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

A quality factor (Q) tuning technique for IF and high-Q continuous-time fil ter biquads is proposed. The method is based on the existing magnitude lock ed loop Q-tuning technique, but it utilizes a modified version of the conti nuous-time adaptive least-mean-squares algorithm to improve the attainable precision. The technique is resistant to center frequency tuning errors, an d 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 filt er at 10.7 MHz with biquad Q-values of 20 was fabricated in a 1.2-mu m n-we ll CMOS process. Experimental results show that the proposed Q-tuning schem e improves on existing methods, with measured accuracies of less than 1% er ror.