As a low-frequency amplifier, appropriate gain is allocated to each stage, and Rc is used in parallel between E emitter and ground to improve the AC feedback depth. Improve the frequency response characteristics. The power amplifier is broken. Can do direct coupling amplification effect is better, no resistance, constant capacitance phase, amplifier sine wave is extremely linear.
Feedback can be divided into negative feedback and positive feedback. The former makes the output play the opposite role to the input, reduces the error between the system output and the system target, and makes the system tend to be stable; The latter makes the output play a role similar to the input, makes the system deviation increase continuously, makes the system oscillate, and can amplify the control function. The study of negative feedback is the core of cybernetics. In addition, there is current negative feedback theory.
Extended data:
If the feedback signal and the input signal have the same polarity or change direction, the net input signal of the amplifier will be greater than the output signal due to the mixing of the two signals. This kind of feedback is called positive feedback. Positive feedback is mainly used in signal generation circuit.
On the other hand, if the polarity of the feedback signal and the input signal are opposite or the change direction is opposite (opposite phase), the net input signal will be weakened due to superposition. This kind of feedback is called negative feedback amplifier circuit, and the automatic control system usually uses negative feedback technology to stabilize the working state of the system.
The use of negative feedback can also greatly reduce the distortion produced by the amplifier in a stable state and weaken various interference levels inside the amplifier. Negative feedback can also broaden the frequency band of the amplifier and make the amplitude-frequency characteristics of the amplifier relatively flat.
Therefore, negative feedback can greatly improve the amplification quality of the amplifier and improve many performance indicators, and the deeper the feedback, the greater the improvement. However, too deep negative feedback may cause the amplifier to fail to work normally and lead to self-excitation, so a stable negative feedback amplifier usually does not exceed three levels.
Baidu Encyclopedia-Negative Feedback