| 摘要 |
PROBLEM TO BE SOLVED: To provide a trans-impedance type preamplifier where fluctuation in a feedback resistance due to dispersion in the threshold level is suppressed. SOLUTION: The preamplifier 3 for optical reception having an inverting amplifier circuit 1 and a feedback resistor 2 consisting of a transistor(TR) connecting in parallel with the inverting amplifier circuit 1 is provided with a dummy TR4 the same type of the TR configuring the feedback resistor 2, a reference resistor 5, 1st and 2nd current sources 6, 7, a level shift circuit 10 and an operational amplifier 8. Then outputs of 1st and 2nd current sources 6, 7 are given to the dummy TR4 and the reference resistor 5, a difference voltage between voltage drops of the dummy TR4 and the reference resistor 5 is given to the operational amplifier 8 and the operational amplifier 8 controls a gate voltage of the dummy TR4 and the TR of the feedback resistor 2 so that the voltage drop of the dummy TR4 and that of the reference voltage are equal to each other through the level shift circuit 10. |
