Efficient Behavioral Simulation of Charge-Pump Phase-Locked Loops

Abstract

The simulation of the full netlist of a phase locked loop (PLL) is resource demanding due to the prohibitive time needed to derive output noise, spurs, and transient performance from detailed transistor-level simulations. To overcome this limitation, behavioral models are needed but they must be accurate and time-efficient. This paper introduces a new behavioral macro-model of the charge-pump PLL, addressing both spectral analysis and lock-in transient computation. To meet both accuracy and simulation efficiency, the model accounts for the time-variant transfer of noise and disturbances, and a novel procedure is introduced to extract the model parameters via transistor-level periodic steady-state simulations. To describe the nonlinear dynamics, the model also includes the voltage-controlled oscillator and charge-pump nonlinear characteristic computed via transistor-level simulations. The proposed macro-model has been tested on a 2.765-GHz PLL, and the results are compared against the noise transient simulation of the PLL full netlist. Phase noise and amplitude of spurious tones, both inherently generated and induced by external disturbances, are predicted within ±2 dB. Lock-in transients are also described with an accuracy within a few percent. On the other hand, the simulation time reduction is two/three orders of magnitude for both spectral analyses and transient simulations, depending on the PLL parameters.