LED TV Light Source Technology: Overview and Advantages of DLP

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This article will explore the effects of Light Emitting Diode (LED) technology and its application in TV products. This article will focus on the application advantages and challenges of this technology, as well as its special advantages for DLP products. Introduction

LED has become a key lighting technology for a wide range of applications. Since its inception, LEDs have been used in a variety of common and household equipment, including watches, calculators, remote controls, and indicator lights. LED technology is developing rapidly, and with the continuous improvement of brightness and efficiency, new applications are emerging. LED History Since the early 20th century, scientists have been searching for a variety of substances that can emit light. In 1907, Henry Joseph Jeanne discovered that silicon carbide (SiC) can emit light. Over the next 50 years, scientists have been discovering compounds that emit light. In the 1950s, with the deepening of research on gallium arsenide (GaAs), the discovery of LEDs finally came to fruition.

1 Bell Labs, Hewlett-Packard, IBM, Monsanto and RCA first started LED research in the 1960s. Both Hewlett-Packard and Monsanto first introduced commercial red LEDs based on gallium arsenide in 1968. In the early 1970s, with the introduction of new products such as calculators and electronic watches from companies such as Texas Instruments, Hewlett-Packard and Sinclair, LED applications soared. Other applications such as indicator lights and alphanumeric displays quickly became mainstream applications for LEDs and continue to this day.

2 LED technology background

As the name suggests, LEDs are diodes that emit light. Diodes are the most basic semiconductor components that function to conduct electricity within a controlled range. The simplest diode consists of a poor electrical conductor and is modified (doped) to increase free electrons. High electron content materials (called N-type materials) are connected to low-electron content materials (called P-type materials) to establish a pathway for free electron flow. This connection is called a PN connection.

The LED is a diode semiconductor with a PN connection that releases photons when energized. This process is known as injecting luminescence and occurs when electrons are filled from a N-type material into a low energy hole of a P-type material. When high-energy electrons enter a low-energy hole, they release energy and produce photons. The materials used for the P-type and N-type material layers, and the spacing between the two, determine the wavelength and energy level at which the light is generated.

There are a variety of materials that can be used to produce LEDs, and the more common applications today are aluminum gallium arsenide (AlGaAs), aluminum indium gallium phosphide (AlInGaP), and indium gallium nitride (InGaN). Indium gallium phosphide is generally used to produce red and yellow light; indium gallium nitride is generally used to produce blue and green light - the photons generated by these materials are all within the visible spectrum. Combined with the new production architecture, they can be made into extremely bright LEDs for general lighting and automotive lighting. Some architectures are beginning to apply additional phosphides to produce white light, competing with ordinary incandescent and fluorescent lamps with very low energy consumption and longer life.

Global LED production has reached about 4 billion per month, with major manufacturers concentrated in Taiwan, Japan and the United States, while Taiwan has the highest share of 50% of global production. Most manufacturers only package LED dies, and only a few have the ability to actually produce LED dies. Figure 1 depicts the respective share of low-brightness and high-brightness LEDs in the LED market.

3 LED technology breakthrough

Recent innovations in the production of die materials and packaging have led to extremely high levels of LED brightness. The substrate uses a new material that enhances thermal conductivity, absorbing more energy and emitting brighter light. The increase in brightness brings new LED applications such as automotive lighting, traffic signals, and the latest TV displays. Figure 2 depicts the new architecture.

Significant improvements in the production levels of aluminum indium gallium phosphide and indium gallium nitride have led to an increase in the brightness of blue and green light, respectively, while other colors such as amber and cyan have also been introduced. These improvements enable the entire system to faithfully reproduce color with brightness equivalent to that of conventional light bulb technology, and last longer. Other performance improvements include system layer features such as instantaneous imaging, mercury free, no color refresh artifacts, dynamically adjustable brightness, and a wider color gamut. Figure 3 compares the gamut range of the LED with the general reference standard (Rec. 709).

