Dual-resonance LC-tank frequency divider implemented with switched varactor bias

A triple-band CMOS LC-tank injection locked frequency divider (ILFD) is proposed and implemented in a 90nm CMOS process. It is realized with a cross-coupled nMOS oscillator with a double-tuned transformer resonator. At the dc drain-source voltage of 0.65 V, the free-running ILFD can have two frequency bands while switching one varactor bias, and the tuning range is from 4.23 (8.89) GHz to 4.47 (10.39) GHz for the low- (high-) frequency band. The measured operational locking range is from 7.6 (15.3) GHz to 10 (19.9) GHz for the low- (high-) frequency band. The double-resonance ILFD has one excited locking frequency band while biasing at the high-frequency band, the excited operational locking range is from 5.75 GHz to 6.3 GHz.