| 摘要 |
PURPOSE:To perform high-precision A/D conversion by optionally setting the upper limit and lower limit of an analog reference voltage for converting photoelectric signals from photoelecdric converting circuits from analog to digital, and then correcting them according to the drift of the photoelectric converting circuits. CONSTITUTION:A photodetector 1 having many photoelectric converting circuits is controlled by a control circuit 2 and a photoelectric signal read out successively by a decoder 3 is inputted to the comparators CP5 of an A/D converting circuit 4. An oscillator 6 is controlled by the output of the CP5 and the count value of a counter 7 which counts a clock signal from the oscillator 6 is inputted to a D/A converting circuit 8, which applies the CP5 with an analog reference voltage which corresponds to the count value. The CP5 stops the oscillator 6 when a level relation between the photoelectric signal and analog reference voltage is inverted, and the count value of the counter 7 at that time is outputted as the A/D-converted signal of the photoelectric signal. In this case, the photodetector 1 generates and applies the lower-limit value and upper- limit value of the analog reference voltage through a lower-limit voltage setter 41 and an upper-limit voltage setter 42 to correct the reference voltage according to the drift of the photoelectric converting circuits. |
