Audio Processing Circuit

Abstract

To disclose an audio processing circuit.SOLUTION: When an audio processing circuit determines that a signal in processing is a small signal, an output stage uses regulated supply voltage provided by a voltage regulator, and the output stage uses an open-loop structure to reduce noise of an output audio signal. When the audio processing circuit determines that the signal in processing is a large signal, the output stage directly uses the supply voltage without using the regulated supply voltage, and the output stage uses a closed-loop structure to reduce the total harmonic distortion of the output audio signal. By using the present invention, the audio processing circuit can have a good performance indicator with small chip area design.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to audio processing circuits. [Background technology]

[0002] Class D output amplifier (power amplifier) ​​is a commonly used technology in audio processing circuits, which has high efficiency in generating output audio signals to drive speakers to reproduce sound, and is therefore widely used in electronic products in personal computers, consumer electronic products, and automotive electronic products. Class D power amplifiers usually have a closed-loop structure to eliminate the noise caused by the supply voltage and the nonlinear phenomenon of the power amplifier itself, so as to improve performance indicators such as total harmonic distortion plus noise (THD+N), intermodulation distortion (IMD) or power supply rejection ratio (PSRR).

[0003] Considering the difference in the format of the received input audio signal, the audio processing circuit can generally be divided into a digital input type and an analog input type. With the increasing progress of the semiconductor process, the digital input type audio processing circuit has better performance in terms of chip area. Also, if most of the circuits in the audio processing circuit can be implemented by digital circuits, the whole product can be made more competitive. However, considering that the class D power amplifier has a closed-loop structure, if the modulation circuit in the audio processing circuit is implemented by digital circuits, it is necessary to place an analog-to-digital converter (ADC) in the feedback path. The ADC, which has an analog circuit, cannot enjoy the benefits of the advanced semiconductor process, that is, it cannot effectively reduce the chip area. Furthermore, in order to maintain the performance of the class D power amplifier, it is necessary to design a larger area ADC to make the feedback signal have better performance, but the large area ADC will hinder further reduction of the chip area of ​​the audio processing circuit. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US Patent Application Publication No. 2010 / 0321116 [Patent Document 2] U.S. Pat. No. 1,065,8988 [Patent Document 3] US Patent Application Publication No. 2018 / 0205347 [Patent Document 4] US Patent Application Publication No. 2019 / 0386626 Summary of the Invention

[0005] Therefore, an object of the present invention is to provide an audio processing circuit that can have good performance with a small chip area so as to solve the problems described in the background art.

[0006] According to one embodiment of the present invention, an audio processing circuit is disclosed, comprising a digital signal processing circuit, a digital modulation circuit, an output stage, a voltage regulator, and a signal detection circuit. The digital signal processing circuit is configured to process a digital audio signal to generate a processed signal. The digital modulation circuit is configured to generate a modulated signal according to the processed signal. The output stage is configured to generate an output audio signal according to the modulated signal. The voltage regulator is configured to receive a supply voltage and generate a regulated supply voltage. The signal detection circuit is configured to detect a signal strength of the digital audio signal and / or the processed signal to generate a first control signal for controlling the output stage to use the supply voltage or the regulated supply voltage to generate the output audio signal.

[0007] According to one embodiment of the present invention, an audio processing circuit is disclosed, comprising a digital signal processing circuit, a digital modulation circuit, an output stage, an ADC, and a signal detection circuit. The digital signal processing circuit is configured to process a digital audio signal to generate a processed signal. The digital modulation circuit is configured to generate a modulated signal according to the processed signal. The output stage is configured to generate an output audio signal according to the modulated signal. The ADC is configured to perform an analog-to-digital conversion process on the output audio signal to generate a digital signal. The signal detection circuit is configured to detect a signal strength of the digital audio signal and / or the processed signal to generate a control signal for controlling whether the digital modulation circuit refers to a feedback signal to generate the modulated signal, the feedback signal being generated according to the analog signal.

[0008] These and other objects of the present invention will no doubt become obvious to those skilled in the art after reading the following detailed description of the preferred embodiments that are illustrated in the various figures and drawings. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 illustrates an audio processing circuit according to one embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram of an audio processing circuit operating in a small signal mode. [Diagram 3] FIG. 1 is a diagram of an audio processing circuit operating in large signal mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] FIG. 1 is a diagram showing an audio processing circuit 100 according to an embodiment of the present invention. As shown in FIG. 1, the audio processing circuit 100 includes an input interface 110, a signal detection circuit 120, a digital signal processing circuit 130, a digital filter 140, a digital modulation circuit 150, a class D amplifier (amplifier) ​​160 serving as an output stage, an ADC 170, a filter 180, a voltage regulator 190, and two switching circuits 102, 104. In this embodiment, the audio processing circuit 100 is used to receive a digital audio signal Din and generate an output audio signal Vout to a speaker to control the speaker to play sound. The audio processing circuit 100 of this embodiment can be incorporated into any electronic device that needs to play sound.

[0011] In the operation of the audio processing circuit 100, first, the input interface 110 receives a digital audio signal Din, where the input interface 110 may be capable of receiving a signal conforming to the I2S specification, pulse density modulation (PDM), or any other digital audio signal type. Then, the digital signal processing circuit 130 can perform digital signal processing, such as volume control and equalization, on the digital audio signal Din to generate a processed signal Din', and the digital filter 140 filters the processed signal Din' to generate a filtered signal Din". Then, the digital modulation circuit 150 modulates the filtered signal Din" to generate a modulated signal Dmod, i.e., the digital modulation circuit 150 encodes the filtered signal Din" into a pulse width modulation (PWM) signal or a pulse density modulation (PDM) signal that drives the class D amplifier 160 to generate the output audio signal Vout.

[0012] The operations of the above-mentioned input interface 110, digital signal processing circuit 130, digital filter 140, digital modulation circuit 150, and class-D amplifier 160 are already well known to those skilled in the art, and therefore detailed operations will be omitted here.

[0013] In the audio processing circuit 100 including the class-D amplifier 160, the total harmonic distortion plus noise (THD+N) is an important performance index. However, when the audio processing circuit 100 needs to generate a loud output audio signal Vout, this performance index (THD+N) is dominated by the total harmonic distortion and the noise has only a small effect on this performance index. On the other hand, when the audio processing circuit 100 needs to generate a low volume output audio signal Vout, this performance index (THD+N) is dominated by the noise and the total harmonic distortion has only a small effect on this performance index. Therefore, the audio processing circuit 100 of this embodiment additionally designs the signal detection circuit 120, the ADC 170, the filter 180, the voltage regulator 190, and the two switching circuits 102, 104 so that the audio processing circuit 100 can adopt different operation modes according to the strength / volume of the signal currently being processed.

[0014] Specifically, the signal detection circuit 120 can detect the signal strength of the digital audio signal Din (e.g., the volume level indicated by the digital audio signal) and / or the signal strength of the processed signal Din' to generate the control signals Vc1 and Vc2. In one example, the signal detection circuit 120 can detect only the signal strength of the digital audio signal Din. In another example, the digital signal processing circuit 130 may adjust the volume of the digital audio signal Din, and therefore the signal detection circuit 120 can detect only the signal strength of the processed signal Din', or can generate the control signals Vc1 and Vc2 by comprehensively considering the signal strengths of the digital audio signal Din and the processed signal Din'.

[0015] The control signal Vc1 is used to control the switching circuit 102 so that the class D amplifier 160 can be powered directly by the supply voltage VDD or by a regulated supply voltage VDD' provided by a voltage regulator 190. The control signal Vc2 is used to control the switching circuit 104 so that the class D amplifier 160 has an open-loop or a closed-loop configuration.

[0016] 2, when the signal detection circuit 120 determines that the signal strength of the current digital audio signal Din and / or the processed signal Din' is a small signal, such as when the power consumption corresponding to the class-D amplifier 160 is less than 100 milliwatts, the signal detection circuit 120 can generate a control signal Vc1 so that the switching circuit 102 connects the supply voltage VDD to the voltage regulator 190. The voltage regulator 190 can be implemented by using a low dropout regulator (LDO), and processes the supply voltage VDD to generate a regulated supply voltage VDD', and the class-D amplifier 160 only receives the regulated supply voltage VDD' from the voltage regulator 190, i.e., the class-D amplifier 160 is not powered by the supply voltage VDD. In addition, the signal detection circuit 120 generates a control signal Vc2 to disconnect the path between the filter 180 and the digital modulation circuit 150. That is, the class D amplifier 160 has an open-loop structure, in which the ADC 170 and the filter 180 do not generate a feedback signal for adjusting the filtered signal Din'' to the digital modulation circuit 150.

[0017] In the audio processing circuit 100 operating in the small signal mode shown in FIG. 2, the voltage regulator 190 suppresses and attenuates the power noise in the supply voltage VDD, so that the class-D amplifier 160 powered by the regulated supply voltage VDD' will have better performance due to less power supply noise. Furthermore, because the class-D amplifier 160 has an open-loop structure, the noise of the ADC 170 will not affect the output audio signal Vout, and therefore the performance of the class-D amplifier 160 can be maintained. As mentioned above, the audio processing circuit 100 can have a low noise level in the case of a small signal (low volume) so as to improve the performance index (THD+N or SNR).

[0018] On the other hand, referring to Fig. 3, when the signal detection circuit 120 determines that the signal strength of the current digital audio signal Din and / or the processed signal Din' is a large signal, such as when the power consumption corresponding to the class-D amplifier 160 exceeds 100mW, the signal detection circuit 120 can generate a control signal Vc1 so that the switching circuit 102 directly connects the supply voltage VDD to the class-D amplifier 160, and the voltage regulator 190 can be disabled at this time. Furthermore, the signal detection circuit 120 generates a control signal Vc2 to connect a path between the filter 180 and the digital modulation circuit 150. That is, the class-D amplifier 160 has a closed-loop structure, and the ADC 170 performs an analog-to-digital conversion process on the output audio signal Vout to generate a digital signal, which is processed by the filter 180 to generate a feedback signal Vfb, which is used to adjust the filtered signal Din".

[0019] 3, the class-D amplifier 160 has a closed-loop structure, so that it can eliminate its own nonlinear phenomenon and the noise caused by the supply voltage VDD. Furthermore, in the case of a large signal (large capacity), the performance index of the class-D amplifier 160 is dominated by the total harmonic distortion, and therefore the noise generated by the ADC 170 has little effect on the performance index.

[0020] Referring to the operation of the audio processing circuit 100 described above, since the ADC 170 only needs to be operated in the large signal mode, and the performance index of the class-D amplifier 160 in the large signal mode is dominated by the total harmonic distortion, the ADC 170 can be designed with a smaller chip area without much consideration of the noise generated by itself. Furthermore, since the class-D amplifier 160 is directly powered by the supply voltage VDD in the large signal mode, and the voltage regulator 190 is only used in the small signal mode, the voltage regulator 190 can also be designed with a smaller chip area without the need to design a circuit structure that supports a larger current. In addition, the signal detection circuit 120 is implemented using a digital circuit, and therefore, it also has a small chip area. In short, the audio processing circuit 100 of this embodiment can maintain a good performance index while having a small chip area.

[0021] It should be noted that the signal detection circuit 120 may have a debounce mechanism to prevent the audio processing circuit 100 from repeatedly switching between the large signal mode and the small signal mode, which may cause some inconsistency in the output audio signal Vout. For example, the signal detection circuit 120 may detect the average signal strength of the digital audio signal Din and / or the processed signal Din' over a period of time to determine whether it should be in the small signal mode or the large signal model. In another example, the signal detection circuit 120 may switch from the small signal mode to the large signal mode only when the signal strength of the digital audio signal Din and / or the processed signal Din' is higher than a first threshold, and may switch from the large signal mode to the small signal mode only when the signal strength of the digital audio signal Din and / or the processed signal Din' is lower than a second threshold, where the first threshold is higher than the second threshold. It should be noted that the above-mentioned switching mechanism between the small signal mode and the large signal mode is not a limitation of the present invention, but is merely an example for explanation.

[0022] In brief, in the audio processing circuit of the present invention, when the audio processing circuit determines that the processed signal is a small signal, the output stage uses the regulated supply voltage provided by the voltage regulator for power supply, and the output stage uses an open loop structure to reduce noise in the output audio signal. When the audio processing circuit determines that the processed signal is a large signal, the output stage uses the supply voltage directly, and the output stage uses a closed loop structure to reduce total harmonic distortion of the output audio signal. By using the audio processing circuit of the present invention, the audio processing circuit can have a good performance index with a small chip area.

[0023] Those skilled in the art will immediately recognize that numerous modifications and variations of the apparatus and methods may be made while retaining the teachings of the invention, and therefore the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims

1. a digital signal processing circuit configured to process the digital audio signal to generate a processed signal; a digital modulation circuit configured to generate a modulated signal in accordance with the processed signal; an output stage configured to generate an output audio signal in accordance with the modulated signal; a voltage regulator configured to receive a supply voltage and generate a regulated supply voltage; a signal detection circuit configured to detect a signal strength of the digital audio signal and / or the processed signal and to generate, in response to the detected signal strength, a first control signal for controlling the output stage to selectively use one of the supply voltage and the regulated supply voltage to generate the output audio signal; having the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the first control signal to control the output stage to use the regulated supply voltage, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the first control signal to control the output stage to use the supply voltage without using the regulated supply voltage. Audio processing circuitry.

2. a switching circuit configured to selectively connect the supply voltage to the output stage or to the voltage regulator; and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the first control signal to control the switching circuit to connect the supply voltage to the voltage regulator, and the output stage does not receive the supply voltage; when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the first control signal to control the switching circuit to connect the supply voltage to the output stage, and the voltage regulator does not generate the regulated supply voltage to the output stage.

2. The audio processing circuit of claim 1.

3. an analog-to-digital converter (ADC) configured to perform an analog-to-digital conversion process on the output audio signal to generate a digital signal; a filter configured to filter the digital signal to generate a feedback signal; and the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal to generate a second control signal for controlling whether the digital modulation circuit refers to the feedback signal to generate the modulated signal; 2. The audio processing circuit of claim 1.

4. 4. The audio processing circuit of claim 3, wherein the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the second control signal to control the digital modulation circuit not to refer to the feedback signal to generate the modulated signal, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the second control signal to control the digital modulation circuit to refer to the feedback signal to generate the modulated signal.

5. a switching circuit configured to selectively connect the filter to the digital modulation circuit; and 5. The audio processing circuit of claim 4, wherein when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the second control signal to disconnect a path between the filter and the digital modulation circuit, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the second control signal to control the switching circuit to connect the filter to the digital modulation circuit.

6. 2. The audio processing circuit of claim 1, wherein the output stage is a class D amplifier.

7. a digital signal processing circuit configured to process the digital audio signal to generate a processed signal; a digital modulation circuit configured to generate a modulated signal in accordance with the processed signal; an output stage configured to generate an output audio signal in accordance with the modulated signal; a voltage regulator configured to receive a supply voltage and generate a regulated supply voltage; an analog-to-digital converter (ADC) configured to perform an analog-to-digital conversion process on the output audio signal to generate a digital signal; a signal detection circuit configured to detect a signal strength of the digital audio signal and / or the processed signal, and to generate, in response to the detected signal strength, a first control signal for controlling the output stage to selectively use one of the supply voltage and the regulated supply voltage to generate the output audio signal, and a second control signal for controlling whether the digital modulation circuit refers to a feedback signal to generate the modulated signal, wherein the feedback signal is generated according to the digital signal; An audio processing circuit having

8. 8. The audio processing circuit of claim 7, wherein the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the second control signal to control the digital modulation circuit not to refer to the feedback signal to generate the modulated signal, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the second control signal to control the digital modulation circuit to refer to the feedback signal to generate the modulated signal.

9. a filter configured to filter the digital signal to generate the feedback signal; a switching circuit configured to selectively connect the filter to the digital modulation circuit; and 9. The audio processing circuit of claim 8, wherein when the signal detection circuit determines that the digital audio signal and / or the processed signal is a small signal, the signal detection circuit generates the second control signal to disconnect a path between the filter and the digital modulation circuit, and when the signal detection circuit determines that the digital audio signal and / or the processed signal is a large signal, the signal detection circuit generates the second control signal to control the switching circuit to connect the filter to the digital modulation circuit.

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