| 摘要 |
PROBLEM TO BE SOLVED: To provide a current-voltage conversion circuit used for the data reproduction from a recording medium such as an optical disk, capable of realizing the high speed and sure read-out of the information recorded on recording medium having the different optical property at the time of reproduction and also capable of inexpensively manufacturing, and to provide a pickup head device using this circuit. SOLUTION: The current-voltage conversion circuit 51a wherein a current signal outputted from a photodetecting part outputting the current signal corresponded to the light quantity of the received reflection light of laser beams emitted on the recording medium at the time of data reproduction with respect to the recording medium such as the optical disk is received and converted into the voltage signal, is furnished with a differential amplifier consisting of transistors Q1, Q2 subjected to negative feedback, current sources I1, I2 making two kinds of idling currents flow into the differential amplifier, and switches SW1, SW2 to change over the current sources I1, I2 for changing over the idling currents made to flow into the differential amplifier in accordance with the intensity of the signal outputted by the photodetecting part or the reflectivity of the recording medium.
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