Abstract: An adaptive noise canceling (ANC) circuit adaptively generates an anti-noise signal from a reference microphone signal that is injected into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone proximate the speaker provides an error signal. A secondary path estimating adaptive filter estimates the electro-acoustical path from the noise canceling circuit through the transducer so that source audio can be removed from the error signal. Tones in the source audio, such as remote ringtones, present in downlink audio during initiation of a telephone call, are detected by a tone detector using accumulated tone persistence and non-silence hangover counting, and adaptation of the secondary path estimating adaptive filter is halted to prevent adapting to the tones. Adaptation of the adaptive filters is then sequenced so any disruption of the secondary path adaptive filter response is removed before allowing the anti-noise generating filter to adapt.

Abstract: A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone is also provided proximate to the speaker to provide an error signal indicative of the effectiveness of the noise cancellation. A secondary path estimating adaptive filter is used to estimate the electro-acoustical path from the noise canceling circuit through the transducer so that source audio can be removed from the error signal. Adaptation of adaptive filters is sequenced so that update of their coefficients does not cause instability or error in the update. A level of the source audio with respect to the ambient audio can be determined to determine whether the system may generate erroneous anti-noise and/or become unstable.

Abstract: A digital signal processing circuit, such as a digital-to-analog converter (DAC) having multiple cascaded processing stages, some of which are selectably placed in a low-power non-operating state according to a lower-power operating mode of the digital signal processing circuit and are placed in an operating state according to another higher-performance operating mode of the circuit. The output sample rates of the stages differ, so that the sample rate through the cascade changes. A signal characteristic determination block generates an indication of one or both of an amplitude and/or frequency of the input signal, so that the operating mode of the digital signal processing circuit is selected in conformity with the indication of amplitude and/or frequency of the input signal.

Abstract: An integrated circuit audio processor having an internal-oscillator generated intermediate frequency reference provides for operation of an audio processor without requiring an external master clock. Input audio streams are sample-rate converted to an intermediate sample rate derived from the internal oscillator, which may be an LC oscillator. One or more output audio streams are generated from the one or more input audio streams at the intermediate sample rate and are converted from the intermediate sample rate to corresponding output sample rates. A divider generates the intermediate sample rate from the oscillator output, and is programmed to control the intermediate sample rate to ensure that the intermediate sample rate is in the proper range for operation of the integrated circuit. The divider can be programmed to accommodate changes in process, voltage and/or temperature of the IC, so that the intermediate sample rate is maintained near an expected frequency.

Abstract: A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cancel ambient audio sounds. A processing circuit implements one or more adaptive filters that control the generation of the anti-noise signal. At least one of the adaptive filters is partitioned into a first portion having a fixed frequency response and a second portion having a variable frequency response. The partitioned filter may be an adaptive filter that generates the anti-noise signal directly from the reference microphone signal. An error microphone may be provided to measure the ambient sounds and transducer output near the transducer, and a secondary path adaptive filter included to generate an error signal from the error microphone signal, which may be partitioned, alone or in combination.

Abstract: A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal that measures the ambient audio and an error microphone signal that measures the output of an output transducer plus any ambient audio at that location and injects the anti-noise signal at the transducer output to cause cancellation of ambient audio sounds. A processing circuit uses the reference and error microphone to generate the anti-noise signal, which can be generated by an adaptive filter operating at a multiple of the ANC coefficient update rate. Downlink audio can be combined with the high data rate anti-noise signal by interpolation. High-pass filters in the control paths reduce DC offset in the ANC circuits, and ANC coefficient adaptation can be halted when downlink audio is not detected.

Abstract: A personal audio device, such as a wireless telephone, includes noise canceling circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone may also be provided proximate the speaker to measure the output of the transducer in order to control the adaptation of the anti-noise signal and to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit that performs the adaptive noise canceling (ANC) function also either adjusts the frequency response of the anti-noise signal with respect to the reference microphone signal, and/or by adjusting the response of the adaptive filter independent of the adaptation provided by the reference microphone signal.

Abstract: A personal audio device, such as a wireless telephone, includes an adaptive noise canceling (ANC) circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone is also provided proximate the speaker to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit determines a degree of coupling between the user's ear and the transducer and adjusts the adaptive cancellation of the ambient sounds to prevent erroneous and possibly disruptive generation of the anti-noise signal if the degree of coupling lies either below or above a range of normal operating ear contact pressure.

Abstract: A method of programming an integrated circuit to operate in a selected operating mode includes assigning different resistance values to correspond to different operating modes of the integrated circuit, wherein the different resistance values are non-zero finite values. The integrated circuit is programmed to operate in one of the modes based on a corresponding one of the different resistance values presented to a terminal of the integrated circuit.

Abstract: An integrated circuit audio processor having an internal-oscillator generated intermediate frequency reference provides for operation of an audio processor without requiring an external master clock. Input audio streams are sample-rate converted to an intermediate sample rate derived from the internal oscillator, which may be an LC oscillator. One or more output audio streams are generated from the one or more input audio streams at the intermediate sample rate and are converted from the intermediate sample rate to corresponding output sample rates. A divider generates the intermediate sample rate from the oscillator output, and is programmed to control the intermediate sample rate to ensure that the intermediate sample rate is in the proper range for operation of the integrated circuit. The divider can be programmed to accommodate changes in process, voltage and/or temperature of the IC, so that the intermediate sample rate is maintained near an expected frequency.

Abstract: Programming circuitry 200 includes a terminal 202 for coupling to a resistor having a resistance representing a corresponding programming state. Current control circuitry 204/205 selectively passes at least one exponentially weighted current through terminal 202. Detection Circuitry 201 then determines the resistance of the resistor from the at least one exponentially weighted current to determine the programming state.

Abstract: A direct digital synthesis (DDS) hybrid phase-lock loop for low-jitter synchronization provides a mechanism for generating a low-jitter clock from a timing reference that has a high jitter level. A DDS circuit provides a clock output and has an input for receiving a rational number. The rational number represents a ratio between the frequency of the clock output and the frequency of another stable clock provided to the circuit. In one implementation, a phase output of the DDS circuit is compared to a phase determined from an incoming timing reference and in another implementation, the low-jitter clock output is utilized to generate a phase number via a counter that is clocked by the clock output and captured by the timing reference.

Abstract: A real-time sample rate converter having a non-polynomial convolution kernel provides reduction in die area and power for performing sample rate conversion in real-time. A non-polynomial convolution kernel, which may be a gaussian operator, is used to determine output sample values from values of an incoming stream of values. If the input sample rate is higher than the output sample rate, the input sample stream is convolved with the gaussian kernel and then decimated to yield the output stream. If the input sample rate is lower than the output sample rate, the input stream is resampled to a small multiple of the output sample rate and convolved with the gaussian kernel to produce the output sample stream directly.