High frequency narrow band pass help

Discussion in 'The Projects Forum' started by Vixpanchalx, Feb 10, 2015.

  1. Vixpanchalx

    Thread Starter New Member

    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?
  2. crutschow


    Mar 14, 2008
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    The PDF in your link is 148 pages long. Which page has your schematic?

  4. Vixpanchalx

    Thread Starter New Member

    Feb 9, 2015
    The schematic is on page 8.77 and there is a link to design example on page 8.95