Electronic Filter Design Calculator

Design Butterworth, Chebyshev, and Sallen-Key active/passive filters. Calculate component values for low-pass, high-pass, and band-pass topologies.

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▸Formula · assumptions · example(IEEE Std 430 · IEC 60384 · Standard E96/E24 Resistor & Capacitor Series)

Formula

f_c = \frac{1}{2\pi R C} \quad (\text{1st Order RC}), \quad f_0 = \frac{1}{2\pi \sqrt{L C}} \quad (\text{2nd Order LC}), \quad H(s) = \frac{1}{1 + \sqrt{2}s/\omega_0 + (s/\omega_0)^2}

Butterworth (maximally flat), Chebyshev (equiripple), and Sallen-Key active analog active/passive filter synthesis.

Assumptions

  • · Ideal op-amp characteristics: infinite open-loop gain, infinite input impedance, zero output impedance
  • · Standard passive component tolerance (1% metal film resistors, C0G/NPO capacitors for low temperature drift)
  • · Passband attenuation at cutoff frequency fc equals -3.01 dB for Butterworth response

Worked example

Worked example — 2nd Order Butterworth Low-Pass (fc = 10 kHz, Sallen-Key topology)

Calculates standard values R1 = R2 = 15.8 kΩ, C1 = 1.5 nF, C2 = 750 pF (damping ratio ζ = 0.707, Q = 0.707) with -40 dB/decade stopband roll-off.