**Ⅰ Introduction**

As for operational amplifier applications, in electronic circuit, it is usually combined with a feedback network to form a certain functional module, with a special coupling circuit and feedback. Its output signal can be input signal addition, subtraction or differentiation, integration, etc, which early used in analog computers to do mathematical operations. Now they widely used in the electronics industry, regarded as precision AC and DC amplifiers, active filters, oscillators and voltage comparators.

This Video is Introducing Operational Amplifier Applications in the Circuit

## Catalog

**1.1 Integrated Op Amp**

**1.1.1 Evaluation Analysis**

Integrated operational amplifiers are one of the most widely used devices in analog integrated circuits. In various systems, because of different application requirements, the performance requirements of operational amplifiers are also different.

Where there are no special requirements, try to use a universal integrated operational amplifier as much as possible, which can reduce costs and easily replace. When using multiple op amps in a system, use as many op amp integrated circuits as possible. For example, **LM324** and **LF347** always integrate four op amps together in a circuit.

The evaluation of integrated op amps depends on their overall performance. Generally, the merit coefficient K is used to measure the excellent degree of integrated operational amplifiers, which is defined as: where SR is the slew rate and the unit is V / ms. The larger the value, the better the AC characteristics of the operational amplifier; The input bias current of the amplifier is lib, the unit is nA; VOS is the input offset voltage in mV. The smaller the Iib and VOS values, the better the DC characteristics of the op amp. Therefore, for circuits that amplify AC signals such as audio and video, op amps with large SR are better; for circuits that handle weak DC signals, op amps with high accuracy are more suitable (both offset current, offset voltage and temperature drift are relatively small).

When selecting an integrated op amp, some factors should be considered in addition to the figure of merit coefficient K. For example, the signal source is a voltage source or a current source; the nature of the load, and whether the output voltage and current of the integrated op amp meet the requirements; operating voltage range, power consumption, and volume of the integrated op amp.

Figure 1. Using Operational Amplifier as a Comparator

**1.1.2 Integrated Op Amp Basics**

- Power supply

The **integrated op amp** has two power terminals + V_{CC} and -V_{EE}, with different power supply methods. For different power supply modes, the requirements for input signals are different.

1) Dual power supply

Op amps are mostly powered in this way. The positive power (+ E) and negative power (-E) relative to the common terminal (ground) are connected to the + V_{CC} and -V_{EE} pins of the op amp, respectively. In this way, the signal source can be directly connected to the input pin of the op amp, and the amplitude of the output voltage can make the positive and the negative symmetrical.

2) Single power supply

Single-supply operation connects the -V_{EE} pin of the op amp to ground. At this time, in order to ensure that the internal unit circuit of the operational amplifier has a suitable static operating point, a DC potential must be added to the input end of the op amp.

- Zero setting

Due to the influence of the input offset voltage and input offset current of the integrated op amp, when the input signal is zero, the output is often not equal to zero. In order to improve the operation accuracy of the circuit, it is required to compensate the error caused by the offset voltage and the offset current. This is the zero setting of the operational amplifier. Commonly used zeroing methods include internal zeroing and external zeroing. For integrated op amps without internal zeroing terminals, external zeroing methods should be used.

- Self oscillation

The operational amplifier is a high-amplitude multi-stage amplifier. Under the condition of deep negative feedback, it is easy to cause self-excited oscillation. To make the amplifier work stably, a certain frequency compensation network must be added to eliminate the self oscillation. In addition, to prevent low-frequency oscillation or high-frequency oscillation caused by the internal resistance of the power supply, an electrolytic capacitor (10mF) and a high-frequency filter capacitor (0.01 mF ~ 0.1mF) should be connected.

- Device protection

There are three aspects to the protection of the integrated op amp safety: power protection, input protection and output protection.

1) Power protection

Common faults of power supply are reverse polarity and voltage jump. For a power supply with poor performance, voltage overshoot often occurs at the moment when the power is turned on and off. Protection measures such as the use of FET current source and voltage regulator clamping protection. The voltage regulator’s voltage value is greater than the normal operating voltage of the integrated op amp and less than the maximum allowable operating voltage of the integrated op amp, and the current of the FET tube should be greater than the normal operating current of integrated op amp.

2) Input protection

If the input differential/common mode voltage of the integrated op amp is too high beyond the limit parameter range of the integrated op amp, it will be damaged.

