| 摘要 |
PROBLEM TO BE SOLVED: To make performable mirror detection stably for both CD and DVD having different OFF track level/ON track level ratio of mirror signal being generated depending on the presence/absence of a track when an optical pickup traverses a disc due to difference of track pitch. SOLUTION: In order to detect the mirror signal of an RF signal SRF, the RF signal SRF is subjected to a bottom detection, respectively, through high speed and low speed bottom detection circuits 1, 2 to produce signals S1, S2 which are then inputted to a variable gain amplifier type subtractor 3 to perform a subtraction and only a mirror signal S4 is taken out. A DVD/CD control circuit 21 switches the gain depending on a disc such that the signal S3 has a substantially equal output amplitude for the DVD and CD. Output amplitude of the substractor 3 is detected by a maximum/minimum value detection circuit 22 and an operating unit 23 generates an intermediate value signal S4. A stabilized mirror detection signal S5 can be outputted by comparing the output S3 from the substractor 3 with a comparison point, i.e., the voltage of the signal S4.
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