In the circuit with feedback loop, when there is input at the input end of the operational amplifier, there will be output at the output end of the operational amplifier, and the output will be fed back to the input end, which will play a role in reducing the input amount. Feedback coefficient can be understood as the ratio of feedback to output? ,? The bigger, the stronger the feedback. The feedback coefficient is the transfer function of the feedback loop, and the constant (pure resistance network) is considered as a constant coefficient-so it is called the feedback coefficient. The specific analysis needs to separate the feedback network and then look at the signal transmission relationship. Now analyze two simple examples-proportional amplifier and inverse proportional amplifier: 1) The feedback resistance of the proportional amplifier is Rf and the grounding resistance is R. Obviously, the output signal of the operational amplifier is divided by Rf and R and fed back to its negative input, so its feedback coefficient is Uf/Uo=R/(R+Rf). According to the relationship between the closed-loop gain of deep negative feedback and the feedback coefficient, we can know that the closed-loop gain is the reciprocal of the feedback coefficient, that is, the (r+Rf)/r 2) inverse proportional amplifier also has a feedback resistor Rf and an input resistor R. It can be seen that the output signal of the operational amplifier is also fed back to its negative input after RF and R frequency division, so the feedback coefficient is also R/(R+Rf). But at this time, the input is different from the proportional amplifier, and the effect of the input on the operational amplifier input is -Rf/(R+Rf) (fixed output, pay attention to its effect on negative input). According to the relationship between the closed-loop gain of deep negative feedback and the feedback coefficient, we can know that the closed-loop gain is the reciprocal of the feedback coefficient, that is, (R+Rf)/R combined with the input relationship (-Rf/(R+Rf)), and the voltage gain of the inverse proportional amplifier is [[-RF/(r+RF)] [(r+RF)/r] =-RF/r]. Obviously, for a voltage feedback operational amplifier, the maximum feedback coefficient of the following voltage operational amplifier is 1.