3) Output protection

When the integrated op amp is overloaded or the output is shorted, the op amp will be damaged if there is no protection circuit. However, some integrated op amps have internal current limit protection or short circuit protection, and no additional output protection is required to use these devices.

Figure 2. An Inverting Op Amp Circuit

**Ⅱ Op-amp Parameters**

To use the op amp better in the circuit, you must have a certain understanding of its internal parameters. Here are the technical parameters closely related to the op amp:

- Unity-gain bandwidth

**Definition**: Under the condition that the closed-loop gain of the op amp is 1 time, a constant amplitude sinusoidal small signal is input to the input end of the op amp, and the closed-loop voltage gain measured from the output end of the op amp is reduced by 3dB (or equivalent to 0.707 times of the input signal of the op amp), that is to say, the frequency at which the output signal is reduced by -3dB is unity-gain bandwidth. It is a very important indicator. For a sinusoidal small signal amplification, the unity-gain bandwidth is equal to the product of the input signal frequency and the maximum gain at that frequency. In other words, when you know the frequency and gain of the signal to be processed, the unity-gain bandwidth (gain bandwidth = amplification * signal frequency) can be calculated to select the appropriate op amp. The higher the bandwidth, the higher the frequency of the signal that can be processed, and the better the high frequency characteristics, otherwise the signal will be easily distorted.

For **small signals**, the unity-gain bandwidth is also called the gain-bandwidth product, which can roughly show the ability of the op amp to process the frequency of the signal. For example, the gain bandwidth of a certain operational amplifier is 1MHz, if the actual closed-loop gain is 100, then the maximum frequency for theoretical processing of small signals is 1MHz / 100 = 10KHz.

For the **bandwidth** of a large signal, that is, the power bandwidth, the influence of the slew rate SR is the major factor, and the unit is V/uS. In this case, the power bandwidth calculated by FPBW = SR / 2πVp-p, that is, the gain bandwidth and power bandwidth must be satisfied at the same time when designing the circuit.

For **DC signals**, bandwidth issues are generally not considered, and accuracy and interference are mainly considered.

When the amplification factor of an amplifier is n times, it does not mean that all input signals are amplified n times. When the signal frequency increases, the amplification capability decreases.

- Open bandwidth

The open-loop bandwidth is defined as: inputting a constant-amplitude sinusoidal small signal to the input of the op amp, the frequency measured at which the open-loop voltage gain decrease 3dB from the output of the op amp to the dc gain of the op amp. This is used for very small signal processing.

- Slew rate SR

With the op amp connected in a **closed loop**, a large signal (including a step signal) is input to the input of the op amp, and the output rise rate of the op amp is measured from the output of the op amp called SR. Because the input stage of the op amp is switched during the conversion, the feedback loop of the op amp does not work, that is, the conversion rate is independent of the closed-loop gain. The slew rate is a very important index for large signal processing. For general op amps, the slew rate SR <= 10V / μs, and the slew rate of high speed op amps is SR> 10V / μs. The highest conversion rate SR of current high-speed op amps reaches 6000V / μs. The larger the SR, the better the response of the op amp to the input signal changing at high speed. The larger the signal amplitude, the higher the frequency, and the greater the SR. This is used for op amp selection in large signal processing.

- Full-power bandwidth

At the rated load, under the condition that the closed-loop gain of the op amp is 1 time, a constant-amplitude sinusoidal large signal is input to the input end of the op amp, so that the output frequency of the op amp reaches the maximum (allowing certain distortion) signal. This frequency is limited by the slew rate SR of the op amp. Approximately, full power bandwidth is calculated by formula SR / 2πVop (Vop is the peak output amplitude of the op amp). It is a very important indicator for op amp selection in large signal processing.

- Setting time

At the rated load, under the condition that the **closed-loop gain** of the op amp is 1 time, the time required to input a step large signal to the input of the op amp to increase the output from 0 to a given value. Because it is a step large signal input, a certain jitter will occur after the output signal reaches a given value. This jitter time is called the stabilization time. At this moment, stabilization time + rise time = settling time. For different output accuracy, there is a big difference in the stabilization time. The higher the accuracy, the longer the stabilization time.

- Equivalent input noise voltage

It refers to any AC random interference voltage generated at the output of an op amp with good shielding and no signal input. When this noise voltage is converted to the input of the op amp, it is called the input noise voltage of the op amp (sometimes expressed by noise current). For broadband noise, the effective value of the input noise voltage of ordinary op amps is about 10 ~ 20μV. This value often corresponds to a certain frequency band.

