amplifier Related Articles

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.

Ⅰ. IntroductionIn electronics, an operational amplifier is a circuit unit with a very high amplification factor. In the actual circuit, usually combined with the feedback network to form a certain functional module. It is an electronic device with a special coupling circuit and feedback. The output signal can be the result of mathematical operations such as addition, subtraction or differentiation, integration, etc, thus it was used in analog computers to implement mathematical operations.CatalogⅠ. IntroductionⅡ. Non-inverting Amplifiers and Inverting Amplifiers   2.1 Terminology   2.2 Non-inverting Amplifier Circuit   2.3 Inverting Amplifier CircuitⅢ. Note: Input ImpedanceⅣ. Amplifier GainⅤ. Differences between Inverting & Non-Inverting Amplifiers   5.1 Facts Consideration   5.2 Differences SummaryⅥ One Question Related to Amplifier and Going Further   6.1 Question   6.2 AnswerAn op amp is a functional unit that can be implemented in discrete devices or in semiconductor chips. With the development of semiconductor technology, most of the op amps exist in the form of a single chip, but there are many types of op amps, which are widely used in the electronics industry. The op amp can be simply viewed as a high-gain direct-coupled voltage amplifying unit with one signal output port (Out) and two high-impedance inputs, non-inverting input and inverting input, so op amps can be used to make the non-inverting, inverting, and differential amplifiers.Difference between Inverting and Noninverting Amplifier Ⅱ. Non-inverting Amplifiers and Inverting Amplifiers2.1 TerminologyAn operational amplifier in an electronic circuit has a non-inverting input and an inverting input. The same polarity of the input and the output is a non-inverting amplifier, on the contrary, it is an inverting amplifier. And the inverting amplifier circuit has a function of amplifying the input signal and inverting the output. 2.2 Non-inverting Amplifier CircuitWhen a positive phase is received, a positive phase is output, whereas the negative phase is output. The phases of non-inverting end and the output end are the same. In other words, the signal is applied to the non-inverting input of the op-amp, and it is not inverted at the output when compared to the input. Figure 1. Non-inverting Amplifier(A signal applied keeps its polarity at the output, and a positive input remains a positive output.)Vin and V-Virtual are short circuit in the figure, where Vin=V-……aBecause of the virtual open circuit, there is no current to the inverting input, the current through R1 and R2 is equal, and the current is set to I, which is obtained by Ohm's law:I=Vout/(R1+R2)……bVin equal to the partial voltage on R2, where Vin=I*R2……cBy a, b, c, where Vout=Vin*(R1+R2)/R2 2.3 Inverting Amplifier CircuitWhen the positive phase is received, the negative phase is output, whereas the positive phase is output. And the non-inverting end and the output end are keeping inverting relation. An inverting amplifier provides the same function as the common emitter and common-source amplifier.Figure 2: The grounding of the op amp is 0V, the inverting end and the non-inverting end are short circuit, so it is also 0V. The input resistance of the inverting input is very high, while it is virtual open. So that there is almost no current injection and outflow, then R1 and R2 are equal to a series connection, the current flowing through each of the components in a series circuit is the same, that is, the current flowing through R1 and the current flowing through R2 are the same. Figure 2. Inverting Amplifier(The polarity of a signal is reversed at the output, and a negative input becomes a positive output.)Current flowing through R1: I1=(Vin-V-)/R1………aCurrent flowing through R2: I2=(V--Vout)/R2……bV-=V+=0………………cI1=I2……………………dBy solving the above algebra equation, we can get the result:Vout=(-R2/R1)*ViThe inverting amplifier circuit has the function of amplifying the input signal and inverting output, which is a negative feedback technique. Negative feedback returns a portion of the output signal to the input. The reason why the inverting amplifier can only connect the signal to the inverting input is because the negative feedback can be formed only in this way, otherwise it will not work in the linear amplification region.When inputting from both ends simultaneously, the size and phase are the same, that is the common mode signal, and the theoretical output is zero. Ⅲ. Note:  Input ImpedanceThe input impedance of the non-inverting input is high, and the input impedance of the inverting input is low. The input impedance of the non-inverting input is basically determined by the bias resistor connected in parallel with the non-inverting terminal, and the resistance can be very large. When the inverting input is connected, the feedback resistor is connected between the inverting terminal and the output terminal, and the resistance is small, so the input impedance of the inverting input is relatively low.1. The magnitude of the input resistance of the non-inverting amplifier does not affect the input impedance, and the inverting amplifier input resistance is approximately equal to the input impedance.2. When the input impedance is required to be high, the non-inverting amplifier should be selected.3. If the input impedance is not required to be large, the non-inverting or inverting can be selected at this time. When the phase is not considered strictly, the inverting amplification is preferred because it only has the differential mode signal.4. The CMRR of the inverting amplifier is better when the CMRR is decisive.Inverting amplifier, the input common mode of the op amp is almost constant, the common mode amplification is not reflected to the output, and the input common mode of the op amp in the non-inverting amplifier changes with the input signal, the common mode amplification of the op amp will be reflected Output. Therefore, the CMRR of