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IntroductionOperational amplifier (op amp for short) is basically a voltage amplifying device designed to be used with components like capacitors and resistors, between its in/out terminals, or is simply a linear Integrated Circuit (IC) having multiple-terminals. In electronics, the open-loop voltage gain of the actual operational amplifier is very large, which can be seen a differential amplifier with infinite open loop gain, infinite input resistance and zero output resistance. In addition, it has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions. And meanwhile, it can be further simplified into an ideal op amp model, referred to as an ideal op amp (also called ideal OPAMP).CatalogIntroductionⅠ Ideal Op Amp Characteristics1.1 Infinite Input Resistance1.2 Zero Output Impedance1.3 Infinite Open-loop Gain1.4 Infinite Common-mode Rejection Ratio1.5 Infinite BandwidthⅡ Assumptions of Ideal Op AmpⅢ Working Characteristics of Ideal Operational Amplifiers3.1 Work in Linear Region3.2 Work in Nonlinear RegionⅣ Analysis of Ideal Operational Amplifier CharacteristicsⅤ Balanced Resistance Presets5.1 The Role of Balanced Resistance5.2 Input Balancing Resistor ExplanationⅥ Ideal Op Amp EquationsⅦ Several Common Op Amp CircuitsⅧ Difference Between Ideal Op-amp and Practical Op-ampⅠ Ideal Op Amp CharacteristicsWhen analyzing various application circuits of operational amplifiers, the integrated operational amplifier is often regarded as an ideal operational amplifier. The so-called ideal op amp is to idealize various technical indicators of op amps, and it must have the following characteristics.Characteristics of An Ideal Op-Amp1.1 Infinite Input ResistanceThe input terminal of an ideal operational amplifier does not have any current to flow in. In electronics, op amps are voltage gain devices. They amplify a voltage fed into the op amp and give out the same signal as output with a much larger gain. In order for an op amp to receive the voltage signal as its input, the voltage signal must be dropped across the op amp. If you know the concept of a voltage divider, voltage drops primarily across components with high impedances, proportionally according to ohm’s law by the formula V=IR. So the greater the resistance (or impedance) of a device, the greater the voltage drop across that device is. To make sure that the voltage signal drops fully on the op amp, it must have a very high input impedance, so that the voltage drops fully across it. If it had a low input impedance, the voltage may not drop across it and it would not receive the signal. This is why op amps must have high-input impedances.It’s also easy to make the input impedance lower (put a resistor in parallel) or the source impedance higher (put a resistor in series).Figure 1. Ideal Op Amp Symbol and Transfer Characteristic Curve 1.2 Zero Output ImpedanceThe output of an ideal op amp is a perfect voltage source, no matter how the current flowing to the amplifier load changes, the output voltage of the amplifier is always a certain value, that is, the output impedance is zero. In practice, zero output impedance is actually a distinct property from infinite input impedance, but for a very long time infinite input impedance was approached only with compromises in offset voltage and noise. 1.3 Infinite Open-loop GainIn an open-loop state, the differential signal at the input has an infinite voltage gain. This feature makes the operational amplifier very suitable for practical applications with upper negative feedback configuration. 1.4 Infinite Common-mode Rejection RatioAn ideal operational amplifier can only respond to the difference between the voltages at both ends of V+ and V-. In addition, the same part of the two input signals (ie common mode signal) will be completely ignored. What’s more, a high CMRR is required when a differential signal must be amplified in the presence of a possibly large common-mode input, such as strong electromagnetic interference (EMI). An example is audio transmission over balanced line in sound reinforcement or recording. 1.5 Infinite BandwidthThe ideal operational amplifier will amplify the input signal of any frequency with the same differential gain, which will not change with the change of signal frequency.Ⅱ Assumptions of Ideal Op AmpThe op amp can be considered a voltage controlled current source, or it is an integrated circuit that can amplify weak electric signals. Based on it, for an ideal OPAMP, what is the relationship between it and these electrical signals?First, assume that the current flowing into the input of the op amp is zero. This assumption is almost completely correct for FET op amps, because the input current for FET op amps is below 1pA. But for dual high-speed op amps, this assumption is not always correct, because the input current of it can sometimes reach tens of microamperes.Second, assume that the gain of the op amp is infinite, so the op amp can swing the output voltage to any value to meet the input requirements. It means that the output voltage of the op amp can reach any value. In fact, when the output voltage is close to the power supply voltage, the op amp will saturate. Maybe this hypothesis does exit, but needs a limit in practical. For example, at higher frequencies, the internal junction capacitors of transistor come into play, thus reducing the output and therefore the gain of amplifier. The capacitor reactance decreases with increase in frequency bypassing the majority of output. The opamp is in saturation state.Figure 2. Op Amp SaturationFor example, as per datasheet of LM741, large signal voltage gain is 200V/mv. It means an open loop gain of 200,000. If you operate an op-amp in open-loop condition(i.e. without negative feedback) ,even microvolts of input voltage (input offset voltage of LM741 is 3mv) will drive the output to saturation.In most of the amplifier circuits op-amp is configured to use negative feedback which greatly reduces the voltage gain (i.e. closed loop gain). In oscillators and schmit triggers, Op-amp is configured to use positive feedback. Comparator circuit is an example of the circuit which utilizes open-loop gain of op-amp. Its output will be always at saturation either positive or negative saturation. In an integrator circuit, the DC gain should be limited by adding a feed back resistor in parallel with capacitor ;else the output will get saturated .Even in amplifier circuits, the amplitude of the input signal and the voltage gain of the circuit should be balanced so that the output voltage does not exceed power supply voltage . For example for a non-inverting amplifier with a voltage gain of 100, the maximum permissible input voltage will be 150 mv if the VCC is 15 Volts. If you apply a signal of 200 mv ,the op-amp output will goto saturation as the required output will be 20 volts which exceeds the VCC of 15 Volts.Third, the assumption of infinite gain also means that the input signal must be zero. The gain of the op amp will drive the output voltage until the voltage (error voltage) between the two input terminals is zero. The voltage between the two input terminals is zero. The zero voltage between two input terminals means that if one input terminal is connected to a hard voltage source like ground, the other input terminal will also be at the same potential. In addition, since the current flowing into the input terminal is zero, the input impedance of the op amp is infinite.Fourth, of course, the output resistance of an ideal op amp is zero. An ideal op amp can drive any load without any voltage drop due to its output impedance. At low currents, the output impedance of most op amps is in the range of a few tenths an ohm, so this assumption is true in most cases. Ⅲ Working Characteristics of Ideal Operational Amplifiers3.1 Work in Linear RegionWhen the ideal op amp works in the linear region, the output and the input voltage show a linear relationship. Where u0 is the output voltage of the integrated op amp; u+ and u- are the voltages at the non-inverting input terminal and the inverting input terminal, respectively. Auo is the open loop differential voltage magnification. According to the characteristics of the ideal op amp, two important characteristics of the ideal op amp in the linear region.1) Zero differential input voltageSince the open-loop differential voltage magnification of an ideal op amp is equal to infinity, and the output voltage is a certain value, the voltage values at the non-inverting input terminal and the inverting input terminal are approximately equal. Just like short circuit between input and output, but it is fake. Because it is an equivalent short circuit, not a real short circuit, so this phenomenon is called "virtual short".2) Zero input currentSince the open-loop input resistance of an ideal op amp is infinite, no current flows into the op amp at either input. At this time, the current at the non-inverting input terminal and the inverting input terminal are both equal to zero. Like an disconnection, but an equivalent disconnection, so this phenomenon is called "virtual break". Virtual short and virtual break are two important concepts for analyzing the ideal op amp working in the linear region.In fact, the ideal operational amplifier has the characteristics of "virtual short" and "virtual break". These two characteristics are very useful for analyzing linear amplifier circuits. The necessary condition for virtual short is negative feedback. When negative feedback is introduced, at this time, if the forward terminal voltage is slightly higher than the reverse terminal voltage, the output terminal will output a high voltage equivalent to the power supply voltage after the amplification of the op amp. In fact, the op amp has a respond time changing from the original output state to the high-level state (the golden rule of analyzing analog circuits: the change of the signal is a continuous change process). Due to the feedback resistance of the reverse end change will inevitably affect its voltage, when the reverse end voltage infinitely close to the forward end voltage, the circuit reaches a balanced state. The output voltage does not change anymore, that is, the voltage at the forward end and the reverse end is always close. (Note: The analysis method is the same when the voltage decreases.) 