Brush up on the theory before designing a high power Class‐E amplifier: Page 10 of 15

June 29, 2016 // By Alfio Scuto, Roberto Cammarata, ST Microelectronics
The most promising switched-mode PA for RF applications, among the several types available, is the Class-E for several reasons: high efficiency, simplicity of the load network, and a satisfying performance even with a non-optimal drive signal.

Figure 9: Harmonic Balance simulation.

Implementing the equations for Class-E plus the device’s losses inside the harmonic balance (Figure 9), we obtained the following results (Figures 10 and 11).

Figure 10: Voltage of the MOSFET.

Figure 11: Current of the MOSFET.

From simulation, we got an efficiency of 93.4% and a power out of 512 W at 13.56 MHz (Figure 12). Using two SD4933 in parallel, we have halved the RDS(on) and the stray inductances, but we doubled the equivalent capacitance Coss.

At this point of the design, the nonlinear characteristic of the Coss versus the drain voltage was under particular consideration.

To depower the negative effects of Coss, we introduced the advantages offered by the finite feed inductor already introduced.

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