| 摘要 |
PURPOSE:To attain stably servo lock-in in a short time by using an output signal via a phase shift circuit of an error signal in zero cross detection of a tracking error signal to synchronize the phase of an output signal of an equalizer of servo loop with the switching timing phase of the servo loop. CONSTITUTION:An output signal from a low pass filter LPF16 is inputted to a zero cross comparator D1 via a high pass filter HPF circuit comprising a capacitor C2 for AC coupling and a resistor R3 and both edge pulses of leading and trailing of the comparator are extracted by a resistor R4, a capacitor C4 and an exclusive OR gate G1 to obtain a zero cross edge pulse G. The phase is advanced by nearly 45 deg. at the cut-off frequency fc in the phase characteristic of the HPF circuit. Thus, in selecting the fc in such characteristic equal to the frequency having the maximum phase shift amount of 45 deg. in the phase characteristic of the equalizer 12, the phase shift amount of an output F of a phase shift circuit 19 and of an output E of the equalizer 12 is made nearly identical.
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