High-Efficiency Class-iF⁻¹ Power Amplifier With Enhanced Linearity

This article presents a new class of power amplifier (PA), designated as Class-iF−1, that utilizes input harmonics to achieve high efficiency with enhanced linearity performance beyond the conventional Class-F−1 PA. The amplitude-to-amplitude modulation (AM/AM) profile of the conventional Class-F−1 PA is mathematically modeled as a function of the input drive level, such that the occurrence of inflection points can be investigated. Theoretical derivation shows that the appropriate utilization of input nonlinearity poses a solution to rectify the double inflection characteristics of the conventional Class-F−1 PA, which, consequently, can be realized by proper manipulation of second harmonic source impedance ( $Z_{2S}$ ). The theoretical findings were validated with load—pull results at 2.3 GHz with a 2-mm gallium nitride (GaN) device, presenting enhanced linearizable output power and efficiency for the Class-iF−1 PA, with a broad second harmonic design space over the open-circuit region. As proof of concept, a Class-iF−1 PA was designed and fabricated, obtaining 40.1–40.8 dBm output power and 71.2%–77.3% drain efficiency (DE) performance at 3-dB gain compression level operating over 2.0–2.6-GHz frequency range. When tested with a 20-MHz 8.5-dB peak-to-average-power-ratio (PAPR) long-term evolution (LTE) signal, around 32.01-dBm average output power was attained at 2.3 GHz with an average DE of 34.59% and −56.05 dBc adjacent channel power ratios (ACPRs) after digital predistortion (DPD) correction.