the inverting amplifier is better when the CMRR of the op amp is decisive. Ⅳ. Amplifier GainBasic Inverting Amplifier Made with an Op-ampNon-inverting AmplifierInverting AmplifierGAIN (AV) = 1+(R2 / R1)Example:if R2 is 1000 kilo-ohm and R1 is 100 kilo-ohm the gain would be :1+ (1000/100) = 1 + 10 or GAIN (AV) = 11If the input voltage is 0.5v the output voltage would be : 0.5 X 11 = 5.5vGAIN (AV) = -R2 / R1Example:if R2 is 100 kilo-ohm and R1 is 10 kilo-ohm the gain would be :-100 / 10 = -10 (Gain AV)If the input voltage is 0.5v the output voltage would be : 0.5v X -10 = -5v Ⅴ. Differences between Inverting & Non-Inverting Amplifiers5.1 Facts ConsiderationIt can be seen that comparing them is from the following aspects: input and output impedance, common mode anti-interference.1. The input impedance of the non-inverting amplifier is equal to the input impedance of the op amp, and they are close to infinity. The input resistance of the non-inverting amplifier does not affect the input impedance; and the input impedance of the inverting amplifier is equal to the resistance of the series resistor of the signal to the input. Therefore, when the input impedance is required to be high, the non-inverting amplifier should be selected.2. The input signal range of the non-inverting amplifier is limited by the op amp's common-mode input voltage range, while it is not the case with the inverting amplifier. Therefore, if the input impedance is required to be low and the phase is free, the inverting amplification is preferred because it only has a differential mode signal. And the anti-interference ability is strong, thus a larger input signal range can be obtained.3. In the design where the same magnification is required, try to select a resistor with a small value, which can reduce the influence of the input bias current and the influence of the distributed capacitance. If you are more concerned about power consumption, you have to compromise on the resistance.4. Determine if an input signal is a non-inverting input or an inverting input. If the input resistance of the amplifier circuit is required to be large, the non-inverting input amplifier circuit should be used because the increase of the input resistance of the amplifier circuit will affect the voltage gain. When the inverting input resistance is increased, the voltage gain of the circuit is reduced, and the voltage gain is also affected by the internal resistance of the signal source. Therefore, when designing the inverting input amplifying circuit, sometimes the input resistance and the voltage gain is difficult to balance. If the bias resistor or the voltage divider is appropriately increased, the input resistance of the amplifier circuit can be increased, and the voltage gain has little or no effect on the voltage gain, which requires a better understanding of the circuit.Figure 3. Integrated Circuit Using Op-amp5.2 Differences SummaryThe integrated amplifier can be connected to the non-inverting or to the inverting amplifier. Is it better to select non-inverting amplification or inverting amplification? Let's look at the difference between them.1）non-inverting amplifiera. AdvantagesThe input impedance is equal to the input impedance of the op amp, which close to infinity.b. DisadvantagesThe amplifying circuit has no virtual ground, so it has a large common mode voltage, and the anti-interference ability is relatively poor. So that the op amp requires a higher common mode rejection ratio, and another disadvantage is that the amplification factor can only be greater than one.2）inverting amplifiera. Advantages The potential of the two input terminals is always approximately zero (the non-inverting terminal is grounded, and the inverting terminal is virtual-grounded), in addition, only the differential mode signal exists, and the device has strong anti-interference ability.b. Disadvantages The input impedance is small, which is equal to the resistance of the series resistance of the signal to the input.3) The gain calculation of the two are different, and their phases are opposite. Ⅵ One Question Related to Amplifier and Going Further6.1 QuestionWhat are non-inverting amplifiers used for?6.2 AnswerThe non-inverting amplifier configuration is one of the most popular and widely used forms of op amp circuit and it is used in many electronic devices. The op amp non-inverting amplifying circuit provides a high input impedance along with all the advantages gained from using an op amp. Frequently Asked Questions about Difference between Inverting and Noninverting Op Amp1. Which is better inverting or noninverting amplifier?Inverting op-amps provide more stability to the system than non-inverting op-amp.In case of inverting op-amp negative feedback is used that is always desirable for a stable system. 2. What are the advantages of non inverting amplifier over inverting amplifier?The advantages of the non-inverting amplifier are as follows: The output signal is obtained without phase inversion. In comparison to the impedance value of the input at the inverting amplifier is high in the non-inverting amplifier. The voltage gain in this amplifier is variable. 3. What is an inverting amplifier used for?The inverting amplifier is an important circuit configuration using op-amps and it uses a negative feedback connection. An inverting amplifier, like the name suggests, inverts the input signal as wells as amplifies it. 4. Where are non-inverting amplifiers used?The non-inverting amplifier configuration is one of the most popular and widely used forms of operational amplifier circuit and it is used in many electronic devices. The op amp non-inverting amplifier circuit provides a high input impedance along with all the advantages gained from using an operational amplifier. 5. Why are inverting amplifiers better than non inverting?Inverting op-amps provide more stability to the system than non-inverting op-amp.In case of inverting op-amp negative feedback is used that is always desirable for a stable system.

