Automotive displays are the primary way drivers and passengers receive vehicle information, and with the number of displays in vehicles steadily increasing, so is the quality of information. However, multiple displays in the cluster, head unit, rear- and side-view mirror replacements, along with rear-seat entertainment systems (even larger-size displays and higher pixel density) are presenting challenges for automotive infotainment and cluster developers.
Just adding functional displays to vehicles is no longer enough, as automakers need to differentiate themselves by meeting consumer demands for aesthetically pleasing interiors, and a seamless experience between smartphones and vehicles. The transition in the consumer display market from standard to high definition (HD) and then to ultra-HD (4K-UHD) for televisions is also affecting expectations for vehicle displays.
To meet these challenges, automakers are enlisting designers and artists to create environments that are more attractive, like the head unit in Figure 1; however, mechanical and electrical engineers will also play a major role in these improvements. As technologies constantly change, it is critical for developers to understand the solutions available and how they’re applied to automotive displays.
Consumers marvel at picture quality, the detail of images, and appreciate the realism and beauty of the objects. Accomplishing this effect requires consideration of both the viewing distance from the display and pixel density. When there are more dots in a given area, an image can appear smoother and more natural. As distance between the viewer and display decreases, pixel density must increase in order to achieve the same viewing experience from a longer distance. This is one reason why the display on a smartphone has a higher pixel density than a computer or television.
The average automotive displays on the road today range from a mere 1.5 to more than 12 inches. There is even a growing trend toward larger display sizes up to 20 inches, with the adoption of solid-state and digital clusters along with the migration toward HD resolutions. Inside a vehicle, regardless of display size, a typical viewing distance of 70 cm (27.5 inches) will require a display with a pixel density of at least 300 pixels per inch (ppi) in order for occupants to see a quality image. The need for larger and higher density displays is leading to implementations of 1080p (2K) and 4K displays. For comparison, one of the most popular smartphones on the market has greater than 600 ppi for a typical viewing distance of 26 cm (10.2 inches).
Automotive Display Technologies
Liquid crystal display (LCD) panels are dependable, durable, and can support a wide range of screen sizes and resolutions, which understandably makes them the most widely used displays in automotive instrumentation, navigation, and entertainment systems. The two common LCD technology variants are passive and active matrix using thin-film transistors (TFTs), shown in Figure 2.
Heating, ventilation, and air conditioning (HVAC) or audio settings commonly use passive matrix or segment displays that show a physically pre-defined row (or sections) of numbers, letters or graphics. Simple odometers, trip meters, and digital clocks typically are in this category as well.
Full-color, active matrix LCD (AMLCD) TFTs remain the incumbent technology for complex and dynamic graphical displays in automotive systems, which won’t likely change in the foreseeable future. However, one key disadvantage of LCD displays is the need for an external light source (like a backlight). An external light source is necessary to illuminate the image formed by liquid crystals. This is typically implemented with LEDs located behind or on the edges of the LCD panel with a light guide. Human image perception factor is governed by the quality of the backlight driver—a feature-specified, performance-enhanced and cost-optimized device that drives the LEDs in a multitude of configurations, with the goal of providing a seamless viewing experience anywhere in the vehicle.
In comparison, active matrix OLED (AMOLED) panels are lighter, sharper, and support luxurious styling with their perfect hue of black without an external backlight. Plastic OLED (which uses plastic instead of a glass substrate) enables even greater design freedom with curved or flexible displays, and works well in automotive environments. Despite these advantages, the challenges of high-temperature reliability, long life span, and low-cost requirements are limiting the number of automakers using OLEDs in the luxury market.
Key Design Requirements For Automotive LCDs
Unlike other display applications, the automotive display market is highly customized and needs unique features to match a vehicle’s brand value. Automotive displays typically need to support five years of vehicle production, in addition to supporting warranties and volume shipments for another few years. Ultimately, displays should last for the lifetime of the vehicle. There are stringent test requirements for thermal operation, mechanical reliability, and electromagnetic compatibility (EMC) in order to guarantee long-term reliability and safety. The combination of limited space and functional safety concerns for vehicles creates unique design considerations for display system engineers.
Let’s take a moment to review a brief list of special considerations for automotive displays:
- High brightness. It’s critical that drivers can easily read displays in various ambient light conditions, ranging from broad daylight to complete darkness.
- Wide viewing angles. Center stack displays should be visible to both drivers and passengers, including those in the rear seat(s).
- Wide temperature ranges. Temperature ranges can typically span from -40°C to more than 105°C.
- High image quality. The migration of superior display technology from consumer electronics to the automotive market creates a need for displays with high resolution, contrast, and color-gamut characteristics.
- Color depth. Higher-resolution displays may need to upgrade from 18-bit red green blue (RGB) to 24-bit RGB to achieve a wider color gamut.
Additional features may include:
- Quick response times and refresh rates. Minimizing lags is critical for warning indicators, and navigation functions like real-time maps and traffic updates.
- Anti-glare and reduced reflection. Interactive displays must provide critical vehicle information to drivers without being distractive.
- Low power consumption. Low power reduces fuel consumption, and allows components to be placed in “hot spots.” These are localized regions on the printed circuit board (PCB) that can be hotter due to uneven power dissipation across the board inside the cabin; either because they are placed in areas exposed to direct sunlight or near other heat-producing systems.
Conclusion
Since LCD displays can provide dynamic information and are interactive, they (along with simple lighting indicators and dials) are replacing traditional human-machine interfaces (HMIs) and mechanical gadgets such as buttons, sliders, and wheels in vehicles. LCD displays are quickly becoming the de facto HMI for audio and media systems, HVAC controls, telematics, and navigation—even social media networking.
Displays spread across the cluster, head unit, and rear-seat entertainment systems—along with larger-sized displays and higher pixel density—are presenting challenges for automotive infotainment and cluster developers, leading them to explore effective solutions. Designers must understand the primary market and technology trends in automotive displays and how they translate into design considerations for the basic building blocks of a typical automotive LCD display subsystem. This will determine the design and selection of critical components and auxiliary blocks.
