Audio processing circuit

Abstract

The present invention discloses an audio processing circuit. When the audio processing circuit determines that the signal being processed is a small signal, the output stage is powered by the regulated supply voltage provided by the voltage regulator circuit, and the output stage uses an open-loop architecture to reduce the noise component of the output audio signal; and when the audio processing circuit determines that the signal being processed is a large signal, the output stage is directly powered by the supply voltage, and the output stage uses a closed-loop architecture to reduce the total harmonic distortion of the output audio signal. Through the present invention, the audio processing circuit can maintain good performance indicators while having a very small chip area.

Description

Technical Field

[0001] The present invention relates to an audio processing circuit. Background Art

[0002] Class-D power amplifiers are currently widely used in audio processing circuits. They have high efficiency in generating output audio signals to drive speakers to play sound, and thus are widely used in electronic products in the personal computer market, consumer market, or automotive market. Class-D power amplifiers usually have a closed-loop architecture to eliminate their own nonlinear phenomena and the noise brought by the supply voltage, so as to improve performance indicators such as total harmonic distortion and noise (THD+N), intermodulation distortion (IMD), power supply rejection ratio (PSRR), and so on.

[0003] Regarding the differences in the formats of the received input audio signals, audio processing circuits can generally be divided into digital input types and analog input types. With the increasingly advanced semiconductor manufacturing process, digital input type audio processing circuits will have better performance in terms of chip area. In addition, if most of the circuits in the audio processing circuit can be implemented using digital circuits, it can make the overall product more competitive. However, considering that class-D power amplifiers have a closed-loop architecture, if the modulation circuit in the audio processing circuit is implemented using a digital circuit, an analog-to-digital converter needs to be set up on the feedback path. As an analog circuit, the analog-to-digital converter cannot enjoy the benefits brought by the advanced manufacturing process, that is, the chip area cannot be effectively reduced. In addition, in order to maintain the performance of the class-D power amplifier, a larger area analog-to-digital converter needs to be designed to make the feedback signal have excellent performance, but this will prevent the chip area of the audio processing circuit from further decreasing. Summary of the Invention

[0004] Therefore, one of the objectives of the present invention is to propose an audio processing circuit that can still have good performance with a smaller chip area to solve the problems described in the prior art.

[0005] In an embodiment of the present invention, an audio processing circuit is disclosed, which includes a digital signal processing circuit, a digital modulation circuit, an output stage, a voltage regulation circuit, and a signal detection circuit. During the operation of the audio processing circuit, the digital signal processing circuit is used to process a digital audio signal to generate a processed signal, the digital modulation circuit is used to generate a modulated signal according to the processed signal, the output stage is used to generate an output audio signal according to the modulated signal, the voltage regulation circuit is used to generate a regulated supply voltage after receiving a supply voltage, and the signal detection circuit is used to detect the 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.

[0006] In an embodiment of the present invention, an audio processing circuit is disclosed, which includes a digital signal processing circuit, a digital modulation circuit, an output stage, an analog-to-digital converter, and a signal detection circuit. During the operation of the audio processing circuit, the digital signal processing circuit is used to process a digital audio signal to generate a processed signal, the digital modulation circuit is used to generate a modulated signal according to the processed signal, the output stage is used to generate an output audio signal according to the modulated signal, the analog-to-digital converter is used to perform an analog-to-digital conversion operation on the output audio signal to generate a digital signal, and the signal detection circuit is used to detect the 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, where the feedback signal is generated according to the digital signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 It is a schematic diagram of an audio processing circuit according to an embodiment of the present invention.

[0008] Figure 2 It is a schematic diagram of the audio processing circuit operating in the small signal mode.

