From: Abe Riazi (email@example.com)
Date: Fri Nov 26 1999 - 22:37:27 PST
Series termination is an excellent choice for the star topolgy.
When the branches are closely matched in delay and impedance, a single
resistor can be used near the driver. The value of this resistor Rt is
related to the trace impedance Zo, number of branches N, and the driver
impedance Ro via:
Rt = (Zo/N) - Ro
If the branches are not well matched then one resistor should be
employed for each branch, becasue using one resistor will be
ineffective. The value of each branch terminator Rn can be calculated
from the branch trace impedance Zn and the driver impedance Ro by means
of the equation:
Rn = Zn - Ro
The following publication includes a nice discussion of this topic:
S. Kuffer, and K. Crisafulli, "Terminating Traces on High Speed
PCBs", Printed Circuit Design, March 1988, pp. 24 -27.
I hope you find this information useful.
>Sent: Friday, November 26, 1999 7:56 AM
>Subject: [SI-LIST] : Star connection termination
>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
>resistance on each line coming up from the star-point? In the latter case,
>is the best value for the resistances?
>Thanks for any help
>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: firstname.lastname@example.org
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