0. Reverse proportional operation circuit
This is a typical parallel feedback negative feedback circuit. The input voltage U1 acts on the reverse input terminal through the resistor R, so the output voltage and the input voltage are reversed, and the non-inverting input terminal is grounded through the compensation resistor R'. The value is reversed when U1=0. The equivalent resistance of the phase input is the parallel connection of the resistances of the branches, so R'=R//Rf. Negative feedback is introduced through Rf, so Un=Up=0, that is, "virtual ground", Ip=In.
For node N, there is Ir=If, so there is
Organize to get:
1. Proportional arithmetic circuit in the same direction
The circuit introduces voltage series negative feedback, it can be considered that the input resistance is infinite and the output resistance is zero, Un=Up=Ui, Ir=If.