- Output impedance

It refers to the ratio of the change in voltage to the corresponding change in current when the signal voltage is applied to the output of the op amp working in the linear region. At low frequencies it only refers to the output resistance of the op amp.

- Common mode input resistence

Refers to the ratio of the change in the input voltage of the common mode to the corresponding change in the input current when the two inputs of the op amp input the same signal. At low frequencies, it behaves as a common mode resistance. Generally, the common mode input impedance of the op amp is much higher than the differential mode input impedance, with a typical value above 108Ω.

- Common mode rejection ratio

Same as the definition in the differential amplifier circuit, it is the ratio of the differential mode voltage gain to the common mode voltage gain, which is usually expressed in decibels. It is a parameter that measures the degree of symmetry of the input stage differential amplifier and the ability of the integrated op amp to suppress common mode interference signals. The larger the value, the better.

- Power supply rejection ratio

The power supply voltage rejection ratio is defined as the change ratio of the input offset voltage of the op amp with the power supply voltage in the linear region. The power supply voltage rejection ratio reflects the effect of power supply changes on the output of the op amp. At present, the power supply voltage suppression ratio is only about 80dB. Therefore, when used for DC signal or small signal processing for analog amplification, the power supply of the op amp needs to be carefully set. Of course, an op amp with a high common mode rejection ratio can compensate a part of the power supply voltage rejection ratio. In addition, when using dual power supplies, the power supply voltage rejection ratio of the positive and negative power supplies may be different.

- Differential mode input resistance

Refers to the **ratio** of the change in voltage at the two input terminals to the corresponding change in current at the input terminals when the op amp is operating in the linear region. The differential mode input impedance includes the input resistance and input capacitance, and refers only to the input resistance at low frequencies. General products specification only give input resistance. The input resistance of the op amp using the bipolar transistor as the input stage is not greater than 10MΩ; the input resistance of the op amp as the input stage of the field effect transistor is generally greater than 109Ω.

- Input offset voltage

When the input voltage is **zero**, the output voltage is divided by the voltage gain, plus the negative sign, which is the offset voltage converted to the input. It is the compensation voltage applied at the input when the output voltage is zero. The input offset voltage actually reflects the circuit symmetry inside the op amp. The better the symmetry, the smaller the input offset voltage. The input offset voltage is a very important indicator of the op amp, especially when it is a precision op amp or used for DC amplification.

The input offset voltage has a certain relationship with the manufacturing process. It is between ± 1 and 10 mV when op amps use the bipolar process (that is, the standard silicon process). If the field effect tube is used as the input stage, it will be greater. For precision op amps, it is generally below 1mV. The smaller the input offset voltage, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps.

- Input offset voltage drift

Within the specified operating temperature range, it is the ratio of the change in input offset voltage with temperature to the change in temperature. It is actually a supplement to the input offset voltage, which is convenient for calculating the drift of the amplifier circuit due to temperature changes within a given operating range. It is an important indicator for measuring the temperature effect to the op amp. Under normal circumstances, it is about (10 ~ 30) uV / C (degree Celsius), the high quality can be <0.5uV / C.

- Input offset current

It is defined as the difference between the base current of the differential pair of the differential input stage when the output DC voltage of the op amp is zero. Used to characterize the degree of asymmetry of the differential input current. The better the symmetry, the smaller the input offset current. Input offset current is a very important indicator for op amps, especially for precision operational amplifier or DC amplifier. The input offset current is approximately one to one-tenth of the input bias current. It has an important impact on small signal precision amplification or DC amplification, especially when a large resistor is used outside the op amp. The effect of input offset current may exceed the effect of input offset voltage on accuracy. The smaller the input offset current, the smaller the intermediate zero offset during DC amplification, and the easier it is to handle. Therefore, it is an extremely important index for precision op amps.

- Input offset current temperature drift

Within the specified operating temperature range, the ratio of the amount of change in input offset current with temperature to the amount of temperature change. It refers to the temperature coefficient of within the specified operating range, and is also an important indicator to measure the temperature effect on the op amp. It is usually about (1-50) nA / C, and the high quality is about several pA / C. This value is only given in the precision op amp parameters, and it needs attention when it is used for DC signal processing or small signal processing.

