RE: [SI-LIST] : Star connection termination

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From: Abe Riazi (ariazi@anigma.com)
Date: Sat Nov 27 1999 - 09:27:49 PST


       Hi Massimo:

      I like to correct a typographical error in my earlier post. The
publication date for the paper by S. Kauffer and K. Crisafulli, is March
1998 (not March 1988).

     The article by Kauffer and Crisafulli offers worthwhile reading for
anyone interested in the subject of termination.

     It discusses several termination schemes (including series,
parallel, AC and diode) and to what type of routing topology they
apply.
     
     In regard to star routing, it points out that if the branches are
well balanced (in terms of characteristic impedance and delay) it is
possible to use a single resistor. However, for unmatched branches it
is undesirable to use a single resistor on the trunk, instead one
resistor per branch should be used.

    Regards,

    Abe

>----------
>From: Abe Riazi
>Sent: Friday, November 26, 1999 10:37 PM
>To: 'si-list@silab.eng.sun.com'
>Subject: RE: [SI-LIST] : Star connection termination
>
> Hi Massimo:
>
> 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.
>
> Abe Riazi
>
> ariazi@anigma.com
>
>
>>----------
>>From: massimo.polignano@esaote.com[SMTP:massimo.polignano@esaote.com]
>>Sent: Friday, November 26, 1999 7:56 AM
>>To: si-list@silab.eng.sun.com
>>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
>>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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