[IEEE 2011 18th IEEE International Conference on Electronics, Circuits and Systems - (ICECS 2011) - Beirut, Lebanon (2011.12.11-2011.12.14)] 2011 18th IEEE International Conference on Electronics, Circuits, and Systems - All-digital 400∼900 MHz power amplifier consuming 0.03 mW/MHz using 0.18 μm CMOS