| 摘要 |
PURPOSE:To eliminate deviation of a lens and to ensure stable signal quality by providing a switch for on/off controlling offset voltage to be added to output of an AGC circuit and a summing amplifier. CONSTITUTION:Reflected light from a medium is photoelectric converted by a bisectional light detector 1, and each output of the bisectional light detector 1 is inputted to a differential amplifier 4 and a summing amplifier 5 through a pre-amplifiers 2, 3. When an addition signal is '1', a switch 12 becomes on, voltage V1 is added by a summing amplifier 8 to an output signal sent out from an AGC circuit 7 to a signal line 11. Thereby, the focus point at reproduc tion power is shifted to a point G. When recording instruction is '1', and a write gate signal E is '0', output of the summing amplifier 8 becomes output signal of the AGC circuit +V1, and when the recording instruction D is '1' and a write gate signal E is '1', the output becomes the output signal of the AGC circuit 7 +0(V). As the value of V1 is set equal to voltage of A-C, the signal becomes a stable signal not influenced by shifting of the focus point. |
