Re : Impedance Software

Chris Heard/US/3Com ([email protected])
31 Jul 96 9:12:16 EDT

It's also worth mentioning that Teradyne in Nashua, N.H. has a tool that runs
as a HyperCard stack (Macintosh) that graphically displays how a stack-up will
meet an impedance tolerance and links that information to a graphical
description of the overall stackup.

This tool uses the method of moments for the analysis, as opposed to tweaked
closed-form equations from the MECL handbook (the more industry-typical method).

It also predicts loaded impedance (for a bus) and d.c. resistance.

Worth a look,

Chris Heard
Principal Engineer - Electronics Packaging
3Com Corporation
----- Previous Message ----------------------------------------------------

To: si-list @ silab.Eng.Sun.COM @ SMTP1
From: tompkins @ (Jim Tompkins) @ SMTP1
Date: Wednesday July 31, 1996 08:27 AM
Subject: Re : Impedance Software

> Does anyone know where I can find an accurate, reliable software program,
> preferably PC-based, that calculates characteristic impedance for
> microstrip, embedded microstrip, stripline, and dual stripline traces on a
> PC board?
> jwf
> ----- End Included Message -----

We use a freeware DOS program called imped from HADCO. It calculates
Zo from geometry information. You can contact their tech centre in
Salem, NH for a copy.

We have found that HADCO can control impedance quite accurately.
We use their calculator to determine trace widths for the desired
impedance and then route with a slightly (0.001") wider track.
Then you specify to them that all X mil tracks on layer Y should be
Z Ohms. They will size the tracks as required to get your specified
impedance. They can easily size down; it's far more difficult to size up.

Not related to HADCO, just fairly satisified with their results.



Jim Tompkins, M.A.Sc., P.Eng.
Hardware Designer                Internet : [email protected]   
Applied Microelectronics Inc.    Voice    : (902) 421-1250 x252
1046 Barrington Street           Fax      : (902) 429-9983
Halifax, NS  CANADA B3H 2R1      WWW      :