3D3D Time-of-flightTime-of-flight distancedistance measurementmeasurement withwith customcustom solid-statesolid-state imageimage sensorssensors inin CMOS/CCD-technologyCMOS/CCD-technology RobertRobert LangeLange 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 Abstract ....................................................................................................................V 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 systems can be replaced by accurate range measurements. Imaging 3D measurement with useful distance resolution has mainly been