A first RF digitally-controlled oscillator for SAW-less TX in cellular systems

A first digitally-controlled oscillator for mobile stations is presented. Combining a MTM capacitor and two NMOS transistor arrays for the varactor as an RF DAC, a highly linear oscillator gain is achieved, and is insensitive to process shift. With a sigma-delta dithering, a fine frequency resolution is obtained while having negligible phase noise degradation. The measured -167dBc/Hz at 20MHz offset from 915MHz carrier proves that this DCO system can be used in a SAWless transmitter for mobile phones.