A low-phase-noise LC-VCO with an enhanced-Q varactor for use in a high-sensitivity GNSS receiver

An LC-VCO with an enhanced quality factor（Q） varactor for use in a high-sensitivity GNSS receiver is presented.An enhanced A-MOS varactor is composed of two accumulation-mode MOS（A-MOS） varactors and two bias voltages,which show the improved Q and linearization capacitance-voltage（C-V） curve.The VCO gain(K_vco) is compensated by a digital switched varactors array（DSVA） over entire sub-bands.Based on the characteristics of an A-MOS,the varactor in a DSVA is a high Q fixed capacitor as it is switched off,and a moderate Q tuning varactor when it is switched on,which keeps the maximal Q for the LC-tank.The proposed circuit is fabricated in a 0.18μm 1P6M CMOS process.The measured phase noise is better than -122 dBc/Hz at a 1 MHz offset while the measured tuning range is 58.2%and the variation of K_VCO is close to±21%over the whole of the sub-bands and the effective range of the control voltage.The proposed VCO dissipates less than 5.4 mW over the whole operating range from a 1.8 V supply.