I want to have a 1 stage analog active filter with a cutoff frequency of 26 kHz. I used the MATLAB analog filter design toolbox to create such a filter. The filter that was provided by MATLAB looks like follows:
I recreated this filter in LTSpice and did a frequency analysis. It looks like the following:
However, when doing the frequency analysis, the filter gain is already at around -20 dB and at cutoff even lower (as expected).
Why does this filter already have such a low gain in the beginning, although I used the exact values that MATLAB gives me?
I changed the op-amp and the gain changed, so I suppose this has something to do with the op-amp. However, shouldnt the op-amp itself have quite a little impact on the frequency response (except the power bandwith product and transition frequency is low)?
Can anyone please explain me why this happens and what I am doing wrong? Would this circuit also behave like this in a real circuit?