| 摘要 |
PURPOSE:To hold an objective lens in a focus position without fail by compensating and amplifying a focus error detecting signal, applying it to an actuator, constituting a focus servo system and controlling an RF detecting signal from a test track in maximum. CONSTITUTION:A difference between focus error detecting signals (b) and (c) is taken by a differential amplifier circuit 1, and a focus error signal (f) corresponding to the deviation from the focus position of the objective lens 6 can be obtained. Said signal (f) is applied to the actuator 5 through a compensating and amplifying circuit 2, an adder circuit 3 and an electric power amplifier circuit 4 so as to constitute a focus control system, and the signal (f) controls the objective lens 6 so as to maintain the focus position. On the other hand, the reproduction RF signal (a) of the test track is envelop-detected by an envelop detecting circuit 8, and its output signal (g) is A/D-converted 9 and read in as an RF signal level in a microcomputer 10, which converts a value to be outputted to a D/A converter 11 so that the RF signal level can be maximized. The output of said converter 11 is applied to an adder 3 and controls the focus servo system. |
