Please note that JavaScript and style sheet are used in this website,
Due to unadaptability of the style sheet with the browser used in your computer, pages may not look as original.
Even in such a case, however, the contents can be used safely.
Volume 61 (Dec 01, 2006)
NEC Electronics' LCD Driver IC Technology for Next-Generation Large-Screen LCD TVs
General Manager,
Display Systems Division
The large-screen LCD market is growing at an annual rate of more than 10% thanks to the growing popularity of notebook PCs, PC monitors and LCD TVs. NEC Electronics has become the leading manufacturer of LCD driver ICs, the device used to drive these products, and recently announced the development of a new LCD source driver IC for full high-definition large-screen LCD TVs. We sat down with Susumu Nakakarumai, general manager of the Display Systems Division, to talk about this new technology and the background behind its development.
Why don't you begin by telling us about current market trends for LCD TVs equipped with this new technology?
Annual shipments of LCD TVs have now reached approximately 50 million units, and an annual growth rate of 30% is anticipated in the future. It is said that shipments will reach 130 million units by 2010 due to upcoming international events such as the 2008 Beijing Olympics and the 2010 FIFA World Cup in South Africa. By that time, LCD TVs are expected to account for over 50% of all household televisions.
While the LCD TVs in the 32- to 37-inch range are currently the most popular, it is thought that dropping prices will lead to greater popularity of 42- to 46-inch and 52- to 57-inch large-screen LCD TVs. A 65-inch type has also made its debut, and the shift toward even larger LCD TVs is certain to continue. And with the transition to digital broadcasting, advancements are also being made in the improvement of picture quality (higher resolution and increased color depth).
What role do LCD driver ICs play in the increasing size of large-screen LCD TVs and the improvement of picture quality?
As LCD TVs increase in size, data transmission systems become an issue. In the driving circuit of an LCD, a timing controller IC controls the LCD driver IC, and when the size of the LCD increases, so does the wiring length between the timing controller IC and the LCD driver IC (Figure 1). The wiring length in the driving circuit of 45-inch and larger LCDs generally exceeds 50 centimeters (cm), thus making transmission difficult via a conventional bus interface (multi-drop system). This is why it became necessary to devise a new transmission system.
The next issue is data processing speed. Even when it comes to playing ordinary TV broadcasts, LCD driver ICs must be capable of transferring video signals at a speed exceeding several hundred megabits per second (Mbps). Since this speed increases in proportion to the resolution of the screen and color depth (bit width), the higher the resolution of the LCD TV, the more necessary it is to transfer video signals at a faster speed. For example, to ensure compatibility with full high definition (HD), the video signal transfer speed for the entire system would need to be approximately 3.6 gigabits per second (Gbps).
The output count of LCD driver ICs is another issue. The higher the resolution, the more LCD driver ICs need to be used. There is an increase in costs as well. To keep costs down, it is necessary to limit the number of LCD driver ICs used and equip one LCD driver IC with as many output circuits as possible.
How does this new LCD driver IC technology solve these issues?
To solve the biggest issue, data transmission, NEC Electronics developed "Point to Point mini-LVDS" (PPmL™), a new interface technology that enables high-speed, large-volume transmission. Since PPmL interface technology also contributes to reductions in part counts, it can aid in the lowering of LCD TV costs.
With conventional bus interfaces, multiple LCD driver ICs were connected via a single bus line (Figure 2 (1)). Therefore, the problem with these interfaces was that the number of wires remained the same regardless of the number of LCD driver ICs, and the resulting load on the bus line made it difficult to increase speed. The PPmL interface technology enables a point-to-point (1:1) link between the timing controller IC and the LCD driver ICs (Figure 2 (2)). Since there is no influence from other LCD driver ICs, high-speed transmission (max. 600 Mbps/lane) is possible even if the wiring length is long. In addition, whereas two to four timing controller ICs were once necessary to control full HD-size screens for LCD TVs in the 45-inch or larger size range, only one timing controller is now needed thanks to the use of PPmL, which ultimately results in reduced costs. Moreover, since PPmL technology uses a standard physical layer (mini-LVDS), implementation in silicon becomes easier and development turnaround time (TAT) is reduced. NEC Electronics used this technology to develop the µPD160290 and µPD160291.
Could you please tell us a little bit about your new LCD driver ICs?
Once digital data that has been transmitted at a high speed is converted to analog signals inside the LCD driver IC, the signals are supplied to each pixel of the LCD and then converted into images. This digital/analog (D/A) converter is an integral part of the LCD driver IC's internal circuitry. With conventional D/A converters, an 8-bit D/A converter is used and all 256 levels of RGB color gradation can be displayed. However, 256-color gradation was inadequate for displaying subtle hues and adjusting display deviation. In the future, there will most likely be a shift toward the use of 10-bit D/A converters capable of at least 1,024 levels of color gradation.
As the trend shifts towards 10-bit and higher products, the issue will be how to limit increases in chip size resulting from the rising bit rate. Generally speaking, when bit rates increase, there is a proportional increase in the circuitry of the D/A converter, which in turn affects chip size. But now new technology has been developed that makes it possible to reduce the size of the D/A converter circuits used in the output blocks of driver ICs. This has allowed us to equip the µPD160290 and µPD160291 with 12-bit linear D/A converters that enable adjustment with more than 1,024 levels of color gradation without increasing circuit size. And thanks to this miniaturization technology, the new chips have 720 output channels (typical chips only have between 414 and 480 output channels). This means that the driver IC requires only eight chips for full HD functionality, thus contributing to a lower part count.
Also, conventional LCD driver ICs were specifically designed to match each LCD as well as ensure that D/A converter characteristics were RGB-compliant, thus making it impossible to adjust colors independently from RGB. But thanks to the adoption of a 12-bit linear D/A converter, programmable gamma control with 10-bit precision for each RGB is now possible. And since the same LCD driver IC can be used in a wide variety of LCDs without having to change peripheral parts, greater efficiency in production and parts management can be achieved.
What are your future plans for development?
Further increases in the size and image quality of LCD TVs are expected. NEC Electronics is working to solve related technical issues one by one to make this a reality, and we believe our PPmL interface technology will serve as the foundation for this endeavor. We are currently disclosing PPmL specifications to component manufacturers for LCDs, and are working together with these manufacturers to promote the creation of an industry standard. NEC Electronics has already acquired a large share of the market for LCD driver ICs for LCD TVs, and is now focusing its efforts on capturing the no.1 spot in the display driver industry by promoting the spread of PPmL interfaces while maintaining a solid position in the LCD TV market.
• PPmL is a trademark of NEC Electronics Corporation in Japan, Korea and China.
187KB)