Gene,
Re: the "valid data" windows.
I received the following e-mail from a non-SI member (a techie type) to respond to your estimates for the RDRAM vs DDR windows...
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Although he thinks he's pointing out a benefit of DDR, actually what he's [Gene's] doing is demonstrating pretty conclusively why Rambus is a more robust technology.
In the Samsung presentation he references, they say that by going to a new package, they can widen the valid data window to 500 ps, then he takes a guess that the RDRAM data valid window must be around 100 ps.
Two observations - first, the new package Samsung is referencing is a CSP - the same used to package RDRAM today, and that the DDR proponents insist is not cost effective.
Second, if you look at the RDRAM data sheet, you'll see that the data valid window at 800 MHz is 630 ps, and at 1066 MHz it is 460 ps. Or if you look at percentages, the valid data window for DDR is 500/5000 (200 MHz) or 10%, while the corresponding percentage for RDRAM is 630/1250 = 50% at 800 MHz and 460/938 = 50% at 1066 MHz.
Of course the argument will be made that if RDRAM can have 50% data valid window, then so can DDR. That's true, if they choose to implement more RDRAM technology in DDR. Already they've used differential clocks, small swing signals, and transmit DLL's. They could add receive DLL's, output driver calibration, matched impedence drivers - any number of things that are available from the Rambus patent portfolio that they seem to think they have free and unfettered access to. And, incidently, these are the same things that JEDEC is talking about incorporating into DDR-II.
Desi Rhoden says that JEDEC uses "Just in time technology" where new technology is only added after it is developed, proven, and needed by the customer. One could interpret this to mean after the pioneers have poured years of research and 100's of millions of dollars into finding the best solutions, and educating the marketplace on the benefits. After the customers recognize the benefits and wake up JEDEC, Desi thinks JEDEC can just step in and use this same technology as they see fit?
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If you have any questions, just respond to this and we'll see if another e-mail comes through.
Have a good evening,
Dave |
