Re: FW: [SI-LIST] : Output Impedance

Arpad Muranyi (
Wed, 01 Apr 98 13:34:00 PST

Text item:

You might as well just use a resistor to Vcc for falling edges and a resistor to
GND for rising edges, after all an (infinitely) long transmission line looks the
same as a resistor to the driver...



Kevin's method will measure dc source resistance of the driver.
AC source impedance can be measured by connecting a long ideal t-line
(eg 25ns) and fairly llow Zo (40 ohms works well, higher if driver has
very hi Z)) to the output of the driver, and applying an edge signal =
the input of the driver. The size of the step (plateau) obtained for
positive and negative edges can be used to determine driver source

Rdrv(rise) =3D Rline(Vfinal/(Vstep-1))

Rdrv(rfall) =3D Rline(Vfinal/(Vstep-1))

(This method was recommended by Hyperlynx for use with their .mod
generation but is equaly applicable to any source R measurement)
From: Kevin Weldon [SMTP:kweldon@BayNetworks.COM]
Sent: Wednesday, April 01, 1998 12:59 PM
To: alaa alani
Cc: si-list@silab.Eng.Sun.COM
Subject: Re: [SI-LIST] : Output Impedance

Hello Alaa,=20

=A0 What I do is connect the input node of the output buffer=20
to Vcc.=A0 Then I=A0connect the output node to Vcc through=20
a resistor.=A0 Then I simply change the value of the resistor=20
until I measure Vcc/2 at the output node of the buffer. The=20
value of the resistor at this point is equal to the output impedance=20
of the buffer.=A0 HSpice's Goal Optimization works well for this.=20
=A0=A0=A0 Is there a simpler way to do this?=20

Kevin Weldon=20
Bay Networks=20
3 Federal St. BL3-02=20
Billerica, MA 01821=20

alaa alani wrote:=20


What is the simplest way to measure the output impedance of a
given just a spice netlist?=20


Alaa Alani=20
LSI Logic


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Date: Wed, 1 Apr 1998 14:17:06 -0500
Subject: FW: [SI-LIST] : Output Impedance
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