A 1.2-V CMOS Limiter / RSSI / Demodulator for Low-IF FSK Receiver

This paper presents low-voltage low-power limiter, RSSI, and demodulator designs for a low-IF wireless FSK receiver. The IF is located at 3 MHz. The FSK demodulator is implemented by a delay-locked loop associated with the techniques of digital offset cancellation and modified phase-frequency detection. The demodulated data can be recovered with one-clock latency. The circuits in limiter and RSSI are all pseudo differential to minimize the requirement of the voltage headroom. Each gain cell with feedforward offset cancellation and common mode stabilization circuits can make sure its functionality against device mismatch. The chip uses a standard 0.18 mum CMOS process. The active area is 0.11 mm2. With a single 1.2-V power supply, measurement results show that the 55 dB gain, 15 MHz bandwidth limiter and the RSSI consume 1.9 mA. The FSK demodulator part consumes 300 muA.