A 900-MHz CMOS low-phase-noise voltage-controlled ring oscillator

A 900-MHz two-stage CMOS voltage-controlled ring oscillator (VCO) with good phase-noise performance is presented. Implemented in a 0.5-mum CMOS technology and at 2.5-V supply voltage, the VCO has a wide operating frequency range from 661.5 MHz to 1.27 GHz with a peak VCO gain (K-VCO) of -630 MHz/V. At 900 MHz, the phase noise of the VCO is -105.5 dBc/Hz st 600-kHz frequency offset with low power consumption of 15.4 mW. The gain and phase mismatches are less than 0.25 dB and 0.5 degrees, respectively, which corresponds to all image rejection of better than 31 dB. The chip area is only 125 X 102 mum(2).