Created by
Created March 02, 2012
Last modified March 09, 2012
Tags active-filter  


Three amplifier SV filter provides Highpass, Bandpass, and Lowpass outputs; a fourth amp is shown implementing a notch filter.


State Variable filter

Provides second order High pass, Lowpass, Bandpass.

OA4 here sums the LP, BP outputs to create a notch filter.

In typical design:

  • R3=R5; C1=C2, and the cutoff frequency is 1/(2piR3*C1)

  • R1=R2=R6

  • Q = (R10+R9)/(3*R10) (Q is the magnitude of response at cutoff; higher Q give more peaking/resonance)

As shown, 1kHz and critical damping (Q=0.7)


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