A Technique for Device Stress Relief in CMOS Class-E RF Power Amplifiers

Class-E power amplifiers are widely used especially for constant envelope modulation applications due to their high efficiency even for switching signals with slow rise/fall edges. However, they have been rarely used in CMOS process for very high power levels, resulting from their intrinsic poorer power output capability. In this paper, we propose a unique way to control the drain voltage stress of the active switch device when the rise/fall edges of the driving signal occupy a significant portion of the switching cycle. Our approach employs internal signals within a differential amplifier by inserting a transformer between the two active device branches. Depending on specific process and power supply levels, the stress can be relieved up to more than 20%, which gives significant room for either higher power level and efficiency or using faster (and therefore easier to breakdown) devices