[0009] Figure 3 It is a schematic diagram of the audio processing circuit operating in the large signal mode. DETAILED DESCRIPTION

[0010] Figure 1 It is a schematic diagram of an audio processing circuit 100 according to an embodiment of the present invention. As Figure 1As shown, 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 160 as an output stage, an analog-to-digital converter 170, a filter 180, a voltage regulation circuit 190, and two switch circuits 102 and 104. In this embodiment, the audio processing circuit 100 is used to receive a digital audio signal Din and then generate an output audio signal to a speaker to control the speaker to play sound. The audio processing circuit 100 of this embodiment can be disposed in any electronic device that needs to play sound.

[0011] In the operation of the audio processing circuit 100, first, the input interface 110 receives the digital audio signal Din, where the input interface 110 can be an interface circuit that can receive digital audio signals conforming to the I2S specification, pulse density modulation (PDM), or any other digital audio signal. Next, the digital signal processing circuit 130 can perform digital signal processing on the digital audio signal Din, such as volume adjustment, equalization operations, etc., to generate a processed signal Din', and the digital filter 140 performs a filtering operation on the processed signal Din' to generate a filtered signal Din". Next, the digital modulation circuit 150 performs a modulation operation on the filtered signal Din" to generate a modulated signal Dmod, that is, encodes the filtered signal Din" into a pulse-width modulation (PWM) signal to drive 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 well known to those of ordinary skill in the art, so more detailed circuit and operation content will not be described here.

[0013] In the audio processing circuit 100 including a class-D amplifier 160, the total harmonic distortion plus noise (THD+N) is an important indicator for measuring its performance. However, when the audio processing circuit 100 needs to generate an output audio signal Vout with a large volume, the THD+N performance indicator is mainly determined by the total harmonic distortion, and the influence of noise is relatively small. On the other hand, when the audio processing circuit 100 needs to generate an output audio signal Vout with a small volume, the THD+N performance indicator is mainly determined by the noise, and the influence of the total harmonic distortion is relatively small. Therefore, the audio processing circuit 100 of this embodiment additionally designs a signal detection circuit 120, an analog-to-digital converter 170, a filter 180, a voltage regulation circuit 190, and two switches 102 and 104, so that the audio processing circuit 100 can adopt different operation modes according to the intensity / volume of the signal being processed currently.

[0014] Specifically, the signal detection circuit 120 can detect the signal intensity of the digital audio signal Din (for example, the represented volume size) and / or the signal intensity of the processed signal Din', to generate control signals Vc1 and Vc2. In one example, the signal detection circuit 120 can only detect the signal intensity of the digital audio signal Din. In another example, since the digital signal processing circuit 130 may adjust the volume of the digital audio signal Din, the signal detection circuit 120 can only detect the signal intensity of the processed signal Din', or consider the signal intensities of the digital audio signal Din and the processed signal Din' as a whole, to generate the control signals Vc1 and Vc2.

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

[0016] Specifically, first refer to Figure 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’ belongs to a small signal, for example, when the power consumption of the corresponding Class D amplifier 160 is less than 100 milli-Watts (mW), the signal detection circuit 120 can generate a control signal Vc1 to cause the switching circuit 102 to connect the supply voltage VDD to the voltage regulating circuit 190. The voltage regulating circuit 190 can be implemented using a Low Dropout Regulator (LDO) to process the supply voltage VDD to generate a regulated supply voltage VDD’. The Class D amplifier 160 will only receive the regulated supply voltage VDD’ from the voltage regulating circuit 190 and will not be directly powered by the supply voltage VDD. On the other hand, 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 architecture, and at this time, the analog-to-digital converter 170 and the filter 180 will not generate feedback signals to the digital modulation circuit 150 for adjusting the filtered signal Din”.

[0017] In Figure 2 In the audio processing circuit 100 in the small signal mode during the operation shown, since the voltage regulating circuit 190 suppresses and attenuates the power supply noise in the supply voltage VDD, the Class D amplifier 160 powered by the regulated supply voltage VDD’ will improve its performance due to less power supply noise. In addition, since the Class D amplifier 160 has an open-loop architecture, the noise of the analog-to-digital converter 170 itself will not affect the output audio signal Vout at this time. Therefore, the performance of the Class D amplifier 160 itself can be maintained. As described above, the audio processing circuit 100 can maintain a low noise level in the case of small signals (low volume) to improve the total harmonic distortion plus noise performance index.

