Continuous-time filter featuring Q and frequency on-chip automatic tuning

The on-chip automatic tuning of digitally programmable continuous-time G(m)-C filters with a wide operation range employing a hybrid analog-digital master-slave scheme is reported in this work. The master system is implemented with a voltage-controlled filter (VCF) with the same programmable transconductance cells as the main filter to enhance the matching between master and slave. The frequency tuning method, for both analog and digital control, is based on a digital phase comparator included in the phase-locked loop achieving high-precision tunability. The digital frequency tuning is obtained with an error of +/-4% and the maximum settling time when changing between two consecutive digital words is 0.3 mu s. Once the digital word is fixed, the analog tuning finely adjusts the value of the characteristic frequency to the reference and corrects for possible temperature variations with a settling time of 0.2 mu s. The analog frequency control covers the whole discrete step with a maximum error of +/-5%. Furthermore, a magnitude-locked loop (MLL) Q-tuning block is simultaneously applied to the system in order to precisely control the quality factor of the G(m)-C filter by using an appropriate envelope detector. According to the obtained results, both post-layout simulation and experimental results, the adopted scheme has resulted as a useful and adequate solution to implement the complete auto-tuning system of digitally programmable continuous-time filters, including frequency and Q-control. Copyright (C) 2008 John Wiley & Sons, Ltd.