[SI-LIST] Re: R: Re: R: LVDS Transmission Problem
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Tue, 27 Sep 2005 16:37:07 -0400
Hi Giovanni,
Since the failure is observed even with a 3m cable, then the cable loss may not
be the
dominant loss in this case. The other components in the data path might be
playing a
larger role.
Best regards.
Hassan.
On Sep 27, "Guasti Giovanni" <Giovanni.Guasti@xxxxxxxxxx> wrote:
>
> Hi Hassan,
> I did a very simple calculation, maybe I'm wrong: an LVDS differential =
> swing at the driver is about 800mV and 150m of cat5 cable is about =
> 20-30dB of losses @30-100MHz. So at the receiver we'll have ABOUT =
> 80-24mV of swing, that is under or near the threshold (100mV). Are you =
> confident about using an LVDS with 150m of cable?
> In the National (DS90LV032ATM & DS90LV031ATM) appl. note 971 there is =
> also a picture of the signal after 10 m of cable @ 155Mb/s. Signal is =
> quite good, but rise and fall time increase a lot.
> Anyway the worst contribute to the signal in this particular case is =
> given by connectors, flexes and the backplane.
> That's why I think that the LVDS is not the FIRST choice. I think that =
> the noise margin could be reduced too much.
> Best regards,
> Giovanni
>
> -----Messaggio originale-----
> Da: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]Per conto di Hassan O. Ali
> Inviato: marted=EC 27 settembre 2005 16.54
> A: si-list@xxxxxxxxxxxxx
> Oggetto: [SI-LIST] Re: R: LVDS Transmission Problem
>
>
>
> Cable loss is certainly not the problem here. Plain old LVDS signaling =
> can be used with=20
> 24 gauge twisted-pair cables even longer than 150 meters! One can refer =
> to the cable=20
> guidelines in the LVDS standard page 25 (<a href='http://ftp.tiaonline.org/tr-
'>http://ftp.tiaonline.org/tr-</a>
> 30/tr302/Public/2000%20Contributions/20005017.pdf)
>
> I think the problem here could be with the data pattern, data rate, or =
> the type of=20
> connection. Relevant questions to consider:
>
> - Is it a dc or ac-coupled link?=20
> - Does the failing data pattern have long runs of zero's and one's that =
> considerably=20
> 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:
> >=20
> > 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 =
> =3D
> > signal polarization due to distributed capacitance?
> > maybe the LVDS suffers the high capacity of the system (maybe is just =
> =3D
> > the shield).
> > After the signal measurement, I would try with these:
> > 1)a scrambled (or a more balanced number of '1' and '0')signal=3D20
> > 2)a unshielded cable / unshilded and shorter cable.
> > 3)replace LVDS with a LVPECL or MLVDS/BLVDS
> > I hope this could help you,
> > Giovanni
> >=20
> >=20
> > Hi=3D20
> >=20
> > =3D20
> >=20
> > We have a system which is build up two subsytem. Data signals between =
> =3D
> > 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 =
> =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 problem somewhat lowered but we have still the problem. =
> What
> > could be the reasons for this problem?
> >=20
> > =3D20
> >=20
> > <mailto:r@xxxxxxxxxxxxxxxxxxx>=3D20
> >=20
> > M.Baris DUZGUN
> >=20
> > Hardware Senior Expert Engineer
> >=20
> > ASELSAN INC. MGEO Division
> >=20
> > P.K. 30 06011
> >=20
> > Etlik ANKARA
> >=20
> > TURKEY
> >=20
> > Tel : +90 312 847 53 00 / 4534
> >=20
> > Fax : +90 312 847 53 20
> >=20
> > e-mail : bduzgun@xxxxxxxxxxxxxxxxxxx =3D
> > <mailto:bduzgunr@xxxxxxxxxxxxxxxxxxx>=3D20
> >=20
> > =3D20
> >=20
> >=20
> We have a system which is build up two subsytem. Data =3D
> > =3D3D
> > signals
> > between the subsystems are in LVDS format. Between these two =
> subsystems =3D
> > =3D3D
> > there
> > is 10m cable. LVDS data signals are carried using shielded twisted =
> pair =3D
> > =3D3D
> > cables.
> > Inside these two subsystem LVDS signals also passed through backplanes =
> =3D
> > =3D3D
> > and flexes
> > . We use national LVDS transmitter and receiver. (DS90LV032ATM &
> > DS90LV031ATM) . The data rate of the LVDS signals are 34MHz. The =
> problem =3D
> > =3D3D
> > is for
> > some data patterns the transmitted and received data is not =
> same? =3D
> > =3D3D
> > As the cable
> > length is shortened to 3m and frequency of LVDS signals is reduced the =
> =3D
> > =3D3D
> > problem
> > somewhat lowered but we have still the problem. What could be the =
> =3D3D
> > reasons for
> > this problem?
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> <a
> href='http://www.freelists.org/webpage/si-list'>http://www.freelists.org/webpage/si-
list</a>
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> <a
> href='http://si-list.org/wiki/wiki.pl?Si-List_FAQ'>http://si-
list.org/wiki/wiki.pl?Si-List_FAQ</a>
>
> List technical documents are available at:
> <a href='http://www.si-list.org'>http://www.si-list.org</a>
>
> List archives are viewable at: =20
> <a href='http://www.freelists.org/archives/si-
list'>http://www.freelists.org/archives/si-list</a>
> or at our remote archives:
> <a href='http://groups.yahoo.com/group/si-
list/messages'>http://groups.yahoo.com/group/si-list/messages</a>
> Old (prior to June 6, 2001) list archives are viewable at:
> <a
> href='http://www.qsl.net/wb6tpu'>http://www.qsl.net/wb6tpu</a>
> =20
>
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> <a
> href='http://www.freelists.org/webpage/si-list'>http://www.freelists.org/webpage/si-
list</a>
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> <a
> href='http://si-list.org/wiki/wiki.pl?Si-List_FAQ'>http://si-
list.org/wiki/wiki.pl?Si-List_FAQ</a>
>
> List technical documents are available at:
> <a href='http://www.si-list.org'>http://www.si-list.org</a>
>
> List archives are viewable at:
> <a href='http://www.freelists.org/archives/si-
list'>http://www.freelists.org/archives/si-list</a>
> or at our remote archives:
> <a href='http://groups.yahoo.com/group/si-
list/messages'>http://groups.yahoo.com/group/si-list/messages</a>
> Old (prior to June 6, 2001) list archives are viewable at:
> <a
> href='http://www.qsl.net/wb6tpu'>http://www.qsl.net/wb6tpu</a>
>
>
>
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
http://www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts: