TWI869034B - Class-d audio amplifier and noise elimination device thereof - Google Patents

Abstract

A noise elimination device for a Class-D audio amplifier includes a residual signal detector and a multiplexer, wherein the multiplexer is electrically connected with a sigma-delta modulator (SDM) and a pulse width modulator (PWM) of the Class-D audio amplifier and the residual signal detector. The residual signal detector is configured to detect whether an input signal of the Class-D audio amplifier is residual. The multiplexer is configured to output zero data into the pulse width modulator when the residual signal detector detects that the input signal of the Class-D audio amplifier is residual.

Description

Class D audio amplifier and noise elimination device

The present disclosure relates to a class D audio amplifier. More specifically, the present disclosure relates to a class D audio amplifier and a noise elimination device thereof, wherein the noise elimination device is capable of detecting whether a residual signal exists in the class D audio amplifier and eliminating noise caused by the residual signal.

Class D audio amplifiers typically use a sigma-delta modulator (SDM) to perform digital-to-analog or analog-to-digital conversion on an audio signal, and a pulse width modulator (PWM) to provide a series of pulses with different widths to a power stage. Generally speaking, the sigma-delta modulator includes a feedback circuit that can cause a residual signal to be generated in the Class D audio amplifier even when the audio input signal of the Class D audio amplifier is turned off. Once the residual signal is output to the pulse width modulator and then enters the power stage, the output of the Class D audio amplifier will contain additional noise. In view of this, it is very important to overcome this problem in this technology.

In order to at least overcome the above-mentioned problems, the present disclosure provides a noise elimination device for a class D audio amplifier. The noise elimination device may include a residual signal detector and a multiplexer. The multiplexer is electrically connected to an integral-differential modulator and a pulse width modulator of the class D audio amplifier and is electrically connected to the residual signal detector. The residual signal detector can be used to detect whether an input signal of the class D audio amplifier has residual. The multiplexer can be used to output zero data to the pulse width modulator when the residual signal detector detects that the input signal of the class D audio amplifier has residual.

In order to at least overcome the above-mentioned problems, the present disclosure also provides a class D audio amplifier. The class D audio amplifier may include an integrator-differential modulator; a pulse width modulator; and a noise elimination device. The noise elimination device may include a residual signal detector and a multiplexer. The multiplexer is electrically connected to the integrator-differential modulator, the pulse width modulator and the residual signal detector. The residual signal detector can be used to detect whether an input signal of the class D audio amplifier has residual. The multiplexer can be used to output zero data to the pulse width modulator when the residual signal detector detects that the input signal of the class D audio amplifier has residual.

The noise elimination device proposed in the present invention can detect whether an input signal of a class-D audio amplifier has residues, and when it detects that the input signal of the class-D audio amplifier has residues, it removes the residue signal from the class-D audio amplifier by forcing zero data into a pulse width modulator, thereby eliminating or reducing the output noise of the class-D audio amplifier caused by the residue signal.

The content of the present invention is not intended to limit the claimed invention, but only to provide a basic overview of the claimed invention. The details of the claimed invention will be explained by various embodiments presented below.

The embodiments disclosed below are not intended to limit the claimed invention to any particular environment, application, structure, process or context. In the accompanying drawings, elements that are not directly related to the claimed invention are not shown. The dimensions and dimensional relationships between the various elements in the accompanying drawings are only illustrative examples and are not intended to limit the claimed invention. Unless otherwise specified, the same element number may correspond to the same element in the following description without being inconsistent with the claimed invention.

The terms used herein are used only for the purpose of describing various embodiments and are not intended to limit the claimed invention. Unless the context clearly indicates otherwise, the singular forms "a and an" are intended to include the plural forms as well. The terms "comprises/comprising", "includes/including", etc. indicate the presence of the described features, integers, operations, elements and/or components, but do not exclude the presence or addition of one or more other features, integers, operations, elements, components and/or groups composed thereof. The term "and/or" includes any and all combinations of one or more of the related listed items. Although the terms "first", "second", etc. may be used herein to describe various elements, such elements should not be limited by such terms. Such terms are only used to distinguish between various elements. Therefore, for example, a first element described below could also be referred to as a second element without departing from the spirit and scope of the claimed invention.

FIG. 1 is a schematic diagram of a class-D audio amplifier including a noise elimination device according to some embodiments of the present disclosure. The content shown in FIG. 1 is only provided for illustrating the embodiments of the present disclosure and should not be interpreted as any limitation to the claimed invention.

Referring to FIG. 1 , a class-D audio amplifier 1 includes a noise elimination device 11. The class-D audio amplifier 1 may be an open-loop class-D audio amplifier, and may basically include, for example, an integral-differential modulator 13, a pulse width modulator 15, a power stage 19, and a signal processor 17. Depending on design requirements, the signal processor 17 is optional. The integral-differential modulator 13, the pulse width modulator 15, the power stage 19, and the signal processor 17 are electrically connected directly or indirectly.

The optional signal processor 17 can be used to perform various signal processing on an input signal S1 (an audio signal) of the class-D audio amplifier 1 to convert it into a signal having a signal form suitable for the input of the integral-differential modulator 13. For example, when the input signal S1 is an analog signal, the signal processor 17 can perform an analog-to-digital conversion and a digital signal processing to convert the input signal S1 into a digital signal having an appropriate signal form required for the input of the integral-differential modulator 13. Alternatively, when the input signal S1 is a digital signal, the signal processor 17 can perform a digital signal processing so that the input signal S1 can meet the signal form required for the input of the integral-differential modulator 13.

The integrator-differential modulator 13 can be used to perform a digital-to-analog conversion or an analog-to-digital conversion on the audio input signal. Taking a digital system as an example, the integrator-differential modulator 13 can convert a digital input signal S1 into a pulse width modulation (PWM) signal so that the pulse width modulator 15 can modulate the pulse width modulation signal to generate a series of pulses with different pulse widths. Then, the power stage 19 can amplify the series of pulses to generate a driving signal for a speaker (not shown in the figure). The integrator-derivative modulator 13 includes a feedback circuit that can cause a residual signal to be generated in the class-D audio amplifier 1 even if the audio input signal S1 of the class-D audio amplifier 1 is turned off. As described below, the adverse effects caused by the residual signal can be reduced by the proposed noise canceling device 11.

The noise elimination device 11 may include a residual signal detector 111 and a multiplexer 113, and the multiplexer 113 is electrically connected to the integral-differential modulator 13, the pulse width modulator 15, and the residual signal detector 111. The multiplexer 113 may include two input terminals and an output terminal, and one of the input terminals is used to receive an output of the integral-differential modulator 13, and the other of the input terminals is used to receive zero data S0. In addition, the output terminal of the multiplexer 113 is used to output a signal from the output of the integral-differential modulator 13 or zero data depending on a selection signal S2 generated by the residual signal detector 111 in response to its detection result. More specifically, the residual signal detector 111 can be used to detect whether an input signal S1 (an audio signal) of the class-D audio amplifier 1 has residues, and in order to reduce the adverse effects of the residual signal, the multiplexer 113 can be used to force the zero data S0 to be output to the pulse width modulator 15 when the residual signal detector 111 detects that the input signal S1 has residues. In the case where the zero data S0 is output to the pulse width modulator 15, the power stage 19 can therefore generate a driving signal with less noise for the speaker (not shown in the figure).

In some embodiments, as shown in FIG. 2A , only one threshold (referred to as the “first threshold”) may be set for the residue signal detector 111. FIG. 2A provides a waveform diagram of the input signal S1, and in FIG. 2A , only one threshold (the first threshold) is provided to show how the residue signal detector 111 detects whether the input signal S1 has residue. The contents shown in FIG. 2A are only used to illustrate the embodiments of the present disclosure and should not be interpreted as any limitation to the claimed invention. In the embodiments, the residual signal detector 111 can detect that the input signal S1 of the class-D audio amplifier 1 has a residue at the time point T1, and at the time point T1, the amplitude of the input signal S1 of the class-D audio amplifier 1 is just lower than the first threshold. On the contrary, as long as the amplitude of the input signal S1 of the class-D audio amplifier 1 is not lower than the first threshold, the residual signal detector 111 will not detect that the input signal S1 of the class-D audio amplifier 1 has a residue.

Alternatively, the residual signal detector 111 may detect that the input signal S1 of the class-D audio amplifier 1 has a residual at a time point T2, at which the amplitude of the input signal S1 of the class-D audio amplifier 1 has been lower than the first threshold for a predetermined first time period. In this case, as long as the amplitude of the input signal S1 of the class-D audio amplifier 1 is not lower than the first threshold for the predetermined first time period, the residual signal detector 111 may not detect that the input signal S1 of the class-D audio amplifier 1 has a residual.

In some embodiments, as shown in FIG. 2B , two thresholds (referred to as “first threshold” and “second threshold”) may be set for the residue signal detector 111. FIG. 2B provides a waveform diagram of the input signal S1. In FIG. 2B , there are two thresholds (first threshold and second threshold) for illustrating how the residue signal detector 111 detects whether the input signal S1 has residue. The contents shown in FIG. 2B are only used to illustrate the embodiments of the present disclosure and should not be interpreted as any limitation to the claimed invention. The second threshold is higher than the first threshold. The first threshold value shown in FIG. 2B is the same as the first threshold value shown in FIG. 2A; that is, the residual signal detector 111 can detect that the input signal S1 of the class-D audio amplifier 1 has a residue at the time point T1 to T2, as described above with respect to FIG. 2A. The difference is that the residual signal detector 111 can detect that the input signal S1 of the class-D audio amplifier 1 is a normal audio signal at the time point T3, and at the time point T3, the amplitude of the input signal S1 of the class-D audio amplifier 1 is just higher than the second threshold value. Alternatively, the residual signal detector 111 may detect that the input signal S1 of the class-D audio amplifier 1 is a normal audio signal at time point T4, and at time point T4, the amplitude of the input signal S1 of the class-D audio amplifier 1 is higher than the second threshold for a predetermined second time period. The predetermined first time period and the predetermined second time period may be different or the same depending on design requirements.

