Low phase noise ring VCO employing input-coupled dynamic current source

A low-phase noise ring voltage-controlled oscillator (VCO) employing input-coupled dynamic current source is presented. By simply coupling the input signal to the gate node of the current source transistor, the proposed inverter has a larger output swing and steeper maximum slope than conventional structures, which directly results in phase noise improvement. Under the same conditions, compared to the conventional structure, the proposed ring VCO achieves 7.5 and 11 dB of phase noise improvement at 100 kHz and 1 MHz offset frequencies, respectively. The proposed ring VCO has a tuning range of 823-1300 MHz and post-layout simulation shows a figure-of-merit of 159-162 dBc/Hz in the entire oscillation frequency range. In the measurement results,the authors recorded a phase noise of -106 dBc/Hz and figure-of-merit reaching 165 dBc/Hz at 1 MHz offset frequency, consuming 1.2 mW from a 1.8 V supply at 1 GHz oscillation frequency. The proposed ring VCO is implemented in 180 nm CMOS process and occupies a size of 0.0024 mm2.