Highly programmable switched-capacitor filters using biquads with nonuniform internal clocks

Programmable switched-capacitor filters based on a cascade of programmable biquadratic sections (BQs) that use nonuniform internal clocking are described. Each section uses switched capacitors clocked a programmable number of times each sampling period without producing undesired spectral components. The clocking scheme uses a uniform input-sampling clock and provides a constant output from each BQ for half of each sampling period, simplifying the design of cascaded BQs. Measured results are presented for a programmable fourth-order low-pass filter and a programmable phone-line equalizer.