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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.
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 (CV) curve. The VCO gain (K vco) is compensated by a digital switched varactors array (DSVA) over the 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 0.18 μm 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 sup ply.