  Op-amp is short for operational amplifier. In practical circuits, they are usually combined with a feedback network to form some kind of functional module. It was named "operational amplifier" because it was used in the early days of analog computers to realize mathematical operations, and the name has been continued to this day. An operational amplifier is a circuit unit named from the point of view of function, and can be implemented by discrete devices or in semiconductor chips. With the development of semiconductor technology, the majority of op amps exist today in the form of a single chip. Nowadays, there is a wide variety of op amps, which are widely used in almost all industries. What is an operational amplifier? Catalog   Working principle of operational amplifier  Why is operational amplifier called op amp? Types of op amp Features of op amp FAQ Working principle of operational amplifier  When an operational amplifier is used, its output is connected to its inverTIng input node to form a negative feedback configuration—negaTIve. The reason is that the voltage gain of the operational amplifier is very large, ranging from hundreds to tens of thousands of times, the use of negative feedback to ensure the stable operation of the circuit. But that doesn't mean the operational amplifiers can't be connected to the positive feedback. On the contrary, in many systems that need to generate oscillatory signals, OP Amp with positive feedback configuration is a common component. Operational amolifier schematic diagram    Why is operational amplifier called op amp? In an actual circuit, the feedback network is usually combined to form a certain functional module. Since it was used in analogue computer to realize mathematical operation, it is named "operational amplifier", which continues to this day. Operational amplifier is a circuit unit based on its function, which can be implemented by discrete devices or semiconductor chips. With the development of semiconductor technology, the vast majority of operational amplifiers are in the form of single chip. Nowadays, there are many kinds of operational amplifiers, which are widely used in almost all industries. History of operational amplifier    Summing amplifier In 1941, the first operational amplifier composed of vacuum tubes was invented by Karl D. Swartzel Jr. Of Bell Labs and got the American patent 2,401,779, named “Summing Amplifier”. Model K2-W In 1952, model K2-W, the first operational amplifier with vacuum tube was sold by George A. Philbrick Researches (GAP/R) in the market. μA702 In 1963, the first operational amplifier in the form of a single IC chip was the μA702 designed by Fairchild Senmiconductors's Bob Widlar, and it was introduced after modification in 1965 named μA709.  μA741 In 1968, Fairchild Semiconductor Inc. Introduced the μA741 still in production, it is one of the most successful operational amplifiers of all the time and one of the very few oldest IC models.   - In 1941, the first operational amplifier composed of vacuum tubes was invented by Karl D. Swartzel Jr. Of Bell Labs and got the American patent 2,401,779, named “Summing Amplifier”. - In 1952, model K2-W, the first operational amplifier with vacuum tube was sold by George A. Philbrick Researches (GAP/R) in the market. - In 1963, the first operational amplifier in the form of a single IC chip was the μA702 designed by Fairchild Senmiconductors's Bob Widlar, and it was introduced after modification in 1965 named μA709.  - In 1968, Fairchild Semiconductor Inc. Introduced the μA741 still in production, it is one of the most successful operational amplifiers of all the time and one of the very few oldest IC models.   Types of op amp - General type: Its performance parameters are suitable for general use (low frequency and slow signal change), such as 741A, LM358 (double OP Amp), LM324 and LF356  with FET as input stage. - High-Z type:The characteristic of this kind of amplifier is that the input impedance of differential mode is very high and the input bias current is very small. The main measure to achieve these targets is to make use of the high input impedance of FET, but the input offset voltage of this kind of operational amplifier is larger. Such operational amplifier have LF356, LF355, LF347, CA3130, CA3140, etc. - Low-temperature drift type:In precision instruments, weak signal detection and other automatic control instruments, the bias voltage of operational amplifier is small and does not change with the temperature. The low temperature drift operation amplifier is designed for this purpose. At present, the commonly used operational amplifier has OP07, OP27, OP37, AD508 and ICL7650 composed of MOSFET device and so on. - High slew-rate type:In fast A/D converter, D/A inverter and video amplifiers, the conversion rate of the operational amplifier must be high, and the BWG of the unit gain bandwidth must be large enough. Common operational amplifier has LM318, 175A and so on. - Low -consumption type: Due to the wide application of portable instruments, low power supply and low power consumption must be used. Commonly used low-power operational amplifier has TL-022C,TL-160C and so on. - High voltage and power type:The output voltage of operational amplifier is mainly limited by power supply. In ordinary operational amplifier, the maximum output voltage is only dozens of volts and the output current is only dozens of Ma. In order to increase the output voltage and current, the auxiliary circuit must be added to the external circuit of the operational amplifier. High-voltage and high-power operational amplifier can output high voltage and high current without any additional circuit.   