CN100566160C - Audio signal amplifying device and method for preventing pop sound - Google Patents

Abstract

An audio amplifier is suitable for an audio playing system, and the audio playing system is provided with an audio source, an isolation capacitor and a load. It includes a power amplifier circuit and a control unit. The power amplifier circuit is coupled to the audio source to receive the audio generated by the audio source. The power amplifying circuit has power for amplifying audio signals and outputs the amplified audio signals to a load through an isolation capacitor, and the power amplifying circuit comprises a bias circuit unit which is used for generating positive and negative direct current bias points of the power amplifier circuit. The control unit is coupled to the power amplifier circuit, when the audio amplifying device is started, if the bias value of the audio output by the power amplifier circuit is lower than a preset potential, the control unit sets the operation type of the power amplifier circuit to be type A; when the bias value of the audio output by the power amplifier circuit reaches a predetermined potential, the control unit sets the operation type of the power amplifier circuit to AB.

Description

Audio amplifying device and method for preventing popping sound

technical field

The present invention relates to an audio amplification device, especially an audio amplification device with the function of preventing popping sound, and a method for preventing popping sound.

Background technique

In general, audio playback systems can be divided into three types of structures for amplifying audio power: single-ended, bridge-tied-load, and fully differential. and other amplification systems. Among them, the single-ended audio amplification system is mostly used to drive headphone loads. Please refer to FIG. 1 , which is a schematic structural diagram of a typical audio playing system. In Fig. 1, the audio playback system 1 is a single-ended amplification structure. In the audio playback system 1, a power amplifier (Power amplifier) is arranged inside the audio amplification device 10 to receive the first audio 14 generated by the audio source 11. , and amplify it as the output of the second audio 15 , and then, the DC bias voltage of the second audio 15 is isolated by the coupling capacitor C _AC1 , and the AC-coupled audio 16 is transmitted to the load 12 for playback.

Next, please refer to FIG. 2A and FIG. 2B , which are voltage diagrams of the second audio 15 and the AC-coupled audio 16 respectively. As shown in Fig. 2A and Fig. 2B, when the audio amplifying device 10 starts (the time in the figure is _T1 ), the potential of the second audio 15 changes from zero volts to the working potential instantaneously, and this instantaneous voltage change causes the AC coupling audio A voltage pulse appears instantaneously at 16 , which further causes the load 12 to generate a Pop phenomenon. Similarly, when the audio amplifying device 10 is turned off, the popping phenomenon will also occur. The popping phenomenon not only makes the user feel uncomfortable, but also accelerates the aging of the load 12 and related circuits, shortening its service life. Therefore, how to prevent the generation of popping sounds is a subject that designers often think about.

At present, the industry controls the bias voltage rise rate of the amplifier to eliminate the instantaneous change of the voltage, so as to avoid the generation of popping sound. Please refer to FIG. 3 , which is a schematic diagram of the system architecture of a prior art audio playback system with anti-popping function. In the audio playing system 2 shown in FIG. 3 , the audio amplifying device 20 has a power amplifier AMP10 . The reference voltage input terminal of the power amplifier AMP10 is connected with a bypass capacitor C _BYPASS . The bypass capacitor C _BYPASS and the high-impedance resistor divider circuit forming the power supply voltage V _DD /2 in the power amplifier AMP10 will form an RC time constant to eliminate the instantaneous voltage change and prevent the load 22 from generating popping sound.

In the above-mentioned prior art, the bias point of the amplifier is controlled by the bypass capacitor C _BYPASS and the related voltage divider resistor so that the system can slowly reach the working potential to avoid the generation of popping sound. The above-mentioned audio amplifying device is usually designed in an integrated circuit chip. In order to prevent popping, the integrated circuit chip must be connected with a bypass capacitor C _BYPASS . Furthermore, this system requires a rather long charging time to reach the operating point of the amplifier AMP10. In view of the above-mentioned defects in the prior art, the inventor proposes a new design concept. Different from the voltage control system in the prior art, the present invention prevents popping based on the current control system. In addition to effectively avoiding the popping phenomenon, the present invention can also improve the defect of the prior art that the amplifier is turned on for too long.

Contents of the invention

The object of the present invention is to provide an audio amplification device and a method for preventing popping sound, which can switch the operation type of the power amplifier circuit through the control unit, and can prevent the popping sound from being generated, and make the bias voltage value of the output audio of the power amplifier circuit quickly reach predetermined potential.

