| 摘要 |
PURPOSE:To reduce an off-set-voltage generated by a servo system and to prevent the bad influence by providing the low-pass area frequency attenuating means of the feed back signal to respective feed back circuits. CONSTITUTION:Between the output side of a tracking phase compensating circuit 3 and a switching circuit 4, an operational amplifying circuit 21 is provided and between this and the input side of the circuit 3 (the first output side of an RF amplifier 2,) a low-pass component detecting circuit 22 is provided. When a tracking error signal TE is given from the circuit 2 to an LPF22d of the circuit 22, the low area frequency component of a signal VTR is taken out and inputted to the non-inverting terminal of an operation amplifier 22d1 and the output VTO of an operational amplifier 21 is inputted through an LPF22e to the non-inverting terminal of an amplifier 22f1 and a difference is taken and inputted to the inverting terminal of the amplifier 21 as a negative feed back signal. An output VTC from the phase compensating circuit 3 is supplied to the non-inverting terminal and a negative feed back is loaded to a signal VTC. Since the enough negative feed back is loaded below a cut-off frequency, in the output side of the operational amplifier 21, an output signal VTO whose off-set voltage is reduced is obtained.
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