Filter for improved driver circuit efficiency and method of operation

A transmitter device, comprising:

• a transmit coil configured to generate a magnetic field for wirelessly transferring power to one or more receiver devices to power or charge respective loads of the one or more receiver devices, a resistive part of an impedance presented to the transmit coil varying over a range of real impedance values in response to changes in positioning or presence of the one or more receiver devices within the magnetic field;
• a class E driver circuit comprising a switch;
• and
• a passive filter circuit electrically connected between the driver circuit and the transmit coil, the passive filter circuit comprising one or more reactive elements including a capacitor and an inductor having fixed values and configured to transform the impedance presented by the transmit coil to the class E driver circuit to one of a range of complex impedance values falling along a contoured line or half circuit when plotted in a complex number coordinate system, the transformed impedance maintaining an efficiency level of the class E driver circuit within 20% of a maximum efficiency of the driver circuit, irrespective of the changes in the positioning or presence of the one or more receiver devices within the magnetic field.

A transmitter device, comprising:

• means for generating a magnetic field for wirelessly transferring power to one or more receiver devices to power or charge respective loads of the one or more receiver devices, a resistive part of an impedance presented to the means for generating a magnetic field varying over a range of real impedance values in response to changes in positioning or presence of the one or more receiver devices within the magnetic field;
• means for driving comprising a switch;
• and
• means for passive filtering, the means for passive filtering being electrically connected between the means for driving and the means for generating, the means for passive filtering comprising one or more reactive elements including a capacitor and an inductor having fixed values, and configured to transform the impedance presented by the means for generating a magnetic field to the means for driving to one of a range of complex impedance values falling along a contoured line or half circuit when plotted in a complex number coordinate system, the transformed impedance maintaining an efficiency level of the means for driving within 20% of a maximum efficiency of the means for driving, irrespective of the changes in the positioning or presence of the one or more receiver devices within the magnetic field.

A method for filtering a transmit signal, comprising:

• generating a magnetic field for wirelessly transferring power to one or more receiver devices to power or charge respective loads of the one or more receiver devices, via a transmit coil, a resistive part of an impedance presented to the transmit coil varying over a range of real impedance values in response to changes in positioning or presence of the one or more receiver devices within the magnetic field;
• driving a signal using a class E driver circuit comprising a switch;
• providing the signal to the transmit coil;
• and
• transforming the impedance presented by the transmit coil to the driver circuit using a passive filter circuit electrically connected between the driver circuit and the transmit coil, the passive filter circuit comprising one or more reactive elements including a capacitor and an inductor having fixed values and configured to transform the impedance presented by the transmit coil to the driver circuit to one of a range of complex impedance values falling along a contoured line or half circuit when plotted in a complex number coordinate system, the transformed impedance maintaining an efficiency level of the class E driver circuit within 20% of a maximum efficiency of the driver circuit, irrespective of the changes in the positioning or presence of the one or more receiver devices within the magnetic field.

A method for designing a power transmitter apparatus, the method comprising:

• selecting characteristics of at least two elements of a group of elements including:
• a class E driver circuit comprising a switch,
• a passive filter circuit configured to transform an impedance presented to the class E driver circuit as a resistive part of an impedance presented to a transmit coil varies over a range of real impedance values in response to changes in positioning or presence of one or more receiver devices within a magnetic field generated by the transmit coil, the transformed impedance in a range of complex impedance values falling along a contoured line or half circuit when plotted in a complex number coordinate system, and
• an impedance shifting element;
• and
• determining, based on the selected characteristics of the at least two elements, a characteristic of a non-selected element such that the transformed impedance maintains an efficiency level of the class E driver circuit within 20% of a maximum efficiency of the driver circuit, irrespective of the changes in the positioning or presence of the one or more receiver devices within the magnetic field.