| 摘要 |
<p>PURPOSE: To compensate for a sensitivity drop and a positional detection error resulting from a dark current increase due to a temperature rise by subtracting a dark current level with a light emitting element turned off from an output signal level with the element turned on. CONSTITUTION: A light emitting diode D1 is turned on with a light emitting diode control means, and signal current outputted from an optical position detection element (PSD) 11 is detected for the conversion thereof into current via a current-voltage converter 22. The current so obtained is sent to an arithmetic operation circuit 41 via an A/D conversion process 42, and stored in a memory (44a and 44b). Also, the diode D1 is turned off and dark current outputted from the PSD 11 is detected. Then, the dark current so detected is converted to voltage through the converter 22, and a signal therefor is sent to the circuit 41 via the process 42 and stored in the memory 44. In this case, an operation for turning on and off the diode D1 is repeated over the preset period, according to an instruction from a microcomputer section 4. Also, both the output signal level and the dark current level stored in the memory 44 are read out, and the dark current level is subtracted from a corresponding output signal level, thereby providing a net signal level.</p> |
