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Technology Stocks : Rambus (RMBS) - Eagle or Penguin -- Ignore unavailable to you. Want to Upgrade?

To: Ali Chen who wrote (34732)	11/16/1999 5:08:00 PM
From: John Walliker	Respond to of 93625

Ali, In 3-rd grade kids are taught that understanding of a problem comes via generating hypotheses and checking them thoroughly. Therefore, the "just guessing" is a necessary element here. (sorry, couldn't resist:) Yes, you were doing the guessing and I was doing the checking:-) "Standing wave, or noise, in the channel turned out to be remarkably worse in three-RIMM designs," said Gelsinger. That is a very unsatisfactory quotation because standing waves and noise are two very different things. I would be grateful if anyone could come up with the source for that quotation. (In other words, when and where did he say it and to whom. What else did he say at the same time?) To have standing waves you need to have reflections somewhere ... And you say: <Simulations ... certainly showed that the matching network is excellent.> Very true. One source is the combination of certain successive reads from chips in adjacent clock domains combined with a reflection of an earlier read from the unterminated end of the bus. This can give rise to a loss of driver transistor output compliance under a very particular set of conditions which I discussed in great detail a few weeks ago. I think you now know the real distance between theory and practice. I have had plenty of practice at doing that over the years. I also know how often problems have been mislabelled - to the detriment of their long term solution. I am coming to believe more and more that my hypothesis is correct. (And I would not have reached it without some prodding from Carl.) It is certainly consistent with "standing wave" comments and because of the relative rarity of the effect it would easily be mistaken for "noise". Indeed, without looking for it explicitly it would be almost impossible to identify. It can happen even if the impedance matching at the individual chips is perfect and is completely prevented if only two RIMMs are allowed. No offence John, sorry to tease you and other Rambus GULLS (tm Glenn "Click"man?) I do feel that I have a slightly different approach... John