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This is a technical article introducing what is operational amplifier, how does op amp works, how many types of op amp are there, and how to choose the right op amp for your circuit, and the last part, we will look at the example expressions of the op amp to better understand this device. Down below is an episode of Electronic Basics will explain the three golden rules when working with OpAmps and how to use them in order to understand and build all kind of OpAmp circuits. The main focus will be the noninverting and inverting amplifier and the comparator circuit.  Catalog  I. What is an Operational AmplifierII. How does Op Amp WorksIII. Seven Types of Op AmpIV. Op Amp Design ConsiderationV. Op Amp Examples ExpressionsVI. ConclusionFAQ  I. What is an Operational Amplifier In an actual circuit, an operational amplifier is a circuit unit with high magnification, which usually combines the feedback network to form a certain functional module. Since it was used in analog computers to realize mathematical operations, it is named "operational amplifier", more commonly known as op-amps.  An operational amplifier is a circuit unit based on its function, which can be implemented by discrete devices or semiconductor chips. With the development of semiconductor technology, the vast majority of operational amplifiers are in the form of a single chip. Nowadays, there are many kinds of operational amplifiers, which are widely used in almost all industries. Figure 1. Op Amp Diagram  II. How does Op Amp Works The operational amplifier has two input terminals a (inverse input), b (in-phase input), and one output.  There are also referred to as backward input end, non-backward input end, and output end respectively. When the voltage U- is applied to the terminal and the public end (the common end is a point where the voltage is zero, it is equal to the reference node in the circuit.), and meanwhile a terminal of the actual direction of the output voltage U is higher than that of the common terminal, the actual direction of the output voltage U is from the common end to the o terminal, that is, the direction of the two terminals is opposite.  When the input voltage U+ is added between the b terminal and the common terminal, the actual direction of U and U+ is exactly the same as that of the common terminal. For the distinction, end a and end b are divided “-” and “+”, also, don't mistake them for the positivity and negativity of the voltage reference direction. The positivity and negativity of a voltage should be marked separately or as an arrow. Figure 2. Op Amp Symbols and Terminals Inverting amplifiers and non-inverting amplifiers are shown below:Figure 3. Inverting Op Amp Fig. 4 Non-inverting Op Amp Generally, the operational amplifier can be simply regarded as a high gain direct coupling voltage amplifier unit with a signal output port (Out) and two in-phase, and inverse high impedance input terminals. Thus, an operational amplifier can be used to fabricate phase, inverse, and differential amplifiers. Operational amplifier power-supply mode can be divided into two types: dual power supply and single power supply. For a dual power-supply operational amplifier, the output can be changed on both sides of the zero voltage, and the output can also be set zero at the differential input voltage of zero. As for the single power supply, an operational amplifier that uses a single power supply, a range of input variations is between the power supply and the ground. The input potential of the operational amplifier is usually higher than a certain value of negative power supply, but lower than a value of positive power supply. Specially designed operational amplifiers can allow input potentials to vary throughout the range from negative to positive power, even slightly higher than positive power supply or slightly lower than the negative source. This operational amplifier is called a rail-to-rail input operational amplifier. The output signal of the operational amplifier is proportional to the voltage difference between the two inputs. In the audio band, the output voltage = A0 (E1-E2), where A0 is the low-frequency open-loop gain of the operational amplifier, E1 is the input signal voltage at the in-phase, and E2 is the input signal voltage at the inverse phase.  III. Seven Types of Op Amp General type: Its performance parameters are suitable for general use (low frequency and slow signal change), such asμ741A, LM358 (double OP Amp), LM324, and LF356  with FET as input stage. They are the most widely used integrated operational amplifiers. High-Z type: The characteristic of this kind of amplifier is that the input impedance of differential mode is very high and the input bias current is very small, general rid > 1GΩ~1TΩ, IB is several to dozens of picoamps. The main measure to achieve these targets is to make use of the high input impedance of FET, using FET as input stage not only has high input impedance and low input bias current but also has the advantages of high speed, wideband and low noise, however,  the input offset voltage of this kind of operational amplifier is larger. Such operational amplifier have LF356, LF355, LF347, CA3130, CA3140, etc. Low-temperature drift type: In precision instruments, weak signal detection, and other automatic control instruments, the bias voltage of the operational amplifier is small and does not change with the temperature. The low-temperature drift operation amplifier is designed for this purpose. At present, the commonly used operational amplifier has OP07, OP27, OP37, AD508, and ICL7650 composed of MOSFET devices and so on. High slew-rate type: In fast A/D converter, D/A inverter, and video amplifiers, the conversion rate of the operational amplifier must be high, and the BWG of the unity gain bandwidth must be large enough. The common operational amplifier has LM318, 175A, and so on, while the SR=50~70V/us, BWG>20MHz... Low-consumption type: Due to the wide application of portable instruments, low power supply, and low power consumption must be used. Commonly used low-power operational amplifier has TL-022C, TL-160C and so on. The operating voltage is ±2V~±18V, and the current consumption is 50 ~ 250μA. At present, the power consumption of some products has reached μW level, for example, the power supply of ICL7600 is 1.5V and the power consumption is 10mW, which can be supplied by a single battery.  High voltage and power type: The output voltage of the operational amplifier is mainly limited by the power supply. In an ordinary operational amplifier, the maximum output voltage is only dozens of volts and the output current is only dozens of Ma. In order to increase the output voltage and current, the auxiliary circuit must be added to the external circuit of the operational amplifier. High-voltage and high-power operational amplifier can output high voltage and high current without any additional circuit. For example, the power supply voltage of the D41 integrated operational amplifier can reach ±150 V, and the output current of μA791 integrated operational amplifier can reach 1A.  Programmable control type: In the usage of instruments will be involved in the measurement range problem. In order to get the fixed voltage output, we must change the magnification of the operational amplifier. For example, there is an operational amplifier with a magnification of 10 times, where the input signal is 1mv, the output voltage is 10mv when the input voltage is 0.1mv, the output is just 1mv. To obtain 10mv, the magnification must be changed to 100. A programmable control operation amplifier is to solve this problem. For example, the PGA103A changes the magnification by controlling the level of pin 1 and pin 2.  IV. Op Amp Design Consideration After knowing some basic types op amps, there are some basic questions you should ask before looking for a suitable op amp. Basics:（1）What is the input signal going to look like?（2）Current-input or voltage-input?（3）What is the expected operating frequency range? Maximum range?（4）What amplitude is needed? (Typical and maximum values.)（5）What’s the impedance of the circuit it’s going into?（6）What is an acceptable output signal going to look like?（7）What is the expected range of frequencies the output signal might cover?（8）What is the expected amplitude range?（9）Will the op-amp be driving another device? If so, how much power will be needed?（10）How accurate or precise does the op-amp need to be? The operating environment:What supply voltage(s) are available?Is there a physical size limitation? You may need to make a list of packages of an acceptable size.What is your operating temperature range? Figure out a Max, Min, and Typical. Look at how the temperature affects your most critical parameters using the graphs in the datasheet. If the information you need is missing, you can contact the company or set it aside and move on to another spec that is more thorough. Buying:Are you restricted to certain manufacturers that your company deals with?Will you need to second source the op amp?What is the lifecycle of the op amp? Do not select any op amp that is Not Recommended for New Design (NRND), End of Life (EOL), or otherwise a special factory order (this might mean that it’s about to go EOL).Price might be a specification of a sort, but this should be one of the last parameters you look at when you are deciding between otherwise identical op amps. Other points:When selecting parameters, it's good to allow a margin of error on the specifications. Not every op amp will be precisely the values as listed, and op amp values change with temperature, age, and stress. Make sure the finalists in your part selection are actually for sale. “Vapor-ware” is when a manufacturer announces a part to be released in the near future, but some parts have been known as “about to release” for a year or more, depending upon the manufacturer. That’s why you second source your product, and why you confirm the product's lifecycle prior to finalizing. V. Op Amp Examples Expressions The ADC architecture, resolution, signal bandwidth, and other specific application details are at work when understanding the various types of operational amplifiers that determine the best way to choose the best amplifiers. We consider these issues in the context of driving SAR ADC in this article. SAR ADC is the mainstay of the A-D converter world. In general, this kind of ADC is located between high resolution, low-speed incremental ADC and high speed, low-resolution pipeline ADC. By virtue of its delay-free feature, SAR ADC is often a better choice than ΔΣ ADC and pipeline ADC in applications with multiplexed signals, or applications that need to implement accurate first-time conversions after an arbitrary idle cycle (such as ATE), what's more, applications where ADC is located in a loop that requires quick feedback. In most cases, the sensor output cannot be directly connected to the SAR ADC input. An amplifier is needed to obtain the optimal SNR and distortion.  