Sallen-Key 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

Enter your values:
Cutoff Frequency:
(Enter any one value - Resistor or Ca or Cb)
Resistor (Ra = Rb):
Capacitor Ca:
Capacitor Cb:


The Sallen-Key type filter was introduced by R.P. Sallen and
E. L. Key of MIT Lincoln Laboratory in 1955.

The circuit produces a 2-pole lowpass response using two resistors, two capacitors and a unity-gain buffer amplifier. This filter topology is also known as a voltage controlled voltage source (VCVS) filter.

The Sallen-Key filter is a simple active filter based on op-amps stages, which is ideal for filtering audio frequencies.

It is one of the most widely used filter topologies. One reason for its popularity is that this configuration shows the least dependence of filter performance on the performance of the op-amp. Another advantage of this configuration is that the ratio of the largest resistor value to the smallest resistor value and the ratio of largest capacitor value to the smallest capacitor value are low, which is good for manufacturability.

A serious drawback is that the filter is not easily tuned.

A Low pass filter is a filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency.