RE: [SI-LIST] : measuring Differential pairs

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From: Larry Miller (ldmiller@nortelnetworks.com)
Date: Thu Aug 03 2000 - 09:21:42 PDT


This has come up before, but here goes:

If you have a Tek SD-24 dual-channel TDR plug-in for an 11801 scope frame,
you can do two things:

1. Have the second channel use an inverted test waveform. I claim that if
you connect one channel to each line, and the two channels are exactly out
of phase, then that cancels the effect of the (common) ground planes.

2. With this instrument you have a vernier control to precisely align the
switching times of the two current generators, which is necessary to launch
your out-of-phase test waves at precisely the same instant.

Using this technique we seem to get what we think are the right
answers......(by the way, you only read one channel; the second channel is
there to provide the mirroring signal.)

Larry Miller

> -----Original Message-----
> From: Sean Murray [SMTP:seandm@mmspec.com]
> Sent: Wednesday, August 02, 2000 11:16 AM
> To: si-list@silab.eng.sun.com
> Subject: [SI-LIST] : measuring Differential pairs
>
> How does one go about measuring (using TDR) differential pairs on a board.
> In other words, how does one measure the ZOD of the pair, be it broadside
> or
> edge-edge?
>
> Regards,
> Sean Murray
> General Manager
>
> M&M Specialties Inc.
> 1236 W. Southern Ave. #106
> Tempe, AZ. 85282-4518
> Phone: (480) 858-0393 x105
> Cell: (602) 684-7859
> Fax: (480) 858-1882
> Email: seandm@mmspec.com
> WWW.mmspec.com
>
>
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