2nd-Order Sallen-Key Active Filter Designer
Design a 2nd-order Sallen-Key active filter using an op-amp. Derives R and C component values for Butterworth, Chebyshev, and Bessel response types, with a live Bode plot.
Design Specifications
Hz
nF
Calculated Component Values
Filter Resistor (R₁ = R₂ = R)15.92 kΩ
Capacitor (C₁ = C₂ = C)10 nF
Feedback Resistor (Rf)5.86 kΩ
Ground Resistor (Rg)10.00 kΩ
Passband Gain (Av)1.586
Pole Quality Factor (Q)0.7071
Circuit Schematic (2nd-Order Sallen-Key)
Bode Plot
Enter specifications to load the chart.
About the Sallen-Key Active Filter
The Sallen-Key topology uses an op-amp to implement a 2nd-order filter using only resistors and capacitors — no inductors required. Because inductors are bulky, have poor tolerance, and introduce electromagnetic noise, active RC filters dominate in precision low-frequency analog signal processing.
Approximation Types Compared
- Butterworth:Maximally flat magnitude response in the passband. Offers a balanced roll-off slope and is the most widely used approximation. Q = 0.7071. Produces slight overshoot in step response.
- Chebyshev:Steepest roll-off into the stopband at the cost of ripple in the passband. This designer uses a 1 dB ripple condition (Q = 0.9565), trading passband flatness for sharper selectivity.
- Bessel:Designed for maximally linear phase delay (constant group delay). Ideal for high-speed pulse transmission or audio where waveform distortion must be minimized. Nearly zero overshoot (Q = 0.5774).