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-/spl mu/m 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/sub VCO/) of -630 MHz/V. At 900 MHz, the phase noise of the VCO is -105.5 dBc/Hz at 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/spl deg/, respectively, which corresponds to an image rejection of better than 31 dB. The chip area is only 125/spl times/102 /spl mu/m/sup 2/.