Name: op-amp gain, feedback, and saturation
Uploaded: 2025-05-22T09:06:14.000Z
Duration: 1 min 17 s
Channel: JoVE

Consider the equivalent circuit model of an operational amplifier. The output section consists of a voltage-controlled source in series with the output resistance.
In the input section, v1 and v2 denote voltages from the inverting and non-inverting terminals to the ground, respectively.
The output voltage of an op amp equals the product of the input voltage difference and the open-loop gain.
For small voltage differences, the op amp behaves linearly. If the voltage exceeds the power supply voltage the op amp saturates.
The combination of applied voltage and negative feedback ensures that the op amp operates within its linear range.
Modern amplifiers have large gains and input resistance, allowing them to be approximated as ideal op amps.
An ideal op amp has infinite open-loop gain, infinite input resistance, and zero output resistance. Both input terminal currents and the input offset voltage are zero in an ideal op amp.
Additionally, It has infinite bandwidth, allowing it to amplify signals of any frequency, and infinite slew rate, signifying its ability to change the output voltage rapidly over time.

characteristics of opamp

The operational amplifier, commonly known as an op-amp, is a specially designed electronic circuit component. Its purpose is to work in conjunction with other circuit elements to execute a defined signal-processing operation. Consider an equivalent circuit model of an op-amp, as depicted in Figure 1; the output section comprises a voltage-controlled source in parallel with the output resistance Ro.
<img alt="Operational amplifier circuit diagram, showing voltage inputs V1, V2, inverting and non-inverting." src="/files/ftp_upload/15077/15077_PT_Figure_1.svg" style="text-align: center; height: 166px;" data-altupdatedat="1754904545000" data-alt="Operational amplifier circuit diagram; V1, V2 inputs, symbols, electrical engineering concept." />
Figure 1: The equivalent circuit of the nonideal op-amp
Figure 1 shows that the input resistance Ri equates to the Th&#279;venin equivalent resistance observable at the input terminals. Similarly, the output resistance Ro corresponds to the Th&#279;venin equivalent resistance discernible at the output. The differential input voltage (vd) is calculated as the difference between the noninverting terminal's voltage relative to the ground and the inverting terminal's voltage relative to the ground.
The op-amp discerns the difference between these two inputs and amplifies it by the gain A, thus generating a voltage that appears at the output. Here, A represents the open-loop voltage gain - named so because it signifies the gain of the op-amp in the absence of any external feedback from the output to the input.
Feedback is an integral concept to comprehend when studying op-amp circuits. Negative feedback can be achieved by feeding the output back to the op-amp's inverting terminal. When a feedback path from output to input exists, the resulting ratio of the output voltage to the input voltage is known as the closed-loop gain.
The op-amp does have its practical limitations. One such limitation is that the magnitude of its output voltage cannot surpass |VCC|. Essentially, the power supply voltage determines and restricts the output voltage. Depending on the differential input voltage, the op-amp can function in one of three modes: positive saturation, linear region, or negative saturation. If an attempt is made to increase vd beyond the linear range, the op-amp reaches saturation, yielding either vo = VCC or vo = -VCC.

Characteristics of OpAmp

The operational amplifier, commonly known as an op-amp, is a specially designed electronic circuit component. Its purpose is to work in conjunction with ...

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Operational Amplifiers

KEY TERMS AND CONCEPTS

op-amp gain, feedback, and saturation

An operational amplifier, or op-amp, is an electronic circuit component used with other circuit parts to carry out a signal-processing task. It is often described with an equivalent circuit model. In that model, the output section includes a voltage-controlled source in parallel with the output resistance, R o.

The model also shows the input resistance, R i, which is the Thevenin equivalent resistance seen at the input terminals. The differential input voltage, v d, is the difference between the noninverting terminal voltage and the inverting terminal voltage, both measured relative to ground. The op-amp compares these two input voltages and amplifies the difference by the gain A to produce an output voltage.

A is called the open-loop voltage gain because it describes the op-amp without feedback from the output back to the input. Feedback is important in op-amp circuits. Negative feedback is created by connecting the output to the inverting terminal. When that feedback path exists, the output-to-input ratio is the closed-loop gain.

Op-amps also have practical limits. Their output voltage cannot exceed the magnitude of the supply voltage, |VCC|. The power supply sets this limit. Depending on the differential input voltage, the op-amp can operate in positive saturation, the linear region, or negative saturation. If v d is pushed beyond the linear range, the output saturates at either v o = VCC or v o = -VCC.

Op-Amp Gain, Feedback, and Saturation

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An operational amplifier, or op-amp, is an electronic circuit component used with other circuit parts to carry out a signal-processing task. It is often described with an equivalent circuit model. In that model, the output section includes a voltage-controlled source in parallel with the output resistance, R o. The model also shows the input resistance, R i, which is the Thevenin equivalent resistance seen at the input terminals. The differential input voltage, v d, is the difference between...

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Op Amp Stages in Series

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key terms and concepts

Learn how an op-amp compares input voltages, uses open-loop and closed-loop gain, and reaches positive or negative saturation when output limits are exceeded.

Op-Amp Gain, Feedback, and Saturation | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Op-Amp Gain, Feedback, and Saturation

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