1. Definition of feedback
To lead part or all of the output signal of the amplifier back to the input of the circuit through a certain circuit form is called feedback.
2. Type of feedback
(1) According to the feedback polarity
Positive feedback: increase the net input signal, increase the amplification factor, mostly used in oscillating circuits.
Negative feedback: the input signal is reduced, the amplification factor is reduced, mostly used for amplifying circuits, to improve the performance of the amplifier.
(2) According to the sampling object of feedback signal
Voltage feedback: the sampling object of the feedback signal is the output voltage, proportional to the output voltage;
Current feedback: the sampling object of the feedback signal is the output current, which is proportional to the output current;
(3) According to the access mode of feedback signal
Series feedback: feedback signal and input signal in the form of voltage addition and subtraction;
Parallel feedback: the feedback signal and the input signal in the form of current addition and subtraction;
(4) Negative feedback according to the nature of power supply
Dc negative feedback: used to stabilize static operating point
Ac negative feedback: used to improve the dynamic performance of amplifier circuits
(5) According to the feedback component
Dc feedback: the feedback quantity only contains DC component;
Ac feedback: the amount of feedback only contains ac components;
3. The influence of negative feedback on the performance of amplifier circuit