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Rambus speeds up chip connections

The memory company branches out of chip design by developing an interconnect technology, dubbed Redwood, that it says does the same job as Hypertransport or Rapid I/O--only faster.

Rambus has developed a technology that it says will make it much easier for chips to communicate with each other.

The Los Altos, Calif.-based memory chipmaker has engineered an interconnect technology called Redwood that lets semiconductors with proximity exchange data at rapid rates. While Redwood performs the same functions as industry standards, including HyperTransport (developed by Advanced Micro Devices) or Rapid I/O, Rambus says that it outruns their speed.

Redwood can transfer data at 6.4GHz, while the current version of HyperTransport goes up to 1.6GHz, according to Rich Warmke, director of marketing for Rambus. Still, a new version of HyperTransport is expected in 2004 that will likely be faster.

Redwood is part of Rambus' effort to branch out of memory chip design. While the company came to prominence marketing a type of memory (called RDRAM), it is now focused on a variety of input-output technologies, including a technology called Raser for connecting different circuit boards.

Part of Redwood's jump in speed comes from its innovation in designing circuit boards. Currently, parallel buses can shift data rapidly, but they generally require that the data remains synchronized while it travels from one chip to another. In turn, the need for synchronization has forced circuit board designers to ensure that the traces--the wires connecting different chips--are precisely equal.

That's not easy. The pins--the metallic fingers that transmit and receive signals-- on one chip are invariably at longer or shorter distances from their counterparts on another chip, depending on how the chips sit on the circuit board. Aligning the pin-to-pin traces has forced designers to create traces that meander or snake about until the wire bridging the shortest distance between two sets of pins is equal to the largest.

To get around the problem, Redwood contains a technology called FlexPhase that allows data to travel asynchronously.

"It gathers all the bits and realigns them for the controller," Warmke said. "What we've found is a way to make parallel buses run really fast."

Redwood will also be compatible with chips rigged for other input-output standards. While it is unclear if the broad market will embrace it, Sony has already said it will incorporate Redwood links into the Cell processor.

A different approach
Rambus is selling Redwood differently than RDRAM, its memory technology. With RDRAM, the company licensed the memory design to manufacturers and charged them royalties on each RDRAM chip sold.

With Redwood, the company will embed it into a customer's chip, and charge fees for engineering design services and for those chips. That will largely make Redwood financially competitive to HyperTransport and Rapid I/O, said Kevin Donnelly, vice president of the logic interface division.

Both HyperTransport and Rapid I/O can be obtained royalty-free. But most companies that want to include those technologies must either dedicate engineering resources to designing a compatible link into a given chip, or hire an outside firm to provide it--and that firm would likely charge fees comparable to Rambus'.

"We are providing them with an I/O cell," said Donnelly. "It is a different approach than what we did in memory."