Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!elroy!cit-vax!cit-vlsi!flaig
From: flaig@cit-vlsi.Caltech.Edu (Charles M. Flaig)
Newsgroups: sci.electronics
Subject: Re: Help with L measurement
Message-ID: <5820@cit-vax.Caltech.Edu>
Date: 16 Mar 88 23:01:18 GMT
References: <1872@mips.mips.COM>
Sender: news@cit-vax.Caltech.Edu
Reply-To: flaig@cit-vlsi.UUCP (Charles M. Flaig)
Organization: California Institute of Technology
Lines: 33
Keywords: inductance of chip ground

In article <1872@mips.mips.COM> mark@mips.COM (Mark G. Johnson) writes:
>
>I have a problem.  I'm trying to measure the inductance of a
>gate-array (IC pin + package trace + bondwire), i.e. the total
>inductance between the ground plane of my printed circuit board and
>the on-chip ground metallization inside my gate-array IC.

[explains he tried ringing a tank circuit, didn't work]

Well, you could try to find the delay of an LC circuit (if you have a fast
enough rise/fall time for your input waveform):

--------             --------------
Square |_____________| Package    |____________ Delayed waveform
Wave   |       |     | Inductance |     |       
--------       |     --------------     |
               |        10-30nH       __|__
               |                      _____ 100pf + Cscope
               V                        |
            Original                  __|__
            waveform                  / / /

After subtracting out the RC delay you should be left with the LC delay,
and be able to calculate L.  If necessary, you could put several package
and capacitor stages in series for longer delays but messier calculations.
I don't remember what the formula for LC delay is, but any electromagnetics
text should have it.

______________________________________________________________________________
  ___   ,               ,                                           ,;,;;;,
 /   Y /|              /|              Charles Flaig                ;/@-@\;
|      |/     __, ,__  |/              flaig@csvax.caltech.edu       | ^ |
|      /^\   /  | | |  /  /\  /\                                      \=/ 
 \____/|  \_/|_/\_/ \_/ \_\/_/_/_/     "What, you think they PAY me for this?"