Simulation and modeling-an improved VCO macromodel

A SPICE macromodel for a phase-locked loop (PLL) featuring design simplicity and a reduced simulation time which was introduced by M. Sitkowski (1991) is reviewed. Two of the primary simplifications in this PLL macromodel were the utilization of a voltage-controlled tuned circuit as the voltage-controlled oscillator (VCO) that does not require feedback to produce an oscillating output, and the use of a nonlinear voltage-controlled voltage source as part of a limiter/comparator that converts the VCO sine wave output to an approximate square wave. Several modifications to the VCO and limiter/comparator macromodel that improve their performance characteristics and eliminate most of the errors caused by the original macromodels are described. The proposed VCO macromodel exhibits a linear transfer function for all non-negative control voltages and requires one less SPICE primitive than Sitkowski´s model.<>