Abstract: Methods and systems for thermal protection of a voice coil of a loudspeaker. The method involves driving the loudspeaker based on an input signal received at an input terminal and monitoring both a voltage applied to the voice coil and a current flowing through the voice coil. From the monitored voltage and current, an estimate of temperature of the voice coil and an estimate of power dissipation in the voice coil is determined. The method includes estimating the voice coil resistance based on the monitored voltage and current and at least the estimate of temperature is determined based the estimate of resistance. A gain control signal for modulating a gain applied to the input signal is generated as a function of both the estimate of temperature of the voice coil and the estimate of power dissipation in the voice coil.

Abstract: Circuitry for biasing a MEMS transducer and associated signal processing circuitry. A reference voltage generator is configured to generate a reference voltage at a reference voltage node. Control circuitry generates a drive signal to control a first current source which is operable to supply a current to the reference voltage generator in response to the drive signal. A switched DC-DC converter, such as a charge pump has a voltage input connected to the reference voltage node and a voltage output for providing a bias voltage for the MEMS transducer. The DC-DC converter cyclically switches in a sequence of states including at least a first state where a first converter capacitance is disconnected from the voltage input followed by a second state where the first converter capacitance is connected to the voltage input. A second current source Is operable to supply a bias current in response to a voltage at a bias control node.

Abstract: Methods and apparatus for Class-D amplifier circuits with D.C. offset control/correction. A Class-D amplifier is described having an output stage, such as a full H-bridge or half bridge, with a plurality of switches operable to provide a plurality of output states comprising at least a positive output state and a negative output state. Control circuitry is configured to receive a first signal based on the input signal and produce a digital control signal, which is used to determine the switch state of the output stage. A digital integrator is configured to receive a feedback signal indicative of the output state of the output stage and to sample the feedback signal at a sample rate and produce an integrated output signal (INT, IVC) indicating the difference in number of instances of the positive output state and the negative output state. Correction circuitry subtracts the integrated output signal from the input signal to produce a D.C. offset corrected signal.

Abstract: A noise cancellation system generates a noise cancellation signal from a signal representing ambient noise by signal processing. The signal processing applies a controllable gain value, and includes a high pass filter with a controllable cut-off frequency. A control block detects a wind amplitude. The cut-off frequency of the high pass filter is controlled based on the detected wind amplitude. A low pass function is applied to the detected wind amplitude, and the controllable gain is adjusted based on the output of the low pass function.

Abstract: A MEMS capacitive transducer with increased robustness and resilience to acoustic shock. The transducer structure includes a flexible membrane supported between a first volume and a second volume, and at least one variable vent structure in communication with at least one of the first and second volumes. The variable vent structure includes at least one moveable portion which is moveable in response to a pressure differential across the moveable portion so as to vary the size of a flow path through the vent structure. The variable vent may be formed through the membrane and the moveable portion may be a part of the membrane, defined by one or more channels, that is deflectable away from the surface of the membrane. The variable vent is preferably closed in the normal range of pressure differentials but opens at high pressure differentials to provide more rapid equalization of the air volumes above and below the membrane.

Abstract: An amplifier circuit, comprising: an input, for receiving an input signal to be amplified; a power amplifier, for amplifying the input signal; a switched power supply, having a switching frequency, for providing at least one supply voltage to the power amplifier; and a dither block, for dithering the switching frequency of the switched power supply. The dither block is controlled based on the input signal. Another aspect of the invention involves using first and second switches, each having different capacitances and resistances, and using the first or second switch depending on the input signal or volume signal. Another aspect of the invention involves controlling a bias signal provided to one or more components in the signal path based on the input signal or volume signal.

Abstract: Methods and apparatus for Class-D amplifier circuits with D.C. offset control/correction. A Class-D amplifier is described having an output stage, such as a full H-bridge or half bridge, with a plurality of switches operable to provide a plurality of output states comprising at least a positive output state and a negative output state. Control circuitry is configured to receive a first signal based on the input signal and produce a digital control signal, which is used to determine the switch state of the output stage. A digital integrator is configured to receive a feedback signal indicative of the output state of the output stage and to sample the feedback signal at a sample rate and produce an integrated output signal (INT, IVC) indicating the difference in number of instances of the positive output state and the negative output state. Correction circuitry subtracts the integrated output signal from the input signal to produce a D.C. offset corrected signal.

Abstract: Noise reduction circuitry for a communication apparatus can apply different noise reduction transfer functions, depending on whether a listening device is connected to the apparatus. If no listening device is connected, the noise reduction transfer function can be adapted for use with microphones (12) and speakers (28) that form an integral part of the communication apparatus, which may be a cellular telephone. If a listening device is connected, the noise reduction transfer function can be adapted for use with microphones (12) and speakers (28) that form a part of the listening device. This allows the noise reduction circuitry to provide improved noise reduction performance.