I'm trying to design a 5th order Butterworth high-pass filter built on the Sallen-key topology with a cut-off frequency at 100Hz. For some reason, the output has a DC offset of around 5mV when the frequency of the input is less than the cut-off frequency even when the input is grounded.
I am using the Op-Amp LT1498 on LTspice and all the capacitor values through all three stages (first order, second order, second order) are 100nF. I'm guessing that its from the output of the op-amp but I'm not really sure.
Link to LT1498 Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/14989fg.pdf
The output is as follows from a 10Hz input:
Any help would be appreciated!