Abstract: An example apparatus includes: programmable circuitry configured to execute machine-readable instructions to: receive first voltages representative of an input signal; receive second voltages and currents, the second voltages and currents representative of voltages and currents of filter circuitry responsive to the first voltages; and determine a transfer function based on the first voltages and the second voltages and currents, the transfer function having coefficients representing the filter circuitry.

Abstract: An audio system includes an amplifier, regulating circuitry, and a filter. The regulating circuitry generates an audio voltage threshold signal based on an estimated value of the supply voltage source of the system, the estimated ESR between the system voltage supply and amplifier voltage supply pin, and the measured output resistance of the system. From these measurements/estimates, an anti-clipping voltage limit signal is generated. Power-budget-based and current-budget-based voltage limit signals are also determined based on first and second functions of the estimated value of the voltage source, respectively. The minimum of these three voltage limit signals is selected as the audio voltage threshold signal. The measurements, estimates and calculations are performed on a periodic basis to continually update the audio voltage threshold signal and thus adaptively regulate the audio system.

Abstract: A system includes a feedforward path coupled to a signal input. The system also includes a speaker coupled to the feedforward path. The system includes a back electromotive force (BEMF) extractor coupled to the speaker, where the BEMF extractor has a first input, a second input, and an output. The BEMF extractor includes a first summing point coupled to the first input. The BEMF extractor includes a resistor amplifier coupled to the second input and the first summing point. The BEMF extractor includes a high pass filter coupled to the second input and to an inductor amplifier. The BEMF extractor also includes a low pass filter coupled to the first summing point. The BEMF extractor includes a second summing point coupled to the low pass filter, the inductor amplifier, and the output.

Abstract: A controller regulates the voltage delivered to the load and current drawn from the battery in an audio system depending on ripple in the battery voltage which is input to the controller to allocate power for audio playback. Regulation maximizes available headroom while avoiding audio clipping. The effect of internal battery and external parasitic resistance (ESR) on ripple is compensated by an iterative process. ESR is rapidly increased whenever the minimum of the battery voltage input to the controller falls below a clipping threshold and slowly decreased whenever such voltage exceeds such threshold and the audio is under compression. A limiter allocates power to utilize more of the available audio headroom. A de-emphasis filter in each audio signal path compensates for capacitive ripple in the battery voltage input to the controller. As the frequency of the audio input changes, the filter(s) allow frequency-dependent power/current regulation to fill the full audio range without distortion.

Abstract: Disclosed embodiments include an apparatus for closed loop control of a linear resonant actuator comprising a motor drive circuit configured to provide a motor drive signal, a current and voltage sensing circuit coupled to the output terminal of the motor drive circuit and across the motor, and having current sense and a voltage sense outputs. A resonant frequency and back emf extraction circuit receives the current sense and voltage sense outputs, and outputs a resonant frequency signal output and a measured back emf signal output. An actuator model circuit has inputs coupled to the output of the motor drive circuit, the resonant frequency signal output, and a mechanical system quality factor signal generated by an adaptation circuit having an input coupled to the error summing circuit output. The error summing circuit has inputs coupled to the output of the actuator model and the measured back emf signal.

Abstract: A method includes converting an audio signal of a current time period to a frequency domain to produce a set of frequency coefficients. For each of the frequency coefficients, the method includes computing a gradient of that frequency coefficient's magnitude relative to a magnitude of the same frequency coefficient from a previous time period. The method then includes summing the gradients computed for the set of frequency coefficients to produce a sum value, and then generating a haptic signal based on the sum value.

Abstract: For a resonator system such as a (haptic) LRA, a methodology for resonant frequency (F0) tracking/control with continuous resonator drive, based on estimating back-emf, including estimating resonator resistance based at least in part on the sensed resonator drive signals, with back-emf estimated based at least in part on the sensed resonator drive signals and the estimated resonator resistance. A phase difference is detected between the resonator drive signals, and the estimated back-emf signals, generating control for resonator drive frequency, which can be used to iteratively adjust the resonator drive frequency until phase coherent with the estimated back-emf signals (F0 lock), such as for driving the resonator at or near a resonant frequency. An amplitude control loop can be used to iteratively adjust resonator drive amplitude based on a difference between estimated back-emf and a target back-emf derived from a rated back-emf and the resonator frequency resonant frequency.

Abstract: In an example, a method includes providing a pulse-width modulation (PWM) excitation signal to a piezo transducer via a transmit path. The method also includes collecting a block of samples of a current and a voltage at the piezo transducer, where the block of samples is collected in sub-blocks of samples between interrupts in a receive path. The method includes processing each sub-block of samples separately from other sub-blocks of samples. The method also includes, responsive to the sub-blocks of the block of samples being processed, analyzing the block of samples. The method includes, responsive to the analysis, modifying the PWM excitation signal.

Abstract: Disclosed embodiments include a method for closed loop phase tracking comprised of determining a first estimated resonant frequency, generating a motor drive signal at the first estimated resonant frequency and applying the motor drive signal to a motor, measuring current and voltage of the motor drive signal, and filtering the measurements of current and voltage of the motor drive signal. The phase difference between the filtered current and voltage waveforms is measured and a second estimated resonant frequency is calculated. The generated motor drive frequency is adjusted to equal the second estimated resonant frequency.

Abstract: A method includes converting an audio signal of a current time period to a frequency domain to produce a set of frequency coefficients. For each of the frequency coefficients, the method includes computing a gradient of that frequency coefficient's magnitude relative to a magnitude of the same frequency coefficient from a previous time period. The method then includes summing the gradients computed for the set of frequency coefficients to produce a sum value, and then generating a haptic signal based on the sum value.

