| 摘要 |
The invention relates to a playback apparatus for retrieving information from an information carrier ( 2 ). The information has been recorded on the information carrier ( 2 ) in the form of variations of a first physical parameter. The playback apparatus scans the information carrier by means of a transducer ( 4 ), which is responsive to said variations of said physical parameter. An information recovering circuit ( 5 ) recovers the information from a first detection signal (D 1 ) received from the transducer ( 4 ). The information recovering circuit ( 5 ) comprises a phase-locked loop ( 51 ). The information carrier ( 2 ) exhibits a second variation of a second physical parameter, which differs from said first physical parameter but which is detectable by means of said transducer ( 4 ). A detection circuit ( 6 ) detects the presence of the second variation on the basis of a second detection signal (D 2 ) received from the transducer ( 4 ). The idea of the invention is that the detection circuit ( 6 ) is capable of using the phase-locked loop ( 51 ) of the information recovering circuit ( 5 ) to detect the presence of the second variation. The invention can be implemented very easily in, for example, DVD players to detect the presence of an information carrier ( 2 ) with DVD+RW format or an information carrier ( 2 ) with DVD-RW format. Only switching means ( 7 ) and some minor electronics have to be added; there is no need for an additional phase-locked loop. |
