NEC Develops First Color LCD With Embedded DRAM Frame-Memory System

NEC LCD Technologies announced development of the world's first thin-film-transistor liquid crystal display prototype module with a DRAM frame memory system, corresponding to 18-bit color (262k colors), embedded onto the glass substrate of the LCD screen. The results of this research are presented on May 24 at SID 2007 at the Long Beach Convention Center in California.

The new LCD module has been realized by a combination of NEC LCD Technologies' own value integrated TFT-LCD (VIT) technology and low-temperature poly-silicon (LTPS) TFT technology, and includes the following key features.

1. Successful design of a system LSI onto the glass substrate of the screen, utilizing 400,000 transistors in the peripheral circuits. The LCD integrates the peripheral circuits, including the frame memory system that incorporates a 230k-bit DRAM and a front-end picture decoder, a picture encoder, 6-bit DAC, and a controller.
2. Adoption of NEC's proprietary graphical data compression / decompression technology, smart pixel-data codec (SPC), enables a reduction in the amount of memory required to store the data of one screen image by two thirds that required by original data that doesn't employ any kind of codec, thereby contributing to a reduction in circuit area and power consumption.
3. Adoption of a RGB horizontal stripe for the pixel arrangement enables high density, a polychrome display, and optimization of cell layout of the graphics frame memory, simultaneously. This kind of pixel arrangement enables greater minimization of the circuit area on the glass substrate, which generally increases along with pixel density, as compared with RGB vertical stripe arrangements.
4. The newly-developed controller enables simultaneous and independent access for writing and reading in graphics frame memory, and achieves a data transfer rate of approximately 30 frames per second, enabling smooth display of a variety of digital movie contents.

Currently, graphics frame memory is realized by a COG-mounting method that attaches system-LSI chips, made on a silicon substrate, directly onto the glass substrate of the LCD. However, this poses a problem for timely manufacturing of new LCD modules as the lead time for mass production of system LSI chips is very long.

Through further development of its VIT technology to integrate peripheral circuits necessary for LCD image display, NEC LCD Technologies aims to realize a Zero Chip Display, which would enable direct connection to the MPU bus line of the system.

Source: NEC LCD Technologies

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