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Technology Stocks : Rambus (RMBS) - Eagle or Penguin
RMBS 94.23-11.1%Dec 12 9:30 AM EST
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To: Ali Chen who wrote (34622)11/15/1999 4:56:00 PM
From: John Walliker  Read Replies (1) of 93625
 
Ali,


<24. MINIMUM RISE OR FALL TIME = 1.000 ns>
Who cares what kind of bogus numbers are used in your
perfect simulations.
Stop fudging your numbers please.


That was quoted from the RIMM design guide. Rambus's own simulation file, not mine.

The RAMBUS spec,
rdram_128d_0059_10.pdf, says on p 44:
CTM and CFM fall and rise times min=0.2ns, max=0.5ns;
Data fall and rise times: min=0.2ns, max=0.65ns.


Agreed. I wonder why Rambus were using 1ns in that simulation. I will look again at exactly what they were doing.

So I guess you are some 100% off, and your simulated
numbers with fudged down simulated parameters are
not very convincing.

Not true. My simulations used an RF design package where fixed frequencies are entered. I chose 400, 800 and 1200 MHz. Rise and fall times were not used. What I did not simulate was the increasing losses with frequency which will attenuate the higher harmonics which are more prone to reflection. Also of course, the signal level of those harmonics is very much lower than the fundamental, reducing their significance. I just recalculated my 6 chip simulation for 2400 MHz (ignoring losses) and found the reflected signal to be 8% of the incident. Still far to low to cause any problems.

Simulations again? How do you expect a system to
run on simulations alone? Not a Monte-Carlo, but
"Real-Field" exercises have shown that there are
problems in mass manufacturability of RAMBUS -
two delays since March do say something. Or
these were the "simulated launches" only?

You said earlier that the impedance matching network was no good. Simulations are an excellent way of understanding the effects of component variations and certainly showed that the matching network is excellent.

Do you know the real cause of the problems? At least I am trying to understand rather than just guessing.

John
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