Multi-Inverter Discrete Backoff: A High-Efficiency, Wide-Range RF Power Generation Architecture

Industrial radio frequency (rf) power applications, such as plasma generation, require high-frequency rf power over a wide dynamic power range and across variable load impedances. It is desired in these applications to maintain high efficiency and fast dynamic response. This paper introduces a scalable 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 paralleled switched-mode PAs, and modulates the number of active PAs to provide discrete steps in rf output voltage. It further employs outphasing among sub-groups of PAs for rapid and continuous output power control over a wide range. In doing so, the architecture can maintain high efficiency and fast rf power control across a very wide backoff range. A device selection and loss optimization method for MIDB architectures is discussed for plasma generation applications. We address the use of GaN FET-based, ZVS class-D PA units, and consider dynamic R_ds,on effects and C_oss losses typical of GaN FETs.