3.2 Work in Nonlinear RegionWhen the op-amp operates in the nonlinear region, the output voltage no longer increases linearly with the input voltage, but saturates. The ideal op amp also has two important characteristics when operating in the nonlinear region.1) When u+ ≠ u-, the output voltage of the ideal op amp reaches the saturation value.When u+ > u-, the op-amp operates works in positive saturation region with a positive output voltage.When u+ < u-, the op-amp operates works in negative saturation region with a negative output voltage.Ideal op amp operates in the nonlinear region, u+ ≠ u-, there is no “virtual short”.2) The input current is equal to zero.Although the input voltage u+ ≠ u- above, the input current is considered to be zero. Ⅳ Analysis of Ideal Operational Amplifier CharacteristicsAs for Op-amp, there's probably a description like this: three-terminal element (circuit structure with double-ended input, single-ended output), ideal transistor, high-gain DC amplifier.(1) High input resistanceUnder this situation, the current flowing into the input terminal is close to 0, almost no signal source current is used, which is close to the voltage control characteristic. And virtual break is derived from this.(2) Lower output resistanceIt has the characteristics of adapting to any load. And the impedance of the subsequent load circuit will not affect the output voltage.(3) Infinite voltage amplification(4) Under a certain supply voltage condition, the amplifier can only work in closed-loop (negative feedback) mode, and the actual amplification is limited. Because op-amps themselves don't have a 0V connection but their design assumes the typical signals will be more towards the center of their positive and negative supplies. Thus, if your input voltage is right at one extreme or forces the output toward one supply, chances are it won't work properly. Working in open-loop mode is the like a comparator, and the output is high level orlow level.In the closed-loop (limited amplification) state, the amplifier is randomly compare the potentials of the two input terminals. The output stage makes immediate adjustments when they are not equal. So the final purpose of amplification is to make the potentials of the two input terminals equal. And virtual short is derived from this. Ⅴ Balanced Resistance Presets5.1 The Role of Balanced Resistance1) A suitable resistance is generally required to ensure that the input impedance is matched.2) In order to reduce the input current imbalance, the in-phase resistor should be equal to the parallel value of the two resistors at the reverse end in theory. In practice, as a result of the closed loop, especially in deep negative feedback conditions, the misalignment is not obvious at the output. And there is no need of in-phase grounding resistor when the misalignment is not the main problem. Because a balanced resistor is the starting point for an ideal op amp. In-phase grounding resistance is useful for bipolar op amps, and has no meanings for MOS-type op amps.3) Ground input termination resistance: it is necessary for impedance matching and high frequency setting.4) Bias current and offset current.For operational amplifiers with bias current greater than offset current, input resistance matching can be reduced, and precision circuits can compensate bias current to a minimum. If the bias current and offset current are similar, the matching resistance will increase the error.5) Set for the bias current at the input, the purpose of which is to equalize the impedance of the invertingand non-inverting inputs, so that two inputs with equal bias currents are assumed to have equal voltage drops, thereby counteraction can be made. 5.2 Input Balancing Resistor ExplanationA op-amp is connected to an inverting amplifier:Set the input resistance for R1, feedback resistance for Rfi,Assume that the non-inverting end is not connected to a balanced resistor, but grounded directly.Set the input bias current for the op-amp IB (same voltage in inverting and non-inverting end).The current flows through R1 and Rf are represented by I1 and If.Inverting voltage is V-, The op-amp gain is A.Use KCL in the inverting end (set the input signal to 0).Where (0-V-)/R1- (A+1)V- /Rf=IBFrom the above equation, it follows that V-=-(IB×R1×Rf/(Rf+(A+1)R1))At this time, the output voltage of the op-amp is Vo=A×(IB×R1×Rf/(Rf+(A+1)R1))The above formula can be approximated as Vo=IB×((A×R1)/Rf)If the in-phase terminal passes through a resistor R2 to ground and R2=R1/Rf, then the voltage at the in-phase terminal is V+=-IB×R2KCL is applied to the inverted terminal, where (0-V-)/R1+(A×(V+-V-)-V-)/Rf=IBAt this time the output voltage of the op-amp is Vo=0. Ⅵ Ideal Op Amp EquationsUnderstanding the basic conditions of an ideal op amp, and combining it with the Kirchhoff's current law (KCL) node voltage method and the superposition theorem of the node, is an effective method to analyze the ideal op amp circuit.As shown below, find the output voltage uoFigure 3. OPAMP Circuit1) Equation based on KCLFrom the concept of virtual break, i+=i-=0, then i1=i2, i3=i4, so (a)Based on virtual break, u+=u-, then (b)2) Node voltage methodList the node voltage equations for node 1 and node 2, and get (c)Note: Because the output current of the op amp is unknown at 1) and 2), it is not possible to list the KCL equation or node voltage equation at the output of the op amp. In addition, the op amp output uo in 2) should be treated as an independent voltage source. 3) Superposition theoremWhen there are multiple signal inputs, choosing the superposition theorem to solve can simplify the analysis and calculation process. The size of the output signal uo can be regarded as the superposition of the output signal obtained by the independent action of u1 and u2. When u1 acts alone, the u2 terminal is grounded, and the op amp output is: (d)Therefore, the final output of the operational amplifier is:   (e) Ⅶ Several Common Op Amp CircuitsNon-inverting Amplifier CircuitA non-inverting amplifier is an op-amp circuit configuration which produces an amplified output signal. It provides a high input impedance along with all the advantages gained from using an operational amplifier. Inverting Amplifier CircuitAn inverting amplifier (also known as an inverting operational amplifier or an inverting op-amp) is a type of operational amplifier circuit which produces an output which is out of phase with respect to its input by 180 degrees out of phase with respect to input signal. In the following figure, two external resistors to create feedback circuit and make a closed loop circuit across the amplifier. Op-amp as AdderAn adder circuit can be made by connecting more inputs to the inverting op amp. The circuit diagram of a summing amplifier is as shown in the following figure. Differential AmplifierDifferential amplifier is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages. It is a very useful op-amp circuit and by adding more resistors in parallel with the input resistors as shown in the following. Composite AmplifierThe composite amplifier is termed as a combination of multiple operational amplifiers that are cascaded together with a negative-feedback loop around the entire network. The resistance in the circuit is generally selected at the K ohm level, the ratio of the resistance affects the gain and bias, in addition, the supply current, frequency response and capacitive load driving capability of the op amp determine their specific values in circuits. If it is used in a high-frequency circuit, the resistance needs to be reduced to obtain a better high-frequency response, but it will increase the input bias current, thereby increasing the current of the power supply. Ⅷ Difference Between Ideal Op-amp and Practical Op-ampIdeal op amps use no power, have infinite input impedance, unlimited gain-bandwidth and slew rate, no input bias current, and no input offset. They have unlimited voltage compliance.Practical op amps consume some power, have very high input impedance have limited gain-bandwidth and limited slew rate, have some input bias current and input offset voltage. Voltage compliance is limited by the power supply rail, or frequently even less.Still practical op amps are very useful because most of the limitations listed above are way better than what your circuit needs.For an ideal amplifier, it does not draw any current at all from its input. Assuming a two input amplifier the signal current in both input probes is zero. In other words the input impedance must be infinite. The output, should operate as the output of an ideal voltage source. This means that the potential between the output and the ground must be A(v2−v1), no matter how much current would a load connected to the output would draw. In other words the output impedance must be zero.For a real amplifier, the input impedance must be as large as possible while the output impedance must be as low as possible.In fact, An op-amp in real life, however, cannot operate with zero current flow. Frequently Asked Questions about Ideal Op Amp1. What is characteristic of ideal opamp?Ideal op amps will have infinite voltage gain, infinitely high impedance, zero output impedance, its gain is independent of input frequency, it has zero voltage offset, its output can swing positive or negative to the same voltages as the supply rails, and its output swings instantly to the correct value. 