Patent ID: 6639469
Filing Date: 2003-10-28
Classification: H03G

Abstract:
A variable-gain amplifier circuit comprising:an adjustable impedance circuit part including a bipolar transistor having a base connected to a control terminal for receiving a controlled bias voltage, one of a collector and an emitter of said bipolar transistor being connected to a first power supply terminal, and the other of said collector and said emitter of said bipolar transistor being connected to a second power supply terminal through a diode located in a forward direction to said second power supply terminal; and a variable-gain amplifying circuit part having an amplifying circuit having an input coupled to an input terminal for receiving an input signal and an output connected to an output terminal, wherein a connection point between said bipolar transistor and said diode is connected through a DC blocking capacitor to said input of said amplifying circuit, and wherein the diode is located in a forward direction when an anode of the diode assumes a higher potential than the cathode.