BeginnerTopic 26 of 104Electronics & Embedded
Feedback in amplifiers
Negative feedback trades gain for stability, bandwidth and linearity.
In depth
Negative feedback reduces gain by (1+Aβ) but desensitises it to component variations, widens bandwidth, reduces distortion and alters impedances (series mixing raises input impedance; shunt sampling lowers output impedance). Too much phase shift makes it unstable.
Key points
- Gain margin and phase margin
- Loop gain Aβ
- Four feedback topologies
ExampleA closed-loop op-amp's gain depends mostly on resistor ratio, not on A.
Negative feedback trades gain for better stability, linearity and bandwidth, which makes almost every practical amplifier work well.
What is Feedback in amplifiers?
Negative feedback trades gain for stability, bandwidth and linearity.
Why is it important to understand feedback in amplifiers?
Negative feedback trades gain for better stability, linearity and bandwidth, which makes almost every practical amplifier work well.
Why does feedback reduce gain?
Part of the output is subtracted from the input, so the amplifier must work harder for the same output, which lowers the closed-loop gain.
Can feedback cause oscillation?
Yes. If the phase shift reaches 180 degrees with enough loop gain, the feedback becomes positive and oscillation starts, which is why compensation is needed.
How is Feedback in amplifiers used in practice?
Typical applications include reducing the distortion of an audio power amplifier with feedback, making an op-amp circuit insensitive to component variations and extending the bandwidth of an amplifier stage with feedback.
What should I learn before Feedback in amplifiers?
Study "555 timer" first (topic 25 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
What are the key points of Feedback in amplifiers?
Gain margin and phase margin. Loop gain Aβ. Four feedback topologies.
Can you give an example of Feedback in amplifiers?
A closed-loop op-amp's gain depends mostly on resistor ratio, not on A.
What comes after Feedback in amplifiers?
The next topic is "Frequency response of amplifiers", which builds directly on this one.
How difficult is Feedback in amplifiers?
It is classed as Beginner in Electronics & Embedded (topic 26 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.