- Input bias current

It is defined as the average value of the bias currents of the two input terminals when the output DC voltage of the op amp is zero, in other words, it is the average current flowing into the input terminal when the operational amplifier is operating in the linear region. The input bias current has a greater impact on the places where input impedance is required, such as high-impedance signal amplification and integrator circuits. The input bias current has a certain relationship with the manufacturing process. If a field effect tube is used as the input stage, the input bias current generally lower than 1nA. It always used to measure the input current of the differential amplifier pair.

- Maximum differential mode input voltage

It is a voltage that the two input ends of the op amp can withstand. When it is exceeded, the reverse breakdown of the differential tube will occur. The NPN tube made by the plane process has a value of about 5V, and the Vidmax of the horizontal PNP tube can reach more than 30V.

- Maximum common mode input voltage

It an allowable range of common mode input voltage under normal operating conditions of the op amp. When the input differential pair saturates, the amplifier loses common mode rejection ability. In the case of interference, it is necessary to pay attention to this problem in the use of the circuit.

- Output peak to peak voltage

Working in the linear region, under the specified load, when the op amp is powered by the large power supply, it is the maximum voltage amplitude that the op amp can output. Except for low voltage op amps, the output peak-to-peak voltage of general op amps is greater than ± 10V, but less than the power supply voltage. This is due to the design of the output stage. The output stage of modern low-voltage op amps has been specially treated. The output peak-to-peak voltage is close to within 50mV of the power supply voltage, so it is called a full-scale output op amp, also known as a rail-to-raid op amp. It should be noted that the output peak-to-peak voltage of the op amp is related to the load, and the value is different for different loads; the positive and negative output voltage swings of the op amp are not necessarily the same. For practical applications, the closer the output peak-to-peak voltage is to the supply voltage, the easier the power supply design.

Figure 3. Input Offset Voltage of an Op-amp

**Ⅲ Application Matters**

1) A single-supply op amp must be DC biased, otherwise it will not work properly. For the virtual ground design, in addition to the DC potential, it is necessary to pay attention to the voltage stabilization (it is best to use the reference voltage chip), and also to ensure low impedance AC decoupling, that is, low-frequency decoupling parallel to at least 10uF and high frequency decoupling under 0.1uF.

2) The input of the non-inverting amplifier must be biased to ground as a DC path.

3) Ordinary op amps cannot directly drive capacitive loads. If there is need, you must use capacitors for phase compensation or output series resistors and then connect the load.

4) For the op amp input of the external interface, a TVS tube must be connected in parallel to the positive and negative input pins to prevent the op amp from reversing the polarity due to the too large input voltage signal, forming a parasitic false signal output.

5) For amplifier circuits with a gain of more than 10 times, pay attention to controlling the bandwidth gain of the op amp to prevent the device from self oscillation.

6) The output of the power amplifier needs to be protected by switching diodes to the power supply and ground, especially when inductive loads are connected.

7) When using multiple op amps to process multiple signals, care must be taken to prevent the instantaneous changes in one of the signals from causing crosstalk to the other signal. Therefore, it is recommended not to use one op amp to process multiple signals.

8) Most op amp chips are ESD sensitive devices, so pay more attention when using them.

9) The pins of unused op amps (excess channels in multiple op amps) should not be left floating, and grounded or connected to positive and negative power supplies. It is recommended to connect it as a follower (the output is connected to the reverse input) and the non-inverting input is connected to a potential between the power rails (the ground of the dual power system or any suitable point in the circuit). They can also used as buffer amplifiers and add them to a small impact location in the system.

Figure 4. Op Amp 741

**Ⅳ Classic Amplifier Circuits**

Figure 5. Inverting Amplifier

Figure 5: The grounded non-inverting terminal of op amp is 0V. The inverting and non-inverting terminals are **short-circuit**, so the inverting end is also 0V. The input resistance of the inverting input terminal is very high, and it is **virtual open**. In other words, there is almost no current pass through. Therefore, the current flowing through each component in a series circuit is the same, that is, the current flowing through R1 and R2 are the same.

Current flowing through R1: **I1 = (Vi-V-)/R1**

Current flowing through R2: **I2 = (V--Vout)/R2**

**V- = V+ = 0, I1 = I2**

Solve the above algebraic equation to get **Vout = (-R2/R1)*Vi**, it is the input-output relationship of the **inverting amplifier**.

Figure 6. Non-inverting Amplifier

In Figure 6, Vi and V- are virtual short, where **Vi = V-**. Because of the virtual open, there is no current flow through at the reverse input terminal, then **R1=R2**. If the current is I, which is obtained by Ohm's law: **I = Vout/(R1+R2)**;Vi is equal to the partial voltage on R2, that is: **Vi = I*R2**.

