Feedback, in the context of amplifier circuits, refers to the process of taking a portion or all of the output of the amplifier circuit and feeding it back into the input circuit of the amplifier in a certain way to influence the input signal.

Positive Feedback and Negative Feedback

Feedback can be classified into positive feedback and negative feedback based on its polarity.

Positive Feedback: Positive feedback is feedback that increases the net input of the amplifier circuit.

Negative Feedback: Negative feedback is feedback that decreases the net input of the amplifier circuit.

Determining the Presence of Feedback in Amplifier Circuits:

The presence of feedback in amplifier circuits can be determined by checking whether there is a feedback path linking the output circuit and the input circuit of the amplifier.

The instantaneous polarity method is generally used to determine positive or negative feedback. If the feedback signal has the same polarity as the original input signal, it is positive feedback. If the feedback signal has the opposite polarity to the original input signal, it is negative feedback.

The purpose of introducing feedback into amplifier circuits:

The static operating point of the amplifier circuit generally fluctuates with temperature, and the amplification factor is unstable. To stabilize the static operating point of the amplifier circuit, a voltage divider-type working point stabilization circuit can be used, introducing a DC current negative feedback in the circuit to improve its performance.

The main advantages are as follows:

1. Reduces the output impedance of the amplifier circuit, improving its load capacity.

2. Increases the input impedance of the amplifier circuit, reducing the current demand from the signal source.

3. Reduces non-linear distortion of the output voltage, improving the output waveform.

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