Dependence of LC VCO oscillation frequency on bias current

LC-tuned voltage controlled oscillators (LC VCOs) are widely used in high performance phase locked loops (PLLs) and frequency synthesizers due to their high spectral purity. The oscillation frequency of an LC VCO is commonly assumed to be the resonant frequency of the LC tank. However, this is not accurate as shown in this paper. The oscillation frequency is also affected by the bias current. By applying our analysis to the Hegazi and Abidi´s LC VCO, we propose a new digital trimming technique which can compensate for process variations and improve the phase noise performance