This paper describes a 2.4-GHz digitally-modulated class-D polar power amplifier (PA) with novel circuit techniques to enhance the average power-added efficiency (PAEave) that becomes increasingly crucial to prolong the battery lifetime. The PA features 5+5-b interactive AM-AM modulation between the class-D unit amplifiers and a novel high resolution dynamic matching network (DMN) to improve the back-off PAE. A novel power-gating technique tailored for class-D PAs is also proposed and embedded into each unit amplifier and its driver (tapped inverter chain), alleviating leakage-current suppression, area reduction of the DMN, and direct-powering by a standard 1.5-V AA battery. An high back-off power efficiency is made possible by introducing a multi-bit capacitively-tuned DMN, which adds low loss while improving the PAE of the unit amplifiers using the load-pull optimization. The DMN also can correct the antenna impedance mismatch for better average Pout (Pout, ave) and PAEave under a practical VSWR (2.5 : 1), and aids to reconfigure the PA between the Pout-optimized and the PAEoptimized modes. For a 20-MHz64-QAM OFDM output at a typical EVM (< -25 dB), the 65-nm CMOS PA exhibits 40.7% PAEave at a 16.3-dBm Pout. The mode switching is demonstrated as a prospective function for battery lifetime extension.