Performance limitations in switched- capacitor filters

Switched-capacitor (SC) filters continue to improve in performance mainly through progress in the design of MOS operational amplifiers (op amps). Ultimate limits to achievable filter performance, however, stem from factors more fundamental than op amp nonidealities, factors independent of process and circuit improvements. This paper develops, from certain basic assumptions, ultimate limits on dynamic range, chip area, and power consumption in SC integrators and low-pass filters. For integrators, minimum area and power requirements are shown to vary as the square of desired dynamic range. Some physically realistic approximations lead to expressions relating filter area, power consumption, and dynamic range which involve only fundamental process parameters, supply voltage and filter cut-off frequency. Comparison with actual performance in typical commercially manufactured SC filters suggests that there is still a strong motivation in improving op amp specifications. A typical commercial fifth-order voiceband filter operating from a +5-V supply with a dynamic range of 95 dB consumes approximately 5 mW and requires an area of approximately 5000 mil’ compared with the theoretical minima of 8.5 pW and 11.2 mil’, respectively.