[SI-LIST] Re: Routing differential lines as single ended traces ?
- From: Danny Damhave <dd@xxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 27 Sep 2011 07:42:14 +0200
Using eg 2116 instead of eg 1080 will increase thickness of the laminate,
thereby the hight of the traces above ref planes and thereby trace width
because Er for the structures width a different laminate is not increased so
much. The overall crosstralk on the PCB has as strong dep of the trace to ref
distance and strong dep of he trace to trace space. Therefore the cross talk
will increase or you will have to increase the trace to trace spacing and have
fewer routing channels.
BR
Danny
On 26/09/2011, at 23.47, asparky@xxxxxxxxxxxxxxxxxxxxxxxx wrote:
> Why do you think changing glass weaves increases crosstalk?
> Thanks,
> Aubrey
> Sent from my Verizon Wireless BlackBerry
>
> -----Original Message-----
> From: Danny Damhave <dd@xxxxxxxxxxx>
> Sender: si-list-bounce@xxxxxxxxxxxxx
> Date: Mon, 26 Sep 2011 21:59:31
> To: <si-list@xxxxxxxxxxxxx>
> Subject: [SI-LIST] Re: Routing differential lines as single ended traces ?
>
> Right, but then we get more crosstalk instead ;-)
> BR Danny Damhave
>
> On 26/09/2011, at 21.45, Lee Ritchey wrote:
>
>> If you use the right glass weave it is not necessary to be concerned about
>> skew. No need for tricky routing.
>>
>>
>> --------------------------------------------------
>> From: "Danny Damhave" <dd@xxxxxxxxxxx>
>> Sent: Monday, September 26, 2011 12:24 PM
>> To: <si-list@xxxxxxxxxxxxx>
>> Subject: [SI-LIST] Re: Routing differential lines as single ended traces ?
>>
>>> Hi,
>>> Routing a LVDS differential pair with a tightly coupling, is sensitive to
>>> production tolerances/variation eg. etching factor/coating.
>>> Having a weak coupling or using the not closer than rule (single ended
>>> traces) is less sensitive.
>>> If your traces are wide and your timing is very critical is probably best
>>> to route with a very weak or weak coupling and match the trace to trace
>>> spacing with the pitch of the glass fibres in your laminate to reduce the
>>> skew between the signals, but of course this can also be achieved by
>>> staying away from 90deg routing and using the not closer rule.
>>> I assume that your signals always have a reference plane, are not close to
>>> any edge of the PCB, do not leave the board , and are not close to noise
>>> sources like DC DC switchers and your signals are not influenced by PCB
>>> resonances or the like.
>>> BR
>>> Danny Damhave
>>>
>>>
>>>
>>> On 26/09/2011, at 03.57, Low Jerry wrote:
>>>
>>>> Hi,
>>>> I recently came across a validation platform where the LVDS differential
>>>> lines are routed as single ended traces traces instead of tightly coupled
>>>> differential pairs. The motivation I found was so that they could use each
>>>> of the pairs as single ended traces when needed as well. When I probed
>>>> deeper it seems like the person who proposed this scheme has left. So I
>>>> would like to seek help here on some clarification
>>>>
>>>> - Will a scheme like this impact the performance of the differential pair
>>>> ? Since I understand that differential routing is more immune to noise.
>>>> - What are the considerations/feasiblity studies that need to be done
>>>> before implementing a scheme like this ?
>>>> - Since this is a validation platform what measures can be taken ensure
>>>> that the performance seen are similar to a production platform if the
>>>> production platform is routed in differential.
>>>>
>>>> Thanks in advance for the feedbacks. Have a great day.
>>>>
>>>>
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