The invention discloses an audio amplification device, which is suitable for an audio playing system. The audio playback system has an audio source, an isolation capacitor and a load. The audio amplification device includes a power amplifier circuit and a control unit. The power amplifier circuit is coupled to the audio source to receive audio generated by the audio source. The power amplifying circuit is used to amplify the power of the audio, and output the amplified audio to the load through the isolation capacitor, the power amplifying circuit includes a bias circuit unit, and the bias circuit unit is used to generate the The positive and negative DC bias points of the power amplifier circuit. The control unit is coupled to the power amplifier circuit, and switches the operation type of the power amplifier circuit according to the bias voltage value of the output audio of the power amplifier circuit. When the audio amplifying device is started, if the bias voltage value of the output audio of the power amplifier circuit is lower than a predetermined potential, the control unit sets the operation category of the power amplifier circuit to Class A; when the audio output of the power amplifier circuit When the bias voltage value reaches the predetermined potential, the control unit sets the operation category of the power amplifier circuit to Class AB.

The present invention further discloses an audio playback system, which includes an audio source, an isolation capacitor, a load and an audio amplification device. The audio source is used to generate an audio. The load is coupled to the isolation capacitor. The audio amplification device includes a power amplifier circuit and a control unit. The power amplifier circuit is coupled to the audio source to receive the audio. The power amplifying circuit is used to amplify the power of the audio, and output the amplified audio to the load through the isolation capacitor, the power amplifying circuit includes a bias circuit unit, and the bias circuit unit is used to generate the The positive and negative DC bias points of the power amplifier circuit. The control unit is coupled to the power amplifier circuit, and switches the operation type of the power amplifier circuit according to the bias voltage value of the output audio of the power amplifier circuit. When the audio amplifying device is started, if the bias voltage value of the output audio of the power amplifier circuit is lower than a predetermined potential, the control unit sets the operation category of the power amplifier circuit to Class A; when the audio output of the power amplifier circuit When the bias voltage value reaches the predetermined potential, the control unit sets the operation category of the power amplifier circuit to Class AB.

The present invention also discloses a method for preventing popping sound in an audio amplifier device, which is suitable for an audio amplifier device. The audio amplifier device has a power amplifier circuit, wherein the power amplifier circuit is used to input and amplify an audio signal. The steps of the method are as follows: , start the power amplifier circuit, and set the operation category of the power amplifier circuit to Class A. A slow-rising current source is provided to control the output current of the power amplifier circuit to gradually rise to a constant current when the power amplifier circuit is started. Secondly, it is judged whether the bias voltage value of the output terminal of the power amplifier circuit reaches a predetermined potential. Finally, if the bias voltage at the output terminal of the power amplifier circuit reaches the predetermined potential, the operation class of the power amplifier circuit is switched to class AB to amplify the power of the audio.

By the above technical characteristics, when it can be learned that the beneficial effects of the present invention are as follows:

The audio amplifying device disclosed in the present invention and its method for preventing popping sound are based on controlling the operation type of the power amplifier circuit, so as to prevent the generation of popping sound, and at the same time make the bias voltage value of the output audio of the power amplifier circuit rise rapidly to a predetermined potential to enter normal amplification audio power work. Moreover, the audio amplifier device of the present invention further provides a slow-rising current source to control its output current, so as to further suppress the factors that may cause the popping phenomenon. In addition, the discharge unit can further prevent popping sound during the closing stage of the audio amplifier device. Compared with the disadvantages of the prior art audio amplification device such as external bypass capacitors and long voltage rise time, the present invention provides a reliable and efficient improvement solution in different structural forms.

The above overview, the following detailed description and accompanying drawings are all for further explaining the ways, means and effects of the present invention to achieve the intended purpose. Other purposes and advantages of the present invention will be described in the subsequent description and accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of the system architecture of a typical audio playback system;

2A and FIG. 2B are voltage schematic diagrams of the second audio and the AC-coupled audio in FIG. 1;

FIG. 3 is a schematic structural diagram of an audio playback system with a pop-sound prevention function in the prior art;

FIG. 4 is a schematic structural diagram of an audio amplification device and an audio playback system disclosed in the present invention;

Fig. 5 is a circuit diagram of an audio amplification device and an audio playback system disclosed in the present invention;

Fig. 6 is the circuit diagram of the ramp-up current source of the present invention;

FIG. 7 is a flow chart of the steps of the method for preventing popping of the audio amplification device disclosed in the present invention; and

FIG. 8 is a voltage schematic diagram of the output terminal voltage and the load voltage of the audio amplifying device in FIG. 5 .

