This paper presents an area-efficient current-mode-logic (CML)-based divider, with a tunable self-resonant frequency for locking range (LR) extension. Specifically, a negative-g_m (NG) cell is inserted between the resonated shunt-peaking inductor and the load resistor to shift the divider's sensitivity curve (SC), enabling concurrently a higher operating frequency and a wider LR. We also use the injection-locking concept, together with a graphical phasor diagram with the frequency-phase information, to systematically explain the LR-extension mechanism. Prototyped in a 65-nm CMOS, the divider occupies a tiny active area of 0.0018 mm². The measured LR is 153% (4-30 GHz) while consuming 4.06-4.28 mW at 30 GHz under a single 1.2-V supply. The performance corresponds to two figure of merits: FOM_P of 25.5 dB and FOMP of 71.5, both compare favorably with the state of the art.