SAR ADC to sample the input to the internal capacitor and to compare the input voltage with the reference voltage with a successive binary-weighted sequence. When the switch to the sampling capacitor is open, the charge is injected into the input node due to the voltage mismatch from the sampling capacitor to the input node. A simple monopole RC filter is arranged between the amplifier and ADC. It not only used to filtering high-frequency noise and aliasing components but also to absorb this injected charge. Care must be taken when selecting cutoff frequencies for such filters. Besides, the cutoff frequency should be set at a low frequency enough, which can effectively absorb the injected charge and filter the noise, but the frequency should be high enough so that the amplifier can achieve stability within the sampling time of the data converter. Since this filter can't limit noise alone, it is generally included at the amplifier input end, and a filter with a lower cut-off frequency is also installed simultaneously. Figure 5. LTC2379 18-bit 1.8Msps  Differential Input SAR ADCSINGLE-ENDED-INPUT SIGNALSINGLE-ENDED-TO-DIFFERENTIAL DRIVER  SAR ADC Drive Differential Input SAR ADC Many of the sound performance SAR ADC use differential input to maximize the dynamic range of low power supply voltage. One such example is the LTC2379-18 shown in Fig, which operates with a 2.5V power supply and a reference of up to 5V to achieve a peak-to-peak differential input range of 10V. If the input signal is differential, all that is needed to buffer the signal and drive the ADC, or maybe a low-noise, fast, and stable dual-channel operational amplifier such as LT6203. These amplifiers are configured which as unit gain buffers for the input signal provides a high impedance input. In many cases, however, the input is single-ended and must be converted to a differential signal. This task can be easily accomplished with amplifiers such as LT6350. This type of amplifier has two stages: the first stage generates a buffered non-invert input signal and the second stage generates an inverted output. If the input signal matches the input range of the ADC, the amplifier can be used to provide a high impedance buffer for the signal, as shown in the upper part of Fig. 6(a). If the signal needs to be expanded and shifted to match the input range of the ADC, it can be done as shown in Fig. 6(b) below.  In this example, a single-ended ±10V signal is converted into a differential signal from 0 to 5V (R2 and R3 are used to shift the signal, and RIN and R1 are used to expand the signal). What is often overlooked inaccurate analog circuits is the need for a high match between gain setting and level shift resistors. If a discrete resistor with 0.1% accuracy is used, the mismatch will vary with time, temperature, and common-mode voltage range, which makes it possible that it will be the main source of the fault circuit. Using precisely matched resistors such as LT5400 will help improve this situation. The amplifier needs space between the supply voltage and the output voltage. To maintain optimal accuracy and linearity, depending on the amplifier, the output must generally be within 0.5V or more of the power rail. This means that the amplifier must be provided with a power supply voltage range wider than the ADC input range, or that the ADC must accept a limited input range from the amplifier.  ADC such as LTC2379-18 includes a "digital gain compression" function. The function sets the full scale of the ADC from the inside and the difference between the ground voltage and the reference voltage is 0.5V. This allows the use of a single 5V amplifier that matches the full scale of the ADC.  Figure 6 (a): Single-to-difference conversion using LT6350 Fig. 6(b): Single-to-difference conversion using LT6350 ADC Driving Pseudo Differential ADC Another way is when converting a single-ended analog signal to a digital signal, skipping the differential conversion completely and using a new pseudo-differential ADC, such as LTC2369-18. The shortcoming is that the noise-signal ratio of SNR which up to 6dB is lost due to a smaller input range.  Besides, differential structures are inherently easier to eliminate even harmonics. However, using it also has some important advantages. The drive circuit is simpler: it can be as simple as using a low-noise, fast, stable operational amplifier, such as LT6202, while another operational amplifier and resistor are not required to establish the inverted input. Apart from using fewer groups, the power and noise of the circuit are generally low. Because a lower noise anti-aliasing filter behind the amplifier can have a higher cut-off frequency. This makes it easier for the amplifier to achieve stability within the ADC conversion time, making it a good choice in applications where successive conversions are likely to change throughout the scale, as is the case with multiplexed signals.  It is necessary to emphasize again that the space of the amplifier must be considered-the supply voltage must be far enough away from the output of the amplifier, which can drive the signal without distortion. In other words, this means that the amplifier must be provided with a negative orbit.  One way to solve this problem is to use products such as LTC6360. This new amplifier (Fig. 7) is optimized to drive the SAR ADC with an integrated ultra-low noise charging pump that generates its own internal negative voltage rail. Although it has a single positive source, this allows the output to swing to the ground, even slightly lower than the ground. The LTC6360 maintains excellent accuracy (250V misalignment, 2.3nV/Hz noise) and is fast and stable (16-bit, 150ns). Figure 7. When using a single power source, the LTC6360 wobbles to 0V  VI. ConclusionSeveral amplifier topologies can be used to drive SAR ADC. The best choice depends on the input signal, ADC input architecture, and application details, such as whether the input signal is multiplexed. Factors to be weighed include power, complexity, performance, and speed (conversion rate and stabilization time). Choosing an op-amp requires matching your requirement to the op-amp datasheet. Blindly assuming that any op-amp will work in any circuit is only going to result in frustration and disappointment. What's more, using the right op-amp can allow you to do things you never thought were possible.  FAQ 1. What is operational amplifier and its types?An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. Op amps usually have three terminals: two high-impedance inputs and a low-impedance output port. 2. Why is it called operational amplifier?Op-amp stands for operational amplifier. ... Originally, op-amps were so named because they were used to model the basic mathematical operations of addition, subtraction, integration, differentiation, etc. in electronic analog computers. In this sense a true operational amplifier is an ideal circuit element. 3. What is the difference between amplifier and operational amplifier?Amplifiers can be either electronic or mechanical in common definition whereas operational amplifiers are electronic amplifiers. Amplifiers, in general, have a limited capability of amplifying DC signals but all op-amps are capable of amplifying DC signals. 4. What is the main function of operational amplifier?An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins. 5. What are the advantages of operational amplifier?Advantages: 1. increased circuit stability2. increased input impedance 3. decreased output impedance 4. increased frequency bandwidth at constant gain. 6. What are op amps used for in real life?Op amps are widely used in amplifiers oscillators, filters, comparators, integrators and differentiation,voltage regulator, current regulator. Non linear applications include precision rectified log amplifier . It is also used in analog to digital and digital to analog converter. 7. Where are operational amplifiers used?Operational amplifiers are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation. 8. What is an ideal operational amplifier?Operational amplifier: The ideal op amp is an amplifier with infinite input impedance, infinite open-loop gain, zero output impedance, infinite bandwidth, and zero noise. It has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. 9. Why op-amps are better than transistors?1 Answer. A transistor is a single electronic element. ... An operational amplifier is the equivalent of many transistors and is thus able to perform much better than a single transistor (e.g. higher input impedance, lower output impedance, higher gain, differential inputs and/or differential outputs, etc.). 10. Why does an operational amplifier need a power supply?Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential. 11. How op-amp can be used as a differentiator?An op-amp differentiator is an inverting amplifier, which uses a capacitor in series with the input voltage. ... Differentiators have frequency limitations while operating on sine wave inputs; the circuit attenuates all low frequency signal components and allows only high frequency components at the output. 12. Is an op amp a transistor?Well for starters, an op amp is simply a combination of transistors, so by varying the transistor you can get different properties. One thing to also remember is that op amps are class A amplifiers which basically means that they are always on and therefore drawing power which can be undesirable. 13. Why is op amp a versatile device?Op Amps or operational amplifiers, are fundamental building blocks in electronic design, mainly because these analog integrated circuits (ICs) are very versatile. ... The term “differential amplifier,” for instance, simply means that the op amp will try to amplify any difference between the signals. 14. Does op amp need ground?An Op Amp inverting input (-) is at zero potential (A virtual ground), even though it does not have a galvanic connection to ground. 15. What is the difference between real ground and virtual ground?Real ground is when a terminal is connected physically to the ground or earth. where as virtual ground is a concept used in Op-Amps in which a node is assumed to have the potential that of the ground terminal.   You May Also LikeOperational Amplifier(OP Amp) TutorialAbout Operational Amplifier LM358: 24 Classical CircuitsA Load Insensitive High-Power Balanced Power Amplifier

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.

