Band pass and notch filters

How it calculates

Band-pass: H(s) = −G(ω0/Q)s/[s²+(ω0/Q)s+ω0²]

Notch: H(s) = (s²+ω0²)/[s²+(ω0/Q)s+ω0²]

Twin-T Q: Q = (1+R5/R4)/4

Fliege Q resistors: RQ = 2 Q R0

Assumptions

• MFB/Deliyannis circuit: input through R1 to N; capacitor C1 from N to V−, C2 from N to output, feedback R3 from output to V−, and optional R2 from N to ground. V+ is grounded. Deliyannis mode omits R2; its core gain is 2Q², followed by an ideal magnitude scaler.
• Twin-T uses R,R,R/2 and C,C,2C with buffered positive feedback at its common reference node. Fliege component labels refer to the linked TI two-op-amp circuit. The ideal notch response does not predict finite-op-amp notch depth. Mismatch plot moves the numerator zero frequency only; it is not a complete component tolerance simulation.

Worked example

These are the calculator's default inputs. Change any input above to recalculate.

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