A high-resolution DCO with MOS capacitors

A digitally controlled oscillator (DCO) that achieves a minimum frequency tuning step of 20 kHz without any dithering is presented. Three tuning stages are employed to obtain a wide frequency range of 1 GHz in the classical LC tank. The fine tuning bank is realized by inverse connection of two pairs of pMOS transistors and a tiny unit capacitance of 0.47 fF is achieved. A prototype integrated in 130nm CMOS technology exhibits a phase noise of −118.7 dBc/Hz @1MHz offset and a power dissipation of 2 mW under a supply of 1.2 V. The core area size is 330um×480um.