Backlight Power Research Articles

A case study on integrating energy‐efficient technologies for display devices

AbstractFor liquid crystal display‐based devices, the memory sub‐system and backlight consume a notable amount of energy, posing a critical concern, especially for portable devices. This work introduces an integrated display system (IDS) aimed at combining technologies for energy‐efficient memory usage and backlight power optimization, which have been addressed independently until now in the existing literature. Two modifications of approximated memory are proposed to find an optimal scheme for energy‐efficient memory usage as part of the proposed IDS schemes. Additionally, three distinct IDS schemes are proposed and compared to identify an optimum solution, ensuring energy efficiency maximization while maintaining image quality for each image. Experimental results demonstrate that 42.19% of energy consumption in memory access and 37.57% of the backlight power consumption can be reduced, while maintaining the image quality in terms of two different metrics.

47‐3: In‐Cell Ambient Light Sensors (ALSs) LCD Integration Using a‐Si TFT photo‐transistor and Four‐Mask Process Architecture Technology

We have developed a new AMLCD with multiple ambient light sensors (ALSs) for reducing backlight (BL) power consumption, and false sensing of ambient illuminance. ALSs perform well in showing BL control for power‐saving, even though one of the sensors is covered by a finger shadow. Architecture of integrated ALS with a‐Si technologies are presented. We fabricate the in‐cell and wide‐dynamic‐sensing ALSs display using a‐Si photo‐transistor sensor technology. Photo‐electrical characteristics with well linearity and reliability under long‐term operation were observed.

Human visual sensitivity based optimal local backlight dimming methodologies under different viewing conditions

An adaptive local backlight dimming algorithm is proposed considering human visual sensitivities under various viewing conditions. Local dimming amount is maximized based on contrast sensitivity function and local image characteristics to minimize perceived luminance and contrast losses maintaining image qualities. Average luminance, contrast and spatial frequency are evaluated as local image characteristics. As dimming based on local characteristics has blocking artifacts, a compensation method using edge luminance difference is proposed considering human responses. The proposed algorithms reduce backlight power consumption by 39.69% on average, with an average SSIM of 0.995. It can be increased by 5.66% with varying viewing conditions, resulting in a 45.35% power consumption reduction on average. The outperformances of the proposed algorithm in power consumption reduction and maintaining image quality are verified with various image quality metrics compared to recent dimming algorithms.

Mini-LED Backlight Technology Progress for Liquid Crystal Display

As consumers pursue higher display quality, Mini-LED backlight technology has become the focus of research in the current display field. With its size advantage (100–200 μm), it can achieve one-thousand-level divisional dimming, and it can also be combined with quantum dot technology to greatly improve the contrast, color gamut, dark state and other element of the display performance of LCD displays. Mini-LED backlight technology is undoubtedly the most ideal solution to realize a highly dynamic range display of LCD displays, and has been widely commercialized in many fields such as TVs, tablet computers, notebook computers, and car monitors. This review mainly introduces the efforts made by researchers to eliminate the halo effect, thinning of the backlight module and reducing the backlight power consumption. The application of quantum dot technology in backlight is also presented. We predict that the number of Mini-LED backlight partitions is expected to reach a level of more than 3000 in the future, further utilizing the advantages of the small size in local dimming, but it will also inevitably be challenged by some issues such as power consumption and heat dissipation.

P‐5.4: Analysis of Low Power Consumption Design of LCD in Circuits and Signal Transmission

Liquid crystal display (LCD) is widely used in notebook computers, TVs, and PC monitors. Its performance, including panel contrast, panel refresh rate, and panel resolution, has made great breakthroughs in recent years. In the context of continuously improving functions, the power consumption of LCD is gradually increasing, especially the LCD that need to be applied to portable devices, which need to maintain superior performance while maximizing working endurance.A current low power consumption determination method is that the power consumption is less than 1w when the panel brightness is 150nit, the refresh rate is 48Hz, and the transmission mode is eDP1.3 or higher. We have produced a 13.3‐inch LCD with a backlight power consumption of 621mW and a panel logic power consumption of 372mW totaling 0.996W, which meets this requirement.This article analyzes the circuit and signal transmission, mainly exploring the limit setting of IC in LCD, the high‐efficiency design method of LED Driver IC under the condition of lower current load, and the communication method between Tcon IC and Source Driver IC. Perform targeted optimization at the circuit design to achieve the purpose of reducing LCD power consumption.

