[ISSCC] New Technologies Expected to Realize Wireless SSD

Feb 21, 2012
Masahide Kimura, Nikkei Electronics

A Japanese research team developed three technologies that are expected to help realize wireless SSD.

The team, whose members include Ken Takeuchi, associate professor at the University of Tokyo, Tadahiro Kuroda and Hiroki Ishiguro, professor and associate professor, respectively, at Keio University, will announce the details of the technologies at ISSCC 2012. The research was conducted as part of the Core Research for Evolutional Science and Technology (CREST), which is sponsored by Japan Science and Technology Agency (JST).

The three technologies are (1) a new error correction technology for NAND controllers (lecture number: 25.2), (2) a high-speed wireless data transmission technology for memory modules (lecture number: 2.8) and (3) a wireless power transmission technology for memory cards (lecture number: 16.8). They were respectively developed by Takeuchi, Kuroda and Ishiguro.

Error correction technology
The error correction technology is especially important for using low-cost multi-value NAND flash memory for SSDs used for servers and other applications that require a high reliability. The existing LDPC (low density parity check) error correction technology requires many reading operations, lowering operation speed.

This time, it became possible to carry out error correction in one reading operation by predicting error probability based on data stored in the surrounding cells, the number of times they have been rewritten, their data retention time, etc. The research team confirmed that, with this measure, it is possible to improve the product life of SSD about 11 times.

High-speed wireless data transmission technology
The high-speed wireless data transmission technology is for wirelessly connecting a DRAM module with a microprocessor. When they are connected by a connector, it is difficult to realize a high-speed data transmission due to impedance mismatch. On the other hand, a data transmission speed of 7 Gbits/second/link was realized by wirelessly connecting them to solve the problem of impedance mismatch.

Wireless power transmission technology
The wireless power transmission technology is for wirelessly supplying power to a memory card by using a coil. In the case of NAND flash memories used for memory cards, data is simultaneously written in multiple chips. As a result, their power consumption tends to fluctuate depending on their operation status.

This time, the research team employed a mechanism that enables to control the output power of a host device at high speeds in accordance with the load applied to a card. As a result, even when the power consumption of the card increases or decreases ten times within several microseconds, the maximum voltage drop of the power-receiving side is only about 2%. The maximum supply capability of the wireless power transmission technology is 0.52W.

The second and third technologies are not related to SSDs. But they will possibly be used for wireless SSDs in the future, the research team said.