Patent ID: 6838934

Claim:
A feedforward amplifier comprising: a distortion detection circuit which includes a main amplifier for amplifying an input signal and detects a nonlinear distortion produced by said main amplifier; and a distortion elimination circuit which includes a first auxiliary amplifier for amplifying the distortion component detected by said distortion detection circuit and cancels the distortion component by injecting the amplified distortion component into the output from said main amplifier; wherein said distortion elimination circuit constitutes a dual loop including a first auxiliary amplifier distortion detection circuit for detecting a nonlinear distortion produced by said first auxiliary amplifier and a first auxiliary amplifier distortion elimination circuit which has a second auxiliary amplifier for amplifying the distortion component detected by said first auxiliary amplifier distortion detection circuit and cancels the distortion component of said first auxiliary amplifier by injecting the amplified distortion component into the output from said first auxiliary amplifier; wherein said distortion detection circuit includes first electrical variable attenuator means and first electrical variable phase shifter means inserted in the input path of said main amplifier; wherein said distortion elimination circuit includes second electrical variable attenuator means and second variable phase shifter means inserted in the input path of said first auxiliary amplifier; wherein said first auxiliary amplifier distortion elimination circuit includes third electrical variable attenuator means and third electrical variable phase shifter means inserted in the input path of said second auxiliary amplifier; wherein said first auxiliary amplifier distortion detection circuit includes fourth electrical variable attenuator means and fourth electrical variable phase shifter means inserted in the input path of said first auxiliary amplifier; and said feedforward amplifier further comprising control means which controls said first variable attenuator means, said first variable phase shifter means, said second variable attenuator means, said second variable phase shifter means, said third variable attenuator means, said third variable phase shifter means, said fourth variable attenuator means and said fourth variable phase shifter means to effect balance control of said distortion detection circuit, said distortion elimination circuit, said first auxiliary amplifier distortion detection circuit and said first auxiliary amplifier distortion elimination circuit.