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Technology Stocks : Rambus (RMBS) - Eagle or Penguin
RMBS 90.19+2.8%3:59 PM EST
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To: Dave B who wrote (19373)4/27/1999 3:09:00 AM
From: Alan Bell  Read Replies (1) of 93625
 
Dave,

A few technical points -

The signaling convention that Rambus uses (RTL) is not all that revolutionary. Similar conventions have been used in the past in the form of GTL+ which is used for the Intel processor bus among other things. There are a number of newer conventions that are also similar - SSTL and HSTL. These all have the convention that they have reduced voltage swing and use a reference voltage.

A scheme like RTL might actually have better noise immunity than LVTTL with its larger voltage swing. This is because the former uses a reference voltage to compare the signals against.

I don't think your comment about driving to 1/2 the level is correct (which is called series termination.) I believe that RTL is fully terminated meaning there are no reflections.

DDR SDram uses SSTL_3 for the clock and data lines (and uses LVTTL for address and control.) This is a limited swing, reference voltage based signaling convention.

The beauty of the Rambus scheme is that they took a systemic approach and started from scratch. They eliminated the stubs by having the signals both go into and come off the Rimm module. They use 2 clocks - one for data going into the chip and one for data sourced from the chip. The clock follows the data so is identical in length. They use a good signaling convention, etc.

-- Alan
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