In some embodiments, an amplifier system can include an amplifier circuit having first and second amplifiers configured to amplify respective first and second portions of an input signal. Each of the first and second amplifiers can include a cascode stage with input and output transistors arranged in a cascode configuration. The amplifier system can further include an envelope tracking bias circuit coupled to the amplifier circuit and configured to provide a bias signal to the output transistor of the cascode stage of at least one of the first and second amplifiers. The amplifier system can further include a supply circuit configured to provide a non-envelope tracking supply voltage to the output transistor of the cascode stage of the at least one of the first and second amplifiers.

Apparatus and methods for capacitive load reduction are disclosed. In one embodiment, a mobile device includes a supply control circuit that controls a voltage of a supply network, a plurality of radio frequency circuits that receive power from the supply network and are selectively enabled by a plurality of enable signals, a plurality of switchable capacitors electrically connected to the supply network, a plurality of field-effect transistors operatively associated with the plurality of switchable capacitors, and a bias control circuit that generates a plurality of control signals that bias the plurality of field-effect transistors based on a state of the plurality of enable signals. Each of the plurality of control signals are operable to selectively bias a corresponding one of the plurality of field-effect transistors in a cutoff mode to provide high impedance or as a dampening resistor to suppress oscillations.

A novel and useful radio frequency (RF) front end module (FEM) circuit that provides high linearity and power efficiency and meets the requirements of modern wireless communication standards such as 802.11 WLAN, 3G and 4G cellular standards, Bluetooth, ZigBee, etc. The configuration of the FEM circuit permits the use of common, relatively low cost semiconductor fabrication techniques such as standard CMOS processes. The FEM circuit includes a power amplifier made up of one or more sub-amplifiers having high and low power circuits and whose outputs are combined to yield the total desired power gain. An integrated multi-tap transformer having primary and secondary windings arranged in a novel configuration provide efficient power combining and transfer to the antenna of the power generated by the individual sub-amplifiers.

A method and system for modulating a drain supply voltage of a power amplifier are disclosed. A low pass envelope of a dual band modulated signal input to the power amplification system is determined. The determined low pass envelope is amplified. A drain supply of the power amplifier is modulated based on the amplified determined low pass envelope.

A power supply for a radio frequency (RF) power amplifier that amplifies an RF input signal into an RF output signal and a method of operation in the power supply. The power supply comprises a first power converter to convert an input voltage to the power supply into a first supply voltage of the RF power amplifier. The power supply comprises a second power converter to receive the input voltage and the first supply voltage and to selectively convert either the input voltage or the first supply voltage into at least a portion of a second supply voltage of the RF power amplifier.

Apparatus and methods for output matching of power amplifiers are provided. In certain configurations, a mobile device includes a power amplifier that amplifies an RF signal to generate an amplified RF signal at an output, an envelope tracker that generates a power amplifier supply voltage based on an envelope of the RF signal, a supply voltage biasing circuit that provides the power amplifier supply voltage from the envelope tracker to the output of the power amplifier, and an output matching circuit connected to the output of the power amplifier via an input node. The output matching circuit includes a first capacitor and a first inductor connected in series between the input node and ground, a second capacitor connected between the input node and ground, a second inductor connected between the input node and an intermediate node, and a DC blocking capacitor connected between the intermediate node and an output node.

A apparatus for radio frequency power amplification, a radio frequency power amplification method, a transmitter, and a base station that can reduce nonlinear signal distortion factors are disclosed. The radio frequency power amplification system includes: a radio frequency signal generation circuit, configured to process a baseband digital signal, to obtain an original radio frequency signal; a radio frequency signal processing circuit, configured to process the original radio frequency signal, to obtain N processed radio frequency signals, where N is greater than or equal to 2; a power amplifier, configured to perform power amplification on each of the N processed radio frequency signals, to obtain N amplified radio frequency signals; and a combiner, configured to combine the N amplified radio frequency signals.

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.

Envelope tracking power converter circuitry is configured to receive a supply voltage, an envelope control signal, and an average power tracking control signal and simultaneously provide an envelope tracking power supply signal for amplifying a first radio frequency (RF) input signal based on the envelope control signal and an average power tracking power supply signal for amplifying a second RF input signal based on the average power tracking control signal.

A linearizer comprises a delay compensation circuit, an envelope reshaping circuit and a phase shift unit. The delay compensation circuit is configured to delay an input signal and to output a delayed input signal to a power amplifier. The envelope reshaping circuit is configured to detect an envelope of the input signal and to generate a reshaped envelope signal. The phase shift unit configured to provide an envelope reshaped capacitance based on the reshaped envelope signal to the delayed input signal to reshape the delayed input signal.