[0018] On the other hand, referring to Figure 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’ belongs to a large signal, for example, when the power consumption of the corresponding class-D amplifier 160 is greater than 100 milliwatts, the signal detection circuit 120 can generate a control signal Vc1 to cause the switching circuit 102 to directly connect the supply voltage VDD to the class-D amplifier 160 for power supply, and at this time, the voltage regulation circuit 190 can be turned off. On the other hand, the signal detection circuit 120 generates a control signal Vc2 to connect the path between the filter 180 and the digital modulation circuit 150, that is, the class-D amplifier 160 has a closed-loop architecture. At this time, the analog-to-digital converter 170 performs an analog-to-digital conversion operation on the output audio signal Vout to generate a digital signal, and this digital signal is then processed by the filter 180 to generate a feedback signal Vfb, which is used to adjust the filtered signal Din”.

[0019] In Figure 3 In the audio processing circuit 100 in the large signal mode as shown, since the class-D amplifier 160 has a closed-loop architecture, the nonlinear phenomenon of itself and the noise brought by the supply voltage VDD can be eliminated. In addition, in the case of a large signal (high volume), the performance index of the class-D amplifier 160 is mainly determined by the total harmonic distortion. Therefore, the noise generated by the analog-to-digital converter 170 has little impact on the overall performance.

[0020] Referring to the above operation of the audio processing circuit 100, since the analog-to-digital converter 170 only needs to operate in the large signal mode, and in the large signal mode, the performance index of the class-D amplifier 160 is mainly determined by the total harmonic distortion, the analog-to-digital converter 170 can use a design with a smaller die area and does not need to consider the generated noise too much. In addition, since the class-D amplifier 160 is directly powered by the supply voltage VDD in the large signal mode, and the voltage regulation circuit 190 is only used in the small signal mode, the voltage regulation circuit 190 can also use a design with a smaller wafer area and does not need to design a circuit architecture that can support a larger current. In addition, the signal detection circuit 120 is implemented using a digital circuit, so it will also have a very small die area. In summary, the audio processing circuit 100 of this embodiment can maintain good performance indexes while having a very small die area.

[0021] Note that, in order to avoid the audio processing circuit 100 repeatedly switching between the large-signal mode and the small-signal mode, which may cause some incoherence in the output audio signal Vout, the signal detection circuit 120 may have some debounce mechanisms. 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 is currently in the small-signal mode or the large-signal mode; or the signal detection circuit 120 may switch from the small-signal mode to the large-signal mode only after detecting that the signal strength of the digital audio signal Din and / or the processed signal Din’ is higher than a first threshold value, and switch from the large-signal mode to the small-signal mode only after detecting that the signal strength of the digital audio signal Din and / or the processed signal Din’ is lower than a second threshold value, where the first threshold value is higher than the second threshold value. Note that the above switching mechanisms between the small-signal mode and the large-signal mode are only for illustrative purposes and are not limitations of the present invention.

[0022] Briefly summarizing the present invention, in the audio processing circuit of the present invention, when the audio processing circuit determines that the signal being processed is a small signal, the output stage is powered by the regulated supply voltage provided by the voltage regulator circuit, and the output stage uses an open-loop architecture to reduce the noise components of the output audio signal; and when the audio processing circuit determines that the signal being processed is a large signal, the output stage is directly powered by the supply voltage, and the output stage uses a closed-loop architecture to reduce the total harmonic distortion of the output audio signal. Through the present invention, the audio processing circuit can maintain good performance indicators while having a very small chip area.

