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

Abstract

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 fmax of the body-contacted devices.