2. How does an ideal op amp work?An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... Open-loop voltage gain runs very high, on the order of 1 million. 3. Why are op amps not ideal?Op-amps with FET inputs have an Ibias that is so small that this method becomes less practical. Instead of measuring the voltage drop across a resistor, one can monitor the change in voltage across a capacitor as it is charged by the bias current. 4. How are real op amps different from ideal op amps?In real op amps, the amplified signal will not fully reach the DC supply rails. They will fall short of it. In an ideal op amp, the output will swing instantly to the amplified voltage value. There will be no time delay between the time the voltage is input into the op amp till the time it is output. 5. What are the four main ideal characteristics of an open-loop op amp?An ideal op amp is usually considered to have the following characteristics:Infinite open-loop gain G = vout / vInfinite input impedance Rin, and so zero input currentZero input offset voltageInfinite output voltage rangeInfinite bandwidth with zero phase shift and infinite slew rateZero output impedance R

Ⅰ IntroductionAs for operational amplifier applications, in electronic circuit, it is usually combined with a feedback network to form a certain functional module, with a special coupling circuit and feedback. Its output signal can be input signal addition, subtraction or differentiation, integration, etc, which early used in analog computers to do mathematical operations. Now they widely used in the electronics industry, regarded as precision AC and DC amplifiers, active filters, oscillators and voltage comparators.This Video is Introducing Operational Amplifier Applications in the CircuitCatalogⅠ Introduction1.1 Integrated Op AmpⅡ Op-amp ParametersⅢ Application MattersⅣ Classic Amplifier CircuitsⅤ One Question Related Op Amp and Going Further5.1 Question5.2 Answer1.1 Integrated Op Amp1.1.1 Evaluation AnalysisIntegrated operational amplifiers are one of the most widely used devices in analog integrated circuits. In various systems, because of different application requirements, the performance requirements of operational amplifiers are also different.Where there are no special requirements, try to use a universal integrated operational amplifier as much as possible, which can reduce costs and easily replace. When using multiple op amps in a system, use as many op amp integrated circuits as possible. For example, LM324 and LF347 always integrate four op amps together in a circuit.The evaluation of integrated op amps depends on their overall performance. Generally, the merit coefficient K is used to measure the excellent degree of integrated operational amplifiers, which is defined as: where SR is the slew rate and the unit is V / ms. The larger the value, the better the AC characteristics of the operational amplifier; The input bias current of the amplifier is lib, the unit is nA; VOS is the input offset voltage in mV. The smaller the Iib and VOS values, the better the DC characteristics of the op amp. Therefore, for circuits that amplify AC signals such as audio and video, op amps with large SR are better; for circuits that handle weak DC signals, op amps with high accuracy are more suitable (both offset current, offset voltage and temperature drift are relatively small).When selecting an integrated op amp, some factors should be considered in addition to the figure of merit coefficient K. For example, the signal source is a voltage source or a current source; the nature of the load, and whether the output voltage and current of the integrated op amp meet the requirements; operating voltage range, power consumption, and volume of the integrated op amp.Figure 1. Using Operational Amplifier as a Comparator1.1.2 Integrated Op Amp Basics Power supplyThe integrated op amp has two power terminals + VCC and -VEE, with different power supply methods. For different power supply modes, the requirements for input signals are different.1) Dual power supplyOp amps are mostly powered in this way. The positive power (+ E) and negative power (-E) relative to the common terminal (ground) are connected to the + VCC and -VEE pins of the op amp, respectively. In this way, the signal source can be directly connected to the input pin of the op amp, and the amplitude of the output voltage can make the positive and the negative symmetrical.2) Single power supplySingle-supply operation connects the -VEE pin of the op amp to ground. At this time, in order to ensure that the internal unit circuit of the operational amplifier has a suitable static operating point, a DC potential must be added to the input end of the op amp. Zero settingDue to the influence of the input offset voltage and input offset current of the integrated op amp, when the input signal is zero, the output is often not equal to zero. In order to improve the operation accuracy of the circuit, it is required to compensate the error caused by the offset voltage and the offset current. This is the zero setting of the operational amplifier. Commonly used zeroing methods include internal zeroing and external zeroing. For integrated op amps without internal zeroing terminals, external zeroing methods should be used. Self oscillationThe operational amplifier is a high-amplitude multi-stage amplifier. Under the condition of deep negative feedback, it is easy to cause self-excited oscillation. To make the amplifier work stably, a certain frequency compensation network must be added to eliminate the self oscillation. In addition, to prevent low-frequency oscillation or high-frequency oscillation caused by the internal resistance of the power supply, an electrolytic capacitor (10mF) and a high-frequency filter capacitor (0.01 mF ~ 0.1mF) should be connected. Device protectionThere are three aspects to the protection of the integrated op amp safety: power protection, input protection and output protection.1) Power protectionCommon faults of power supply are reverse polarity and voltage jump. For a power supply with poor performance, voltage overshoot often occurs at the moment when the power is turned on and off. Protection measures such as the use of FET current source and voltage regulator clamping protection. The voltage regulator’s voltage value is greater than the normal operating voltage of the integrated op amp and less than the maximum allowable operating voltage of the integrated op amp, and the current of the FET tube should be greater than the normal operating current of integrated op amp.2) Input protectionIf the input differential/common mode voltage of the integrated op amp is too high beyond the limit parameter range of the integrated op amp, it will be damaged.3) Output protectionWhen the integrated op amp is overloaded or the output is shorted, the op amp will be damaged if there is no protection circuit. However, some integrated op amps have internal current limit protection or short circuit protection, and no additional output protection is required to use these devices.Figure 2. An Inverting Op Amp CircuitⅡ Op-amp ParametersTo use the op amp better in the circuit, you must have a certain understanding of its internal parameters. Here are the technical parameters closely related to the op amp: Unity-gain bandwidth Definition: Under the condition that the closed-loop gain of the op amp is 1 time, a constant amplitude sinusoidal small signal is input to the input end of the op amp, and the closed-loop voltage gain measured from the output end of the op amp is reduced by 3dB (or equivalent to 0.707 times of the input signal of the op amp), that is to say, the frequency at which the output signal is reduced by -3dB is unity-gain bandwidth. It is a very important indicator. For a sinusoidal small signal amplification, the unity-gain bandwidth is equal to the product of the input signal frequency and the maximum gain at that frequency. In other words, when you know the frequency and gain of the signal to be processed, the unity-gain bandwidth (gain bandwidth = amplification * signal frequency) can be calculated to select the appropriate op amp. The higher the bandwidth, the higher the frequency of the signal that can be processed, and the better the high frequency characteristics, otherwise the signal will be easily distorted.    