[SI-LIST] Re: DDR3 clock failing radiation Tests

Hmmm...just noticed the links were removed in my last post. Now you should be 
able to click on the link "Subscribe to Newsletter" (below) to obtain the list 
of troubleshooting tips and past newsletters.
Cheers, Ken
_______________________
Kenneth Wyatt
Wyatt Technical Services LLC
Woodland Park, CO
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On Jan 7, 2012, at 5:23 PM, Ken Wyatt wrote:

> Great reply Alfred - lots of good troubleshooting tips. 
> 
> Your comment on the PSA2701T caught my eye, as I've been using one of these 
> for several years. However, few people have heard of the TTi Spectrum 
> Analyzer, which is too bad. It's an incredible handheld (truly handheld!) 
> instrument manufactured in the UK and distributed by Newark Electronics and 
> Saelig Co. here in the US. Saelig actually has a slightly better price at 
> $1,887. If anyone is interested in additional info on the TTi PSA2701T 
> spectrum analyzer, I posted a comprehensive review on my web site: 
> http://www.emc-seminars.com/Technical_Articles/files/TTi_PSA2701T_Spectrum_Analyzer_Wyatt.pdf.
> 
> I'm also glad you referenced Doug Smith's web site. It's chock-full of 
> high-frequency, EMC and ESD measurement techniques and tips. He's at: 
> http://emcesd.com/
> 
> By the way, anyone who registers for my free quarterly EMC newsletter will 
> receive a link to a free list of troubleshooting tips, as well as all past 
> newsletters. Click on the link below...
> 
> References:
> 
> Newark: 
> http://www.newark.com/aim-tti-instruments/psa2701t/analyzer-spectrum-1mhz-to-2700mhz/dp/54M5938
> 
> Saelig: http://www.saelig.com/category/TEEMCEE.htm
> 
> Cheers, Ken
> _______________________
> Kenneth Wyatt
> Wyatt Technical Services LLC
> Woodland Park, CO
> Email Me! | Web Site | Blog
> Subscribe to Newsletter
> Connect with me on LinkedIn
> 
> On Jan 7, 2012, at 1:16 PM, alfred1520list wrote:
> 
>> Guess one more post does not alter the SNR significantly:)
>> 
>> Quarter wave of 513 MHz in free space is 5.76", and roughly
>> half that in FR4.  I guess you don't happen to have a 3" tall
>> metal standoff that's mounted close to the ASIC to act as
>> an antenna, right?  Any way, controlled impedance traces aren't
>> efficient antenna compare to other physically large structure.
>> As some one else pointed out, common mode current can
>> couple to other physically large structures and they become
>> efficient radiator.  I find Doug has a few excellent papers
>> on EMI on his site:
>> 
>> http://emcesd.com
>> 
>> I find this particular interesting:
>> 
>> "Current Probes, More Useful Than You Think":
>> http://emcesd.com/pdf/iprobe98.pdf
>> 
>> One other suggestion from experience.  When you have 20 suspects
>> areas, it might be easier trying to make it worst to see which one
>> of them is the dominant source.  Even though all 20 suspects can all
>> radiate, probably only one of them is order of magnitude higher
>> than others.  If you can find that one and knock it down, you made
>> significant progress.  Since at 513 MHz it still needs significant physical
>> dimension (like an 1" long???) to radiate efficiently, use a piece of metal
>> like X-Acto knife, to touch everything and see if it make it worst.  Any
>> where you touch and made it worst is worth a closer look, especially
>> places where you don't expect, e.g. power supply, etc.
>> 
>> Speaking of sniffing radiation, I have used PSA2701T:
>> http://www.tti-test.com/products-tti/rf/spectrum-analyzer.htm
>> 
>> It's a great piece of gear and low enough in cost (a couple of US dollar as
>> I recall).  Since you aren't making certification measurement, you can
>> simply use any length of wire that register a reading at the frequency of
>> interest and make relative measurement.  I used a cheap US$30 discone
>> antenna.  If you make the spike smaller, you have made it better.
