A fully differential LC-VCO using a new varactor control structure

This paper presents a fully differential inductor-capacitor voltage-controlled oscillator (LC-VCO) with a new differentially-tuned varactor structure. The proposed LC-VCO has lower phase noise and better robustness to the injected common-mode noise than the differentially-tuned LC-VCO using the previous antiparallel structure. The LC-VCO implemented using 0.5-μm SiGe BiCMOS technology is tunable from 4.251 to 4.428 GHz and the measured phase noise is -119 dBc/Hz at 1-MHz offset over the entire tuning range. Its core current is only 1.7 mA at 2.5-V supply voltage.