| 摘要 |
PROBLEM TO BE SOLVED: To facilitate the design of a circuit in the succeeding stage of an optical disk reproducing device and to improve the operability by setting the gain control sensitivity of a gm amplifier to be approximately equal in a range, where the control voltage input of a current control circuit is lower than a reference potential and in a range where this control voltage input is higher with respect to. SOLUTION: A head amplifier 12, which amplifies the output signal of an optical pickup 11 and a gain variable RF amplifier 20 which amplifies the output signal of the head amplifier 12 and is automatically controlled, so as to output a signal having a prescribed fixed amplitude are provided, and the gain variable RF amplifier 20 is provided with a current control circuit 30, which has the current output changed according to function different between the range, where the control voltage input is lower than the reference potential and the range where this control voltage is higher, and a gm amplifier. In the gm amplifier, the collector current of a transistor for amplification is controlled by the current output of the current control circuit 30 to change gm, and the gm amplifier has approximately equal gain control sensitivities in both the range, where the control voltage is lower than the reference potential and the range where the control voltage is higher.
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