Patent ID: 6891405

Claim:
A variable gain amplifier comprising: a first differential amplifier circuit and a second differential amplifier circuit supplied with a common input signal first and second current sources; a combining circuit for combining output signals of said first differential amplifier circuit and said second differential amplifier circuit wherein, said first differential amplifier circuit and said second differential amplifier circuit each including a first transistor and a second transistor forming a differential pair, said first transistor and said second transistor having bases supplied with said input signal and collectors outputting signals to said combining circuit, and said first differential amplifier circuit and said second differential amplifier circuit having amplification degrees different from each other, wherein in the second differential amplifier a first resistor is connected between the first transistor and the second current source and a second resistor is connected between the second transistor and the second current source; and a current control circuit for changing a ratio between the current of the first current source of said first differential amplifier circuit and the current of the second current source of said second differential amplifier circuit based on a gain control signal, said current control circuit having a constant current source and a third resistor are series connected to the collector of a third transistor.