An adaptive power amplifier and a radio frequency transmitter thereof are described. The radio frequency transmitter is a transmitter to transmit a transmission signal for a wireless communication system. The radio frequency transmitter includes at least one direct-current (DC) to direct-current (DC) converter coupled to an external power supply device for operation, a digital-to-analog converter configured to convert a digital signal into an analog signal, a filter configured to filter a harmonic component of the analog signal to generate an input signal, a RF up-converter configured to up-convert the input signal according to a desired channel frequency for generating a modulated signal, and a power amplifying circuit coupled to the DC-to-DC converter and the external power supply device, for selectively receiving one of different supply voltages for operation, and amplifying the modulated signal to generate a RF output signal.

A radio frequency (RF) receive circuit is described herein. In accordance with one embodiment, the RF receive circuit includes a mixer configured to receive an RF input signal to down-convert the RF input signal into a base-band or intermediate frequency (IF) band, an analog-to-digital converter (ADC), and a signal processing chain coupled between the mixer and the ADC. The signal processing chain includes at least two circuit nodes. The RF receive circuit further includes an oscillator circuit that is configured to generate a test signal. The oscillator circuit is coupled to the signal processing chain and is configured to selectively feed the oscillator signal into one of the at least two circuit nodes.

Certain aspects of the present disclosure generally relate to an amplifier configured to process signals received in different frequency bands, where at least a portion of the amplifier is shared between different modes corresponding to the different frequency bands. One example circuit generally includes an amplifier having at least one first transistor configured to amplify a first signal received in a first mode of operation (e.g., associated with a particular frequency band), and at least one second transistor configured to amplify a second signal received in a second mode of operation. The amplifier may also include a transformer comprising a primary winding and a secondary winding, and one or more switches configured to selectively couple the primary winding to the first transistor or the second transistor based on the first mode or the second mode of operation, respectively. In certain aspects, the transformer may be coupled to a transconductance circuit.

Disclosed are an apparatus and method of processing an audio signal to optimize audio for a room environment. One example method of operation may include recording the audio signal generated within a particular room environment and processing the audio signal to create an original frequency response based on the audio signal. The method may also include identifying a target sub-region of the frequency response which has a predetermined area percentage of a total area under a curve generated by the frequency response, determining whether the target sub-region is a narrow energy region, creating a filter to adjust the frequency response, and applying the filter to the audio signal.

A radio frequency receiver having a plurality of parallel receiving paths, wherein each path can receive a radio frequency signal in one of a plurality of radio frequency bands and amplify the received signal in a low noise amplifier. The amplified signals from the plurality of parallel paths are combined to one combined radio frequency signal in a common summation node and down-converted to a lower frequency signal in a mixer circuit. Each low noise amplifier comprises a low noise transconductance circuit providing a current signal to drive the common summation node, and an automatic gain control circuit in each path compensates for variations in signal strength independently of signal strengths of signals received by the other receiving paths. The receiver is suitable for simultaneous multiple band reception, where received signal strength can vary between the frequency bands.

A compound semiconductor device includes: a GaN-based channel layer; a barrier layer of nitride semiconductor above the channel layer; and a cap layer of nitride semiconductor above the barrier layer, wherein the cap layer includes: a first region doped with Fe; and a second region above the first region, a concentration of Fe in the second region being lower than a concentration of Fe in the first region.

The present invention relates in one aspect to a class D audio amplifier with improved output driver topology supporting multi-level output signals such as 3-level, 4-level or 5-level pulse width or pulse density modulated output signals for application to a loudspeaker load. The present class D audio amplifiers are particularly well-suited for high-volume consumer audio applications and solutions.

Provided are a semiconductor device and an operating method thereof. A semiconductor device includes a mixer configured to upconvert a baseband signal using a local oscillator (LO) signal; and a notch filter configured to receive the upconverted signal from the mixer and filter notch frequency components, the notch filter further configured to resonate at a fundamental frequency to provide a higher impedance and resonate at a notch frequency different from the fundamental frequency to provide a lower impedance.

Provided are a semiconductor device and an operating method thereof. A semiconductor device includes a mixer configured to upconvert a baseband signal using a local oscillator (LO) signal; and a notch filter configured to receive the upconverted signal from the mixer and filter notch frequency components, the notch filter further configured to resonate at a fundamental frequency to provide a higher impedance and resonate at a notch frequency different from the fundamental frequency to provide a lower impedance.

A power amplifier is provided. The power amplifier comprises: a universal pulse converter configured to: receive at least one analog input; and modulate an in-phase component of the at least one analog input and a quadrature component of the at least one input signal; a processor configured to process the in-phase and quadrature components, the processor comprising: a clock configured to produce a clock signal; a pulse processor configured to remove non-essential information from the modulated in-phase and quadrature components; and a pulse converter configured to output a control signal based on a selected amplifier class; and a switching network configured to actuate one or more switches based on the control signal to output an amplified signal.