Patent ID: 8648807

Claim:
An illuminance sensor including a first light receiving element and a second light receiving element which are different from each other in spectral-response characteristic, the illuminance sensor comprising: (A) a first analog-digital conversion circuit for carrying out an analog-digital conversion with respect to a first current which flows through the first light receiving element in correspondence with an intensity of light received by the first light receiving element, the first analog-digital conversion circuit including an integrating analog-digital conversion circuit which includes: an integrating circuit that includes an integrating capacitor for integrating an electric charge corresponding to the first current inputted to the integrating circuit and that outputs a voltage corresponding to a result of the integration by the integrating capacitor; a comparing circuit that compares (i) a magnitude of the voltage outputted by the integrating circuit with (ii) a magnitude of a reference voltage so as to output a result of the comparison as a binary pulse signal; an output circuit for receiving the pulse signal outputted by the comparing circuit, the output circuit (i) including a counter for counting a number of active pulses included in the pulse signal received and (ii) outputting, as an analog-digital conversion value for the first current, a result of the count by the counter; and a discharging circuit that receives from the output circuit a time series stream of the active pulses as a bitstream signal and that outputs a current during an active pulse period of the bitstream signal so as to discharge the integrating capacitor; (B) a current output circuit for receiving the bitstream signal from the output circuit and outputting a current during the active pulse period of the bitstream signal; and (C) a second analog-digital conversion circuit including an integrating analog-digital conversion circuit for carrying out an analog-digital conversion with respect to a third current obtained by subtracting the current outputted by the current output circuit from a second current which flows through the second light receiving element in correspondence with an intensity of light received by the second light receiving element.