Abstract: An audio processing system is described including an amplifier configured to receive a first audio signal and output the first audio signal to an acoustic transducer comprising a voice coil. A sensor detects a signal corresponding to voice coil current of the acoustic transducer. A controller compares the first audio signal and the detected signal and determines a second audio signal from the comparison. The second audio signal is representative of an external sound source detected via the acoustic transducer. The audio processing system may simultaneously output the first audio signal and receive the second audio signal using the same acoustic transducer.

Abstract: An audio processing system is described including an amplifier configured to receive a first audio signal and output the first audio signal to an acoustic transducer comprising a voice coil. A sensor detects a signal corresponding to voice coil current of the acoustic transducer. A controller compares the first audio signal and the detected signal and determines a second audio signal from the comparison. The second audio signal is representative of an external sound source detected via the acoustic transducer. The audio processing system may simultaneously output the first audio signal and receive the second audio signal using the same acoustic transducer.

Abstract: Aspects are directed to an amplifier circuit including a signal processing circuit and a calibration circuit. In certain specific embodiments, the signal processing circuit includes a signal combiner and a closed-loop feedback path, and the signal processing circuit is designed to provide a loop transfer function for a derived signal partly representing contributions from an audio input signal, a control or pilot signal having a target frequency range, and a calibration signal. The signal combiner is designed to combine aspects of the control or pilot signal and aspects of the audio input signal, and the calibration circuit is designed to adjust an effective gain of the derived signal in response to whether a unity-gain frequency of a signal in the closed-loop feedback path, as provided via the loop transfer function, is higher or lower than the target frequency range.

Abstract: Some embodiments include a resistor that may be used in audio conversion for an ADC. The resistor may be made up of an n-well as well as a p-well polysilicons. The n-well and p-well polysilicons may include a shallow trench isolator. The n-well and p-well components may be in series with other n-well or p-well components respectively. Similarly, multiple n-well components which are in series, may be in parallel with multiple p-well components.

Abstract: A current limiter for Class-D amplifiers measures and stores a position of an over-current event. By comparing the stored position, output signals can be selectively inverted. As a result, the Class-D amplifier remains in a defined modulation scheme even during period of current limiting.

Abstract: One example discloses a class-D amplifier apparatus, comprising: an amplifier circuit, having a set of input terminals, a set of output terminals, a quiescent circuit configuration, and an active circuit configuration; an amplifier control device, coupled to the amplifier circuit; wherein the amplifier control device is configured to place the amplifier circuit in the quiescent circuit configuration before measuring a voltage between the set of output terminals; wherein the amplifier control device is configured to add the output terminals voltage from the set of input terminals before placing the amplifier circuit in the active circuit configuration.

Abstract: One example discloses a class-D amplifier apparatus, comprising: an amplifier circuit, having a set of input terminals, a set of output terminals, a quiescent circuit configuration, and an active circuit configuration; an amplifier control device, coupled to the amplifier circuit; wherein the amplifier control device is configured to place the amplifier circuit in the quiescent circuit configuration before measuring a voltage between the set of output terminals; wherein the amplifier control device is configured to add the output terminals voltage from the set of input terminals before placing the amplifier circuit in the active circuit configuration.

Abstract: A current limiter for Class-D amplifiers measures and stores a position of an over-current event. By comparing the stored position, output signals can be selectively inverted. As a result, the Class-D amplifier remains in a defined modulation scheme even during period of current limiting.

Abstract: Some embodiments include a resistor that may be used in audio conversion for an ADC. The resistor may be made up of an n-well as well as a p-well polysilicons. The n-well and p-well polysilicons may include a shallow trench isolator. The n-well and p-well components may be in series with other n-well or p-well components respectively. Similarly, multiple n-well components which are in series, may be in parallel with multiple p-well components.

Abstract: A method of adjusting the frequency or phase of operation of a Class-D amplifier is disclosed. The method comprises making a series of step changes in the frequency or phase to adjust the frequency or phase from a start value to a desired end value, each step change in frequency or phase causing a corresponding disturbance of an output of the Class-D amplifier to produce a series of disturbances, each of which varies from an initial magnitude in first and second senses to exhibit a first peak and then in the first sense to exhibit a second peak. The time between the step changes is selected so that the second peak of each disturbance other than a final disturbance in the series overlaps the first peak of an immediately succeeding disturbance.

Abstract: A method of adjusting the frequency or phase of operation of a Class-D amplifier is disclosed. The method comprises making a series of step changes in the frequency or phase to adjust the frequency or phase from a start value to a desired end value, each step change in frequency or phase causing a corresponding disturbance of an output of the Class-D amplifier to produce a series of disturbances, each of which varies from an initial magnitude in first and second senses to exhibit a first peak and then in the first sense to exhibit a second peak. The time between the step changes is selected so that the second peak of each disturbance other than a final disturbance in the series overlaps the first peak of an immediately succeeding disturbance.