A first RF digitally-controlled oscillator for mobile phones

We propose and demonstrate the first RF digitally-controlled oscillator (DCO) for cellular mobile phones. The DCO is part of a single-chip fully-compliant quad-band GSM transceiver realized in a 90 nm digital CMOS process. Frequency tuning is achieved through digital control of an array of standard n-poly/n-well MOSCAP devices. The finest varactor step size is 12 kHz at the 1.6-2.0 GHz output. We analyze the effect of high-speed varactor dithering on the phase noise and show that it can be made sufficiently small. The measured phase noise at 20 MHz offset in the GSM900 band is -165 dBc/Hz and shows no degradation due to the dithering.