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

About this list Date view Thread view Subject view Author view

From: Ron Miller ([email protected])
Date: Thu May 04 2000 - 17:02:15 PDT


What are you going to measure it with?

All the microwave test equipment is at 50 ohms, as are
the cables, and waveguide.

Only IF and video, TV use 75 ohms and above.

So, you can use any impedance you want if you also are willing
to develop ca bles, test equipment and all the infastructur you need.

Good luck

Ron Miller

> -----Original Message-----
> From: Bill Owsley
> Sent: Thursday, May 04, 2000 10:41 AM
> To: [email protected]
> Subject: Re: [[SI-LIST] : Trace Impedance Selection]
>
> 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
> ****
>

**** 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 - 10:50:11 PST