A two-point tuning LC VCO with minimum variation of KVCO2 for quad-band GSM/GPRS/EDGE polar transmitter in 65-nm CMOS

A two-point tuning VCO with switchable secondary tuning gain K_VCO2 is designed in 65nm CMOS for a two-point modulation PLL-based phase modulator that is to serve as phase-modulating part of a quad-band GSM/GPRS/EDGE polar transmitter. The two-point tuning VCO employs two varactor banks for dual tuning capability. The second varactor bank is a differentially tuned structure and its gain K_VCO2 is switchable to minimize its variation for maintaining optimum second-point modulation gain. Fabricated in 65nm CMOS, the VCO draws 8 mA from 2 V supply. It covers the 2930-4150 MHz. The phase noise is -142dBc/Hz at 10MHz offset for 3.9 GHz output frequency. The silicon area of the VCO and accompanying dividers is 810 × 600 μm².