Cost questions cloud Rambus' 3.2-GHz signaling technology

Cost questions cloud Rambus' 3.2-GHz signaling technology
By Paul Kallender and Mike Clendenin, EE Times
October 24, 2001 (1:50 p.m. EST)
URL: http://www.eetimes.com/story/OEG20011022S0048

TOKYO — Rambus Inc. is due to unveil its next-generation Yellowstone signaling technology at the Rambus Developer Forum in San Jose, Calif., Monday (Oct. 22), implementing a differential-signaling approach that hits 3.2-GHz frequencies on the data bus. Rambus claims that Yellowstone will meet the bandwidth demands of mulitgigahertz processors, but analysts and OEMs are questioning whether Rambus will be able to meet the cost structures of quad- and double-data-rate SDRAMs.

Yellowstone's octal-data-rate scheme boosts the memory's 400-MHz clock to 1.6 GHz. The phase-locked loop samples on both the rising and falling edges, allowing Yellowstone to pump out data at 3.2 GHz.

Rambus is not talking about how the basic technology will be implemented, but if the current 16-bit-wide Rambus channel were extended to the Yellowstone technology, each device would deliver 6.4 Gbytes/second of bandwidth.

Laura Fleming, vice president of Rambus' special -products division, said the company has developed a new circuit scheme it calls Differential Rambus Signaling. It uses on-chip termination that is bidirectional and achieves an ultralow 200-millivolt swing between 1 and 1.2 V with a low-power I/O.

"DDR SRAM needs those discrete termination resistors on each pin on both ends," she said. "But we've put [termination] on-chip, saving board space, minimizing routing complexity and providing a superior signaling environment to achieve this high speed."

Yellowstone will deliver four times the performance of current RDRAMs shipping at 800 MHz (a 400-MHz clock with double-data-rate capability). "We are already in discussions with customers and leading technical partners and system providers," said Fleming.

In June Rambus outlined its plans to boost the bandwidth of Rambus-in-line memory modules fourfold by 2005 and identified Samsung Electronics Co. Ltd., Toshiba Semiconductor Co. and Elpida Memory Inc. as key partners. With Yellowstone, however, Rambu s officials declined to say who its partners were and when systems would hit the market.

"It's not within our control to produce, our partners and our customers are the ones to drive it," said Avo Kanadjian, the company's vice president of worldwide marketing.

Rambus has produced test chips and successfully demonstrated PLLs boosting the 400-MHz system clock to the 1.6-GHz target. The setup achieved jitter of 30 picoseconds, one-third that of previous RDRAMs, he said.

Bandwidth bottleneck

Yellowstone's adoption in the PC market could be delayed by a significant bandwidth bottleneck with Intel Corp.'s front-side bus, said IDC memory analyst Soo Kyoum Kim, based in Seoul, South Korea. The Intel bus can handle up to 4.2 Gbytes/s. This disparity led Kim to call Yellowstone's capabilities a bit "over the forecast for PC bus bandwidth."

A potentially cheaper dual-channel 266-MHz DDR DRAM would be capable of delivering the front-side bus' maximum 4.2 Gbytes.

"It's too much fo r PCs, where the need is for around a 7- to 8-Gbyte/s memory bus by 2005," Kim said. "I agree that the possible usage could come from graphics, for example in the Playstation III or special networking parts that need more bandwidth. But it's difficult to say who would make [such a product] at the moment."

Rambus' Kanadjian suggested that Yellowstone was primarily aimed at gaming and networking applications.

PC OEMs and system designers on the front line of the industry were skeptical about another high-technology, and potentially high-memory-bandwidth, solution from the memory chip designer. In Taiwan, major system designers said future technology advances made by Rambus would do little to help the company today. Since the September release of Intel's i845 chip set supporting PC133 SDRAM, motherboard and PC makers have witnessed a precipitous decline in demand for Rambus-based products.

At Asustek Computer and Gigabyte Technology, two of Taiwan's top motherboard makers, Rambus-based Pentium 4 motherboards account for only about 10 to 15 percent of Pentium 4 board shipments. At Acer, sales for its i845 SDRAM-based systems outpace those for i850 RDRAM systems by 9 to 1.

"It [Yellowstone] is a great technology but a lot of business things have to happen to allow the technology to go mainstream," said K.C. Chao, a product line manager at Acer Brand Operations. "Rambus has basically overplayed it."

Uncertain demand

Motherboard makers suggested there is a high degree of uncertainty about demand for upcoming products using the PC1066 RDRAM module or future PC1200 RDRAMs. "There will be a niche market for it but it's not going to be a high-volume product, because double-data-rate SDRAM [support] is coming out and it will be cheaper," said a source at Asustek, which has the closest relationship with Intel among Taiwan's motherboard makers. "Rambus still carries a large premium over DDR and when the 1066 comes out it will probably be even more."

Asustek will demo its first PC106 6 design at the Taiwan Intel Developer Forum Monday, but no firm date has been set for the release. The company is not focusing much in the way of marketing resources to promote its Rambus boards, but says it will continue to design Rambus into its future products as long as Intel supports the architecture.

Steve Cullen, a semiconductor analyst with Cahners In-Stat Group, said cheap DDR prices have made life difficult for Rambus. Cullen said a source in Taiwan, who tracks DRAM contract prices, reported last week that a 128-Mbit DRAM sells for $1.20 and a 256-Mbit part for $2.60.

"Rambus' problem is that they are competing with basically free DRAMs," Cullen said.

Intel's determination to back Rambus also appears to be waning, or it is at least difficult to read, according to industry players here. Rambus and Intel recently signed a five-year patent cross-licensing agreement that will add about $10 million to Rambus' bottom line each quarter. Rambus said the deal shows that the two companies will continue to work together to develop faster versions of the Rambus channel, which currently supports a peak memory bandwidth of 1.6 Gbytes/s. Intel's i850 chip set supports a dual-channel architecture, delivering a peak of 3.2 Gbytes/s from two Rambus DRAM modules.

However, recent reports of Intel's decision to drop development of the Rambus-based Tulloch chip set were interpreted here as a signal that Intel will more closely embrace DDR SDRAM as the most viable high-volume memory solution. The Tulloch would have worked with cheaper, four-bank Rambus chips instead of today's 32-bank version.

Intel will reportedly focus its attention on an upgraded version of the i850 chip set, catering to high-end workstations and PCs.

Waning influence

"It is very clear that Intel is going step by step in phasing out the Rambus designs and they will embrace the DDR," said Benson Chang, associate vice president at Taiwanese motherboard maker Gigabyte. "They already have a dual-channel DDR chip set planned for next year in the workstation space. So for the next few years, we don't think Rambus will have much influence."

In general, the opinions of Taiwan's system makers are usually based upon the price/performance relationship between Rambus and DDR. Rambus is generally regarded as the better performance technology, but its higher price restricts it to high-end systems. DDR SDRAM offers enough performance — and sometimes equal performance, depending on the application — at a much lower price, they said.

"Rambus will stay in the high end because the module price is still very high," Chang said. "For the follow-on memory architecture, it seems that DDR is getting more support and the module price is very close to that of SDRAM."

Gigabyte expects "that DDR memory and architecture will be in the mainstream" late in the first quarter of 2002, he said, "and the crossover between SDR [single data rate] and DDR will probably take place around the Q3 time frame."