Patrick Stanley Riehl

Wireless Power Systems for Mobile Devices Supporting Inductive and Resonant Operating Modes

We demonstrate a family of wireless power devices that operate in a variety of operating modes. A multimode wireless power receiver unit (PRU) allows a mobile device to charge from any one of three wireless power standards: Qi, Power Matters Alliance, or Rezence. A coil arrangement and matching network is introduced that is resonant in both 6.78-MHz and 100-kHz bands, allowing the same power conversion circuitry to operate in either mode. The multi-mode PRU converts 5 W of ac power to a regulated 5-V output with an efficiency of up to 83% in Rezence mode and up to 86% in Qi mode. A wireless charging power transfer unit (PTU) using the Rezence specification charges three such PRUs at a power level of 5 W each with a power transfer efficiency of 66%. An in-band communications protocol provides enhanced capabilities to the Rezence system. Multiple layers of encoding ensure reliable delivery of messages under difficult channel conditions. Another PTU design allows the same receiver to charge through a table of 30-mm thickness while maintaining the in-band communications link. We show that a wide variety of multimode devices are possible, enabling widespread adoption of wireless power even in the absence of a single unified standard.

An AC-coupled hybrid envelope modulator for HSUPA transmitters with 80% modulator efficiency

High-data-rate wireless technologies such as HSUPA and LTE are power-hungry because of the fundamental correlation between data rate and transmit power. Furthermore, the high peak-to-average power ratio (PAPR) of the modulated signals causes a degradation in PA efficiency, since the supply voltage of the PA must be high enough to provide the peak output voltage without loss of linearity. Envelope tracking modulators have been proposed to improve the efficiency and linearity of transmitters. Modulators using multiple input voltages have been shown to improve efficiency, but generating multiple supplies imposes substantial overhead. Several recent works have demonstrated a hybrid modulator, combining the output current of a buck output stage with that of a linear amplifier. The hybrid modulator has the notable advantage that the low-frequency power (which constitutes the majority of power, even in high-PAPR scenarios) can be provided through the efficient buck stage. The inherently less efficient linear amplifier stage needs only to supply the high-frequency power. The efficiency of hybrid modulators degrades at moderate power levels, when the ac amplitude is much less than the supply voltage of the linear amplifier. At low power levels, the power savings afforded by the modulator do not offset its own quiescent current, resulting in a lower efficiency than can be achieved using a fixed-drain, average-power-tracking (FD-APT) supply.

Wireless power receiver for mobile devices supporting inductive and resonant operating modes

We demonstrate a compact wireless power receiver for mobile phones that operates either in a resonant mode at 6.78 MHz or an inductive mode in the 110 to 205 kHz range. A coil arrangement and matching network is introduced that is resonant in both frequency bands, allowing the same power conversion circuitry to operate in either mode. The receiver converts up to 5 W of AC power to a regulated 5 V supply with a peak efficiency of 84% in inductive mode and 82% in resonant mode.

A 3D resonant wireless charger for a wearable device and a mobile phone

A resonant wireless power transfer (WPT) system that allows for free positioning of a wearable device about a 360° axis of rotation and simultaneous charging of a mobile phone is proposed. A 3D transmitter coil structure is introduced to provide a cylindrical charging surface with a uniform magnetic field. A prototype charging system including an amplifier and a rectifier operating at 6.78 MHz is demonstrated. The prototype delivers 1 W to a wearable device and 5 W to a mobile phone simultaneously with a power transfer efficiency of 48%.

3-D wireless charging system with flexible receiver coil alignment

A 3-D wireless charging system with spatial freedom of positioning is proposed in this paper. By independently adjusting the phase and the amplitude of the input signals, the blind spots within a cylindrical volume are eliminated. Moreover, the symmetric arrangement of the transmitting coils yields a uniform magnetic field around longitudinal axis. Experiments were conducted on a wearable device and a cell phone at 6.78 MHz. The system including a power amplifier and rectifiers achieved an overall power transfer efficiency of 39% for supporting two devices simultaneously.

In-Vehicles Wireless Charging System for Portable Devices

A cup-shaped in-vehicle wireless charging system that allows free alignment for charging portable devices is proposed in this paper. A 3D transmitter coil structure is designed to provide the sufficient magnetic flux density perpendicular to each charging surface. By adding the flexible ferrite sheet surrounding the structure, the leakage of magnetic flux is eliminated to meet the electromagnetic compatibility (EMC) requirement. The whole system is designed and simulated according to the A4WP specification.