An audio signal control circuit includes an impedance calculator, a suppression value setter, a level detector, and a level controller. The impedance calculator is configured to calculate impedance of a speaker from voltage and current of an audio signal to be outputted to the speaker. The suppression value setter is configured to set a suppression value of the audio signal, using the impedance. The level detector is configured to perform level detection using: i) the voltage when the impedance is equal to or more than a switching threshold value, and ii) the current when the impedance is less than the switching threshold value. The level controller is configured to perform level control of the audio signal using: i) a level of a detection signal that has been detected by the level detector, and ii) the suppression value.

Methods and apparatus for providing amplifier protection for a radio frequency (RF) front-end circuit. An example RF front-end circuit generally includes an amplifier with a gain, a first sensor configured to sense a first power (or voltage) of a first node coupled to an input of the amplifier, a second sensor configured to sense a second power (or voltage) of a second node coupled to an output of the amplifier, and logic coupled to the first and second sensors. The logic is generally configured to determine that the second power (or voltage) is outside a range based on the gain and the first power (or voltage) and to take an action to protect the amplifier based on the determination. By utilizing the techniques and apparatus described herein, protection can be provided to the amplifier(s) in an RF front-end circuit without significantly impacting the performance of the RF front-end circuit.

An apparatus for detecting difference in operating characteristics of a main circuit by using a replica circuit is presented. In one exemplary case, a sensed difference in operating characteristics of the two circuits is used to drive a tuning control loop to minimize the sensed difference. In another exemplary case, several replica circuits of the main circuit are used, where each is isolated from one or more operating variables that affect the operating characteristic of the main circuit. Each replica circuit can be used for sensing a different operating characteristic, or, two replica circuits can be combined to sense a same operating characteristic.

A Class-D amplifier includes a plurality of power rails, a quantizer, and a driver stage. The quantizer and the driver stage have a combined gain. For each power rail of the plurality of power rails, the Class-D amplifier senses a voltage value for the power rail and determines a ramp amplitude based on the sensed voltage value. The Class-D amplifier concurrently switches from the driver stage using a first power rail to a second power rail of the plurality of power rails and switches from the quantizer using the ramp amplitude associated with the first power rail to using the ramp amplitude associated with the second power rail so that the combined gain is constant.

A Class-D amplifier that includes a driver stage operable in a plurality of modes having different respective output impedances, a loop filter having an output, and a circuit configured to sense a current at a load of the Class-D amplifier, determine, based on the sensed current, an IR drop for a respective output impedance of the driver stage, and add the IR drop to the loop filter output to compensate for the respective output impedance of the driver stage to reduce distortion.

Disclosed are digital predistortion implementations, including a method that includes obtaining a first set of digital predistortion (DPD) non-linear functions for controlling operation of a digital predistorter of a wireless device operating on a received at least one input signal directed to a power amplification system comprising a transmit chain with at least one power amplifier that produces output with non-linear distortions. The method further includes determining an expanded set of DPD non-linear functions comprising the first set of DPD non-linear functions and additional one or more sets of DPD non-linear functions derived based on the first set of DPD non-linear functions and on operating condition parameters associated with operation of the wireless device, and configuring the digital predistorter with DPD coefficients determined for the expanded set of the DPD non-linear functions based on observed samples of the transmit chain responsive to the at least one input signal.

A power converter produces power at a greater voltage than provided by a power source, while drawing power from the power source, wherein the power converter has a variable input current limit or a variable input power limit. One or more audio amplifiers are configured into i) drawing power from the power source bypassing the power converter and ii) drawing power from the power converter, according to audio signal amplitude, during audio playback and in accordance with an audio signal being amplified. A load of each amplifier is determined for when the amplifier is drawing power from the power source bypassing the power converter. The variable input limit of the power converter is adjusted in accordance with the determined load, during the audio playback. Other aspects are also described and claimed.

An audio device is adapted to receive and process a digital audio signal and output an analog audio signal. The audio device includes an adder, a digital-to-analog conversion circuit, an amplifying circuit, a voltage detecting circuit and an offset compensating circuit. The voltage detecting circuit detects a supply voltage received by the amplifying circuit. The offset compensating circuit generates a DC offset compensation value according to the supply voltage. The adder adds the digital audio signal and the DC offset compensation value to output an added signal. The digital-to-analog conversion circuit converts the added signal into a converted analog audio signal. The amplifying circuit amplifies the converted analog signal to output an amplified analog signal. Accordingly, the audio device can reduce pop noise caused by a DC offset.

Modern modulator drivers must be capable of delivering a large output voltage into a tens of ohms modulator, while minimizing the amount of distortion added by the driver. The driver should deliver the output voltage without exceeding a maximum distortion while minimizing the DC power consumption. Accordingly, a modulator driver includes a final stage amplifier with auxiliary transistors that turn on when the conventional differential pair of transistors approaches their maximum voltage of the linear region of their transfer function, thereby providing a more linear transfer function, in particular at large input voltages.

A radio frequency amplifying device according to an embodiment includes load impedance calculating circuitry and controlling circuitry. The load impedance calculating circuitry is configured to calculate a load impedance on the basis of information about a voltage standing wave rate and a phase on an output side of radio frequency amplifying circuitry. The controlling circuitry is configured to adjust a gain and a phase of a signal to be input to the radio frequency amplifying circuitry, in accordance with the load impedance calculated by the load impedance calculating circuitry.