Behaviors of EER Transmitter with Class-E Amplifier due to MOSFET Parasitic Capacitances

The class-E amplifier [1]-[11] is remarked as the next candidate of digital wireless power transmitters. Non-switching power amplifiers suffer from low power-conversion efficiency due to their inherent power loss in high back off area. Hence, switching power amplifiers such as class-D and E are remarked as a remedy for improving power-conversion efficiency and prolonging battery lifetime of portable devices. In order to modulate the amplitude and phase of output signal of the switching amplifier, several methods were proposed [1], [2]. Among them, envelope elimination and restoration (EER) is remarked because it does not require power combining circuit at output port of the amplifier. In the EER transmitter using a class-E amplifier, the output-voltage amplitude is modulated with varying the dc-supply voltage of the class-E amplifier. It is well known that if the shunt capacitance of the class-E amplifier is linear, the output amplitude is in proportion to the dc-supply voltage [3]-[5]. However, the MOSFET drain-to-source parasitic capacitance is dominant in the shunt capacitance at high frequencies, which has a nonlinear characteristic [6]-[8]. This nonlinearity of the shunt capacitance results in the output amplitude not being in proportion to the dc-supply voltage. In addition, the MOSFET gate-to-drain capacitance affects waveforms of the class-E amplifier [9]. Additionally, it was stated in [9] that the driving voltage also affects the class-E-amplifier behavior through the MOSFET gate-to-drain capacitance. Therefore, it is thought that EER transmitter characteristics are affected by the MOSFET gate-to-drain and drain-to-source parasitic capacitances of the class-E amplifier as well as the driving signal. This paper presents the MOSFET-parasitic-capacitance effects on the output envelope of the EER transmitter with the class-E amplifier. This paper considers not only the MOSFET drain-to-source nonlinear capacitance but also the MOSFET gate-to-drain linear capacitance. It is clarified from analytical results that the driving-voltage waveform also affects the relationship between the driving and output voltages. Generally, it is stated that the driving signal should expresses only the frequency and the phase exactly in EER system. The results of this paper suggest that it is important to design Video power conditioner Envelope detector dc supply (modulated)