Embodiments of circuits for use with an amplifier that includes multiple amplifier paths include a first circuit and a second circuit in parallel with the first circuit. The first circuit includes a first input coupled to a first power divider output, a first output coupled to a first amplifier path of the multiple amplifier paths, and a first adjustable phase shifter and a first attenuator series coupled between the first input and the first output. The second circuit includes a second input coupled to a second power divider output, a second output coupled to a second amplifier path of the multiple amplifier paths, and a second adjustable phase shifter coupled between the second input and the second output.

Apparatus and methods for envelope tracking systems are disclosed herein. In certain implementations, an envelope tracking system for generating a power amplifier supply voltage for a power amplifier is provided. The envelope tracking system includes a DC-to-DC converter that generates a regulated voltage from a battery voltage and controls a voltage of the regulated voltage using a low frequency feedback signal. The envelope tracking system further includes an error amplifier that generates an output current using an envelope signal and a high frequency feedback signal. The low frequency feedback signal is based on a low frequency component of the power amplifier supply voltage and the high frequency feedback signal is based on a high frequency component of the power amplifier supply voltage. The error amplifier generates the power amplifier supply voltage by adjusting the magnitude of the regulated voltage using the output current.

A class D audio amplifier provides both an audio output signal and a DC bias voltage to an electrostatic transducer (9). In the amplifier, a modulated sequence of pulses is generated by an input module (1) in response to an input audio signal. The sequence of pulses is amplified by an output module (3) using high speed switching output transistors (4, 5). An output signal is generated by applying a low pass filter (8) to the amplified pulses, and the output signal is provided to the transducer to produce audible output. The amplified sequence of pulses is also used to drive a voltage multiplier module (10) to provide bias voltage for the electrostatic transducer (9). In other embodiments, the bias voltage is provided by a bias voltage module which reverses the bias voltage at intervals, and a phase reverser (13) reverses the phase of the signals fed to the output module (3) simultaneously with reversal of the bias voltage.

Apparatus and methods for envelope tracking in a mobile device are disclosed herein. In certain configurations, a method includes amplifying a radio frequency (RF) input signal using a power amplifier, providing power to the power amplifier from a power amplifier supply voltage, controlling a voltage level of the power amplifier supply voltage based on a control voltage using a DC-to-DC converter, adjusting the voltage level of the power amplifier supply voltage based on an envelope of the RF input signal using an error amplifier, low pass filtering the power amplifier supply voltage to generate a filtered voltage using a low pass filter, and generating the control voltage based on comparing the filtered voltage to a reference voltage using a comparator.

A radio frequency (RF) amplification device comprises an RF amplification circuit, and a dynamic level shifter (DLS) circuit coupled between a supply voltage and the RF amplification circuit. The DLS circuit is configured to provide a first shifted voltage to the RF amplification circuit via a first diode when the supply voltage is above a first threshold voltage level. The DLS circuit is further configured to provide a second shifted voltage to the RF amplification circuit via a first shunt transistor when the supply voltage is below the first threshold voltage level, wherein the supply voltage less the second shifted voltage is less than the supply voltage less the first shifted voltage.

A power amplifier cell includes a first input arranged to receive an in-phase control signal, a second input arranged to receive a quadrature control signal, an input stage arranged to output a drive signal based at least partly on the received in-phase and quadrature control signals, and an output stage arranged to receive at an input thereof the drive signal output by the input stage, and to generate an output signal for the power amplifier cell in response to the received drive signal.

Embodiments of circuits for use with an amplifier that includes multiple amplifier paths include a first circuit and a second circuit in parallel with the first circuit. The first circuit includes a first input coupled to a first power divider output, a first output coupled to a first amplifier path of the multiple amplifier paths, and a first adjustable phase shifter and a first attenuator series coupled between the first input and the first output. The second circuit includes a second input coupled to a second power divider output, a second output coupled to a second amplifier path of the multiple amplifier paths, and a second adjustable phase shifter coupled between the second input and the second output.

A power amplifier cell includes a first input arranged to receive an in-phase control signal, a second input arranged to receive a quadrature control signal, an input stage arranged to output a drive signal based at least partly on the received in-phase and quadrature control signals, and an output stage arranged to receive at an input thereof the drive signal output by the input stage, and to generate an output signal for the power amplifier cell in response to the received drive signal.