Patent ID: 7772925

Claim:
Amplifier apparatus having an operating frequency in the radio frequency or microwave or higher ranges comprising: a pre-distorter for a power amplifier, the characteristics of said power amplifier comprising a distortion from a linear transfer function, said pre-distorter comprising a first path including a first pre-distorter amplifier, a second path including a second pre-distorter amplifier, said first and second pre-distorter amplifiers having substantially identical physical characteristics, pre-distorter input means responsive to an input signal for applying respective first and second pre-distorter input signals to said first and second paths, and combining means for combining first and second path signals from said first and second paths to produce a pre-distorted signal, the transfer characteristics of said pre-distorter comprising a distortion relative to a linear transfer function such as to tend to compensate for the distortion of the transfer function of said power amplifier, wherein said input means and said combining means are each arranged to introduce substantially orthogonal relative phase shifts between said first and second paths, such that said first and second path signals are combined substantially in anti phase to produce said pre-distorted signal, one of said input means and said combining means presenting high-pass and the other low-pass transfer characteristics whose variations with frequency tend to compensate each other, and said power amplifier comprising at least one stage of similar technology and topology to said first and second pre-distorter amplifiers but of larger power capacity.