Embodiments of radio frequency (RF) systems include a power amplifier having a primary winding and a secondary winding. The primary winding can be biased in different states in transmit and receive modes such that a difference between center frequencies of the primary winding and the secondary winding are significantly different in the different modes.

Aspects of this disclosure relate to efficient power amplifiers, such as class-F power amplifiers. A power amplifier transistor can provide an amplified RF signal. A termination can be coupled to an output of the power amplifier transistor and configured to provide a short circuit at a second harmonic. In some instances, the termination circuit can provide an open circuit at a third harmonic. A resonant circuit can be coupled to the output terminal of the power amplifier transistor and configured to provide an open circuit at the third harmonic. In certain embodiments, an input termination circuit coupled to an input terminal of the power amplifier transistor can provide a short circuit at the second harmonic. The power amplifiers of this disclosure can be implemented, for example, in envelope tracking applications.

An open-loop switch-mode boost converter includes a switching signal generator circuit that receives a time-varying input signal and outputs a switching signal. A duty-cycle of the switching signal has a first non-linear relationship to an amplitude of the time-varying input signal. An amplifier receives the switching signal and outputs a time-varying output signal, an amplitude of which has a second non-linear relationship to the duty-cycle of the switching signal. The time-varying output signal has a linear relationship to the time-varying input signal based on the first non-linear relationship and the second non-linear relationship. A filter circuit receives the time-varying output signal and outputs a filtered time-varying output signal which has a maximum frequency component that is substantially the same as a maximum frequency component of the time-varying input signal. The switching signal generator circuit is communicatively isolated from the voltage output node and the filter output node.

A multi-standard transmitter architecture with digitally upconverted intermediate frequency (IF) outphased signals is disclosed. The transmitter architecture includes a Gallium Nitride (GaN) power amplifier (PA) circuit having a Current Mode Class-D (CMCD) configuration. The GaN PA circuit includes a lower switching device electrically coupled to an input to receive an input RF signal and an upper switching device to switchably electrically couple the first switching device to a power supply to drive an antenna circuit based on the input RF signal. Thus, a reconfigurable transmitter architecture is disclosed that utilizes a high-speed Gallium Nitride (GaN) driver to achieve a peak drain efficiency of at least 85% while delivering output power of 10 W at 1 GHz frequency, for example.

Aspects of this disclosure relate to a radio frequency system that includes an envelope generator configured to generate an envelope signal corresponding to an envelope of a radio frequency signal and at least two radio frequency components coupled to the envelope generator. One of the radio frequency components is a radio frequency switch configured to pass the radio frequency signal. The radio frequency switch is configured to receive the envelope signal to cause intermodulation distortion associated with the radio frequency switch to be reduced.

Envelope trackers providing compensation for power amplifier output load variation are provided herein. In certain configurations, a radio frequency (RF) system includes a power amplifier that amplifies an RF signal, an output detector coupled to an output of the power amplifier and that generates an output detection signal, an input detector coupled to an input of the power amplifier and that generates an input detection signal, and an envelope tracker that generates a power amplifier supply voltage for the power amplifier based on an envelope of the RF signal. The envelope tracker compensates the power amplifier for output load variation based on the output detection signal and the input detection signal.

Certain aspects of the present disclosure provide methods and apparatus for operating an envelope tracking power supply. The method may include receiving, from a modem of a device, information indicative of a transmit waveform statistic of a signal to be wirelessly transmitted by the device. The method may further include adjusting a configuration of the envelope tracking power supply based on the transmit waveform statistic of the signal.

An apparatus of a transmitter and method are provided, the apparatus comprising a processor that calculates a supply voltage (SV) value (SVV) to provide as an SV for a power amplifier (PA) of the transmitter for transmissions during a transmission time slot (TS). When the SV < an envelope tracking (ET) threshold (ETT), then the processor configures the PA to transmit a signal in an average power tracking (APT) mode that maintains the SV at the SVV during the TS. When the SV?ETT, and an APT condition is met, then the processor configures the PA to transmit the signal in the APT mode. When the SV?ETT, and the APT condition is not met, then the processor transmits by an adjustment to the SVV to track an amplitude modulation envelope during the TS in an ET mode.

An audio amplifier circuit for providing an output signal to an audio transducer may include a power amplifier and a control circuit. The power amplifier may include an audio input for receiving an audio input signal, an audio output for generating the output signal based on the audio input signal, and a power supply input for receiving a power supply voltage, wherein the power supply voltage is variable among at least a first supply voltage and a second supply voltage greater than the first supply voltage. The control circuit may be configured to predict, based on one or more characteristics of a signal indicative of the output signal, an occurrence of a condition for changing the power supply voltage, and responsive to predicting the occurrence of the condition, change, at an approximate zero crossing of the signal indicative of the output signal, the power supply voltage.

A method for biasing a power amplifier using a transmission signal having a time-varying envelope is provided. The method comprises producing a time-varying signal indicative of an amplitude of the envelope of the transmission signal and comparing the time-varying signal to a plurality of distinct threshold voltages. The method further comprises, for each of the plurality of distinct threshold voltages exceeded by the time-varying signal, providing a respective bias voltage to a respective input of a summing device and producing, using the summing device, an output bias voltage that is at least a sum of the respective bias voltages provided to the respective inputs of the summing device. The method further comprises biasing the power amplifier with the output bias voltage and amplifying the transmission signal using the power amplifier biased at the output bias voltage.