I'm doing a project and one of the steps consists of filtering a signal through a low-pass, band-pass and high-pass filter.
All the filters are Sallen-Key with a passband gain of 1. The pass-band filter uses a Sallen-Key low-pass and high-pass circuit. The low-pass should ideally have a cut-off frequency of 100Hz, high-pass 4kHz, and the pass-band has a 100Hz high-pass filter and a 4kHz low pass. All the filter orders are 4 (n=4).
The output of these filters should be added in an adder circuit, with variable gain through a potentiometer. The problem I'm having is that I'm getting some flutuations of gain around the cuttoff frequencies, since for example if the cut-off frequencies are perfectly matched, the adder circuit adds 2 signals with 1/sqrt(2) of a specific gain, resulting in a gain of 3db.
Since my filters are not perfectly matched, the effect I'm having is getting some attenuation. Regardless of that, is there any method I can use to get rid of, or attenuate this problem?