Abstract: A predictive back-emf protection methodology for an electromechanical system, including a signal processor that processes a source signal to provide a modified source signal, a driver that converts the modified source signal to a drive signal, and an electromechanical transducer that generates, from the drive signal, a transducer response, and a back-emf signal coupled back to the driver output. A predictive back-emf generator (such as a routine in the signal processor) is characterized by a back-emf transfer function (linear parameterized model of the electromechanical transducer) for transforming an input signal into a transform back-emf representation of a back-emf signal predicted by the back-emf transfer function as a response of the electromechanical transducer to such input signal. The signal processor processes the source signal based on the transform back-emf representation to generate the modified source signal input to the driver.

Abstract: A predictive back-emf protection methodology for an electromechanical system, including a signal processor that processes a source signal to provide a modified source signal, a driver that converts the modified source signal to a drive signal, and an electromechanical transducer that generates, from the drive signal, a transducer response, and a back-emf signal coupled back to the driver output. A predictive back-emf generator (such as a routine in the signal processor) is characterized by a back-emf transfer function (linear parameterized model of the electromechanical transducer) for transforming an input signal into a transform back-emf representation of a back-emf signal predicted by the back-emf transfer function as a response of the electromechanical transducer to such input signal. The signal processor processes the source signal based on the transform back-emf representation to generate the modified source signal input to the driver.

Abstract: A digital audio system including a combination of analog and digital volume control is disclosed. A variable power supply voltage biases a power amplifier for each channel, and applies a bias voltage corresponding to an analog volume control signal. In one disclosed embodiment, digital gain control circuitry compares the bias voltage with the level expected for the analog volume control signal; if the bias voltage has not dropped in response to a reduction in the analog volume control signal, the digital gain control circuitry reduces the digital gain of the input digital audio signal, until the bias voltage responds to the reduced volume. In another disclosed embodiment, modeling or characterization of the audio system is used to derive a digital gain control signal based on the desired volume signal and the amplitude of the digital audio signal itself.

Abstract: A digital audio processor for a digital audio receiver having an improved automute sequence is disclosed. The digital audio processor includes automute detection circuitry that monitors the amplitude of digital audio signals before and after the application of digital filters by digital audio processing circuitry. The amplitude of the input signals are compared against a first threshold level, while the amplitude of the output signals are compared against a second threshold level. In response to the amplitude of the input signals for all of the audio channels falling below the first threshold for a selected time period, a gain stage in each channel ramps down the volume to a mute level, and pulse-width-modulation circuitry is disabled. If the output signal amplitude falls below a second threshold for a channel, the pulse-width-modulation circuitry for that channel is disabled. Hysteresis for the input signal amplitude is preferably added into the automute exit determination.

Abstract: Overcurrent and overload protection for the power output of a pulse-width-modulated digital audio system is disclosed. The overcurrent protection circuitry includes a latch that is set in responsive to output current from the power output stage that exceeds an overcurrent threshold; the output of the latch gates the pulse-width-modulated control signal to block power output for the remainder of the current pulse-width-modulated cycle; upon the end of the cycle, or the beginning of the next, the latch is cleared to enable power output in that next cycle. Overload protection is provided by circuitry including counters for counting the relative number of overcurrent cycles to normal, non-overcurrent cycles, and generating an overload signal to block power output in the event of too frequent overcurrent cycles.

Abstract: A multiple-channel audio processor (10) and an associated plurality of power stages (22) in an audio system are disclosed. The audio processor (10) includes a plurality of audio amplifier channels (22), each of which includes a pulse-code-modulation (PCM) to pulse-width-modulation (PWM) conversion function (25), which generates PWM signals for application to the plurality of power stages (22). The audio amplifier channels (20) each also include an interchannel delay function (28) for delaying the PWM edges relative to other channels (20), for reducing noise. The audio amplifier channels (20) each also include delay adjust circuitry (32) for gradually increasing and decreasing the interchannel delay of the channel (20) on startup and shutdown. This permits a single control terminal (VALID) at the processor to globally enable and disable all of the power stages (22).