For small signals, the unity-gain bandwidth is also called the gain-bandwidth product, which can roughly show the ability of the op amp to process the frequency of the signal. For example, the gain bandwidth of a certain operational amplifier is 1MHz, if the actual closed-loop gain is 100, then the maximum frequency for theoretical processing of small signals is 1MHz / 100 = 10KHz.For the bandwidth of a large signal, that is, the power bandwidth, the influence of the slew rate SR is the major factor, and the unit is V/uS. In this case, the power bandwidth calculated by FPBW = SR / 2πVp-p, that is, the gain bandwidth and power bandwidth must be satisfied at the same time when designing the circuit.For DC signals, bandwidth issues are generally not considered, and accuracy and interference are mainly considered.When the amplification factor of an amplifier is n times, it does not mean that all input signals are amplified n times. When the signal frequency increases, the amplification capability decreases. Open bandwidthThe open-loop bandwidth is defined as: inputting a constant-amplitude sinusoidal small signal to the input of the op amp, the frequency measured at which the open-loop voltage gain decrease 3dB from the output of the op amp to the dc gain of the op amp. This is used for very small signal processing. Slew rate SRWith the op amp connected in a closed loop, a large signal (including a step signal) is input to the input of the op amp, and the output rise rate of the op amp is measured from the output of the op amp called SR. Because the input stage of the op amp is switched during the conversion, the feedback loop of the op amp does not work, that is, the conversion rate is independent of the closed-loop gain. The slew rate is a very important index for large signal processing. For general op amps, the slew rate SR <= 10V / μs, and the slew rate of high speed op amps is SR> 10V / μs. The highest conversion rate SR of current high-speed op amps reaches 6000V / μs. The larger the SR, the better the response of the op amp to the input signal changing at high speed. The larger the signal amplitude, the higher the frequency, and the greater the SR. This is used for op amp selection in large signal processing. Full-power bandwidthAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, a constant-amplitude sinusoidal large signal is input to the input end of the op amp, so that the output frequency of the op amp reaches the maximum (allowing certain distortion) signal. This frequency is limited by the slew rate SR of the op amp. Approximately, full power bandwidth is calculated by formula SR / 2πVop (Vop is the peak output amplitude of the op amp). It is a very important indicator for op amp selection in large signal processing. Setting timeAt the rated load, under the condition that the closed-loop gain of the op amp is 1 time, the time required to input a step large signal to the input of the op amp to increase the output from 0 to a given value. Because it is a step large signal input, a certain jitter will occur after the output signal reaches a given value. This jitter time is called the stabilization time. At this moment, stabilization time + rise time = settling time. For different output accuracy, there is a big difference in the stabilization time. The higher the accuracy, the longer the stabilization time. Equivalent input noise voltageIt refers to any AC random interference voltage generated at the output of an op amp with good shielding and no signal input. When this noise voltage is converted to the input of the op amp, it is called the input noise voltage of the op amp (sometimes expressed by noise current). For broadband noise, the effective value of the input noise voltage of ordinary op amps is about 10 ~ 20μV. This value often corresponds to a certain frequency band. Output impedanceIt refers to the ratio of the change in voltage to the corresponding change in current when the signal voltage is applied to the output of the op amp working in the linear region. At low frequencies it only refers to the output resistance of the op amp. Common mode input resistenceRefers to the ratio of the change in the input voltage of the common mode to the corresponding change in the input current when the two inputs of the op amp input the same signal. At low frequencies, it behaves as a common mode resistance. Generally, the common mode input impedance of the op amp is much higher than the differential mode input impedance, with a typical value above 108Ω. Common mode rejection ratioSame as the definition in the differential amplifier circuit, it is the ratio of the differential mode voltage gain to the common mode voltage gain, which is usually expressed in decibels. It is a parameter that measures the degree of symmetry of the input stage differential amplifier and the ability of the integrated op amp to suppress common mode interference signals. The larger the value, the better. Power supply rejection ratioThe power supply voltage rejection ratio is defined as the change ratio of the input offset voltage of the op amp with the power supply voltage in the linear region. The power supply voltage rejection ratio reflects the effect of power supply changes on the output of the op amp. At present, the power supply voltage suppression ratio is only about 80dB. Therefore, when used for DC signal or small signal processing for analog amplification, the power supply of the op amp needs to be carefully set. Of course, an op amp with a high common mode rejection ratio can compensate a part of the power supply voltage rejection ratio. In addition, when using dual power supplies, the power supply voltage rejection ratio of the positive and negative power supplies may be different. Differential mode input resistanceRefers to the ratio of the change in voltage at the two input terminals to the corresponding change in current at the input terminals when the op amp is operating in the linear region. The differential mode input impedance includes the input resistance and input capacitance, and refers only to the input resistance at low frequencies. General products specification only give input resistance. The input resistance of the op amp using the bipolar transistor as the input stage is not greater than 10MΩ; the input resistance of the op amp as the input stage of the field effect transistor is generally greater than 109Ω. Input offset voltageWhen the input voltage is zero, the output voltage is divided by the voltage gain, plus the negative sign, which is the offset voltage converted to the input. It is the compensation voltage applied at the input when the output voltage is zero. The input offset voltage actually reflects the circuit symmetry inside the op amp. The better the symmetry, the smaller the input offset voltage. The input offset voltage is a very important indicator of the op amp, especially when it is a precision op amp or used for DC amplification.The input offset voltage has a certain relationship with the manufacturing process. It is between ± 1 and 10 mV when op amps use the bipolar process (that is, the standard silicon process). If the field effect tube is used as the input stage, it will be greater. For precision op amps, it is generally below 1mV. The smaller the input offset voltage, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset voltage driftWithin the specified operating temperature range, it is the ratio of the change in input offset voltage with temperature to the change in temperature. It is actually a supplement to the input offset voltage, which is convenient for calculating the drift of the amplifier circuit due to temperature changes within a given operating range. It is an important indicator for measuring the temperature effect to the op amp. Under normal circumstances, it is about (10 ~ 30) uV / C (degree Celsius), the high quality can be <0.5uV / C. Input offset currentIt is defined as the difference between the base current of the differential pair of the differential input stage when the output DC voltage of the op amp is zero. Used to characterize the degree of asymmetry of the differential input current. The better the symmetry, the smaller the input offset current. Input offset current is a very important indicator for op amps, especially for precision operational amplifier or DC amplifier. The input offset current is approximately one to one-tenth of the input bias current. It has an important impact on small signal precision amplification or DC amplification, especially when a large resistor is used outside the op amp. The effect of input offset current may exceed the effect of input offset voltage on accuracy. The smaller the input offset current, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps. Input offset current temperature driftWithin the specified operating temperature range, the ratio of the amount of change in input offset current with temperature to the amount of temperature change. It refers to the temperature coefficient of within the specified operating range, and is also an important indicator to measure the temperature effect on the op amp. It is usually about (1-50) nA / C, and the high quality is about several pA / C. This value is only given in the precision op amp parameters, and it needs attention when it is used for DC signal processing or small signal processing. Input bias current   It is defined as the average value of the bias currents of the two input terminals when the output DC voltage of the op amp is zero, in other words, it is the average current flowing into the input terminal when the operational amplifier is operating in the linear region. The input bias current has a greater impact