A Low-Power Memory-in-Pixel Circuit for Liquid Crystal Displays Comprising Low-Temperature Poly-Silicon and Oxide Thin-Film Transistors

In this paper, a new pixel structure using low-temperature polycrystalline silicon and oxide (LTPO) thin-film transistors (TFTs) for low-power liquid crystal displays (LCDs) is proposed. The extremely low off-state current of oxide semiconductor TFTs enables the proposed circuit to operate at a very low frame frequency of 1/60 Hz, so that the power consumption can be significantly reduced. In addition, the low-temperature polycrystalline silicon TFTs with high reliability directly drive pixels, which can achieve stable and flicker-free LCDs. The proposed circuit is fabricated using the LTPO TFT backplane and successfully verified by simulation and measurement results. The measurement results prove that the proposed circuit operates well without further programming for 60 s, and the power consumption in the panel (except backlight power) can be reduced to 0.02% of that of conventional LCD.

Study and reduction of waterfall effect caused by dimming backlight in LCD based on amorphous silicon TFT

Liquid crystal display (LCD) is one of the most popular displays nowadays, and the amorphous silicon thin film transistors are adopted in LCD as active devices due to the low cost, low process issue and high stability. In the LCD device, the backlight unit consumes almost one third of the power of the LCD device. Therefore, reducing backlight power consumption is important to lower the total power consumption. Dimming backlight, which decreases brightness of the backlight and thereby reduces power consumption without affecting the display quality, is the most popular and effective method. However, because of photon assisted current effect of amorphous silicon, the conductivity of the amorphous silicon is different when backlight unit (BLU) turns on and off, which will cause a waterfall phenomenon. Compared to the traditional 4‐mask process, the difference between AS tail and N+ tail in novel 4‐mask process is smaller. The waterfall phenomenon of novel 4‐mask is not obvious but still visible. In this paper, we analyzed the mechanism of waterfall effect and modified the novel 4‐mask process to solve this issue. By combining capacitance extraction and charging simulations, we simulated the variation of grayscale caused by backlight switching. It was shown that there were about 4 gray levels of brightness change under 24 gray levels. Then we examined the cause of the formation of AS tail and N+ tail, and reduced the difference between AS tail and N+ tail by changing the process, which effectively modified the waterfall issue.

28‐2: A Novel Local Dimming algorithm with HDR for VR system based on GPU

As the screen of VR is very close to human eye and the optical lens has amplification effect, VR needs high PPI to meet people's visual requirements. High PPI panel with side‐emitting LED backlight is difficult to realize high contrast ratio(CR). Local Dimming based on direct‐illumination LED can not only save backlight power consumption but also improve the CR of the VR system. The point spread function(PSF) of LED plays an important role in Local Dimming technology. However traditional PSF always adopts approximate calculation method with low accuracy, which causes luminance distortion. In this paper, a method of PSF measurement and data processing was proposed. It can describe the spread strength and range of one single block LED actually. One improved LCD compensation algorithm was demonstrated in this paper. The light leakage characteristic of liquid crystal was considered. It can keep the hue consistent. The proposed Local Dimming method has low distortion and high dynamic contrast range. This paper also presents a method for implementing Local Dimming algorithm by GPU, which can display Local Dimming effect in real time of VR system with high frame rate.

A rapid local backlight dimming method for interlaced scanning video

AbstractThis paper presents a rapid local backlight dimming method for interlaced video to improve the efficiency of displaying interlaced video. In the proposed method, we combine the line average deinterlacing algorithm with the local backlight dimming algorithm. In order to reduce the computational complexity and the backlight power consumption, three novel methods are proposed. The first is to add the sparse method to process the deinterlaced image. Second, the improved dynamic threshold method is used to calculate the dimming factor. And third, the odd field and even field of the same frame use the same backlight brightness to do backlight dimming. The simulation results show that the proposed method can reduce the computational complexity and power consumption, and the experiment results verify that the method can provide high display effect.

