Augmentation of Class-E PA reliability under load mismatch conditions

Highly efficient switch-mode Class-E power amplifiers (PAs) are sensitive to load impedance variations. For voltage standing wave ratios (VSWRs) up to 10:1, the peak switch voltage and average switch current can increase by a factor 1.7 and 2.5, respectively, with respect to the nominal load condition, thereby imposing serious reliability risks. This work introduces a technique to self-protect/self-heal Class-E PAs against the effects of load variations, with only a minor impact on output power and efficiency. To validate the proposed technique, load-pull measurements are conducted on a ClassE PA implemented in a standard 65nm CMOS technology, employing an off-chip matching network, augmented with a fully automated self-protective/self-healing control loop. Under nominal operating conditions, the PA provides 17.5dBm output power into 50Ω from a 1.2V supply with 67% efficiency when all the losses of the matching network are included. It is shown that the proposed self-protective PA can reduce its peak switch voltage to below the value allowed by the technology for all load mismatch conditions with VSWR up to 19:1 while output power and efficiency are not considerably affected. Furthermore, a PA with an average current safety factor of 2.5 can reliably handle VSWRs up to 19:1.