been established.5) Check whether the static operating point meets the requirements: positive output swing limit=VCC-IE·RC, negative output swing limit=IE·RC-VE. It is necessary to ensure that the amplified output voltage does not exceed the swing limit (usually the swing limit is larger). If RC is too large, there will be a downside clipping, so is the small RC. In addition, determine whether the power exceeds the limit: PC=VCE·IC.6) Determine the base bias voltage as follows: According to VBE=0.6V, it is easy to get VB=VE+0.6 (divide the voltage from the power supply through the resistor). Since ib is considered to be small and negligible, the current IB0 flowing through the base voltage divider resistors (R1, R2 in the above figure) should be much larger than ib. ib is approximately calculated as IC/β, and IB0 is about an order of magnitude larger than ib, so R2=VB/IB0, R1=(VCC-VR2)/IB0.7) Finally, determine the AC coupling capacitor value and the power supply decoupling capacitor value.Let's first use a designed common-emitter amplifier circuit to intuitively understand the waveforms of the next parts: Figure 2. Transistor Common Emitter Amplifier Circuit Design As shown in the figure, the circuit uses 2SC2240 tube, 15V power supply, and the input and output are AC coupled. The output signals are as following:  Figure 3. 4-channel Signal Waves The pale blue waveform is the input signal, selecting the sine wave of 1kHz, 1Vpp.The green is the output signal, amplified by about 5 times, and it is inverted.The blue is the base signal, which can be seen because the DC level is raised due to the influence of the base bias resistance.The red is the emitter signal, which is only a fixed value away from the base signal.   2.2 Circuit Analysis First, perform a DC analysis, that is, determine the static operating point. In the initial design process, the design and verification of static operating points are also the first to proceed. The static potential of the base can be easily calculated according to the base bias resistance, and the static potential of the emitter can be determined according to the voltage drop of the base-emitter tube as a constant. Therefore, according to the magnitude of the emitter resistance, the magnitude of the collector-emitter current can be obtained, and then the collector static potential can be obtained from the power supply voltage.Why is the static operating point important? Take the NPN transistor as an example, which is equivalent to two back-to-back diodes. If requiring the diode work, you must give it a proper bias to make it reasonably conductive. In the circuit, the base-collector diode prevents internal feedback, and the base-emitter diode is the key to achieving amplification. In other words, it is enough to design an external circuit so that the current flows normally in the base-emitter diode. This idea will be mentioned in the analysis of the carrying capacity of the emitter follower.Find the AC voltage gain. When the input voltage changes △vi, it will cause the emitter current to produce an AC change △ie. Since the base emitter voltage drop is constant, it does not contribute to the AC change, so △ie=vi/RE. Therefore, the emitter AC output voltage can be determined as vo=△ieRC=vi·RC/RE, and the AC gain is Av=RC/RE. This conclusion can quickly analyze the magnification of the common-emitter circuit.The output power rails are VCC and VE respectively, which are determined by the current characteristics of the transistor during operation, and there is generally no rail-to-rail output. According to the output power rail and the AC amplification factor, the circuit can be used.When the input and output are not AC coupled, the input (especially for DC) will cause the output waveform to be distorted.   2.3 Common-emitter Circuit Design After understanding the circuit characteristics, you can design the common emitter circuit according to the design steps at the beginning of this section. The static operating point and magnification have been determined during the analysis, and the other parts are designed below.Supply voltage: According to the swing of the output voltage, we can determine the size of the voltage. Usually the power supply voltage is larger than the output peak-to-peak value.Transistor: Select the appropriate transistor according to the operating frequency, required power, noise level and β, etc.Emitter current: Determine the size of the emitter current according to the frequency characteristics by consulting the device manual.RC and RE: Determined by the emitter voltage and current, and the magnification, pay attention to review the upper and lower limits of the swing and the rated power.Base bias resistance: VB is determined according to VE, thereby determining the voltage divider resistance of the power supply. Note that the current flowing through the voltage divider resistor should be one to two orders of magnitude higher than the base current. The base current is calculated by dividing the collector-emitter current by β.Coupling capacitor: The AC coupling capacitor is generally 10uF. Note that the coupling capacitor of the output stage and the input impedance of the next stage will form a high-pass filter. The cutoff frequency of the filter should be handled carefully.   2.4 Circuit Performance Parameters Through the method of AC analysis, we can obtain some characteristic parameters of the designed circuit, such as input and output impedance, magnification and so on.Input impedance: According to AC analysis, the input impedance is the parallel value of the base bias resistance. In small signal analysis, the base emitter dynamic resistance rbe should also be connected in parallel.Output impedance: The method to determine the output impedance is to add a load to the circuit. When the peak-to-peak output value drops to half of the no-load, the load impedance is the output value. Generally, the output impedance of the common-emitter amplifier circuit is the collector resistance RC.Magnification: Due to the influence of the base current, the actual magnification is about 10% lower than the design value. So the design formula is more practical.   