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

To: Bilow who wrote (31388)	10/2/1999 12:39:00 AM
From: Jdaasoc	Read Replies (3) \| Respond to of 93625

Bilow: How does FCC testing differ from CE testing. VC820 already has CE Declaration of Conformity. The CC820 board does not. ftp://download.intel.com/design/litcentr/ce_docs/desktop/boards/pentiumiii/b0059.pdf john

To: Bilow who wrote (31388)	10/2/1999 4:00:00 AM
From: Tenchusatsu	Respond to of 93625

Thanks for your post, Bilow. It was pretty educational. <I think that it is really weird that INTC hasn't announced more about the cause of the problem. Maybe they are giving suggestions to their big customers ...> Makes sense, especially if none of the workarounds are painless. Tenchusatsu

To: Bilow who wrote (31388)	10/2/1999 4:50:00 AM
From: John Walliker	Read Replies (1) \| Respond to 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

To: Bilow who wrote (31388)	10/2/1999 9:38:00 AM
From: gnuman	Respond to of 93625

Carl, re: Multi layer boards and Rambus It's been awhile, but my guess is the best solution requires more than four layers. The physical properties of the Rambus traces and dielectric must be tightly controlled to maintain 28 ohm characteristic impedance with minimal losses. If I assume traces over a ground plane, the image currents in the ground plane occur at 2X the dielectric thickness H. After specifying the dielectric material, the parameters W, H and T, (trace width, dielectric thickness and distance between traces), determine the characteristic impedance. The narrower the trace, the smaller the thickness for a given impedance. (For the recommended trace width of 18 mils, the dielectric thickness is 4.5 mils). My guess is in the rambus design the image current must be an identical mirror of the trace. A pretty hairy proposition, and requires very tight control over the physical properties of the layout. And of course these properties must be carried through the RIMM, RIMM connector and PCB. Perhaps in the rambus area of the MOBO the engineers laminate a two layer circuit onto the MOBO? (Ground plane, dielectric and traces?) Like I said, it's been a long time.