| 摘要 |
PURPOSE:To amplify a photocurrent excellently even when the photocurrent varies greatly and to perform accurate distance measuring operation by the amplification by detecting reflected light from a body to be measured by a photoelectric conversion element. CONSTITUTION:The photoelectric conversion element which is a semiconductor position detecting device (PSD) 1 detects the reflected light from the body to be measured. The output current of this PSD 1 is supplied to a logarithmic compressing circuit 15, whose output is supplied to an arithmetic circuit 16 and a voltage comparing circuit 17 in common. This circuit 17 is supplied with the output reference voltage of a reference voltage generating circuit 18 and compares it with the output voltage of the circuit 15 to outputs a voltage corresponding to their difference. Then when the measuring operation is not performed, a switch circuit 19 is on, the output of the PSD 1 is a photocurrent irrelevant to the distance measuring operation, and the output voltage of the circuit 15 is held constant. When the measuring operation is performed, on the other hand, the circuit 19 turns off and a photocurrent based upon the reflected light from the body to be measured flows together with the constant photocurrent irrelevant to the distance measuring operation and the circuit 16 performs proper arithmetic operation for those outputs, thereby finding the distance to the object body. |
