| 摘要 |
PURPOSE:To attain stable and sure tracking servo operation by providing a means extracting an envelope component of a reproducing signal, a means generating a binary error signal, a means holding a level of the error signal and a means amplifying a signal component corresponding to the holding state. CONSTITUTION:An output summing signal (a+b) from photodetecting regions (a, b) of a photodetector 17 and an output summing signal (c+d) from photode tector regions (c, d) are added by an adder circuit 22 to generate an RF signal being a reproducing signal. The signal connects to a non-inverting input termi nal (+) of a comparator circuit 24 via an envelope detection circuit 23 and reference voltage Es outputted from a constant voltage source 25 is fed to an inverting input terminal (-) of the comparator circuit 24. On the other hand, an output terminal of the said subtraction circuit 18 connects to the inverting input terminal (-) of a subtraction circuit 26, connects to a non- inverting input terminal (+) of the subtraction circuit 26 via a sample-and-hold circuit 27 and an amplifier circuit 28, and an output terminal of the subtraction circuit 26 connects to an input terminal of a phase compensation circuit 19.
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