Explanation of symbols in the figure

1, 2, 3: Audio playback system

10, 20, 30: audio amplification device

11, 21, 31: audio source

12, 22, 32: load

14: First Audio

15: Second audio

16: AC coupled audio

300: Power Amplifier Circuit

302: Control unit

304: Static current control unit

305: Bias circuit unit

306: ramp up current source

307: Comparison unit

308: discharge unit

AMP1, AMP10: Amplifiers

C ₁ , C ₅ , C _AC1 , C _AC2 , C _AC3 , C _BYPASS : capacitance

R ₁ , R ₂ , R ₃ , R ₅ : Resistance

Q _P1 , Q _P31 , Q _P32 Q _N1 , Q _N2 , Q _N31 , Q _N51 , Q _N52 , Q _N53 , Q _N54 , Q _N55 :

transistor

SW1, SW2: toggle switch

I _S : current source

CTRL: control signal

Detailed ways

First, please refer to FIG. 4 , which is a schematic structural diagram of an audio amplification device and an audio playback system disclosed in the present invention. As shown in FIG. 4 , an audio playback system 3 has an audio source 31 , an audio amplification device 30 , an isolation capacitor C _AC3 and a load 32 . The audio amplifying device 30 is set in the audio playing system 3 and has a power amplifier circuit 300 and a control unit 302 .

The power amplifier circuit 300 is coupled to the audio source 31 for receiving audio generated by the audio source 31 and amplifying the power of the audio. The audio amplified by the power amplifier circuit 300 is output to the load 32 for playing after the DC bias voltage is filtered by the isolation capacitor C _AC3 . The control unit 302 is coupled to the power amplifier circuit 300 , and the control unit 302 switches the operation type of the power amplifier circuit 300 according to the bias voltage value of the output audio of the power amplifier circuit 300 . In the start-up stage of the audio amplifier 30, when the bias voltage value of the output audio of the power amplifier circuit 300 is lower than a predetermined potential, the control unit 302 sets the operation category of the power amplifier circuit 300 to Class A; when the power amplifier circuit 300 outputs audio When the bias voltage value of the power amplifier circuit 300 is higher than a predetermined potential, the control unit 302 sets the operation category of the power amplifier circuit 300 as the AB category. Moreover, the predetermined potential is the common-mode voltage V _cm of the power amplifier circuit 300 .

Please refer to FIG. 5 , which is a circuit diagram of the audio amplification device 30 and the audio playback system 3 in FIG. As shown in FIG. 5 , the power amplifier circuit 300 has an input stage amplifier AMP1 , a PMOS transistor Q _P1 , and an NMOS transistor Q _N1 . The input terminal of the input stage amplifier AMP1 is used to connect to the audio source 31, and the voltages PB, NB are used as its positive and negative DC bias points. The power amplifier circuit 300 has a bias circuit unit 305, which shows the generation circuit of the above-mentioned positive and negative DC bias points PB, NB. Moreover, the power amplifier circuit 300 further includes a quiescent current controller 304 for providing a DC bias voltage of the output signal of the power amplifier circuit 300 . Moreover, the circuit structure of the quiescent current control unit 304 is existing, and will not be repeated here.

In Fig. 5, the control unit 302 includes a comparison unit 307 and two switchover switches SW1, SW2, the switchover switches SW1, SW2 respectively control the connection state of the gate terminals of the transistors _QP1 , _QN1 , to switch the operation category of the power amplifier circuit 300 . The comparison unit 307 is used to compare the potential of the gate terminal NOB of the terminal transistor Q _N1 with the potential of the bias point NB of the power amplifier circuit 300 to output a control signal CTRL, which can control the switch SW1, the gate of Q _P1 The terminal SA is connected to the DC bias point of the power amplifier circuit 300, and the terminal SB is connected to the output terminal of the input stage amplifier AMP1. The comparison unit 307 may include a comparator circuit to realize the above-mentioned potential comparison system. Moreover, the audio amplifying device 30 further includes a discharge unit 308 coupled to the output end of the power amplifier circuit 300, and the transistor _QN2 of the discharging unit 308 is only turned on when the audio amplifying device 30 is turned off.

Here, the operation system for preventing popping sound generation of the audio amplification device 30 in the startup and shutdown phases will be described in detail through the circuit structure of FIG. 5 .

First, in the opening stage of the audio amplifier 30, the operating system for preventing popping sounds includes the following two steps:

The first step: when the power amplifier circuit 300 starts, the switching switch SW1 connects the gate of the transistor Q _P1 to the terminal SA, and at the same time, the switching switch SW2 connects the gate of the transistor Q _N1 to the terminal SN, so that the power amplifier circuit 300 operates In class A, charge the blocking capacitor C _AC3 with a constant current; and

Second step: when the potential of transistor Q _N1 gate terminal NOB is higher than the bias point NB potential of the power amplifier circuit 300, it means that the power amplifier circuit 300 has reached the predetermined potential required by the design (that is, the common voltage of the power amplifier circuit 300 mode voltage V _cm ). At this time, the comparing unit 307 can control the switching switch SW1 to switch the gate of the transistor Q _P1 from the terminal SA to the terminal SB, so that the power amplifier circuit 300 operates in class AB for normal amplifying audio power.

