Multi-rate switched capacitor filter design with aggressive sampling-rates: filtorX in action

A methodology to accurately design multirate switched-capacitor (SC) filters is derived. Multirate SC filter design is an effective means of minimizing silicon area for bandpass systems. The theory derived allows designs to achieve maximal area savings by employing sampling rates approaching the minimum allowed by sampling theory. Designing filters to simultaneously operate at different sampling rates can require numerical optimization to correct for the effects of multirate operation, filtorX, a computer-aided filter design tool, was employed to design a CCITT V.22 high-band modem filter as a test of the derived design methodology. The result was an improvement of the uncorrected multirate filter, which had exceeded passband tolerances, to one which was within tolerances. The multirate filter, operating at sampling rates of 128 kHz and 8 kHz, required 70% less capacitor area than the equivalent single-rate filter operating at a sampling rate of 128 kHz