Patent ID: 7603043
Filing Date: 2009-10-13
Classification: G11B

Abstract:
1. A light receiving element circuit comprising: a plurality of light receiving elements which photoelectrically convert light signals carrying information, respectively; a plurality of first amplification circuits which amplify electric signals from the light receiving elements, respectively, wherein each of the plurality of first amplification circuits includes a current-voltage conversion circuit which converts a current obtained from the light receiving element into a voltage; a selecting section which selectively outputs one of the signals amplified by the plurality of first amplification circuits; and a second amplification circuit which amplifies the signal output from the selecting section and which supplies the signal to an output, wherein the second amplification circuit includes a differential output circuit which amplifies an output signal of the current-voltage conversion circuit and which outputs the signal as a differential signal, wherein the light receiving element circuit further comprises: a negative-phase-side reference voltage generation circuit which generates a negative-phase-side reference voltage of the differential output circuit from a power supply voltage and a reference voltage of the light receiving element circuit, wherein the differential output circuit comprises: a positive-phase output-side amplification circuit having a non-inverting input terminal to which an output signal of a photoelectric conversion circuit is supplied, and an inverting terminal to which the reference voltage is supplied as the positive-phase-side reference voltage, which outputs a positive-phase-side reference voltage when the light receiving element is not irradiated with light; and a negative-phase output-side amplification circuit having a non-inverting input terminal to which the output signal of the photoelectric conversion circuit is supplied, and an inverting terminal to which the negative-phase-side reference voltage is supplied, which outputs a predetermined voltage higher than the positive-phase-side reference voltage when the light receiving element is not irradiated with the light.