A bipolar transistor includes a collector layer, a base layer, and an emitter layer that are formed in this order on a compound semiconductor substrate. The emitter layer is disposed inside an edge of the base layer in plan view. A base electrode is disposed on partial regions of the emitter layer and the base layer so as to extend from an inside of the emitter layer to an outside of the base layer in plan view. An insulating film is disposed between the base electrode and a portion of the base layer, with the portion not overlapping the emitter layer. An alloy layer extends from the base electrode through the emitter layer in a thickness direction and reaches the base layer. The alloy layer contains at least one element constituting the base electrode and elements constituting the emitter layer and the base layer.

The disclosed technology can include a power amplifier comprising an input, an output, and a transformer. The power amplifier can include a primary inductor coil coupled to the input, a secondary inductor coil coupled to the output, and three harmonic branches coupled to the primary coil. Each branch can comprise at least one electrical component having a tunable impedance.

A Doherty amplifier module includes first and second amplifier die. The first amplifier die includes one or more first power transistors configured to amplify, along a first signal path, a first input RF signal to produce an amplified first RF signal. The second amplifier die includes one or more second power transistors configured to amplify, along a second signal path, a second input RF signal to produce an amplified second RF signal. A phase shift and impedance inversion element is coupled between the outputs of the first and second amplifier die. A shunt circuit is coupled to the output of either or both of the first and/or second amplifier die. The shunt circuit includes a series coupled inductance and high-Q capacitor (e.g., a metal-insulator-metal (MIM) capacitor), and the shunt circuit is configured to at least partially resonate out the output capacitance of the amplifier die to which it is connected.

Certain aspects of the present disclosure provide methods and apparatus for operating a power amplifier. In one example, the apparatus includes a power amplifier configured to amplify an input signal having a frequency to produce a radio frequency (RF) output signal at an output and a harmonic tuning circuit coupled between a power supply and the power amplifier output, the harmonic tuning circuit configured to reduce a current or voltage provided to the power amplifier via a resonance at one or more harmonics of the frequency of the input signal.

A high-frequency front end circuit includes an antenna terminal, a reception circuit that is directly or indirectly connected to the antenna terminal, and a transmission circuit that is directly or indirectly connected to the antenna terminal, wherein the transmission circuit has an amplification circuit, the amplification circuit includes an input terminal and an output terminal, an amplification element provided on a path connecting the input terminal and the output terminal, and a bias circuit having an LC resonance circuit and connected to between the amplification element and the output terminal. A frequency pass band of the transmission circuit is lower than a frequency pass band of the reception circuit, and a value of a resonant frequency of the bias circuit is smaller than a value of a frequency pass band width of the transmission circuit.

A wireless access point is configured to regularly monitor the status of WLAN, WAN and ePDG data links to determine whether the current connections are sufficient to support VoWiFI services. When a device connects to the WLAN of the hub and attempts to switch from its VoLTE service to VoWiFi via the hub, the hub is configured to determine whether the current conditions can satisfy a VoWiFi connection. If the VoWiFi service can support the connection, the request is routed to the ePDG associated with the mobile device's subscriber LTE network. However, if the current conditions cannot satisfactorily support a VoWiFi connection such that incoming calls may be missed or the quality of active calls would not be clear, then the hub is configured to block the request so that the client device will time out and remain connected to VoLTE.

A radio frequency amplifier circuit has a signal input and a signal output. A primary amplifier is connected to the signal input and the signal output. A low dropout voltage regulator is connectible to an external power supply and to the primary amplifier, and generates a set voltage to bias the primary amplifier from a variable voltage provided by the external power supply. An equivalent capacitance circuit is connected to the primary amplifier and to the low dropout voltage regulator. The equivalent capacitance circuit defines a low dropout voltage regulator output capacitance in a nano-Farad to micro-Farad range absent any passive capacitor components corresponding thereto to maintain linearity of the primary amplifier.

A power amplifier module includes a power amplifier circuit and a control IC. The power amplifier circuit includes a bipolar transistor that amplifies power of an RF signal and outputs an amplified signal. The control IC includes an FET, which serves as a bias circuit that supplies a bias signal to the bipolar transistor. The FET is operable at a threshold voltage lower than that of the bipolar transistor, thereby making it possible to decrease the operating voltage of the power amplifier module.

A power amplifier (PA) system is provided for multi-mode multi-band operations. The PA system includes one or more amplifying modules, each amplifying module including one or more banks, each bank comprising one or more transistors; and a plurality of matching modules, each matching module being configured to be adjusted to provide impedances corresponding to frequency bands and conditions. A controller dynamically controls an input terminal of each bank and adjusts the matching modules to provide a signal path to meet specifications on properties associated with signals during each time interval.

A power amplifier includes a two-dimensional matrix of NM active cells formed by stacking main terminals of multiple active cells in series. The stacks are coupled in parallel to form the two-dimensional matrix. The power amplifier includes a driver structure to coordinate the driving of the active cells so that the effective output power of the two-dimensional matrix is approximately NM the output power of each of the active cells.