3D Time-of-flight distance measurement with custom solid-state ...

3D Time-of-flight distance measurement
with custom solid-state image sensors
in CMOS/CCD-technology
Robert Lange
3D Time-of-Flight Distance Measurement
with Custom Solid-State Image Sensors in
CMOS/CCD-Technology


A dissertation submitted to the

DEPARTMENT OF ELECTRICAL ENGINEERING AND
COMPUTER SCIENCE AT UNIVERSITY OF SIEGEN

for the degree of

DOCTOR OF TECHNICAL SCIENCES


presented by
Dipl.-Ing. Robert Lange

born March 20, 1972


accepted on the recommendation of

Prof. Dr. R. Schwarte, examiner
Prof. Dr. P. Seitz, co-examiner

Submission date: June 28, 2000
Date of oral examination: September 8, 2000









To my parents
3D Distanzmessung nach dem
„Time-of-Flight“- Verfahren mit
kundenspezifischen Halbleiterbildsensoren
in CMOS/CCD Technologie


VOM FACHBEREICH ELEKTROTECHNIK UND INFORMATIK
DER UNIVERSITÄT-GESAMTHOCHSCHULE SIEGEN

zur Erlangung des akademischen Grades

DOKTOR DER INGENIEURWISSENSCHAFTEN
(DR.-ING.)


genehmigte Dissertation
vorgelegt von
Dipl.-Ing. Robert Lange
geboren am 20. März 1972


1. Gutachter: Prof. Dr.-Ing. R. Schwarte
2. Gutachter: Prof. Dr. P. Seitz
Vorsitzender der Prüfungskommission: Prof. Dr.-Ing H. Roth


Tag der Abgabe: 28. Juni 2000
Tag der mündlichen Prüfung: 8. September 2000









Meinen Eltern

I

Contents
Contents .................................................................................................................... I
AbstractV
Kurzfassung............................................................................................................IX

1. Introduction.......................................................................................................... 1

2. Optical TOF range measurement ....................................................................... 9
2.1 Overview of range measurement techniques.......................................... 11
2.1.1 Triangulation ................................................................................... 11
2.1.2 Interferometry.................................................................................. 13
2.1.3 Time-of-flight 16
2.1.4 Discussion....................................................................................... 24
2.2 Measuring a signal’s amplitude and phase ............................................. 26
2.2.1 Demodulation and sampling ........................................................... 26
2.2.2 Aliasing ........................................................................................... 36
2.2.3 Influence of system non-linearities ................................................. 46
2.2.4 Summary......................................................................................... 47

3. Solid-state image sensing ................................................................................ 49
3.1 Silicon properties for solid-state photo-sensing....................................... 52
3.1.1 Photodiodes in CMOS .................................................................... 52
3.1.2 MOS photogate............................................................................... 57
3.1.3 Transport mechanisms for charge carriers..................................... 62
3.1.4 Noise sources ................................................................................. 68
3.1.5 Sensitivity and Responsivity ........................................................... 71
3.1.6 Optical fill factor .............................................................................. 72
3.2 Charge coupled devices: CCD - basic principles .................................... 73
3.3 Active pixel sensors: CMOS APS............................................................ 81
3.4 Discussion ............................................................................................... 83 II


4. Power budget and resolution limits................................................................. 85
4.1 Optical power budget............................................................................... 85
4.2 Noise limitation of range accuracy........................................................... 90

5. Demodulation pixels in CMOS/CCD 99
5.1 Pixel concepts ....................................................................................... 102
5.1.1 Multitap lock-in CCD ..................................................................... 102
5.1.2 4-tap lock-in pixel.......................................................................... 104
5.1.3 1-tap lock-in pixel 109
5.1.4 Summary: Geometry and speed performance.............................. 113
5.2 Characterization of 1-tap pixel performance.......................................... 116
5.2.1 Charge to voltage conversion ....................................................... 116
5.2.2 Measurement setup, expectations and predictions ...................... 120
5.2.3 Determination of optimal control voltages..................................... 130
5.2.4 Influence of optical power and integration time @ 20 MHz .......... 134
5.2.5 Demodulation contrast versus frequency and wavelength ........... 137
5.2.6 Phase accuracy measurements ................................................... 139
5.2.7 Noise performance and dynamic range........................................ 142
5.2.8 Comparison of measured distance accuracy with theory ............. 143
5.2.9 Summary....................................................................................... 145
5.3 Outlook: Two-photosite demodulation pixel .......................................... 147
III

6. Imaging TOF range cameras .......................................................................... 151
6.1 Camera electronics................................................................................ 152
6.1.1 Digital sequencer board................................................................ 152
6.1.2 Driving electronics board .............................................................. 155
6.1.3 Modulated illumination .................................................................. 158
6.2 2D range camera................................................................................... 159
6.2.1 108 pixel lock-in line sensor.......................................................... 159
6.2.2 System architecture ...................................................................... 163
6.2.3 2D range measurement ................................................................ 167
6.3 3D range camera 169
6.3.1 64 x 25 pixel lock-in image sensor................................................ 169
6.3.2 System architecture 171
6.3.3 3D range measurement 173
6.4 Discussion ............................................................................................. 180

7. Summary and Perspective.............................................................................. 181

8. Appendix .......................................................................................................... 187
8.1 Physical constants................................................................................. 187
8.2 Typical parameters of a 2 µm CMOS technology.................................. 188
8.3 Conversion: LUMEN, WATT and CANDELA......................................... 189
8.4 Measurement conditions (MCD) for Chapter 5...................................... 191

References ........................................................................................................... 195
Acknowledgments............................................................................................... 203
Curriculum Vitae.................................................................................................. 205
V

Abstract
Since we are living in a three-dimensional world, an adequate description of our
environment for many applications includes the relative position and motion of the
different objects in a scene. Nature has satisfied this need for spatial perception by
providing most animals with at least two eyes. This stereo vision ability is the basis
that allows the brain to calculate qualitative depth information of the observed
scene. Another important parameter in the complex human depth perception is our
experience and memory. Although it is far more difficult, a human being is even
able to recognize depth information without stereo vision. For example, we can
qualitatively deduce the 3D scene from most photos, assuming that the photos
contain known objects [COR].
The acquisition, storage, processing and comparison of such a huge amount of
information requires enormous computational power - with which nature fortunately
provides us. Therefore, for a technical implementation, one should resort to other
simpler measurement principles. Additionally, the qualitative distance estimates of
such knowledge-based passive vision