Optimal Local Dimming Based on an Improved Shuffled Frog Leaping Algorithm

The local backlight dimming technology has recently been presented for liquid crystal displays in order to reduce the power consumption of backlight and improve the quality of the display. Therefore, exploiting the tradeoff between the image quality and power consumption has become the focus of local backlight dimming technology. This paper considers the local backlight dimming as an optimization problem, i.e., how to preserve the image quality perception with a certain low backlight power consumption. To achieve this goal, we use the swarm intelligence algorithm. Specifically, an improved shuffled frog leaping algorithm is proposed for local backlight dimming. Simulation results show that the proposed algorithm achieves the better tradeoff between power consumption and image quality when compared to other algorithms based on image parameters.

42‐2: Low Power Consumption 8K Liquid Crystal Display with Oxide Semiconductor/Oxide Conductor Pixel (Transparent Pixel)

We developed a large ultra‐high‐definition (8K) liquid crystal display with a high aperture ratio by making the source and drain electrodes, wirings, storage capacitors, and contact portions transparent. This increased the aperture ratio from 37.3% to 47.1% and reduced the backlight power consumption by approximately 21%.

A Novel Adaptive Local Dimming Backlight Control Chip Design Based on Gaussian Distribution for Liquid Crystal Displays

In this paper, a novel hardware-oriented adaptive local dimming backlight control algorithm is proposed for very large-scale integration implementation. The proposed algorithm includes a novel dimming algorithm to save energy of the liquid crystal display (LCD) backlight module and a novel contrast enhancement algorithm to compensate the dimming of brightness in displaying images. In order to improve the power-saving rates and image quality, a block-based model and a Gaussian distribution model were added. After obtaining a clipped point by the Gaussian distribution model, a pixel compensator was used to compensate the brightness value of each pixel to satisfy the human vision. In the meantime, a power width modulation module produced power control signal for the LCD backlight module. To meet the performance standards for displaying video in real time, the proposed algorithm was implemented by an eight-stage pipelined architecture. In addition, a new color-space YEF transform composed of integer adders and shifters was used to realize the grayscale converter to replace floating point multipliers. Moreover, the high-complexity operations, such as square root, multiplication, and division, required for the Gaussian distribution model were simplified by using a lookup table technique, which could reduce the hardware cost of the proposed design efficiently. This design was fabricated by a TSMC 0.18-μm CMOS process, and the chip area is 630 105 μm2. Compared with previous local dimming backlight control algorithms, this work improved the average peak signal to noise ratio by 6.89 dB and saved 7.61% more backlight power consumption than previous studies.

Optimized Backlight Power Saving Algorithm Using Joint Power-PSNR Characteristics Among Multiple Frames

In this paper, an optimized backlight power saving algorithm using joint power-peak signal-to-noise ratio (PSNR) characteristics among multiple frames is proposed. In existing state-of-the-art methods, the optimal decision for clipping point is made only with consideration of current frame, and the target frame PSNR are set the same for all frames. Therefore they have the same power-PSNR performance. In the proposed work, we show that better power-PSNR performance can be achieved by assigning different target frame PSNR for different frames. In the proposed algorithm, the decisions for clipping points associated with all frames are made at once. The inefficiency ratio of each clipping point is evaluated and put into the algorithm design. An optimization problem is formulated, and a solution-search procedure is proposed. Compared with state-of-the-art methods, the proposed work performs better in both aspects of power and PSNR; the BD-PSNR and the BD-Power of the proposed work against all other methods are better for every tested video; the BD-PSNR and the BD-Power can be as high as 19.80 dB on average, and the BD-Power can be as low as – 26.25% on average.

A 2D-3D Display With a 120-Hz Hybrid Spatial-Temporal Color LCD

A hybrid spatial-temporal color (STC) 2D-3D display is proposed using a 120-Hz liquid crystal panel with two color filters and light emitting diode matrix backlight. 3D mode was added to a Two Fields and Two Color Filters (2F2CF) STC LCD without adding any hardware element. This new configuration has 1.5 times higher resolution and around 1.5 times higher light efficiency than other currently used commercial 2D-3D LCDs because only two color filters are used. The backlight power consumption could be further reduced by applying the local dimming technology. The performances of the display with different backlight resolutions were analyzed with simulation on the aspect of image quality and power consumption. A perceptual experiment was also carried out to investigate the visual perception of stereoscopic impression, color nature and visual comfort by simulating specially at 3D mode. To balance the image quality and cost, 18 × 32 backlight segments was suggested for the optimal configuration.

