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

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POWER BUDGET AND RESOLUTION LIMITS 93 contrast Cdemod, which depends on the pixel performance, (usually less than 100%), have to be considered: A = Cmod ⋅ Cdemod ⋅PEopt Equation 4.15 For 100% modulated optical signal we obtain: demod opt PE C A ⋅ = Equation 4.16 Thus we can rewrite Equation 4.11: L background + Npseudo + PEopt ∆ L = ⋅ Equation 4.17 8 2 ⋅ Cmod ⋅ Cdemod ⋅ PEopt For the following example we assume a 100% modulated light source (Cmod=1) with a total optical power of Popt=700 mW. The light source emits at 630 nm, where the sensor has a quantum efficiency of 65%. We use a CS-mount lens with a focal length of f=2.6 mm and a F/# of 1.0. The pixel size is 12.5 µm x 14.4 µm. With a beam divergence of 50° (LED) we get an image size at the sensor plane of 4.6mm 2 ({2.6 mm * tan25°} 2 ⋅π). With optical losses of lens (0.7) and interference filter (0.5) we obtain klens=0.35. Choosing an integration time of Tint=25 ms we can easily calculate the number of electrons Ne generated in one pixel by rearranging Equation 4.7: ⎛ ⎞ ⎜ ⎟ 2 ⎜ P light source ⋅ ρ ⋅ D ⋅ klens ⋅ QE( λ) ⋅ λ ⋅ Tint ⎟ 1 Ne = ⎜ ⎟ ⋅ Aimage 2 Equation 4.18 ⎜ 4 ⋅ ⋅ h ⋅ c ⎟ R ⎜ A ⎟ ⎝ pix ⎠ Choosing a target with 20% reflectivity we get the number of electrons per pixel, which now only depends on the distance R in meters (R/[m]): Ne ≈ 170,000 photoelectrons / (R/[m]) 2 . Hence, for a distance of 5 meters, we will integrate a number of 34,000 electrons in one pixel. The following overview summarizes the chosen parameters.
94 CHAPTER 4 Cmod = 1 QE(λ) = 0.65 klens = 0.35 Popt = 700 mW lens 1:1.0, 2.6 mm Tint = 25 ms λ = 630 nm D = 2.6 mm ρ = 0.2 beam divergence = 50° Apixel = 180 µm 2 Aimage = 4.6 mm 2 Figure 4.4 to Figure 4.8 clarify the influence of the single parameters and give numerical values for the range resolution that can be expected under certain conditions. Figure 4.4 shows both the received power and the number of generated electrons per pixel depending on target distance and reflectivity. Figure 4.5 illustrates the corresponding range resolution. In Figure 4.6 the demodulation contrast varies; this was previously chosen as 40%. The influence of an additional background illumination on the range resolution is shown in Figure 4.7. Figure 4.8 plots the range resolution versus the optical power per pixel rather than the distance in meters. Additionally the integration time varies. This figure is of special importance. In Chapter 5 we present real range measurement values and compare them to the prediction of Figure 4.8. We will demonstrate an excellent fit between measurement and theory, which also confirms the predicted range accuracies of Figure 4.5, Figure 4.6 and Figure 4.7. Assuming an integration time of Tint = 25 ms, the modulation period of Tmod=50 ns, which we choose for our TOF application (fmod=20 MHz, L=7.5 m), is a factor of 500,000 times shorter than Tint. Therefore, if a number of 50,000 photoelectrons (c.f. Figure 4.4, light power: 700 mW) is generated in one pixel within the integration time, only one photoelectron is collected every 10 th modulation period statistically speaking. Therefore, the demodulation pixels introduced in Chapter 5 will have to work with single photoelectrons, and at this point we understand, why self-induced drift does not contribute to the charge transport in our application (compare Chapter 3.1.3). According to Figure 4.8, the number of only 50,000 photoelectrons (1000 fW @ Tint=25 ms) leads to a range accuracy of about 2 centimeters.
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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 11 2.
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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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Page 95 and 96: 78 CHAPTER 3 charge carriers the CT
Page 97 and 98: 80 CHAPTER 3 without causing short
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DEMODULATION PIXELS IN CMOS/CCD 143
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IMAGING TOF RANGE CAMERAS 151 6. Im
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IMAGING TOF RANGE CAMERAS 153 contr
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IMAGING TOF RANGE CAMERAS 155 6.1.2
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IMAGING TOF RANGE CAMERAS 157 gate
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IMAGING TOF RANGE CAMERAS 159 6.2 2
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IMAGING TOF RANGE CAMERAS 161 n+ di
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IMAGING TOF RANGE CAMERAS 163 pixel
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IMAGING TOF RANGE CAMERAS 165 Power
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IMAGING TOF RANGE CAMERAS 167 Delay
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IMAGING TOF RANGE CAMERAS 169 6.3 3
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IMAGING TOF RANGE CAMERAS 171 Gate
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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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