Realizations of high-order switched-capacitor filters using multiplexing technique

A new SC design methodology using multiplexing technique is proposed to realize arbitrary high-order filters. In this methodology, the filter transfer function is transformed as the combination of biquads and their outputs are computed sequentially by the multiplexing SC biquad circuit. Four basic function SC circuits are introduced and a filter can be implemented by various combinations of these circuits. This makes the proposed method more versatile and practical. Because of the efficient use of multiplexing techniques, the realized high-order filters have less op-amps, switches, and capacitors, and thus small chip area, but at the cost of increasing clock phases. An eighth-order Butterworth low-pass filter design example is presented to demonstrate how to apply the proposed method to the design of high-order filters. Moreover, an eighth-order low-pass filter has been designed and fabricated in 1.2 μm CMOS double-poly double-metal process. Both computer simulation and experimental results have successfully verified the function correctness and the performance of the proposed design method