The development of modern telecommunications systems imposes stringent criteria on the linearity of RF amplifiers. Linearity of an amplifier is usually specified by the level of Inter-Modulation (IM), normally by the third and sometimes by the fifth order intermodulation. The issue of amplifier linearization is solved in a number of ways, namely, feedback, feedforward, and predistortion. Harmonic injection is a subclass of the predistortion method and relies on the injection of signals at harmonic frequencies in order to linearize an amplifier.
This paper addresses the issue of multi-order harmonic injection where the injected signals are a combination of low and triple frequency signals. Mathematical analysis of this new power amplifier linearization technique is presented in order to establish the potential of the proposed technique. The analysis shows that the injection of the difference frequency signal reduces IM3, though it influences IM5. However, any deterioration of IM5 improves significantly as a result of the injection of the triple frequency signals without disturbing the advantage gained by the difference frequency injection on the levels of IM3. For the validation of the theoretical results, an experimental amplifier system operating at 880 MHz was built. The two-tone measurement confirmed the theoretical predictions.