[SI-LIST] Re: Guard Traces

  • From: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>
  • To: doh@xxxxxxxxxx, "weirsi@xxxxxxxxxx" <weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 13 Mar 2012 15:12:08 -0700 (GMT-07:00)

I'm not sure what you are asking.


-----Original Message-----
>From: "Oh, Dan" <doh@xxxxxxxxxx>
>Sent: Mar 9, 2012 10:08 AM
>To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>, "weirsi@xxxxxxxxxx" 
><weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
>Subject: [SI-LIST] Re: Guard Traces
>
>Hi Ritchy, 
>Are you indicating that my explanation is valid if we stay with the circuit 
>concept?
>Maybe I am missing radiation impact here which I do not have much experience 
>so I will take your words. 
>I will try to continue this thread offline since it may not be interested to 
>others.
>Best,
>-Dan Oh
>
>-----Original Message-----
>From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] 
>Sent: Friday, March 09, 2012 8:58 AM
>To: Oh, Dan; weirsi@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: Re: [SI-LIST] Re: Guard Traces
>
>Dan, it's basic physics.  You need to cease looking at the problem in terms of 
>current loops and start looking at it as fields and waves.
>
>
>-----Original Message-----
>>From: "Oh, Dan" <doh@xxxxxxxxxx>
>>Sent: Mar 9, 2012 8:52 AM
>>To: Lee Ritchey <leeritchey@xxxxxxxxxxxxx>, "weirsi@xxxxxxxxxx" 
>><weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
>>Subject: [SI-LIST] Re: Guard Traces
>>
>>Hi Ritchey,
>>Perhaps, you can elaborate why???
>>The reason why we placed ground guards closer to the signal is to reduce the 
>>current loop (assuming they are sufficiently stitched). This will reduce 
>>coupling from other current loops (which is also small). Of course, this 
>>depends on the height of trace which I assumed is fairly large compare to 
>>spacing. Otherwise, it would not help as you indicated.
>>So, the answer would be depends. But I want to make sure when the trace is 
>>located high; then, the ground guard is a very effective way to mitigate this.
>>May I am missing something here and need your lecture here.
>>Best,
>>-Dan Oh
>>-----Original Message-----
>>From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx]
>>Sent: Friday, March 09, 2012 8:46 AM
>>To: Oh, Dan; weirsi@xxxxxxxxxx; si-list@xxxxxxxxxxxxx
>>Subject: Re: [SI-LIST] Re: Guard Traces
>>
>>Inductive coupling is precisely what guard traces cannot block.  If they 
>>could we would not have motors and transformers or bandpass filters in 
>>microwave applications.
>>
>>
>>-----Original Message-----
>>>From: "Oh, Dan" <doh@xxxxxxxxxx>
>>>Sent: Mar 9, 2012 8:40 AM
>>>To: "weirsi@xxxxxxxxxx" <weirsi@xxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" 
>>><si-list@xxxxxxxxxxxxx>
>>>Subject: [SI-LIST] Re: Guard Traces
>>>
>>>Hi Steve and Doug,
>>>I also agree with you. You guys have one more vote. The guard trace is very 
>>>effective to reduce the inductive coupling which cannot be easily reduced by 
>>>spacing.
>>>Best,
>>>-Dan Oh
>>>-----Original Message-----
>>>From: si-list-bounce@xxxxxxxxxxxxx
>>>[mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir
>>>Sent: Thursday, March 08, 2012 9:23 PM
>>>To: si-list@xxxxxxxxxxxxx
>>>Subject: [SI-LIST] Re: Guard Traces
>>>
>>>Doug, I agree that guard traces can help in certain situations.  In most, 
>>>and particularly when inserted without doing the requisite engineering work, 
>>>they can make a good mess of things.
>>>
>>>Best Regards,
>>>
>>>
>>>Steve.
>>>On 3/8/2012 8:22 PM, Doug Smith wrote:
>>>> Hi Lee,
>>>>
>>>> Your statement is true for most cases, but for two layer boards 
>>>> (every household has several of these with processors on them) guard 
>>>> traces can stabilize impedance, improve grounding, and lower noise 
>>>> coupling.
>>>> I agree with you for advanced electronics.
>>>>
>>>> We should always state the assumptions made when citing design or 
>>>> other rules. I see this a lot in EMC books where an equation is 
>>>> given (such as slot radiation) but the (sometimes many) assumptions 
>>>> are not given and people use the equations when they don't apply. 
>>>> Shielding effectiveness is another case where the common equations 
>>>> do not apply in many cases (far field conditions are assumed when in 
>>>> fact they are not met). Under every equation in EMC and other books 
