US Patent 6873208 High-frequency amplifier

A high-frequency amplifying unit 2 in which a steep gain variation developed according to a change in the amplitude of input high-frequency signal is suppressed is provided. It amplifies an input high-frequency signal with a plurality of transistors 12-1 to 12-N at the same time a measuring circuit 27 measures amplitude of the input high-frequency signal, and a bias control circuit 26 continuously controls a bias applied to each transistors 12-1 to 12-N according to the value of amplitude measured by the measuring circuit 27. Thus it is possible to suppress a steep gain variation produced according to a variation in the amplitude of input high-frequency signal.