A Range-Shift Technique for TOF Range Image Sensors.pdf
0.73MB
Introduction
- Both long measurement range and high range resolution is required for ToFs
- There is a trade-off between the maximum range and range resolution
- Range-shift technique can be used to improve range resolution wthout loss of the measurement range
- If the TG/TC is reduced, the range resolution is further improved for whole range, because the shot noise due to ambient light is reduced
- TG gate timing is reduced from TG = 100 ns to TS = 10 ns
- Range resolution is improved by 10 times
- Equations for range of conventional operation and range-shift operation are shown below:
- Here, N1 and N2 are the number of signal electrons in the two FD nodes
- Range resolution could be estimated by considering the variance of Eq. (3) which is written as
- Here, N12 is the sum of N1 and N2
because N1 and N2 are not correlated
Therefore, the covariance square of N2 and N12 are given by:
- By Eqs. 3, 4, 5, and 6, the theoretical range resolution is given by:
- Fig. 4 shows the theoretical range resolution with and without range shifting as a function of the range
- In the range shifting, the light pulse width, TS and the number of shifts are 25 ns and 4, respectively
- The range resolution is improved by a factor of T0/TS = 4
