Frontline Technology

Technologies and Trends for Vehicular Displays

Technologies and Trends for Vehicular Displays

Displays have become an integral part of the driving experience.  The author takes a brief look back at the history of displays and then a look forward at how displays in vehicles will meet the ever-increasing demands put on them.

by Silviu Pala

VEHICLES have practically become our homes and offices on wheels.  According to the National Highway Traffic Safety Association (NHTSA), vehicles will ultimately enable all productivity and infotainment features used in homes and offices, and drivers will have almost no responsibilities regarding actual driving.  (The NHTSA refers to these operative capabilities as Level 4.  See the sidebar “NHTSA Levels and Definitions” for the other levels.)  Many experts are estimating that we will be at Level 4 by 2020, but that may be too optimistic.  Due to sensor reliability and the need for safer redundancy, we may be looking much farther down the road – at least two automotive cycles or more than 10 years from now.

In the meantime, we are starting to see Advanced Driver Assistance Systems (ADAS) features such as autonomous cruise control with “collision imminent” braking, lane-departure warnings, autonomous parking, and so forth, combined with more information and safety features related to Level 2 autonomous drive and anticipating Level 3.  In addition, consumer desire for better connectivity is prompting designers of vehicle interiors to create vehicular extensions of our smartphones, smartwatches, etc., through displays that are larger, more strategically located, and sunlight readable.

This article offers a short history and overview of vehicle-display technology and a longer look at current automotive-display requirements and the technologies required to realize them.

Vehicle-Display Background

Up until the late 1970s, all displays and controls inside a car were mechanical gauges that were illuminated by bulbs.  Futaba’s vacuum-fluorescent display (VFD) helped start the digital display revolution in cars by introducing the first digital clock for autos in 1976 (Fig. 1).

Fig. 1:  The first digital clock in an American automobile was a vacuum-fluorescent display from Futaba, in the 1976 Dodge Aspen.  Image courtesy Ben DiCicco/Chrysler.

>Futaba also began replacing analog indicators with digital segmented or dot-matrix displays.  This technology dominated the automotive market until the early 2000s.  The key advantages of VFD technology, as achieved by companies such as Futaba and Noritake, were its modern (for the time) appearance and high reliability.  The main drawbacks were the bulkiness of the package, limited color, and low resolution due to the high voltage needed to operate each dot.

A new technology contender appeared in 1984 with the passive-matrix LCD from Delco and Hitachi, which was introduced in a digital speedometer and tachometer (Fig. 2).

Fig. 2:  The first digital speed and tachometer LCDs, by Hitachi and Delco, appeared in the 1984 Corvette.  Image courtesy Bob Bordo, GM.

This was a multicolor high-resolution instrument-cluster design, revolutionary at the time but very expensive.  The manufacturing cost was about $250 for the speedometer and about $275 for the tachometer, according to Bob Bordo, the GM manager involved in their design.  The backlight illumination was achieved with bulbs.  Large heat dissipation and operation at low temperatures were just some of the many display-integration challenges.  Despite LCD technology drawbacks such as long response times at low temperature and low viewing angles, the high resolution and multicolor capability combined with a smaller package and improved reliability put this display ahead of VFDs by the late 1990s.

The CRT was another technology used in automotive displays.  GM introduced an IR touch screen over a CRT display in its 1989 Oldsmobile and Buick (Fig. 3).

Fig. 3:  The first automotive digital information center with a touch screen was introduced in the Oldsmobile Toronado in 1989.  It featured a color CRT display with infrared touch by Denso.  Monocolor for the Buick Riviera by Delphi.

This display was the grandfather of the “tablet in the center stack” that we know today, but it arrived on the market too early.  Turn-by-turn navigation and smartphone capability, which would have made the display more desirable, did not exist, and the display was too bulky for the space it occupied in the instrument panel.  (The instrument cluster and center stack area of the panel are some of the most valuable real estate in a vehicle due to HVAC air ducts, cables, etc., competing for space there.)

LCD-based vehicle panels, despite being high resolution for the time – 100 dpi – lacked the crisp-looking output of analog meters.  So, automotive engineers developed a custom solution to achieve interior designer requests:  electroluminescent (EL) technology for a transparent digital information center over analog meters, as introduced in 1998 by Toyota in a display featuring a Denso cluster meter with a Planar transparent EL display.  EL has very high reliability and optical performance – the space shuttle was using it at the time.  However, lack of full color and improvements in TFT-LCDs prevented EL gains in the market.

OLEDs started to be used in 2005 by GM and Chrysler in small information center displays.

