Low frequency equivalent circuit schematic diagram

The integrated operational amplifier is treated as a complete independent device in the circuit. Therefore, we use equivalent circuits instead of integrated operational amplifiers during analysis and calculation. Integrated operational amplifiers are mainly used in situations where the frequency is not high, so the equivalent circuit at low frequency is given, as shown in the figure below.

Because the op amp has two signal input terminals and one output terminal, only these three terminals are drawn in the figure. Use a triangle to represent the op amp. Among the two input terminals, the one marked "+" is the non-inverting input terminal; the one marked "-" is the inverting input terminal. In the input circuit, both IIB and IIO are considered; UIO and the differential mode input resistor rid are also considered. The voltage on the rid is the differential mode voltage UID. When viewed from the output end, it is equivalent to considering the differential mode amplification factor. The voltage source Aod*UId and the equivalent voltage source Aoc*(U+ + U-)/2 considering the common mode amplification factor and the output resistance ro (U+ and U- represent the voltages at the non-inverting terminal and the inverting terminal respectively).