Switchless Class-G Power Amplifiers: Generic Theory and Design Methodology Using Packaged Transistors

This article develops a complete theory of the switchless Class-G (SLCG) power amplifier (PA) and proposes a new design method that allows for operating commercial packaged transistors in high-efficiency SLCG mode over a wide frequency band. It starts with a comprehensive analysis that investigates the impact of various transistor and circuit parameters on the SLCG PA’s key performances. Then, design equations are derived to produce SLCG prototypes with optimal back-off efficiency and gain flatness. Moreover, to overcome the difficulty of applying classical SLCG circuits to packaged devices, a new SLCG output combining network (OCN) is developed to absorb various transistors and package parasitic while maintaining the load conditions that enable the wideband SLCG operation. This expands the applicable scope of the SLCG technique and yields packaged-transistor-based, wideband, and high-efficiency SLCG PAs. For validation, a 1–3-GHz SLCG PA is designed using the proposed method with commercial packaged transistors. Measurements under continuous-wave (CW) excitations reveal that, over 1–3 GHz, the proposed SLCG PA can provide the saturation output power ( $P_{\mathrm{sat}})$ of 36.5–38.7 dBm and deliver the drain efficiency (DE) of 39.2%–49.1%, 45.4%–51.2%, and 47.8%–57.7% at power levels that are 7.5-, 6-, and 0-dB back-off from $P_{\mathrm{sat}}$ , respectively. Moreover, when excited by a 40-MHz 64-quadrature amplitude modulation (QAM) modulated signal over 1–3 GHz, the PA realizes an average DE of 39%–49.2% at an average output power of 28.8–31.6 dBm and maintains an error vector magnitude (EVM) of about 1.2% and adjacent channel power ratio (ACPR) of below $-$ 46 dBc after digital predistortion (DPD).