Research on the technology of reducing power consumption of video terminals

0 Introduction

New technologies such as AIoT, Internet of Things, 5G, and 8K are developing rapidly. Terminal display plays an important role in information presentation. The "screen" is a device that goes hand in hand with the "chip". Display technology is an important link in the technological innovation chain. People's requirements for terminal display devices are also getting higher and higher.

The power consumption of video terminals is divided into panel power consumption, backlight power consumption, peripheral circuit power consumption, etc. Whole machine manufacturers usually adopt the following ideas to reduce power consumption.

1) Intelligent control: Use intelligent sensing systems to control the power management system and select different power management modes in real time to achieve energy saving. Intelligent control technology can put the TV into standby mode when there is no signal or operation, thus achieving energy saving of the power system, up to 50%. At the same time, some TVs are equipped with light sensors to automatically adjust the image brightness according to the brightness of the environment, thereby reducing unnecessary energy consumption.

2) Starting from power management and circuit design, adopt a new power system structure, optimize the drive circuit and power circuit, improve the line conversion efficiency, thereby improving the energy conversion efficiency of the whole machine, and ultimately reduce energy waste and achieve energy saving for the whole TV.

3) By adopting dynamic backlight control technology and low-energy consumption module design, as well as rationally utilizing the CPU's I/O and relay control, the main power supply circuit voltage can be completely cut off during standby mode, which can effectively reduce the standby power consumption of the entire TV product.

1 HDR Power Control Technology

HDR refers to the high dynamic range of images. In bright vision, the human eye can perceive brightness ranging from a few thousandths of cd/m2 to several million cd/m2, and the instantaneous contrast can reach 10,000:1. However, the brightness of display terminals and mobile phones on the market is generally around 200-500 cd/m2, and the contrast range is generally 1500:1. Therefore, the brightness and contrast resolution of the human eye are much higher than that of current terminal display devices. HDR display technology aims to improve the brightness and contrast range of the display, so that the image colors we see are closer to the real world (as shown in Figures 1 and 2). Compared with ordinary images, HDR can provide more dynamic range and image details [1], and can better reflect the visual brightness changes in the real environment. The improvement in image quality brought by HDR technology can be distinguished by the naked eye even by ordinary viewers, so many manufacturers of televisions, mobile phones, etc. have equipped their terminal display products with HDR technology.

The application of HDR technology is not a single link, but is related to the entire ecosystem of picture display. Among the current technical parameters of ultra-high-definition display terminals and video transmission, HDR is a key technical indicator. It provides more image details and layers, can show the brightness range from the darkest to the brightest, and provide a better image "immersion". It can provide higher picture contrast at different brightness levels, improve edge sharpness, and provide a wide range of colors and brighter colors [1].

There are currently four HDR standards: Dolby Vision, HDR10, HLG, and SL-HDR1. Regardless of which standard is used, power control must be considered. For example, if the brightness of a TV is 400cd/m2, when the TV is played directly, the part of the screen that exceeds 400cd/m2 will be displayed as 400cd/m2, which will cause the screen to be overexposed, and the power consumption of the entire machine will increase. Although each TV manufacturer will do some mapping on their own and the specific power consumption will vary, it is very obvious that the power increase caused by overexposure of the picture is very obvious. Adapting HDR to reduce power consumption can prevent the overall picture brightness from being overexposed, and the contrast distribution is more in line with the contrast distribution of the original HDR, thereby saving energy compared to direct playback.

2 Backlight Control Technology

2.1 Local Dimming

Currently, most display devices use LED backlights, with many LED lights distributed behind the LCD panel. In the past, global dimming (overall brightness adjustment) was used to control the light. Therefore, in the dark area of ​​some display images, the brightness is changed only by switching the LCD, and the backlight of this part of the image is still on. The existence of these backlights obviously increases power consumption and also reduces the contrast of the displayed image.

Local dimming dynamic backlight technology divides the entire screen into several small areas and controls the backlight brightness separately. The entire screen is divided into several small areas, each of which has an LED light panel (as shown in Figure 3). The backlight is turned off in the dark screen position. Compared with the method of lighting the backlight of the entire screen, energy consumption is greatly reduced.

There are two different LED backlight technologies in LED TV backlight solutions: side-entry backlight and direct-down backlight. The direct-down backlight method can better realize backlight partition control, which can not only improve the color performance and image contrast of the picture, but also greatly reduce power consumption.

The terminal display chip calculates each frame of video signal, obtains the grayscale information of each frame after processing, and outputs it to the corresponding backlight area. Figure 4 is a flowchart of the algorithm implementation of image content analysis. First, the segmented image is histogram-counted, and the backlight brightness is adjusted according to its characteristics; at the same time, the image processing parameters are adjusted using the image characteristics of the histogram statistics to obtain a better image contrast effect, and the image clarity is prevented from being reduced through boundary compensation.

Figure 5 shows a complete LED dynamic backlight TV system. After the core board completes the image calculation function, the data is sent to the dynamic backlight control board. The control chip analyzes the video data to obtain the best LED backlight control solution and generates the LCD panel display signal and LED backlight data signal respectively. The LCD panel display signal is sent to T-con, and the LED backlight data signal is sent to the LED backlight, so as to dynamically adjust the LED backlight according to the image information, thereby reducing the power of the whole machine.

When playing dynamic videos, the backlight changes with the image content. In the black part or relatively dark area of ​​the picture, the backlight of the area is turned off or the backlight brightness of this part is reduced. Through the power meter test, for the same picture, turning on Local Dimming will reduce the power by 35% and improve the display contrast by 10%. While reducing power consumption, the display quality is improved.

2.2 Backlight circuit reduces power consumption

Power consumption is also generated by electronic circuits. Although different circuit designs may have the same functions, their power consumption is often very different [2]. As the performance of microprocessors improves, power consumption is divided into static power consumption and dynamic power consumption, with static power consumption accounting for an increasing proportion. There are many factors to consider in circuit design and component selection, such as dynamically adjusting the chip's clock frequency and supply voltage. Dynamic voltage scaling (DVS) technology uses the fact that the peak frequency of a CMOS process chip is proportional to the supply voltage. If the core supply voltage of the chip is reduced and the chip's clock frequency is reduced, the chip's power consumption will also be greatly reduced. Currently, the core voltage of some SoCs has been reduced to 1.5V.

3 Conclusion

The local dimming and new HDR architecture can significantly reduce power consumption and is suitable for terminal video devices.

Of course, in addition to the above methods discussed in this article, there are also many other methods to control power consumption, such as interrupts, external expansion, and software architecture optimization. Moreover, with the advancement of technology, new requirements will be put forward for reducing power consumption.

References:

[1] ITU-R BT.2100-0:Image parameter values ​​for high dynamic range television for use in production and international program exchange[S].2016.

[2] Yang Suxing. A Brief Tutorial on the Basics of Analog Electronics[M]. Beijing: Higher Education Press, 2006.