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
    I'm just looking at this application note...

    ...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 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,
  2. crutschow


    Mar 14, 2008
    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.