[SI-LIST] Re: CHGND connection in DVI connector
- From: steve weir <weirsi@xxxxxxxxxx>
- To: qantrix <qantrix@xxxxxxxxx>
- Date: Fri, 07 May 2010 06:10:13 -0700
In the picture I sent you the entire solid red line is the join.
I think trying to DC isolate common through DVI with capacitors is a
mistake.
Steve.
qantrix wrote:
> OK. I understood. It will provide connection with lowest impedance.
> H.Ott write about it in his book.
> Did you connected it on all layers or outer only?
> If i don't want DC flowing through my chassis - i need to connected it
> to gnd in each point with few capacitors 10n, 1n, 100pf in parralel?
>
>
> 2010/5/6 Grasso, Charles <Charles.Grasso@xxxxxxxxxxxx>:
>
>> We have several designs that are laid out just like Steve is recommending.
>> Do not add moats where they are not needed.
>>
>> Also - I would NOT add the internal shields to the chassis ground at the I/O.
>> This is an ideal way of letting EMI out and cause immunity problems.
>>
>> ________________________________________
>> From: si-list-bounce@xxxxxxxxxxxxx [si-list-bounce@xxxxxxxxxxxxx] On Behalf
>> Of steve weir [weirsi@xxxxxxxxxx]
>> Sent: Tuesday, May 04, 2010 7:34 AM
>> To: qantrix
>> Cc: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] Re: CHGND connection in DVI connector
>>
>> I disagree with the recommended design.
>>
>> I would connect signal and chassis grounds through a peninsula at the
>> chassis side of the DVI connector. Depending on what else is going in
>> and out of the box, bonding at other locations would also be
>> appropriate. At a minimum you need to do it at the DVI connector. The
>> basic premise is to reduce antenna efficiency and reduce energy pumped
>> into the antenna. Big loops make for efficient antennas. Extending the
>> chassis ground into the main PCB while still moating from signal ground
>> is likely going to create coupling issues that will bite you, never mind
>> the SI degradation you will get from crossing the moat.
>>
>> Much has been written on this area of interest. Doug Smith has a number
>> of short articles and demonstrations showing how various grounding
>> schemes work and fail.
>>
>> Steve.
>> qantrix wrote:
>>
>>> Steve,
>>>
>>> http://img504.imageshack.us/i/currentdesign.png/
>>> you can find current design. data(diff.pairs) shield connected to sgnd.
>>>
>>> suggested design see here
>>> http://img266.imageshack.us/i/suggested.png/
>>>
>>> As you can see ch_gnd will cover all area of dvi connector and pins of
>>> data pairs shield connected to ch_gnd.
>>> diff.pairs will pass under separation between planes.
>>>
>>> Idea make it like this seems like bad.
>>>
>>> But it's possible to connect pairs shield to ch_gnd without creating
>>> slot under pairs and cable will have only quite ch_gnd shield for each
>>> pair and not dirty sgnd. Question is - does this shield carrying
>>> return currents ? How it will work from EMC point ?
>>>
>>>
>>>
>>> 2010/5/4 steve weir <weirsi@xxxxxxxxxx>:
>>>
>>>
>>>> Is there a reason you want to isolate signal common from chassis? Common
>>>> practice is to join the two near the chassis boundary. If you attempt to
>>>> isolate them, you will have lots of capacitive sneak paths. If they are
>>>> joined you will not have a CM discontinuity issue.
>>>>
>>>> Steve.
>>>>
>>>> qantrix wrote:
>>>>
>>>>
>>>>> I have question about CHGND connection in DVI connector/cable.
>>>>> There is two kind of shields - one - is shield for data/clock pair;
>>>>> second - whole cable shield.
>>>>> http://en.wikipedia.org/wiki/Digital_Visual_Interface
>>>>>
>>>>> We had some EMC consultation - was suggested to connect internal pairs
>>>>> shield to chgnd.
>>>>> on pcb make polygone chgnd that cover area up to end of dvi connector.
>>>>> So diff.pairs will run under slot of gnd.separation.
>>>>>
>>>>> Question is - how should be connected internal shields in DVI
>>>>> conenctor - to sgnd or to chgnd?
>>>>>
>>>>> diff. pairs running on the slot - seems like bad idea?
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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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>> --
>> Steve Weir
>> IPBLOX, LLC
>> 150 N. Center St. #211
>> Reno, NV 89501
>> www.ipblox.com
>>
>> (775) 299-4236 Business
>> (866) 675-4630 Toll-free
>> (707) 780-1951 Fax
>>
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
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