Design Considerations for High Power VHF Amplifiers for Transient and Dynamic Loads

Modern semiconductor and display manufacturing industries strongly rely on plasma processes wherein ionized gases are used to chemically or physically treat surfaces to create precise thin films and delicate microstructures. Accurately regulated RF power generators in the frequency range of 1 to 100MHz and power levels of 10W to 100kW provide the excitation energy to plasma reactors for these applications. The pronounced non-linear electrical properties of plasmas make them challenging loads which exhibit quickly changing transient impedances and non-linear behavior. The RF generator should maintain a stable output power under these variable load conditions without being thermally or electrically destroyed. In this talk the behavior of the plasma load is analyzed and implications on the amplifier design are discussed. Balanced PA design and supply modulation are playing a key role in mitigating undesired thermal and electrical effects.