sid 2015 foward looking light sensor

Strictly Private and Confidential

Paul Weindorf, Visteon Corporation

56.4: Forward Looking Light Sensor for Automatic Luminance Control

Outline

Introduction

Historical Background

Implementation Issues and Solutions

Automotive Automatic Luminance Control System

Demonstration Hidden Touch Experience Hardware

Conclusion

Introduction

Number of displays used per vehicle is increasing year over year

Increasing level of focus on safety and readability, resulting in displays being placed higher (closer to the eye line) and consequently increased vulnerability to reflections

Display luminance levels are increasing due to increased background reflections

High luminance required for high ambient conditions are distracting and cause undesirable pupil contraction for lower ambient conditions

Backlight power levels are increasing!

Thermal management issues are leading to active cooling resulting in more cost and noise

Problem: existing Automatic Luminance Control systems do not work properly

Solution: properly designed Automatic Luminance Control System– Provide both Ambient Light Sensor and Forward Looking Light Sensor Control– Only provide the higher luminance when needed– Allows higher peak luminance levels with cooler thermal mass until de-rating occurs

Background - Forward Looking Light Sensor

Dr. Louis Silverstein: The Forward Looking Light Sensor “compensates for conditions of transient adaptation or eye adaptation mismatch”

AmbientLightSensor

ForwardLookingLightSensor

Background - Power Function

Higher offset BO is often used to compensate for not having a Forward Looking Light Sensor

Ambient Light Sensor Power Function Relationship: (Required Display Luminance (ESL) as a function of Background Luminance (DBL))

CO DBLBESL

Background - Silverstein GF Function

GF = Gain Factor

FFVI = Forward Field of View Intensity

WSI = Display White Stroke Intensity

2982.0log125.1

WSI

FFVIGF

Background - Silverstein Control System

Dr. Louis Silverstein Automatic Luminance Control Block Diagram

Internallightsensor

PWI = peak white intensityWSI = white stroke intensityFFVI = forward field of view intensityTC = time constantEXP = exponential function

fc .273X

Log potmanual

XPWI100

XFFVIWSI

Log

Remotelightsensor

X1.126

+0.2982

fc %PWI

TC↑ = 1 secTC↓ = 60 sec

exp

WSI

(fL)

> 1

SetGF = 1

No

X YesGammacorrect

Tovideoamps

FFVI (fL)

Gain factor

Foward Looking Light SensorAmbient Light Sensor

Implementation Issues and Solutions

The use of linear light sensors in conjunction with A/D converter resolutions do not have the sufficient dynamic range of 6-8 decades.

The processor throughput required to compute the automatic luminance control mathematical functions needs to be minimized for processors used in automotive applications which are used to process a variety of vehicle functions.

SOLUTIONS:

Step # ND

Display cd/m2

LN

Display Background Luminance

cd/m2 DBLN

Log 10bit A/D

Linear 10bit A/D

0 38.71 0.68 23 0.68

1 50.00 1.41 123 1.42

2 64.58 2.94 223 2.95

3 83.41 6.10 323 6.13

4 107.72 12.66 423 12.74

5 139.13 26.30 523 26.46

6 179.69 54.64 623 54.96

7 232.08 113.49 723 114.15

8 299.74 235.73 823 237.11

9 387.13 489.63 923 492.51

10 500.00 1017.03 1023 1023.00 Logarithmic Light Sensors

Simplifies mathematics Huge dynamic range

Luminance Ratio Lookup Tables Silverstein Power Function with equal A/D light sensor deltas Logarithmic user preference control by shifting operation Allows gain factor multiplication by shifting operation

Automotive Automatic Luminance Control System

ALSLogAmp

LogarithmicAmbientLight Sensor(ALS)

21

A/DLuminance Ratio Table

0 38.71 23

1 50.00 123

2 64.58 223

3 83.41 323

4 107.72 423

5 139.13 523

6 179.69 623

7 232.08 723

8 299.74 823

9 387.13 923

10 500.00 1023

ND LSEL 10 bit

A/D GF Table

DisplayUser Bias

∆NBD

DISPLAY5

ESLD

4 43 KNNK BDD

∆N

GF ∆N 1 0

1.328803 1 1.765719 2 2.346293 3 3.117763 4 4.142894 5 5.505092 6 7.315185 7 9.720443 8 12.91656 9 17.16357 10

LogarithmicFowardLookingLight Sensor(FFLS)

FLLS

LogAmp

A/D

Luminance Ratio Table

0 49.60 23

1 84.33 123

2 143.35 223

3 243.70 323

4 414.29 423

5 704.30 523

6 1197.30 623

7 2035.42 723

8 3460.21 823

9 5882.35 923

10 10000.00 1023

NH ESLH 10 bit

A/D

1.125log10 (L

SEL )

GF

21 KNK H

0.2982

1.125log10 (FFVI) ESLH

HUD

13 DBD C

ODNN

D DBLBR

HUD UserBias ∆NBH

12

9

10

11

3

6

7

8

Luminance Ratio Table

GF multiplication shifting

Log Light Sensors provide dynamic range and simplify math

Forward Looking Light Sensor Prototype

Dr. Louis Silverstein: “The forward-facing or remote light sensor should have a lens that attenuates incident light as a function of the square of the cosine of the angle of incidence of light to the sensor”

3-wire Logarithmic Light Sensor

Simple hole structure with correct dimensions provides cosine2(θ) function

Demonstration Hidden Touch Experience Hardware

Forward Looking Light Sensor

Ambient Light Sensor

Output with Forward Light Sensor

Output with Ambient Light Sensor

Advanced Auto Luminance Take3.mp4

Conclusion

Logarithmic Light Sensors enable a successful Automatic Luminance Control System

A Forward Looking Light Sensor is required to compensate for light adaptation

Luminance ratio structure enables easy mathematical implementation

Reduces display power

Improves display visibility

Advanced Automatic Luminance Control System successfully demonstrated

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