Class of High-Efficiency Tuned Switching Power Amplifiers

The previous literature on tuned power amplifiers has not made clear the fundamental differences between amplifiers in which the output device acts 1) as a current source, or 2) as a switch. Previous circuits have often operated in contradiction to their design assumptions, resulting in the need for “cut-and-try” design. The new class of amplifiers deseribed here is based on a load network synthesized to hWe a transient response which maximizes power efficiency even if the active device switching times are substantial fractions of the ac cycle. The new class of amplifiers, named “Class E; 1 is defined and is iflustnated by a detailed description and a set of design equations for one simple member of the class. For that circuit the authors measured 96 percent transistor efficiency at 3.9 MHr at 26-W output from a pair of Motorola 2N3735 TO-5 transistors. Advantages of Class E are unusually high efficiency, a priori designability, large reduction in second-breakdown stress, low sensitivityy to activedevice characteristics, and potential for high-efficiency operation at higher frequencies than pI eviously published Class-D circuits. Harmonic output and power gain are comparable to those of conventional amplifiers.