on the places where input impedance is required, such as high-impedance signal amplification and integrator circuits. The input bias current has a certain relationship with the manufacturing process. If a field effect tube is used as the input stage, the input bias current generally lower than 1nA. It always used to measure the input current of the differential amplifier pair. Maximum differential mode input voltageIt is a voltage that the two input ends of the op amp can withstand. When it is exceeded, the reverse breakdown of the differential tube will occur. The NPN tube made by the plane process has a value of about 5V, and the Vidmax of the horizontal PNP tube can reach more than 30V. Maximum common mode input voltageIt an allowable range of common mode input voltage under normal operating conditions of the op amp. When the input differential pair saturates, the amplifier loses common mode rejection ability. In the case of interference, it is necessary to pay attention to this problem in the use of the circuit. Output peak to peak voltageWorking in the linear region, under the specified load, when the op amp is powered by the large power supply, it is the maximum voltage amplitude that the op amp can output. Except for low voltage op amps, the output peak-to-peak voltage of general op amps is greater than ± 10V, but less than the power supply voltage. This is due to the design of the output stage. The output stage of modern low-voltage op amps has been specially treated. The output peak-to-peak voltage is close to within 50mV of the power supply voltage, so it is called a full-scale output op amp, also known as a rail-to-raid op amp. It should be noted that the output peak-to-peak voltage of the op amp is related to the load, and the value is different for different loads; the positive and negative output voltage swings of the op amp are not necessarily the same. For practical applications, the closer the output peak-to-peak voltage is to the supply voltage, the easier the power supply design.Figure 3. Input Offset Voltage of an Op-ampⅢ Application Matters1) A single-supply op amp must be DC biased, otherwise it will not work properly. For the virtual ground design, in addition to the DC potential, it is necessary to pay attention to the voltage stabilization (it is best to use the reference voltage chip), and also to ensure low impedance AC decoupling, that is, low-frequency decoupling parallel to at least 10uF and high frequency decoupling under 0.1uF.2) The input of the non-inverting amplifier must be biased to ground as a DC path.3) Ordinary op amps cannot directly drive capacitive loads. If there is need, you must use capacitors for phase compensation or output series resistors and then connect the load.4) For the op amp input of the external interface, a TVS tube must be connected in parallel to the positive and negative input pins to prevent the op amp from reversing the polarity due to the too large input voltage signal, forming a parasitic false signal output.5) For amplifier circuits with a gain of more than 10 times, pay attention to controlling the bandwidth gain of the op amp to prevent the device from self oscillation.6) The output of the power amplifier needs to be protected by switching diodes to the power supply and ground, especially when inductive loads are connected.7) When using multiple op amps to process multiple signals, care must be taken to prevent the instantaneous changes in one of the signals from causing crosstalk to the other signal. Therefore, it is recommended not to use one op amp to process multiple signals.8) Most op amp chips are ESD sensitive devices, so pay more attention when using them.9) The pins of unused op amps (excess channels in multiple op amps) should not be left floating, and  grounded or connected to positive and negative power supplies. It is recommended to connect it as a follower (the output is connected to the reverse input) and the non-inverting input is connected to a potential between the power rails (the ground of the dual power system or any suitable point in the circuit). They can also used as buffer amplifiers and add them to a small impact location in the system.Figure 4. Op Amp 741Ⅳ Classic Amplifier CircuitsFigure 5. Inverting AmplifierFigure 5: The grounded non-inverting terminal of op amp is 0V. The inverting and non-inverting terminals are short-circuit, so the inverting end is also 0V. The input resistance of the inverting input terminal is very high, and it is virtual open. In other words, there is almost no current pass through. Therefore, the current flowing through each component in a series circuit is the same, that is, the current flowing through R1 and R2 are the same.Current flowing through R1: I1 = (Vi-V-)/R1Current flowing through R2: I2 = (V--Vout)/R2V- = V+ = 0, I1 = I2Solve the above algebraic equation to get Vout = (-R2/R1)*Vi, it is the input-output relationship of the inverting amplifier. Figure 6. Non-inverting AmplifierIn Figure 6, Vi and V- are virtual short, where Vi = V-. Because of the virtual open, there is no current flow through at the reverse input terminal, then R1=R2. If the current is I, which is obtained by Ohm's law: I = Vout/(R1+R2);Vi is equal to the partial voltage on R2, that is: Vi = I*R2.Virtual short: Vi = V-, R1=R2Ohm's law: I = Vout/(R1+R2), Vi = I*R2Where Vout=Vi*(R1+R2)/R2, represents the non-inverting amplifier. Figure 7. AdderFigure 7: Knowing from the Kirchhoff's law and virtual open theory, the sum of the current through R2 and R1 is equal to the R3, V- = V+ = 0 (short circuit), so (V1 – V-)/R1 + (V2 – V-)/R2 = (Vout – V-) /R3 can be transferred as V1/R1 + V2/R2= Vout/R3. If R1=R2=R3, then the formula becomes Vout=V1+V2, which is an adder. Figure 8. AdderIn Figure 8, because of the virtual open, no current flows through the non-inverting terminal, where V+ = V-, R1=R2, R4=R3, therefore, (V1 – V+)/R1 = (V+-V2)/R2, (Vout – V-)/R3 = V-/R4 can be simplified as V+ = (V1 + V2)/2 V- = Vout/2. So Vout = V1 + V2 is also an adder. Figure 9. SubtractorFigure 9 shows that the current through R1 is equal to the R2, and R4=R3, therefore, (V2– V+)/R1 = V+/R2, (V1 – V-)/R4 = (V--Vout)/R3. If R1=R2, then V+ = V2/2; if R3=R4, then V- = (Vout + V1)/2, because of V+ = V-, so Vout =V2-V1 is a subtractor. Figure 10. Integrator CircuitIn Figure 10, the input voltage at the inverting terminal is equal to the non-inverting terminal because of short circuit; the current through R1 is equal to the C1 because of virtual open. The current flowing through R1 and C1 are Ri=V1/R1, Ci=C*dUc/dt=-C*dVout/dt, respectively. So Vout=((-1/(R1*C1))∫V1dt, which is a integrator circuit. If V1 is a constant voltage U, then the above formula is transformed to Vout = -U*t/(R1*C1)t, then the Vout is a straight line that changes with time. Figure 11. Differential CircuitIn Figure 11, the current through capacitor C1 and resistor R2 is equal because of virtual open; V+ = V- because of short circuit, where Vout = -i * R2 = -(R2*C1)dV1/dt, which is a differential circuit. If V1 is a DC voltage, the output Vout corresponds to a pulse in the opposite direction to V1. Figure 12. Differential Amplifier CircuitFigure 12:Vx = V1……a, Vy = V2……bthen R1, R2, R3 can be regarded as a series, R1=R2=R3, the current I=(Vx-Vy)/R2……cwhere Vo1-Vo2=I*(R1+R2+R3) = (Vx-Vy)(R1+R2+R3)/R2 ……dIf R6=R7, then Vw = Vo2/2 ......e, similarly, if R4=R5, then Vout – Vu = Vu – Vo1, so Vu = (Vout+Vo1)/2 ……fdue to short circuit, Vu = Vw ……g, based on efg formulas, Vout = Vo2 – Vo1 ……hGet from dh, Vout = (Vy – Vx) (R1+R2+R3)/R2, where (R1+R2+R3)/R2 is a fixed value. This value determines the amplifier multiple of the difference (Vy-Vx), thus it is a differential amplifier circuit. Figure 13. Amplifier CircuitIt is a relatively common amplifier circuit. Many controllers accept 0~20mA or 4~20mA current from various measuring instruments. The circuit converts the current into voltage signal to become a digital signal by ADC. Figure 13 is such a typical circuit. As shown in Figure, 4~20mA current flows through the sampling 100Ω resistor R1, there will be a voltage difference of 0.4~2V on R1. Due to virtual open circuit, R3= R5 and R2=R4.Therefore: (V2-Vy)/R3 = Vy/R5 ……a  (V1-Vx)/R2= (Vx-Vout)/R4 ……bShort circuit: Vx = Vy ……cCurrent changes from 0~20mA, then V1 = V2 + (0.4~2) ……dPut cd formulas into b formula: (V2 +(0.4~2)-Vy)/R2 = (Vy-Vout)/R4 ……eIf R3=R2 , R4=R5, then e-a gets Vout =-(0.4~2)R4/R2 ……fIn Figure 13, R4/R2=22k/10k=2.2, then f formula Vout = -(0.88~4.4)V, that is to say, the current of 4~20mA is converted into a voltage range of -0.88~-4.4V. Current can be converted into voltage, and voltage can also be converted into current. Figure 14 is such a circuit. The negative feedback in the above figure does not directly feedback through the resistor, but the emitter junction of the transistor Q1 is connected in series. But it isn't a comparator. As long as it is an amplifying circuit, the law of short circuit and virtual open still conforms.Figure 14. Amplifier CircuitDue to virtual open, no current flows through the input of the op amp,Then (Vi – V1)/R2 = (V1 – V4)/R6 ……aSimilarly (V3 – V2)/R5 = V2/R4 ……bsince short circuit, V1 = V2 ……cIf R2=R6, R4=R5, then V3-V4=Vi can be obtained from abc.The above formula shows that the voltage across R7 is equal to the input voltage Vi, then the current through R7 is I=Vi/R7. If the load RL<100KΩ, the current through R1 and R7 are basically the same. Ⅴ One Question Related to Op Amp and Going Further5.1 QuestionWhat the Application of an Op Amp as a Phase Shifter?5.2 AnswerIn electronic circuit, op amp is used for direct coupling procedure and so DC voltage level at the emitter terminal increases from phase to phase. This rapidly increasing DC level is likely to shift the operating point of the upcoming stages. Thus to move down the increasing voltage swing, this phase shifter is applied.The phase shifter performs by adding a DC voltage level to the output of fall stage to pass the output to a ground level. Frequently Asked Questions about Operational Amplifier Applications1. Why is it called operational amplifier?It's called an “operational” amplifier because it performs a mathematical operation. The most obvious one is multiplication - it amplifies an input signal by a constant. ... But many different 'operations' can be performed by different circuit topologies. 