115GHz CMOS VCO with 4.4% tuning range

To satisfy consumer demand for ultrahigh-speed wireless communication, voltage controlled oscillators (VCOs) in the D-band using CMOS as well as compound semiconductors are under development. However, the tuning range of such oscillators is limited by the small-size of the varactors. In this paper, a 115 GHz CMOS VCO with a 4.4% tuning range is proposed. To improve the tuning range of the VCO, the conventional varactors are removed and the variation of the gate-drain capacitance in the cross-coupled MOSFETs with supply voltage is utilized. The proposed VCO is fabricated by the 65 nm 1P12M CMOS process and has a core area of 550 mum times 390 mum including the output buffer and pads. The oscillator can be tuned from 113.6 GHz to 118.8 GHz in the voltage range of 1.2 V to 0.6 V. A phase noise of -85.3 dBc/Hz at 1 MHz offset is achieved. The proposed VCO consumes a power of 6.2 mW at the supply voltage of 0.7 V. In the phase-noise measurement in the D-band, since it is shown that, 1/f noise generated by small-size MOSFETs is dominant; a new figure of merits (FOM) for D-band VCOs is proposed and discussed.