High-Efficiency and High-Linearity Class-F ^ Power Amplifier With AM-AM and AM-PM Improvement

In this article, a high-efficiency and high-linearity Class-F ^{{-1}} power amplifier (PA) is presented. The input nonlinearity effect on Class-F ^{{-1}} PA is investigated in depth, and the input nonlinearity factors \gamma and \varphi_{{2}} are utilized to improve the AM-AM and AM-PM characteristics. In practice, the linearity of Class-F ^{{-1}} PA is enhanced by manipulating the second-harmonic source impedance, without sacrificing the drain efficiency (DE). The design space is clearly defined for high-efficiency and high-linearity operation. For demonstration, a PA example working at 3.5-3.9 GHz was designed, fabricated, and measured. It exhibits the saturated output power greater than 40.2 dBm, the saturated gain is 8.9-14.3 dB, and DE is 65.7%-74.2%. When tested with a 40-MHz 64-QAM signal with an 8.5-dB peak-to-average-power-ratio (PAPR), the adjacent channel power ratio (ACPR) is below - 44.41 dBc without digital predistortion (DPD) and - 56.4 dBc with DPD. At 3.8 GHz, the fabricated PA realizes an AM-AM of 0.7 dB and an AM-PM of -1^{\circ} without DPD and an AM-AM of 0.2 dB and AM-PM of -0.7^{\circ} with DPD.