Patent ID: 7230897

Claim:
A defect detection device comprising: an amplification section for amplifying a reflection signal corresponding to the intensity of light reflected from an optical disc irradiated with a light beam, with a gain corresponding to a control signal indicating which is performed, recording or playback, for the optical disc, and outputting the amplified signal; an envelope detection section for obtaining an envelope of the output of the amplification section and outputting the obtained envelope; a first pulse generation section for outputting a pulse of a predetermined length when the level of the control signal changes; an integration section for integrating the output of the envelope detection section and outputting the integrated results; a differential signal generation section for receiving the output of the envelope detection section as a first input signal and the output of the integration section as a second input signal, generating a differential signal corresponding to a difference between the first input signal and the second input signal, and outputting the generated differential signal; and a comparison section for comparing the output of the differential signal generation section with a predetermined value, and outputting the results as a defect detection signal indicating the presence/absence of a defect, wherein the second input signal of the differential signal generation section is changed so as to reduce the possibility that the defect detection signal may indicate the presence of a defect during the time period for which the first pulse generation section outputs a pulse.