Patent ID: 8742314
Filing Date: 2014-06-03
Classification: G01J,H03F

Abstract:
1. A light amount detecting apparatus comprising: a photoelectric converting element for converting amount of light inputted to a current; a current/voltage converting device having a positive input terminal connected to a first terminal of said photoelectric converting element, a negative input terminal connected to a second terminal of said photoelectric converting element, a negative output terminal for reversing polarity of a current inputted to the positive input terminal and outputting it as a voltage, a positive output terminal for reversing polarity of a current inputted to the negative input terminal and outputting it as a voltage, a first negative feedback resistor connected between the positive input terminal and the negative output terminal, and a second negative feedback resistor connected between the negative input terminal and the positive output terminal, said current/voltage converting device setting said photoelectric converting element in zero bias and converting the converted current to the voltage; an amplifying device for amplifying the converted voltage; a modulating device for modulating a voltage signal of the converted voltage by reversing polarity of the converted voltage with an odd-numbered period defined by a predetermined frequency which is higher than a frequency of the converted current and by not reversing the polarity of the converted voltage with an odd-numbered period defined by the predetermined frequency; and a demodulating device for demodulating the voltage signal of the converted voltage by reversing the polarity of the converted voltage with the even-numbered period and by not reversing the polarity of the converted voltage with the even-numbered period, said light amount detecting apparatus further comprising, as said modulating device: a first switching device for changing between a first connection state and a second connection state at the predetermined frequency, wherein in the first connection state, the first terminal and the positive input terminal are connected and the second terminal and the negative input terminal are connected, and in the second connection state, the first terminal and the negative input terminal are connected and the second terminal and the positive input terminal are connected.