2.8 A Class-G voltage-mode Doherty power amplifier

In modern communication, wideband and high-spectral-efficiency modulation results in high peak-to-average power ratio (PAPR), up to 8 to 10dB. Well-known PA-efficiency-enhancement techniques, such as Doherty and outphasing, offer reduced efficiency improvement beyond 6dB back-off, limiting the efficiency enhancement obtainable with high PAPR modulation. Recent works have shown that a combination of different techniques [1–3] can result in improved efficiency well beyond 6dB back-off. However, these combined techniques have come at a cost of glitches due to mode-transitions, when power supply voltage or load impedance undergo large variations at critical power levels. In [1,2] switching between power supply voltages causes significant glitches, which degrade the EVM and ACPR of the transmitted signal. In [1], reasonable EVM is achieved, by reducing the average output power so that power supply switching is less frequent. A “skipping window” technique is proposed in [3] to skip high-frequency mode-transitions reducing overall glitching. While this improves the ACPR, the efficiency is degraded since there is no enhancement during a skipped transition.