A multi-channel noise reduction system provides improved noise reduction with direct instrument tracking of all channels. In a two channel noise reduction system, both channels detect and track the input level and dynamic range of the guitar directly with one channel of dynamic noise reduction between the guitar and the input of a guitar amplifier to eliminate the noise of the instrument and another channel of noise reduction connected in the effects loop of the guitar amplifier. Multiple channels of noise reduction can be implemented with separated threshold controls and with low level expansion and dynamic filtering being combined so as to detect and track the input level and dynamic range of the guitar directly. A buffer amplifier can be used to feed the direct guitar signal to the detectors of the noise reduction system and the input of a stereo guitar system.

Embodiments disclosed in the detailed description relate to a pseudo-envelope follower power management system used to manage the power delivered to a linear RF power amplifier.

Apparatus and methods for envelope shaping in power amplifier systems are provided. In certain implementations, a power amplifier system includes a modulator for generating a RF signal, a power amplifier for amplifying the RF signal, a gain control circuit for controlling the gain of the power amplifier, and an envelope tracking system for controlling a voltage level of the power amplifier's supply voltage based on an envelope signal corresponding to the RF signal's envelope. The gain control circuit includes a gain adjustment table, and the envelope tracking system includes an envelope shaping circuit including an isodistortion table. The isodistortion table can be used to map the envelope signal to a shaped envelope signal so as to maintain a substantially constant distortion in the system's transmit and/or receive bands across the envelope signal's range.

A power amplifier module includes an amplifier transistor and a bias circuit. A first power supply voltage based on a first operation mode or a second power supply voltage based on a second operation mode is supplied to the amplifier transistor. The amplifier transistor receives a first signal and outputs a second signal obtained by amplifying the first signal. The bias circuit supplies a bias current to the amplifier transistor. The bias circuit includes first and second resistors and first and second transistors. The first transistor is connected in series with the first resistor and is turned ON by a first bias control voltage which is supplied when the first operation mode is used. The second transistor is connected in series with the second resistor and is turned ON by a second bias control voltage which is supplied when the second operation mode is used.

An RF communications system, which includes an RF power amplifier, an envelope tracking power supply, and supply control circuitry, is disclosed. The RF communications system operates in one of a normal operation mode and a calibration mode. During the calibration mode, the RF power amplifier receives and amplifies an RF input signal to provide an RF transmit signal using an envelope power supply signal, which is provided by the envelope tracking power supply. Further, the supply control circuitry controls the envelope tracking power supply to cause a sharp transition of the envelope power supply signal when a setpoint of the envelope power supply signal transitions through a setpoint threshold of the envelope power supply signal.

The present disclosure is directed to an envelope tracking supply modulator for multiple PAs. The envelope tracking supply modulator is configured to provide, for each of the multiple PAs, a separate supply voltage that is modulated based on the envelope of the respective RF input signal to the PA. Each of the modulated supply voltages is constructed from a DC component and an alternating current (AC) component. The DC component for each modulated supply voltage is generated by a main switching regulator that is shared by the multiple PAs. In one embodiment, the AC component for each modulated supply voltage is generated by an auxiliary switching regulator that is shared by the multiple PAs and a separate linear regulator for each of the multiple PAs. In another embodiment, the AC component for each modulated supply voltage is generated by a separate buffer.

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.

Methods of calibrating a power amplifier system to compensate for envelope amplitude misalignment are provided. In certain configurations, a method of calibrating a power amplifier system includes amplifying a radio frequency signal from a transceiver using a power amplifier and generating a supply voltage of the power amplifier using an envelope tracker, including generating a scaled envelope signal based on a power control level signal and an envelope signal, and shaping the scaled envelope signal using a shaping table generated at a target gain compression. The method further includes changing a scaling of the scaled envelope signal using a calibration module, monitoring an output of the power amplifier to determine an amount of scaling of the scaled envelope signal at which a detected gain compression of the power amplifier corresponds to the target gain compression of the shaping table, and calibrating the power amplifier system based on the determination.

Envelope tracking can be employed to reduce power consumption of a power amplifier, but envelope tracking can introduce nonlinearities to a power amplifier. These nonlinearities can manifest themselves as noise at the output of the power amplifier. Embodiments described herein provide techniques for characterizing a parameter indicative of power amplifier noise when envelope tracking is employed. Measurement of this parameter can permit power amplifier designers to decide whether to forgo envelope tracking if a power amplifier is too susceptible to such noise, redesign the power amplifier to improve compatibility with envelope tracking, or to employ distortion compensation circuitry to reduce the noise output by the power amplifier. Counterintuitively, this distortion compensation circuitry may involve increasing the power, such as the envelope tracking power supply. However, increasing the power may be a desirable trade-off for increased linearity.

A power amplifier module can include one or more switches, a coupler module, input signal pins, and a controller having first and second output terminals. The input signal pins can receive a voltage input/output signal, a clock input signal, and a data input signal. The controller can (i) set a mode of the one or more switches using a synchronous communication protocol in which the controller outputs a synchronous clock signal on the first output terminal and a data signal on the second output terminal, when the power amplifier module is in a first operating mode, or (ii) set a mode of the coupler module using an asynchronous communication protocol in which the controller outputs a first asynchronous control signal on the first output terminal and a second asynchronous control signal on the second output terminal, when the power amplifier module is in a second operating mode.