IntroductionPrinted Circuit Board(PCB) is a board of most modern electronic devices that has lines and pads that connect various points together. Even if it is a small board, its manufacturing process is very cumbersome and exquisite. Here will introduce the PCB manufacturing process steps by steps with pictures and video.How is PCB made?The following are the detailed PCB producing processes:IntroductionStep 1. PCB CAD FileStep 2. Plate ProductionStep 3. PCB Inner LayersStep 4. Board Punching and CheckingStep 5. LaminationStep 6. DrillStep 7. Copper Chemical Precipitation on the HolesStep 8. PCB Outer LayersStep 9. Computer Control and Copper ElectroplatingStep 1. PCB CAD FileThe first step in PCB production is to organize and check the PCB layout. The PCB manufacturers get the CAD files from the PCB design company, and they will convert them into a unified format-Extended Gerber RS-274X or Gerber X2, because each CAD software has its own unique file format. Then the electronic engineers will check whether the PCB layout conforms to the manufacturing process, and whether there are any defects and other issues.Figure 1. PCB CAD FileWhen making a PCB at home, the PCB layout can be printed on paper with a laser printer, and then transferred to the copper clad laminate. During the printing process, because the printer is prone to lack of ink and breakpoints, it is necessary to manually fill up the ink with an oil-based pen. Figure 2. PCB Laser PrintingHowever, the factory generally uses photocopying to print the PCB layout on the film. If it is a multi-layer PCB, the layout film photocopied on each layer will be arranged in order.Figure 3. PCB Film Arranged in OrderThen the film will be punched with alignment holes. Alignment holes are very important, which is essential to align the materials of each layer of the PCB.Step 2. Plate ProductionClean the copper plate. If there is dust, it may cause the final circuit to be short-circuited or broken.Figure 4. Clean the Copper PlateThe figure below is an example of an 8-layer PCB, which is actually made up of 3 copper clad laminates plus 2 copper films, and then glued them together with prepregs. The production sequence is to start with the middle board (4th- and 5th-layer of circuits), continuously stack together, and then fix. The production of 4-layer PCB is similar, including one core board and two copper films.Figure 5. 8-layer PCB Plate DisplayStep 3. PCB Inner LayersFirst, make the two-layer circuit of the middle core board. After the copper clad laminate is cleaned, it will be covered with a photosensitive film on the surface. This film will solidify when exposed to light, forming a protective film on the copper foil.Figure 6. PCB CoreInsert the two-layer PCB layout film and the double-layer copper clad laminate into the upper PCB layout film to ensure that the upper and lower PCB layout films are stacked accurately.Figure 7. PCB Layout Film PlacingThe machine irradiates the photosensitive film on the copper foil with a UV lamp. The transparent film is cured under the light, and there is still no cured photosensitive film. The copper foil covered under the cured film is the required PCB layout, which is equivalent to the function of the laser printer ink of the manual PCB. In addition, the copper foil covered by the black film will be corroded away, and the cured transparent film will be preserved.Figure 8. Cured Photosensitive FilmClean the uncured photosensitive film with lye, and the required copper foil circuit will be covered by the cured film.Figure 9. Clean Uncured Photosensitive FilmThen use a strong base, such as NaOH, to etch away the unnecessary copper foil.Figure 10. Copper Foil EtchingTear off the cured photosensitive film to expose the copper foil of the required PCB layout.Figure 11. Tear Off the Cured Photosensitive FilmStep 4. Board Punching and CheckingThe core board has been successfully produced. Then punch alignment holes on it to facilitate with other materials.Figure 12. Punch Alignment Holes on PCBOnce the core board is pressed together with other layers, it cannot be modified. So PCB checking is very important. The machine will automatically compare with the PCB layout drawing to find out the error.Figure 13. PCB Layout Drawing ComparisonThe first two layers of PCB boards have been made.Step 5. LaminationA new raw material is introduced here called Prepreg, which is the adhesive among the core boards(PCB layers>4), as well as the core board and the outer copper foil, and it also plays a role in insulation.Figure 14. PCB Prepreg and CopperThe lower copper foil and the two layers of prepreg have been fixed in advance through the alignment hole and the lower iron plate, and then the finished core board is also placed in the alignment hole, and finally the two layers of prepreg, a layer of copper foil and a layer of pressure-bearing aluminum plate covers the core plate.Figure 15. Fixed PCB Prepreg and CopperIn order to improve work efficiency, this factory will stack three different PCB boards together before fixing them. The upper iron plate is magnetically attracted to facilitate alignment with the lower iron plate. After the two layers of iron plates are successfully aligned by inserting the alignment pins, the machine compresses the space between the iron plates as much as possible, and then fixes them with nails.Figure 16. Fixed PCB LayersThe PCB boards clamped by the iron plates are placed on the holder, and then sent to the vacuum heat press for laminating. The high temperature can melt the epoxy resin in the prepreg and fix the core boards and copper foils together under pressure.Figure 17. PCB Layers LaminationAfter the lamination, remove the upper iron plate that presses the PCB. Then remove the pressure-bearing aluminum plate. The aluminum plate also plays the role of isolating different PCBs and ensuring the smoothness of the outer copper foil of the PCB. Finally the PCB taken out at this time will be covered by a layer of smooth copper foil.Figure 18. Remove the Upper Iron Plate and Aluminum PlateStep 6. DrillSo how to connect 4 layers of copper foils that are not in contact with each other in the PCB? First, make the through-hole through the PCB, and then metalize the hole wall to conduct electricity.Figure 19. PCB DrillPut a layer of aluminum plate on the punching machine, and then put the PCB on it. Since drilling is a relatively slow process, in order to improve efficiency, according to the number of layers of the PCB, 1 to 3 identical boards are stacked for drilling together. Finally, cover the uppermost PCB with a layer of aluminum plate. The upper and lower of aluminum plates are used to prevent the copper foil on the PCB from tearing when drilling.Figure 20. PCB DrillNext, you only need to select the correct drilling program on the computer, and the rest is done automatically by the drilling machine. The drill bit is driven by air pressure, and the maximum rotation speed can reach 150,000 revolutions per minute. Because such a high rotation speed is sufficient to ensure the smoothness of the hole wall.Figure 21. Drill ProgramThe replacement of the drill bit is also automatically completed by the machine according to the program. The smallest drill bit can reach a diameter of 100 microns, while the diameter of a human hair is 150 microns.Figure 22. Drill ReplaceIn the previous process, the molten epoxy was squeezed out of the PCB, so it needed to be cut off. Here the profiling milling machine cuts its periphery according to the correct XY coordinates of the PCB.Figure 23. Cuts PCB PeripheryStep 7. Copper Chemical Precipitation on the HolesSince almost all PCB designs use perforations to connect different layers of lines, a good connection requires a 25-micron copper film on the hole wall. The thickness of the copper film needs to be realized by electroplating, but the hole wall is composed of non-conductive epoxy resin and glass fiber board. So the first step is to deposit a layer of conductive material on the hole wall, and form a 1 micron copper film on the entire PCB surface by chemical deposition. The entire process such as chemical treatment and cleaning is controlled by the machine.Step 8. PCB Outer LayersNext, the PCB outer layer is transferred to the copper foil. The process is similar to the transfer principle of the previous PCB inner core board. The PCB layout is transferred to the copper foil by photocopying film and photosensitive film. The only difference is positive films will be used as boards.The transfer of the internal PCB layout described above uses the subtractive method, and the negative film is used as the board. The PCB is covered by the cured photosensitive film as a circuit, and the uncured film is cleaned. After the exposed copper foil is etched, the PCB layout circuit is protected by the cured film. The transfer of the outer PCB layout adopts the normal method, and the positive film is used as the board. The non-circuit area is covered by the cured photosensitive film on the PCB. After cleaning the uncured film, electroplating is performed. Where there is a film, it cannot be electroplated, and where there is no film, copper is plated first and then tin is plated. After the film is removed, alkaline etching is performed, and finally the tin is removed. So the circuit pattern remains on the board because it is protected by tin.Put the cleaned PCB on both sides of the copper foil into the laminating machine, and the photosensitive mold will be pressed onto the copper foil.Figure 24. LaminatorFix the printed PCB layout film of the upper and lower layers through the holes, and put the PCB board in the middle. Then, the photosensitive film under the light-transmitting film is cured by the irradiation of the UV lamp, which is the circuit that needs to be reserved.Figure 25. PCB Expose to the UV LightAfter cleaning off the unnecessary and uncured photosensitive film, inspect the PCB board.Figure 26. PCB CheckingClamp the PCB with clips, and electroplate the copper. As mentioned earlier, in order to ensure that the holes have sufficient conductivity, the copper film plated on the hole walls must have a thickness of 25 microns, so the entire system will be automatically controlled by the computer to ensure its accuracy.Figure 27. PCB Copper PlatingStep 9. Computer Control and Copper ElectroplatingAfter the copper film is electroplated, the computer gives instructions to electroplate a thin layer of tin. Then, check to ensure that the thickness of the plated copper and tin is correct.Figure 28. Electroplated Copper and Tin InspectionNext, a complete automated assembly line completes the etching process. Then, clean the cured photosensitive film on the PCB.Figure 29. Clean Cured Photosensitive FilmThen use a strong alkali to clean the unnecessary copper foil covered by it.Figure 30. Clean the Unnecessary Copper FoilFinally, use the tin stripping solution to strip the tin plating on the PCB layout copper foil. After cleaning, the 4-layer PCB layout is complete. Frequently Asked Questions about PCB Manufacturing Process1. Which are the techniques of PCB manufacturing?There are several PCB manufacturing methods that a PCB can be submitted to before reaching the final product. These methods include preparing the board's surface, placing components, soldering, cleaning, and inspection and testing. 2. What is PCB design process?Step 1 – The DesignStep 2 – Printing the DesignStep 3 – Creating the SubstrateStep 4 – Printing the Inner LayersStep 5 – Ultraviolet LightStep 6 – Removing Unwanted CopperStep 7 – Inspection.Step 8 – Laminating the Layers 3. Which software is best for PCB design?Top 8 Best PCB Design Software of 2021PROTEL (Altium Designer)PADS (PowerPCB)ORCADAllegroEagle (Easily Applicable Graphical Layout Editor)KicadEasyEdaFritzing 4. What is a PCB layer?A PCB is defined as a number of copper layers in a well defined sequence. Copper layers of a PCB are usually just named layers or also called SIGNAL layer. However, to define the complete PCB, other layers are required. They are usually named by their functionality and position. 5. What are the components of a PCB?Some common PCB components include:Battery: provides the voltage to the circuit.Resistors: control the electric current as it passes through them. They’re colour coded to determine their value.LEDs: light emitting diode. Lights up when current flows through it, and will only allow current to flow in one direction.Transistor: amplifies charge.Capacitators: these are components which can harbour electrical charge.Inductor: stores charge and stops and change in current.Diode: allows current to pass in one direction only, blocking the other.Switches: can either allow current or block depending if they are closed or open.

