[SI-LIST] Re: OUTPUT IMPEDANCE CALCULATION [IBIS]

Another method to establish the source impedance (Zs) of a driver from
an IBIS model is in a simulation (still using Ohms law):

Create a circuit with the ibis model driving a very long transmission
line (12 inches) with a known trace impedance (Zo). Drive the line both
high and low and observe the porch in the waveform. The porch is caused
by the ratio of Zs and Zo. Zs can be solved by rearranging this very
familiar equation :

Vout =3D Vin * (Zo/(Zo+Zs)) ...solve for Zs, Vout is Vporch and Vin is =
the
total voltage swing

The porch will last as long as 2x the propagation time of the T-line.

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Scott McMorrow
Sent: Monday, September 18, 2006 4:48 PM
To: torocar@xxxxxxxxx
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: OUTPUT IMPEDANCE CALCULATION [IBIS]

Carlos

Ohms law (Z=3D V/I).  You have a V/I curve at min/typ/max device =
corners.


regards,

Scott

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed(r) is the registered service mark of Teraspeed Consulting
Group LLC



Carlos Toro wrote:
> Hello members of the SI list.
> Does anyone has experience with calculating the output impedance of a=20
> microcontroller pin given its IBIS model?.
>
> I don't have access to the silicon yet, just the IBIS for now. I=20
> intend to match impedances of critical PCB traces of our design.
>
> Thanks in advance.
>
>
>  =20
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