Rambus (RMBS) - Eagle or Penguin Message Board

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Technology Stocks : Rambus (RMBS) - Eagle or Penguin

RMBS 104.08

+1.3%

Dec 8 3:59 PM EST

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To: Bilow who wrote (31388)	10/2/1999 4:50:00 AM
From: John Walliker	Read Replies (1) of 93625

Carl, One of the worst experiences for a design is having to pass FCC requirements, by the way. There is a big test at an FCC testing site, (frequently owned by the corporation), where emissions are tested for the system. The FCC engineers ask for changes to the circuitry, not all of it in the direction of improving signal integrity. (G) But I wouldn't think that the FCC guys would be allowed near the Rambus termination, it is just too optimized to trick around with. I would have thought that Rambus would have problems with FCC, but none of the reports indicate this. The Rambus channel is actually less likely to cause radio emissions problems than DDR. This is partly because there is little ringing which if present concentrates emissions in a narrow frequency band that then is more likely to exceed the limit. The lower impedance also helps here. I recently measured the emissions from a system shipped by one of the major PC manufacturers using PC100 memory. It was only just below the limit at the CPU clock frequency (450 MHz I think), and only achieved this through spread spectrum clocking. Incidentally, it seems that you never see boards with an odd number of layers (except single layer boards). I believe that this is because the equipment always does two sides at a time... Boards are made by stacking up layers of partly cured epoxy impregnated fibreglass (prepreg) and pressing them in a huge heated press. Even numbers of layers are natural for this technique, although not essential. However, it is important to maintain symmetry about the power planes to avoid warping of the boards. John

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