[SI-LIST] Re: [IS-LIST] Source termination of LVDS drivers

From: Robert Kezer <Robert.Kezer@xxxxxxxxxxxxx>
To: "'sunil-chandra.kasanyal@xxxxxx'" <sunil-chandra.kasanyal@xxxxxx>,si-list@xxxxxxxxxxxxx
Date: Tue, 28 Jan 2003 09:00:03 -0500

The problem I see with a series termination is a drop of around 800 mV
across
a 200 ohm resitor. This assumes a 4mA current being sourced and sunk by the 
LVDS I/O.

As long as the driver has the dynamic range to provide an extra drop, this
will
work fine, but for low voltage devices, this may pose a problem.

Currently most LVDS outputs have a 2.5V rail, but this may change in the
future.

Bob

-----Original Message-----
From: sunil-chandra.kasanyal@xxxxxx
[mailto:sunil-chandra.kasanyal@xxxxxx]
Sent: Tuesday, January 28, 2003 4:47 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Source termination of LVDS drivers




Hello,
        In LVDS interfacing 100 ohm resistance is provided at receiver end
to
terminate the differential lines. To absorb the reflections from receiver
end, due to mismatching between differential lines and termination
resistance, source termination at driver end is also provided. This
source termination resistance causes extra power dissipation. Partial
source termination with source termination resistance value 200 ohm shows
a good compromise for overall performance of reflection and power
dissipation.
        Instead of this one 200 ohm resistance, I use two series 100 ohm
resistance with their common point is connected to a voltage source of
1.2V. This architecture is very common for LVDS drivers to make output
offset voltage at a constant value of 1.2V.
        My question is whether the second architecture (which has 1.2V
source)
also fulfills the purpose of partial source termination. If not, why?

Thanks in advance

Thanks and Regards,
Sunil C Kasanyal
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[SI-LIST] Re: [IS-LIST] Source termination of LVDS drivers

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