Subject: RE: [IBIS-Users] LVDS modeling method
From: Shee Kian Wong (SKWONG@altera.com)
Date: Wed Aug 28 2002 - 02:33:55 PDT
Hi,
Thanks for your interest. Sorry for not specifying my question clearly.
The LVDS standard specifies a differential output voltage range of 0.25V <
Vod < 0.45V. Also, the terms "common-mode voltage" and "offset voltage"
refer to the average of A and B (the outputs of the driver), (A +B)/2. And
LVDS has a typical output common-mode voltage of 1.25 V. This simply means
that A+B=2.5.
Let say if one output is at 1.5V (during sweeping of an external voltage
source), the other output will try to achieve 1V so as to maintain a fixed
Vcm. However, Vod is now 500mV which is out of the Vod range. When one
output is -2V, the other one will be 4.5V, which consequently giving rise to
a Vod of 6500mV. This should not be the behavior of an LVDS buffer.
My question was: Is it possible to model an LVDS buffer by controlling both
vcm and vod?
Please correct me if I'm wrong. Thanks.
Best Regards,
Shee Kian Wong
Applications Engineer,
Altera Corporation (M) Sdn. Bhd.
-----Original Message-----
From: Hegazy, Hazem [mailto:hazem_hegazy@mentorg.com]
Sent: Wednesday, August 28, 2002 4:45 PM
To: 'Shee Kian Wong'; ibis-users@eda.org
Subject: RE: [IBIS-Users] LVDS modeling method
Hi,
Could please clarify the question? The common mode voltage is very
important for the model generation and which method to use. While the Vod is
a model parameter and you can even put it in the model after finishing all
current/wave form tables.
Hazem Hegazy
-----Original Message-----
From: Shee Kian Wong [mailto:SKWONG@altera.com]
Sent: Wednesday, August 28, 2002 10:40 AM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] LVDS modeling method
Hi all,
I've seen a lot of LVDS modeling methods only take care of vos (output
offset voltage) or vcm (common mode voltage).
But how come very seldom people make use of vod (output differential
voltage)? Isn't as important as other parameters?
Please advice.
Best Regards,
Shee Kian Wong
Applications Engineer,
Altera Corporation (M) Sdn. Bhd.
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