GAIN VARIABLE AMPLIFIER AND OPTICAL RECEIVER USING THE SAME

PROBLEM TO BE SOLVED: To provide a low power and wide band gain variable amplifier whose band can be prevented from being decreased even at the time of changing a gain. SOLUTION: A gain variable amplifier is provided with transistors Q1 and Q2 whose emitters are connected through a resistance to each other, and connected to a power source, transistors Q3 and Q5 whose collectors are connected to one input of a load circuit LD, transistors Q4 and Q6 whose collectors are connected to the other input of the load circuit LD, resistances Rc1 and Rc2 whose one edges are respectively connected to the emitters of the transistors Q3 and Q4, and resistances Rc3 and Rc4 whose one edges are respectively connected to the emitters of the transistors Q5 and Q6. In this case, the other edges of the resistances Rc1 and Rc2 are connected to the collector of the transistor Q1, and the other edges of the resistances Rc3 and Rc4 are connected to the collector of the transistor Q2, and a gain control signal Vcont is impressed to the bases of the transistors Q3-Q6, and an input signal is impressed to the bases of the transistors Q1 and Q2.