Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!
Amplifier Solutions Corporation (ASC) - RF Cafe

PLL phase coherence - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster


Post subject: PLL phase coherence Posted: Mon Jan 23, 2006 1:56 pm

Hi all,

Just wondering if anyone has any methods of getting 2 PLLs, which are running off the same reference, to have the same RF phase?




Post subject: Posted: Mon Jan 23, 2006 4:00 pm

Everthing else being equal you should be in phase. The higher you go in freq the less this is true, due to mismatch of the VCO.



Post subject: Posted: Tue Jan 24, 2006 8:24 am

differences in leakage currents between the PLLs?



Post subject: PLL phase matchingPosted: Tue Jan 24, 2006 3:34 pm

1. You'll want a real third-order loop, to force the phase error at the detector to zero and keep it there. See PLL books such as Gardner's classic.

2. The two loops should be physically identical, and equidistant from the reference and the point where the output phase difference is measured. (Assuming a UHF/microwave PLL - you weren't very specific).

Good Luck!


guest who asked

Post subject: Posted: Wed Jan 25, 2006 1:14 pm

thanks for your suggestions, but if there are leakage currents, then no amount of filtering will remove them. a 10uA leakage current will flow regardless of whether you use a 2nd, 3rd or 4th order loop filter. The charge pump will then force a phase error at the PFD inputs...

RFout is in the 1-5GHz range, PFD's of the order of 1-20MHz.



Post subject: PLLPosted: Wed Jan 25, 2006 8:59 pm

Leakage currents are controllable, so they can be reduced - almost always to negligible levels, given modern FETs. Whether or not you want to go to the effort is your choice. Still, you're using multiplication ratios in the 1000-5000 range, so phase error at the PFD would have to be tiny.

At that point, many PFD's have dead-zone and transition-time issues. So I wouldn't count on the phase matching too closely.

So I agree with your pessimism, "guest who asked".

Good Luck anyway!


guest who asked

Post subject: Posted: Thu Jan 26, 2006 7:59 am

thanks for replying. yes that's why im pessimistic. If one part heats up by 10 degrees and the other doesn't, the leakage current would double in the higher temp one. Depending on N divide ratios/ base leakage currents, it could translate to a huge phase difference at RF.



Post subject: Posted: Thu Jan 26, 2006 2:02 pm

I do not understand very well the involvment of PLL leakage current in the process of generating a phase error.

From my understanding, even a second order loop under a fixed reference signal, would give no phase error if we look at the closed loop phase error transfer function evaluated at T= ininite.

I the phase is different the charge pump will generate a pulse every cycle, the only condition driving to no pulse is a very small jitter around perfect phase. As far as we are concerned about what is going on in the loop, the phase must be exact

Under a moving phase reference then only a 3rd order loop makes the job from what I read but that is another question.

I see more the other facter around the PFD to Charge pump section to be contributiing to the error (reference conditionning circuitry, LO amplificatoin circuitry, and tranmsission lines exlectrical lenght variation due to whatever factor will indeed deteriorate the phase error.

I am missing something regarding charge pump leakage current?

Posted  11/12/2012

Triad RF Systems Amplifiers - RF Cafe
ConductRF Phased Matched RF Cables - RF Cafe
Windfreak Technologies Frequency Synthesizers - RF Cafe
withwave microwave devices - RF Cafe
Innovative Power Products Passive RF Products - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free


About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024


    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 World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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: