Automatic power controlled, load compensated magnetic resonant wireless power transmitter

Abstract

As compared to other wireless transfer mechanism, like the inductive coupling method, magnetic resonance-based wireless power transfer can achieve power transfer over a larger distance. However, as the transmission range increases, the change in the load impedance lowers the transmission efficiency in the currently available magnetic resonance-based wireless power transmitters. This article presents a CMOS transmitter for magnetic resonant wireless battery charging system. A class-E power amplifier (PA) with an automatic power control loop and load compensation circuit is proposed to improve the power efficiency. The transmitted power is controlled by adjusting the signal applied to the gate of the power control transistor. In addition, a parallel capacitor is also controlled to enhance the efficiency and compensate for the load variation. The proposed design is implemented using 0.35 μm BCD technology with an active area of around 5 mm × 2.5 mm. The transmitter provides an output power control range of 9–30.2 dBm. The measured maximum power efficiency of the PA is 70.2%.