Patent ID: 6285257
Filing Date: 2001-09-04
Classification: H03F,H03G

Abstract:
A feedback type variable gain amplifier comprising:a first inductor and a first field effect transistor connected in series across a power-supply potential terminal and a ground potential terminal, the one end of said first inductor connecting to the power-supply potential terminal, the one end of said first field effect transistor connecting to the ground potential terminal, the gate of said first field effect transistor being used as a signal input terminal, and the other end of said first field effect transistor being used as a signal output terminal;a second inductor, a second field effect transistor and a capacitor connected in series between the drain and the gate of said first field effect transistor; anda resistor connected between the drain and the source of said second field effect transistor;wherein the values of the inductance of said second inductor and the capacitance of said capacitor are set to proper values so that the phase difference between the signal input to the gate of the first field effect transistor and the signal fedback to the gate of the first field effect transistor goes through said second inductor, and said second field effect transistor and said capacitor is approximately 180.degree. when the value of the resistance between the drain and the source of said second field effect transistor is set to a minimum value by controlling the voltage applied to the gate of said second field effect transistor.