Embodiments of the present disclosure include a harmonic power amplifying circuit with high efficiency and high bandwidth and a radio-frequency power amplifier. The circuit comprises an input matching network (11), a transistor (M), and an output matching network (12); a gate of the transistor (M) connected to an output end of the input matching network (11), a drain thereof connected to an input end of the output matching network (12), and a source thereof being grounded; wherein the output matching network (12) enables a lower sideband of the harmonic power amplifying circuit to work in a continuous inverse F amplification mode and an upper sideband of the harmonic power amplifying circuit to work in a continuous F amplification mode; wherein the output matching network (12) and a parasitic network of the transistor (M) form a low pass filter. By transitioning from the continuous inverse F power amplifier working mode to the continuous F power amplifier working mode, the efficiency of a continuous harmonic control power amplifier is effectively improved to be higher than 60%, a relative bandwidth is improved to be higher than 80%, and the harmonic impedance is simple to match and easy to realize.

A fixed speaker system comprising a speaker housing mountable in or to a ceiling, wall or floor; at least one speaker for outputting audio content, wherein each speaker comprises at least one speaker input and at least one speaker output; a processor configured to receive the or each speaker input and generate the or each speaker output; an amplifier coupled to the processor and configured to drive the speaker; a DC power input configured for direct electrical coupling with a mains power source; a power-over-ethernet (POE) interface module, comprising an interface housing that is removably connected to the speaker housing, wherein the module is configured to input power from a POE source to the DC power input.

Certain aspects of the present disclosure are generally directed to circuitry and techniques for voltage-to-current conversion. For example, certain aspects provide a circuit for signal amplification including a first amplifier; a first transistor, a gate of the first transistor being coupled to an output of the first amplifier and a drain of the first transistor being coupled to an output node of circuit; a first resistive element coupled between a first input node of the circuit and an input of the first amplifier; a second amplifier; a second transistor, a gate of the second transistor being coupled to an output of the second amplifier and a drain of the second transistor being coupled to the output node of circuit; and a second resistive element coupled between a second input node of the circuit and an input of the second amplifier.

A power supply modulator includes: a first switching element in which a first voltage is applied to the first terminal and the second terminal is connected to an output terminal; a second switching element in which the third terminal is connected to the output terminal and the second terminal, and a second voltage is applied to the fourth terminal; a first driver circuit in which the first voltage is applied to the fifth terminal and the sixth terminal is grounded, to control opening and closing of the first switching element by a change in a resistance value between the fifth and sixth terminals; and a second driver circuit in which the seventh terminal is grounded and the second voltage is applied to the eighth terminal, to control opening and closing of the second switching element by a change in a resistance value between the seventh and eighth terminals.

A power supply modulator includes: a first switching element in which a first voltage is applied to the first terminal and the second terminal is connected to an output terminal; a second switching element in which the third terminal is connected to the output terminal and the second terminal, and a second voltage is applied to the fourth terminal; a first driver circuit in which the first voltage is applied to the fifth terminal and the sixth terminal is grounded, to control opening and closing of the first switching element by a change in a resistance value between the fifth and sixth terminals; and a second driver circuit in which the seventh terminal is grounded and the second voltage is applied to the eighth terminal, to control opening and closing of the second switching element by a change in a resistance value between the seventh and eighth terminals.

A signal coupling system may include a directional coupler that includes a first conductor and a second conductor. The first conductor may include a first end and a second end and may be generally arranged along a first plane. The second conductor may include a third end and a fourth end and may generally be arranged as a plurality of windings along a second plane. The signal coupling system may also include a transceiver, electrically conductively conducted to the first end; and an antenna, electrically conductively conducted to the second end. The second conductor may be configured to generate a coupling with the first conductor when the first conductor conducts an electric signal, such that the coupler conducts a first electrical signal from the first end to the second end at a second power, and conducts the electrical signal via the coupling to the third end at a third power.

A signal coupling system may include a directional coupler that includes a first conductor and a second conductor. The first conductor may include a first end and a second end and may be generally arranged along a first plane. The second conductor may include a third end and a fourth end and may generally be arranged as a plurality of windings along a second plane. The signal coupling system may also include a transceiver, electrically conductively conducted to the first end; and an antenna, electrically conductively conducted to the second end. The second conductor may be configured to generate a coupling with the first conductor when the first conductor conducts an electric signal, such that the coupler conducts a first electrical signal from the first end to the second end at a second power, and conducts the electrical signal via the coupling to the third end at a third power.

A device for controlling wireless charging output power based on a PWM integrating circuit includes a magnetic-resonance transmitting module and a magnetic-resonance receiving module. The magnetic-resonance transmitting module includes a wireless charging base, a Bluetooth master circuit, a DC/DC regulator circuit, a PWM integrating circuit, a radio-frequency power amplifier source, a radio-frequency current sampling circuit and a magnetic-resonance transmitting antenna. Both the radio-frequency power amplifier source and the magnetic-resonance transmitting antenna are mounted at the wireless charging base. The magnetic-resonance transmitting antenna is connected to the magnetic-resonance receiving module. The magnetic-resonance receiving module includes a cooling fin, a magnetic-resonance receiving antenna, a Bluetooth slave circuit, a receiving rectifier and regulator circuit and a charging control circuit. The magnetic-resonance receiving antenna, the receiving rectifier and regulator circuit and the charging control circuit are connected successively. The magnetic-resonance receiving antenna is arranged directly above the magnetic-resonance transmitting antenna.

A device for controlling wireless charging output power based on a PWM integrating circuit includes a magnetic-resonance transmitting module and a magnetic-resonance receiving module. The magnetic-resonance transmitting module includes a wireless charging base, a Bluetooth master circuit, a DC/DC regulator circuit, a PWM integrating circuit, a radio-frequency power amplifier source, a radio-frequency current sampling circuit and a magnetic-resonance transmitting antenna. Both the radio-frequency power amplifier source and the magnetic-resonance transmitting antenna are mounted at the wireless charging base. The magnetic-resonance transmitting antenna is connected to the magnetic-resonance receiving module. The magnetic-resonance receiving module includes a cooling fin, a magnetic-resonance receiving antenna, a Bluetooth slave circuit, a receiving rectifier and regulator circuit and a charging control circuit. The magnetic-resonance receiving antenna, the receiving rectifier and regulator circuit and the charging control circuit are connected successively. The magnetic-resonance receiving antenna is arranged directly above the magnetic-resonance transmitting antenna.

A method for performing predictive maintenance of an amplifier module is described. At least one parameter of at least one amplifier module is acquired via a measurement data acquisition unit. The at least one parameter acquired is analyzed via a measurement data analyzing unit so as to predict the probability and/or time of default of the at least one amplifier module. Further, a system is described.