Post subject: PLL's an more important Low pass
folter Posted: Thu Aug 09, 2007 2:27 am
Joined: Wed Sep 15, 2004 3:15 am
Well first i would like to know if anyone knows
any online places that have goos info on pll's? searching i only
came up woth some very basic stuff like wkipedia.
But my main
question is on the after the phase comparator the lpf (can this
be a band pass?) and how exactly does it effect settleing time.
I would think a narrower bandiwidth will lock loop faster since
it would pass less noise. And i thought that the filters job was
just to pass dc because thats what input to the varactor on the
Sorry for the "newb" question but i actually never
seen a pll circuit, we use it internal to the chip so i cant probe
Post subject: Posted:
Thu Aug 09, 2007 5:39 am
Feb 17, 2006 12:07 pm
Location: London UK
That site provides design guides and design
routines for Mathcad
Hope it helps.
Post subject: Posted: Thu Aug 09, 2007 10:36 am
Joined: Mon Jun 27, 2005 2:02 pm
The only filter possible in PLL is a LPF.
The purpose of the LPF is to smooth the output of the FPD (Frequency
Phase Detector) and it sets the speed of the loop.
filter will cause the loop to react faster, since the filter's pole(s)
is/are located far, therefore, the filter has a wider reponse. The
tradeoff, as you mentioned, will be a degradation in phase noise
and vice versa.
Posted: Thu Aug 16, 2007 4:33 pm
Wed Sep 15, 2004 3:15 am
Location: Huntington beach
Thanks. i had not had the chance to thank you guys been doing
alot of reading.
I do understand pll better but not enough yet.