High-selectivity SC filters with continuous digital Q-factor programmability

This paper describes a quality factor (Q) programming technique for high-Q switched-capacitor (SC) filters. Although the selectivity is digitally programmed by varying the effective sampling frequency of an SC branch, without modifying any capacitor value, a continuous Q-factor tunability is obtained, avoiding, in principle, the inherent quantization error associated to any traditional programming approach. Automatic Q-factor tuning is performed, using a scheme based on an amplitude-locking loop approach. Experimental results obtained from a 0.8-μm CMOS second-order SC bandpass filter are given.