LED-backlight feedback control system with integrated amorphous-silicon color sensor on an LCD panel

Abstract

Abstract— Thin‐film‐transistor liquid‐crystal displays (TFT‐LCDs) have the largest market share of all digital flat‐panel displays. An LCD backlighting system employing a three‐color red‐green‐blue light‐emitting diode (RGB‐LED) array is very attractive, considering its wide color gamut, tunable white point, high dimming ratio, long lifetime, and environmental compatibility. But the high‐intensity LED has problems with thermal stability and degradation of brightness over time. Color and white luminance levels are not stable over a wide range of temperature due to inherent long‐term aging characteristics. In order to minimize color point and brightness differences over time, optical feedback control is the key technology for any LED‐backlight system. In this paper, the feasibility of an optical color‐sensing feedback system for an LED backlight by integrating the amorphous‐silicon (a‐Si) color sensor onto the LCD panel will be presented. To minimize the photoconductivity degradation of a‐Si, a new laser exposure treatment has been applied. The integrated color‐sensor optical‐feedback‐controlled LED‐backlight system minimized the color variation to less than 0.008 Δu'v' (CIE1976) compared to 0.025 for an open‐loop system over the temperature range of 42–76°C.

Sensor applications of thin‐film devices originating in display technologies

“…Backlight brightness sensors are other applications of the visible‐light sensors. A backlight brightness sensor using a‐Si devices is shown in Figure . The feasibility of an optical color‐sensing feedback system for an LED backlight by integrating the a‐Si color sensor onto the LCD panel is presented in order to minimize color point and brightness differences over time.…”

Optical Properties of a-SiGe:H Thin Film Transistor for Infrared Image Sensors in Touch Sensing Display

“…Also, theoretically higher touch resolutions as well as much lower cost for touch function are expected when sensors are inserted in each pixel [1], [2]. Many different in-cell touch technologies have been developed to implement multi-touch functions into the display panel, such as the digital switching technology [3], the projected capacitive method [4], [5] and the photo sensor type [6]- [8]. These have their own advantages over other methods that they have been applied in a different sized or types of display panel.…”

“…In case of the photo-type in-cell touch, the concept of putting a light-sensing element into each pixel was first introduced in 2003 [9], and after that, several materials like a-Si or low temperature poly-silicon optical sensors were successfully embedded into small-sized LCD panel [6]- [8]. Recently photo type in-cell touch panel using continuous grain silicon was firstly produced commercially at touch pad [2].…”

Shadow-Free Moire Interferometer with Dual Projection for In-Line Inspection of Light Emitting Diodes

“…Due to its compact size, low power consumption, low heat generation, high light efficiency, long operating hours, and high contrast ratio it is a technology trend that traditional backlighting units composed of cold cathode fluorescent lamps (CCFL) have been replaced with LED backlighting units gradually (Harbers et al 2007;Harbers et al 2002;Lee et al 2006). In addition, comparing with CCFL, LEDs used for backlight are environmentally-friendly products without hazardous material.…”