| 摘要 |
PURPOSE:To provide a device for detecting light quantity of each beam of a multi-beam optical pickup with high accuracy. CONSTITUTION:This device is provided with a bisected photodetector 1 receiving the sum of the light quantity of two beams from a light source, an I-V converting circuit 6 for detecting the light quantity of a low power beam 2 among the two beams, a sample-and-hold circuit 8 connected to the relevant I-V converting circuit 6 and an I-V converting circuit 7 for detecting the light quantity of a high power beam 3 between the two beams. The device comprizes a sample-and-hold circuit 9 connected to the I-V converter circuit 7 and a differential amplifier 10 for calculating a difference between the output of the I-V converting circuit 7 and the output of the sample-and-hold circuit 9, the gain of the I-V converting circuit 6 is made larger than that of the I-V converting circuit 7, both sample-and-hold circuits 8, 9 are made to be a sampling mode when only the low power beam is turned on, the light quantity of the low power beam is obtained from the output of the sample-and-hold circuit 8 and the light quantity of the high power beam is obtained from the output of the differential amplifier 10. |
