A Voltage-Controlled Ring Oscillator With VCO-Gain Variation Compensation

A voltage-controlled oscillator (VCO) with VCO-gain (KVCO) variation compensation is proposed to reduce KVCO variation in a current-mode logic (CML) ring oscillator by introducing a cross-coupled pair with capacitive degeneration that mitigates the nonlinearity of KVCO. Designed and fabricated in a standard 0.18-μm CMOS process, the proposed VCO can be tuned from 1.78 to 2.53 GHz, with the VCO gain variation less than 14.01%, while occupying a core area of 0.185 × 0.081 mm2and consuming 20 mA including the bias circuitry, from a 1.8-V supply voltage. The phase noise is measured to be -92.68 dBc/Hz at 1 MHz offset and -114.97 dBc/Hz at 10 MHz offset from the high-band carrier frequency, respectively.