For ideal signal detection, the threshold voltage (i.e., the negative input voltage) of the comparator should be slightly higher than the offset voltage of the Op-Amp (i.e., the positive input voltage of the comparator). In this case, the minimum signal detection level can be low. If the offset voltages are the same between the elements in the array, the ideal signal detection can be easily realized with a common threshold voltage for all elements. However, in actuality, the offset voltage has unavoidable dispersion between elements. Figure 8 shows this dispersion of the offset voltage. This offset voltage was measured by changing the setting of the threshold voltage and finding out the boundary condition for the peak detector to work. If the offset voltage is much higher than the threshold, S/H TRG is not output in the cases of small signals. This means that small signals cannot be detected. If the offset voltage is lower than the threshold, SH TRG continues to be output. In this case, the S/H circuit in the TAC does not hold the ramp voltage and consequently, the ranging function does not work. To resolve this issue, we have added the function of setting the optimum threshold voltage for S/H TRG. That voltage is configured by a digital-to-analogue converter (DAC). The DAC accesses the random access memory which is integrated in each ROIC element. Using this function, we can set the threshold slightly higher than the offset voltage of the Op-Amp for all elements and the ideal signal detection can be realized. The ROIC has another additional function in switching the measurement range width. That can be realized by controlling the current in TAC. The current is controlled by the external input of digital value as shown in Fig. 9. Figure 9(a) shows the designed measurement range width versus the digital value. Figure 9(b) shows the measured results of input time (corresponding to TOF) versus output voltage of the ramp, respectively. The ramp voltage characteristic was measured by changing the input timing of a pulse signal. The range width was obtained by measuring the time width from the start and end of the ramp. In Fig. 9(b), the two lines correspond to the ramp voltage in case of and 53, respectively. The range widths, which are obtained from Fig. 9(b), are 450 and 75 m (corresponding to 3000 and 500 ns) for and 53. These values agree with the designed ones shown in Fig. 9(a). In the developed ROIC, we can set the measurement range width depending on the flexible user’s request in time. If the ranging width is set to be short, the gradient of the time-to-amplitude in the TAC becomes steep and it contributes to the high precision ranging. On the other hand, when the ranging width is set to be long, it is suitable for long-range imaging. These additional functions (setting the optimum threshold voltage for S/H TRG and switching the measurement range width) are realized owing to the feature of the larger area of linear array concept which was described in Sec. 1.