Analog-digital converting apparatus

摘要

In an analog-digital converting apparatus including a row of light receiving units with each unit having a light receiving element and a sample-hold circuit, a counter for producing a digital signal whose value is increased successively, a digital-analog converter for receiving the digital signal and producing an analog reference signal whose amplitude increases successively from a lower limit value to an upper limit value in step-shaped manner, comparators for comparing the output signals of the light receiving units with said analog reference signal, respectively, memories for receiving the digital signal and controlled by the comparators, respectively to store instantaneous digital values when the corresponding comparators change their states, there is provided a second light receiving unit having substantially the same construction as that of the first mentioned light receiving unit except that a light receiving element provided therein is covered with a light shielding mask so as to produce an output equivalent to a dark current component of the light receiving element, the output of which unit is used as a lower limit voltage source for said digital-analog converter. The apparatus may further include a third light receiving unit having substantially the same as that of the first light receiving unit except that the light receiving element is removed and the input of the sample-hold circuit is connected to a supply voltage so as to produce an output equivalent to a saturation value of the light receiving element, the output of which unit is used as an upper limit voltage source for the digital-analog converter.