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Rambus shows mobile memory interface

Posted: 04 Feb 2009     Print Version  Bookmark and Share

Keywords:memory interface  mobile devices  signalling  clocking 

Rambus Inc. will demonstrate at DesignCon 2009 a new memory interface aimed at mobile devices that delivers 16 times the bandwidth of today's technologies at a fraction of the power they would consume. Analysts said the technology is unique and promising, but faces several hurdles on the road to adoption.

The new interface combines signalling and low power technology Rambus described in a February 2007 paper with clocking techniques used in its existing XDR interface. The result is an interconnect that can deliver as much as 4.3Gbps per link using as little as a quarter of the power today's interfaces would require.

The approach uses a very low swing differential signalling technique that uses signals close to ground with a 100mV swing, about a tenth the swing of today's interfaces. Rambus first disclosed the technique in the 2007 paper, describing a 6Gbps Serdes transceiver that consumed just 2.2mW perGbps in a 90nm process.

Relatively simple design
The approach uses a slightly modified version of the FlexClocking technique used on the Rambus XDR interface, implemented on the Sony Playstation3. Like XDR, the mobile interface drives most of its complexity to the controller, keeping the DRAM design relatively simple.

What's new with the mobile technique is a capability to pause the clock. That feature saves power in mobile devices that often require fast switching between low and high bandwidth memory modes. The mobile interface uses a 2GHz DDR clock and no PLL.

Rambus will show at DesignCon two 40nm test chips mounted in a package-on-package arrangement with one acting as a receiver and the other as a transmitter. The device will deliver 4.3Gbps at 3mW perGbps.

The company is taking the technology through a 6-12 month test and qualification cycle before it releases its work to customers. It would require silicon support in both the memory controller and the DRAM.

Rambus believes today's smart phones and portable media players will scale over the next few years to processors that require more than 12GBps. A combination of applications will drive that growth including high definition video and 3D gaming.

"We're pretty comfortable with these projections," said Judy Chen, director of strategic marketing at Rambus, adding that tomorrow's smart phones will act like mobile desktops and portable projectors.

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