Enhanced architecture for microwave currentmode class-D amplifiers applied to the design of an S-band GaN-based power amplifier

An enhanced architecture for the design of current-mode class-D (CMCD) power amplifiers (PAs) at microwave frequencies is presented. In the proposed structure, the harmonic impedance loading conditions of CMCD amplifiers are realised by using multiharmonic output impedance transformation networks instead of a combination of balun and lumped element tanks, typically used in CMCD PA designs. The advantage of the proposed approach is to remove design complexity from the balun and lumped element tank. A 39 dBm GaN- based CMCD PA was designed at 2.35 GHz - to the best knowledge of the authors the highest frequency for a CMCD PA reported in open literature - to validate and to demonstrate the capabilities of this architecture. The fabricated PA achieves 68% DC-to-RF efficiency (eta) and 65% power added efficiency. A comparison between this S-band amplifier and a conventional wideband-balun-resonant-tank CMCD PA at 1 GHz using a similar commercial active device demonstrates the frequency coverage and performance improvement of the proposed topology.