2. What is inside an operational amplifier?Operations amplifiers — op-amps for short, are integrated circuits, constructed mostly out of transistors and resistors. These integrated circuits multiply an input signal to a larger output. You can use these components with voltage and current in both DC and AC circuits. 3. What are operational amplifiers used for?Op amps are used in a wide variety of applications in electronics. Some of the more common applications are: as a voltage follower, selective inversion circuit, a current-to-voltage converter, active rectifier, integrator, a whole wide variety of filters, and a voltage comparator. 4. What are linear applications of op amp?A linear amplifier like an op amp has many different applications. It has a high open loop gain, high input impedance and low output impedance. It has high common mode rejection ratio. Due to these favourable characteristics, it is used for different application. 5. How does an operational amplifier work?An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... That is, the output gets fed back to the inverting input through some impedance. 6. What do you mean by differential amplifier?A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages. 7. What are the non linear applications of op amp?Non-Linear Applications of Op AmpVoltage comparator.Two applications of comparator as window detector and zero crossing detector.Schmitt trigger circuit with the extension of regenerative comparator.Multivibrator circuits.Precision rectifier or super diode with the combination of op amp as voltage follower and a diode. 8. Why do we use differential amplifier?Differential amplifiers are used mainly to suppress noise. ... Noise is generated in the wires and cables, due to electromagnetic induction, etc., and it causes a difference in potential (i.e., noise) between the signal source ground and the circuit ground. 9. What does an operational amplifier do?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. 10. 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.

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

IntoductionAn operational amplifier, or op-amp for short is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential that is typically hundreds of thousands of times larger than the potential difference between its input terminals, and is a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. They are used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.In this video, the basic introduction of the Operational Amplifier (Op-Amp) has been given and different characteristics of ideal and real Op-amp (General Purpose 741 Op-Amp) has been discussed. CatalogIntroductionⅠ Operational Amplifier Basics1.1 Amplification Principle1.2 Balance Resistor1.3 Feedback Resistor in Parallel with a Capacitor 1.4 Pulling Down Resistor and Pulling Up the Capacitor1.5 Parasitical Resistor as an Integrator1.6 Parasitical Resistors and Capacitors1.7 Balance Resistor Failure1.8 Magnification, Input Impedence, Voltage1.9 Open Loop Gain1.10 Virtual ShortⅡ Op Amp ApplicationⅢ Op Amp SamplingⅣ Op Amp Reference VoltageⅤ Importance of Op AmpⅠ Operational Amplifier BasicsWhen using op amp, there will be more problems confusing us, what are they? Listing all of them is impossible, but we can seek the core of these problems, which are the following lists.1.1 Amplification PrincipleThere are many types of op amps with many functions, and their circuits are inconsistent, but the internal block diagrams are basically the same. It consists of three parts: input stage, intermediate stage, and output stage. The input stage consists of a differential amplifier circuit that uses circuit symmetry to improve overall circuit, and the main function of the intermediate voltage amplifier stage is to increase the voltage gain. It can be composed of one or more stages of amplifying circuits; the output stage has a voltage gain of 1, but can provide a certain amount of power, and the circuit consists of two power supplies V+ and V-. The entire amplifier circuit is designed with two inputs P and N, and one output O. The voltages of the three terminals are represented by Vp, Vn, and Vo, respectively. The two ends of P and N are respectively called the non-inverting input terminal and the inverting input terminal, which means that when the P terminal is added with the voltage signal Vp (Vn = 0), it is obtained at the output end. The voltage Vo is in-phase with Vp, when the voltage signal Vn (Vp = 0) is applied to the N terminal, the output voltage Vo obtained at the output is inverted from Vp.The operational amplifier is actually a differential amplifier. Look at its structure, two transistors are connected back to back to share the crossing current source. One of the transistors is the positive input of the op amp and the other is the inverting input. The positive input is amplified and sent to a power amplifier circuit to amplify the output. Thus, if the voltage at the forward input rises, the output naturally becomes larger. If the voltage at the inverting input rises, the reverse current is large, and the forward current is small, because the inverting tertiary tube and the forward tube share a same current source.1.2 Balance ResistorGenerally, there is a balance resistor in the inverting / non-inverting amplifier circuit. What is the role of this balance resistor?(1) Provide a suitable static bias for the transistors inside the chip.The internal circuit of the chip is usually directly coupled, and it can automatically adjust the static operating point, but if an input pin is directly connected to the power supply or the ground, its automatic adjustment function can not work normally. Because the voltage of the ground cannot be raised by the inside transistors, and the voltage of the power supply cannot be reduced, which causes the chip to fail to meet the conditions of virtual short and virtual open.(2) Eliminate the influence of the static base current on the output voltage, and the value should be balanced with the equivalent resistance value of the external DC of the two input terminals.(3) In non-inverting op amp circuit, if it not connecting a balance resistor, the op amp will be burned, because the resistor acts as a voltage divider. 1.3 Feedback Resistor in Parallel with a Capacitor What is the role of the feedback resistor in parallel with a capacitor when using non-inverting op amp?(1) The feedback resistor and capacitor form a high-pass filter, so that local high-frequency amplification is particularly noticeable.(2) Prevent self-excitation. 1.4 Pulling Down Resistor and Pulling Up the CapacitorWhat role does the role of pulling down resistor and pulling up the capacitor at the input of the op amp play?To get positive feedback and negative feedback, depending on the specific circuit connection. For example, if the input voltage signal and the output voltage signal are taken to the input, the partial output signal passes through the balance resistor to obtain a new voltage value, that is, shunting the input voltage to make the input voltage smaller, and this is a negative feedback. Since the signal output from the signal source is always constant, the output signal can be corrected by negative feedback. 1.5 Parasitical Resistor as an IntegratorWhat is the function of the resistor RF connected to the op amp as an integrator at the two ends of the integrating capacitor?Adjust resistance to prevent the output voltage from running out of control. 1.6 Parasitical Resistors and CapacitorsWhy are resistors and capacitors connected in series at the input of the op amp?Regardless of the type of op amp, it consists of transistors or MOS transistors. In the absence of an external components, the op amp is a comparator actually. When the voltage of the non-inverting terminal is high, it will output a level similar to the positive voltage, and vice versa, but this op amp does not seem to have much use. Only when the external circuit is formed to generate the feedback will make the real op amp function. 1.7 Balance Resistor FailureWhat is the consequence of the balance resistor doesn't work well in non-inverting amplifier circuit?(1) The non-inverting end is unbalanced. For example, there will be an output although the input is 0. When the input signal is output, the output value is always larger (or smaller) than the theoretical output value by a fixed number.(2) The error caused by the input bias current cannot be eliminated. 