A Low-Power Low-Phase-Noise VCO with Self-Adjusted Active Resistor

This letter presents a low-power low-phase-noise VCO with self-adjusted active resistor (SAAR). A pair of PMOS transistors is introduced between cross-coupled pairs and LC-tank, serving as the SAAR. When cross-coupled transistor resides in the saturation region, SAAR exhibits small resistance, enabling fast switching and suppressing flicker noise up-conversion to 1/f³ phase noise. Moreover, as cross-coupled transistor enters triode region, SAAR will adjust to larger resistance and prevent the small conducting resistance of the cross-coupled transistor degrading the quality factor of LC tank. Fabricated in a 65 nm CMOS technology, the proposed VCO demonstrates a tuning range of 5.07-6.35 GHz (22.4%) with only 0.42 mW power consumption at 0.6 V supply. The phase noise in the worst case is -40.8 dBc/Hz at 1 kHz and -111 dBc/Hz at 1 MHz, respectively.