Abstract: In some embodiments, a low voltage system can include a capacitor between an output node of an amplifier and ground, with the output node connectable to a load, and the amplifier configured to operate with a series of pulses. The low voltage system can further include a monitoring circuit configured to monitor a voltage at the capacitor against a desired low voltage value, and a control system configured to generate the series of pulses for the amplifier, and to control charging and discharging of the capacitor based on an output of the monitoring circuit to regulate the voltage at the output node at approximately the desired low voltage value.

Abstract: Bride combiners with resonators for radio-frequency applications. A bridge combiner can be implemented as a coupling circuit that includes a common node and configured to couple the common node to a first group of filters through a first path and to couple the common node to a second group of one or more filters through a second path. The coupling circuit can include a resonator such that an impedance provided by each filter of the first group for a signal in each band of the second group results in the signal being sufficiently excluded from the first path, and such that an impedance provided by each filter of the second group for a signal in each band of the first group results in the signal being sufficiently excluded from the second path.

Abstract: Low noise amplifiers (LNAs) with low noise figure are provided. In certain embodiments, an LNA includes a single-ended LNA stage including an input for receiving a single-ended input signal from an antenna and an output for providing a single-ended amplified signal, a balun for converting the single-ended amplified signal to a differential signal, and a variable gain differential amplification stage for amplifying the differential signal from the balun. Implementing the LNA in this manner provides low noise figure, high gain, flexibility in controlling gain, and less sensitivity to ground/supply impedance.

Abstract: Circuits, methods, and devices for protecting against accidental fuse programming are discussed herein. For example, a fuse circuit may include a fuse, a first switch coupled to a first point and coupled in series with the fuse, and a second switch coupled in series with the fuse between the fuse and a second point.

Abstract: An electronic device package comprises an electronic acoustic device including a primary microphone having a frequency response having a resonance frequency, and a reference microphone having a frequency response including a resonance frequency. The primary microphone and the reference microphone are configured to substantially simultaneously receive a common acoustic signal to produce a transduced signal of the primary microphone and a transduced signal of the reference microphone, the resonance frequency of the reference microphone being different than the resonance frequency of the primary microphone. An equalization module is configured to equalize the frequency response of the microphone based on the transduced signal of the microphone and the transduced signal of the reference microphone. The package defines a first back cavity of the primary microphone and a second back cavity of the reference microphone, the second back cavity being acoustically isolated from the first back cavity.

Abstract: Antenna systems with both single-ended and differential signal feeds are provided herein. In certain embodiments, a mobile device includes a front end system including a first radio frequency signal conditioning circuit configured to condition a first radio frequency signal that is single-ended and of a first frequency, and a second radio frequency signal conditioning circuit configured to condition a second radio frequency signal that is differential and of a second frequency. The mobile device further includes an antenna including a first signal feed connected to the first radio frequency signal conditioning circuit and a pair of second signal feeds connected to the second radio frequency signal conditioning circuit.

Abstract: A clamping circuit comprises a first field-effect transistor (FET) having a gate, a source, and a drain, a diode, a first voltage source, and coupling circuitry configured to couple the first voltage source to the drain of the first FET and the diode to the source of the first FET.

Abstract: Asymmetric Doherty power amplifiers are disclosed. In certain embodiments, a Doherty power amplifier includes a carrier amplifier that generates a radio frequency carrier signal based on amplifying a radio frequency input signal, a peaking amplifier that generates a radio frequency peaking signal based on amplifying the radio frequency input signal, and a phase shifting and combining circuit configured to combine the radio frequency carrier signal and the radio frequency peaking signal to generate a radio frequency output signal. The carrier amplifier and the peaking amplifier have asymmetric amplifier sizes.

Abstract: A radio frequency (RF) switch arrangement that improves the voltage handling capacity of a stack of switching elements (e.g., field-effect transistors (FETs)). The RF switch arrangement can include a ground plane and a stack arranged in relation to the ground plane, the stack including a plurality of switching elements coupled in series with one another. The RF switch arrangement can also include a plurality of capacitive elements, each of the plurality of capacitive elements providing a capacitive path across respective terminals of a corresponding one of the plurality of switching elements.

Abstract: In some embodiments, a calibration circuit for an audio amplification system can include a tone generator configured to provide a tone having a frequency to an input path of an audio amplifier, such that an input signal provided to the audio amplifier includes the tone, a a first sampling circuit configured to sample an output signal at an output node of the audio amplifier, and a second sampling circuit configured to sample the input signal at an input node of the audio amplifier. The calibration circuit can further include a gain adjustment circuit configured to generate a correction signal based on the sampled output signal and the sampled input signal to correct for a gain variation of the audio amplifier.

Abstract: Devices and methods related to wideband multiplexer for radio-frequency (RF) applications. In some embodiments, a multiplexer may include a common path configured to receive a plurality of RF signals. The multiplexer may further include a first path having an output coupled to the common path and configured to provide a band-pass response for a frequency band BX. The multiplexer may further include a second path having an output coupled to the common path such that RF signals in the first and second paths are combined and routed through the common path. The second path may be configured to provide a band-stop response for the frequency band BX such that the common path includes a wideband response that includes the frequency band BX and one or more other frequency bands.

