Infrared proximity sensor bandpass filter calculation

Discussion in 'General Electronics Chat' started by peskywinnets, May 31, 2012.

  1. peskywinnets

    Thread Starter Active Member

    Jan 19, 2009
    47
    0
    I'm just looking at this application note...

    http://www.maxim-ic.com/app-notes/index.mvp/id/4622

    ...on the receiver side they have a '2nd order bandpass filter centred at 10khz' (10khz being the carrier frequency they used)....I'd like to use the same circuit but would need the carrier frequency to be a bit higher at 15.625Khz ....how can a decide on the capacitor/resistor values for the bandpass filtered to be centred at 15.625khz?

    I tried to find the formula...but then I spontaneously combusted.

    Many thanks,
    pesky.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    If you change the values of the 2.49kΩ and 475kΩ resistors by the ratio of 10kHz/15.625kHz the center frequency of the filter should change to be near 15.625kHz. Simulating in LTspice I determined that the original center frequency was closer to 9kHz rather than 10kHz and that standard resistor values of 1.24kΩ and 249kΩ give a nominal center frequency of 16.5kHz -- close enough for this application.
     
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