[SI-LIST] Re: R: LVDS Transmission Problem
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 27 Sep 2005 10:54:01 -0400
Cable loss is certainly not the problem here. Plain old LVDS signaling can be
used with
24 gauge twisted-pair cables even longer than 150 meters! One can refer to the
cable
guidelines in the LVDS standard page 25 (http://ftp.tiaonline.org/tr-
30/tr302/Public/2000%20Contributions/20005017.pdf)
I think the problem here could be with the data pattern, data rate, or the type
of
connection. Relevant questions to consider:
- Is it a dc or ac-coupled link?
- Does the failing data pattern have long runs of zero's and one's that
considerably
alter the dc balance of the signal? More so if ac-coupled.
- Is 34MHz below the low frequency limit of the LVDS receiver/driver?
Best regards.
Hassan.
On Sep 27, "Guasti Giovanni" <Giovanni.Guasti@xxxxxxxxxx> wrote:
>
> I think LVDS is not the first choice for a so long path.
> How is the measured signal? Is a problem of losses, reflections or a =
> signal polarization due to distributed capacitance?
> maybe the LVDS suffers the high capacity of the system (maybe is just =
> the shield).
> After the signal measurement, I would try with these:
> 1)a scrambled (or a more balanced number of '1' and '0')signal=20
> 2)a unshielded cable / unshilded and shorter cable.
> 3)replace LVDS with a LVPECL or MLVDS/BLVDS
> I hope this could help you,
> Giovanni
>
>
> Hi=20
>
> =20
>
> 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?
>
> =20
>
> <mailto:r@xxxxxxxxxxxxxxxxxxx>=20
>
> 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>=20
>
> =20
>
>
We have a system which is build up two subsytem. Data =
> =3D
> signals
> between the subsystems are in LVDS format. Between these two subsystems =
> =3D
> there
> is 10m cable. LVDS data signals are carried using shielded twisted pair =
> =3D
> cables.
> Inside these two subsystem LVDS signals also passed through backplanes =
> =3D
> and flexes
> . We use national LVDS transmitter and receiver. (DS90LV032ATM &
> DS90LV031ATM) . The data rate of the LVDS signals are 34MHz. The problem =
> =3D
> is for
> some data patterns the transmitted and received data is not same? =
> =3D
> As the cable
> length is shortened to 3m and frequency of LVDS signals is reduced the =
> =3D
> problem
> somewhat lowered but we have still the problem. What could be the =3D
> reasons for
> this problem?
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