1.8 Magnification, Input Impedence, VoltageWhat is the amplification factor and input impedence of an ideal integrated operational amplifier? What is the voltage between the non-inverting input and the inverting input?The magnification is infinite, the input impedance is infinitesimal, and the voltage is almost the same (the voltage is not 0V, for example, the non-inverting end is 10V and the inverting end is 9.99V). 1.9 Open Loop GainWhy is the open loop gain of an ideal op amp infinite?1) The actual open loop gain of the op amp is very large, so imagine it as infinity and derive the virtual ground from it.2) Deriving virtual ground is not only an inverting amplifier for the negative feedback connection, because there is no virtual ground for positive feedback.The open-loop gain of the op amp is infinite, when design the circuit, the closed-loop gain can be independent of the open-loop gain, and only depends on the external components. It is to use the large open loop gain in exchange for the stability of the closed loop gain.3) Assuming that the gain is small, the difference between the voltages applied across the op amp is relatively large for an output voltage. If it is connected to a negative feedback state, the voltage across the op amp will be different, causing amplification.We all know that the op amp’s output voltage Vo is equal to the difference Vid between the non-inverting input voltage and the inverting input voltage, multiplied by the op amp’s open-loop gain A, that is, Vo = Vid * A = (VI + - VI-) * A ( 1 ). Since the output voltage of the op amp does not exceed the supply voltage in practice, it is a finite value. In this case, if A is large, (VI+ - VI-) is necessarily small; if (VI+ - VI-) is small enough, then we can actually treat it as 0, at this time,  there will be VI+ = VI-, that is, the voltage at the non-inverting input of the op amp is equal to the voltage at the inverting input. This is what we call “virtual short”. Note that they are not really connected together, and there is resistance between them.In the above discussion, how did we get the result of “virtual short”? Our starting point is the formula (1), which is based on the characteristics of the op amp. Then, we made two important assumptions, one is that the output voltage of the op amp is limited, and it not exceed the power supply voltage; the second is that the open loop gain A of the op amp is large. The A of a normal op amp usually reaches 106 or 107 or even larger, but the actual open loop gain of the op amp is also related to its working state. For example, if the op amp is not working in the linear area, the value A may be small, so second assumption is conditional.Therefore, we know that when the open loop gain A of the op amp is large, the op amp can have a virtual short. But it is one of the possibilities, and it is not suitable for every op amp in any case to say their inputs are virtual short, in other words, virtual short can only be achieved in circuits under certain conditions.The conditions of virtual short:a. The open-loop gain of operational amplifier should be large enough.b. There should be a negative feedback circuit. From the above we know when we need to analyze the virtual short in the circuit. In reality, condition (1) is true for most op amps, and the important point is to look at the work area. If it is a circuit drawing, judge by calculation; if it is an actual circuit, it is reasonable to use the instrument to measure amplifier output voltage.There is also a situation related to virtual short called “virtual ground”, that is, there is a virtual short when the input is grounded. Some books say that virtual short will be exist under deep negative feedback conditions, but in reality, the op amp is more likely to work in the linear region under this situation. But this is not absolute, when the input signal is too large, the op amp with deep negative feedback will still be saturated. Therefore, it should be judged to be the most reliable with the output voltage value. 1.10 Virtual ShortAdd the input signal directly to the non-inverting input, and the inverting input is grounded through the resistor. Why is U-= U+ = Ui≠0? Is it not a virtual short? What are the conditions that the virtual ground exists?(1) In the non-inverting amplifier circuit, the output affects by the feedback, so that U(+) automatically tracks U(-), so they will be close to zero. It seems that the two ends are short circuit, so it is called virtual short.(2) Due to the virtual short phenomenon and the high input resistance of the op amp, the current flowing through the two input terminals is small, approaching 0. This phenomenon is called virtual open, which is derived from virtual short.(3) The virtual ground is in the inverting op amp circuit, the (+) terminal is grounded, and the (-) is connected to the input and feedback network. Due to the virtual short, U(-) and U(+) are very close, which is said to be virtual ground.(4) About the conditions: the virtual short is an important feature of the closed-loop (negative feedback) operating state of the non-inverting amplifier circuit; the virtual ground is an important feature of the inverting amplifier circuit in the closed-loop operating state. Ⅱ Op Amp ApplicationWhen a operational amplifier is connected as a non-inverting amplifier, the potentials of the two inputs are the same. If the waveform of the input is measured, it will be the same. This is like a common-mode signal. In fact, there are still small differential mode signal on the two inputs, but the differential mode signal can not be measured by the general instrument. As a result, the virtual short artificially increases the common-mode signal at the two inputs, which poses a challenge to the performance of the operational amplifier. Why is an op amp used like this?(1) The common mode signal of the non-inverting amplifier is much larger than the inverting amplifier, and strict to the common mode rejection ratio.(2) For single-ended input, the equivalent common-mode value is half of the input value, whether non-inverting or inverting input. However, since the input impedance of the non-inverting amplifier is usually larger than the inverting amplification, the anti-interference ability is a little poor.As mentioned above, when the inverting input is performed, the voltage at the inverting terminal is almost zero, so the differential influence on the tube collector voltage that has only one tube change. When the input is in phase, the voltage at the inverting terminal is equal to the non-inverting terminal voltage, so the common mode voltage and the input voltage are equivalent. That is to say, the collector voltage of the differential tube has variable quantity that changes in the same direction when the two tubes have portions that change in different directions at the same time, which is the common mode output voltage. It is added in phase with the voltage of one of the tubes. Therefore, it is easy to cause the tube to become saturated (or cut off), fortunately, the amplification of the common mode voltage is only tens of thousands of parts of the differential mode amplification.However, this does not mean that the common mode rejection suppression ratio of the differential mode input and the common mode input of the amplifier is different. It should be that the non-inverting input is added with a common mode signal equivalent to the input volume, so it should be careful to use non-inverting amplification mode when the input signal is large. Ⅲ Op Amp SamplingWhy is the amplifier circuit composed of operational amplifiers generally sampling the inverting input mode?(1) The significant difference between the inverting input and the non-inverting input mode is:When inverting input, because there is a balanced resistor connected to the ground at the same phase, and there is no current on this resistor (because the input resistance of the op amp is extremely large), this non-inverting terminal is approximately equal to the ground potential, and  the potential at the non-inverting terminal is extremely close to the inverting terminal, so there is a virtual ground at the inverting end. The advantage of having a virtual ground is that there is no common mode input signal, even if the common mode rejection ratio is not high, there is no common mode output. The non-inverting input mode has no virtual ground. When a single-ended input signal is used, a common-mode input signal is generated. Even if an operational amplifier with a high common-mode rejection ratio is used, there is still a common-mode output. Therefore, it is best to use the inverting input method.(2) The positive phase is the oscillator, and the inverting can stabilize the amplifier and access the negative feedback.(3) From the principle point of view, it is possible to connect to the same analog circuit. However, the signal (differential mode signal) that is amplified during the actual application tends to be small, thus it is necessary to pay attention to suppressing noise (usually expressed as a common mode signal). In the same way, the amplification circuit has a poor ability to suppress the common mode signal, and the signal that needs to be amplified is submerged in the noise, which is not conducive to post processing. Therefore, an inverting proportional amplification circuit with better suppression capability is good.