Patent ID: 7570119

Claim:
A cascode-connected amplifier circuit comprising: a first transistor having a grounded emitter or a first field-effect transistor having a grounded source; (a) a second transistor, having a grounded base, which is cascode-connected to the first transistor or to the first field-effect transistor, or (b) a second field-effect transistor, having a grounded gate, which is cascode-connected to the first transistor or to the first field-effect transistor; a selecting unit causing a collector of the first transistor or a drain of the first field-effect transistor to be grounded; a first voltage control unit controlling a voltage to be applied to the base of the second transistor or to the gate of the second field-effect transistor, wherein: the first voltage control unit controls a voltage to be applied to the base of the second transistor while the selecting unit grounds the collector or the drain, so as to reduce a current flowing through the second transistor, or the first voltage control unit controls a voltage to be applied to the gate of the second field-effect transistor while the selecting unit grounds the collector or the drain, so as to reduce a current flowing through the second field-effect transistor, and wherein the first voltage control unit operates before the selecting unit grounds the collector or the drain, so as to reduce in advance the voltage to be applied to the base of the second transistor or to the gate of the second field-effect transistor.