Re: [SI-LIST] : Star connection termination

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From: Chuck Hill (chuckh@altaeng.com)
Date: Fri Nov 26 1999 - 18:22:58 PST


Massimo,

Try the following:
Put a series termination resistor of around 20ohm in each of the star
connected traces, all resistors being located at the source. The actual
value depends on the trace impedances but this should get you close. After
you fabricate the board, you can adjust the resistor values. You will need
a high drive buffer probably.

You don't want a resistance equal to the characteristic impedance; you also
don't need it. Theoretically, 0.707 of the line impedance gives a faster
risetime (analogous to damping ratio, not 1.0 but 0.707 gives faster
risetime). Besides, you can tolerate some ringing.

Charles Hill, consultant

At 04:56 PM 11/26/99 +0100, massimo.polignano@esaote.com wrote:
>
>
>Does anybody out of there have any suggestion about the following basic, but
>
>really important and frequent, problem: how a star-point (a point from which
>
>many traces going to other ICs start) must be series-terminated?
>
>Do one have to put a resistance equal to the characteristic impedance of the
>
>trace before the point from which the traces start? Or is it better to
insert a
>
>resistance on each line coming up from the star-point? In the latter case,
what
>
>is the best value for the resistances?
>
>
>
>Thanks for any help
>
>m.p.
>
>-------------------------------------------------------------
>
>ESAOTE S.p.A. Massimo Polignano
>Research & Product Development Design Quality Control Mngr
>Via di Caciolle,15 tel:+39.055.4229402
>I- 50127 Florence fax:+39.055.4223305
> e-mail: massimo.polignano@esaote.com
>
>
>
>
>
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