Complex BPF for Low-IF Receivers with an Automatic Digital Tuning Circuit

We explore an architecture and implementation of automatic digital tuning circuit for complex BPF in low-power and low-cost transceivers. Active RC filter realization presents an area advantage of 2.35 over g_m-C filter. The principle of simultaneous tuning on center frequency and bandwidth through the calibration of a capacitor array is illustrated, and a scalable automatic digital tuning circuit with only 835 gates is presented. The developed capacitor tuning technique can achieve a tuning error below plusmn3.5%, and reduce a peaking in the passband of filter characteristics. An experimental tunable complex BPF is designed using a 0.18 mum CMOS, and can successfully reduce the tuning error from -20% before the tuning to below plusmn2.5%.