Re: [SI-LIST] : Non-standard bus termination (2nd posting)

Ron Miller (rmiller@Brocade.COM)
Wed, 22 Sep 1999 10:24:32 -0700

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Use tie all the common sides of the resistors together, and use one capacitor from the
common point to ground.

Ron Miller

Kassem Abdallah wrote:

> > Has anybody out of there any suggestion about the following problem? (I think it
> > is quite a common one).
> >
> > I?ve got a board with a non-standard bus of 34 traces. The bus drives a group of
> > memories.
> > The lenght of the bus is necessarily higher than the critical lenght (lcr =
> > tr/2tpd): a termination could be useful. The problem: there are so many traces
> > that one has to use too many components (34 resistors and 34 capacitors for AC
> > parallel termination).
> >
> > What shall I do?
> > Are there any special components (array) to terminate this type of bus?
> > Shall I terminate the bus or not? (In past experience not always a termination
> > was mandatory)
>
> I am not the expert on SI Issues, but there are several resistor_packs
> for termination available from a variety of vendors. However, You have
> to be very carefull, because these packs sometimes cause noise and make
> things worst. It depends on how the resistors network is packaged for
> current/GND leads.( I suggest to look carfully at the schematics and do
> some noise analysis).
>
>
> Also, I "think" a 34-bit bus is not that WIDE, and if it is critical
> data path, you might be better off terminating with single loads( may
> be you can stick them on the backside of your board ?? It is a
> compromise).
>
> ********************
> |Kassem M. Abdallah|
> |Digital Designer |
> |EMC Corp. |
> |Hopkinton MA 01748|
> ********************
>
> **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****

--
Ronald B. Miller  _\\|//_  Signal Integrity Engineer
(408)487-8017    (' 0-0 ') fax(408)487-8017
     ==========0000-(_)0000===========
Brocade Communications Systems, 1901 Guadalupe Parkway, San Jose, CA  95131
rmiller@brocade.com,  rbmiller@sjm.infi.net

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<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> Use tie all the common sides of the resistors together, and use one capacitor from the
common point to ground.

Ron Miller

Kassem Abdallah wrote:

> Has anybody out of there any suggestion about the following problem? (I think it
> is quite a common one).
>
> I?ve got a board with a non-standard bus of 34 traces. The bus drives a group of
> memories.
> The  lenght  of  the  bus  is necessarily higher than the critical lenght (lcr =
> tr/2tpd):  a  termination could be useful. The problem: there are so many traces
> that  one  has to use too many components (34 resistors and 34 capacitors for AC
> parallel termination).
>
> What shall I do?
> Are there any special components (array) to terminate this type of bus?
> Shall  I  terminate the bus or not? (In past experience not always a termination
> was mandatory)

I am not the expert on SI Issues, but there are several resistor_packs
for termination available from a variety of vendors. However, You have
to be very carefull, because these packs sometimes cause noise and make
things worst. It depends on how the resistors network is packaged for
current/GND leads.( I suggest to look carfully at the schematics and do
some noise analysis).
 

 Also, I "think" a 34-bit bus is not that WIDE, and if it is critical
 data path, you might be better off terminating with single loads( may
 be you can stick them on the backside of your board ?? It is a
 compromise).

********************
|Kassem M. Abdallah|
|Digital Designer  |
|EMC Corp.         |
|Hopkinton MA 01748|
********************

**** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP.  si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****

-- 
Ronald B. Miller  _\\|//_  Signal Integrity Engineer
(408)487-8017    (' 0-0 ') fax(408)487-8017                 
     ==========0000-(_)0000=========== 
Brocade Communications Systems, 1901 Guadalupe Parkway, San Jose, CA  95131
rmiller@brocade.com,  rbmiller@sjm.infi.net
  --------------633E6AF209401BE8947E7588-- **** To unsubscribe from si-list: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu/si-list ****