A digital automatic tuning technique for high-order continuous-time filters

A digital automatic tuning technique for high-order continuous-time filters is proposed. Direct tuning of overall response is achieved without separating individual biquad sections, eliminating switches and their parasitics. Output phase of each biquad section is tuned to known references, which are generated by a frequency synthesizer. The core tuning circuit consists of D flip-flops (DFF) and simple logic gates. DFFs are utilized to perform binary phase detection. Frequency and quality factor tuning loops for each biquad are controlled digitally, providing more stable tuning by activating only one loop at a given time. The tuning system was verified by a prototype sixth-order bandpass filter which was fabricated in a conventional 0.5 /spl mu/m CMOS process with /spl plusmn/1.5 V power supply.