Electronic – Circuit inverts at high frequency and is unity at low frequency

filteroperational-amplifiertransfer function

Does anyone recognize this op amp setup?

I've figured that at low frequencies C1 is as short circuit, putting the +ve and -ve inputs to \$V_{in}\$ and at high frequencies it will be as open circuit putting +ve and -ve to virtual ground, making it an inverting op amp (unity inverting?).

I have to find the transfer function (and subsequently, bode plots), and my attempts so far haven't quite worked.

schematic

simulate this circuit – Schematic created using CircuitLab

I was wondering if it had a name I could do some research on to understand how to go about it.

Best Answer

This looks like an all-pass filter used to shift phase without affecting the amplitude.

From Wikipedia, LINK:

enter image description here

The transfer function is:

enter image description here

So the magnitude can be flat, because the pole and zero cancel, but the phase exhibits a shift, I.e. the filter has unity-gain magnitude for all frequencies (until the op-amp runs out of steam). The filter introduces a different delay at each frequency and reaches input-to-output quadrature at ω=1/RC (i.e., phase shift is 90°)