| 摘要 |
The present invention enables to stably output an optical beam. The present invention provides an upper limit value comparator for comparing a low bandwidth signal according to an output intensity of an optical beam emitted to an optical disk in the case of reproducing data from the optical disk with an upper limit value, a lower limit value comparator for comparing the low bandwidth signal with the lower limit value smaller than the upper limit value, and an up-down counter for decreasing the counter value from the counter value immediately before when the low bandwidth signal is larger than the upper limit value, increasing the counter value from the counter value immediately before when the low bandwidth signal is smaller than the lower limit value and holding the counter value at the counter value immediately before when the low bandwidth signal is smaller than the upper limit value and larger than the lower limit value.
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