Texas Instruments Corporation

Texas Instruments Denmark

Thomas Morch

Lars Risbo

Niels Anderskouv

David Edward Zaucha

Anker Bjorn-Josefsen

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. In another disclosed embodiment, a slew rate limiter slows the rate of change of the control signal applied to the variable power supply, in which case the slowed control signal is used in the comparison or calculations of the reduced digital gain.

Digital compensation of analog volume control gain in a digital audio amplifier

In a method and an amplifier for the compensation of unlinearities e.g. of the class D type, wherein an audio signal is pulse-width modulated, e.g. with a carrier wave signal in the form of a triangular signal to provide a pulse-width modulated small-signal, the so-called multiplicative error signals, which occur prior to the provision of a pulse-width modulated great-signal (), are detected in a detector ()). It is noted that the carrier wave signal could be analog as well as digital. The signal from the detector, which is derived on the basis of differences between the pulse widths of the small-signals and the pulse widths of the great-signals, is used for changing the carrier wave signal so that the amplifier gets a constant gain in the entire audio range and is thereby linearized. To compensate additionally for the multiplicative errors which manifest themselves in the pulse height as well as the pulse width of the pulse-width modulated great-signal (), the value of the carrier wave signal is changed as a function of the pulse-width modulated small-signal () multiplied by the pulse-width modulated great-signal and the inverted pulse-width modulated small-signal multiplied by the inverted pulse-width modulated great-signal.

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Soborg, Denmark

Thomas Morch