Cirrus Logic Inc.

Roberto Napoli

Jason William Lawrence

Jie Su

Rong Hu

Roger David Serwy

Stefan Williams

Firas Azrai

Ivan Perry

Philip Clarkin

Mark H Tovell

David Rhodes

Anthony James Magrath

Thomas H Hoff

Ross Crawford Morgan

Kemal S Demirci

Philip B J Clarkin

Sandeep P Sira

Hezi Zhu

Waleed Eshmawy

This application relates to methods and apparatus for clipping prevention. A driver apparatus for driving a transducer has a switching driver configured to switch at least one output node between different switching voltages with a controlled duty-cycle to drive an output signal across the transducer. A clipping prevention controller is configured to control a gain applied to the input signal so as to provide limiting of the input signal to avoid clipping of the output signal. The clipping prevention controller is configured to dynamically control at least one limiting threshold used to determine when to apply limiting of the input signal based on an indication of load resistance of the transducer and the input voltage to the switching driver.

Clipping prevention in switched mode drivers

This disclosure provides techniques for determining a reference resistance of a loudspeaker, such as in a mobile device. The reference resistance value may be used, among other applications, for speaker protection by reducing overdrive of the loudspeaker beyond safe temperature, which could damage the loudspeaker, while allowing driving of the loudspeaker closer to safety limits to improve performance of the loudspeaker. In a first aspect, a method of audio device monitoring includes applying a first signal to a loudspeaker; measuring a voltage and a current for the loudspeaker while applying the first signal to the loudspeaker; and determining a reference resistance for the loudspeaker based on the voltage and the current. Other aspects and features are also claimed and described.

On-device loudspeaker reference resistance determination

The present disclosure relates to circuitry comprising: amplifier circuitry configured to receive a variable supply voltage, wherein the supply voltage varies according to an output signal of the amplifier circuitry; monitoring circuitry configured to monitor one or more parameters of an output signal of the amplifier circuitry; and processing circuitry configured to receive an indication of the voltage of the variable supply voltage and an indication of the monitored parameters from the monitoring circuitry and to apply a correction to one or more of the monitored parameters to compensate for coupling between the variable supply voltage and the monitoring circuitry.

Amplifier systems

A method for compensating for a change in back electric motive force in a transducer in a device, wherein the transducer is driven by an output signal output by an amplifier, and a back volume of the transducer is formed by an enclosure within the device. The method comprises: receiving an input signal; determining, based on a characteristic of the transducer that the transducer has moved from an equilibrium position within the device; and based on the determination, adjusting a gain applied to the input signal by the amplifier to generate the output signal.

Audio distortion compensation

Embodiments described herein provide methods and apparatus for predicting the excursion of a transducer. The method comprises determining whether an input signal to the transducer is a periodic signal; and responsive to determining that the input signal is a periodic signal, calculating the predicted excursion based on a direct current ('DC') offset associated with the transducer.

Methods and apparatus for transducer excursion prediction

This application relates to methods and apparatus for loudspeaker protection. A loudspeaker protection system receives a digital audio signal comprising a plurality of samples at an input node. A delay block delays the digital audio signal and a gain block applies a controlled gain to the delayed digital audio signal. An excursion predictor is configured to receive a version of the audio signal from the signal path upstream of the delay block and determine a predicted excursion for a loudspeaker based on the audio signal. A gain controller controls a gain setting of the gain block in response to the predicted excursion and a first loudspeaker impulse response model and a predetermined excursion limit. The gain controller is configured to determine at least one gain setting {gg} to be applied to a set of samples {V. . . V} of the audio signal delayed by the delay block where the set of samples of the audio signal corresponds to a time-span which is less than an impulse response settling time of the loudspeaker.

Loudspeaker protection

This application describes methods and apparatus for loudspeaker protection. A loudspeaker protection system () is described having a first frequency band-splitter () for splitting an input audio signal (Vin) into a plurality of audio signals (v, v. . . ,vn) in different respective frequency bands (&#x3c9;. . . &#x3c9;&#x3b7;). A first gain block () is configured to apply a respective frequency band gain (gt, gt. . . ,gt) to each of the audio signals in the different respective frequency bands and a gain controller () is provided for controlling the respective band gains. A thermal controller () determines, for each of a plurality of the different respective frequency bands, a power dissipation for the loudspeaker in that frequency band and also determines a respective thermal gain setting based on the determined power dissipation for that frequency band. The gain controller is configured to control the respective frequency band gains based on the thermal gain settings.

