The effect of the turn 'On' resistance of an active device and the Q factor of the load harmonic network on the efficiency and efficiency bandwidth of a class E amplifier

In this paper the active device for a class E amplifier is modelled as switch in series with a turn on resistance ‘Ron’. Assuming an ideal harmonic load is used the switch equations for the voltage and current waveforms are reviewed and then used to examine how ‘Ron’ affects the efficiency of dc to ac power conversion. This ideal harmonic network is assumed to have optimum input impedance at the design frequency and an open circuit at all harmonics of the current waveform. In a practical amplifier the ideal harmonic network cannot be realised and therefore it is normally replaced by a series resonant circuit. This circuit is designed to have the required optimum input impedance at the design frequency and a high ‘Q’ factor to reduce the harmonic currents in the load resistance. It is not possible to obtain an analytical solution to show how the losses due to the harmonic currents affect efficiency. Consequently a Genetic Algorithm (GA) based on a stochastic search method is used obtain a design graph to show the relationship between the ‘Q’ factor, the resonant of the above circuit and efficiency. The effect of ‘Ron’ and the ‘Q’ factor on the efficiency and the efficiency bandwidth is also investigated.