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

To: Bilow who wrote (33582)	11/2/1999 1:07:00 PM
From: John Walliker	Read Replies (1) \| Respond to of 93625

Carl, If you look in the data sheet for RDRAM, you will notice that the outputs are specified for 30mA to 90mA. The typical worst case output current is 60mA. The "typical" is for a standard impedance bus. The worst worst case output current, from the RDRAM specs, is 90mA. Engineers generally design for worst case specifications, and I believe that the Intel engineers are no different than other engineers in this. So I used about 90mA for my calculations. This is why my numbers are about 3x yours. The incoming data bus width is 18 signals wide, but there are also some clocks to take care of. Anyway, try redoing some of the calculations with these comments in mind. I had exactly this in mind when I posted because I thought that you were basing your figures on the drive capability of the Rambus outputs rather than the current that they actually deliver. When the system is first switched on and at regular intervals subsequently the drive level is calibrated to ensure that the correct signalling level is used. This means that the worst case current will be quite close to the value I quoted because the impedance specification of systems using RIMMs is +/- 10%. As we have discussed previously the drive current must be neither too low nor too high for the system to work correctly. The drive current is defined by the bus impedance and the Rambus signalling level, both of which have well defined tolerances. The fact that the transistors are capable of sinking 3 times more current than is needed in a 28 ohm system just shows how conservative the specifications are in this respect. John