The Secrets of PC Memory: Part 4
 

For better signal quality at higher speed grades, DDR3 adopts a so called “Fly-by” architecture for the commands, addresses and clock signals. This effectively reduced the number of stubs and signalling length from the DDR2 T-Branch architecture to a more elegant and straightforward design.

The Fly-by topology generally connects the DRAM chips on the memory module in a series, and at the end of the linear connection is a grounded termination point that absorbs residual signals, to prevent them from being reflected back along the bus.

We recently asked Aaron Boehm, an Application Engineer at Micron about how important the Fly-by topology is to DDR3. He said that the Fly-by design was “ very important in DDR3. Probably one of the biggest advantages of moving to the Fly-by topology is that we are able to achieve a much faster slew rate for the signal. This gives us a bigger data-eye, which is very important in DRAM.”

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