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AR head-up display is a new big invention in the automotive industry

Augmented Reality (AR) Head-Up Displays (HUDs) are a major new invention in the automotive industry. Today, the technology has attracted the attention of automakers and Tier 1 suppliers, and has entered the stage of active development of AR windshield HUDs.

By Mike Firth, Texas Instruments

Augmented Reality (AR) Head-Up Displays (HUDs) are a major new invention in the automotive industry. Today, the technology has attracted the attention of automakers and Tier 1 suppliers, and has entered the stage of active development of AR windshield HUDs.

A true AR Display requires a wide field of view (FOV) of at least 10 degrees and a virtual image distance (VID) of 7.5 meters or more. FOV represents the display size in degrees, while VID represents the distance over which the image is projected. In a car HUD, the VID represents how far the image appears on the road.

The idea behind AR technology is to superimpose digital information on top of the real world, enhancing the driver’s understanding of the current situation and improving their driving experience. The larger the FOV, the longer the virtual image distance, and the better the display effect.

The two biggest challenges in designing AR displays have always been issues of brightness and solar load. AR displays need to be as wide and bright as possible, which requires a lot of light from the imager. The driver also needs to project the image as far as possible onto the road. Today’s HUDs can achieve FOVs of 7 to 8 degrees or less, and can “project” images on the road 2.0 to 2.5 meters ahead. The images appear to be floating on the hood of the car. People want to use AR HUD to project the image farther, so that the image can really enhance and interact with the driver’s field of vision.

In order to extend the distance of the virtual image, it is not uncommon to design a system with a magnification of 25 to 30 times, but the disadvantage of such a design is that the solar load (ie solar energy) is concentrated in a very small area on the HUD imager panel. . This high magnification will move the imager panel closer to the focal point of the HUD optics, increasing the concentration of solar energy per unit area, as shown in Figure 2.

Note that this is not an ambient temperature issue, but a technical overheating issue due to the focused solar energy and more light entering the system (due to the AR HUD’s larger glare trap).


Figure 2: HUD optics amplify solar loads onto a diffuser screen or thin film transistor (TFT) panel

Utilizing the unique intermediate diffuser screen structure of DLP® technology, it is possible to design HUDs that can withstand the thermal loads generated by the amplification of sunlight. As shown in Figure 3, a DLP-based HUD can project an image onto a diffuser screen, which is then magnified and projected onto the windshield by the HUD optics for presentation in the driver’s line of sight. In a TFT HUD, the TFT panel is connected to the HUD optics, replacing the diffuser screen and auxiliary electronics.


Figure 3: Example of HUD architecture based on DLP technology

To better understand why diffuser screens are advantageous, let’s take a look at the physical properties of diffuser screens versus conventional TFT panels (Figure 4). The two main advantages that diffuser screens have is that they can operate at higher temperatures, and it is even more important that diffuser screens do not absorb much of the solar incident visible spectrum. (spectral infrared[IR]and UV[UV]Sections are easily filtered. )


Figure 4: TFT and Diffuser

The incident solar load is focused onto the diffuser by the HUD optics, just as it is for TFT panels. In the diffuser, however, the transmitted light is actually spread out, eliminating the amplification effect of the HUD optics, and thus making it easier to deal with thermal loads. With a TFT panel, solar energy is absorbed and the panel’s operating temperature can easily be raised above the maximum rating. It is the benefits of this solar load, along with its superior brightness, contrast ratio and color gamut, that enable automakers and Tier 1 suppliers to design and launch next-generation AR HUDs.

By Mike Firth, Texas Instruments

Augmented Reality (AR) Head-Up Displays (HUDs) are a major new invention in the automotive industry. Today, the technology has attracted the attention of automakers and Tier 1 suppliers, and has entered the stage of active development of AR windshield HUDs.

A true AR display requires a wide field of view (FOV) of at least 10 degrees and a virtual image distance (VID) of 7.5 meters or more. FOV represents the display size in degrees, while VID represents the distance over which the image is projected. In a car HUD, the VID represents how far the image appears on the road.

The idea behind AR technology is to superimpose digital information on top of the real world, enhancing the driver’s understanding of the current situation and improving their driving experience. The larger the FOV, the longer the virtual image distance, and the better the display effect.

The two biggest challenges in designing AR displays have always been issues of brightness and solar load. AR displays need to be as wide and bright as possible, which requires a lot of light from the imager. The driver also needs to project the image as far as possible onto the road. Today’s HUDs can achieve FOVs of 7 to 8 degrees or less, and can “project” images on the road 2.0 to 2.5 meters ahead. The images appear to be floating on the hood of the car. People want to use AR HUD to project the image farther, so that the image can really enhance and interact with the driver’s field of vision.

In order to extend the distance of the virtual image, it is not uncommon to design a system with a magnification of 25 to 30 times, but the disadvantage of such a design is that the solar load (ie solar energy) is concentrated in a very small area on the HUD imager panel. . This high magnification will move the imager panel closer to the focal point of the HUD optics, increasing the concentration of solar energy per unit area, as shown in Figure 2.

Note that this is not an ambient temperature issue, but a technical overheating issue due to the focused solar energy and more light entering the system (due to the AR HUD’s larger glare trap).


Figure 2: HUD optics amplify solar loads onto a diffuser screen or thin film transistor (TFT) panel

Utilizing the unique intermediate diffuser screen structure of DLP® technology, it is possible to design HUDs that can withstand the thermal loads generated by the amplification of sunlight. As shown in Figure 3, a DLP-based HUD can project an image onto a diffuser screen, which is then magnified and projected onto the windshield by the HUD optics for presentation in the driver’s line of sight. In a TFT HUD, the TFT panel is connected to the HUD optics, replacing the diffuser screen and auxiliary electronics.


Figure 3: Example of HUD architecture based on DLP technology

To better understand why diffuser screens are advantageous, let’s take a look at the physical properties of diffuser screens versus conventional TFT panels (Figure 4). The two main advantages that diffuser screens have is that they can operate at higher temperatures, and it is even more important that diffuser screens do not absorb much of the solar incident visible spectrum. (spectral infrared[IR]and UV[UV]Sections are easily filtered. )


Figure 4: TFT and Diffuser

The incident solar load is focused onto the diffuser by the HUD optics, just as it is for TFT panels. In the diffuser, however, the transmitted light is actually spread out, eliminating the amplification effect of the HUD optics, and thus making it easier to deal with thermal loads. With a TFT panel, solar energy is absorbed and the panel’s operating temperature can easily be raised above the maximum rating. It is the benefits of this solar load, along with its superior brightness, contrast ratio and color gamut, that enable automakers and Tier 1 suppliers to design and launch next-generation AR HUDs.


"Augmented Reality (AR) Head-Up Displays (HUDs) are a major new invent…