Abstract: A switching circuit comprises a first series switch coupled to a first output port, the first series switch including a first field-effect transistor (FET), a second FET, a third FET, a fourth FET, a fifth FET, and a sixth FET, a second series switch coupled to a second output port, and coupling circuitry configured to couple a gate of the fifth FET and a gate of the sixth FET to a first node, a source of the fifth FET and a drain of the sixth FET to a second node, a source of the first FET and a drain of the second FET to a third node, a gate of the first FET and a drain of the fifth FET to a fourth node, a gate of the second FET and a source of the sixth FET to a fifth node, the fourth node and the fifth node to a first gate voltage, and the first node to a second gate voltage that is different than the first gate voltage.

Abstract: Aspects of this disclosure relate to multiplexers with acoustic wave resonators. The multiplexer includes a first filter and a second filter. The first filter includes a plurality of bulk acoustic wave resonators and a shunt surface acoustic wave resonator. The shunt acoustic wave resonator can have a resonant frequency in a passband of the second filter. The passband of the second filter is below a passband of the first filter. In certain applications, the first filter is a receive filter and the second filter is a transmit filter.

Abstract: Aspects of this disclosure relate to acoustic wave filter. The acoustic wave filter can include different types of acoustic wave resonators. The acoustic wave filter can include shunt acoustic wave resonator that has lower second harmonic distortion than other acoustic wave resonators of the acoustic wave filter. In certain embodiments, the shunt acoustic wave resonator can be a surface acoustic wave resonator. Related multiplexers, radio frequency modules, wireless communication devices, and methods are also disclosed.

Abstract: A circumaural headset having a first earcup and a second earcup can include a first transducer disposed with the first earcup and configured to transmit a first non-audible signal with an audible signal, a second transducer disposed within the second earcup and configured to receive the first non-audible signal from the first transducer, and an off-ear detection processor configured to determine whether the headset has been removed from the user's head based on the second transducer receiving the first non-audible signal from the first transducer.

Abstract: Multiplexers are disclosed. A multiplexer can include a first filter and a second filter that are coupled to a common node. The second filter can include a first type of acoustic wave resonators (e.g., bulk acoustic wave resonators) and a series acoustic wave resonator of a second type (e.g., a surface acoustic wave resonator) that is coupled between the acoustic wave resonators of the first type and the common node. The first filter can provide a single-ended radio frequency signal. In certain embodiments, the first filter can be a receive filter and the second filter can be a transmit filter.

Abstract: Envelope tracking systems for power amplifiers are provided herein. In certain embodiments, an envelope tracker is provided for a power amplifier that amplifies a radio frequency (RF) signal. The envelope tracker controls a power amplifier supply voltage of the power amplifier based on an envelope signal indicating an envelope of the RF signal. The envelope tracker includes a first controllable resistance between a first regulated voltage and the power amplifier supply voltage and a second controllable resistance between a second regulated voltage and the power amplifier supply voltage. The first regulated voltage and the second regulated voltage are of different voltage levels.

Abstract: The present disclosure relates to devices and methods for detecting and preventing occurrence of a saturation state in a power amplifier. A power amplifier module can include a power amplifier including a cascode transistor pair. The cascode transistor pair can include a first transistor and a second transistor. The power amplifier module can include a current comparator configured to compare a first base current of the first transistor and a second base current of the second transistor to obtain a comparison value. The power amplifier module can include a saturation controller configured to supply a reference signal to an impedance matching network based on the comparison value. The impedance matching network can be configured to modify a load impedance of a load line in electrical communication with the power amplifier based at least in part on the reference signal.

Abstract: Beamforming communication systems with crossbar switches are provided herein. In certain embodiments, a beamforming communication system includes an antenna array partitioned into a plurality of sub-arrays, a plurality of front-end channels each operatively associated with one of the sub-arrays, a plurality of data conversion channels, and a crossbar switch electrically connected between the data conversion channels and the front-end channels. Including the crossbar switch allows for a flexible allocation of the data conversion channels to the front-end channels and subsequently to each individual antenna element in the array.

Abstract: Amplifying a signal includes outputting an output signal from a Class D amplifier configured to operate as a current driver to a load, such as a loudspeaker, the output of the Class D amplifier controlled by a feedback loop, and, in the feedback loop: performing analog filtering using an active analog filter on an error signal that is based on the output of the Class D amplifier and a reference signal, digitizing a filtered output of the analog filter to produce a sequence of digital values, performing digital filtering on the sequence of digital values to produce a sequence of filtered digital values, and generating a pulse signal to control the output of the Class D amplifier based on the sequence of filtered digital values. The digital filter reduces a destabilizing effect of the loudspeaker's inductance. Associated circuits, systems, modules and electronic devices are disclosed.