Highpass and bandpass 2nd-order switched-capacitor filters

Abstract

Highpass and bandpass switched-capacitor filters derived from Sallen and Key, and Bach's RC active highpass filters have been described. The bandpass filters have been shown to be realisable by simple modification of the highpass filters, using Laker's method of obtaining 1st-order lowpass filters from 1st-order highpass filters under certain input conditions. A single amplifier version of a recently described bandpass filter has also been discussed. All the realisations have been compared regarding the capacitor spread required to realise desired pole frequency and pole Q for given sampling frequency and optimised for minimal capacitor spread.