Combined Low Frequency and Third Harmonic Injection in Power Amplifier Linearization

Simultaneous injection of the difference frequency and triple frequency signals into the main RF amplifier (alongside the fundamental frequency signals) offers an independent improvement of IM3 and IM5. This advantage is not achievable by other reported techniques. Mathematical analysis of this new power amplifier linearization 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 may influence 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.