Electronic Design

Feature-Phone Memory: Making It Multimedia-Fit

As feature-phone growth skyrockets (Gartner Dataquest forecasts sales of close to 500 million units in 2005), designers are restructuring memory architectures to make them multimedia-fit. This means providing adequate memory to handle an ever-growing range of multimedia applications—MMS, Java applications, photo albums, streaming video, high-resolution cameras, MPEG4 video, MP3 and streaming audio, 3D games, and Web browsing—and make the user experience with multimedia addictive. (The more multimedia applications users download, the more the feature-phone value chain can gain.) At the same time, designers must keep the design simple and the bill of materials (BOM) low.

It is widely acknowledged that this challenge is too much for NOR flash technology. NAND flash technology, with its higher density and smaller silicon die size, fits the bill (of materials). Its far superior write speed, which is up to 10 times faster than NOR, is a far better fit for multimedia requirements.

But because NAND flash is vying for a place in a former NOR flash stronghold, designers must overcome the lack of a NAND flash interface in standard architectures. And although designers recognize that NAND flash can trim the BOM, they continue to search for the most cost-effective NAND of the lot.

The lack of a NAND flash interface is most apparent in the baseband-centric architecture used in low- to mid-range feature phones. It implements a baseband processor with a back-end IC or an integrated baseband processor with multimedia capabilities. Many vendors offer popular baseband processors, but without an appropriate interface, it is almost impossible to connect them to NAND flash for data storage.

The higher end of the feature-phone market uses a coprocessor/applications processor-based architecture. Although a NAND flash interface is more common here, especially with a dedicated applications processor, NAND flash still suffers from immature software support. Moreover, no standard NAND flash driver exists to overcome this difficulty.

Lack of a NAND flash interface can mean serious integration problems for software designers accustomed to working exclusively with NOR. These problems, in turn, can cause reliability issues and time-to-market delays.

Many designers have realized the solution is to use a NAND flash device with a NOR-like interface. This lets designers work effectively with a familiar interface while providing the high-capacity, high-performance, smaller-silicon-size benefits of NAND flash. It results in cleaner and smoother integration to help bring products to market more quickly.

Solving interface problems is relatively easy, while delivering added value is the more difficult hurdle. This is particularly important at the higher end, where feature-phone designers must keep costs low while providing higher-capacity flash to enable the widest multimedia functionality.

Newly available, high-density multilevel cell (MLC) NAND—with four voltage levels instead of the traditional two to store twice the amount of data in a given die—meets the cost challenges. Until recently, MLC NAND had difficult data reliability and performance issues compared with standard single-level cell (SLC) NAND, making it unusable as on-board memory in feature phones. But new hardware and software approaches now make MLC NAND every bit as reliable as SLC NAND, and with competitive performance.

Multimedia requirements for space- and cost-constrained feature phones are keeping memory designers on their toes. MLC NAND has been made multimedia-fit with new NOR-like interfaces, high reliability, and high performance. It also has been endowed with eXecute In Place (XIP) capabilities to replace NOR flash for boot functionality, reducing both cost and space requirements. For further space savings, MLC NAND can be used in multichip packages that stack a full memory system in one package.

As feature phone architectures continue to undergo upgrades for even broader multimedia support, making feature phones multimedia-fit will spur the shift from traditional architectures and inspire new and innovative memory products.

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