[SI-LIST] Re: using spice to calculate driver output impedance

Think of this as a voltage divider.  There is an open circuit voltage from
the driver, easy to measure.  There is a voltage when the driver is loaded
into say a 50 Ohm load.  Measure that.  Use Ohms Law to compute the unknown
resistance, the output impedance of the buffer.  This is the real part of
the output impedance.  But remember the output impedance of a buffer changes
with the swing of the driver.

The imaginary part is C_comp.

There are several methods of measuring C_comp, see the archives for articles
and messages about that.

Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
http://www.teraspeed.com
tom@xxxxxxxxxxxxx

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of eric steimle
Sent: Tuesday, February 22, 2005 4:11 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] using spice to calculate driver output impedance


Hi all, I'm having some trouble thinking of the right
way to calculate driver impedance using spice.  I have
finally a functioning model of the driver in question
and I've been able to run some simulations with it.  I
was hoping that there might be an accepted way of
calculating driver impedance out there that I don't
know about, or perhaps some literature you could point
me to.  Any help would be greatly appreciated.

Best Regards,
Eric



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