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Technology Stocks : Rambus (RMBS) - Eagle or Penguin

RMBS 87.04

-0.2%

12:56 PM EST

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To: John Walliker who wrote (29402)	9/13/1999 5:38:00 AM
From: Bilow	Read Replies (2) of 93625

Hi John Walliker; Re IBM's output load for AC Timing Parameters... Those of us who are familiar with how spec sheets are written know that part parameters are always tested in some form of worst case. In IBM's case, they chose a 25 ohm resistor into a 30pF capacitor to ground, then a 25 ohm resistor to Vtt. I fail to see the point behind that kind of "termination". In fact, it's not a termination suggestion. The 30pF capacitor models a high capacitance load. In actual use, the stray capacitance would be a lot less. All they are doing is showing that you can "arc-weld" with their output buffers. This has very little to do with how the part would be used in real life. If you want to know about termination options for SSTL_2, you have to go look at the data sheet for SSTL_2, not the output load for the IBM chip. You can look up the SSTL_2 definition on the Jedec web site. 4.1 Push-pull output buffer for unterminated loads In many applications where interconnections are short, there is no need for any termination at all. An example of this is shown in figure 6. This application can be served by a Class I or Class II type buffer and an SSTL_2 type receiver. jedec.org The whole idea behind SSTL_2 is to allow the driving of transmission line stuff, not to force it. Since the data lines in the design example at hand have only two pins, and very little capacitance, the push-pull type termination would be used. -- Carl

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