Quality factor tuning of high-frequency high-Q filter biquads using adaptive signal processing

Abstract

A quality factor (Q) tuning technique for high-frequency and high-Q continuous-time filter biquads is proposed. The method is based on the existing magnitude locked loop Q-tuning technique, but it utilizes the continuous-time adaptive LMS algorithm to improve upon several aspects of the old scheme. The technique is resistant to frequency tuning errors, and can use an easily generated clock pulse as its reference signal. Discrete component tests were conducted, with the Q value being tuned to within 1.1%. Two test chips consisting of fourth order bandpass filters at IO.7MHz and IMHZ with biquad Q-values of 20 were fabricated in a 1.2/-Lm nwell CMOS process. Experimental results show that the proposed Q-tuning scheme greatly improves on existing methods, with accuracies of less than 1% error for the 10.7MHz case.