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Digital control of an analog filter bandwidth

Discussion in 'General Electronics' started by Richard Webb, Apr 25, 2004.

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  1. Richard Webb

    Richard Webb Guest

    From your description we don't know mcuh about how you've tackled this
    problem. There are two suggestions I can give. Either use a digital
    potentiometer to adjust your current 2 op-amp filter. Or perhaps use a
    switched capacitor filter. Maxim's website ( is a good
    place to look for information.
  2. Pini

    Pini Guest

    I'm willing to filter a signal in 1-300 Hz or 300-4000Hz filter.
    Is there a single IC component with a digital switch between the bandwidth?
    I've implemented an active filter with 2 OpAmp. How can I control digitally
    over the required operating range?
  3. iQbal

    iQbal Guest

    What you could also do is replace the gain stages with VCA.
    Design a state varaible filter.
    Replace the two integrators with VCA's.
    Your cutoff frequency is now a function of the control voltage to the
    VCA's. This control volatge could be supplied by DA.

    Thats it

  4. Also, you can switch between two ranges by using 4066, 4053 or similar
    analogue switch.

    Tomislav Canic
  5. Pini

    Pini Guest

    The system will acquire analog data with input amplitudes starting with 20uV
    (this signal will be amplified by 100 before filtering).
    I'm afraid of noise leakage from the switch capacitor filters to the
    acquired signal.
    What is the solution for such problem?
    The analog band pass filter footprint should be as small as possible.
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