Abstract: A monolithic low-power and low-phase-noise digitally controlled oscillator (DCO) based on a symmetric spiral inductor with center-tap and novel capacitor bank was implemented in a 0.18 μm cmos process with six metal layers. A third new way to change capacitance is proposed and implemented in this work. Results show that the phase noise at 1 MHz offset frequency is below –122.5 dBc/Hz while drawing a current of only 4.8 mA from a 1.8 V supply. Also, the DCO can work at low supply voltage conditions with a 1.6 V power supply and 4.1 mA supply current for the DCO's core circuit, achieving a phase-noise of –121.5 dBc/Hz at offset of 1 MHz. It demonstrates that the supply pushing of DCO is less than 10 MHz/V.

Key words: digitally controlled oscillator