Abstract

Outphasing amplifiers (OPAs) have attracted attention as amplifiers that achieve high efficiency from saturated output to high backoff output. Mixed-mode Symmetric Outphasing Amplifiers (MSOPA), which change amplitude as well as phase below high backoff, are also attracting attention. Conventionally, an outphasing amplifier consists of two amplifiers with the same saturated output power and a Chireix power combiner. In this paper, we propose a mixed-mode asymmetric outphasing amplifier (MAOPA) using two amplifiers with different saturated output power to achieve higher efficiency at backoff output. The design of the output matching circuit for MAOPA requires an output port for each amplifier at two power conditions, i.e., four matching conditions must be realized simultaneously. However, the four matching conditions interfere with each other, making circuit design and evaluation difficult. Therefore, this paper proposes a design method for MAOPA design in which the four matching conditions can be adjusted independently. The proposed method first derives an analytical solution to match optimal loads under two power conditions using the invariants of a lossless matching circuit. Based on this analytical solution, impedance transformation to resistive loads done by matching circuits using offset lines enables the design of each amplifier and power combiner, to be done independently. MSOPA and MAOPA show that the dynamic ranges of the drain efficiency above 50% are 9dB, 12dB, respectively.