Patent ID: 7602247

Claim:
A variable gain amplifier comprising: a first power supply terminal arranged to be connected to a first end of a power supply; a second power supply terminal arranged to be connected to a second end of the power supply; a transconductance amplifier including a first initial stage transistor having an emitter, a base and a collector, a second initial stage transistor having an emitter connected to the emitter of the first initial stage transistor at a node, a base and a collector, and an output terminal for outputting a current corresponding to a difference between a potential of the base of the first initial stage transistor and a potential of the base of the second initial stage transistor; a first PN junction element having a first end connected to the base of the first initial stage transistor and a second end; a second PN junction element having a first end connected to the base of the second initial stage transistor and a second end connected to the second end of the first PN junction element; a voltage drop element connected between the second end of the first PN junction element and the first power supply terminal; a first resistor connected between the base of the second initial stage transistor and a first signal source serving which is a voltage source; a current-generating transistor having a collector connected to the base of the first initial stage transistor, a base connected to the first signal source, and an emitter; a second resistor connected between the emitter of the current-generating transistor and the second power supply terminal; and a current mirror connected to the node, the current mirror allowing a current to flow to the node, the current being identical to a current flowing from a second signal source which is a current source.