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

  • From: Ken Wyatt <ken@xxxxxxxxxxxxxxxx>
  • To: SI-LIST <si-list@xxxxxxxxxxxxx>
  • Date: Sat, 7 Jan 2012 18:36:54 -0700

OK, I guess SI-LIST removes links in signatures...
Here's the link to the newspaper registration. Sorry for the high noise to 
signal, as someone mentioned.

http://www.emc-seminars.com/Newsletter/Newsletter.html
_______________________
Kenneth Wyatt
Wyatt Technical Services LLC
Woodland Park, CO
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On Jan 7, 2012, at 6:14 PM, Ken Wyatt wrote:

> 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
> Email Me! | Web Site | Blog
> Subscribe to Newsletter
> Connect with me on LinkedIn
> 
> 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
>>>> 
>>>> 
>>>> 
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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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