Patent ID: 7289575

Claim:
Signal processing apparatus comprising: a signal amplifier and a frequency converter which operate in succession on an input signal, a pilot signal generator adapted to introduce a pilot signal into the input signal prior to frequency conversion and amplification, and a lineariser which is provided between the amplifier and the frequency converter to introduce a correction signal that is adapted to make the overall input and output characteristic of the apparatus more linear by linearising both the amplifier and frequency converter, wherein: a feedback signal, derived from the output of the apparatus and containing distortion components from the pilot signal produced by at least one of the frequency converter and the amplifier, is used by the lineariser to adapt the correction signal, the pilot signal is removed from the output of the apparatus by a filter or by the introduction of a pilot cancellation signal, the lineariser comprises a distortion generator for producing the correction signal from the output signal of whichever of the amplifier and the frequency converter precedes it, and the distortion generator comprises a non-linearity generator arranged to generate a third-order non-linearity by mixing the input to the non-linearity generator with itself and then with its input.