High-frequency amplifier

Abstract

A high-frequency module, includes a circuit substrate, a first transistor having a source connected to ground; a second transistor forming a cascode circuit with the first transistor; a series circuit connected between a gate of the second transistor and the ground, the series circuit being formed by a first resistive element and a series resonant circuit connected in series with each other; and a second resistive element connected in parallel to the series circuit. The first transistor, the second transistor, the series circuit and the second resistive element are arranged on the circuit substrate.

What is claimed is: 
     
         1 . A high-frequency module, comprising:
 a circuit substrate;   a first transistor having a source connected to ground;   a second transistor forming a cascode circuit with the first transistor;   a series circuit connected between a gate of the second transistor and the ground, the series circuit being formed by a first resistive element and a series resonant circuit connected in series with each other; and   a second resistive element connected in parallel to the series circuit,   wherein the first transistor, the second transistor, the series circuit and the second resistive element are arranged on the circuit substrate.   
     
     
         2 . The high frequency module according to  claim 1 , wherein the high-frequency module satisfies 1/gm<R 1  R 2 ≦30/gm, provided that resistance values of the first and second resistive elements are R 1  and R 2 , respectively, and transconductance of the second transistor is gm. 
     
     
         3 . The high-frequency module according to  claim 2 , wherein the series resonant circuit is formed by an LC circuit, and the series circuit includes the first resistive element between LC elements. 
     
     
         4 . The high-frequency module according to  claim 3 , comprising:
 a plurality of series circuits each having different LC element values,   wherein each of the series circuits is connected between the gate of the second transistor and the ground.   
     
     
         5 . The high-frequency module according to  claim 4 , comprising:
 a plurality of series circuits each having different LC element values,   wherein each of the series circuits is connected between the gate of the second transistor and the ground.   
     
     
         6 . The high-frequency module according to  claim 2 , wherein the first transistor is a GaAs MESFET or a GaAs hetero junction FET and the second transistor is a GaN FET.