| 摘要 |
PURPOSE:To obtain a focusing error signal not to be diffracted by a guide groove by forming the focusing error signal only by reflected light from a land when a condenser spot crosses the guide groove by utilizing the fact that the condenser spot on the land is not widely diffracted like the condenser spot on the guide groove. CONSTITUTION:An information carrier 6 composed of a guide groove 8 and a land 26 is irradiated with a condenser spot 7 and the output waveform of an adder amplifier 21 is changed by diffraction when crossing the guide groove 8. Next, the output waveform is compared with a certain threshold value Vth by a comparator 22 and it is discriminated whether the spot is on the guide groove 8 or the land 26. In such a case, when the spot 7 is on the land 26, an 'H' level is set and when the spot 7 is on the groove 8, an 'L' level is set. The pulse of certain fixed width T is generated from a pulse generator 23 synchronously with rise from 'L' to 'H' and a focusing error signal 17 of the spot 7 is outputted from a differential amplifier 16. Afterwards, only the output of the land 26 is held by an S/H circuit 24 and the error signal is obtained without ripple 18 caused by the groove 8. |
