Brush up on the theory before designing a high power Class‐E amplifier: Page 6 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.

3.3. Design equations for finite QL

When QL (defined as 2πfL2/R) decreases, the above equations progressively produce less accurate results.

In some cases, Dr. Raab’s equations (2) have been represented in tabular form with the output power, C1 and C2 as function of QL.

Table 1: Tabular Raab’s equations versus QL.


Even if QL is a free-choice design variable from the theory, it must satisfy the condition QL ≥ 1.7879; when QL = ∞ we may recognize the results already found.

In (4) Dr. Sokal found compact design equations representing the data shown in Table 1 using polynomial functions in QL.

→ Equation 20

→ Equation 21

→ Equation 22


L2 = QLR/ω → Equation 23

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