Abstract: Disclosed embodiments include an apparatus for closed loop control of a linear resonant actuator comprising a motor drive circuit configured to provide a motor drive signal, a current and voltage sensing circuit coupled to the output terminal of the motor drive circuit and across the motor, and having current sense and a voltage sense outputs. A resonant frequency and back emf extraction circuit receives the current sense and voltage sense outputs, and outputs a resonant frequency signal output and a measured back emf signal output. An actuator model circuit has inputs coupled to the output of the motor drive circuit, the resonant frequency signal output, and a mechanical system quality factor signal generated by an adaptation circuit having an input coupled to the error summing circuit output. The error summing circuit has inputs coupled to the output of the actuator model and the measured back emf signal.

Abstract: Disclosed embodiments include a method for closed loop phase tracking comprised of determining a first estimated resonant frequency, generating a motor drive signal at the first estimated resonant frequency and applying the motor drive signal to a motor, measuring current and voltage of the motor drive signal, and filtering the measurements of current and voltage of the motor drive signal. The phase difference between the filtered current and voltage waveforms is measured and a second estimated resonant frequency is calculated. The generated motor drive frequency is adjusted to equal the second estimated resonant frequency.

Abstract: An audio circuit includes an amplifier, a voltage sensor, a current sensor, and an excursion control circuit. The voltage sensor is coupled to an output of the amplifier. The current sensor is coupled to the output of the amplifier. The excursion control circuit is coupled to the amplifier, the voltage sensor, and the current sensor. The excursion control circuit includes back electro-magnetic force (EMF) measurement, a back-EMF model, and excursion protection. The back-EMF measurement is to measure back electro-magnetic force of a speaker based on voltage measurements received from the voltage sensor and current measurements received from the current sensor. The back-EMF model is updated based on measurements of the back-EMF and is converted to an excursion model. The excursion protection is to limit amplitude of audio signal provided to the amplifier based on the excursion model of the speaker and amplitude of an audio input signal.

Abstract: An audio circuit includes an amplifier, a voltage sensor, a current sensor, and an excursion control circuit. The voltage sensor is coupled to an output of the amplifier. The current sensor is coupled to the output of the amplifier. The excursion control circuit is coupled to the amplifier, the voltage sensor, and the current sensor. The excursion control circuit includes back electro-magnetic force (EMF) measurement, a back-EMF model, and excursion protection. The back-EMF measurement is to measure back electro-magnetic force of a speaker based on voltage measurements received from the voltage sensor and current measurements received from the current sensor. The back-EMF model is updated based on measurements of the back-EMF and is converted to an excursion model. The excursion protection is to limit amplitude of audio signal provided to the amplifier based on the excursion model of the speaker and amplitude of an audio input signal.

Abstract: An audio circuit includes an amplifier, a voltage sensor, a current sensor, and an excursion control circuit. The voltage sensor is coupled to an output of the amplifier. The current sensor is coupled to the output of the amplifier. The excursion control circuit is coupled to the amplifier, the voltage sensor, and the current sensor. The excursion control circuit includes back electro-magnetic force (EMF) measurement, a back-EMF model, and excursion protection. The back-EMF measurement is to measure back electro-magnetic force of a speaker based on voltage measurements received from the voltage sensor and current measurements received from the current sensor. The back-EMF model is updated based on measurements of the back-EMF and is converted to an excursion model. The excursion protection is to limit amplitude of audio signal provided to the amplifier based on the excursion model of the speaker and amplitude of an audio input signal.

Abstract: For a resonator system such as a (haptic) LRA, a methodology for resonant frequency (F0 tracking/control with continuous resonator drive, based on estimating back-emf, including estimating resonator resistance based at least in part on the sensed resonator drive signals, with back-emf estimated based at least in part on the sensed resonator drive signals and the estimated resonator resistance. A phase difference is detected between the resonator drive signals, and the estimated back-emf signals, generating control for resonator drive frequency, which can be used to iteratively adjust the resonator drive frequency until phase coherent with the estimated back-emf signals (F0 lock), such as for driving the resonator at or near a resonant frequency. An amplitude control loop can be used to iteratively adjust resonator drive amplitude based on a difference between estimated back-emf and a target back-emf derived from a rated back-emf and the resonator frequency resonant frequency.

Abstract: A system includes a filter circuit configured to adjust digitized audio signal values based on filter parameters. The system also includes a filter parameter selection circuit configured to determine an audio signal bandwidth estimate based on back-EMF analysis and to supply different sets of filter parameters to the filter circuit based on the audio signal bandwidth estimate and a predetermined threshold. The system also includes a digital-to-analog converter (DAC) configured to convert an output of the filter circuit into an analog audio signal to be amplified.

Abstract: A system includes a gain control circuit configured to dynamically select a gain value based on an estimated temperature for a speaker voice coil, a base gain value, and a threshold temperature value. The system also includes a power control circuit configured to determine a power limit value based on the gain value. The system also includes a filter circuit configured to adjust values of a digitized audio signal based on the power limit value. The system also includes a digital-to-analog converter (DAC) coupled to the filter circuit and configured to convert a digital output of the filter circuit to an analog audio signal.

Abstract: A method and apparatus for active noise canceling. The method includes retrieving an input sample from at least one of a feedback or feedforward microphone digitized through the sigma-delta converter, retrieving the input sample and a related filter, wherein the filter is customized to the particular headset, outputting a filtered signal through a speaker without any interpolation and reducing order of CIC filters, and outputting a response sharply tapered down.

Abstract: A method and apparatus for active noise canceling. The method includes retrieving an input sample from at least one of a feedback or feedforward microphone digitized through the sigma-delta converter, retrieving the input sample and a related filter, wherein the filter is customized to the particular headset, outputting a filtered signal through a speaker without any interpolation and reducing order of CIC filters, and outputting a response sharply tapered down.