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PLL confusion

P

peterken

Jan 1, 1970
0
jim said:
Ok, I'm just about there,so you're saying that amplitude variation has
no effect on the phase relationships?

that's the idea yes, amplitude is on the vertical axis and phase is on the
horizontal axis
we're only comparing the horizontal axis, and (almost) ignoring the vertical
unless to "select" a reference point

the phase of a single signal has to do with the 360deg (2*pi rad) between
two instances of a repetitive cycle
whatever the amplitude, the 360deg is a given constant for every cycle of
this signal
whatever the time is to go through the full 360deg doesn't matter too, so
ignore the aspect "time" too (disconnect "time" from "phase" for a moment in
your mind)

now, given the initial 5Hz and 10Hz of this thread, starting from a specific
coinciding point of two signals (assume zero crossing) one can start
counting the completed cycles as 360deg for every signal
the 5Hz sig will have done 360deg after 1 cycle, whilst the 10Hz will be at
720deg (= two cycles) at the finishing point of this first 5Hz cycle
thus the phase difference of both signals will always increment, no matter
how long you look at them (*unless* you take a new reference point and start
counting from scratch but that's a new measurment)
an integral part of a pll is a phase comparator (usually phase detector
combined with an integrator) giving the "measure" for the phase difference
to be able to adjust a vco which is another part of a pll
 
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