Predistortion linearizer circuit

The invention relates to a predistortion linearizer circuit and a method on which it is based. The predistortion linearizer circuit of the invention is primarily intended to be used to predistort the amplitude and phase of the input signal of a travelling wave tube amplifier in order to cancel the amplitude and phase distortion caused by the amplifier. To be more precise, the purpose of the predistortion linearizer circuit of the invention is that the third and fifth order intermodulation distortion, AM/AM and AM/PM response, AM/PM transition and noise/power ratio of the linearized travelling wave tube amplifier can be substantially minimized. A predistortion linearizer circuit comprising an amplitude distorting part (AM/AM) and a phase distorting part (AM/PM). At least the phase distorting part (AM/PM) comprises broadband biasing means () and a non-linear transmission line (L/Dto L/D) responsive to them. The biasing means () are arranged to bias the non-linear transmission line (L/Dto L/D) to a substantially phase distorting area. The characteristics of the circuit can be changed by adjusting a biasing voltage (VB) or by switching some of the diodes (DD) inactive by activation signals (VAVA). The amplitude distorting part (AM/AM) and the phase distorting part (AM/PM) can be similar in structure, but the diodes (Dto D) are partly forward-biased, whereby the losses caused by them decrease the amplitude of the signal.