A 900-MHz 2.5-mA CMOS frequency synthesizer with an automatic SC tuning loop

A 900-MHz phase-locked loop frequency synthesizer implemented in a 0.6-mum CMOS technology is developed for the Wireless Integrated Network Sensors applications. It incorporates an automatic switched-capacitor (SC) discrete-tuning loop to extend the overall frequency tuning range to 20%, while the VCO gain (K-VCO) resulting from the CMOS varactor continuous-tuning is kept low at only 20 MHz/V in order to improve the reference spurs and noise performance. This frequency synthesizer achieves a phase noise of -102 dBc/Hz at 100 kHz offset frequency and reference spurs below -55 dBc. The synthesizer, including an on chip VCO, dissipates only 2.5 mA from a 3-V supply.