BEHAVIORAL MODELING PHASE-LOCKED LOOPS FOR MIXED-MODE SIMULATION

Phase-locked Loops(PLLs) are a class of feedback systems with wide ran ge of applications. A PLL in its entirety can be viewed as a closed-lo op servosystem, comprised of three major functional subsystems; 1) Pha se detectors, 2) Loop filters and 3) Voltage/Current controlled oscill ators. The overall characteristics of the phase-locked loop are depend ent on the realization of individual subsystems which have mixed analo g-digital implementations. In simulating a PLL, one has to deal with t he mixed-signal nature of most implementations, as well as the problem of simulating the PLL over a large number of signal cycles. Long simu lation run times plague the simulation of a PLL using a conventional s imulator, sometimes making such simulation impractical. In the methodo logy described in this paper, these drawbacks are overcome by the use of behavioral models and a mixed-signal simulation platform. This pape r presents a general mixed-mode behavioral simulation methodology and the derivation of behavioral simulation models for various kinds of PL Ls. The top-down and bottom-up modeling paradigms are illustrated thro ugh the use of examples of actual PLL designs. The simulation models a re generated for the AT&T Bell Laboratories mixed analog-digital simul ator, ATTSIM.