TEXAS A&M UNIVERSITY

Department of Electrical Engineering

College Station, Texas 77843-3128

TEL (409) 845-7498 FAX (409) 845-7161

http://amesp02.tamu.edu/

S E M I N A R

Room 119A ZEC

Monday December 1, 2003, 3:00 p.m. 3:50 p.m.

DIGITAL TUNING OF CONTINUOUS-TIME HIGH-Q FILTERS

by

Taner Sumesaglam

Texas A&M University.

Analog Mixed-Signal

Abstract: Integration of analog high-Q filters on chip requires adaptive tuning circuits that will correct the filter parameters such as center frequency and quality factor (Q). Three different digital tuning techniques will be presented. All the methods proposed provide more stable and reliable tuning due to robust digital control. Frequency and quality factor tuning are controlled digitally, providing more stable tuning by activating only one loop at a given time. In the tuning, passband gain and Q equality is not assumed so that the technique can be applied to active LC filters as well.

The phase based digital tuning (PDT), which is verified with 1% tuning accuracy, uses phase information for both Q and center frequency tuning. Output phase is tuned to the 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. The second method (HPDT), high-order phase based digital tuning is an extension of PDT to high-order analog filters without depending on Master-slave approach. Direct tuning of overall response is achieved without separating individual biquad sections, eliminating switches and their parasitics. The tuning system was verified by a prototype 6th order bandpass filter which was fabricated in a conventional 0.5 micron CMOS process. Finally, Magnitude based tuning (MDT) employs an envelope detector to compare output magnitudes at three reference frequencies.

Taner Sumesaglam received his Bachelor's degree in Electrical Electronics Engineering from Bilkent University, Turkey in 2000. He is currently working toward the Ph.D degree in the area of analog & mixed signal at Electrical Engineering Department of Texas A&M University. His research interests include adaptive tuning circuits, continuous-time filters, and RF communication circuits.