The optimum high-frequency Class-F loading conditions are inferred, accounting for the effects of actual output device behavior, and deriving useful charts for an effectiveuddesign. The important role of the biasing point selection is stressed, demonstrating that it mustudbe different from the Class-B theoretical one to get the expected improvement. The IMD behavior of the Class-F amplifier is presented and the large-signal sweet-spot origin in theudIMD output characteristics is discussed, together with possible strategies to improve intermodulationuddistortion performances. The control of the sweet spot position is demonstratedudvia proper terminating impedances, both at fundamental and harmonic frequencies and low frequencies.
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