| 摘要 |
PURPOSE:To provide a computing circuit for computing a height of an object to be measured from an incident position where a reflected light from the object to be measured to which a laser beam is irradiated is incident upon a position detecting element, by providing means for precisely obtaining the height while preventing a circuit element having a linear characteristic from being saturated due to variations in the quantity of light incident upon the position detecting element. CONSTITUTION:A compression circuit such as a root amplifier 21 or a log circuit is connected to amplifiers 11, 12 connected to output terminals 8, 9 of a position detecting element 7, and output voltages Va, Vb based upon detected currents Ia, Ib detected at output terminals 8, 9 are compressed so as to compute a height Z by means of computing parts 22, 23, 24. |
