Voltage ripple suppression in a transmission circuit is disclosed. The transmission circuit includes a power amplifier circuit coupled to an envelope tracking integrated circuit (ETIC) via a conductive path. Notably, the ETIC and the conductive path can present a large source impedance to the power amplifier circuit, which can cause a ripple in the modulated voltage received by the power amplifier circuit. In a conventional approach, the large source impedance may be isolated by a large decoupling capacitor at the expense of increased voltage switching time and battery current drain. In contrast, the ETIC disclosed herein can determine and apply a correction term to the modulated voltage generated by the ETIC to thereby suppress the ripple without requiring the large decoupling capacitor. By eliminating the large decoupling capacitor, the transmission circuit can thus achieve fast voltage switching with lower battery current drain.

Envelope tracking (ET) voltage correction in a transmission circuit is provided. The transmission circuit includes a transceiver circuit and a power amplifier circuit(s). The transceiver circuit generates a radio frequency (RF) signal(s) from a time-variant modulation vector and the power amplifier circuit(s) amplifies the RF signal(s) based on a modulated voltage and provides the amplified RF signal(s) to a coupled RF front-end circuit. Herein, the transceiver circuit is configured to apply an equalization filter to a selected form of the time-variant modulation vector to compensate for a voltage distortion filter created across a modulation bandwidth of the RF signal(s) by coupling the power amplifier circuit with the RF front-end circuit. As a result, it is possible to reduce undesired instantaneous excessive compression and/or spectrum regrowth resulting from the voltage distortion filter to thereby improve efficiency and linearity of the power amplifier circuit(s) across the modulation bandwidth of the RF signal(s).

An apparatus and method for improving the efficiency of a D class amplifier, particularly at lower output levels. A class D amplifier having a load with inductance, such as a transducer, is configured to concurrently act as its own buck regulator. A capacitor connected to ground and to both ends of the transducer through switches functions as the buck regulator in connection with the inductance of the transducer, providing the class D amplifier with additional voltage levels such as might be provided by a G/H class amplifier but without the added complexity or expense of the G/H configurations. Better efficiency is possible than that provided by a 100% efficient conventional buck regulator. No envelope detector is required, nor any change to the gain of the digital signal to the class D amplifier. Feedback may be used if desired, but is not required to obtain a high quality output signal.

An envelope tracking (ET) integrated circuit (ETIC) operable with multiple types of power amplifiers is provided. The ETIC is configured to provide one or more ET voltages to a power amplifier(s) for amplifying a radio frequency (RF) signal. In embodiments disclosed herein, the ETIC can be configured to generate the ET voltages at same or different voltage levels based on specific types of the power amplifier(s), such as multi-stage power amplifier and Doherty power amplifier, and for a wider modulation bandwidth of the RF signal. As such, the ETIC can be flexibly adapted to enable a variety of power management scenarios and/or topologies.

According to some example embodiments, an apparatus includes a buck-boost converter, a first buck converter connected at an output terminal of the buck-boost converter, a second buck converter connected at the output terminal of the buck-boost converter, a first LA including a first supply voltage input connected to the output terminal of the buck-boost converter, and an output terminal connected to an output terminal of the first buck converter, where the first LA is configured to provide a first modulated supply voltage to a first PA of a first transmitter, and a second LA including a second supply voltage input connected to the output terminal of the buck-boost converter, and an output terminal connected to an output terminal of the second buck converter, where the second LA is configured to provide a second modulated supply voltage to a second PA of a second transmitter.

An audio system has an amplifier for driving an audio actuator and includes a switched-mode power supply that draws power from a power source (e.g., battery) to supply power to the amplifier, a capacitor charged by the switched-mode power supply to supply power to the amplifier, and a feed-forward compressor that performs dynamic range compression of an audio input to provide an audio output for amplification by the amplifier. The compressor includes a sidechain frequency-biasing filter that generates a frequency-biased version of the audio input that is attenuated as frequency increases which causes the compressor to decrease the compression as frequency increases. A control block limits current drawn from the battery by the switched-mode power supply independent of audio input frequency, but the frequency-biasing filter enables the amplifier to service audio power transients greater than the current-limited power supply can supply by advantageously concurrently sourcing extra power from the capacitor.

Apparatus and methods for envelope tracking systems with automatic mode selection are provided herein. In certain configurations, a power amplifier system includes a power amplifier configured to provide amplification to a radio frequency signal and to receive power from a power amplifier supply voltage, and an envelope tracker including a signal bandwidth detection circuit configured to generate a detected bandwidth signal based on processing an envelope signal corresponding to an envelope of the radio frequency signal. The envelope tracker further includes a switch bank configured to receive a plurality of regulated voltages, a filter configured to filter an output of the switch bank to generate the power amplifier supply voltage, and a mode control circuit configured to control a filtering characteristic of the filter based on the detected bandwidth signal.

Systems, methods and apparatus for practical realization of an integrated circuit comprising a stack of transistors operating as an RF amplifier are described. As stack height is increased, capacitance values of gate capacitors used to provide a desired distribution of an RF voltage at the output of the amplifier across the stack may decrease to values approaching parasitic/stray capacitance values present in the integrated circuit which may render the practical realization of the integrated circuit difficult. Coupling of an RF gate voltage at the gate of one transistor of the stack to a gate of a different transistor of the stack can allow for an increase in the capacitance value of the gate capacitor of the different transistor for obtaining an RF voltage at the gate of the different transistor according to the desired distribution.

Envelope tracking systems for power amplifiers are provided herein. In certain embodiments, an envelope tracker is provided for a power amplifier that amplifies an RF signal. The envelope tracker includes a multi-level switching circuit having an output that provides an output current that changes in relation to an envelope signal indicating an envelope of the RF signal when the envelope tracker is operating in an envelope tracking mode. The multi-level switching circuit includes a multi-level supply (MLS) modulator that receives multiple regulated voltages of different voltage levels, and an MLS control circuit that controls the selection of the MLS modulator over time based on the envelope signal. When transitioning the MLS modulator from selection of one regulated voltage level to another regulated voltage level, the MLS control circuit provides a soft transition to gradually switch the regulated voltage levels.

Apparatus and methods for power amplifier distortion networks are disclosed. In one aspect, there is provided a power amplifier system including a power amplifier configured to amplify a radio frequency input signal. The power amplifier including an input configured to receive the radio frequency input signal and an output configured to generate an amplified radio frequency signal. The power amplifier system further includes a distortion network electrically coupled to either the input or the output of the power amplifier. The distortion network including a plurality of channelized resistors. The channelized resistors connected in series to either an input or an output of the power amplifier.