In some embodiments, the residual signal detector 111 may include a counter for determining the time points T1 to T4 and the predetermined first time period and the predetermined second time period.

The first threshold and the second threshold may be predetermined. For example, in the case of providing a 24 volt power supply to a load having 8 ohms, the first threshold may be in the range of -90 decibels (dB) to -110 dB, preferably -110 dB, and the second threshold may be in the range of -80 dB to -100 dB, preferably -100 dB.

Without being inconsistent with the claimed invention, various combinations, modifications and/or alternative forms of the embodiments disclosed directly or indirectly are substantially included in the entire disclosure, even if such combinations, modifications and/or alternative forms are not specifically mentioned above. The scope of the claimed invention is defined by the scope of the patent application attached below.

1: Class D audio amplifier

11: Noise Elimination Device

13: Integral-Differential Modulator (SDM)

15: Pulse Width Modulator (PWM)

17:Signal Processor

19: Power Level

111: Residual signal detector

113: Multiplexer

S0: zero data

S1: Input signal/audio input signal/digital input signal

S2: Select signal

T1, T2, T3, T4: time points

FIG. 1 illustrates a schematic diagram of a class-D audio amplifier including a noise elimination device according to some embodiments of the present disclosure. FIG. 2A provides a waveform diagram of an input signal of the class-D audio amplifier. In FIG. 2A, there is only one threshold value, which is used to show how the noise elimination device detects whether the input signal has residuals. FIG. 2B provides a waveform diagram of an input signal of the class-D audio amplifier. In FIG. 2B, there are two threshold values, which are used to show how the noise elimination device detects whether the input signal has residuals.

without

1: Class D audio amplifier

11: Noise elimination device

13: Integral-differential modulator (SDM)

15: Pulse Width Modulator (PWM)

17:Signal processor

19: Power level

111: Residual signal detector

113:Multiplexer

S0: zero data

S1: Input signal/audio input signal/digital input signal

S2: Select signal

Claims (11)

A noise elimination device for a class D audio amplifier includes: a residual signal detector for detecting whether an input signal of the class D audio amplifier has residuals; a multiplexer electrically connected to a sigma-delta modulator and a pulse width modulator of the class D audio amplifier, and also electrically connected to the residual signal detector, and used to output zero data to the pulse width modulator when the residual signal detector detects that the input signal of the class D audio amplifier has residuals. The noise elimination device as described in claim 1, wherein when an amplitude of the input signal of the class-D audio amplifier is lower than a first threshold, the residual signal detector detects that the input signal of the class-D audio amplifier has residual. The noise elimination device as described in claim 2, wherein when the amplitude of the input signal of the class-D audio amplifier is higher than a second threshold, the residual signal detector detects that the input signal of the class-D audio amplifier has no residue, wherein the second threshold is higher than the first threshold. The noise elimination device as described in claim 1, wherein when an amplitude of the input signal of the class-D audio amplifier has been lower than a first threshold for a period of time, the residual signal detector detects that the input signal of the class-D audio amplifier has residual. A noise elimination device as described in claim 1, wherein the class-D audio amplifier is an open-loop class-D audio amplifier. A class D audio amplifier includes: an integrator-differential modulator; a pulse width modulator; and a noise elimination device, including: a residual signal detector for detecting whether an input signal of the class D audio amplifier has residual; and a multiplexer, electrically connected to the integrator-differential modulator, the pulse width modulator and the residual signal detector, and used to output zero data to the pulse width modulator when the residual signal detector detects that the input signal of the class D audio amplifier has residual. The class D audio amplifier as described in claim 6 further comprises: a signal processor electrically connected to the integrator-differential modulator and used to process the input signal of the class D audio amplifier as an input of the integrator-differential modulator; and a power stage electrically connected to the pulse width modulator and used to generate a driving signal for a speaker according to an output of the pulse width modulator. A class D audio amplifier as described in claim 6, wherein when an amplitude of the input signal of the class D audio amplifier is lower than a first threshold, the residual signal detector detects that the input signal of the class D audio amplifier has residual. A class D audio amplifier as described in claim 8, wherein when the amplitude of the input signal of the class D audio amplifier is higher than a second threshold, the residual signal detector detects that the input signal of the class D audio amplifier has no residue, wherein the second threshold is higher than the first threshold. A class D audio amplifier as described in claim 6, wherein when an amplitude of the input signal of the class D audio amplifier has been lower than a first threshold for a period of time, the residual signal detector detects that the input signal of the class D audio amplifier has residual. A class D audio amplifier as described in claim 6, wherein the class D audio amplifier is an open-loop class D audio amplifier.

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