ABC Tools
Active Filter Designer (Sallen-Key) illustration

Active Filter Designer (Sallen-Key)

Designs unity-gain Sallen-Key active filters up to 8th order: pick low-pass or high-pass, the response family (Butterworth, Chebyshev 0.5/1 dB, Bessel), the cutoff frequency and a component scale, and get exact R and C values for every op-amp stage plus the full Bode magnitude and phase plots.

Read the full guide to this tool

For Chebyshev this is the ripple band edge, otherwise the -3 dB point.
Both resistors of each low-pass stage use this value; capacitors are computed from it.
Both capacitors of each high-pass stage use this value; resistors are computed from it.

Notes

  • All stages are unity-gain Sallen-Key sections (plus one RC stage for odd orders), cascaded lowest-Q first.
  • Computed capacitor values are exact; round them to the nearest standard value and expect the response to shift slightly — the E-series solver helps pick combinations.
  • Chebyshev trades passband ripple for a steeper rolloff; Bessel trades rolloff steepness for constant group delay (clean pulse shapes).

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