| 摘要 |
PURPOSE:To detect more stably the reflected light of an object by controlling the detection sensitivity by using the second photodetector for detecting the direct projection light of a light source. CONSTITUTION:The output of the second photodiode 3 is fed back to a light emitting diode driving circuit 5, and the output of a light emitting diode 1 becomes constant. A light beam emitted from the light emitting diode 1 is reflected by an object 4 and made incident on the first photodiode 2, and converted to an electric signal. In this state, when the characteristics of the first and the second photodiodes 2, 3 are made equal, the characteristic variation of the first photodiode 2 is compensated. That is to say, it is considered that the characteristic variation by an environmental temperature is generated equally in the photodiodes 2, 3, and when the output of the photodiode 2 drops due to the characteristic variation, the same output drop is generated in the photodiode 3, as well, and from the drop of a feedback to a light emitting diode driving circuit 5, the light emitting diode driving circuit 5 increases a current conducting to the light emitting diode 1, and the output of the photodi ode 2 is stabilized. |
