Low-harmonic push-pull class-E power amplifier with a pair of LC resonant networks

This paper proposes a novel push-pull Class-E series-parallel resonant power amplifier (PA), which parallels two basic one-inductor, one-capacitor Class-E high-efficiency switching-mode tuned PA (Sokal, 1981) circuits. This proposed topology utilizes a push-pull scheme to realize sinusoidal output voltage. The previously published Class-E circuits (Sokal, 1981) can be implemented in a very simplified circuit. However, the simplified circuit is only appropriate for applications in which the harmonic content of output is not an important criterion. The proposed amplifier with two series-parallel resonant load networks will allow sinusoidal output voltage to be achieved by associating with the positive and negative quasi-sinusoidal waveforms. The complementarily activated configuration will provide continuous high-ripple-frequency input-current waveforms; this approach significantly reduces electromagnetic interference and requires very little filtering. With the symmetry of the push-pull Class-E circuit, there is the additional benefit that the even harmonics are suppressed at the load, and thus there are fewer harmonic distortions. However, each switch is symmetrically driven with a duty ratio of less than 0.5 to meet the nominal Class-E operating conditions, which leads to a narrower operating frequency variation. A prototype of the proposed PA shows over 95% efficiency at 48-V input, with 18-W output and an operating frequency of 900 kHz.