>>>> there should be a list of assumptions given.
>>>>
>>>> Doug
>>>>
>>>> On 3/8/12 10:52 AM, Lee Ritchey wrote:
>>>>> With all the feedback on this forum that guard traces are a bad idea, why 
>>>>> is this discussion still going on?  Are there still people who cling to 
>>>>> the notion that guard traces are useful, even in the face of mounting 
>>>>> evidence that they don't help?
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>>> From: Dennis<dennis.han@xxxxxxxxx>
>>>>>> Sent: Mar 7, 2012 12:59 PM
>>>>>> To: si-list@xxxxxxxxxxxxx
>>>>>> Subject: [SI-LIST] Re: Guard Traces
>>>>>>
>>>>>> In addition to what Wolfgang has stated, if the guard traces are too 
>>>>>> close to the signal traces, and most people who believe in ground traces 
>>>>>> put them too close (ground fill also falls in this category), the 
>>>>>> impedance of the signal traces is lowered and there are less crosstalk 
>>>>>> and radiation because of it if the now mismatched terminations don't 
>>>>>> cause other problems.
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> --- In si-list@xxxxxxxxxxxxxxx, Gwen and Wolfgang<gwmaichen@...>   wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> first, the short answer: simply don't use guard traces here, they 
>>>>>>> won't help much with isolation of high speed signals, and they 
>>>>>>> use up way too much routing space (on all layers, because of the 
>>>>>>> stitching vias necessary). Much easier to just increase the 
>>>>>>> distance between diff pairs etc. and you get the same benefit. 
>>>>>>> (in fact, I suspect the reason many people believe in the magic 
>>>>>>> power of guard traces in this setting - high speed signaling - is 
>>>>>>> because those traces _force_ you to have enough space between 
>>>>>>> signal lines...). Guard traces have their place in low-current / 
>>>>>>> low-leakage / high-voltage applications, but NOT in high speed digital. 
>>>>>>> At least that's my opinion.
>>>>>>>
>>>>>>> If you do need grounded traces, stitch them to the ground planes 
>>>>>>> with vias spaced no further than a quarter wavelength from the 
>>>>>>> signal trace and at an interval of no less than a quarter wave 
>>>>>>> length from each other. The wavelength given of course by 
>>>>>>> bandwidth connected with the signal rise time, BW = 0.33 / Tr, or 
>>>>>>> a bit more conservatively, the knee frequency f_knee = 0.5 / Tr.
>>>>>>> No special termination needed at the ends of those traces because 
>>>>>>> they are already solidly grounded along their full length.
>>>>>>>
>>>>>>> Wolfgang
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On 3/7/2012 7:31 PM, Aaditya Kandibanda wrote:
>>>>>>>> Hello Everyone,
>>>>>>>> I have few questions about the guard traces.
>>>>>>>>
>>>>>>>> 1. How do I terminate the guard traces?
>>>>>>>> 2. While using the guard traces for differential pair, how shall 
>>>>>>>> I place them between the differential pair?
>>>>>>>> 3. How should I place the vias for guard traces?
>>>>>>>> 4. What are disadvantages of Guard traces?
>>>>>>>>
>>>>>>>> Thanks and regards
>>>>>>>> Aaditya
>>>>>>>>
>>>>>>>>
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>>>>>>
>>>>> I just used the energy it took to get mad and wrote some blues.  
>>>>> Count Basie
>>>>>
>>>>> Lee W. Ritchey
>>>>> Speeding Edge
>>>>> P.O. Box 2194
>>>>> Glen Ellen, CA
>>>>> 707-568-3983
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>>>>>
>>>>>
>>>
>>>
>>>--
>>>Steve Weir
>>>IPBLOX, LLC
>>>150 N. Center St. #211
>>>Reno, NV  89501
>>>www.ipblox.com
>>>
>>>(775) 299-4236 Business
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>>>
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>>
>>
>>I just used the energy it took to get mad and wrote some blues.  Count 
>>Basie
>>
>>Lee W. Ritchey
>>Speeding Edge
>>P.O. Box 2194
>>Glen Ellen, CA
>>707-568-3983
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>>
>
>
>I just used the energy it took to get mad and wrote some blues.  Count Basie
>
>Lee W. Ritchey
>Speeding Edge
>P.O. Box 2194
>Glen Ellen, CA
>707-568-3983
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>  
>


I just used the energy it took to get mad and wrote some blues.  Count Basie

Lee W. Ritchey
Speeding Edge
P.O. Box 2194
Glen Ellen, CA
707-568-3983
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