[SI-LIST] Re: Phase/Frequency Detector!
- From: "Ingraham, Andrew" <a.ingraham@xxxxxxxx>
- To: <parthsv@xxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 20 Aug 2003 10:19:12 -0400
The output of the phase/frequency detector has an indication of both the
phase difference when the frequencies are the same, and of the frequency
difference when they aren't. Thus, the average (DC) output is non-zero when
the frequencies differ; unlike a plain PD whose average output is zero under
the same conditions.
Thus, the PFD provides a PLL with the signal it needs to quickly steer the
VCO's frequency back into lock, even if the low-pass filter is very narrow.
Some literature says a PFD's output is proportional to the frequency
difference, but that's not quite true.
Regards,
Andy
> Whats the difference between Phase detector and
> Phase/Freq Detector?
>
> Why is PFD advantageous to PF?
> - Normally PF has low acquisition range limited by
> usage of Low Pass Filter. In PFD we use charge pump
> instead of LPF. Is that the main reason?
>
> Thanks in Advance,
>
> Regards,
> Partha!
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