Virtual short: **Vi = V-, R1=R2**

Ohm's law: **I = Vout/(R1+R2), Vi = I*R2**

Where **Vout=Vi*(R1+R2)/R2**, represents the **non-inverting amplifier**.

Figure 7. Adder

Figure 7: Knowing from the Kirchhoff's law and virtual open theory, the sum of the current through R2 and R1 is equal to the R3, **V- = V+ = 0** (short circuit), so **(V1 – V-)/R1 + (V2 – V-)/R2 = (Vout – V-) /R3** can be transferred as **V1/R1 + V2/R2= Vout/R3**. If **R1=R2=R3**, then the formula becomes **Vout=V1+V2**, which is **an adder**.

Figure 8. Adder

In Figure 8, because of the virtual open, no current flows through the non-inverting terminal, where **V+ = V-, R1=R2, R4=R3**, therefore, **(V1 – V+)/R1 = (V+-V2)/R2, (Vout – V-)/R3 = V-/R4** can be simplified as **V+ = (V1 + V2)/2 V- = Vout/2**. So **Vout = V1 + V2** is also an **adder**.

Figure 9. Subtractor

Figure 9 shows that the current through R1 is equal to the R2, and R4=R3, therefore, **(V2– V+)/R1 = V+/R2, (V1 – V-)/R4 = (V--Vout)/R3**. If **R1=R2**, then** V+ = V2/2**; if **R3=R4**, then **V- = (Vout + V1)/2**, because of **V+ = V-**, so **Vout =V2-V1** is **a subtractor**.

Figure 10. Integrator Circuit

In Figure 10, the input voltage at the inverting terminal is equal to the non-inverting terminal because of short circuit; the current through R1 is equal to the C1 because of virtual open. The current flowing through R1 and C1 are **Ri=V1/R1**, **Ci=C*dUc/dt=-C*dVout/dt**, respectively. So **Vout=((-1/(R1*C1))∫V1dt**, which is a **integrator circuit**. If V1 is a constant voltage U, then the above formula is transformed to **Vout = -U*t/(R1*C1)t**, then the Vout is a straight line that changes with time.

Figure 11. Differential Circuit

In Figure 11, the current through capacitor C1 and resistor R2 is equal because of virtual open; **V+ = V-** because of short circuit, where **Vout = -i * R2 = -(R2*C1)dV1/dt**, which is a **differential circuit**. If V1 is a DC voltage, the output Vout corresponds to a pulse in the opposite direction to V1.

Figure 12. Differential Amplifier Circuit

Figure 12:

**Vx = V1……a, Vy = V2……b**

then R1, R2, R3 can be regarded as a series, **R1=R2=R3**, the current **I=(Vx-Vy)/R2……c**

where **Vo1-Vo2=I*(R1+R2+R3) = (Vx-Vy)(R1+R2+R3)/R2 ……d**

If **R6=R7**, then **Vw = Vo2/2 ......e**, similarly, if **R4=R5**, then **Vout – Vu = Vu – Vo1**, so **Vu = (Vout+Vo1)/2 ……f**

due to short circuit, **Vu = Vw ……g**, based on efg formulas, **Vout = Vo2 – Vo1 ……h**

Get from dh,** Vout = (Vy – Vx) (R1+R2+R3)/R2**, where **(R1+R2+R3)/R2** is a fixed value. This value determines the amplifier multiple of the difference **(Vy-Vx)**, thus it is a **differential amplifier circuit**.

Figure 13. Amplifier Circuit

It is a relatively **common amplifier circuit**. Many controllers accept 0~20mA or 4~20mA current from various measuring instruments. The circuit converts the current into voltage signal to become a digital signal by ADC. Figure 13 is such a typical circuit. As shown in Figure, 4~20mA current flows through the sampling 100Ω resistor R1, there will be a voltage difference of 0.4~2V on R1. Due to virtual open circuit, **R3= R5** and **R2=R4**.

