[SI-LIST] Re: Source impedance?

  • From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
  • To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
  • Date: Tue, 8 Jan 2002 16:29:27 -0800

If we use a little bit more imagination. Suppose you have
a 50 ohm control impedance source in a bi-directional 
point to point bus. When are done driving, turn on the
high or low side constantly and you become a receiver
terminator. turn on half high/ half low you become a
CTT terminator. Very convenient.
Now if both side drive at the same time, you've got 
a very nice simultaneously bi-directional I/O. 
Very neat.

-----Original Message-----
From: David Kaiser [mailto:david.kaiser@xxxxxxxxxx]
Sent: Tuesday, January 08, 2002 2:39 PM
To: 'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Source impedance?



Theory question. Assume perfect world with no parasitics.

If a 50 Ohm trace on a board is terminated with a 50 Ohm resistor at the end
of the trace, is there any advantage in terms of SI
to driving the trace with a source that has 50 Ohm output impedance compared
to a source with 10 or 20 Ohms of output impedance?

It seems to me that the only thing the series source impedance would do to a
50 Ohm line that is terminated with a 50 Ohm resistive load would be to
divide the amplitude in half without improving the signal integrity.
Correct?

David 
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