A passband lock loop circuit system for band pass filter

This paper proposes a passband lock loop for tunable band-pass-filter (BPF). AC-coupling, swing amplification, peak conversion and low-noise S/H circuit are designed to differentiate several hundred uV of swing difference. All-digital peak-tracking-controller and FSM are also realized for easy verification and low area. The proposed loop was integrated with a BPF cell with 7-bits controls and 30M∼50MHz of tuning range. In 0.18um technology, the proposed loop and BPF cell respectively occupied active area of 0.0046mm² and 0.027mm², and consume currents of 0.51mA and 1.44mA. With a 625kHz reference clock, the maximum period for passband tracking is 192 clock cycles.