RE: [SI-LIST] : Transmission line termination

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From: Peters, Stephen (stephen.peters@intel.com)
Date: Fri Apr 06 2001 - 08:35:53 PDT


Hi Sunil:

  From a transmission line perspective you are correct -- there is no
difference between the two. However, you do have to look at the output
characteristics of the driver. If, for example, the driver was able to sink
more current that it could source (typical TTL), then a termination to a Vtt
would be preferred. (Obviously, if the driver is open-collector, then a
termination (pullup) to Vtt is required). Power dissipation is another
factor. If the signal is a control signal that spends most of it's time in
the high state, then a termination to Vtt will dissipate less power than one
to ground.

  Regards,
  Stephen Peters
  Intel Corp.
    

-----Original Message-----
From: sunil-chandra.kasanyal@st.com
[mailto:sunil-chandra.kasanyal@st.com]
Sent: Friday, April 06, 2001 12:57 AM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : Transmission line termination

Hello all,
          What is the difference between these two terminations?Why?
1)
             -----------------------
DRIVER->-----| TRANSMISSION LINE |-------------RECIEVER
             ----------------------- \
                Zo=50ohms /Rtt=50ohms
                                          \
                                          /
                                         ---GND
2)

             -----------------------
DRIVER->-----| TRANSMISSION LINE |-------------RECIEVER
             ----------------------- \
                Zo=50ohms /Rtt=50ohms
                                          \
                                          /
                                        ------TERMINATION VOLTAGE=Vtt

If signals of 5V come from drivers,no reflection will take place at the
reciever ends.Since in above two cases,way of termination is
different,what exactly the different uses of these two terminations.

Regards
Sunil

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