more frequency tracking..

[Martin Czech]

PLL:

-> chordman at flash.net (Scott Gravenhorst) is the 4046 man, i remember now
;->. He said and published it all.

I mean with distortion: it can be that the vco square output looks
like a pulse wave if the loop has locked.

> 
> anyone care to explain to me how a phase comparator works, incidentally?
>

Some principles I remember:

Phase comparators:

1.) A Sample & Hold  can be used as phase comparator. Think of two 
    incomming waves, a square wave (reference) and a tri wave (to be 
    syncronised). If both signals have the same frequency, the phase 
    difference can be observed by sampling the tri at -say- the falling 
    egde of the square.

2.) Use a multiplier. If we have s1=sin(w1*t) and s2=sin(w2*t+p), then
    s1*s2= 0.5*[cos((w1-w2)*t-p)+cos((w1+w2)*t+p)]. If w1~w2 the
    difference w1-w2 will be ~0, the average (low pass filtered) of
    s1*s2 will be ~0.5*cos(p). This is a measure of the phase difference