| 摘要 |
PURPOSE:To prevent the noise which is generated due to the effect of bits by delaying one of the outputs of two divided photodetectors and performs a subtraction between these two outputs. CONSTITUTION:In case a delay circuit 5 is not connected, the noise equivalent to 2.DELTAt are generated by a time difference DELTAt between output changes of adders 2 and 3 at the rise and fall positions of the bit for the output of a subtractor circuit 4, i.e., a focus error signal FE when the output of an output adder circuit 3 of photodetectors 1c and 1d is subtracted from the output of an output adder circuit 2 of photodetectors 1a and 1b. Therefore the output waveform of the circuit 2 is delayed by DELTAt by setting the delay time at DELTAt after connecting the circuit 5. Thus no noise is produced to the signal FE. |
