High frequency narrow band pass help

Thread Starter


Joined Feb 9, 2015

I'm looking for help in choosing the best op amp filter topology for the following use case:

The input signal is generated using a microphone and I want the filter to pass only 40 kHz signals. So the band pass should be narrow (38 kHz - 42 kHz) which corresponds to a Q factor of 10. And the curve should be as steep as possible to ensure attenuation for signals @ 25 kHz.

I've recently tried simulating on multisim and breadboarding the state variable filter but there seems to be constant noise on the output even without an input. Could this be oscillations from the op amp? The op amps I have tried are OPA2134 and MCP6002. The filter circuit is given on http://www.analog.com/library/analogDialogue/archives/43-09/EDCh 8 filter.pdf

Are there any better alternatives which would provide a narrow, steep band pass for a 40 kHz signal? And which op amps would you suggest for this application?