Answer: The effect of feedback on the total gain of the system is significant, and this effect depends on the type of feedback (positive feedback or negative feedback) and the phase relationship between the feedback signal and the input signal.
Answer analysis:
The effect of positive feedback on the total gain of the system
1. Gain increase: Positive feedback means that the feedback signal is in the same or similar phase as the input signal, which increases the system gain. In a positive feedback circuit, if the phase difference between the feedback signal and the input signal is 0 degrees or close to 0 degrees, the feedback signal will strengthen the input signal, thereby increasing the system gain.
2. Stability effect: However, positive feedback may also cause system stability problems. In particular, when the phase difference between the feedback signal and the input signal is 90 degrees, the system gain will increase significantly, which may cause system instability, self-oscillation or periodic pulse output.
The effect of negative feedback on the total gain of the system
1. Gain reduction: Negative feedback means that the feedback signal is in the opposite phase to the input signal, which reduces the system gain. In a negative feedback circuit, the feedback signal weakens the input signal, thereby reducing the gain of the entire circuit.
2. Improved stability: Negative feedback not only reduces the system gain, but also improves the stability of the system. Because negative feedback has a "self-regulating" ability, when the system is subject to external interference or internal parameter changes, negative feedback can automatically adjust the system state to keep it near the stable operating point.
3. Linearity and noise suppression: In addition, negative feedback can also improve the linearity and noise suppression of the system. Negative feedback reduces the nonlinear distortion and noise interference of the system by feeding back part of the output signal to the input end and comparing and offsetting it with the input signal.
Phase relationship between feedback signal and input signal
1. The influence of phase difference: Whether it is positive feedback or negative feedback, the phase difference between the feedback signal and the input signal has an important influence on the system gain and stability. When the phase difference is 0 degrees or close to 0 degrees, positive feedback will enhance the system gain; when the phase difference is 180 degrees or close to 180 degrees, negative feedback will weaken the system gain and improve stability.
2. Stability criterion: When designing and analyzing feedback systems, it is necessary to consider the stability criterion of the system. For example, in a negative feedback system, the stability of the system can be evaluated by calculating parameters such as loop gain and phase margin.
In summary, the effect of feedback on the total gain of the system is complex, and it depends on the type of feedback, the phase relationship between the feedback signal and the input signal, and the specific design of the system. In practical applications, it is necessary to select the appropriate feedback type and parameter configuration according to specific needs to optimize the performance of the system.