| 摘要 |
<p>A radio frequency signal is read out from a disk by using a pickup controlled by a servo circuit (10), and the servo circuit generates servo control signals (FCNY, TCNT) on the basis of an error signal (FER, TER) obtained from the radio frequency signal. Envelope detection means (23) generates an envelope signal (EVP) which follows up the change of a peak value of the radio frequency signal. Comparison means (5) compares the envelope signal with a reference level, detects dropouts of the radio frequency signal due to scratches, etc., and inputs the period of each dropout to the servo circuit as a flaw detection signal (DET) to compensate for the servo control signal during that period. The envelope detection means includes means for switching a detection time constant at the time of the detection of the change of a peak value of the radio frequency signal, reduces the detection time constant so as to let the envelope signal satisfactorily follow up the dropout period of the radio frequency signal when the radio frequency signal is high, and improves accuracy of the flaw detection signal so as to prevent track jump and focus fall at the time of information readout.</p> |
