An accurate quality factor tuning scheme for IF and high-Q continuous-time filters

A quality factor (Q) tuning technique for IF 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 a modified version of the continuous-time adaptive least-mean-squares algorithm to improve the attainable precision. The technique is resistant to center 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% in the worst case. A test chip consisting of a fourth-order bandpass filter at 10.7 MHz with biquad Q-values of 20 was fabricated in a 1.2-/spl mu/m n-well CMOS process. Experimental results show that the proposed Q-tuning scheme improves on existing methods, with measured accuracies of less than 1% error.