3D Time-of-flight distance measurement with custom - Universität ...

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DEMODULATION PIXELS IN CMOS/CCD 121 we describe the measurements that we will perform later and the setup that we use for these measurements. In addition, we will make predictions about how the pixel performance will change as a function of different parameters. What is “demodulation contrast”? We already discussed in Section 4.2 that, for a good phase accuracy, not only the contrast (or modulation depth) of the modulated light source but also the shutter efficiency is of essential importance. Both define the measured contrast, which directly influences the ranging accuracy (c.f. Equation 4.10). In optics the modulation is defined as follows: Imax − I modulation = min Imax + I Equation 5.1 min Similarly, we define the demodulation contrast Cdemod as: measured amplitude Cde mod = measured offset Equation 5.2 There are several parameters attenuating the measured amplitude. In Chapter 2 we mentioned that the integrative acquisition process of the sampling points Ai leads to a decrease in measured amplitude (c.f. Equation 2.18). For the distance measurement, we operate the lock-in sensor at a modulation frequency of 20 MHz with a sampling interval of 25 ns. Thus, the integration time for the sampling point acquisition is half the modulation period. Therefore, according to Figure 2.7, the measured amplitude is only 64% of the real amplitude. In addition to this more system theoretical amplitude attenuation, there are also physical effects (shutter inefficiency) that lower the measured amplitude and increase the measured offset. The demodulation contrast quantifies the CCD’s (im)perfection of charge separation. It should be as high as possible in order to achieve large signal amplitude and hence a good signal-to-noise ratio for the phase detection. The shutter efficiency depends on the following parameters: • Demodulation frequency: The higher the demodulation frequency (or sampling frequency) the shorter is the time available for the single charge carriers to travel
122 CHAPTER 5 from their site of optical generation to the storage area. If they do not reach the right storage site in time, they will contribute to a wrong sampling point and lower the demodulation amplitude. • Fringing fields: The higher the fringing fields between two adjacent electrodes the higher is the speed of charge transfer and thus the resulting demodulation efficiency increases, especially at high frequencies. • Gate length: The smaller the gate length the more quickly the photoelectrons arrive at the storage sites and the higher becomes the influence of fringing fields. A small gate length is therefore the key parameter for a fast demodulation performance. • Wavelength: The use of long wavelength light leads to a large penetration depth of the incident light. This again causes long diffusion times and blurred diffusion directions. The effective charge capturing area grows. This reduces the sharpness (crosstalk) and leads to a lower demodulation contrast. Long diffusion times lower the demodulation cut-off frequency, while the blurring effect (also opaque CCD gates directly collect photogenerated charge) also appears at low modulation frequencies or even under DC conditions. Optical measurement setup Figure 5.11 shows the optical test setup for the measurements described below. The lock-in sensor chip is mounted on the camera board, which is fixed to an XYtable under a microscope. This microscope is used to illuminate the chip with a variable amount of optical power. LEDs of different wavelength are used to illuminate the pixels. They can be plugged into a fast LED driver module (MV-LED1 [CS1]), which is capable of modulating them up to 20 MHz, depending on their internal capacitances. The light of the LED passes through an iris (or pinhole) and the objective of the microscope. The distance from the objective to the lock-in chip is adjusted such that the light beam is not in focus on the chip. In this way we get a homogenous light spot on top of the chip, leading to an equal illumination of all the pixels. By varying the distance of the objective to the chip we can adjust the size of the light spot and, hence, the illumination intensity on the chip. By measuring the total power of the light spot and the diameter of the spot, the total optical power on the photogate can
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3D Time-of-flight distance measurem
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To my parents
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Meinen Eltern
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II 4. Power budget and resolution l
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Abstract Since we are living in a t
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centimeter accuracy. With the singl
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X Eine elegantere Methode zur Entfe
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INTRODUCTION 1 1. Introduction One
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INTRODUCTION 3 light source observe
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INTRODUCTION 5 Propagation time, ho
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INTRODUCTION 7 Chapter 3 gives a sh
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OPTICAL TOF RANGE MEASUREMENT 9 2.
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OPTICAL TOF RANGE MEASUREMENT 13 pr
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OPTICAL TOF RANGE MEASUREMENT 15 hi
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OPTICAL TOF RANGE MEASUREMENT 17 Pu
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OPTICAL TOF RANGE MEASUREMENT 19 Ad
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OPTICAL TOF RANGE MEASUREMENT 21 pr
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OPTICAL TOF RANGE MEASUREMENT 23 wh
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OPTICAL TOF RANGE MEASUREMENT 25 δ
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OPTICAL TOF RANGE MEASUREMENT 27 c(
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OPTICAL TOF RANGE MEASUREMENT 29 A
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OPTICAL TOF RANGE MEASUREMENT 31 ph
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OPTICAL TOF RANGE MEASUREMENT 33 Ts
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OPTICAL TOF RANGE MEASUREMENT 35 f1
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OPTICAL TOF RANGE MEASUREMENT 37 an
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OPTICAL TOF RANGE MEASUREMENT 39 in
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OPTICAL TOF RANGE MEASUREMENT 41 Ss
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OPTICAL TOF RANGE MEASUREMENT 43 Fr
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OPTICAL TOF RANGE MEASUREMENT 45 1
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50 CHAPTER 3 the smearing effect, r
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52 CHAPTER 3 3.1 Silicon properties
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54 CHAPTER 3 (a) Figure 3.3 Optical
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56 CHAPTER 3 Quantum efficiency in
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58 CHAPTER 3 The different operatio
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60 CHAPTER 3 (a) (b) Depletion widt
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62 CHAPTER 3 Very special processes
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64 CHAPTER 3 1 kT Dn = ⋅ vth ⋅
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66 CHAPTER 3 The proportionality fa
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68 CHAPTER 3 difference of only 1 V
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Page 91 and 92: 74 CHAPTER 3 amount of the charge p
Page 93 and 94: 76 CHAPTER 3 substrate (Equation 3.
Page 95 and 96: 78 CHAPTER 3 charge carriers the CT
Page 97 and 98: 80 CHAPTER 3 without causing short
Page 99 and 100: 82 CHAPTER 3 Over an address decode
Page 101 and 102: 84 CHAPTER 3 Orbit’s 2.0µm CMOS/
Page 103 and 104: 86 CHAPTER 4 Figure 4.1 P lens Lamb
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Page 111 and 112: 94 CHAPTER 4 Cmod = 1 QE(λ) = 0.65
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IMAGING TOF RANGE CAMERAS 171 Gate
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IMAGING TOF RANGE CAMERAS 173 Bound
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IMAGING TOF RANGE CAMERAS 175 Figur
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IMAGING TOF RANGE CAMERAS 177 Final
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IMAGING TOF RANGE CAMERAS 179 #5 #6
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SUMMARY AND PERSPECTIVE 181 7. Summ
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SUMMARY AND PERSPECTIVE 183 into th
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SUMMARY AND PERSPECTIVE 185 or phas
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188 CHAPTER 8 8.2 Typical parameter
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190 CHAPTER 8 Spectral luminous int
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192 CHAPTER 8 MCD03S: Conditions SC
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194 CHAPTER 8 MCD06S: Measurement c
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196 [BRK] Brockhaus, “Naturwissen
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198 [KAI] I. Kaisto, et al., “Opt
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200 [SP1] T. Spirig et al., “The
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ACKNOWLEDGMENTS 203 Acknowledgments
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206 Publication list 1. R. Lange, P
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