What is Breadboard?When learning how to build a circuit, the breadboard is one of the most basic parts. There are many small jacks on the breadboard, which are specially designed and manufactured for solderless experiments of electronic circuits. A breadboard consists of plastic block holding a matrix of electrical sockets of a size suitable for gripping thin connecting wire, component wires or the pins of transistors and integrated circuits (ICs). The sockets are connected inside the board, usually in rows of five sockets. Since various electronic components can be inserted or pulled out at will according to needs, welding is eliminated, circuit assembly time is saved, and components can be reused, so it is very suitable for the assembly, debugging and training of electronic circuits.What is Breadboard?Topics Covered in this GuideWhat is Breadboard?Why are breadboards called breadboards?How Breadboard Looks like?IC & DIPHow to Use Breadboards?Types of BreadboardsBasic Principles of Breadboard WiringBreadboard Using Tips for BeginnersMaintenance of the BreadboardsWhich Breadboard is Best?What are the Holes in the Breadboard Called?Is a Breadboard Necessary?How much Voltage can a Breadboard Handle?How Does Current Flow in a Breadboard?How Many Amps Can a Breadboard Take?Why are breadboards called breadboards?The name of the breadboard can be traced back to the era of vacuum tube circuits. At that time, most of the circuit components were large in size. People usually fixed them on a wooden board for cutting bread with screws and nails for connection. Later, the circuit components became more and more smaller, but the name of the breadboard is still used. The breadboard most commonly used today is usually made of white plastic and is a pluggable (solderless) breadboard. It was designed by Ronald J. Portugal in 1971.It is a process of verifying ideas by creating an initial model. If you are not sure how a circuit will react normally under a given parameter setting, it is best to build a prototype to test it. For those who are new to electronic circuits, the breadboard is a good start. The advantage of a breadboard is that it can hold the simplest and most complex circuits at the same time. If your circuit cannot be accommodated by the current breadboard, you can splice other boards to adapt to all circuits of different sizes and complexity. Such as integrated circuits (ICs). When you try to master how a module works and need to rewire multiple times, you certainly don't want to solder the circuit interface every time. Once you find a problem, you can disassemble each part to prepare for some troubleshooting. How Breadboard Looks like?The shape of the breadboard is mostly cuboid, with different sizes. The breadboard generally has two layers, the top is a grid shape with double-sided tape adhering to it( you can tore it to fix the breadboard in a certain position). The upper layer of the breadboard is composed of a grid of rows and columns, and there is no conduction between rows.The whole board is made of thermosetting phenolic resin, and there are metal strips at the bottom of the board. Holes are punched at the corresponding positions on the board so that the components can be in contact with the metal strips when inserted into the board, so as to achieve the purpose of conducting electricity. Generally, every 5 orifice plates are connected by a metal strip. There are two rows of vertical jacks on both sides of the board, also a group of 5. These two sets of jacks are used to provide power to the components on the board.Breadboard Layout ExampleSome breadboards have two columns on the left and right sides. These two columns are customarily used as the positive and negative poles of the power supply (This is not necessarily true, depending on your own usage habits and circuit needs). Each of the five grids in the same column of the two columns is a group, which is conductive. But there is no conduction between columns. Then in the middle part, every five columns of grids form a group, and the five grids in this group are conductive. There is generally a groove in the center of the board, which is designed for the needs of integrated circuit (IC) and chip testing, and is used to separate the left and right parts of a board. Some breadboards do not have two columns on the left and right sides due to the size, but the other structures are the same.The motherboard uses a glass fiber board with a conductive layer of copper foil, which is used to fix the solderless breadboard and lead out the power terminal.There may be slight differences in the structure between different breadboards, but they are basically the same. IC & DIPAn unique feature of the breadboard is: Integrated Circuit (IC) and Dual in-line Package (DIP)Dual in-line Package (DIP) Chip：MA2053Do you see the small gap in the middle of the breadboard? There is a reason for this gap, the use of integrated circuits. There are ICs in almost every electronic device. They run motors, regulate voltage, act as timers, perform logic tasks, and perform almost everything you need to perform.ICs can have different numbers of pins, sizes and functions. However, many ICs are suitable for a standard called dual in-line packaging (DIP), which means they all share a set width. As you guessed, the width fits the gap in the middle of the breadboard. This makes it easier to use the IC without having to worry about connecting the wrong pins together. the holes of the breadboard are spaced 0.1” (2.54mm) apart in both the X and Y direction which is the spacing used for adjacent DIP IC leads as well as many other components such as headers.IC & DIP Example on Breadboard How to Use Breadboards?You can use breadboard to make quick electrical connections between components- like resistors, LEDs, capacitors, etc, so that you can test your circuit before permanently soldering it together. Without welding and manual wiring, the circuit and components can be tested by inserting the component into the hole, which is convenient to use. Before use, determine which component's pins should be connected together, and then insert them into the same group of 5 small holes.How to Use a Breadboard?Example: LED Lighting1) MaterialsOne breadboard, several connecting wires (the connecting wires should use needle-shaped wires at both ends), one led light, and one 3V button battery.2) First, put the battery into the battery holder (this can be bought online), and plug it into the breadboard. Then, insert the battery holder into the left and right parts of the breadboard. Parts are separated by grooves to avoid short circuit between the positive and negative poles of the power supply).3) Lead two wires from the positive and negative poles of the battery, and then plug the LED into any two grids that are not conductive on the breadboard (the long pin of the led is positive and the short pin is negative), and finally connect the wires from the positive and negative poles of the battery to the two LED segments.Types of Breadboards1) Solderless BreadboardA solderless breadboard is a motherboard that does not serve as a base, and does not have a soldering power socket to draw out but can expand a single breadboard. Connect the two poles of the power supply to the sockets on both sides of the breadboard, and then you can plug in the components for experiment (the power supply should be disconnected during the process of inserting the components). When more than 5 components or a set of jacks cannot be inserted, you need to connect multiple sets of jacks with a breadboard cable.The advantages of solderless breadboards are small size and easy to carry, but the disadvantages are relatively simple, inconvenient power connection, and small area. It is not suitable for large-scale circuit experiments. If you want to use it for large-scale circuit experiments, you need to fix multiple breadboards on a large wooden board with screws, and then connect them with wires.2) Single BreadboardA single breadboard is a part with a motherboard as a base and a dedicated terminal for power access, and even some breadboards that can perform high-voltage experiments include ground terminals. This kind of board is more convenient to use, that is, directly connect the power supply to the terminal, and then insert the components for experiment (the power supply should be disconnected during the process of inserting the components) when more than 5 components or a set of jacks cannot be inserted, you need to use breadboard cables to connect multiple sets of jacks.The advantage of a single breadboard is that it is small in size, easy to carry, and can easily switch on and off the power supply, but it has a small area and is not suitable for large-scale circuit experiments.3) Composite breadboardComposite breadboard is a board composed of many solderless breadboards. Generally, 2-4 solderless breadboards are fixed on the motherboard, and then the power cords of each board are connected together with the copper foil in the motherboard. The kind of breadboards is also specially designed for different circuit units to control the power supply, so that each board can carry different voltages according to the needs. The use of the composite breadboard is the same as the single breadboard.The advantage of the composite breadboard is that it can conveniently switch on and off the power supply, has a large area to carry out large-scale experiments, and is highly mobile, and has a wide range of uses. However, it is large and heavy for carrying, so it is suitable for laboratories and electronic hobbyists use. Basic Principles of Breadboard WiringComplete the circuit overlap on the breadboard, different people have different styles. However, no matter what style or habit, the following basic principles must be paid attention to when completing the circuit overlap:1. The fewer connection points, the better.Each additional connection point actually increases the probability of failure artificially. There are common faults such as impassability in the breadboard hole, loose wire, and broken wire inside.2. Try to avoid overpasses.The so-called "overpass" means that components or wires ride on other components or wires. Beginner is easy to make such mistakes. It will bring trouble to the replacement of components in the later stage. On the other hand, in the event of a failure, the messy wires can easily make people lose confidence.3. Try to be as reliable as possible.There are two phenomena that need attention:① Breadboard integrated circuits are easy to loosen. Therefore, for integrated circuits such as operational amplifiers, it is necessary to press down forcefully. Once it is not reliable, the position needs to be changed.