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

  • From: steve weir <weirsi@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Sat, 07 Jan 2012 18:59:25 -0800

Ken, another really good alternative is the Signal Hound USB based 
analyzer for $919.   From 100Hz to 3.3GHz it goes down to -135dB, and it 
is usable from 1Hz to 4.4GHz.

  http://www.signalhound.com/

Best Regards,


Steve
On 1/7/2012 4:23 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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