Written by ChatGPT but checked against the data-sheet calculations.

#!/usr/bin/env python3
"""
2nd-order unity-gain Butterworth Sallen-Key low-pass calculator
Based on TI SBOA226 design steps:

Usage:
For 22k resistors and a cut-off  $f_c$ of 500Hz:

$ python3 --R 22E3 500

![[butter_plot.py]]
![[butter_plot.py]]
## Example

$ python3 butter_plot.py --R 22E3 500
2nd-order unity-gain Butterworth Sallen-Key LPF (ideal)
fc   = 0.5 kHz
R1=R2= 22 kohm
C1   = 20.46 nF  (norm 1.414)
C2   = 10.23 nF  (norm 0.707)
Q    = 0.707107