Sallen-Key Active Butterworth Low Pass Filter Calculator

Enter value and click on calculate. Result will be displayed.


Ra = Filter Resistor
Rb = Filter Resistor
(Ra = Rb)
Ca = Filter Capacitor
Cb = Filter Capacitor
Ca = Sqrt(2) / [2 × 3.14 × Cutoff Frequency × Resistor]
Cb = Ca / 2

Cutoff Frequency:

(Enter any one value - Resistor or Ca or Cb)

Resistor (Ra = Rb):
Capacitor Ca:
Capacitor Cb:

A Sallen-Key Active Butterworth Low Pass Filter Calculator is a tool used to design a Sallen-Key low-pass filter with a Butterworth response, ensuring a maximally flat frequency response in the passband.

How It Works
The calculator helps determine:

Resistor values (R1, R2)
Capacitor values (C1, C2)
Cutoff frequency (fc)
Operational amplifier (Op-Amp) configuration
Formula for a 2nd-Order Sallen-Key Low-Pass Filter
The cutoff frequency is given by:



For a Butterworth response, component values are selected to ensure a damping factor (Q = 0.707) for a smooth roll-off.

Key Features
Used in audio processing, signal filtering, and anti-aliasing applications.
Achieves -3 dB attenuation at cutoff frequency.
Uses an Op-Amp for active filtering, eliminating inductor usage.