This paper presents a constant-current-controlled class-C VCO using a self-adjusting replica bias circuit. The proposed class-C VCO is more suitable in real-life applications as it can maintain constant current which is more robust in phase noise performance over variation of gate bias of cross-coupled pair comparing to a traditional approach without amplitude modulation issue. The proposed VCO is implemented in 180 nm CMOS process. It achieves a tuning range of 4.8–4.9 GHz with a phase noise of -121 dBc/Hz at 1 MHz offset. The power consumption of the core oscillators is 4.8 mW and an FoM of -189 dBc/Hz is achieved.