[0023] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

[0024]

Symbol Description

[0025] 100: Audio processing circuit

[0026] 102: Switching circuit

[0027] 104: Switching circuit

[0028] 110: Input interface

[0029] 120: Signal detection circuit

[0030] 130: Digital signal processing circuit

[0031] 140: Digital filter

[0032] 150: Digital modulation circuit

[0033] 160: Class-D amplifier

[0034] 170: Analog-to-digital converter

[0035] 180: Filter

[0036] 190: Voltage regulator circuit

[0037] Din: Digital audio signal

[0038] Din’: Processed signal

[0039] Din”: Filtered signal

[0040] Dmod: Modulated signal

[0041] Vc1, Vc2: Control signals

[0042] Vfb: Feedback signal

[0043] Vout: Output audio signal

[0044] VDD: Supply voltage

[0045] VDD’: Regulated supply voltage.

Claims

1. An audio processing circuit, comprising: A digital signal processing circuit for processing a digital audio signal to generate a processed signal; A digital modulation circuit for generating a modulated signal according to the processed signal; An output stage for generating an output audio signal according to the modulated signal; A voltage stabilizing circuit for receiving a supply voltage and generating a stabilized supply voltage; And A signal detection circuit for detecting the 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 stabilized supply voltage to generate the output audio signal.

2. The audio processing circuit according to claim 1, wherein when the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal and 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 stabilized 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 instead of the stabilized supply voltage.

3. The audio processing circuit according to claim 2, further comprising: A switching circuit for selectively connecting the supply voltage to the output stage or the voltage stabilizing circuit; 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 first control signal to control the switching circuit to connect the supply voltage to the voltage stabilizing circuit, and the output stage does not receive the 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 switching circuit to connect the supply voltage to the output stage, and the voltage stabilizing circuit does not generate the stabilized supply voltage to the output stage.

4. The audio processing circuit according to claim 1, further comprising: An analog-to-digital converter for performing an analog-to-digital conversion operation on the output audio signal to generate a digital signal; A filter for filtering the digital signal to generate a feedback signal; Wherein the signal strength of the digital audio signal and / or the processed signal is detected to generate a second control signal for controlling whether the digital modulation circuit refers to the feedback signal to generate the modulated signal.

5. The audio processing circuit according to claim 4, wherein when the signal detection circuit detects the signal strength of the digital audio signal and / or the processed signal, and 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 generate the modulated signal with reference to the feedback 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 generate the modulated signal with reference to the feedback signal.

6. The audio processing circuit according to claim 5, further comprising: a switch circuit for selectively coupling the filter to the digital modulation circuit; 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 control the switch circuit to block the 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 switch circuit to couple the filter to the digital modulation circuit.

7. The audio processing circuit according to claim 1, wherein the output stage is a class D amplifier.

8. An audio processing circuit, comprising: a digital signal processing circuit for processing a digital audio signal to generate a processed signal; a digital modulation circuit for generating a modulated signal according to the processed signal; an output stage for generating an output audio signal according to the modulated signal; an analog-to-digital converter for performing an analog-to-digital conversion operation on the output audio signal to generate a digital signal; a voltage stabilizing circuit for generating a regulated supply voltage after receiving a supply voltage; a signal detection circuit for detecting the signal strength of the digital audio signal and / or the processed signal to generate a control signal for controlling whether the digital modulation circuit generates the modulated signal with reference to a feedback signal, wherein the feedback signal is generated according to the digital signal, and the signal detection circuit is used to detect the signal strength of the digital audio signal and / or the processed signal to generate another control signal for controlling the output stage to use the supply voltage or the regulated supply voltage to generate the output audio signal.

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

10. The audio processing circuit according to claim 8 further comprises: A switch circuit for selectively coupling the filter to the digital modulation circuit; 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 control signal to control the switch circuit to block the path between the analog-to-digital converter 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 control signal to control the switch circuit to couple the analog-to-digital converter to the digital modulation circuit.

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