This technology has excellent optical performance (contrast ratio, view angle, resolution).  The key challenge for OLED displays is differential aging, especially for full-color displays.  Futaba, one of the lead automotive VFD makers, is now manufacturing monochrome PMOLEDs for automotive applications. (See the article “Automotive Applications for Passive-Matrix OLEDs” in this issue.)  Futaba’s technology is just one among many that are being deployed to meet the challenges faced by today’s vehicular displays, from which ever more functionality is expected.  The rest of this article looks at those challenges and requirements, including some of the products that have been developed to meet them.

Tough Requirements

It is important to measure automotive-display performance in terms of specific stress tests, including mechanical vibrations and shock, as well as operation at different voltage variations, such as low battery, nominal, and high alternator voltage.  (In the early 1990s, the author measured a 512-V spike on a 12-V battery line due to a door-lock event.)   Displays are also measured under conditions of temperature variations from -40°C to 85°C and at thermal and humidity cycles combined with thermal shock.  These last events might include opening the door of the car when the interior is hot and the outside is freezing or when the car is air conditioned but it very hot outside, such is in summer in Arizona.   Another factor to consider is electromagnetic compatibility (EMC), which prevents the display from introducing electromagnetic noise to the electronic modules or the radio (especially in the AM band).

Look, Feel, and Legibility

Display appearance or “look and feel” has traditionally been implemented by designers and engineers, then followed by validation from a focus group.  There are many anecdotes about the wife of the boss changing the design look and feel after the first prototype vehicle was built!  Vehicle displays for radio and HVAC used to be judged primarily on comfort and convenience.  Legibility requirements were secondary to brand image and shape (see the sidebar, “Sunlight and Aging Eyes”).  Of course, the speedometer, odometer, PRNDL, and warning-icon displays were all subject to regulatory standards.

More recently, the proliferation of mapping, turn-by-turn navigation, and more complex driver information and ADAS features have brought about the need for the International Organization for Standardization (ISO) and Society of Automotive Engineers (SAE) to adopt more quantifiable metrology for display legibility.  The latest SAE revision of J1757 was approved in January 2015 and it is included in the next revision of ISO 15008 (in progress).

The look and feel of a display are also very much determined by its shape.  Curved shapes with round corners and a high ratio between the display’s active area and the total display surface to minimize packaging volume are essential requirements, enabling vehicle interior designers more freedom in “non-flat” instrument-panel designs.  Improvements in contrast ratio combined with free-form displays such as those now being developed by Sharp are providing instrument-panel designers with freedom to design more advanced looking interiors with better ergonomics.

According to a recent brief from Sharp, “Conventional LCDs are rectangular because of the circuitry required to drive the pixels that are conventionally located around the perimeter of the display.  Sharp moves the drive circuitry away from the perimeter and disperses it throughout the pixels on the display.”  There are tradeoffs, however.  Sharp continues: “As with any new technologies, there are challenges in bringing [these free-form displays] to large-scale manufacturing.”  Such challenges include meeting automotive requirements and implementing high-volume production of the glass cutting and fabrication of the in-pixel driver circuit process.  Last, notes Sharp, the final shape of the display, the complexity of the design, and how efficiently it is used from the motherglass can impact cost.

The size of the display module also relates to look and feel.  In general, the smaller the package the better because it can be more easily and optimally incorporated into the vehicle.  A slimmer profile is helped by advances such as Kyocera’s On-Cell Touch (OCT) technology, which uses a projected-capacitive (PCAP) touch-sensor layer built into the LCD structure.  By adding a fractional amount of thickness to the LCD module, Kyocera eliminates a full touch-screen panel over the display surface, resulting in a thin and light-weight structure.  Additionally, according to the company, by eliminating a touch substrate layer, it eliminates the interior optical reflections and improves visibility, without making the display significantly more fragile.

Beyond the Dashboard

One of the most promising display technologies for vehicles are head-up displays (HUDs) that remove the display from the dashboard, where it forces drivers to look down, to the windshield, where it allows them to keep their eyes on the road.  Two articles in this issue take an in-depth look at HUD technology, “Emissive Projection Technology Enables a Full-Windshield Head-Up Display” and “Next-Generation Head-Up Displays.”  The sidebar “QPI Benefits for HUD Designs,” from the 2014 SID Best Prototype award winner Ostendo Technologies, offers a glimpse of a new technology that may increase the viability of HUDs as a market-ready technology.

