[SI-LIST] Re: Routing differential lines as single ended traces ?
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>, "Danny Damhave" <dd@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Tue, 27 Sep 2011 12:19:55 -0700
Another weave that is great for minimizing skew is 3313. That is my
favorite as it gives a good balance between trace width, dielectric
thickness and crosstalk. Been using this for about 5 years in all kinds of
stackups running up to 24 Gb/S with no skew problems.
--------------------------------------------------
From: "Ken Cantrell" <Ken.Cantrell@xxxxxxxxxxxxxxxx>
Sent: Tuesday, September 27, 2011 8:22 AM
To: "Danny Damhave" <dd@xxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Routing differential lines as single ended traces ?
> Danny,
> Agreed that with your material choice you would lose routing density.
> However there are other material options available.
>
> Material Thickness
> 1080 - 2.5 mils
> 2116 - 3.8 mils
> 1086 - 2.0 mils
> 1067 - 1.3 mils
>
> 1080 is 60x47
> 2116 is 60x58
> 1086 is 60X60
> 1067 is 70x70
>
> 1086 and 1067 are square symmetric where the others are not, and would be
> better choices than 2116. They also offer the advantage of being thinner,
> so routing density would be improved over 1080 or 2116. With the correct
> laminate choice for your particular application, it is possible to achieve
> low/no laminate induced skew, and maintain low crosstalk and high routing
> density.
>
> Ken
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Danny Damhave
> Sent: Monday, September 26, 2011 11:42 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Routing differential lines as single ended traces
> ?
>
>
> 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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