Ⅲ Common-emitter Amplifier Circuit Expansion By improving the general common-emitter amplifier circuit, various application circuits with other characteristics can be obtained. This section introduces the means to increase the magnification, the low-voltage power supply circuit, the differential output circuit, and the tuning amplifier circuit. 3.1 Increase Magnification According to the introduction of the design circuit, the voltage gain is mainly determined by the ratio of the collector resistance RC to the emitter resistance RE. So it is common to change the ratio of the resistance to change the gain. However, the problem arises: these two resistors are responsible for determining the working current at the same time. Because the DC operating point is changed arbitrarily, the circuit is likely to be distorted or even not work.From another perspective, voltage gain belongs to the category of "AC Analysis", and the static operating point belongs to "DC Analysis". So add some reactive components to the circuit to change the ratio under the AC perspective, the resistance value during DC analysis does not change.This can be achieved by connecting the emitter resistor in parallel, or making the resistor in parallel with the capacitor, that is, modifying the circuit in the first section: Figure 4. Common-emitter Amplifier Circuit Pay attention to the emitter in the above figure. In the AC analysis, the resistor R4 is short-circuited by the capacitor. At this time, it is equivalently considered that the emitter resistor is only R7 (330Ω). From the signal source and the oscilloscope, the signal has been amplified nearly 50 times at this time. It is much larger than the original design value (10k/2k=5), thus realizing the expansion of voltage gain. If the original emitter resistance is not split, but the entire capacitor is connected in parallel, the maximum gain βRC/rbe will be obtained at this time.How to choose the capacitance value? It should be noted that after the capacitors are connected in parallel, the entire circuit will have high-pass characteristics, and the cut-off frequency is f=1/2πRC. If this high-pass characteristic is not required, the C capacitance value can be selected to a larger value between 47uF~100uF.In addition, the capacitor C6 has the function of temperature compensation. 3.2 Low-voltage and Low-loss Circuit If the op amp circuit is powered by a dry battery (1.5V), it is not realistic, but the transistor circuit can be done. The key is to use the conduction voltage drop of the external diode to offset the base-emitter voltage and have small small. The circuit in the figure below can still amplify small signals as designed even under 1.5V power supply: Figure 5. Common-emitter Amplifier Circuit But the disadvantage is that the maximum voltage of the system is always below the supply voltage. Because of the small circuit loss, it is suitable for low power consumption. 3.3 Differential Output Circuit Fully differential op amps can provide dual-mode output, and many transmission lines also require differential transmission. Transistor circuits can also perform differential output. In addition to the principle of a common emitter amplifier circuit, the principle of an emitter follower is also used. The following figure shows the circuit connection of the differential output. Figure 6. Common-emitter Amplifier Circuit It can be seen that two differential signals with the same shape and opposite phase are output. The collector signal is in phase with the input signal, and the emitter output signal is in phase with the input signal. However, the output impedance of the two signals is different due to the different lead-out positions. The output impedance of the inverted output is higher (RC), and the output impedance of the non-inverted output is lower, which is suitable for driving the load. The inverted output is generally connected to the emitter follower before driving.In addition, the static potential of the base should be set between VCC and GND as much as possible to expand the undistorted output range.   3.4 Filter and Tuning Amplifier Circuit The introduction of reactive components in the circuit will cause the properties of the circuit to change with the frequency. We can use this property to design LPF, HPF, and tuning amplifier commonly used in high-frequency circuits. Actually, it uses the characteristic that the impedance of the reactance element changes with the frequency, and then changes the voltage gain at the current frequency. The impedance at the resonance frequency is often purely resistive and has an extreme value to achieve frequency selective amplification. The following show low-pass, high-pass and frequency selective amplifiers at specific frequencies:① LPF Figure 7. Common-emitter Amplifier Circuit As shown in the figure, a low-pass filter is constructed (the input of the bode tester is placed at the base instead of the output of the signal generator, because the input coupling capacitor will form a high-pass filter with the input resistor, which affects the observation effect), and its cut-off frequency is about 1.06kHz, calculated by f=1/2πRcC.From the sinusoidal steady-state analysis, the impedance of the RC parallel loop is R/√(1+(wRC)^2). As the frequency increases, the impedance decreases, so the voltage gain decreases, forming a low-pass characteristic.② HPF Figure 8. Common-emitter Amplifier Circuit As shown in the figure, a high-pass filter is constructed, and the calculation of its cut-off frequency is similar to that of LPF.At the gain peak point, the voltage gain reaches 50dB, which is close to the β value of the transistor. Then the gain is attenuated due to the deterioration of the transistor's frequency characteristics.