[SI-LIST] Re: Convergence problem with DDR DRAM IBIS model

Hello, Ravinder,

It would help to know the exact convergence message and the simulator.

There are many things that could be associated with a model/simulation
problem.
Not all of these apply to every simulator.

Given your description of symptoms, things to look at could include:
* Anything unusual in the "problem" IBIS model
* Do all I-V tables (including Clamps) cover -Vcc to +2Vcc, or is there
potentially an extrapolation issue.
* Has the vendor submitted the "problem model" to the IBIS Model Review
Committee?  (Feel free to suggest it.)
* "DC/initial" failures? First/second transition failures?  Or further into
simulation?
* Vendor's preferred Options settings (tolerances, convergence algorithm,
timestep control, etc)
* What are the node voltages when convergence fails - are any nodes outside
of [-Vcc, 2Vcc]?
* What is time before first transition, compared to edge time?

Happy debugging.  :-)

- Lynne


"IBIS training when you need it, where you need it."

Dr. Lynne Green
Green Streak Programs
http://www.greenstreakprograms.com
425-788-0412
lgreen22@xxxxxxxxxxxxxx




-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Ravinder.Ajmani@xxxxxxxxxxxxxx
Sent: Wednesday, June 20, 2007 9:55 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Convergence problem with DDR DRAM IBIS model

I am running IBIS simulation on a 32-bit DDR1 point-to-point interface. In
case of one DRAM vendor, the simulator reports errors due to convergence
problem under Typical simulation on 22 Data bits and 4 DQS bits when DDR is
driving.  There is no problem with remaining 10 bits in Typical, or all the
bits in Fast and Slow simulation.  I have run similar simulation with two
other vendor part, and a die-shrink part from the same vendor without any
problems.  I am baffled with these selective errors.  I have looked at the
package parasitic and do not see anything unusual.  Has anyone else seen
this kind of problem.
Thanks.

Regards,
Ravinder Ajmani
Server PCB Development
Hitachi Global Storage Technologies


Email: Ravinder.Ajmani@xxxxxxxxxxxxxx


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