Multi-output stacked class-E millimetre-wave power amplifiers in 45 nm silicon-on-insulator metal–oxide–semiconductor: theory and implementation

Series stacking of multiple devices in power amplifiers is a promising technique that has been explored recently at millimetre-wave frequencies to overcome some of the fundamental limitations of metal-oxide-semiconductor (CMOS) technology. Stacking multiple devices improve the output power and efficiency by increasing the achievable output voltage swing. Switching power amplifiers (PAs), such as Class-E PAs, are capable of high efficiency operation and can benefit from device stacking. This study presents a new topology for stacked Class-E-like PAs. In this technique, an appropriate Class-E load network is used for each stacked device, which imparts a true Class-E behaviour to all the devices in the stack. In addition, output power is available from multiple corresponding output nodes. The resulting topology is called the multi-output stacked Class-E PA. Two Q-band prototypes - a unit cell with two devices stacked, and a power-combined version employing two such unit cells - have been fabricated in IBM´s 45 nm silicon-on-insulator CMOS technology using the 56 nm body-contacted devices. Measurements yield a peak PAE of 25.5% for the unit cell with saturated output power of 17.9 dBm, and a peak PAE >16% for the power-combined version with saturated output power >19.1 dBm. Owing to the proposed technique, the performance metrics are at par with the current state-of-the-art despite the higher ON-resistance and poor f_max of the body-contacted devices.