# How to calculate the input impedance and transfer function

I have the following circuit, that is used as a signal conditioning circuit in a audio system project. I am trying to calculate the transfer function and the Zin(input impedance) and Zout(output impedance)

in Zin, I know how to calculate the impedance of the rc filter but im getting confused because there are one more resistor of 10M that makes the offset of the voltage.

So, how can i calculate the transfer function,Zin and Zout of this circuit?

• The two 10-Meg resistances are in parallel for the small-signal analysis. This is because you consider the 5-V source at a 0-V ac level (imagine a decoupling cap. on this 5-V line). Sep 24, 2020 at 20:18
• 10M resistor values are too high unless you buy and measure many LM324 ICs to pick ones with very low input bias current. The half the supply voltage divider is wrong because the input bias current pulls the inputs to a high enough voltage where they do not work. Sep 25, 2020 at 1:37