| 摘要 |
An amplitude variation detection circuit that can reliably detect the mirror portion independently of the type of optical recording medium, as well as a type of information regenerating apparatus that contains said amplitude variation detecting circuit. Voltage division of top envelope signal Ste and bottom-hold signal Sbh of RF signal Srf is performed by voltage divider ( 16 ); then, after amplification by gain control amplifier ( 19 ) with a gain that corresponds to the type of optical disc ( 1 ), a prescribed offset is added by offset circuit ( 22 ) to the signal, and the resulting signal is input as mirror detection threshold signal Smt to comparator ( 24 ). The high-frequency noise component of bottom envelope signal Sbe of RF signal Srf is removed by low-pass filter ( 21 ); after amplification by gain control amplifier ( 20 ) with a gain that corresponds to the type of optical disc ( 1 ), the signal is input to comparator ( 24 ). Depending on the result of the comparison of the level of said amplified bottom envelope signal S 4 with that of mirror detection threshold signal Smt, mirror detection signal Sm is generated.
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