High-Efficiency Wide-Range RF Power Generation Systems With Discrete Power Back-Off From Multiple Inverters

Industrial radio frequency (rf) power applications, such as plasma generation for semiconductor processing, require the delivery of rf power over a wide dynamic power range and across variable load impedances. It is desirable for the rf power system to maintain high efficiency, continuous power control, and fast dynamic response over the operating power range. This article introduces a scalable switched-mode power amplifier (PA) architecture and control approach suitable for such applications. This approach, which we refer to as multi-inverter discrete backoff (MIDB), losslessly combines the outputs of switched-mode PAs, and modulates the number of active PAs to provide discrete steps in rf output. It further employs discrete supply modulation and outphasing among groups of PAs for rapid, efficient, and continuous output power control over a very wide range. A system prototype is built with 4 GaN-based, zero-voltage switching Class-D PA units, 2-level discrete supply modulation, and calibrated Chireix outphasing. The system achieves and maintains high efficiency and continuous power control over the designed continuous-wave operating range of 5 W–1 kW, and dynamically over 5 W–5 kW, with micro-second level transient performance. The proposed system demonstrates reduced power losses compared with existing linear-amplifier based solutions.