② The pins of some components on the breadboard are too thin, so please be careful to move them slightly. If you find that they are not secure, you need to change the position.Electronic BreadboardBreadboard Using Tips for Beginners1. When installing discrete components, it should be easy to see their polarity and signs. After placing the component pins, bend them where needed. In order to prevent the exposed leads from short-circuiting, a wire with a sleeve must be used, and the component pins are generally not cut to facilitate repeated use. Generally, do not insert components with a pin diameter> 0.8mm, so as not to damage the elasticity of the contact piece inside the socket.2. The pins of integrated circuits that have been used many times must be repaired neatly, the pins cannot be bent, and all the pins should be slightly skewed outward, so that the lead angles and the jacks can be reliably contacted. The arrangement of the components on the breadboard should be determined according to the circuit diagram in order to facilitate the wiring. In order to be able to correctly route and facilitate wire checking, the insertion direction of all ICs must be kept the same, and which cannot be inserted upside down for the convenience of temporary wiring or to shorten the length of the wire.3. According to the sequence of the signal flow, the method of installation and debugging is adopted. After the components are installed, first connect the power cord and the ground wire. In order to check the line conveniently, try to use different colors for the line. For example, the positive power supply generally uses a red wire, the negative power supply uses the blue, the ground wire uses the black, and the signal wire uses the yellow. Other colors can also be selected according to the real conditions.4. The breadboard should use a single-strand wire with a diameter of about 0.6mm. Cut the wire according to the distance of the wire and the length of the jack. The wire end is required to be cut into a 45º, and the stripped length of the wire end is about 6mm. All the wires are required to be inserted into the bottom plate to ensure good contact. In addition, bare wires should not be exposed to prevent disconnection with other wires.5. The connection is required to be tightly attached to the breadboard to avoid collision and ejection of the breadboard, resulting in poor contact. The wiring must pass around the integrated circuit, and it is not allowed to cross the integrated circuit, and the wires must not be overlapped with each other, try to be horizontal and vertical. This is conducive to line wiring and checking, and components replacement.6. It is best to connect a capacitor with a capacity of tens of microfarads in parallel between the input terminal of each power supply and the ground, so as to reduce the impact of current during transients. In order to suppress the high-frequency components in the power supply, a high-frequency decoupling capacitor should be connected in parallel at both ends of the capacitor, generally 0.01~0.047Uf.7. During the wiring process, it is required to place the various components on the corresponding position on the breadboard and mark the pin numbers used on the circuit diagram to ensure the smooth progress of debugging and troubleshooting.8. All ground wires must be connected together to form a common reference point. Maintenance of the BreadboardsUsing a breadboard is more convenient than using a soldering method, easy to replace wires and components, and can be used multiple times. However, the breadboard should be maintained during daily use. In the multiple use of the breadboard, the spring sheet will become loose and the elasticity will become poor, which is easy to cause poor contact and virtual welding. They are difficult to find out.The breadboard that has been used many times should be uncovered from the back, and the spring sheet with poor elasticity should be taken out, repaired and then inserted into the original position. This can enhance the elasticity and increase the reliability and service life of the breadboard. In addition, pay attention to where the breadboard is used. Large-volume, high-quality or high-power components cannot be plugged into the breadboard because the breadboard jacks are small and the leads of such large components are relatively thick. At this time, the components can only be placed outside the board. Use a single strand of hard wire to solder to the lead, and then insert it into the breadboard.Breadboards are not suitable for high-frequency circuits, because the lead inductance and distributed capacitance of the breadboard are relatively large, which has a great impact on the performance of high-frequency circuits. Breadboard is suitable for integrated circuits, especially for digital integrated circuits, because digital integrated circuits usually have low operating frequency and low power, and they use fewer RC components. It is more difficult for discrete component circuits to use breadboards, especially for circuits with high frequency and high power. Which Breadboard is Best?Best Breadboard Kit ReviewsELEGOO Upgraded Electronics Fun KitREXQualis Electronics Component Fun KitElegoo EL-CP-003 3 MB-102 830-pin solderless PCB board kitFreenove Solderless Breadboard Ultimate Starter KitKeywishbot Electronic Component BreadboardREXQualis Solderless BreadboardKuman GPIO expansion kit for Raspberry PieBoot 3 400-point solderless circuit breadboardPaxcoo 4 breadboard kits with 120 jumper wires for ArduinoSmraza Basic Starter KitSunFounder breadboard kit RAB holderTEKTRUM Solderless plug-in breadboard kitMicrotivity IB401 400-point experiment breadboardElenco 9440 breadboard with 350 jumper wire set kitMakeronics Breadboard + Electronics Fun Kit What are the Holes in the Breadboard Called?Breadboards are designed to work with through-hole electronic components. They have many tiny sockets (called 'holes') arranged on a 0.1" grid. The leads of most components can be pushed straight into the holes. ICs are inserted across the central gap with their notch or dot to the left.The holes in the top-most rail are highlighted in orange and the holes in the bottom-most one are highlighted in green. In the central area of the board are vertical lines of five holes that are electrically connected. These lines of five holes are known as nodes. Is a Breadboard Necessary?Although a breadboard is essential to prototype circuits without having to solder them together and when you have verified that the circuits works you can solder it onto a perfboard. But note that breadboards are never necessary. A properly-milled and constructed panel should generally stay flat under normal conditions, so the only time I add a breadboard end is if I think the design benefits from it visually.In addition, high frequency (above 10MHz) Where the additional breadboard capacitance would present problems (oscillators, etc) Where glitches due to poor wire connections would result in poor operation. Where most of the parts are not through hole 0.1" (2.54mm) centers. How much Voltage can a Breadboard Handle?Breadboards are mostly used for low voltage and current applications, however, breadboards can handle 12 volts. Breadboards are made by different manufacturers, so the voltages they can handle depends on how they are constructed. How Does Current Flow in a Breadboard?The vertical columns of the breadboard are called terminals, while the horizontal long rows are called power rails because they are mostly used to connect the power supply to the breadboard. The positive rails are indicated by red lines, while the negative rails are indicated by black ones. That means our electric current, which is made up of moving charges, flows out of the positive side of the battery, through the wire and into the breadboard power bus. It then flows out of the black wire and into the second power bus, through the power bus and back to the negative side of the battery. How Many Amps Can a Breadboard Take?Due to the temporary nature of the contacts, most breadboard has a current limit of one amp or less. Breadboard generally cannot handle frequencies greater than ten megahertz because of the nature of the contacts, which create a stray capacitance of around two to twenty picofarads (pFs) for every connection.

