On MOS LC-VCO´s oscillation condition using the short-channel MOS model equations

This paper presents new considerations on the oscillation start-up condition for LC-oscillators implemented in sub-micron MOS technologies. Short-channel MOS model equations are employed to derive an accurate expression of the oscillation condition. The obtained start-up condition predicts new current boundaries and a minimum losses level (Rp_min) preventing any oscillation whatever is the oscillator bias current. Theoretical results are confronted to simulations in different MOS technologies (0.25-μm, 0.13-μm and 90-nm) in order to confirm the resulting predictions. Simulation results are shown to fit more accurately with the short-channel based condition than with the traditional long-channel based oscillation condition.