automotive oled luminance consumption control methods

Strictly Private and Confidential

Paul Weindorf

Automotive OLED Luminance Consumption Control Methods

Introduction

Why are there not a lot of automotive OLEDs?– Higher luminances of more than 600 cd/m2 are generally not available and are

therefore not practical in high reflection rate environments.– Luminance consumption permanently causes burned-in images when the same

image is displayed for long periods of time (automotive use case).– Suffer from other problems like color shift over time and temperature.– Expensive

Many techniques are possible to reduce luminance consumption– Gaussian spatial distribution of symbology over time– Improved thermal designs to minimize OLED temperatures– Minimize OLED display operating ratios to keep the temperature down– Pixel compensation techniques– Automatic luminance control– Luminance consumption rate limit

OLED Luminance Consumption Rate

All OLEDs suffer a decrease in luminance as a function of both temperature and luminance levels.

Luminance Consumption Rate – the rate at which the luminance is permanently decreased in nits/hour

Heuristic formulas may be developed based on testing that describe the Luminance Consumption Rate.

hournits

KLL

CR op

5.10751042.61.0

310max

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Lop= Operating LuminanceLmax= Maximum Display Luminance for the device tested°K = Temperature in Kelvin

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0 500 60

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25354555657585

Lop Luminance

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ur

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Automatic Luminance Control

Automatic luminance control reduces the average operational luminance.

Average operational luminance also reduces operational temperatures

hournitsCR

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5.10753181042.61.0

300600

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310

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Case 1: 600 cd/m2 at 45°C (318°K)

AmbientLightSensor

ForwardLookingLightSensor

P. Weindorf, “Forward Looking Light Sensor Utilization for Automatic Luminance Control”, 2015 SID Symposium Proceedings

hournitsCR

CR

0267.0

5.10753081042.61.0

300300

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310

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Case 2: 300 cd/m2 at 35°C (308°K

Luminance Consumption Rate Limit

Limit the Luminance Consumption Rate to a predetermined level

Limit control may occur infrequently under hot start conditions

hournits

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Lop for CRmax=0.4

Lop for CRmax=0.3

Lop for CRmax=0.2

Lop for CRmax=0.1

Lop for CRmax=0.05

Lop for CRmax=0.01

Figure 2.2-1. Lop versus Temperature for Different CRs

Consumption Rate Limit Control ExampleHot start exponential temperature decrease from +85°C to +45°C.

Consumption rate limit set to 0.15 nits/hour

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Normal CR

Limit CR

Temp °C

Normal Lop (cd/m^2)

Limit Lop (cd/m^2)

Figure 2.2-2. Hot Start Example

hournitse

LL

CRtop

1.044

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1001.21008.1

Figure 2.2-2. Hot Start Example

nitseEtELL

LD

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101.208.1

SteadyState Transient

startnitsLD

eLD

00704.0

02412.0247.01296.015.0 1.0247.0

OLED Automotive Life Example Assumptions

10 years at 15K mi/year for a total of 150K miles. At an average speed of 30 miles/hour, the total number of operational hours is 5000 hours.

3,650 hot summer starts (2 hot +85°C starts/summer day X 182.4 days/year X 10 years). Note that 182.4 days assumes 6 months of hot days per year such as in Phoenix Arizona.

The morning and afternoon peak 600 cd/m2 automatic luminance conditions are assumed to occur in a 20° sun angle aperture and only in 2 directions resulting in a 12% occurrence percentage.

An automatic luminance level of 300 cd/m2 is assumed for most of the 2200 daytime hours and 600 cd/m2 is used for the peak luminance occurrences of 300 hours (12% of the time).

A consumption rate limit of 0.15 nits/hours is used for the “Auto” hot start at 600cd/m2 scenario.

OLED Automotive Life Example

ConditionNormalcd/m2

Normal OLED Temp°C

Normal Decreasecd/m2

Normal Consumption Rate (nits/hr)

Autocd/m2

Auto OLED Temp°C

AutoDecreasecd/m2

Auto Consumption Rate (nits/hr)

3168 Day +85C HotStarts @ Auto=300 nits 600 45 76.41

0.02412 nits/start(Eq. 2.2-4) 300 45 19.10

0.00603nits/start

432 Day +85C Hot Starts@ Auto=600 nits 600 45 10.41

0.02412 nits/start(Eq. 2.2-4) 600 45 3.04

0.00704nits/start(Eq. 2.2-5)

2200 Hours DaytimeNominal Luminance 600 45 286.66

0.130303336(Eq. 2.1-2) 300 35 58.83

0.026743516(Eq. 2.1-3)

300 Hours DaytimeAuto Peak Luminance 600 45 39.09

0.130303336(Eq. 2.1-2) 600 40 35.35

0.117861979(Eq. 2.1-3)

2500 Hours NightTime Operation 40 25 0.98 0.000394923 40 25 0.98 0.000394923Total Luminance DecreaseEnd of Life (cd/m2) 413.58 117.33% Decrease 68.93% 19.55%

20% compensation at the pixel level may be possible by the OLED manufacturer

Dual OLED Demonstrator

Dual OLED Demonstrator has both a forward looking and ambient light sensor automatic luminance control system

Rate limit control can be artificially activated by increasing offset temperature

Conclusions

Automotive OLED implementation is possible by utilizing a variety of techniques to manage image burn in artifacts.

Automatic luminance control system is expected to provide the most benefit by lowering the average luminance and average temperature.

Consumption rate limit control provides some benefit, but is highly dependent on the number of hot starts under high luminance conditions.

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