| 摘要 |
<p>PURPOSE:To accurately detect a light position by subtracting a leak current component from the current output of a light position detecting element and extracting only a real photocurrent. CONSTITUTION:On the main surface of a semiconductor substrate 1, n type island areas 3a and 3b are formed. The pn junction of a leak current compensating element 21 is also biased reversely with a voltage which is almost VCC/2, but a photodetection surface is covered with a light shield film 19, so only leak currents are led out of its electrodes 9a and 10b. The leak currents flow to primary-side transistors(TR) 23 and 26 in current mirror circuits 22 and 25 and the same leak currents also flow to secondary-side TRs 24 and 25. The collectors of the TRs 24 and 27 are connected to electrodes 9 and 10 of a light position detecting element 11, so the leak currents flowing to the TRs 24 and 27 are subtracted from output currents I1 and I2 of the element 11. Consequently, only the real photocurrent is led out of the element 11 as a current for the projection position arithmetic of light. The projection position of the light is therefore detected with accuracy without any error.</p> |
