| 摘要 |
PURPOSE:To perform highly accurate tracking control, by deriving the squared difference of the high frequency component of each light quantity detected at each pair produced by dividing a quartering photodiode with one dividing line X and passing the demodulated signals through a low-pass filter, and then, outputting the signals as tracking error signals. CONSTITUTION:The output of the 1st or 2nd signal wave pickup device, namely, a high frequency component A or B which is obtained by cutting off the DC component of a sum a+b or c+d of the light quantities of each diode (a) and (b) or (c) and (d) forms a signal wave having a positive and negative values in such a way that the vibration center of the A or B changes at a relatively low frequency while vibrating at a relatively high frequency. A<2> or B<2> obtained as a calculated result of a multiplier 20 is the size of the amplitude of the positive or negative vibrating high frequency component A or B and A<2>-B<2> represents the squared difference in amplitude. This squared difference in amplitude A<2>-B<2> also changes at a low frequency while vibrating at a high frequency and, when the changed part at a low frequency is fetched out by a low-pass filter, the fetched one is a tracking error signal. |
