Various methods and circuital arrangements for biasing one or more gates of stacked transistors of an amplifier are presented, where the amplifier can be an envelope tracking amplifier. Circuital arrangements to generate reference gate-to-source voltages for biasing of the gates of the transistors of the stack are also presented. Particular biasing for a case of an input transistor of the stack is also presented.

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.

Various envelope tracking amplifiers are presented that can be switched between an ET (envelope tracking) mode and a non-ET mode. Switches and/or tunable components are utilized in constructing the envelope tracking amplifiers that can be switched between the ET mode and the non-ET mode.

Various methods and circuital arrangements for biasing one or more gates of stacked transistors of an amplifier are presented, where the amplifier can have a varying supply voltage that varies according to a control voltage. The control voltage can be related to a desired output power of the amplifier and/or to an envelope signal of an input signal to the amplifier. Particular biasing for selectively controlling the stacked transistors to operate in either a saturation region or a triode region is also presented. Benefits of such controlling, including increased linear response of an output power of the amplifier, are also discussed.

A transimpedance amplifier includes a first and a second power supply terminal for receiving a positive constant supply voltage, wherein the second power supply terminal represents a ground, and an input terminal adapted to be connected to a current source. The transimpedance amplifier further comprises a transistor comprising a control terminal and two further terminals, wherein the input terminal is connected to the control terminal of the first transistor. An inductor is connected between the first of the two further terminals of the transistor and the first power supply terminal, and a bias network is connected between the second of the two further terminals of the transistor and ground. Specifically, the transimpedance amplifier is configured such that the resistance between said first of said two further terminals of said first transistor and said first power supply terminal is small enough, such that said transimpedance amplifier operates as a differentiator.

A transimpedance amplifier includes a first and a second power supply terminal for receiving a positive constant supply voltage, wherein the second power supply terminal represents a ground, and an input terminal adapted to be connected to a current source. The transimpedance amplifier further comprises a transistor comprising a control terminal and two further terminals, wherein the input terminal is connected to the control terminal of the first transistor. An inductor is connected between the first of the two further terminals of the transistor and the first power supply terminal, and a bias network is connected between the second of the two further terminals of the transistor and ground. Specifically, the transimpedance amplifier is configured such that the resistance between said first of said two further terminals of said first transistor and said first power supply terminal is small enough, such that said transimpedance amplifier operates as a differentiator.

A parallel resonant circuit with excellent distortion and saturation characteristics is provided at low power consumption. A first power-supply voltage is applied to the parallel resonant circuit. In the parallel resonant circuit, a variable resistor includes one or more parallel-connected branches. Each of the branches includes a series circuit of a resistor and a MOS switch. A second power supply supplies power of control signals applied to respective gates of the MOS switches, and supplies back gate voltages to the MOS switches. A power-supply voltage of the second power supply is higher than the first power-supply voltage.

Optimization methods via various circuital arrangements for amplifier with variable supply power are presented. In one embodiment, a switch can be controlled to include or exclude a feedback network in a feedback path to the amplifier to adjust a response of the amplifier dependent on a region of operation of the amplifier arrangement (e.g. linear region or compression region).

Systems and method for improving operation of a radio frequency system are provided. One embodiment describes a radio frequency system, which includes a first switching power amplifier that outputs an amplified analog electrical signal based on a first input analog electrical signal and voltage of an envelope voltage supply rail. The first switching power amplifier includes a first transistor with a gate that receives the first input analog electrical signal, a source that is electrically coupled to the envelope voltage supply rail, and a drain that is electrically coupled to an output of the first switching power amplifier; a second transistor with a gate that receives the first input analog electrical signal, a source electrically coupled to ground, and a drain electrically coupled to the output of the first switching power amplifier; and a third transistor with a gate that receives the first input analog electrical signal, a drain electrically coupled to the envelope voltage supply rail, and a source electrically coupled to an output of a second switching power amplifier.