[SI-LIST] Re: diff pair signal
- From: steve weir <weirsp@xxxxxxxxxx>
- To: <tom@xxxxxxxxxxxxx>, <gil.gafni@xxxxxxxx>, <gopalak@xxxxxxxxxxx>,<si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 Jun 2004 10:27:14 -0700
Tom, that doesn't sound a bit surprising.
Regards,
Steve.
At 10:10 AM 6/30/2004 -0700, Tom Dagostino wrote:
>In the past I've seen significant differences in the performance of one side
>of LVDS with the other side loaded vs. unloaded. I would recommend loading
>(50 Ohms to Vcm) any unused LVDS output if it's pair is used.
>
>Tom Dagostino
>Teraspeed Consulting Group LLC
>503-430-1065
>tom@xxxxxxxxxxxxx
>www.teraspeed.com
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx
>[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
>Sent: Wednesday, June 30, 2004 9:53 AM
>To: gil.gafni@xxxxxxxx; gopalak@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: diff pair signal
>
>
>Gil, I don't know of any specific problems with leaving one leg of an LVDS
>driver open but it might cause some timing issues as the current source
>goes from unloaded to loaded. We disagree on how best to get a reliable
>switching reference as noted in earlier postings. Given the low swing of
>LVDS, if it is a poor man's translator, AC coupling would seem mandatory
>due to the low swing.
>
>Regards,
>
>
>Steve.
>At 09:35 AM 6/30/2004 -0700, Gil Gafni wrote:
> >To my humble opinion, it is all about the transmitter (driver).
> >
> >If it a true current logic, like the LVDS and alike, you have to close
> >the current loop, otherwise it will not work properly (or at all)...
> >If you driver is build of two "independent" drivers it will be easier.
> >In such case you can connect one output to the receiver.
> >You will have to address few issue though:
> >1. What should you do with the other output, i.e. can you leave it open
> >or is would you need any termination
> >2. assuming that the receiver is not a single ended, you will have to
> >address the Vref, I would recommend to generate it from the driver's
> >Vddq (IO voltage)
> >3. Do you need to AC couple
> >
> >And so on
> >
> >By the way there are plenty of Application Notes that discuss single to
> >diff, to name one -
> >http://www.saronix.com/pdf/applications/AN047.pdf
> >
> >Good luck
> >
> >
> >Cheers,
> >
> >
> >
> >Gil Gafni
> >
> >
> >
> >-----Original Message-----
> >From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> >On Behalf Of Gopalakrishnan Sethuraj
> >Sent: Wednesday, June 30, 2004 7:09 AM
> >To: si-list@xxxxxxxxxxxxx
> >Subject: [SI-LIST] diff pair signal
> >
> >
> >Hello
> >
> >
> >Is there any scenario where one (positive) of the differential pair
> >signal output will be connected to single pin in LVDS or other logical
> >interfaces ?
> >
> >
> >
> >
> >
> >Thanks&Regards
> >
> >Gopalakrishnan
> >
> >
> >
> >
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