Getting the Balance Right in Display Screen Lighting

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:

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.

Local Dimming On Off (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:

John Brady_Photo (002)

John Brady (pictured, left) is senior director of automotive programs for Synaptics for touchscreens, display driver ICs and touch display driver integration.