A method of varactor capacitance modulation reduction in CMOS LC-VCOs

A method of varactor capacitance modulation reduction is proposed based on the varactor elements with different degrees of nonlinearity. Two fully integrated LC-voltage-controlled oscillators (VCOs) were fabricated in CMOS technology. VCO1 has a traditional varactor configuration whereas VCO2 utilized the proposed linearization method. VCO2 exhibits an average of 10 dB phase noise improvement at 100 kHz offset across the tuning range around a 4 GHz carrier. Each VCO consumes 20 mA at 1.8 V supply voltage.