How does the open-loop gain of a real operational amplifier compare to that of an ideal op-amp?

A real op-amp has finite open-loop gain, whereas an ideal op-amp has infinite open-loop gain.

Why is the assumption of infinite open-loop gain unrealistic for practical op-amp circuits?

Real operational amplifiers can only provide a finite open-loop gain, so the output cannot increase without limit for infinitesimally small input differences.

How does the input impedance of a real operational amplifier differ from that of an ideal op-amp?

A real op-amp has finite input impedance, whereas an ideal op-amp has infinite input impedance.

What practical consequence arises from a real op-amp having finite input impedance rather than infinite?

A small current is drawn from the input signal source, which can affect the signal voltage and load the preceding circuit.

How does the output impedance of a real operational amplifier compare to that of an ideal op-amp?

A real op-amp has non-zero output impedance, whereas an ideal op-amp has zero output impedance.

Why does non-zero output impedance in a real op-amp matter when driving a load?

Some voltage is dropped across the internal output impedance, so the output voltage delivered to the load is reduced compared to the ideal case.

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Real operational amplifiers

5 things to know
Paper 3, section B

Overview

Finite gain, the gain-bandwidth product, slew rate and offset voltage.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What is the gain-bandwidth product, and how are frequency response axes scaled?

Numbers

What is needed to find bandwidth from the gain-bandwidth product, what formula gives it, and how is it widened?

Numbers

What is slew rate, and why might a real op-amp output something with equal inputs?

Process

Explain what happens to the bandwidth of an op-amp circuit if the closed-loop gain is increased

Key term

What effect does reducing the closed-loop gain of an op-amp circuit have on its bandwidth?

Questions from this subtopic

Each one with the model answer underneath.

1
How does the open-loop gain of a real operational amplifier compare to that of an ideal op-amp?
Model answer
A real op-amp has finite open-loop gain, whereas an ideal op-amp has infinite open-loop gain.
2
Why is the assumption of infinite open-loop gain unrealistic for practical op-amp circuits?
Model answer
Real operational amplifiers can only provide a finite open-loop gain, so the output cannot increase without limit for infinitesimally small input differences.
3
How does the input impedance of a real operational amplifier differ from that of an ideal op-amp?
Model answer
A real op-amp has finite input impedance, whereas an ideal op-amp has infinite input impedance.
4
What practical consequence arises from a real op-amp having finite input impedance rather than infinite?
Model answer
A small current is drawn from the input signal source, which can affect the signal voltage and load the preceding circuit.
5
How does the output impedance of a real operational amplifier compare to that of an ideal op-amp?
Model answer
A real op-amp has non-zero output impedance, whereas an ideal op-amp has zero output impedance.
6
Why does non-zero output impedance in a real op-amp matter when driving a load?
Model answer
Some voltage is dropped across the internal output impedance, so the output voltage delivered to the load is reduced compared to the ideal case.

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