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   25th Feb 09

 New interface technology to connect timing controller IC with LCD driver IC

NEC Electronics has developed a technology named 'Advanced PPmL', a new interface technology for connecting timing controller ICs with LCD driver ICs. It uses clock-embedded technology, which embeds a clock data recovery (CDR) circuit in the interface in order to separate the video data from the clock signal. The target application for this technology is large screen LCD TV.

With the start of terrestrial digital television broadcasts, the television market has been evolving recently toward larger screens and higher video resolution. In particular, LCD televisions require chips to drive the LCD as well as a timing controller chip to send video data to multiple driver chips without delay. With large-screen LCD televisions, however, the wiring connecting the timing controller chip with the driver chips grows quite long; this could push the size of the boards to the limits of manufacturing capabilities, which would make handling these connections via a conventional bus interface
unfeasible. Conventionally, this was remedied by either reducing the wiring distance by splitting up control using multiple timing controller chips, or by reducing the frequency by splitting the video into multiple regions, thereby reducing the amount of data per bus. This method, however, increases the number of components, which causes cost to increase.

NEC Electronics addressed this issue in April 2006 with the release of PPmL, a point-to-point interface technology that transmits display data between timing controller chips and driver chips in a one-to-one relationship. PPmL makes it possible to conduct high-speed transmission using a single timing controller chip, regardless of wiring distance or the number of driver chips. This technology also permits system architecture with fewer components, helping to reduce the cost of developing large-screen LCD televisions. The new Advanced PPmL technology was developed to further reduce development costs, as well as to satisfy market needs for the development of large-screen televisions: improved design aesthetic and faster LCD driving speeds in order to reduce motion blur.

The key advantage of this new technology is the number of wires reduced by half in comparison to NEC's own PPmL technology. With conventional PPmL technology, the video data and clock signal were transmitted in separate wires, but this new technology uses single wire for the same task. The other merits of this technology are, driver chips can be mounted on thinner circuit boards, and making it easy to synchronize the I/O timing of video data and clock signals.

The new technology was made possible through the use of clock-embedded technology. Clock-embedded technology encodes and decodes data to superimpose clock signal on data when it is sent and received. It is widely used in such high-speed digital communications as PCI Express and Ethernet. However, LCD driver ICs are made with relatively slow transistors, and this technology was not feasible until now because a great deal of power was consumed during high-speed (Gigahertz-range) communication, and the encoding/decoding logic circuit was too complex. NEC Electronics solved these challenges by developing a dedicated process for LCD driver ICs that enables high-speed transistors to be manufactured at low cost, and by developing a circuit with power consumption and scale optimized for LCD driver ICs.

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