Features of op amp The input resistance is very high, the output resistance is very small, the voltage magnification is very large, and the zero drift is very small. Characteristics of ideal operational Amplifier in Linear region - Virtual Ground: When the operational amplifier is in a linear state, the potential of the inverse input is zero. - Virtual Short Circuit: When the operational amplifier is in a linear state, the two input terminals can be regarded as equipotential, which is called virtual short circuit. But both sides are not real short circuit. - Virtual Open Circuit: When the operational amplifier is in a linear state, two input terminals can be regarded as equivalent open circuit, which is called virtual open circuit. Obviously, it doesn’t break the two inputs actually.   FAQ   1. What is an op amp used for? What is an Operational Amplifier (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.   2. What is op amp in electronics? An operational amplifier (op amp) is an analog circuit block that takes a differential voltage input and produces a single-ended voltage output. ... The inverting input is denoted with a minus (-) sign, and the non-inverting input uses a positive (+) sign.   3. How do op amps work? An operational amplifier only responds to the difference between the voltages on its two input terminals, known commonly as the “Differential Input Voltage” and not to their common potential. Then if the same voltage potential is applied to both terminals the resultant output will be zero.   4. What is a 741 op amp used for? The most common Op-Amp is the 741 and it is used in many circuits. The OP AMP is a 'Linear Amplifier' with an amazing variety of uses. Its main purpose is to amplify (increase) a weak signal - a little like a Darlington Pair. The OP-AMP has two inputs, INVERTING ( - ) and NON-INVERTING (+), and one output at pin 6.   5. What are the characteristics of op amp? -Infinite open-loop gain G = vout / v. in -Infinite input impedance Rin, and so zero input current. -Zero input offset voltage. -Infinite output voltage range. -Infinite bandwidth with zero phase shift and infinite slew rate. -Zero output impedance R. out -Zero noise. -Infinite common-mode rejection ratio (CMRR)   6. Where are op amps used? Op-amps are linear devices that are ideal for DC amplification and are used often in signal conditioning, filtering or other mathematical operations (add, subtract, integration and d3.   7. 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.   8. Why is it called operational amplifier? Op-amp stands for operational amplifier. ... Originally, op-amps were so named because they were used to model the basic mathematical operations of addition, subtraction, integration, differentiation, etc. in electronic analog computers. In this sense a true operational amplifier is an ideal circuit element.   9. What is the difference between amplifier and operational amplifier? Amplifiers can be either electronic or mechanical in common definition whereas operational amplifiers are electronic amplifiers. Amplifiers, in general, have a limited capability of amplifying DC signals but all op-amps are capable of amplifying DC signals.   10. What is the main function of operational amplifier? An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins.   11. What are the advantages of operational amplifier? Advantages:  1. increased circuit stability 2. increased input impedance  3. decreased output impedance  4. increased frequency bandwidth at constant gain.   12. What are op amps used for in real life? Op amps are widely used in amplifiers oscillators, filters, comparators, integrators and differentiation,voltage regulator, current regulator. Non linear applications include precision rectified log amplifier . It is also used in analog to digital and digital to analog converter.   13. Where are operational amplifiers used? Operational amplifiers are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.   14. 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.   15. Why does an operational amplifier need a power supply? Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals. ... Without the dual supplies the output signal would clip at the ground potential.   16. How op-amp can be used as a differentiator? An op-amp differentiator is an inverting amplifier, which uses a capacitor in series with the input voltage. ... Differentiators have frequency limitations while operating on sine wave inputs; the circuit attenuates all low frequency signal components and allows only high frequency components at the output.   17. Is an op amp a transistor? Well for starters, an op amp is simply a combination of transistors, so by varying the transistor you can get different properties. One thing to also remember is that op amps are class A amplifiers which basically means that they are always on and therefore drawing power which can be undesirable.   18. Why is op amp a versatile device? Op Amps or operational amplifiers, are fundamental building blocks in electronic design, mainly because these analog integrated circuits (ICs) are very versatile. ... The term “differential amplifier,” for instance, simply means that the op amp will try to amplify any difference between the signals.   19. Does op amp need ground? An Op Amp inverting input (-) is at zero potential (A virtual ground), even though it does not have a galvanic connection to ground.   20. What is the difference between real ground and virtual ground? Real ground is when a terminal is connected physically to the ground or earth. where as virtual ground is a concept used in Op-Amps in which a node is assumed to have the potential that of the ground terminal.  