This application describes methods and apparatus for loudspeaker protection. A loudspeaker protection system () is described having a first frequency band-splitter () for splitting an input audio signal (Vin) into a plurality of audio signals (v, v. . . , vn) in different respective frequency bands (&#x3c9;. . . , &#x3c9;n). A first gain block () is configured to apply a respective frequency band gain (g, g. . . , g) to each of the audio signals in the different respective frequency bands and a gain controller () is provided for controlling the respective band gains. A displacement modeller () determines a plurality of displacement signals (x, x. . . , xn) based on the input audio signal (Vin) and a displacement model () where each displacement signal corresponds to a modelled cone displacement for the loudspeaker for one of said different respective frequency bands. The gain controller () is configured to control the respective frequency band gains based on the plurality of displacement signals.

A speaker model may implement a direct voltage-to-excursion model in an adaptive filter for modeling the speaker without developing a first electrical-only model and then converting the model to a mechanical model. The voltage-to-excursion model may allow for modeling of different kinds of speakers, such as sealed, ported, or vented speakers. A transfer function may be developed in the adaptive filter for the voltage-to-excursion model, and that transfer function re-used for prediction of excursion values based on an audio signal. Speaker protection may be performed to take steps to prevent speaker damage when a predicted excursion value exceeds safe limits. The voltage-to-excursion model may operate in displacement or displacement-related domains (e.g., velocity and back emf).

Speaker adaptation with voltage-to-excursion conversion

Speaker protection may be based on multiple speaker models with oversight logic that controls the speaker protection based on the multiple speaker models. At least one of the speaker models may be based on a speaker excursion determined from feedback information from the speaker, such as a current or voltage measured at the speaker. Excursion based on the speaker feedback may be used to determine an error in an excursion prediction made from the audio signal. The excursion prediction may then be compensated for that error. In some embodiments, a direct displacement estimate of excursion generated from speaker monitor signals is used to correct a fixed excursion model applied to an input audio signal.

Speaker protection excursion oversight

The reliability and resilience of a speaker in a portable device may be improved by enabling the device to determine a status of an enclosure of a transducer. The impedance profiles of transducers vary depending on the enclosure status, whether the enclosure is leaky, ported, or sealed. Determination of parameters related to an impedance of a transducer may aid in a determination of the status of the enclosure. Once an enclosure status is determined, that information may be used to determine an excursion model for the transducer. Adapting the excursion model or other audio processing parameters can improve protection and performance of the transducer.

Speaker enclosure status

A method of thermal protection of a voice coil of a loudspeaker comprises: determining an estimate of a temperature of the voice coil, determining an estimate of a rate of change of the temperature of the voice coil, determining an estimate of power dissipation in the voice coil, and generating a gain control signal for modulating a gain applied to an input signal in a signal path between an input terminal and the loudspeaker. The gain control signal is generated as a function of all of the estimate of the temperature of the voice coil, the estimate of the rate of change of the temperature of the voice coil, and the estimate of the power dissipation in the voice coil.

Loudspeaker protection systems and methods

This application relates to methods and apparatus for loudspeaker protection. A loudspeaker protection system () receives a digital audio signal comprising a plurality of samples at an input node (IN). A delay block () delays the digital audio signal and a gain block () applies a controlled gain to the delayed digital audio signal. An excursion predictor () is configured to receive a version of the audio signal from the signal path upstream of the delay block and determine a predicted excursion for a loudspeaker based on the audio signal. A gain controller () controls a gain setting (g) of the gain block in response to the predicted excursion and a first loudspeaker impulse response model and a predetermined excursion limit. The gain controller () is configured to determine at least one gain setting {gg} to be applied to a set of samples {V. . . V} of the audio signal delayed by the delay block where the set of samples of the audio signal corresponds to a time-span which is less than an impulse response settling time of the loudspeaker.

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Milan, Italy

Roberto Napoli