Ⅳ Op Amp Reference VoltageSome op amps will have an output even if no voltage is input after power-on, and the output is not small, so VCC/2 is often used as the reference voltage.The output is output signal without any input, this is called the input offset voltage Vos, which is caused by the asymmetry of the design structure of the op amp. It is a very important performance indicator of the op amp. The op amp commonly used VCC/2 as the reference voltage is because the op amp is in a single power supply state. At this time, the real reference of the op amp is VCC/2, so a DC offset of VCC/2 is often provided at the positive terminal of the op amp. When having positive and negative dual power supply, it is often referenced to the ground.The selection of op amps requires attention to many things. Under less stringent conditions, it is often necessary to consider the operating voltage, output current, power consumption, gain bandwidth product, and price of the op amp. Of course, when using it under special conditions, different factors must be considered in practice. Ⅴ Importance of Op Amp(1) If the voltage on both inputs of the op amp is 0V, the output voltage should also be equal to 0V. But in fact, there is always some voltage at the output, that is, the offset voltage Vos. If the offset voltage at the output is divided by the noise gain of the circuit, the calculated result is called the input offset voltage or the input reference offset voltage. The Vos is considered to be a voltage source in series with the inverting input of the op amp. A differential voltage must be applied to both inputs of the amplifier to produce a 0V output.(2) The input impedance of an ideal op amp is infinite, so no current flows into the input. However, a real op amp using a bipolar junction transistor (BJT) in the input stage requires some operating current, which is called bias current (IB). There are usually two bias currents: IB+ and IB-, which flow into the two inputs, respectively. The range of IB values is large, with bias currents of lower at 60fA for special op amps and up to tens of mA for some high-speed op amps.(3) The power supply voltage range required for the first single-chip op amp to operate normally is ±15V. Today, op amps are moving toward low voltages due to increased circuit speeds and power supplies from low-power sources such as batteries. Although the op amp’s voltage specifications are usually specified as symmetrical two-pole voltages ±15V, these voltages do not necessarily require a symmetrical voltage or a two-pole voltage. For an op amp, as long as the input is biased in the active region (within the common-mode voltage range), the ±15V supply is equivalent to a +30V/0V supply, or a +20V/-10V supply. The op amp does not have a ground pin unless the negative voltage rail is grounded in a single-supply application.The input voltage swing of high speed circuits is smaller than that of low speed devices. The higher the speed of the device, the smaller its geometry, which means the lower the breakdown voltage. Due to the low breakdown voltage, the device must operate at a lower supply voltage. Today, op amps typically have a breakdown voltage of around ±7V, so high-speed op amps can work at a supply voltage of ±5V, and they can also operate at a single supply voltage of +5V.For general-purpose op amps, the supply voltage can be as low as +1~8V. These op amps are powered by a single power supply, but this does not mean that a low supply voltage must be used. Because the terms single supply voltage and low voltage are two related and independent concepts. Frequently Asked Questions about Operational Amplifiers Problems1. How can you tell if an op amp is blown?Re: how to tell whether an op amp is burned out? measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. 2. How do I know if my op amp is broken?measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. if they are the same, the opamp is most likely ok and the problem is something else. 3. What errors you have to consider with real operation amplifiers?These errors include input bias current, input offset current, input offset voltage, CMRR, PSRR, and finite input impedance. In reality, all these errors will occur at the same time. 4. How do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output. 5. Why do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output.

Fujitsu today announced the development of a gallium-nitride (GaN) high-electron mobility transistor (HEMT) power amplifier for use in W-band (75-110 GHz) transmissions.This can be used in a high-capacity wireless network with coverage over a radius of several kilometers. In areas where fiber-optic cable is difficult to lay, to achieve high-speed wireless communications of several gigabits per second, one promising approach is to use high-frequency bands, such as the W band, which uses a wide frequency band. In order to get good long-distance coverage in these frequencies, however, it is necessary to increase the output power of the power amplifier to the scale of watts. Fujitsu succeeded in developing a power amplifier for W-band transmissions using GaN-HEMT technology capable of high output at 100 GHz. Evaluations of the newly developed power amplifier confirmed it to have 1.8 times increased output performance than before, which would translate to an increase of over 30% in transmission range when used in a high-speed wireless network. A portion of this research was conducted as part of a project of the National Institute of Information and Communications Technology (NICT) on "Agile Deployment Capability of Highly Resilient Optical and Radio Seamless Communication Systems." Details of this technology are being presented at Power Amplifiers for Wireless and Radio Applications (PAWR2016), opening January 24 in Austin, Texas.High-frequency wireless communications, using the frequency band known as the W band (75-110 GHz), are drawing increasing interest, both as a way to temporarily set up high-capacity communications channels for handling special events where large numbers of people gather, or for responding to disasters, and also as a way to bring communications to remote areas where fiber-optic cables are difficult to lay. Compared to today's mobile phones, which use frequencies in the 0.8-2.0 GHz range, the W band uses a frequency band more than 50 times as broad with 50 times the speed, meaning it is a frequency band that is well-suited to these high-capacity wireless communications.In order to transmit wireless signals over a distance of several kilometers, the transmission antenna needs a power amplifier capable of a high output on the order of several watts. Existing power amplifiers for high-frequency transmissions in the millimeter-wave band (30-300 GHz), which are built using gallium arsenide or CMOS semiconductors, are limited by their operating voltage to an output of about 0.1 W, and it has not been possible to increase this. GaN-HEMT power amplifiers have achieved high output performance in the microwave range (3-30 GHz), but the problem up until now was that their output performance declined in the W-band range. To solve these problems, Fujitsu developed a GaN-HEMT device with a unique structure capable of increasing output in the millimeter band (Figure 1). This uses a layer of indium-aluminum-gallium-nitride (InAlGaN), and double-layer silicon nitride (SiN) passivation film to increase current density by a factor of about 1.4, resulting in 3.0 W of output power from a transistor per 1-mm of gate width, at a high frequency of 100 GHz. In developing this transistor, Fujitsu collaborated with Professor Yasuyuki Miyamoto of the Tokyo Institute of Technology in developing a device-simulation technology.Fujitsu succeeded in developing a power amplifier with the world's highest W-band output performance using this GaN-HEMT device with a proprietary structure (Figure 2). In order to successfully design a power amplifier with high output performance, Fujitsu precisely measured and modeled the characteristics of GaN-HEMT during high-frequency operation. Based on that, a circuit was designed where pairs of GaN-HEMTs were grouped together into compact, high-gain units with low power loss. In order to maximize the power from these units, GaN-HEMTs were connected in a series by the interstage circuit where the signal lines and the device layouts were carefully laid out. Using a model of these compact, high-gain units, Fujitsu conducted simulations to optimize the distributor and combiner matching circuits between the units, and their layouts and signal lines, resulting in a high-amplitude power amplifier (Figure 3). A prototype power amplifier had amplitude that multiplied its input by a factor of 80, producing 1.15 W of output power. Power output per transistor, a measure of power-amplifier performance, was 3.6 W per 1 mm of gate width, the highest in the world.The newly developed power amplifier achieved a 1.8 times increase in power-amplifier output over previous W-band power amplifiers, with the world's highest output performance (Figure 4). This translates to an improvement of over 30% in terms of range for wireless communications at speeds of several gigabits per second.Fujitsu plans to apply this power-amplifier technology to high-capacity long-range wireless communications, and to implement high-speed wireless communications systems that can be used for high-expediency temporary communications infrastructure for use during special events and when fiber-optic links have been broken in the event of disasters.