Semiconductor amplifying circuit having improved bias circuit for

Abstract

A semiconductor amplifying circuit of the present invention comprises: an amplifying field effect transistor device having a gate supplied with an input signal and a drain for outputting an amplified output signal; and a bias circuit for supplying a bias voltage to said gate of said amplifying transistor device. The bias circuit includes: a first bias voltage generator having a first dummy field effect transistor device formed on a same substrate as said amplifying transistor device is formed, and a voltage feedback bias circuit for supplying a bias voltage to a gate of said first dummy transistor device; and a second bias voltage generator for supplying a lower potential to said voltage feedback bias circuit when a drain current of said field effect transistor device increases, and supplying a higher potential to said voltage feedback bias circuit when said drain current decreases. A gate voltage of said first dummy transistor device is supplied as a bias voltage to said gate of said amplifying transistor device. The power supply can be applied directly to the drain of the amplifying transistor so as to maximizing the transistor performance.