Re: [[SI-LIST] : Trace Impedance Selection]

About this list Date view Thread view Subject view Author view

From: Bill Owsley ([email protected])
Date: Thu May 04 2000 - 10:40:41 PDT

Arbitary seems right; tho' I've tended to favor higher impedances for lower
current reasons, considering a lower enough impedance to get the load
capacitance charged in the time constraints. but I recently heard another
reason? for picking a certain value - in this case 50 ohms. This matches the
impedance of a small coax used to sample the signals for measurment. 8^)

Doug Brooks <[email protected]> wrote:
> OK, gurus....
>
> Lets say I have a trace on a board between two devices. There is nothing
> that determines what the characteristic impedance of the trace should be.
> That is, there are no device considerations, no space considerations, no
> power considerations, etc. that would favor one value of characteristic
> impedance over another. It is my opinion that as long as the characteristic

> impedance is constant over the length and properly terminated, the choice
> of impedance value in this situation is completely arbitrary.
>
> Does anyone (having accepted the assumptions above) have a different
> opinion? In particular, are there any EMI reasons that would favor one
> value of characteristic impedance over another? (But don't tell me the
> assumptions above are wrong! That's not the question!)
>
> Doug Brooks
> .
> ************************************************************
> See our updated message re in-house seminars on our web page
> .
> Doug Brooks, President [email protected]
> UltraCAD Design, Inc. http://www.ultracad.com
>
>
> **** To unsubscribe from si-list or si-list-digest: send e-mail to
> [email protected]. In the BODY of message put: UNSUBSCRIBE
> si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> si-list archives are accessible at http://www.qsl.net/wb6tpu
> ****

____________________________________________________________________
Get your own FREE, personal Netscape WebMail account today at http://webmail.netscape.com.

**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected]. In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****

About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Wed Nov 22 2000 - 10:50:10 PST