2.8 A broadband CMOS digital power amplifier with hybrid Class-G Doherty efficiency enhancement

Abstract

Spectrum-efficient modulations in modern wireless systems often result in large peak-to-average power ratios (PAPRs) for the transmitted signals. Therefore, PA efficiency at deep power back-off (PBO) levels (e.g., -12dB) becomes critical to extend the mobile's battery life. Classic techniques, i.e., outphasing, envelope tracking, and Doherty PAs, offer marginal efficiency improvement at deep PBO in practice. Dual-mode PAs require switches at the PA output for high-/low-power mode selection [1,2], posing reliability and linearity challenges. Although simple supply switching (Class-G) is effective at deep PBO, it only offers Class-B-like PBO efficiency in each supply mode [3,4]. Multi-level outphasing PA requires multiple supplies and frequent supply switching [5], resulting in substantial DC-DC converter overhead and exacerbated switching noise.