I'm needing to improve an existing fourth order active filter design.
The filter amplifies 10-100 kHz signals as desired, however the phase shift is causing problems. 10 kHz signals are phase shifted around 200 degrees, but 100 kHz signals are phase shifted around 600 degrees.
The varying phase shift for desired signals is rather unhelpful. Ideally I would want the same phase shift for the entire frequency range. The magnitude of phase shift itself is of no concern, so increasing the phase shift at 10 kHz so that it is constant up to 100 kHz wouldn't be a problem.
- Is there a type of (allpass) filter that introduces a decreasing phase shift? - for instance 360 degrees for 10 kHz and 180 degrees for 100 kHz?
- Where should I start, how should I work, when trying to achieve constant phase shift in filter design?