Figure 4 offers a look at the sort of free-form all-encompassing display panel that is becoming more common in today’s vehicles.  The major challenges involved in achieving optimal display aesthetics and functionality in vehicles today include better (lower) power consumption and better (higher) contrast ratio at low and high ambient illumination.  Of course, safety and usability remain chief concerns.  As previously mentioned, one technology that offers a great deal of promise is head-up displays (HUDs), which augment the windshield view to provide valuable information while allowing drivers to keep their eyes on the road.

Fig. 4:  The large curved display (with capacitive touch) demonstrated in a concept car from Chrysler in 2009 demonstrates the direction that vehicle manufacturers are headed in terms of vehicle displays.  Image courtesy Ross Maunders Chrysler Interior Design.

Down the Road

Key trends for the automobile of tomorrow relate to autonomous drive and technologies enabling similar life styles whether in vehicle or home/office.  There are many multi-modal human–machine interface systems under development that relate to Levels 2 and 3 and eventually Level 4.  However, based on the Yerkes–Dodson law of performance vs. workload/stress, more information will generate more distraction and lower performance, and increased automation may also reduce performance.  Finding the optimal range requires a good quantifiable measurement tool.  DENSO with MIT AgeLab, Touchstone, Honda, Jaguar, and Subaru have founded the AHEAD (Human Factors Evaluator for Automotive Distraction) consortium to develop this multi-modal tool kit.  Within the next 10 years, HUDs and AR will become very important to the “robot” – “driver” tandem paradigm.

Vehicles at this level of automation will enable the driver to cede full control of all safety-critical functions under certain traffic or environmental conditions, and in those conditions to rely heavily on the vehicle to monitor for changes that would require a transition back to driver control.  The driver would be expected to be available for occasional control (this is one of the greatest challenges), but with a sufficiently comfortable transition time.  An important aspect to this evolution in levels, of course, is consumer acceptance of the new capabilities.  Not so long ago, people were wary of cruise control, and a bit farther back, automatic transmissions, but we have since learned to accept these “augmented” capabilities in our vehicles.  •

 

NHTSA Levels and Definitions
NHTSA defines vehicle automation as having five levels:
    1.   No Automation (Level 0):  The driver is in complete and sole control of the primary vehicle controls – brake, steering, throttle, and motive power – at all times.

    2.   Function-Specific Automation (Level 1):  Automation at this level involves one or more specific control functions.  Examples include electronic stability control or pre-charged brakes, where the vehicle automatically assists with braking to enable the driver to regain control of the vehicle or stop faster than possible by acting alone.

    3.   Combined Function Automation (Level 2):  This level involves automation of at least two primary control functions designed to work in unison to relieve the driver of control of those functions.  An example of combined functions enabling a Level 2 system is adaptive cruise control in combination with lane centering.

    4.   Limited Self-Driving Automation (Level 3):  Vehicles at this level of automation enable the driver to cede full control of all safety-critical functions under certain traffic or environmental conditions and in those conditions to rely heavily on the vehicle to monitor for changes in those conditions requiring transition back to driver control.  The driver is expected to be available for occasional control, but with sufficiently comfortable transition time.

    5.   Full Self-Driving Automation (Level 4):  The vehicle is designed to perform all safety-critical driving functions and monitor roadway conditions for an entire trip.  Such a design anticipates that the driver will provide destination or navigation input but is not expected to be available for control at any time during the trip.  This includes both occupied and unoccupied vehicles (http://www.nhtsa.gov/).

 

Sunlight and Aging Eyes
Beginning in the 1930s, transportation legibility began to be studied with respect to character sizes and proportions for road signage and military applications.  In the 1950s and 1960s, legibility within the automotive industry focused on buttons, switches, and gauges, typically with white-painted graphics and black backgrounds.  In more recent years, the introduction of flat-panel displays within the vehicle posed unique challenges to legibility, especially under daytime conditions when sunlight can flood the displays and reduce contrast.
     In addition to these factors, the human eye and its capabilities change as we age.  For instance, contrast sensitivity declines and sensitivity to glare increases as we grow older.  The typical retina at 65 years of age sees about 40% of the light that a typical 20-year-old retina sees.  The author conducted a study in which licensed drivers were asked to read a line of letters and numbers presented in a display, using occlusion goggles to simulate a driving environment.  Text height, width, and stroke width were varied with a range that included easy and difficult text to read.  The subjects ranged in age from 25 to 91 years, binned into three groups.  Figure A shows the percent reading errors for the three age groups, resulting from each of the 15 reading tasks ordered from easy to difficult.  The older age group had significant difficulty reading fonts that the two younger age groups could read relatively easily.
     When bright daylight conditions are added to the mix, legibility becomes an even greater challenge, especially for aging eyes.  The author conducted another study in which subjects were asked to read a line of text in overcast and direct-sunlight conditions.  The overcast condition used only diffused light shining on the display measured at 5 klx, whereas the direct-sunlight condition added directional lighting at 45 klux, both in accordance with SAE standard practice J1757.  Reading tasks were varied by luminance contrast and color contrast in 32 combinations.  Figure B shows the effect of age on the percentage of text read correctly across all reading tasks.  Here, it is clearly evident that aging eyes struggle to perform under typical daytime lighting conditions unless strong luminance and color contrast is provided.  Color contrast is reduced to a minor contributor under bright sunlight conditions; however, luminance contrast is key.  Figure C shows the results of the reading tasks for only the older age group (60 and up) relative to the recommended ISO 15008 contrast levels.
     Legibility will always be a concern as long as displays are placed in vehicles and as long as human eyes age.  Font characteristics such as height, width, and stroke width, as well as text to background contrast under the challenges posed by daytime conditions, can have a huge effect on the ability of older eyes to read the important information that displays present.

