Included in at least one reviewed higher-education syllabus.
S4-1.4 Negative Feedback Amplifiers
You can classify the four feedback topologies, predict their effect on gain and impedances, and analyse practical feedback circuits.
Negative feedback is the most important single idea in analog design: give away raw gain and receive stability, wider bandwidth and predictable impedances in return. This topic classifies the four feedback topologies and works through their analysis, sitting late in the amplifier sequence because it needs everything built so far. The confusion everyone hits is telling the topologies apart — anchor on what is sampled at the output, voltage or current, and how it is mixed back at the input, series or shunt, and the impedance effects stop being memorisation and start being logic.
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The feedback concept and general characteristics of negative feedback
Feeding part of the output back to the input, out of phase, gives away raw gain and receives stability, wider bandwidth and predictable behaviour in return. It is the single most important idea in analog design and it returns in control systems and op-amps.
Effect of negative feedback on input and output impedances
Feedback does not only change gain: depending on how it is connected it raises or lowers the input and output impedances, often by large factors. That is frequently the actual reason a designer adds it.
Method of analysis of feedback amplifiers
A repeatable procedure for analysing a feedback amplifier rather than guessing at it: identify what is sampled, identify what is mixed back, then open the loop and calculate. Having a method matters because these circuits resist intuition.
Voltage-series, voltage-shunt, current-series, current-shunt circuits
The four topologies, named by what is sampled at the output and how it is returned at the input. Anchor on those two questions and the impedance effects follow without memorisation, which is what stops the four names blurring together.
NPTEL: Analog Circuits · CourseLab: add feedback to an amplifier in simulation and measure the gain/bandwidth trade
Add feedback to an amplifier in simulation and measure what happens to gain and bandwidth. The product of the two staying roughly constant is the trade made visible.
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