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

DEMODULATION PIXELS IN CMOS/CCD 143
Signal-to-noise ratio SNR:
⎛ voltage swing in V
SNR = 20 ⋅ log⎜
⎝ rms noise of voltage swing in
Dynamic range D/R:
V
⎞
⎟
⎠
Equation 5.3
⎛ maximum voltage swing in V ⎞
D / R = 20 ⋅ log⎜
⎟
Equation 5.4
⎝ floor noise in V ⎠
Table 5.4 summarizes the measured noise performance, SNR and D/R of the
BCCD realization of the demodulation pixel. The additional noise of the analog
electronics of the camera board and the frame grabber is only 54 µV rms and can
be neglected.
Fixed pattern noise: 38 mV
Noise floor: 0.60 mV
Dark noise (12.5 ms): 0.63 mV=175 electrons
Bright noise (12.5 ms, 9000 fW): 3 mV
Voltage swing (9000 fW): 1100 mV
Maximum voltage swing: 3000 mV
Signal-to-noise ratio SNR: 50 dB
Dynamic range D/R: 73 dB
Table 5.4 Noise performance of buried channel 1-tap demodulation pixel.
Integration time for the bright noise measurement: 12.5 ms.
5.2.8 Comparison of measured distance accuracy with theory
With the knowledge of the dark noise, we can now estimate the range accuracy of
the demodulation pixels by means of Equation 4.16. The demodulation contrast at
20 MHz is Cdemod=40%, the modulation depth of the LEDs about Cmod=100%. The
dark noise of 0.63 mV and 175 noise-equivalent electrons results in a number of
Npseudo=30,000 pseudo electrons. The measurements have been performed under
the microscope without additional background illumination. The results are
illustrated in Figure 5.25.