PHASE-LOCKED loops (PLLs) are difficult to model with conventional fre
quency domain software circuit simulators or time-domain SPICE tools,
Fortunately, the advantages of both frequency- and time domain simulat
ion are available within a new type of software simulator that can ass
ist PLL designers, The novel software allows PLL signals to be represe
nted as a few carriers within time-varying modulation envelopes.