Abstract: This disclosure provides systems, methods and apparatus for increasing the efficiency of an amplifier when driven by a variable load. In one aspect a transmitter device is provided. The transmitter device includes a driver circuit characterized by an efficiency. The driver circuit is electrically connected to a transmit circuit characterized by an impedance. The transmitter device further includes a filter circuit electrically connected to the driver circuit and configured to modify the impedance to maintain the efficiency of the driver circuit at a level that is within 20% of a maximum efficiency of the driver circuit. The impedance is characterized by a complex impedance value that is within a range defined by a real first impedance value and a second real impedance value. A ratio of the first real impedance value to the second real impedance value is at least two to one.

Abstract: An embodiment of a system for wirelessly charging a wrist-worn device may include a radio frequency (RF) charging energy generating element, and an antenna configured to radiate the RF charging energy, the antenna comprising a first coil and a second coil, the first coil and the second coil each comprising a plurality of windings, the windings of the first coil being wound in a direction opposite the direction of the windings of the second coil. An embodiment of a wrist-worn charge-receiving device may include an antenna coil adapted to receive radio frequency (RF) charging energy, the antenna coil comprising non-uniform windings; and a rechargeable power source coupled to the antenna coil, the antenna coil adapted to provide the RF charging energy to the rechargeable power source.

Abstract: This disclosure provides systems, methods, and apparatus for transferring power wirelessly via a wireless power transmitter. In one aspect, the transmitter comprises a first circuit configured to generate a first signal, where the first circuit includes a first inductor. The transmitter further comprises a second circuit configured to generate a second signal out of phase with the first signal. The second circuit includes a second inductor inductively coupled with the first inductor. The first inductor and the second inductor may have a leakage inductance of at least a minimum value so as to not produce a substantially square waveform at an output of the first circuit and an output of the second circuit. The transmitter further comprises a filter circuit configured to filter the first signal and the second signal.

Abstract: An embodiment of a system for wirelessly charging a wrist-worn device may include a radio frequency (RF) charging energy generating element, and an antenna configured to radiate the RF charging energy, the antenna comprising a first coil and a second coil, the first coil and the second coil each comprising a plurality of windings, the windings of the first coil being wound in a direction opposite the direction of the windings of the second coil. An embodiment of a wrist-worn charge-receiving device may include an antenna coil adapted to receive radio frequency (RF) charging energy, the antenna coil comprising non-uniform windings; and a rechargeable power source coupled to the antenna coil, the antenna coil adapted to provide the RF charging energy to the rechargeable power source.

Abstract: This disclosure provides systems, methods, and apparatus for transferring power wirelessly via a wireless power transmitter. In one aspect, the transmitter comprises a first circuit configured to generate a first signal, where the first circuit includes a first inductor. The transmitter further comprises a second circuit configured to generate a second signal out of phase with the first signal. The second circuit includes a second inductor inductively coupled with the first inductor. The first inductor and the second inductor may have a leakage inductance of at least a minimum value so as to not produce a substantially square waveform at an output of the first circuit and an output of the second circuit. The transmitter further comprises a filter circuit configured to filter the first signal and the second signal.

Abstract: This disclosure provides systems, methods and apparatus for increasing the efficiency of an amplifier when driven by a variable load. In one aspect a transmitter device is provided. The transmitter device includes a driver circuit characterized by an efficiency. The driver circuit is electrically connected to a transmit circuit characterized by an impedance. The transmitter device further includes a filter circuit electrically connected to the driver circuit and configured to modify the impedance to maintain the efficiency of the driver circuit at a level that is within 20% of a maximum efficiency of the driver circuit. The impedance is characterized by a complex impedance value that is within a range defined by a real first impedance value and a second real impedance value. A ratio of the first real impedance value to the second real impedance value is at least two to one.