The loads are high impedance, for design purposes they are purely
reflective.  That is inherent in the reflective wave approach because it
eleiminates switching power being consumed at the load.

Tim

-----Original Message-----
From: Brian Guralnick [mailto:[EMAIL PROTECTED]]
Sent: Monday, August 06, 2001 5:16 PM
To: Protel EDA Forum
Subject: Re: [PEDA] 5/5 Manufacturing Issues


| Dude, I wasn't trying to be analytical but was only referring to the
example
| I posed earlier, 50 ohm source impedance looking into the driver from the
| reflected wave and a 10 ohm source resistor which at frequency, forms a
| voltage divider that absorbs power in roughly that manner I think.
|
| Tim

    Not quite.  Remember, you are driving a capacitive load for the most
part.  The
ICs you are driving probably have an input resistive load greater than 100K,
if the
parts are CMOS, the load can easily be in the megaohms.

    Now, on the other hand, if you are driving a 5pf load, for example, the
50 ohm
source + the additional 10 ohms will make a R/C filter softening the signal
as well
as the surge created by IO switching on your power supply.  These softened
current
surges, slower signal transitions, also affect signals across trace-trace, &
IO-IO,
and the lessened supply spikes can make a gigantic difference.

____________
Brian Guralnick


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