IntroductionFLASH is a type of non-volatile memory that retains data even when power is disconnected. Unlike RAM, which can rewrite data at the byte level, flash memory operates differently. A flash memory chip consists of an array of data storage cells organized into blocks, with each block containing multiple pages (typically 64 to 256 pages in modern devices, though older devices used 32 pages). A page is usually 2KB, 4KB, 8KB, or 16KB in modern NAND flash, though the original specification was 512 bytes plus spare area, as flash was initially developed as a disk replacement technology.What Is Flash Memory?Ⅰ Types of Flash MemoryFlash memory is widely used as a storage medium in digital cameras, smartphones, tablets, USB drives, SSDs, and various consumer electronics. Flash memory cards come in various form factors depending on manufacturers and applications, including USB flash drives, CompactFlash (CF card), MultiMediaCard (MMC card), Secure Digital (SD card, microSD), Memory Stick, and XD-Picture Card (XD card). Note that SmartMedia (SM card) and Microdrive have been discontinued. While these flash cards have different physical formats and specifications, their underlying technical principles remain similar.Flash memory includes two main architectural types: NOR Flash and NAND Flash. NOR Flash is a random access device with dedicated address and data lines (similar to SRAM), allowing byte-level read and write operations and direct access to any memory location, making it an excellent ROM alternative, such as in computer BIOS chips. NAND Flash, however, lacks dedicated address lines and cannot be directly addressed. It is controlled by sending commands and addresses through an I/O interface, meaning NAND Flash can only be accessed in pages, making it more suitable for sequential data storage.Ⅱ NAND Flash MemoryNAND Flash is extensively used in high-capacity storage devices such as memory cards, USB drives, SSDs, eMMC, and UFS storage. NAND Flash cells are categorized by the number of bits stored per cell: SLC (Single-Level Cell), MLC (Multi-Level Cell), TLC (Triple-Level Cell), and QLC (Quad-Level Cell). SLC stores 1 bit per cell, MLC stores 2 bits, TLC stores 3 bits, and QLC stores 4 bits per cell.As more bits are stored in a single cell, the read/write performance decreases, endurance diminishes, but cost per gigabyte is reduced, making higher-density options more economical for consumer applications.ItemsSLCMLCTLCQLCBits Per Cell1234P/E Cycles50,000-100,0003,000-10,0001,000-3,000100-1,000Read Time (μs)255075100Program Time (μs)200-300600-900900-13501350-2000Erase Time (ms)1.5-234.56-8SLC is primarily used in enterprise, industrial, and military applications due to its high-speed writing, low error rate, and exceptional durability.MLC is targeted at consumer and prosumer applications, offering twice the capacity of SLC at lower cost. It's suitable for USB drives, smartphones, digital cameras, and consumer-grade SSDs.TLC has become the mainstream choice for consumer SSDs and SD cards due to its balance of cost, capacity, and acceptable performance for everyday use.QLC, introduced more recently, offers even higher density and lower cost per gigabyte, making it increasingly popular in budget SSDs and high-capacity storage solutions, though with reduced endurance.As a practical solid-state storage medium, NAND Flash has unique physical characteristics requiring specialized management. Designers face several key challenges:1) Erase-before-write requirement: Data cannot be overwritten directly; blocks must be erased before new data can be written2) Wear mechanism: Limited program/erase (P/E) cycles impose durability constraints3) Read/write interference: Operations can cause data errors in adjacent cells4) Data retention: Charge leakage over time can cause data loss5) Bad block management: Both factory defects and runtime failures must be managedKey technologies addressing these challenges include:1) Cell type selection: Choosing appropriate NAND type (SLC/MLC/TLC/QLC) based on application requirements2) Wear leveling algorithms: Distributing write operations evenly across all blocks to maximize lifespan3) Bad block management: Identifying and mapping out defective blocks to ensure data integrity4) Error Correction Code (ECC): Detecting and correcting bit errors using advanced algorithms like BCH or LDPC5) Write amplification mitigation: Minimizing unnecessary write operations to extend device life6) Garbage collection: Consolidating valid data and reclaiming space from partially used blocksData is stored as electrical charge in Flash memory cells. The amount of stored charge depends on the voltage applied to the Control Gate, which controls whether charge is injected or removed from the floating gate.1) For programming (writing) NAND Flash, voltage is applied to the Control Gate to inject electrons into the floating gate. When charge exceeds the threshold voltage (Vth), the cell represents a logical 0.2) For erasing NAND Flash, electrons are removed from the floating gate. When charge falls below the threshold voltage (Vth), the cell represents a logical 1. Ⅲ NOR Flash MemoryNOR Flash, similar to conventional memory, supports random access, enabling XIP (eXecute In Place) functionality. This allows code execution directly from the flash without copying to RAM, making it ideal for boot code, BIOS/UEFI firmware, and embedded system applications requiring immediate code execution.NOR Flash is categorized into two types based on host interface: Parallel NOR Flash and Serial NOR Flash.Parallel NOR Flash connects directly to the host controller with its contents mapped into the CPU address space, eliminating the need to copy to RAM. Early BIOS implementations used the FWH (Firmware Hub) interface, a parallel connection that has been largely obsoleted due to pin count and speed limitations.Serial NOR Flash is more cost-effective than Parallel NOR Flash and typically connects to the host processor or Platform Controller Hub (PCH) via SPI (Serial Peripheral Interface), Quad-SPI (QSPI), or Octal-SPI interfaces. Modern implementations support higher speeds through multi-lane configurations.Today, virtually all UEFI/BIOS firmware, embedded systems, IoT devices, and many consumer electronics use NOR Flash. Typical capacities range from 1MB to 256MB, with 16MB-128MB being common for modern UEFI implementations. While more expensive per gigabyte than NAND, NOR Flash offers superior reliability and random access performance.NOR Flash has slower erase speeds and lower erase cycle counts compared to NAND, but these limitations rarely impact BIOS/firmware performance or cause device failures due to the infrequent update nature of firmware. Ⅳ NAND Flash vs NOR FlashCompared with NOR flash memory, NAND flash memory requires fewer transistors per cell to store the same amount of data, resulting in smaller die size and higher storage density. This architectural difference makes NAND significantly more cost-effective for high-capacity storage applications.In terms of read speed, NOR flash memory offers faster random access than NAND flash memory, with typical access times of 50-100ns compared to NAND's page-based access. However, NAND flash memory significantly outperforms NOR in sequential write and erase operations. NAND's block-based erase operation is simpler and faster, erasing entire blocks (typically 128KB-4MB) at once.NOR flash memory requires all bits to be set to 1 during erase operations before programming. While NOR flash memory provides faster random access and simpler byte-level operations, its lower storage density and higher cost make it more suitable for code storage and execution. NAND flash memory provides extremely high cell density (modern single chips can exceed 1TB capacity), making it ideal for mass data storage with fast write and erase speeds. Additionally, NAND flash operates on page-based read/write units (typically 4KB-16KB) and block-based erase units, making it functionally similar to traditional disk drives.NAND Flash is more susceptible to bit errors than NOR Flash, necessitating robust Error Detection and Correction (EDC/ECC) algorithms. Modern NAND implementations use advanced ECC schemes like BCH (Bose-Chaudhuri-Hocquenghem) or LDPC (Low-Density Parity-Check) codes. Additionally, NAND Flash develops bad blocks over its lifetime. File systems like FAT on SD cards experience frequent rewrites of the file allocation table, and the P/E cycle count per block is critical to NAND Flash longevity. Balancing erase cycles across all blocks and managing bad blocks requires specialized firmware-level functionality including bad block management, wear leveling, ECC, and garbage collection. This management layer is called the FTL (Flash Translation Layer). Based on FTL implementation location, Flash Memory is categorized as Raw Flash or Managed Flash.Raw Flash requires the host system to implement FTL functionality, giving designers complete control but requiring significant software development. Managed Flash (such as eMMC, UFS, SD cards) includes an integrated controller that handles FTL operations transparently, simplifying host system design at the cost of reduced low-level control.Ⅴ Universal Flash Storage Versions ComparisonStorage performance significantly impacts device responsiveness and user experience. Universal Flash Storage (UFS) has become the dominant standard for high-performance mobile and embedded storage, replacing the older eMMC standard. UFS provides a standardized flash storage specification optimized for smartphones, tablets, automotive systems, and other performance-critical applications. Version numbers indicate generational improvements, with higher versions offering substantially better performance, features, and efficiency.✔️Version Comparison (Main Parameters)UFS Version1.01.12.02.13.03.14.0Introduced2011-02-242012-06-252013-09-182016-04-042018-01-302020-01-302023-09-14Bandwidth per lane300 MB/s600 MB/s1450 MB/s (HS-G3)2900 MB/s (HS-G4)5800 MB/s (HS-G5)Max. number of lanes12Max. total bandwidth300 MB/s1200 MB/s2900 MB/s (HS-G3)5800 MB/s (HS-G4)11600 MB/s (HS-G5)M-PHY version1.03.04.15.0UniPro version1.41.61.82.0✔️UFS 2.1 vs UFS 2.2The primary enhancement in UFS 2.2 over UFS 2.1 is the Write Booster feature, which significantly improves write performance. Write Booster uses SLC (Single-Level Cell) cache to accelerate write operations, providing faster application launches, improved browser cache loading, reduced video encoding times, and enhanced overall system responsiveness. This feature is particularly beneficial for burst write scenarios common in mobile devices.As eMMC has been phased out from mainstream consumer devices and NAND flash prices have decreased, UFS adoption has accelerated. UFS 2.2 briefly served as a transitional standard before UFS 3.x became mainstream in flagship devices.