ZHCSQB3A january 2023 – july 2023 THS2630
PRODUCTION DATA
Figure 8-5 shows a multiple-feedback (MFB) lowpass filter. The transfer function for this filter circuit is:
K sets the pass band gain, fc is the cutoff frequency for the filter, FSF is a frequency scaling factor, and Q is the quality factor.
where Re is the real part, and Im is the imaginary part of the complex pole pair. Setting R2 = R, R3 = mR, C1 = C, and C2 = nC results in:
Start by determining the ratios, m and n, required for the gain and Q of the filter type being designed, then select C and calculate R for the desired fc.