Radio frequency amplifier with reduced intermodulation distortion

A method of amplifying a signal, comprising:

• receiving an input radio frequency signal at the base of an input transistor coupled to an output transistor in a cascode configuration, the input transistor having an emitter degeneratively coupled to a reference point through a series inductive circuit;
• amplifying the input signal to provide an output signal at the collector of the output transistor;
• and
• rejecting third order intermodulation distortion products at the output transistor by feeding the output signal back to the input transistor through a shunt capacitive feedback network characterized by an impedance of substantially zero resistance and non-zero reactance.

An apparatus configured to amplify a signal, comprising:

• first and second amplification stages, wherein each amplification stage comprises
• an input transistor and an output transistor coupled together in a cascode configuration with the base of the input transistor defining an input of the amplification stage and the collector of the output transistor defining an output of the amplification stage,
• a shunt capacitive feedback network coupled between the input and the output and characterized by an impedance of substantially zero resistance and non-zero reactance the network configured to reject third order intermodulation distortion products and
• a series inductive feedback network coupled between the base of the input transistor and a reference point and consisting essentially of inductive reactance;
• wherein the inputs of the amplification stages are coupled together to form an input of the apparatus, and the outputs of the amplification stages are coupled together by an isolator.