✔️UFS 3.0 vs UFS 3.1UFS 3.1 introduces three significant enhancements over UFS 3.0:1) Write Booster (Enhanced)Write Booster in UFS 3.1 is an enhanced version that increases device write speed substantially. This feature can boost write speeds up to 700 MB/s, compared to UFS 3.0's typical sequential write performance of around 500 MB/s. The mechanism works similarly to SLC caching in SSDs: a portion of TLC/QLC storage is dynamically configured to operate in SLC mode, providing faster write performance. Data is initially written to this high-performance buffer, then migrated to standard storage during idle periods, freeing the cache for subsequent operations.2) Deep Sleep ModeDeep Sleep enables the flash memory to enter an ultra-low-power state during extended idle periods, significantly reducing standby power consumption. This feature helps extend battery life during device standby and contributes to overall device thermal management. Deep Sleep can reduce idle power consumption by up to 40% compared to standard sleep modes.3) Host Performance Booster (HPB)HPB addresses long-term performance degradation by improving random read performance. As devices are used over time, file system fragmentation and the need to frequently reload the Logical-to-Physical (L2P) mapping table can cause performance degradation. HPB leverages the host device's RAM to cache portions of the L2P mapping table, reducing latency for random read operations. This is particularly effective at maintaining consistent performance after extended use, preventing the "slowdown over time" phenomenon common in storage devices. HPB can improve random read IOPS by up to 70% in fragmented scenarios.✔️UFS 4.0 - The Latest GenerationReleased in September 2023, UFS 4.0 represents the latest advancement in mobile storage technology. Key improvements include:• Doubled bandwidth: Up to 11.6 GB/s (5800 MB/s per lane with dual-lane configuration) using HS-G5 gear• Improved power efficiency: Lower power consumption per bit transferred compared to UFS 3.1• Enhanced thermal management: Better heat dissipation characteristics for sustained performance• Advanced features: Builds upon Write Booster, Deep Sleep, and HPB with further optimizationsUFS 4.0 is designed for next-generation flagship smartphones, tablets, and high-performance mobile devices requiring extreme storage bandwidth for 8K video recording, advanced computational photography, and AI workloads. Frequently Asked Questions about Flash Memory1. What are the different types of flash memory?Flash memory comes in two fundamental architectural types: NOR and NAND. NOR flash offers random access and execute-in-place capabilities, making it ideal for code storage. NAND flash provides higher density and faster write speeds, making it suitable for data storage. Within NAND flash, there are further subdivisions based on bits per cell: SLC (1 bit), MLC (2 bits), TLC (3 bits), and QLC (4 bits), each offering different trade-offs between performance, endurance, and cost. 2. What are the characteristics of flash memory?Flash memory has several distinctive characteristics: it is significantly less expensive than EEPROM and doesn't require batteries for data retention unlike SRAM. It is non-volatile, meaning data persists without power. Flash offers fast read access times (microseconds), high resistance to physical shock compared to hard disk drives, low power consumption, and silent operation. However, it has limitations including finite write/erase cycles, block-level erase requirements, and potential for bit errors requiring ECC. 3. What is the purpose of flash memory?Flash memory serves as a non-volatile storage solution widely used in embedded systems, consumer electronics, and enterprise storage. It retains data without power, can be electrically erased and reprogrammed, and offers advantages over traditional magnetic storage including faster access times, lower power consumption, better durability, and compact form factors. Flash memory evolved from EEPROM technology and has become the dominant storage technology for mobile devices, SSDs, USB drives, memory cards, and embedded systems. 4. What is the difference between NAND flash and NOR flash?NOR flash provides faster random read access and supports execute-in-place (XIP), allowing direct code execution without copying to RAM, making it ideal for firmware and boot code. However, it's more expensive and has slower erase/write operations. NAND flash offers higher storage density, lower cost per gigabyte, and much faster sequential write and erase speeds, making it ideal for mass storage applications. NAND is accessed serially through a shared I/O interface, while NOR has parallel address and data buses allowing random access. NAND requires more complex error correction due to higher bit error rates. 5. What is the difference between UFS and eMMC?UFS (Universal Flash Storage) is the successor to eMMC (embedded MultiMediaCard) and offers several significant advantages: UFS supports full-duplex operation allowing simultaneous read and write operations, while eMMC is half-duplex. UFS uses a faster serial interface with higher bandwidth (up to 11.6 GB/s in UFS 4.0 vs. 400 MB/s in eMMC 5.1). UFS also features command queuing for better multitasking performance, lower latency, and improved power efficiency. These advantages make UFS the preferred choice for modern flagship smartphones and high-performance mobile devices. 6. How does wear leveling work in flash memory?Wear leveling is a technique used to extend flash memory lifespan by distributing write and erase cycles evenly across all memory blocks. Since flash memory has a limited number of program/erase cycles per block, repeatedly writing to the same blocks would cause premature failure. Wear leveling algorithms track the erase count of each block and preferentially use blocks with lower erase counts for new writes. This ensures all blocks wear out at approximately the same rate, maximizing the overall device lifespan. Modern flash controllers implement sophisticated wear leveling algorithms as part of the Flash Translation Layer (FTL). 7. What is 3D NAND technology?3D NAND (also called V-NAND) is a flash memory architecture that stacks memory cells vertically in multiple layers, rather than arranging them in a single planar layer. This technology allows for higher storage densities without requiring smaller manufacturing process nodes. Modern 3D NAND implementations can have over 200 layers, significantly increasing capacity while improving performance and endurance compared to planar NAND. 3D NAND also offers better power efficiency and can achieve higher performance due to reduced cell-to-cell interference. This technology has become the standard for modern SSDs and high-capacity storage devices.

IntroductionThe transistor is one of the basic semiconductor components, which has the function of current amplification in electronic circuit. It is made of two PN junctions very close to each other on a semiconductor substrate. Two PN junctions divide the entire semiconductor into three parts: The middle part is the base area, and the two sides are the emitter and the collector. What is NPN Transistor? For BeginnerCatalogIntroductionⅠ NPN Transistor Arrangement and SymbolⅡ How Do NPN Transistors Work?Ⅲ NPN Transistor Uses: A Controllable ValveⅠ NPN Transistor Arrangement and SymbolBefore explaining the principle, let's first understand the basic structure and symbols of the NPN transistor. To identify the NPN transistor pins, it will be Collector (c), Base (b) and Emitter (e).Figure 1. NPN Transistor Structure and SymbolNPN transistor is composed of two N-type semiconductors and one P-type semiconductor. Generally, an NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). The arrangement is shown in the Figure 1. Ⅱ How Do NPN Transistors Work?Here is the main description to illustrate the basic principle and function of NPN transistors.1) Current AmplificationThe following analysis is only for NPN silicon transistors. As shown in the figure above, we call the current flowing from the base B to the emitter E the base current Ib; the current flowing from the collector C to the emitter E is called the collector current Ic. The directions of these two currents are both flowing out of the emitter, so an arrow is used on the emitter E to indicate the current direction.The amplification function of the transistor is: the collector current is controlled by the base current (assuming that the power supply can provide a large enough current to the collector), and a small change in the base current will cause a large change in the collector current: the change in the collector current is β times the change in the base current, that is, the current change is amplified by β times, so we call β the magnification of the transistor (β is generally much larger than 1). If we add a changing small signal between the base and the emitter, it will cause a change in the base current Ib. After the change in Ib is amplified, it leads to a big change in Ic. If the collector current Ic flows through a resistor R, it can be calculated according to the Ohm's Law formula U=R*I, and the voltage on this resistor will change greatly. According to the voltage on this resistor, so we can get the amplified voltage signal. In short, the change satisfies a certain proportional relationship.2) Bias CircuitWhen the transistor is used in the actual amplifier circuit, it is also necessary to add a suitable bias circuit. There are several reasons for this. First of all, due to the non-linearity of the transistor's BE junction (equivalent to a diode), the base current must be generated after the input voltage reaches a certain level (for silicon tubes, 0.7V is often used). When the voltage between the base and the emitter is less than 0.7V, the base current can be considered as zero. However, in practice, the signal to be amplified is often much smaller than 0.7V. If no bias is applied, such a small signal is not enough to cause a change in the base current (because when it is less than 0.7V, the base current is all 0).Add a suitable current to the base of the transistor (called the bias current, and the resistor in the figure used to provide this current, is called the base bias resistor). When a small signal follows this bias current are superimposed together, a small signal will cause a change in the base current, and the change in the base current will be amplified and output on the collector. Another reason is meeting the requirement of the output signal range. If there is no bias, then only those increased signals will be amplified, but the decreased signals will be invalid (because the collector current is 0 when there is no bias, and it cannot be reduced). With bias, let the collector have a certain current in advance. When the input base current becomes smaller, the collector current can be reduced; when the input base current increases, the collector current increases. Both the reduced signal and the increased signal can be amplified.3) NPN Transistor SwitchLet's talk about the saturation mode of the transistor. As shown in the figure above, because of the limitation of resistance Rc (Rc is a fixed value, then the maximum current is U/Rc, where U is the power supply voltage), the collector current cannot increase indefinitely. When the base current increases and the collector current cannot continue to increase, the transistor enters a saturated state. The general criterion for judging whether the transistor is saturated is: Ib*β>Ic.In a saturation state, the voltage between the collector and the emitter of the transistor will be very small, which can be understood as a switch. In this way, when the base current is 0, the collector current is 0 (this is called the triode cut-off), which is equivalent to the switch off; when the base current is large, it is equivalent to the switch on. In cut-off and saturation state, a transistor is equal to a switch.4) Operational StateIf we replace the resistor Rc with a bulb in the above figure, then when the base current is 0, the collector current is 0, so the bulb is off. If the base current is relatively large (greater than the