This article mainly tells about what's an op amp, and then briefly introduce LM358 about its features and parameters, the last we present you the 24 classical circuits of LM358.     Catalog   I. What is an Op Amp? II. LM358 Introduction      2.1 What is LM358?      2.2 LM358 Features      2.3 LM358 Parameters III. 24 Classic Circuits of LM358 FAQ   I. What is an Op Amp? This is a tutorial video introducing what's an opearational amplifier in details.   II. LM358 Introduction   2.1 What is LM358? The LM358 includes two independent, high gain, internal-frequency compensated dual operational amplifiers that are suitable for single power sources with a wide range of voltages, as well as dual-power operation modes. Under recommended operating conditions: the power supply current is independent of the power supply voltage. Its applying range includes sensor amplifiers, DC gain modules, audio amplifiers, industrial control, DC gain components, and all other situations where operational amplifiers can be used with a single power supply.   The LM358 has plug-in type and the patch type packaging which are the plastic package with double-row 8 lead wires.     2.2 LM358 Features       2.3 LM358 Parameters Input bias current 45 nA Input offset current 50 nA Input offset voltage 2.9mV Power suppression ratio (100dB) Common-mode suppression ratio (80dB) Input common-mode voltage maximum VCC about 1.5 V   III. 24 Classic Circuits of LM358   Schematic diagrams are as shown as following:  Figure 1. DIP Plastic Pin Diagram Figure 2. Circular Metal Shell Packaging Pin Diagram Figure 3. Internal Circuit Schematic Diagram Figure 4. DC Coupled Low Pass RC Active Filter Figure 5. LED Driver Figure 6. TTL Drive Circuit Figure 7. RC Bandpass Filter (BPF) Figure 8. Squarewave Oscillator Figure 9. Hysteresis Comparator Figure 10. Bandpass Filter (BPF) Figure 11. Lamp Driver Figure 12. Current Monitor Figure 13. Low Drift Peak Value Detector Figure 14. Voltage Follower Figure 15. Power Amplifier Peripheral Circuit Figure 16. Voltage Controlled Oscillator (VCO) Figure 17. Fixed Current Source Figure 18. Pulser Figure 19. AC Coupled Inverting Amplifier Figure 20. AC Coupled Non-Inverting Amplifier Figure 21. Adjustable Gain Instrument Amplifier Figure 22. DC Amplifier Figure 23. Pulser Figure 24. Bridge Current Amplifier FAQ   1. What is lm358 op amp? LM358 is a dual op-amp IC integrated with two op-amps powered by a common power supply. It can be considered as one half of LM324 Quad op-amp which contains four op-amps with common power supply. The differential input voltage range can be equal to that of power supply voltage.   2. What is lm358 used for? LM358 can be used as transducer amplifier, DC gain block etc. It has large dc voltage gain of 100dB. This IC can be operated on wide range of power supply from 3V to 32V for single power supply or from ±1.5V to ±16V for dual power supply and it also support large output voltage swing.   3. How does an lm358 work? IC LM358– LM358 consists of two independent, high gain operational amplifiers in one package. Important feature of this IC is that we do not require independent power supply for working of each comparator for wide range of power supply. LM358 can be used as transducer amplifier, DC gain block etc.   4. How do I know if my lm358 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.   5. What is the difference between lm386 and lm358？ The LM386 is a complete audio power amplifier, the LM358 is a dual operational amplifier. When using the LM358 e.g. as a pre-amplifier, you will have to supply a separate power amplifier.   6. How to import lm358 into LTspice? 1. Download model file and unzip.2. Place .cir file in same folder as schematic.3. Place "opamp2" symbol on schematic.4. Change "opamp2" value to LMX58_LM2904.5. Place directive on schematic ". lib LMx58_LM2904. CIR" without quotes.   7. How many comparators are in LM358? 2 comparator. In this tutorial LM358 IC is used. It has got 2 comparator.   8. What is the difference between LM358 and LM741? Two commonly used opamp are LM741 & LM358. Difference between LM358 & LM741 is, LM358 is newer and have two OP-AMP on chip while in 741 only one OP-AMP is present. Both the IC's have 8 pins.   9. Why does an op amp require both positive and negative supply voltages? Without the dual supplies the output signal would clip at the ground potential. Operational amplifiers have two power supply rails because they usually need to swing bipolar - output voltages that go either positive or negative in response to the normal range of input signals.   10. Does op amp need ground? An Op Amp inverting input (-) is at zero potential (A virtual ground), even though it does not have a galvanic connection to ground. You May Also Like Rectifiers and Filters Notes A Load Insensitive High-Power Balanced Power Amplifier Discussion on the influencing factors of clock in FPGA design Brief introduction to the Application of some IC chips in Maxim Integrated DIY Community: Let's make amplifier Rechargable Pokect Sized Amplifier Portable - Mini Amplifier Speaker

