Rauch multiple-feedback low-pass
8 parts
One op-amp, three resistors and two capacitors give a second-order low-pass that inverts while it filters — the multiple-feedback, or Rauch, structure. The input here is a 300 Hz signal with a 6 kHz interferer stacked on top of it by a second source wired in series, and the filter's job is to separate them. Because both op-amp inputs sit at a virtual ground the signal never appears as a common-mode voltage, which is the usual reason to reach for this topology instead of a Sallen-Key.
- V1 2V·300Hz
- V2 1V·6kHz
- R1 1kΩ
- R2 1kΩ
- R3 1kΩ
- C1 220nF
- C2 47nF
- OP1