current flowing through the bulb divided by the magnification β), the transistor will saturate, and the bulb will light up. Since the control current only needs to be a little larger than β of the bulb current, a small current can be used to control the on and off of a large current. If the base current increases slowly, the brightness of the bulb will also increase (which is a saturation process).The figure below is a basic transistor switch circuit. The base should connect a base resistor (R2), and the collector connects with a load resistor (R1).Operational ModeNPNCut-offUne<UonUc>UbActiveUbe>UonUc>UbSaturationUbe>UonUc<UbNPN transistor uses the B-E current (IB) to control the C-E current (IC). The E pole has the lowest potential, and usually the C pole has the highest potential during normal amplification, that is, VC>VB>VE.NPN base extremely high voltage, the collector and emitter are short-circuit and low-voltage, and the collector and emitter are open-circuit.NPN is suitable for two situations:If the input is a high level and the output needs a low level, NPN is better.If the input is a low level and the output needs a high level, NPN is better.2N2222 NPN Transistor PinoutⅢ NPN Transistor Uses: A Controllable ValveNPN is a component that uses b (base) current Ib to drive the current Ic flowing through CE, and its working principle is much like a controllable valve.Figure 2. A Controllable ValveThe blue water flow in the thin pipe on the left impacts the lever to open the valve of the large water pipe, allowing the larger red water flow to pass through the valve. The larger the blue water flow, the greater the red water flow in the big pipe. If the magnification is 100, then when the blue water flow is 1 kg/hour, then 100 kg/hour of water is allowed to flow through the large pipe. The principle of the transistor is the same. When Ib (base current) is 1mA, a current of 100mA is allowed to pass through Ice.Figure 3. NPN Transistor DiagramLet's analyze this circuit. If its magnification is 100, and ignore the base voltage. The base current is 10V÷10K=1mA, so the collector current should be 100mA. According to Ohm's law, the voltage on Rc is 0.1A×50Ω=5V. Then the remaining 5V is on the C and E poles of the transistor. Now if we let Rb be 1K, then the base current is 10V÷1K=10mA, according to the magnification of 100, is Ic 1000mA? If it is really 1A, then the voltage on Rc is 1A×50Ω=50V. The power supply voltage has been exceeded, and the transistors have become generators? This is not the case. See below:Figure 4. NPN Transistor Compared to A ValveContinue the metaphor. When the control current is 10mA, the valve on the main water pipe is opened to allow 1A current to flow, but can 1A be realized? No, because there is a resistor on it, it is equivalent to a fixed valve. It is stringed on top of the main water pipe. When the opening of the lower controllable valve is greater than the opening of the upper fixed resistor, the water flow will not increase any more, but will be equal to the water flow passing through the fixed valve opening above. Therefore, it is useless to open the lower transistor to a large opening. Therefore, we can calculate the maximum current of the fixed resistor 10V÷50Ω=0.2A, which is 200mA. That is to say, in the circuit, the base current increases and the collector current also increases. When the base current Ib increases to 2mA, the collector current increases to 200mA. When the base current increases again, the collector current will no longer increase, and it will not move at 200mA. At this time, the upper resistor also acts as a current limiter.  Let us understand the status of the IO in the microcontroller.Figure 5. AT89S51/52 The circuits with 24 IO ports of P1-P3 in the single-chip microcomputer are as shown in the figure above. Usually the purpose of using electronic circuits is to allow devices to obtain a certain current to make them work. For example, to make light-emitting diodes bright, a current of more than 1mA is generally required. However, the single-chip microcomputer is a smart chip. It can make logical analysis and judgments by detecting the voltage value of each IO port, and outputs high or low voltage as the result signal. Therefore, it can be seen that the IO ports of the single-chip microcomputer focus on voltage, not the current flowing through R and the transistor. Here what is the relationship between the voltage and current of the IO port in the single-chip microcomputer?  Continue the water pipe example.Suppose we let the valve of R open larger and let the control valve below be fully closed. At this time, as shown in Figure 6, it can be seen that the pressure at point P is the same as the water tank. When we fully open the following control valve, as shown in Figure 7, the water will flow through the pipeline with a large flow, and the pressure at point P is 0 at this time. This principle is very similar to electronic circuits. The logic quantity measured at the output point P is 1 (power supply voltage) or 0 (0 potential) by transistor turning off or on. However, there is a problem with this process, that is, when the output of point P is required to be 0, the transistor will be turned on very large, and the current flowing through it will be very large. There are 32 IO ports on the single-chip microcomputer, which consumes a lot of power. Look at Figure 8. If we close the upper valve R very small and close the lower control valve fully, then the pressure at point P will still the same as the water tank, which is the same as in Figure 6 above. When we open the control valve greatly, as shown in Figure 9, although the pressure at point P is also 0, the flow of water passing through at this time is greatly reduced. In this way, we can either output 1 or 0. So very little water is consumed. The circuit in the single-chip microcomputer does exactly this. The resistance R on it is about 50K, and the maximum current is 5V÷50K=0.1mA. In other words, when P outputs 1, no current is consumed, and when P outputs 0, the current consumed is 0.1mA. Because of its large pull-up resistance R, for beginners, it is necessary to have certain methods to directly drive LEDs or other loads. Here to share the various situations when the IO port is connected to the load.Figure 10. AT89S51/52 & 74HC373Let's take a look at the situation of connecting TTL devices first. When P1.0 is connected to an input pin of 74HC373, and the input impedance of TTL is very high, about a few hundred K to M ohm level. We assume 500K resistor to P1.0 to ground. In this way, when the transistor is turned on, the P1.0 point is at a low level, and a current of 0.1mA flows through Rc and then through the transistor to the ground, and no current flows through Ri. When the transistor is cut off, the current flows through Rc and then flows to the ground through Ri. Due to the resistor voltage divider effect, there are partial voltages on Rc and Ri, and the voltage at point P1.0 is the divided voltage of Rc and Ri. Total current is 5V÷(50K＋500K)=0.009mA, then the voltage at point P1.0 is 0.009mA×500K=4.5V. TTL stipulates that output 2.4~5V is high level. So this connection is correct. Now let's take a look at the situation of using S51 to drive the LED.AT89S51 Correct ConnectionLet’s take a look at the situation in Figure 11. Obviously, only P1.0 is a high potential to light the luminous tube, so the transistor must be cut off. In this case, the current flows through Rc to the luminous tube and then to the ground. To make the luminous tube turn on, there must be a threshold voltage exceeding 2.1V at both ends of the luminous tube. Therefore, the current flowing through the luminous tube is (5V-2.1V)÷50K=0.058mA, which is too weak to conduct.Look at Figure 12. It can be seen from the figure that P1.0 must be at a low potential if the luminous tube turned on. The transistor of the P1.0 port must be turned on. At this time, the current flows all the way through Rc to the transistor and then to the ground. The other way consumes 2.1V on the luminous tube. Then current flows through with almost no resistance, but the maximum current of the triode of the IO port cannot exceed 15mA. If it exceeds, the triode will be burned out, so this connection method is incorrect. So how can these two connections be able to drive the light-emitting tube? See below: AT89S51 Incorrect ConnectionLooking at Figure 13, a resistor Ri is connected between P1.0 and Vcc. When the transistor is turned on, two currents will flow through its c, e pole, one is the 0.1mA current on the internal R, and the other is the current on Ri. In order to prevent the transistor from over-current and burn out, we must make sure the resistance value, Ri=5V÷15mA=0.333K, which is about 330 ohms. At this time, the current flowing through the transistor is about 15mA, and the light-emitting tube is not bright at this time. When the transistor is turned off, both currents will flow through the luminous tube. The current flowing through the internal resistance of S51 is (5V-2.1V)÷50K=0.06mA, which is so small that we can ignore it. The current flowing through Ri is (5V-2.1V)÷330Ω=0.0087A, which is 8.7mA. However, the current consumed when the luminous tube is off is greater than the current consumed when the luminous tube is on. If many IO ports are used to light up many LEDs, such a circuit is not economical.Look at Figure 14, after connecting a resistor in series with the luminous tube between Vcc and P1.0. When the transistor is turned on, the two currents will flow through the c, e after confluence. The current on the internal resistance is still 0.1mA. The current on the ce should be less 15mA. If exceeds 15mA, the resistance is determined as (5V-2.1V) ÷ 15mA = 0.193K, which is about 200 ohms. In this way, the current flowing through the luminous tube is about 15mA, and the luminous tube is on. When the transistor is cut off, it blocks the paths of these two currents, so no current is consumed. Low level P1.0 directly drives the light-emitting tube. It can be seen that this circuit consumes 15mA of current when the light-emitting tube is on, and does not consume current when it is off, so this circuit is effective. S51 direct drive digital tube generally also uses this principle. Frequently Asked Questions about NPN Transistor1. What is meant by NPN transistor?An NPN transistor is the most commonly used bipolar junction transistor, and is constructed by sandwiching a P-type semiconductor between two N-type semiconductors. An NPN transistor has three terminals– a collector, emitter and base. The NPN transistor behaves like two PN junctions diodes connected back to back. 2. How do NPN transistors work?The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter "emits" electrons into the base, which controls the number of electrons the emitter emits. ... The transistor is kind of like an electron valve. 3. What is a NPN transistor used for?NPN transistors are mainly used in switching applications. Used in amplifying circuit applications. Used in the Darlington pair circuits to amplify weak signals. NPN transistors are used in the applications where there is a need to sink a current. 4. Which is better PNP or NPN transistor?A NPN transistor has electrons as majority charge carriers whereas the PNP transistor has holes as majority charge carrier. ... mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that's why they are preferred. 5. What does NPN mean?NPN stands for Negative, Positive, Negative. Also known as sinking.