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 65㎚ 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 65㎚ CMOS, the VCO draws 8 ㎃ from 2 V supply. It covers the 2930 ? 4150 ㎒. The phase noise is -142㏈Bc/㎐ at 10㎒ offset for 3.9 ㎓ output frequency. The silicon area of the VCO and accompanying dividers is 810 x 600 ㎛².