Three Pole Low Pass Filter

This Javascript is adapted from the best material available on the web for designing a three pole lowpass filter in a single opamp. Eventually, we hope to put it into the unreleased (and therefore unofficial and unsupported version) of FilterPro.

Filter design notes:

  1. This calculator supports only unity gain Butterworth response
  2. An "equal resistors" strategy is employed.
  3. For best filter performance, pick a resistor value that allows you to use NPO/COG capacitors in the circuit. Values 1000pF or higher tend to get expensive and large.
  4. Select capacitors that are larger than 10pF. Smaller values of capacitor can be used, but PC board parasitics will change the tuning of the circuit.
  5. Use 1% capacitors, or 2% at worst. Performance of the circuit with 5% capacitors will be degraded.

Enter Desired Cutoff Frequency (Hz):
Enter Resistor Value (Ohms):
Select Capacitor Sequence:
 
C1R1
C2R2
C3R3