A high-output-power balanced power amplifier is designed with power-combining architecture for satellite communication terminals. The power-combining architecture introduces a ±45° phase shift in the output matching network of two amplifiers, which makes the balanced power amplifier more tolerant to load mismatch and less sensitive to load variation. This balanced power amplifier is implemented with InGaP/GaAs HBT process. Under the band of 1.5 GHz to 1.7 GHz and the supply voltage of 5 V, the measured results show that 32 dB of the gain, 38 dBm of the saturated output power and 43% of power added efficiency (PAE) are achieved, and a good radio frequency performance can be maintained under load mismatch conditions. Power Amplifier ( PA ) Basics and fundamental tutorial on radio frequency   Catalog Ⅰ Introduction of Power Amplifier 1.1 Background of power amplifier 1.2 Application of power amplifier in   power combination scheme 1.3 High power balanced power amplifier Ⅱ Design and Analysis of balanced Power   Amplifier 2.1 Design of Integral circuit 2.2 Circuit Analysis Ⅲ Test result Ⅳ Conclusion FAQ     Ⅰ Introduction of power amplifier 1.1 Background of power amplifier In recent years, with the development of economy, satellite communication and navigation systems are widely used in electronics and automobile industry,and the demand for power amplifiers of handheld terminal transmitters is increasing.These power amplifiers require greater power output and better stability to meet the performance requirements of satellite communications and navigation systems. Therefore, it is of great significance to study the practical and reliable high power integrated power amplifier used in the handheld terminal of satellite communication and navigation system. The traditional single-terminal multi-stage integrated power amplifier is not only low in output power, due to the influence of its own semiconductor physical characteristics and the limitations of processing technology, heat dissipation, impedance matching, etc, but the output power will also decrease rapidly with the increase of frequency. In order to improve the output power, the power combination technology is a practical and easy method to implement. At the same time, the balanced power amplifier is widely used in the power synthesis scheme because of its insensitive load and wider bandwidth than the single-ended power amplifier.    1.2 Application of power amplifier in power combination scheme In reference, a high linearity and high efficiency power amplifier is realized by balanced synthesis method. The power amplifier has the advantages of flat gain characteristics and more stability than the corresponding single-ended amplifier in a wide band. However, the introduction of orthogonal 3dB couplers at the input and output ends makes the power amplifier require more discrete devices, which is not conducive to miniaturization and integration. In reference, a novel balanced synthesis architecture was used to design a load insensitive power amplifier.This kind of power amplifier adds ±45 °phase shift network to the upper input and lower output terminals, and finally combines the two power channels through the Wilkinson synthesizer at the output end. This design not only achieves high efficiency and linearity, but also has good stability when the load changes. It is widely used in 3G WCDMA mobile phone terminals. However, the introduction of Wilkinson synthesizer also brings many disadvantages, such as large insertion loss, increasing integration cost and complexity. In reference, on the basis of reference, the ±45°phase shift network in the output end of the power amplifier is improved and optimized, the Wilkinson synthesizer is removed either, which makes the power amplifier insensitive to the load change while achieving high efficiency and high linearity.This design reduces the integrated devices, reduces the cost, and is widely used in modern 3G smart phone terminals.   1.3 High power balanced power amplifier Based on the comprehensive consideration of output power and stability, a high power balanced power amplifier based on InGaP/GaAs HBT process, operating in the 1.5-1.7 GHz band, is designed in this article. The test results show that the balanced power amplifier has high output power and power addition efficiency (PAE), and the circuit can still maintain good RF performance when the load mismatches. Ⅱ Design and analysis of balanced power amplifier 2.1 Design of Integral circuit  Due to the superior linearity and high efficiency of HBT process in RF IC design, a balanced power amplifier working in 1.5-1.7 GHz band is designed by using InGaP/GaAs HBT process in this article. The overall circuit structure is shown in figure 1. The balanced power amplifier circuit includes the same upper and lower branch amplifiers, and the input and output matching circuits of ±45°phase-shifting networks. In order to obtain a higher gain, the upper and lower branches are designed using a three-stage power amplifier structure, in which the first stage works in a class A to obtain a high linearity; in order to take into account the linearity and efficiency of the overall power amplifier, the second and third stages work in Class AB.   Figure 1. A balanced power amplifier circuit   In order to achieve a good compromise between efficiency and linearity, the biasing circuit adopts self-adaptive linearizing bias.By adding one inductor and one capacitance to the input matching circuit of the upper and lower branches, the balanced power amplifier generates ±45°phase shift to the input signal, thus realizing that the upper and lower channels of the amplifier work in an orthogonal state. A LC resonant network with a resonant frequency of 2Ω0 is added to the output matching, where Ω0 is the fundamental frequency, which is equivalent to getting a load of second harmonic short circuit at the same time, thus realizing the suppression of the second harmonic. The structure is similar to that of F power amplifier, and is beneficial to obtain higher efficiency. The main characteristic of the circuit in this article is that the output matching circuit of the upper and lower branches added a ±45°phase shift network, the upper branch adds a -45°phase shift network with a low pass filter structure, and the lower branch adds a +45°phase shift network with a high pass filter