Rambus Aims for New Ultralow-Power DRAM

New mobile-memory initiative aimed at high-bandwidth, low-power smart phones

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2 February 2009—Rambus, in Los Altos, Calif., says it has developed a technology to create ultrafast, ultralow-power memory chips for today’s cellphones and future generations of all-purpose mobile platforms. The goal is a single DRAM device with 17 gigabytes per second of bandwidth, 16 times as much as what the low-power DDR3 memory chips in laptops have now. Rambus will demonstrate its test chip this week at DesignCon 2009, in Santa Clara, Calif.

Because consumers are demanding more from smaller packages—the iPhone is a prime example—there are more chips in a smart phone, and they have to be squeezed in pretty tightly. That creates two problems: space constraints and reduced battery life. The Rambus technology aims to kill two birds with one stone. Higher bandwidth means that you can gain access to more memory without adding more chips, and by optimizing the power consumption in the memory, you can increase battery life for the entire phone.

The DRAM in today’s generation of smart phones is capable of less than 1 GB/s memory bandwidth, but next-generation products will likely require more than 10 times that amount. Battery technology is not keeping pace. Delivering 10 GB/s would require 10 memory chips—not an option for a device that needs to fit in your pocket. The Rambus architecture, however, can deliver a single device with a total bandwidth of 17 GB/s. That’s almost what you find in a PlayStation 3. The voltage levels needed to transmit a bit over an interconnect in the new technology are lower than what’s used now, so signals switch faster and at lower power.

With the new advances, says Judy Chen, a strategic marketing director at Rambus, ”you’re pushing the data across with much less power.” Rambus’s test chip has a 16-fold higher bandwidth than LPDDR1—the memory commonly used in mobile devices—and is four times as fast as LPDDR3, which is in laptops. The test chip has a power efficiency of 3 milliwatts per gigabit per second, and Rambus is rapidly heading for 2 mW, Chen says, adding, ”Low power is the new beauty contest.”

The test chip Rambus is demonstrating this week, if placed into a smart phone, would increase the 2.5-hour standard battery life by 50 minutes. ”That’s just from the memory savings alone,” says Chen.

One of the key elements of how the Rambus technology will improve memory is called Flex-Clocking, which enables the chip to cycle very quickly between ”wake up” and ”deep power down”—a state consuming almost no power, which happens when a mobile phone is idle, for example. ”We are able to go from ’deep power down’ to ’full on’ within 50 nanoseconds,” Chen says. By contrast, LPDDR1 takes 200 ns.

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