— Shannon O’Day
Ford Motor Co., Core Ergonomics Research Engineer

Fig. A:  Reading errors by age group increased drastically for the more difficult tasks at right in subjects over 60 years of age.


Fig. B:  The chart shows percent of text read correctly across all reading tasks by age of the participant in overcast and direct-sunlight conditions.  Direct sunlight caused errors in all age groups, but particularly in the older participants.


Fig. C:  The chart shows the percent of reading errors for the 60 and older age group for all 32 reading tasks as measured by luminance contrast.  The ISO 15008 recommended contrast correlates to an error rate of 10% or less.

 

QPI Benefits for HUD Designs
The quantum photonic imager (QPI) is a three-dimensional integrated-circuit (3D-IC) semiconductor device comprising a high-density array of digitally addressable micro-sized pixels.  Each pixel (see Fig. D) consists of a vertical stack of multiple light-emitting-diode (LED) layers, each of which generates light of a different primary (red-green-blue) color.
     3D-IC techniques are used to meld the patterned photonic material to an equivalently patterned CMOS digital logic comprising an array of the pixel’s control circuits.  The result is an array of digitally addressable “smart” pixels, each containing its own light-generating material as well as all of the needed logic to control it.  The QPI architecture alleviates many drawbacks of existing microdisplay devices – in particular, those related to power efficiency, compactness, and cost.  The small footprint of the QPI combined with its high luminance and low power consumption makes QPI an ideal candidate for head-up displays (HUDs).
     In terms of high brightness, for mobile applications the QPI device can create a luminance of more than 20,000 cd/m2 for a power consumption of less than 300 mW.  The power consumption includes the driving electronics and the light creation.  For a HUD application in which the power consumption can be increased further, the QPI luminance can theoretically be dialed up to more than 100,000 cd/m2, based on Ostendo’s lab experiments.
     The QPI does not require any external light source or driving electronics; both the light source and the driving logic are part of the display chip, and therefore inefficiencies in having separate devices are eliminated.  The compact size of the QPI enables multiple QPIs to be used in advanced HUD concepts such as using the full windshield as a HUD, while taking up a much smaller space compared to existing HUD solutions.
     The multiple colors generated by the RGB QPI share the same pixel aperture.  This feature is completely novel and sidesteps the artifacts associated with conventional field-sequential and spatial color display architectures.  In terms of better contrast and power efficiency, QPI beam divergence can be adjusted to match the étendue of the system optics.  This means that the light generated by the QPI is used completely by the system and is not wasted, resulting in no stray light and improved image contrast while consuming less power.  The QPI pixel structure does not allow light to leak from a pixel to its adjacent pixels, and when the QPI pixels are off they are truly off, resulting in high image contrast and reduced power consumption.
     Last, the QPI does not require temperature tuning and because the modest amount of heat generated is uniformly distributed over the entire device surface, thermal management is not a problem.  As a result, a thermoelectric cooler is not required.  Currently, Ostendo is designing advanced prototypes that can achieve state-of-the-art results in HUD performance while significantly reducing volume.

— Zahir Y. Alpaslan
Director of Display Systems, Ostendo Technologies, Inc.

and

— Erhan Ercan
VP of Marketing, Ostendo Technologies, Inc.

Fig. D:  Each pixel of the quantum-photonic-imager device consists of a vertical stack of multiple LED layers.

 


Silviu Pala is with DENSO International America in Southfield, Michigan.  He can be reached at silviu_pala@denso-diam.com.