A 1-V 3.8 - 5.7-GHz wide-band VCO with differentially tuned accumulation MOS varactors for commonmode noise rejection in CMOS SOI technology

In this paper, a 1-V 3.8 - 5.7-GHz wide-band voltage-controlled oscillator (VCO) in a 0.13-(mu)m silicon-oninsulator (SOI) CMOS process is presented. This VCO features differentially tuned accumulation MOS varactors that: 1) provide 40% frequency tuning when biased between 0 - 1 V and 2) diminish the adverse effect of high varactor sensitivity through rejection of common-mode noise. This paper shows that, for differential LC VCOs, all low-frequency noise such as flicker noise can be considered to be common-mode noise, and differentially tuned varactors can be used to suppress common-mode noise from being upconverted to the carrier frequency. The noise rejection mechanism is explained, and the technological advantages of SOI over bulk CMOS in this regard is discussed. At 1-MHz offset, the measured phase noise is -121.67 dBc/Hz at 3.8 GHz, and -111.67 dBc/Hz at 5.7 GHz. The power dissipation is between 2.3 - 2.7-mW, depending on the center frequency, and the buffered output power is -9 dBm. Due to the noise rejection, the VCO is able to operate at very low voltage and low power. At a supply voltage of 0.75 V, the VCO only dissipates 0.8 mW at 5.5 GHz.