Capacitor Roles In High-Power Class E RF Generators

Radio frequency (RF) generators produce AC at specific frequencies from kilohertz to gigahertz, powering applications across telecommunications, medical devices, industrial processes, semiconductor manufacturing, and scientific research. Among RF topologies, the Class E amplifier is notable for its switching-mode operation, achieving efficiencies of 85–95% by leveraging Zero-Voltage Switching (ZVS), which minimizes switching losses and heat generation. Class E designs typically offer output powers from a few watts up to over one kilowatt, using resonant load networks, automatic load adaptation, and simplified, robust circuits.

Capacitors are central to Class E amplifier operation. The shunt capacitor connected across the transistor enables ZVS by shaping the drain voltage waveform and reducing peak voltage stress. The series capacitor couples the load to the transistor via a series-tuned circuit, optimizing power transfer and maintaining impedance relationships. Beyond the Class E topology, capacitors in RF generator circuits set pulse widths, form resonant tank circuits, provide output matching to 50 Ω loads, suppress harmonics, isolate DC, and maintain continuous power flow.

Selecting capacitors for high-power RF generators requires high voltage ratings, ultra-low ESR, high Q, thermal stability, and power-handling capability. Knowles offers capacitors engineered for these demanding conditions, including stocked and custom solutions tailored for Class E and other high-efficiency RF generator designs. By carefully specifying capacitors, engineers ensure waveform integrity, efficient power delivery, and reliable operation across diverse high-frequency applications.