OEMs are increasingly focused on differentiating their infotainment human-machine interface displays and catching up to the technological advances now common in smartphones, tablets and television displays.
Synaaptics
According to Strategy Analytics, the annual number of automotive displays sold will nearly double from 2020 to 2028. liquid-crystal displays (LCDs) currently dominate the market while organic light-emitting diode (OLED) displays are beginning production in some vehicles, and both technologies are competing for this growing market.
Local dimming was developed to improve the contrast ratio of LCDs as it effectively dims the dark segments of an image and increases the brightness of illuminated segments. Local dimming elevates automotive displays to the next level with high contrast ratios and reduced power consumption. What’s more, local dimming benefits apply to large-sized, curved and freeform designs, as well as being increasingly power efficient.
Automotive specifications, multiyear design cycles and challenging environmental conditions have traditionally caused automotive displays to lag the consumer display industry in contrast ratio, black levels, resolution, curvature and form factor. OEMs are increasingly focused on differentiating their infotainment human-machine interface displays and catching up to the technological advances now common in smartphones, tablets and television displays.
Unlike those in consumer applications, automotive displays must deal with many more environmental circumstances – such as varying ambient light conditions (very bright sunlight or nighttime), prolonged extreme hot and cold temperatures, EMI and vehicle vibration. Technical advances in consumer displays haven’t needed to address this to the same degree. Many have turned to OLEDs, but their widespread acceptance in automotive applications has been hindered by lifetime limits, peak brightness and cost concerns.
While there have been several recent advancements, there are still challenges in fully addressing automotive-specific issues. LCDs are as ubiquitous as USB ports in virtually every new vehicle sold today, but many of these displays suffer from image quality, which can make them difficult to read under varying conditions. The approaches that have netted some results include:
Full-Array Local Dimming.Like mini-LED solutions but with fewer LED lights, full-array systems employ hundreds of zones behind the screen that are dimmed individually. This produces extra-dark darkened areas, while bright areas stay bright. It’s a technology that calls for more spacing, which makes for a slightly thicker display. The downside of full-array technology is that it’s not ideal for off-axis viewing, as black areas can become washed out. OLEDs.These have made a valiant attempt at addressing many challenges. Notably, displays in the Audi e-tron, Cadillac Escalade and Mercedes S-Class. Such displays have raised the bar by offering a high contrast ratio and fewer viewing-angle degradations. But concerns about cost, lifetime reliability and peak brightness have limited OLED adoption in automotive. Micro-LEDs. This nascent technology has some noteworthy optical and electrical characteristics over LCDs and OLEDs. Among these are long lifetimes, high reliability, high brightness and faster response times with tiny pixels. However, due to high production costs, it’s expected that consumer applications will adopt this technology first and improve it before it is a viable alternative for automotive applications.
The Solution: A Bold Approach to Local Dimming
Local dimming (pictured, below) was developed to improve LCD optical performance. It dims parts of the screen that should be dark and keeps bright those parts of the screen that should be bright. This results in improved contrast ratios and an easier-to-read display in varying conditions.
Synaptics
One implementation approach that is gaining traction is a local-dimming system deployed with a direct-lit architecture where LEDs are directly behind the LCD panel. With it, each LED or zone of LEDs can dim individually to illuminate only those pixels of the display needed, thus dynamically adapting to the image content on the display.
This approach allows the system to analyze the image as it arrives, determining the optimal brightness level per pixel and setting the correct illumination level for each LED using a specially designed algorithm. The updated image is output to the display while the LED settings are communicated to LED drivers on the backlight module.
This level of local dimming provides greater contrast ratios and high peak luminance within automotive environmental and cost limits. This bridging technology can be paired with a TDDI (Touch Display Driver Integration) chip which has both the display driver and touch sensor on one chip.
The benefits of such a solution with a full-array local dimming architecture include:
Savings of 60%-80% in power consumption compared to globally dimmed backlights since the LEDs are not lit unless needed. The mitigation of halo effect or light leakage from adjacent bright and darker image. Improved contrast ratios (up to 10,000:1) depending on the number of zones, peak brightness and the native contrast ratio.
Clearly, the right local dimming technology can drastically improve the impact and readability of automotive displays. It sets a new high-water mark in a highly competitive arena, achieving ultrahigh contrast ratios, deep blacks, high resolutions and wide color gamuts. What’s more, these results can be achieved with today’s increasingly larger and curved displays and with unprecedented power efficiencies.
John Brady (pictured, left) is senior director of automotive programs for Synaptics for touchscreens, display driver ICs and touch display driver integration.
Keyword: Getting the Balance Right in Display Screen Lighting