structure. The balanced power amplifier designed by this synthetic structure has the advantages of small space usage, simple structure and easy implementation. At the same time, it can make the balanced power amplifier more tolerant to load mismatch and insensitive to the change of load.   2.2 Circuit Analysis When the balanced power amplifier is in operation, the input signal is coupled to the A node through the blocking capacitor, and two signals are separated from the A node into the upper and lower branches respectively, because the three-stage amplifier in the upper and lower branches is exactly the same, they sharing an equal input impedance, so the power of the two signals separated at the A node is equal. The separated signals are transmitted to the input end of the amplifier through the opposite 45°phase change of the upper and lower branches respectively, and then the orthogonal signals are amplified by the three-stage amplifier of the upper and lower branches. The orthogonal signal of the upper and lower branches undergoes an opposite phase shift of 45° in the output matching network, so the same signal with the same phase and the same amplitude is realized at point B, and the output power of point B is the sum of those of the two amplifiers, finally the balanced power amplifier can obtain higher output power. The balanced power amplifier is equivalent to the three-port network shown in figure 2. Because the upper and lower branch of amplifiers are exactly the same,it can be considered that the amplifiers of the upper and lower branches have the same output reflection coefficient ΓPA. After passing through ±45°phase shift network, we can obtain ΓPAе −j2ΔΦ and ΓPAе +j2ΔΦ respectively. Therefore, the equivalent output impedance of the upper and lower branches viewed from the ab surface to the left in figure 2 is respectively as follows:   The equivalent output impedance ZL of the network viewed from the terminal to the left can be obtained in parallel by ZL1 and ZL2: The output reflection coefficient of node B is: By substituting formula (1)-(3) into equation (4) and simplifying, the output reflection coefficient of the balanced power amplifier is as follows: When ΔΦ=45°, you have: It is shown that the output reflection coefficient and VSWR of the balanced power amplifier are twice as much as that of the single branch power amplifier. Therefore, when the load mismatch occurs, the load mismatch tolerance of the balanced power amplifier is higher than that of the single-branch power amplifier after the ±45°phase shift output matching network is introduced. Figure 2. Circuit equivalent diagram In order to analyze the performance of the balanced power amplifier in the case of load mismatch, the equivalent circuit of figure 2 is simulated and analyzed. When the load mismatch (such as VSWR=3:1), the load impedance (normalized) of the upper and lower branch amplifiers varies with the phase ψ of the reflection coefficient Γ, as shown in figure 3. By comparing the load impedance of the upper and lower branches, it can be seen that they have a phase difference of 180°. Because of the change of the load impedance of the upper and lower branches, the corresponding current is changed, and the phase difference of 180°occurs between the two. The collector of the two third-stage amplifiers of the balanced power amplifier is single power supply, so the current of the upper and lower branches compensates each other, resulting in little change in the total current, as shown in Figure 4. Therefore, when the load mismatch of the balanced power amplifier occurs, the change of working current is relatively small, that is, not sensitive to the change of load. The load insensitive effect of using this balancing architecture is similar to that of classical balanced power amplifier which is realized by using orthogonal 3 dB coupler. Figure 3. Changes in the load of the structure (normalized) when VSWR=3:1 In the case of terminal mismatch (VSWR=3:1), the single end circuit architecture and the present balanced architecture are compared as shown in Fig. 5 with the same output power of 38 dBm. It can be seen from figure 5 that the output power of the single-ended circuit architecture fluctuates greatly with of the phase ψ of the reflection coefficient Γ, while the output power of the balanced architecture in this article is relatively flat. At the same time, compared with the circuit architecture without phase shift, the in-phase circuit architecture has more advantages than the single-ended circuit architecture, but the output power of the balanced architecture is the flattest and can work stably. Figure 4. Changes of current of the structure (normalized) when VSWR=3:1 Figure 5. Comparison with the output power (normalized) changes in three kinds of circuits when VSWR=3:1   Ⅲ Test result  In this post, the balanced power amplifier is fabricated by InGaP/GaAs HBT technology. The three-stage amplifier and bias circuit with upper and lower branches are realized in the chip with an DIE area of 0.9 mm×0.8 mm. The choke inductor, input matching and output matching circuit are realized out of the chip. Considering the heat dissipation of the power amplifier, the whole thing is integrated on the Fr4 substrate with an area of 8 mm×8 mm. Figure 6 is the physical diagram of the circuit.The working voltage of the balanced power amplifier is 5 V and the total static current is about 310 mA. Using Agilent's network analyzer E5071C to measure the small signal S parameters S21, S11, S22 of the balanced power amplifier, as shown in figure 7: S21 > 31 dB (in the band of 1.5 GHz-1.7 GHz with a variation of less than 1 dB) S11 < -12 dB S22 < -10 dB The test results show that the design has good