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

To: John Walliker who wrote (43965)	6/10/2000 6:31:00 PM
From: Bilow	Respond to of 93625

Hi John Walliker; Re "Of course you know - to some extent - what kind of transmission lines will be used by DDR. They will have stubs leading off the motherboard to all the chips on each memory module. (Unless extra buffering components are used, in which case the stubs will be shorter.) These stubs have a reactive impedance and will cause reflections and ringing." Actually, I was writing about DDR-II, not DDR as you suggest, but I was thinking about the next generation beyond DDR-II, sorry for the mistake. By the way, if you have an hour or two, a great technical discussion of the techniques used in DDR DIMM module design is at: silicontech.com Re your very simple question which you are sure I can answer: "Given that a variable number of memory modules may be inserted into the motherboard, how do you terminate the bus to remove the reflections that will occur between those modules, each of which has a reactive impedance?" We went over this already 8 months ago. The fact is that you do not have to "remove" the reflections, you only have to damp them out fast enough that they die away before the receiver samples the data. For Rambus, with the 800MHz data sampling rate, "fast enough" means much faster than 1.25ns, so they have to remove the reflections pronto. With PC266 DDR, with its 266MHz data rate, three times as long (plus margin) is available. Three times is a big factor in electronics. The idea behind electronics is not to make every signal look perfect, but instead to simply transfer the data. -- Carl