Equation-based phase-noise optimization technique for MOS LC-VCOs

This paper presents an equation-based phase noise optimization technique for MOS LC-VCOs in contrast with feedback-based optimization architectures. The proposed technique relies on a simplified equation relating the bias current to the oscillation amplitude and the equivalent tank losses. The applied technique takes also into account the tank losses dependency on frequency setting in wideband LC-VCOs. The control algorithm aims to predict by feed-forward action the optimal bias current giving the optimum phase noise performance. Performed simulations are based on a 0.13 μm CMOS implementation for the oscillator part while the control algorithm is implemented using behavioral blocks. Simulation results show equivalent phase noise control accuracy to automatic amplitude control (AAC) architectures, while achieving superior performance in terms of control speed, parasitic load and extra noise-sources elimination.