A power amplifier circuit includes a first transistor having a first terminal to which a voltage corresponding to a variable power supply voltage is to be supplied and a second terminal to which a radio-frequency signal is to be supplied, the first transistor being configured to amplify the radio-frequency signal, a bias circuit configured to supply a bias current or voltage to the second terminal of the first transistor, and an adjustment circuit configured to adjust the bias current or voltage in accordance with the variable power supply voltage supplied from a power supply terminal.

An apparatus is disclosed for phase-shifting signals. In example implementations, the apparatus includes a phase shifter. The phase shifter includes a first port, a second port, a vector modulator coupled to the first port, and a signal phase generator. The signal phase generator includes multiple amplifiers coupled between the vector modulator and the second port. The signal phase generator also includes multiple capacitors that couple the multiple amplifiers together to form a loop. Each respective capacitor of the multiple capacitors is coupled between a respective pair of consecutive amplifiers of the multiple amplifiers to form the loop.

A radio frequency (RF) signal transceiver is provided. The RF signal transceiver includes a first transformer, a signal transceiving processor, a signal receiving amplifier, and a signal transmitting amplifier. The first transformer is coupled to an antenna through a first end of a primary side, and two endpoints of a secondary side of the first transformer receive and transmit a pair of differential signals. The signal transceiving processor receives a pair of input differential signals from the secondary side of the first transformer and generates a pair of processed differential signals. The signal receiving amplifier is coupled to the signal transceiving processor and is configured to receive and amplify the pair of processed differential signals. The signal transmitting amplifier is coupled to the secondary side of the first transformer and provides a pair of transmission differential signals to the secondary side.

Disclosed herein are improved communication systems and methods for operating in a lightly-licensed, shared frequency spectrum. In one aspect, the disclosed systems and methods may involve a small cell having a coverage area and comprising a radio frequency integrated circuit (RFIC), a switch, an antenna, a power amplifier, and a low noise amplifier (LNA). A receiver RF chain of the small cell may be defined by an interconnection between the antenna, the switch, the LNA, and the RFIC, and a transmitter RF chain of the small cell may be defined by an interconnection between the RFIC, the power amplifier, the switch, and the antenna. In accordance with the present disclosure, the LNA may be configured with at least one parameter that is defined based on an uplink link-budget deficiency associated with a client terminal having a given power class and located at a given location of the coverage area.

An electrical system includes a power supply and an electrical circuit coupled to the power supply and including an operational amplifier. The operational amplifier includes an input stage and a pre-driver stage coupled to the input stage, wherein the pre-driver stage includes a first input terminal, a second input terminal, and a voltage supply terminal. The operational amplifier also includes an output stage with bipolar transistors coupled to the pre-driver stage. The pre-driver stage is configured to: detect a voltage differential across the first and second input terminals of the pre-driver stage; and provide an adjustable bias current based on the voltage differential.

Disclosed herein is an operational amplifier including a non-inverting input terminal, an inverting input terminal, a P-type metal oxide semiconductor input differential pair, a first input tail current source, an N-type metal oxide semiconductor input differential pair, a second input tail current source, an output stage, a first correction circuit, and a second correction circuit. The first correction circuit and the second correction circuit operate over an operation region of the P-type metal oxide semiconductor input differential pair, an operation region of the N-type metal oxide semiconductor input differential pair, and a transition region in which both the P-type metal oxide semiconductor input differential pair and the N-type metal oxide semiconductor input differential pair operate.

A data transmitter includes: a plurality of parallel driver slices, a first slice of the plurality of parallel driver slices having a first signal generator circuit with a first transistor coupled to a data signal and in series with a second transistor coupled to a first bias signal; and a first bias circuit including a third transistor and a fourth transistor in series with a first current source, the first bias circuit further including a first operational amplifier (op amp) having a first input coupled to a first reference voltage and a second input coupled between the fourth transistor and the first current source, an output of the first op amp configured to provide the first bias signal to the second transistor and to the third transistor.

Certain aspects of the present disclosure are generally directed to circuitry and techniques for current sensing. For example, certain aspects provide a circuit for signal amplification including a first amplifier, a second amplifier, and a third amplifier. The circuit also includes a first capacitive element coupled between a first output of the first amplifier and a first input of the third amplifier, a second capacitive element coupled between a second output of the first amplifier and a second input of the third amplifier, a third capacitive element coupled between a first output of the second amplifier and the first input of the third amplifier, and a fourth capacitive element coupled between a second output of the second amplifier and the second input of the third amplifier.

A power amplifier includes a 3-dB coupler which splits a first signal into a second signal and a third signal lagging behind the second signal by 90°, a carrier amplifier, a peak amplifier, and a hybrid coupler. The carrier amplifier amplifies the second signal and outputs a fourth signal when the first-signal power level is a first level or higher. The peak amplifier amplifies the third signal and outputs a fifth signal when the first-signal power level is a second level or higher, which is higher than the first level. The hybrid coupler includes a first transmission line receiving the fourth signal at its first terminal, and a second transmission line receiving the fifth signal at its first terminal and being open at its second terminal. The first transmission line outputs, from its second terminal, an amplified first signal obtained by combining the fourth and fifth signals.

A power amplifier module includes a substrate, an amplifier circuit including a plurality of transistors to be mounted on the substrate and a bump connected to the plurality of transistors, a harmonic termination circuit and an output matching circuit that are disposed in or on the substrate and configured to be electrically connected to the amplifier circuit, a connection pad disposed on the substrate and configured to be connected to the bump, and a plurality of connection wiring lines branching from the connection pad. The plurality of connection wiring lines include at least a first connection wiring line that connects the connection pad and the harmonic termination circuit to each other, a second connection wiring line that connects the connection pad and the output matching circuit to each other, and a third connection wiring line that connects the connection pad and an external power supply to each other.