The color gamut of LED lighting is very wide (40% wider than the color standard of HDTV [Rec. 709]), so the color is more faithful. LED technology is particularly attractive for TV products with extremely high lifetime and color reproduction. With the continuous development of LED technology, its influence on the TV industry is also increasing. Figure 4 depicts the evolution of LED technology and the brightness efficiency over the next few years. 4

LED technology challenge

Controlling the thermal stability of the LED die is the key to LED spin-off performance and stability. The diffused light emitted by the LED structure is directed from the surface and the periphery of the PN structure to various directions (evenly distributed in a space of 180 degrees). Although this seems to be very efficient, in reality most of the light is absorbed by adjacent dies, substrates, or other LED surfaces. This absorption causes an increase in the thermal load of the entire LED device. In order to achieve maximum light output and reliability, the heat problem must be handled properly. In addition, for applications that require the collection of light energy into small display devices such as DLP HDTVs, any light that exceeds the optical angle of the system is not available and can also cause heat and increase system power consumption. Therefore, controlling the absorption of light, matching the divergent shape of the light with the optical angle of the system and increasing the thermal efficiency, dissipating heat from the grains is critical to improving the output and usability of the LED.

For traditional applications, LEDs are typically driven in a continuous wave mode (100% duty cycle). But for high-brightness applications, this model has no advantage. Since the average temperature of the PN connection determines the output brightness and lifetime of the LED, it is necessary to drive the LED with a small duty cycle. After the duty cycle is small, the LED's current load can be higher and the light output is increased with a lower average PN junction temperature. The challenge to achieve this is that the driver circuit must be able to generate fast-changing waveforms that exchange very large currents within a few microseconds. This is a challenge for the design of LED power drivers. But the solution has been designed to solve this problem easily.

Another challenge with higher temperature loads is color shift. As the PN connection temperature changes, the wavelength of the output light will shift by more than 10 nm. This color shift not only affects the color point of the color, but also affects the white point of the entire system, because white is a mixture of various colors. In order to fundamentally solve the problem of color shift, the LED must operate at a lower power or maintain a very high thermal stability. But with the feedback on system feedback and proper power control calculus, today's technology can achieve white stability while maintaining high brightness efficiency.

DLP TV with LED lighting

Texas Instruments has developed a DLP HDTV that takes full advantage of LED lighting technology, and its brightness performance is comparable to that of a bulb-based system. By using a new generation of high-brightness LEDs and implementing a unique feedback system, DLP HDTVs have been able to take advantage of LED lighting. Figure 5 depicts the basic optical structure of the system.

Through a unique feedback algorithm, Texas Instruments has demonstrated that any color shift that may affect white spots can be controlled to a range that is not visible to the naked eye.

Currently, DLP products using LED technology use Texas Instruments' DSP components to process system information in real time, providing stability over a wide range of operating temperatures and maximizing brightness and reliability. DLP product performance advantages

The fast switching capability of LED technology and the fast exchange performance of DLP technology seamlessly match each other. With the high speed of DMD and LED, the color refresh rate is much higher than the existing design level; the random arrangement of colors is also possible. In the end, the image has a darker color, better dynamic effects, and higher brightness. Increasing the switching frequency of the LEDs allows for greater energy drive and reduces the thermal load on the PN connection. The fast switching capability of DLP technology leverages the newly developed color of LEDs to achieve multiple color configurations through a single DMD device for greater flexibility. In a DLP system, the LEDs do not need to be polarized as long as the light is accurately reflected off the DMD. Light is used on demand, with extremely high efficiency, maximizing brightness and system efficiency, and reducing heat generation. The end result is a reduction in system cost, increased brightness, and widened gamut, far beyond traditional systems that utilize common lighting sources.

in conclusion

As LED technology continues to increase brightness and stability, LED lighting is likely to become the mainstream light source for many applications in the future. Future technological developments will further leverage LED's fast switching capabilities to enhance video performance and contrast without the need for opto-mechanical components; the resulting adjustable color gamut will far exceed traditional lighting sources. The new products will soon benefit from these basic features, offering new and unique designs – including instantaneous imaging, better color, and better image quality through the high-speed response of DLP micromirror arrays. With the combination of LED and DLP technology, the performance and reliability of DLP HDTV will even exceed that of existing DLP HDTV products.

Editor: Li Jie