[SI-LIST] Re: low inductance resistor
- From: "Greim, Michael" <mgreim@xxxxxxxxxxxx>
- To: "'RMELLISON@xxxxxxx'" <RMELLISON@xxxxxxx>, si-list@xxxxxxxxxxxxx
- Date: Mon, 1 Oct 2001 13:51:33 -0400
Are you sure that you wish to rely on ibis sims at 2.5GBaud?
Take a look at the pinout of the device and see if the pins that
you need to attach to are at the edge of the ball pattern. It
may be conceivable that you could place a component topside and
fan directly into the pin. Perhaps the cts part that I mentioned
a couple of weeks ago might be a good fit for this need. Perhaps
you could get your mfg folks to allow via in pad? Everything that
you can do to reduce parasitics and minimize the distance to what
you are terminating with help your cause.
Just my 0.02
Best of luck,
MG
-----Original Message-----
From: RMELLISON@xxxxxxx [mailto:RMELLISON@xxxxxxx]
Sent: Monday, October 01, 2001 12:55 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] low inductance resistor
Hello SI Gurus
I'm working on a design for operation at 2.5GBaud. In modeling the path
from a Stratos Lightwave PECL driver to the TLK2501 receiver, I noticed that
it is not as clean as in the other direction. After much modelling, I'm
convinced that the problem is two-fold. First, the MLC driver is low
impedance and must be backmatched--a CML part with internal 50 ohms to Vcc
would have been a better choice. The backmatching resistor must be placed
as
close as possible to the source, but via inductance and driver pin
inductance
limits how effective this resistor is. Second, and definitely the worst
offender, is the fact that the TLK device requires external 50 ohm resistors
for the end terminations--this leaves stubs that ring, caused by the
inductance and capacitance of the pins, bond wires and input transistors.
Three questions:
1) Does anyone have any modelling information (internal pin models,
driver characteristics, risetimes, etc.) on the Stratos MLC-25-7-2-TL
Optical
ATM OC-48 part? I'm using Pspice, but IBIS would be a help.
2) Does anyone know if the CML version offered by Stratos has
internal 50 ohms to Vcc? (I haven't had any success getting information
from
the apps engineer at Stratos).
3) I've been able to control the ringing caused by the pin
inductance
and input C of the TLK2501 by inserting a perfect 27 ohm resistor in series
with the input pin (the 50 ohm terminations are placed on the bottom of the
card, with the resistor being placed between the termination via and the
input pad on top of the card). The question is, what is the smallest
lowest-inductance part that I can use for this purpose?
Any help would be greatly appreciated.
Richard Ellison
Ellison Consulting
214-544-1920 bus
214-544-1924 fax
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