| 摘要 |
PROBLEM TO BE SOLVED: To provide an amplitude variation detection circuit which can stably detect a mirror part, independent of the kind of an optical recording medium, and an information reproducing apparatus having the same. SOLUTION: A top envelope signal Ste of an RF (radio frequency) signal Srf and a bottom hold signal Sbh, of which the voltages are divided by a voltage dividing circuit 16, are added to a prescribed offset at an offset circuit 22 after being amplified by a gain control amplifier 19 with the gain according to the kind of an optical disk 1, and inputted to a comparator 24, as a mirror detection threshold signal Smt. A bottom envelope signal Sbe of the RF signal Srf, of which the high-frequency noise component is removed by a low-pass filter 21, is inputted to the comparator 24 after being amplified by a gain control amplifier 20 with the gain according to the kind of the optical disk 1. A mirror detection signal Sm is generated according to the comparison result of the level of the amplified bottom envelope signal S4 with that of the mirror detection threshold signal Smt.
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