A wideband low-phase-noise CMOS VCO

A CMOS VCO has been designed and fabricated in a commercial 0.25 mum CMOS process. Using a combination of switched binary-weighted capacitors and standard varactors, this VCO achieves a 28% tuning range with a control voltage ranging from 0-2 V, while maintaining a tuning sensitivity of less than 75 MHz/V over its entire frequency range. Compact choke inductors are used in place of resistors to provide a low noise bias point to the varactors. The choke inductors achieve more than 90 nH of effective inductance while consuming a die area of only 92 x 92 mum(2). The measured single-sided phase noise is -127 dBc/Hz at a 600 kHz offset from a 1.24 GHz carrier when the VCO core is drawing 3.6 mA from a 2 V supply.