>> 
>> 
>> Best Regards,
>> Alfred Lee
>> 
>> Web: www.mds.com
>> 
>> ----- Original Message ----- 
>> From: "Eric Steimle" <eric.steimle@xxxxxxxxxx>
>> To: "vinod ah" <ah.vinod@xxxxxxxxx>; "SI-LIST" <si-list@xxxxxxxxxxxxx>
>> Sent: Saturday, January 07, 2012 11:27 AM
>> Subject: [SI-LIST] Re: DDR3 clock failing radiation Tests
>> 
>> 
>>> I agree that seeing the most emissions coming out of the ASIC is pretty 
>>> common, especially if it's your ASIC ;), and unless you 
>>> have some kind of crazy expensive (possible magic) software, simulation 
>>> can't save you now.  I don't know what your application is 
>>> but in the past I did a lot of unshielded consumer designs that used 
>>> DDR2/3, and most  of them would not have made it through scan 
>>> without spread spectrum.   I also agree that going to an expert EMI 
>>> consultant could be well worth it, if your in NC I know a good 
>>> one.
>>> Anyway I like to tackle emi problems by cutting everything into smaller and 
>>> smaller pieces.  I don't know what your production 
>>> options are but  here's one thing to try.  If you want to narrow things 
>>> down you could build yourself a shield for your ASIC as a 
>>> test.  Just get some Kapton tape, and some copper tape.  Kapton tape all 
>>> around the ASIC, then copper tape over that.  Then ground 
>>> the heck out of that copper tape, I usually do that by taking an exacto 
>>> knife and cutting down to my gnd plane, but do what you 
>>> can do.  After that sniff it again, or go pre-scan it if you can afford it.
>>> 
>>> If that does nothing, at least you know you have additional problems 
>>> elsewhere.  If it cleans it up, hurray just ship everything 
>>> with copper tape.  Kidding but you could re-spin the board to accommodate a 
>>> shield, and get the product out the door.
>>> 
>>> This is just one of hundreds of things to try, but you asked for help 
>>> finding the source.  The best advice I can give is to start 
>>> eliminating things, by shielding / pulling parts off the board, changing 
>>> clock frequencies, anything you can think of to narrow 
>>> down the problem.   Keep track of how each change affects your emissions.  
>>> One time we ripped 12 ASICs off a large board and still 
>>> had the problem! It was a lot easier to find without all those extra parts 
>>> to question though.
>>> 
>>> Good luck.
>>> 
>>> 
>>> Eric F. Steimle
>>> Hardware Engineering Manager
>>> 
>>> +1 732-440-1280 x210 Office
>>> +1 732-212-9424 Fax
>>> 
>>> 444 Route 35 South
>>> Building B
>>> Eatontown, NJ 07724 USA
>>> 
>>> eric.steimle@xxxxxxxxxx
>>> www.altior.com
>>> 
>>> 
>>> 
>>> ****Confidentiality Statement****
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>>> ________________________________________
>>> From: si-list-bounce@xxxxxxxxxxxxx [si-list-bounce@xxxxxxxxxxxxx] On Behalf 
>>> Of vinod ah [ah.vinod@xxxxxxxxx]
>>> Sent: Saturday, January 07, 2012 12:27 AM
>>> To: SI-LIST
>>> Subject: [SI-LIST] DDR3 clock failing radiation Tests
>>> 
>>> Hi all,
>>> I am facing problems related to EMI. I am having a ASIC with 2 DDR3
>>> controllers running at 513MHz clock. I am interfacing 2 memories to each of
>>> the controller. So totally 4 memory chips on board, all running at 513MHz
>>> clock. During pre-compliance radiation testing in FCC certified lab, we
>>> observed 513MHz in the spectrum with 15dB above the CISPR class B limits
>>> i.e. test failing by 15dB !!!!!
>>> 
>>> I tried to corelate this result with Hyperlynx spectrum analyzer simulation
>>> and SI simulation. The waveforms and radiation level looks fine in
>>> Hyperlynx i.e. no issues seen. Initially i had suspected the layout, but
>>> hyperlynx SI simulation looks fine and also the clock & dqs waveforms in
>>> CRO looks fine i.e. no ringing/overshoot etc. The DDR3 clock is routed in
>>> inner layer 3 of six layer stack up of the board.
>>> 
>>> I have tried using EMI shield, but still i am failing by 8dB. Only thing i
>>> have not yet tried is spread spectrum clocking. But I am unable to find the
>>> source of problem. Can you please help me out in finding the sourceto this
>>> problem.
>>> 
>>> I understand that it is very tuff to provide solution to this problem
>>> without seeing the layout, but i am expecting some tips so that i can move
>>> ahead in debugging the problem.
>>> 
>>> Regards
>>> Vinod A H
>>> 
>>> 
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