# A Class E Power Oscillator for 6.78-MHz Wireless Power Transfer System

• Received : 2017.05.05
• Accepted : 2017.09.01
• Published : 2018.01.01

#### Abstract

A class E power oscillator is demonstrated for 6.78-MHz wireless power transfer system. The oscillator is designed with a class E power amplifier to use an LC feedback network with a high-Q inductor between the input and the output. Multiple capacitors are used to minimize the variation of the oscillation frequency by capacitance tolerance. The gate and drain bias voltages with opposite characteristics to make the frequency shift of the oscillator are connected in a resistance distribution circuit located at the output of the low drop-out regulator and supplied bias voltages for class E operation. The measured output of the class E power oscillator, realized using the co-simulation, shows 9.2 W transmitted power, 6.98 MHz frequency and 86.5% transmission efficiency at the condition with 20 V $V_{DS}$ and 2.4 V $V_{GS}$.

#### File

Fig. 1. Schematic of the proposed class E power oscillator

Fig. 2. Transient waveforms in the circuit simulation of theclass E power oscillator

Fig. 3. Schematic for EM circuit co-simulation of the classE power oscillator considering the effects of thelayout design on PCB

Fig. 4. Transient waveforms using EM circuit co-simulation in each node of the power oscillator. (a)At the gate node, (b) the drain node of the transistorand (c) the output port connected to the 50-Ωreference impedance

Fig. 5. Proposed class E power oscillator module. The overall size of the module is 35 mm (W)×65 mm(L)×30 mm (H) including a LDO regulator, a SMPS connector, a metal heat sink, a cooling fan, and interconnections to BLE module, which can be used to control the regulator operation

Fig. 6. Measured fundamental oscillation frequencies of thepower oscillator depending on the bias voltages,which are the VGS (an opened circle line) and theVDS (a closed box line)

Fig. 7. Measured power conversion efficiency andtransmitted power of the power oscillator dependingon the VDS at 2.4 V VGS

Fig. 8. Output power spectrum of the power oscillator with30 dB attenuator

Table 1. Comparison of the capacitances in the feedback loop designed to generate the 6.78-MHz oscillation frequency in both simulations

Table 2. Design parameters of the power oscillator in Fig. 1

Table 3. Comparisons of the class E oscillator in the MHz range

#### Acknowledgement

Supported by : Yeungnam University

#### References

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