Mirror detection signal generator

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 S4 with that of mirror detection threshold signal Smt, mirror detection signal Sm is generated.