Out-Phasing Power Amplifier Configured With Multifunctional Networks Using Microstrip Parallel-Coupled Line

A design strategy with multifunctional network for out-phasing power amplifier (OPA) is proposed. The multifunctional (M-F) network using coupled lines is implemented to achieve reactive loading compensation of the fundamental wave and harmonic controlling, thereby enhancing efficiency. Leveraging the characteristics of the coupled lines, this configuration achieves conjugate reactance matching for upper and lower branches of the OPA using single network. In addition, the multifunctional network performs as the drain bias circuit, reducing the number of components needed for the output network. Benefiting from the proposed design strategy, efficiency enhancement and simplified circuit structure can be simultaneously obtained. An OPA using GaN devices with harmonic control coupled network is designed and implemented. The designed OPA achieves 44.3-dBm saturated power at 2.4 GHz. Meanwhile, 72.5% and 58.7% drain efficiencies are obtained respectively at 6-dB output power back-off and saturation output power. For the down-link long-term evolution (LTE) signal with a channel bandwidth of 20 MHz and a peak-to-average power ratio (PAPR) of 8 dB, the average adjacent channel power ratio and error vector magnitude of the fabricated OPA reach −51.2 dBc and 1.48% after digital pre-distortion.