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A new diode-based curve-fitting predistortion lineariser for GaN power amplifier

In this article, a new strategy is presented for selecting the breakpoints on a typical characteristic of a lineariser for a saturating nonlinear amplifier. As a proof of concept, using this strategy, a new Schottky-diode based curve-fitting predistortion lineariser for a 1.65 GHz centre frequency, 50 MHz bandwidth, 30 W GaN power amplifier is developed. The proposed lineariser is tested using the two-tone test and the Quadrature Phase-Shift Keying (QPSK) modulated signal. The results show that a 3 dB improvement in the overall gain of the linearised amplifier is achieved. Moreover, for output power levels up to 36 dBm, the linearised power amplifier provides better rejection of the third-order intermodulation. Because of the hard nonlinearity of the GaN power amplifier at the high end, this improvement in intermodulation rejection vanishes for output power levels around 41 dBm.