Abstract: A digital audio system including a combination of analog and digital volume control is disclosed. A variable power supply voltage biases a power amplifier for each channel, and applies a bias voltage corresponding to an analog volume control signal. In one disclosed embodiment, digital gain control circuitry compares the bias voltage with the level expected for the analog volume control signal; if the bias voltage has not dropped in response to a reduction in the analog volume control signal, the digital gain control circuitry reduces the digital gain of the input digital audio signal, until the bias voltage responds to the reduced volume. In another disclosed embodiment, modeling or characterization of the audio system is used to derive a digital gain control signal based on the desired volume signal and the amplitude of the digital audio signal itself.

Abstract: An audio system includes a switch mode amplifier that provides an output signal at an output for driving a load based on at least one control signal. A control system provides the at least one control signal to control the amplifier according to an operating mode of the audio system. In a first mode, the control system providing the at least one control signal to actively control an equivalent output impedance at the output of the amplifier, gradually adjusting the equivalent output impedance from a high-impedance state to a low impedance state, so as to mitigate a voltage drop across the load (e.g., including one or more speakers) when the amplifier is activated to a second mode corresponding to the low impedance state.

Abstract: A digital audio processor (20) for a digital audio receiver (21) having an improved automute sequence is disclosed. The digital audio processor (20) includes automute detection circuitry (42) that monitors the amplitude of digital audio signals before and after the application of digital filters by digital audio processing circuitry (20d). The amplitude of the input signals are compared against a first threshold level, while the amplitude of the output signals are compared against a second threshold level. In response to the amplitude of the input signals for all of the audio channels (44) falling below the first threshold for a selected time period, a gain stage (50) in each channel ramps down the volume to a mute level, and pulse-width-modulation circuitry (54) is disabled. If the output signal amplitude falls below a second threshold for a channel, the pulse-width-modulation circuitry (54) for that channel is disabled.

Abstract: An audio system includes a switch mode amplifier that provides an output signal at an output for driving a load based on at least one control signal. A control system provides the at least one control signal to control the amplifier according to an operating mode of the audio system. In a first mode, the control system providing the at least one control signal to actively control an equivalent output impedance at the output of the amplifier, gradually adjusting the equivalent output impedance from a high-impedance state to a low impedance state, so as to mitigate a voltage drop across the load (e.g., including one or more speakers) when the amplifier is activated to a second mode corresponding to the low impedance state.

Abstract: Overcurrent and overload protection for the power output of a pulse-width-modulated digital audio system is disclosed. The overcurrent protection circuitry includes a latch that is set in responsive to output current from the power output stage that exceeds an overcurrent threshold; the output of the latch gates the pulse-width-modulated control signal to block power output for the remainder of the current pulse-width-modulated cycle; upon the end of the cycle, or the beginning of the next, the latch is cleared to enable power output in that next cycle. Overload protection is provided by circuitry including counters for counting the relative number of overcurrent cycles to normal, non-overcurrent cycles, and generating an overload signal to block power output in the event of too frequent overcurrent cycles.

Abstract: A digital audio-visual receiver (10) with improved digital control of audio volume is disclosed. Upon receipt of a user volume command, via a front panel (25) or a remote control and infrared receiver (27), sequential logic (36) in a volume command processor (35) in a PWM audio processor (20) of the receiver (10) initiates a timer (38), which measures or counts a selected interval. If additional volume commands are received during the interval, sequential logic (36) resets and restarts the timer (38). Upon the timer (38) interval elapsing without another volume command, the volume command processor (35) generates a ramping volume output signal to reach the volume level of the last received volume command over a selected time duration. Audible artifacts during changes in audio volume are thus avoided.

Abstract: A multiple-channel audio processor (10) and an associated plurality of power stages (22) in an audio system are disclosed. The audio processor (10) includes a plurality of audio amplifier channels (22), each of which includes a pulse-code-modulation (PCM) to pulse-width-modulation (PWM) conversion function (25), which generates PWM signals for application to the plurality of power stages (22). The audio amplifier channels (20) each also include an interchannel delay function (28) for delaying the PWM edges relative to other channels (20), for reducing noise. The audio amplifier channels (20) each also include delay adjust circuitry (32) for gradually increasing and decreasing the interchannel delay of the channel (20) on startup and shutdown. This permits a single control terminal (VALID) at the processor to globally enable and disable all of the power stages (22).