③ 10.7MHz Figure 9. Common-emitter Amplifier Circuit By replacing RC with an LC network with a resonance frequency of 10.7MHz, a frequency selective amplifier can be obtained. As shown in the figure, the amplification factor is 35dB at 10.7M, while the amplification factor when detuning 1MHz is only 12.6dB. The disadvantage is that the pass-band is slightly wider, the rectangular coefficient is not good enough, and the equivalent quality factor of the loop is about 65.2, which is relatively large. In addition, the high-frequency decoupling capacitor has been changed to 1uF. Resonant Amplifier Circuit Example: Figure 10. Resonant Amplifier Circuit Example   Ⅳ Summary Transistor amplifier circuit is the basis of an operational amplifier circuit, and common-emitter configuration is the most commonly used form. Drawing lessons from the feature that the amplifier's magnification can be easily determined by the ratio of two resistors, and the gain of the common emitter amplifier can also be approximated by the ratio of the two resistors.   Ⅴ FAQ 1. What are transistor amplifiers used for?Amplifiers are derived from the transistors because they are capable of operating under three regions active, cut-off and saturation. For the purpose of amplification, the focus will be on the active region. The main purpose of these amplifiers is to enhance the strength of the applied input signal without alteration. 2. How does a transistor amplify current?Transistors are normally used as amplifiers. ... The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. 3. What is a common emitter transistor amplifier?The common emitter amplifier is a three basic single-stage bipolar junction transistor and is used as a voltage amplifier. The input of this amplifier is taken from the base terminal, the output is collected from the collector terminal and the emitter terminal is common for both the terminals. 4. Why common emitter is used in amplifier?Common emitter (CE) configuration. ... Common emitter transistors are used most widely, because a common emitter transistor amplifier provides high current gain, high voltage gain and high power gain. This type of transistor gives for a small change in input there is small change in output. 5. What is the use of CE amplifier?In electronics, a common-emitter amplifier is one of three basic single-stage bipolar-junction-transistor (BJT) amplifier topologies, typically used as a voltage amplifier. It offers high current gain (typically 200), medium input resistance and a high output resistance. 6. How does transistor work as amplifier?A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition. ... Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier. 7. What is common emitter amplifier circuit?The Common Emitter Amplifier circuit has a resistor in its Collector circuit. The current flowing through this resistor produces the voltage output of the amplifier. ... The Base of the transistor used in a common emitter amplifier is biased using two resistors as a potential divider network. 8. What are the main parts of a transistor amplifier circuit?A Single stage transistor amplifier has one transistor, bias circuit and other auxiliary components. The following circuit diagram shows how a single stage transistor amplifier looks like. When a weak input signal is given to the base of the transistor as shown in the figure, a small amount of base current flows. 9. What is the phase difference in common emitter amplifier?The phase difference between the input and output voltage of CE amplifier circuit is. The phase difference of 1800 between the signal voltage and output voltage in a common emitter amplifier is known as phase reversal. 10. When an NPN transistor is used as an amplifier?For a npn transistor to be used as an amplifier, forward bias has to be applied on the transistor. Thus, when an npn transistor is used as an amplifier, holes move from base to emitter. So, the correct answer is option D i.e. holes move from base to emitter. 11. When an NPN junction transistor is used as an amplifier in CE mode?A transistor is used in the common emitter mode as an amplifier then: (A) the base emitter junction is forward baised. (B) the base emitter junction is reverse baised. (C) the input signal is connected in series with the voltage applied to bias the base emitter junction. 12. How is an NPN transistor used as an amplifier show with its circuit diagram?The circuit of a common-emitter amplifier using an n-p-n transistor is shown below : In a common emitter amplifier circuit, the input signal voltage and output collector voltage are in opposite phase. i.e 180° out of phase. Thus the phase difference between the input signal and output voltage is 180°. 13. How does a common emitter amplifier work?Operation of Common Emitter AmplifierWhen a signal is applied across the emitter-base junction, the forward bias across this junction increases during the upper half cycle. This leads to an increase in the flow of electrons from the emitter to a collector through the base, hence increases the collector current. 14. What is β for a CE configuration?Base Current Amplification Factor (β)The base current amplification factor is defined as the ratio of the output and input current in a common emitter configuration. In common emitter amplification, the output current is the collector current IC, and the input current is the base current IB. 15. What is current gain CE configuration?The current gain of a transistor in CE configuration is defined as the ratio of output current or collector current (IC) to the input current or base current (IB). The current gain of a transistor in CE configuration is high. Therefore, the transistor in CE configuration is used for amplifying the current.