Yes, I think this make sense. Because in this case the
PFD actually add some delay into the equation.
In general linear model, we usually assume that
the feedback happens in a very small instant and
ignore any delay effect. This assumption hold true
when you are useing laplace model because what you
are modelling is actually a tiny disturbance to
the system, for example, a samll step input.
That is my understanding. But if the PFD works slow
relatively, the accumption of "instant" does not hold true.
So I think the geneal formula will hold when the
system is changing in a relatively slow
fashion compared with your PFD. That means it
is varying in a quite narrom bandwidth, or,
by a big time constant.
qslazio said:
I've read some papers.
They said that in pll, when the PFD update frequency is comparable to the loop bandwidth, the delay around the feedback loop introduces excessive phase shift.
I can't understand this. Can anyone explain it to me?
Thanks
Added after 2 minutes:
what i mean is that:
1) what does the delay mean? what determines it?
2) is it any relationship with the PFD sample effect?
Thanks