small signal performance. Using Agilent's signal generator N5182A and spectrometer N9030A to build the test platform, inputting continuous wave (CW) and the performance of the balanced power amplifier is measured at 1.5,1.616 and 1.7 GHz, as shown in figure 8. It can be seen from the diagram that the gain of the balanced power amplifier in the frequency band is about 32 dB, the in-band gain flatness is ±0.3 dB, the saturation power is more than 38 dBm/6.3 WN, and the power additional efficiency is greater than 43 dB. At the same time, according to the gain curve of each frequency point, the balanced power amplifier has good AM-AM characteristic and 1dB compression point is about 37 dBm. The third order intermodulation distortion (IMD3) and the fifth order intermodulation distortion (IMD5) of the balanced power amplifier are measured by using a two-tone signal with a deviation of 2 MHz, as shown in figure 9. The results show that the balanced power amplifier has good linearity. In general, the balanced power amplifier not only has high gain, high output power and high efficiency, but also has good linearity.  Figure 6. Chip physical diagram Figure 7. S parameter test results Figure 8. Test performance in frequency band when CW signal is input In order to verify the tolerance of the balanced power amplifier to the load mismatch and the load insensitivity, and the balanced power amplifier can still work properly when VSWR=20:1, a microwave manual tuner is connected to the output of the power amplifier. And when the working frequency is 1.616 GHz, the input power Pin=10 dBm and voltage standing-wave ratio VSWR=3:1, the output power of the balanced power amplifier changes with the reflection coefficient phase, as shown in Figure 10. The figure shows that the output power is about 35.7 dBm, with a range of ±0.7 dBm. Therefore, the performance of the balanced power amplifier is stable when the load is mismatched to a certain extent. Figure 9. Test performance of IMD3 and IMD5 Figure 10. Changes of output power when VSWR=3:1 Ⅳ Conclusion In this post, a high power balanced power amplifier is designed by using the balance architecture, the chip area is 8 mm×8 mm by using InGaP/GaAs HBT process and the total static current is about 310 mA at a operating voltage of 5V. When the CW signal is input, the gain can be up to 32 dBm in the band of 1.5-1.7 GHz, the saturation output power psat is 38 dBm, and the additional power efficiency is 43%. Beyond that, it can still work stably when the load mismatches. This balanced power amplifier is practical, reliable and safe, and can be used in handheld terminal of the satellite communication and navigation system.   FAQ     1. What is a power amplifier used for? The function of a power amplifier is to raise the power level of input signal. It is required to deliver a large amount of power and has to handle large current. The base of transistor is made thicken to handle large currents.   2. How does a power amplifier work? The power amplifier works on the basic principle of converting the DC power drawn from the power supply into an AC voltage signal delivered to the load. Although the amplification is high the efficiency of the conversion from the DC power supply input to the AC voltage signal output is usually poor.   3. Does a power amp make a difference? A better amp will make your speakers play louder and sound better, but it won't make bad speakers sound like good speakers. Many speakers have a "maximum wattage rating" on the back. ... High-end amplifier companies make amps with more than 1,000 watts, and you could plug in a $50 speaker into it with no problem.   4. What is power amplifier circuit? A power amplifier circuit is used to drive the loads like speakers with minimum output impedance. ... In this mode the output is an inverted amplified signal which is at low power. Two Darlington power transistors are arranged in a class AB configuration to amplify the power level of this signal.   5. How do you make a power amp circuit? Amplifier power gain and design. As power is the voltage multiplied by the current in a circuit, the power gain can simply be expressed as the product of the two. It is also possible to use the voltage and current levels to provide gain expressed in dB, but any changes in impedance must be accounted for.   6. What is balanced amplifier? A balanced amplifier has two amplifying devices that are run in quadrature. That is, they are operating 90 degrees apart in transmission phase. ... Balanced amplifiers may more immune to load pull effects than in-phase power combining schemes, because the two reflection coefficients are seen 180 degrees out of phase.   7. What is the difference between amplifier and power amplifier? The crucial difference between a voltage amplifier and a power amplifier is that a voltage amplifier increases the voltage level of the applied input signal.   8. Why do we need power amplifier? The function of a power amplifier is to raise the power level of input signal. It is required to deliver a large amount of power and has to handle large current. The base of transistor is made thicken to handle large currents.   9. What power amplifier do I need? Generally you should pick an amplifier that can deliver power equal to twice the speaker's program/continuous power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load.   10. Does a power amp improve sound quality? No, amplifiers don't improve sound quality. They just increase the signals to required levels. However if amplifiers have equaliser or other signal processing facility, they can make it sound different and possibly more suitable for listening pleasure. But again that is the work of signal processing part of amplifier.