| 摘要 |
PURPOSE:To detect a locked-track with extremely simple costitution by detecting the locked-track according to the level of a reproduction signal by a pickup. CONSTITUTION:The sums of outputs of the counter elements 1a and 1b, and 1c and 1d of a photodetector 1 are supplied to two inputs of a differential amplifier 2, whose output (a) is a focus servo error signal. An in-focus detector 6, when the signal (a) exceeds a certain level, generates and supplies a low-level defocusing detection signal (d) to one input of an AND gate 7. Further, the total of the outputs of the photodetector 1 is obtained by an amplifier 8 to generate a reproduction RF signal (b), and an RF envelope level detector 9 generates a high-level detection signal (c) when said signal has a low level within prescribed level range. This signal (c) is supplied to the other input of the gate 7, whose gate output (e) is used as a locked-track detection signal to drive a locked-track resetting circuit 30, and also used as a control signal for a gain control amplifier 3. |
