| 摘要 |
PURPOSE:To attain the stable detection of a focus with no dependence on an optical recording medium by detecting the DC component of a focus error signal when the focus is detected and then subtracting the DC component from the focus error signal. CONSTITUTION:Both photodetectors 1 and 2 are set adjacent to each other at a position 1/2q (q: standardized pitch of recording track). At the same time, photodetectors 3 and 4 are set adjacent to each other at a position y=-1/2q. The outputs of these photodetectors 1-4 are referred to as S1-S4 respectively. A switch SW1 is closed when no tracking control is carried out. Then the DC component of a signal (S1+S4)-(S2+S3) supplied from a terminal T1 is detected by a DC component detecting circuit 22 and held by a holding circuit 23. When the tracking control is started, the switch SW1 is opened. Thus the DC component held by the circuit 23 is subtracted from the signal (S1+S4)-(S2+S3) by a subtraction circuit 23. As a result, a focus error signal free from the DC component is obtained from the circuit 24. This secures the stable detection of a focus. |
