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

130 CHAPTER 5
5.2.3 Determination of optimal control voltages
It is obvious that the demodulation contrast depends on the amplitude of the control
voltages of the photogates. With our control and driving electronics we can switch
the control signals between 0 V and an adjustable voltage value. Additionally, the
setup allows the rise and fall times to be varied by changing an additional
capacitive load on the driver’s output. Also, the pulse width can be varied by some
nanoseconds. The rise and fall times as well as the duty cycle (pulse width) gain
importance only for high modulation frequencies. Since, however, the exact
adjustments of both rise and fall time and signal pulse width are very timeconsuming,
we determine the best voltages firstly for 1 MHz and, based on these
results, we only perform a fine-tuning for 20 MHz modulation. For both realizations,
the demodulation contrast reaches a maximum for PGL/PGR modulated with 8 V
amplitude (Figure 5.16). The ideal voltage of the middle photogate at 20 MHz
modulation frequency is 3.5 V for the BCCD version and 6.5 V for the SCCD.