A low noise bulk-coupled colpitts CMOS quadrature VCO

This paper proposes a quadrature voltage-controlled oscillator (QVCO) using 0.18-mum 1P6M standard CMOS process. The QVCO is realized by combining two differential oscillators via the bulk terminals. Using this approach, we can reduce the power dissipation and remove the noise from the additional coupling transistors compared with conventional QVCOs. To improve the phase noise, the oscillator is composed of Colpitts topology for lower phase noise than its cross-coupled counterpart. Moreover, the Colpitts oscillator adopts only PMOS to achieve a better phase noise performance because PMOS has less 1/f noise than NMOS. The VCO operates from 4.9 to 5.5 GHz with more than 11% tuning range. The measured phase noise at 600-kHz offset is -117 dBc/Hz at 5.2 GHz. The QVCO dissipates 10.8 mW at 1.8 V and achieves a good FOM of 185 dB.