High-efficiency isolated SEPIC converter with reduced conduction losses for LED displays

This paper proposes a high-efficiency isolated bridgeless single-ended primary inductor converter (SEPIC) for light-emitting-diode (LED) displays. The proposed isolated SEPIC converter can supply LED back-light power with reduced conduction losses. Switching power losses as well as conduction losses are reduced. The proposed converter is theoretically analysed. Experimental results based on a 28 V, 300 W back-light power are discussed to verify the performance of the proposed converter.

Weighted roll-off scheme to remove block artifacts for low power local dimming liquid crystal displays

A roll-off algorithm has been incorporated into adaptive dimming LCDs to enhance the details of high gray levels. However, because a roll-off algorithm generates block artifacts in local dimming LCDs with 1-D or 2-D local blocks, we introduced a new roll-off algorithm for block artifact reduction in 2011 based on an ideal backlight without any light spreads. Whereas, this paper demonstrates a weighted roll-off local dimming scheme for low power LCD applications which eliminates block artifacts at a real backlight with light spreads. Both simulation and experimental results represent that a proposed weighted algorithm alleviates color difference values as well as block artifacts without any increases in power consumption. The measured backlight power consumption in a weighted roll-off 1-D dimming LCD of 5 local blocks is 27.60 W over 24 test images, on the average, compared to 62.45 W of a constant backlight. • Novel roll-off algorithms are introduced for ideal and real local dimming backlights. • Block artifact reduction scheme is evaluated by simulation and measurement. • A new weighted roll-off algorithm achieves better image quality at the same power consumption.

Multi-Block Gray Statistics Local Dimming Algorithm

Multi-block gray statistics local dimming algorithm is proposed to automatically control the brightness of the backlight for reducing energy consumption and enhancing the image quality. The large blocks are used to determine the value of backlight matrix and small blocks are to determine the image block brightness. With the use of BMA (Blur-mask approach) to blur the backlight brightness matrix and compensate LCD control signal, local dimming function is realized.The simulation results show that: for pictures, the average backlight power consumption is decreased markedly by 19.9% and the contrast ratio is increased by 53%.

50.1: Innovative 5‐inch FHD and 7‐inch WQXGA Displays for Next Generation Smartphones and Tablets

AbstractWe have developed two types of innovative LCD displays: a 5‐inch FHD and a 7‐inch WQXGA. Both feature 0.96mm module thickness with 1mm narrow border, a 50% less backlight power consumption by adopting a unique RGBW display technology. They are also equipped with an in‐cell touch panel system which achieves stylus input.

A Highly Power-Efficient LED Back-Light Power Supply for LCD Display

This paper proposes a highly power-efficient light-emitting diode (LED) back-light power supply for liquid crystal display (LCD). The proposed converter integrates the power factor correction (PFC) circuit with the dc–dc converter. It provides an isolated dc voltage without using any full-bridge diode rectifier. Conduction losses are reduced by eliminating the full-bridge diode rectifier. Switching power losses are also reduced by achieving zero-voltage switching (ZVS) operation of power switches. By reducing power losses, the power efficiency of the LED back-light power supply can be improved. The experimental results are presented to verify the feasibility of the proposed converter for a 100 W LED back-light power.

Display power analysis and design guidelines to reduce power consumption

Cold cathode fluorescent lamps (CCFLs) are used to provide lighting for liquid crystal displays (LCDs). This paper presents a set of guidelines for measurement characterization and design to reduce the power consumption of CCFL LCD backlight inverters and panel electronics. The proposed methods aim to reduce the backlight power consumption by fine-tuning a backlight inverter for a specific LCD, using several methods. First, the authors describe their power measurement methodology; and next, they identify different areas for tuning a backlight inverter for a given display. The experiment results showed that power savings can range from 50 to 200 mW if the backlight inverter is properly tuned. This paper also proposes an optimized configuration for light-emitting device (LED) panels to reduce power loss by selecting a LED with a specific input voltage and number of cells to help minimize power loss.