Electronics World Cover,TOC,and list of posted Popular Electronics articles QST Radio & TV News Radio-Craft Radio-Electronics Short Wave Craft Wireless World About RF Cafe RF Cafe Homepage RF Cafe in Morse Code Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs Twitter LinkedIn Crosswords Engineering Humor Kirt's Cogitations Engineering Event Calendar RF Engineering Quizzes AN/MPN-14 Radar 5CCG Notable Quotes App Notes Calculators Education Magazines Software,T-Shirts,Coffee Mugs Articles - submitted by RF Cafe visitors Simulators Technical Writings RF Cafe Archives Test Notes Wireless System Designer RF Stencils for Visio Shapes for Word Search RF Cafe Sitemap Advertising Facebook RF Cafe Forums Thank you for visiting RF Cafe!

PLL's An More Important Low Pass Filter - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

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
Posts: 4
Location: Huntington beach
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 vco?

Sorry for the "newb" question but i actually never seen a pll circuit, we use it internal to the chip so i cant probe around.


Post subject: Posted: Thu Aug 09, 2007 5:39 am


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Try www.circuitsage.com
That site provides design guides and design routines for Mathcad
Hope it helps.


Post subject: Posted: Thu Aug 09, 2007 10:36 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
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.

A wide 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.


Post subject: Posted: Thu Aug 16, 2007 4:33 pm


Joined: Wed Sep 15, 2004 3:15 am
Posts: 4
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.

Posted  11/12/2012

RF Cafe Software

   Wireless System Designer - RF Cafe
Wireless System Designer

RF & EE Symbols Word
RF Stencils for Visio
Calculator Workbook
RF Workbench
Smith Chartâ„¢ for Visio
Smith Chartâ„¢ for Excel

About RF Cafe

Kirt Blattenberger - RF Cafe WebmasterCopyright
1996 - 2022
Kirt Blattenberger,

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

Try Using SEARCH
to Find What You Need. 
There are 1,000s of Pages Indexed on RF Cafe !