1. All the practical circuit to introduce negative feedback, to improve or control amplifier circuit performance indicators, such as: to enhance the stability of gain, decrease the nonlinear distortion, and suppress interference and noise, expanding broadband, control input resistance and output resistance and so on, but came at the expense of lower gain at the expense of,

2. To have positive feedback amplifier circuit is not stable, but in the waveform generating circuit to introduce the positive feedback, to form the conditions of the self-excited oscillation,

3. The feedback is part or all of the output feedback to the input, to influence the input and output of a process, feedback to reflect is a reaction of the signal,

4. The parasitic feedback: by stray capacitance and stray inductance will output feedback to the input signal, this feedback is harmful, to avoid and eliminate, or hard work,

5. The influence of dc performance: the static working point, etc.
Performance on the impact of communication: gain, input and output resistance, bandwidth, etc.

Instantaneous polarity method
6.
7. Feedback with the input node: parallel no intersection point: series
Feedback intersects with the output: no intersection point: current voltage

Series 8. When the signal source resistance Rsi should be as small as possible, in parallel, the signal source is the bigger the better,

9. Feedback amplifier circuit of four configuration
(1) voltage series negative feedback amplifier circuit
Voltage control the voltage source, can realize the voltage amplification
(2) the current parallel negative feedback amplifier circuit
Current controlled current source, which can realize current amplification
(3) voltage parallel negative feedback amplifier circuit
Current controlled voltage source, which can realize current into a voltage
(4) the current series negative feedback amplifier circuit
Voltage controlled current source, voltage conversion can be realized for current