| 摘要 |
PURPOSE:To attain the miniaturization at low cost by providing a current switch controlling the bias current of a preamplifier converting a current signal into a voltage signal so as to apply DC coupling between the preamplifier and an equalizing amplifier thereby reducing the number of components. CONSTITUTION:An input current signal is inputted from an input terminal 10 and converted into a voltage signal by a preamplifier 1 comprising transistors (TRs) Q1, Q2, a collector resistors 101, 102, an emitter resistor 104 and a feedback resistor 103 and inputted to the equalizing amplifier 4, to which a reference voltage 31 is also inputted and its output is supplied as a prescribed amplitude signal from terminals 41, 42. An offset of the output signal is detected by an offset detector 5 to activate a current switch 7 via the amplifier 6. The switch 7 adjusts the bias current of the collector resistor of the output TR Q2 of the preamplifier 1 to compensate the offset. |
