| 摘要 |
PROBLEM TO BE SOLVED: To provide a current amplifier circuit which produces a precise ratio current even if an input current becomes very weak and in which a bias current cancel circuit is unnecessary, and a servo error signal producing circuit which uses the current amplifying circuit. SOLUTION: This current amplifier circuit is constituted of two bias circuits 101, 102 which are constituted of two signal input terminals T101, T102, MOS transistors M102, M105 which set the signal input terminals to be specified voltages, and current sources I101, I102, two logarithmic compression circuits 103, 104 which are constituted of a first voltage source E101 connected with the bias circuits in common and bipolar transistors Q101, Q104 for performing logarithmic compression of input signal currents, two reverse logarithmic expansion circuits 105, 106 which are constituted of bipolar transistors Q103, Q106 for performing reverse logarithmic expansion of output signals of the logarithmic compression circuits, a first current source I103 which is connected with the reverse logarithmic expansion circuits in common, and two signal output terminals T103, T104 which are connected with output of the respective reverse logarithmic expansion circuits.
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