Aspects of this disclosure relate to a cascode circuit electrically coupled between an amplifier configured to amplify a radio frequency (RF) signal and different loads. The cascode circuit can function as a switch to selectively provide an output from the amplifier to a number of different loads. In certain embodiments, the cascode circuit can be electrically coupled between different stages of a multi-stage power amplifier. For instance, the amplifier can be a first stage of the multi-stage power amplifier and the different loads can include different power amplifier transistors of a second stage of the multi-stage amplifier. The cascode circuit can be implemented by bipolar transistors according to certain embodiments.

Aspects of this disclosure relate to a cascode circuit electrically coupled between an amplifier configured to amplify a radio frequency (RF) signal and different loads. The cascode circuit can function as a switch to selectively provide an output from the amplifier to a number of different loads. In certain embodiments, the cascode circuit can be electrically coupled between different stages of a multi-stage power amplifier. For instance, the amplifier can be a first stage of the multi-stage power amplifier and the different loads can include different power amplifier transistors of a second stage of the multi-stage amplifier. The cascode circuit can be implemented by bipolar transistors according to certain embodiments.

Power amplification system with shared common base biasing. A power amplification system can include a plurality of cascode amplifier sections. Each one of the plurality of cascode amplifier sections can include including a first transistor and a second transistor. The power amplification system can include a plurality of common emitter biasing components. Each one of the plurality of common emitter biasing components can be coupled to a base of the first transistor of a respective one of the plurality of cascode amplifier sections and can be controllable to bias the first transistor of the respective one of the plurality of cascode amplifier sections. The power amplification system can include a common base biasing component coupled to a base of the second transistor of each of the plurality of cascode amplifier sections and controllable to bias the second transistor of each of the plurality of cascode amplifier sections.

Power amplification system with shared common base biasing. A power amplification system can include a plurality of cascode amplifier sections. Each one of the plurality of cascode amplifier sections can include including a first transistor and a second transistor. The power amplification system can include a plurality of common emitter biasing components. Each one of the plurality of common emitter biasing components can be coupled to a base of the first transistor of a respective one of the plurality of cascode amplifier sections and can be controllable to bias the first transistor of the respective one of the plurality of cascode amplifier sections. The power amplification system can include a common base biasing component coupled to a base of the second transistor of each of the plurality of cascode amplifier sections and controllable to bias the second transistor of each of the plurality of cascode amplifier sections.

An envelope tracking system is employed in a power amplification module that supports multiple frequency bands. The power amplification module includes multiple power amplification circuits, each of which includes: a first transformer to which a radio frequency signal is input; a differential amplification circuit, in which a first radio frequency signal output from transformer is input to a control electrode and in which a second radio frequency signal output from the transformer is input to a control electrode, the differential amplification circuit outputting an amplified signal obtained by amplifying a difference between the first and second radio frequency signals; and a second transformer for supplying, to the first differential amplification circuit, power-supply voltage varying according to the amplitude of the radio frequency signal and to which the first amplified signal is input.

An envelope tracking system is employed in a power amplification module that supports multiple frequency bands. The power amplification module includes multiple power amplification circuits, each of which includes: a first transformer to which a radio frequency signal is input; a differential amplification circuit, in which a first radio frequency signal output from transformer is input to a control electrode and in which a second radio frequency signal output from the transformer is input to a control electrode, the differential amplification circuit outputting an amplified signal obtained by amplifying a difference between the first and second radio frequency signals; and a second transformer for supplying, to the first differential amplification circuit, power-supply voltage varying according to the amplitude of the radio frequency signal and to which the first amplified signal is input.

Embodiments described herein relate to an envelope tracking system that uses a single-bit digital signal to encode an analog envelope tracking control signal, or envelope tracking signal for brevity. In certain embodiments, the envelope tracking system can estimate or measure the amplitude of the baseband signal. The envelope tracking system can further estimate the amplitude of the envelope of the RF signal. The system can convert the amplitude of the envelope signal to a single-bit digital signal, typically at a higher, oversample rate. The single-bit digital signal can be transmitted in, for example, a low-voltage differential signaling (LVDS) format, from a transceiver to an envelope tracker. An analog-to-digital converter (ADC or A/D) can convert the single-bit digital signal back to an analog envelope signal. Moreover, a driver can increase the power of the A/D output envelope signal to produce an envelope-tracking supply voltage for a power amplifier.

Various implementations include circuits, devices and/or methods that provide open loop current limiting power amplifiers and the like. In some implementations, an open loop current clamp includes a trim module to provide a control value and a limiting source having respective input and output terminals. The input terminal is coupled to the trim module to receive the control value. The output terminal coupled to a control terminal of the first transistor to provide a limiting electrical level produced in response to the control value by the limiting source. The limiting electrical level substantially setting a first mode of operation for the first transistor such that the current draw of the first transistor is substantially determined by the first mode of operation and the limiting electrical level such that a voltage at an output terminal of the first transistor exerts reduced influence on the current draw.

Various implementations include circuits, devices and/or methods that provide open loop current limiting power amplifiers and the like. In some implementations, an open loop current clamp includes a trim module to provide a control value and a limiting source having respective input and output terminals. The input terminal is coupled to the trim module to receive the control value. The output terminal coupled to a control terminal of the first transistor to provide a limiting electrical level produced in response to the control value by the limiting source. The limiting electrical level substantially setting a first mode of operation for the first transistor such that the current draw of the first transistor is substantially determined by the first mode of operation and the limiting electrical level such that a voltage at an output terminal of the first transistor exerts reduced influence on the current draw.

Compression control through power amplifier load adjustment. 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 power amplifier bias controller including 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.