| 摘要 |
PURPOSE:To exclude the effect of a pit and to improve the accuracy by extracting an error signal obtained from the condensed light spot while being reflected only at a part on the recording medium where no pit exists and obtaining a focusing error signal through a smoothing circuit. CONSTITUTION:A focusing error detector consists of an adder circuit 16a of photodetectors 6a, 6b, an adder circuit 16b of photodetectors 6c, 6d, an adder circuit 17 obtaining an RF signal 24 and a subtraction circuit 18 obtaining the focusing error signal. Then a comparator 19 inputting a part of the RF signal 24 uses a signal at a land 11 and generates a pulse. Then the focusing error signal of the subtractor circuit 18 is led to a gate circuit 20, sampled by an output of the comparator 19 and inputted to a low-pass filter 21 and an amplifier 22, then the focusing error signal 23 with high accuracy while excluding the effect of the recording pit 10 is obtained. |
