I. Introduction
The demand for increased communication data rates with wideband, high peak-to-average power ratio (PAPR) modulated signals is complicated by a competing need for high-efficiency performance. Tremendous efforts to beat the linearity–efficiency tradeoff for PAs have led to a wide variety of architectures. One potential solution is the outphasing system, also known as linear amplification with nonlinear components (LINC) [1], [2]. In the outphasing system, shown in Fig. 1(a), an input signal containing both amplitude and phase modulation is divided into two constant-envelope phase-modulated signals [3]. An amplified version of the original signal is achieved by varying the phases of these two signals and summing the amplified branch signals with a passive power combiner. The maximum envelope is obtained when the branches are in-phase, while the minimum envelope is obtained when the branches are antiphase. The advantage of this technique is that highly efficient nonlinear PAs can be used to amplify the two constant envelope signals, increasing the overall efficiency without degrading linearity.