Therefore: **(V2-Vy)/R3 = Vy/R5 ……a (V1-Vx)/R2= (Vx-Vout)/R4 ……b**

Short circuit: **Vx = Vy ……c**

Current changes from 0~20mA, then **V1 = V2 + (0.4~2) ……d**

Put cd formulas into b formula: **(V2 +(0.4~2)-Vy)/R2 = (Vy-Vout)/R4 ……e**

If **R3=R2 , R4=R5**, then e-a gets **Vout =-(0.4~2)R4/R2 ……f**

In Figure 13, **R4/R2=22k/10k=2.2**, then f formula **Vout = -(0.88~4.4)V**, that is to say, the current of 4~20mA is converted into a voltage range of -0.88~-4.4V.

Current can be converted into voltage, and voltage can also be converted into current. Figure 14 is such a circuit. The negative feedback in the above figure does not directly feedback through the resistor, but the emitter junction of the transistor Q1 is connected in series. But it isn't a comparator. As long as it is an amplifying circuit, the law of short circuit and virtual open still conforms.

Figure 14. Amplifier Circuit

Due to virtual open, no current flows through the input of the op amp,

Then **(Vi – V1)/R2 = (V1 – V4)/R6 ……a**

Similarly **(V3 – V2)/R5 = V2/R4 ……b**

since short circuit, **V1 = V2 ……c**

If **R2=R6, R4=R5**, then **V3-V4=Vi** can be obtained from abc.

The above formula shows that the voltage across R7 is equal to the input voltage Vi, then the current through R7 is **I=Vi/R7**. If the load **RL<100KΩ**, the current through R1 and R7 are basically the same.

**Ⅴ One Question Related to Op Amp and Going Further**

**5.1 Question**

What the Application of an Op Amp as a Phase Shifter?

**5.2 Answer**

In electronic circuit, op amp is used for direct coupling procedure and so DC voltage level at the emitter terminal increases from phase to phase. This rapidly increasing DC level is likely to shift the operating point of the upcoming stages. Thus to move down the increasing voltage swing, this phase shifter is applied.The phase shifter performs by adding a DC voltage level to the output of fall stage to pass the output to a ground level.

**Frequently Asked Questions about Operational Amplifier Applications**

1. Why is it called operational amplifier?

It's called an “operational” amplifier because it performs a mathematical operation. The most obvious one is multiplication - it amplifies an input signal by a constant. ... But many different 'operations' can be performed by different circuit topologies.

2. What is inside an operational amplifier?

Operations amplifiers — op-amps for short, are integrated circuits, constructed mostly out of transistors and resistors. These integrated circuits multiply an input signal to a larger output. You can use these components with voltage and current in both DC and AC circuits.

3. What are operational amplifiers used for?

Op amps are used in a wide variety of applications in electronics. Some of the more common applications are: as a voltage follower, selective inversion circuit, a current-to-voltage converter, active rectifier, integrator, a whole wide variety of filters, and a voltage comparator.

4. What are linear applications of op amp?

A linear amplifier like an op amp has many different applications. It has a high open loop gain, high input impedance and low output impedance. It has high common mode rejection ratio. Due to these favourable characteristics, it is used for different application.

5. How does an operational amplifier work?

An operational amplifier, or op amp, generally comprises a differential-input stage with high input impedance, an intermediate-gain stage, and a push-pull output stage with a low output impedance (no greater than 100 Ω). ... That is, the output gets fed back to the inverting input through some impedance.

6. What do you mean by differential amplifier?

A differential amplifier is a type of electronic amplifier that amplifies the difference between two input voltages but suppresses any voltage common to the two inputs. It is an analog circuit with two inputs and and one output in which the output is ideally proportional to the difference between the two voltages.

7. What are the non linear applications of op amp?

Non-Linear Applications of Op Amp

Voltage comparator.

Two applications of comparator as window detector and zero crossing detector.

Schmitt trigger circuit with the extension of regenerative comparator.

Multivibrator circuits.

Precision rectifier or super diode with the combination of op amp as voltage follower and a diode.

8. Why do we use differential amplifier?

Differential amplifiers are used mainly to suppress noise. ... Noise is generated in the wires and cables, due to electromagnetic induction, etc., and it causes a difference in potential (i.e., noise) between the signal source ground and the circuit ground.

9. What does an operational amplifier do?

An operational amplifier is an integrated circuit that can amplify weak electric signals. An operational amplifier has two input pins and one output pin. Its basic role is to amplify and output the voltage difference between the two input pins.

10. What is an ideal operational amplifier?

Operational amplifier: The ideal op amp is an amplifier with infinite input impedance, infinite open-loop gain, zero output impedance, infinite bandwidth, and zero noise. It has positive and negative inputs which allow circuits that use feedback to achieve a wide range of functions.

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