Injection-Locked Frequency Divider With a Resistively Distributed Resonator for Wide-Locking-Range Performance

Distributed LC resonator and resistively distributed resonator belong to the same technique used to extend the locking range of injection-locked frequency divider (ILFD). ILFD using the former resonator often has one locking range, and extension of locking range is attributed to oscillation frequency increment. This paper measures and analyzes the input sensitivity of a CMOS ILFD with a resistively distributed resonator and with the divide-by-3 and divide-by-2 functions, and the input sensitivity shows a wide single-band locking range. The fabricated 0.18-μm CMOS ILFD is made of a pair of cross-coupled n-type transistors, two direct-injection MOSFETs, and a resistively dualresonance resonator. The wide single-band locking range of the designed ILFD is owing to the overlapped locking ranges, and it is verified by the smooth tuning range without forbidden region and nonoverlapped locking ranges measured on the same chip with the unbalanced injection structure. The frequency tuning is obtained with large tank resistance, which also reduces the frequency tuning hysteresis effect.