State_Variable_2

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

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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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State_Variable_2 PUBLIC