RE: [SI-LIST] : Parallel Termination in Theory and Practice

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From: abe riazi (ariazi@serverworks.com)
Date: Mon Jul 31 2000 - 09:52:12 PDT


        Scott:

  It seems to me that when the resistor is placed before the receiver pin, the stub length should be kept as short as possible because there will be reflections along the stub due to impedance mismatch between the receiver and transmission line.

  When the terminator is located beyond the receiver pin, there will be negligible amount of reflections along the stub if the resistor is chosen to be a perfect match. Hence, the stub length is less critical for such cases.

 Regards,

Abe

-----Original Message-----
From: Scott McMorrow [SMTP:scott@vasthorizons.com]
Sent: Monday, July 31, 2000 1:20 AM
To: abe riazi
Cc: 'si-list@silab.eng.sun.com'; 'j-gaborian@ti.com'
Subject: Re: [SI-LIST] : Parallel Termination in Theory and Practice

Abe,

The stub length from receiver pin to die is also extremely important at
high frequencies no matter where the parallel terminator is placed. The
package can even form a very nice quarter-wave resonator.

In fact, with gigabit and beyond signalling a significant amount of jitter
is induced by package stubs. That's why many devices now parallel
terminate on-die.

regards,

scott

--
Scott McMorrow
Principal Engineer
SiQual, Signal Quality Engineering
18735 SW Boones Ferry Road
Tualatin, OR  97062-3090
(503) 885-1231
http://www.siqual.com

abe riazi wrote:

> Hi Jerry: > > The stub length (between the resistor and receiver pin) is important when the resistor is placed before the chip. For this case the capacitive loading of the stub can be minimized by making its length shorter than the critical length [Lc = (1/6)(Tr/D)]. > > When the resistor is located beyond the receiver, the stub length is not so critical if the value of termination resistor is properly selected to match the characteristic impedance of the trace. > > Best regards, > > Abe > -----Original Message----- > From: Gaboian, Jerry [SMTP:j-gaboian@ti.com] > Sent: Monday, July 24, 2000 5:10 AM > To: 'abe riazi'; 'si-list@silab.eng.sun.com' > Subject: RE: [SI-LIST] : Parallel Termination in Theory and Practice > > << File: ATT00000.html >> Abe, > > If you calculated the critical length for the stub in each case and divided > it by six as Howard recommends, would there be any differences in the > capacitive loading? > > Thanks, > Jerry Gaboian > > -----Original Message----- > From: abe riazi [mailto:ariazi@serverworks.com] > Sent: Saturday, July 22, 2000 1:18 AM > To: 'si-list@silab.eng.sun.com' > Subject: [SI-LIST] : Parallel Termination in Theory and Practice > > **** To unsubscribe from si-list or si-list-digest: send e-mail to > majordomo@silab.eng.sun.com. 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 > ****

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