[SI-LIST] Re: LVDS Transmission Problem
- From: Scott McMorrow <scott@xxxxxxxxxxxxx>
- To: weirsi@xxxxxxxxxx
- Date: Tue, 27 Sep 2005 09:24:05 -0400
Baris
To follow on with what Steve has stated, a quick calculation will show
that your cable delay is somewhere on the order of 40 to 50 ns. If you
have any significant mismatches along the cable or at the ends, you will
set up a standing wave resonance pattern that would have somewhere near
a 10 MHz half wave resonance. A TDR of the cable should help you uncover
the problem. I would guess that you have a large impedance mismatch in
your system. As a guess, I think your cable impedance is significantly
higher than the impedance of either of your attached systems. The other
possibility is that you are not correctly terminating the ends of the line.
regards,
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
Teraspeed® is the registered service mark of
Teraspeed Consulting Group LLC
steve weir wrote:
>Baris,
>Your data rate is quite low, so I do not suspect ISI. More than likely,
>your issues arise from standing waves in the transmission line, and/or
>excessive DC offset between the chassis'. For a sizeable cable, even mode
>termination is pretty much a must. If you exceed the CM range of the
>receiver life will be bad.
>
>Steve.
>At 03:32 PM 9/27/2005 +0300, Baris Duzgun wrote:
>
>
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>>From: "Baris Duzgun" <bduzgun@xxxxxxxxxxxxxxxxxxx>
>>To: <si-list@xxxxxxxxxxxxx>
>>Subject: LVDS Transmission Problem
>>Date: Tue, 27 Sep 2005 15:32:48 +0300
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>>Hi
>>
>>
>>
>>We have a system which is build up two subsytem. Data signals between the
>>subsystems are in LVDS format. Between these two subsystems there is 10m
>>cable. LVDS data signals are carried using shielded twisted pair cables.
>>Inside these two subsystem LVDS signals also passed through backplanes and
>>flexes . We use national LVDS transmitter and receiver. (DS90LV032ATM &
>>DS90LV031ATM) . The data rate of the LVDS signals are 34MHz. The problem is
>>for some data patterns the transmitted and received data is not same? As
>>the cable length is shortened to 3m and frequency of LVDS signals is
>>reduced the problem somewhat lowered but we have still the problem. What
>>could be the reasons for this problem?
>>
>>
>>
>> <mailto:r@xxxxxxxxxxxxxxxxxxx>
>>
>>M.Baris DUZGUN
>>
>>Hardware Senior Expert Engineer
>>
>>ASELSAN INC. MGEO Division
>>
>>P.K. 30 06011
>>
>>Etlik ANKARA
>>
>>TURKEY
>>
>>Tel : +90 312 847 53 00 / 4534
>>
>>Fax : +90 312 847 53 20
>>
>>e-mail : bduzgun@xxxxxxxxxxxxxxxxxxx <mailto:bduzgunr@xxxxxxxxxxxxxxxxxxx>
>>
>>
>>
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>>
>>Hi
>>
>>
>>
>>We have a system which is build up two subsytem. Data = signals between
>>the subsystems are in LVDS format. Between these two subsystems = there is
>>10m cable. LVDS data signals are carried using shielded twisted pair =
>>cables. Inside these two subsystem LVDS signals also passed through
>>backplanes = and flexes . We use national LVDS transmitter and receiver.
>>(DS90LV032ATM & DS90LV031ATM) . The data rate of the LVDS signals are
>>34MHz. The problem = is for some data patterns the transmitted and
>>received data is not same? = As the cable length is shortened to 3m and
>>frequency of LVDS signals is reduced the = problem somewhat lowered but we
>>have still the problem. What could be the = reasons for this problem?
>>
>>
>>
>>=
>>
>>M.Baris = DUZGUN
>>
>>Hardware Senior = Expert Engineer
>>
>>ASELSAN INC. MGEO = Division
>>
>>P.K. 30 = 06011
>>
>>Etlik = ANKARA
>>
>>TURKEY
>>=
>>
>>Tel : +90 312 847 53 00 / = 4534
>>
>>Fax : +90 312 847 53 = 20
>>
>>e-mail : bduzgun@xxxxxxxxxxxxxxxxxxx
>>
>>
>>
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