In addition, the present inventor considers that when the power amplifier circuit 300 is operated in Class A, if a constant current is supplied instantaneously to charge the isolation capacitor C _AC3 , the voltage V _load will still cause a slight potential jump, thereby causing the load 32 to have the possibility of popping sex. Therefore, a slow ramp-up current source (Slow ramp-up current source) 306 is provided in the bias circuit unit 305, so that the bias voltage value V _{out of} the output audio of the power amplifier circuit 300 rises slowly after starting up, so as to suppress the possibility of popping sound factor.

Please refer to FIG. 6 , which is a circuit example of the ramp-up current source 306 disclosed in the present invention. As shown in FIG. 6, the slow-rising current source 306 is a current mirror circuit (Current mirror), which controls the potential _V1 of the drain to rise slowly through the resistor R5 and the capacitor C5 connected to the gate of the transistor _QN52 , Furthermore, the gate-source voltage V _gs of the transistor Q _N51 is controlled. After starting up, the output value of the mirror current I _out is gradually increased by controlling the charging time of the resistor R5 and the capacitor C5, thereby controlling the positive and negative bias point voltages of the bias circuit unit 305 to rise slowly, and the output of the power amplifier circuit 300 The current is gradually increased from zero to a certain current. We can control the current rise time here through the firmware to optimize it.

Secondly, in the closing stage of the audio amplifier 30, the operating system of the audio amplifier 30 to prevent popping is as follows:

When the power amplifier circuit 300 is turned off, the switches SW1 and SW2 respectively connect the gates of the transistors Q _P1 and Q _N2 to the terminal PD to turn off the transistors Q _P1 and Q _N2 . In order to prevent the potential of the voltage V _out from dropping suddenly, causing a surge in the voltage V _load of the load 32 and causing popping sound, at this time, the audio amplifier 30 turns on the transistor Q _N2 to make the resistor R2 and the isolation capacitor C _AC3 form a discharge circuit. The voltage value V _out of the output terminal of the audio amplifier 30 is gradually reduced to prevent the load 32 from producing popping sound during the shutdown phase of the audio amplifier 30 .

Please refer to FIG. 7 , which is a flow chart of the steps of the method for preventing popping sound of the audio amplification device disclosed in the present invention. For the relevant system architecture, please refer to Figure 5 and Figure 6 at the same time. As shown in Figure 7, this method includes the following steps:

First, start the power amplifier circuit 300, and the control unit 302 sets the operation category of the power amplifier circuit 300 to Class A (step S700);

Next, the control unit 302 judges whether the bias voltage V _out of the output terminal of the power amplifier circuit 300 reaches a predetermined potential (step S702); and

Finally, if the voltage V _out of the output signal of the power amplifier circuit 300 reaches a predetermined level, the control unit 302 switches the operation class of the power amplifier circuit 300 to class AB to amplify the power of the audio (step S704 ).

The audio amplification device 30 further includes a discharge unit 308 coupled to the output end of the power amplifier circuit 300 . The above method further includes a step of activating the discharge unit 308 if the power amplifier circuit 300 is turned off.

The step S700 of the method for preventing popping sound of the present invention further includes a step of providing a ramp-up current source 306 to control the output current of the power amplifier circuit 300 to gradually rise to a constant current when the power amplifier circuit 300 starts up.

Finally, please refer to FIG. 8 , which is a voltage schematic diagram of the output terminal voltage V _out and the load 32 voltage V _load of the audio playback system 3 in FIG. 5 . As shown in FIG. 8 , the power amplifier circuit 300 is turned on during the period t ₀ -t ₃ , and the power amplifier circuit 300 is turned off during the period t ₃ -t ₄ .

When the _time is between t ₀ and t ₂ , the power amplifier circuit 300 operates in class A, wherein the ramp-up current source 306 is used to control the power amplifier circuit 300 in the time between t ₀ and t 1 so that the output current increases slowly until the time is t ₁ When a certain current is reached. When the time is between t ₁ and t ₂ , the power amplifier circuit 300 operates in class A. At this time, the voltage V _load rises linearly, and the power amplifier circuit 300 charges the isolation capacitor C _AC3 with a constant current. When the time is between t ₂ and t ₃ , the power amplifier circuit 300 operates in class AB, and the voltage V _{load of the load} 32 converges. When the power amplifier circuit 300 operates in class AB, it can amplify audio power normally, and the voltage V _load of the load 32 gradually converges to zero potential. Finally, when the time is between t ₃ -t ₄ , the audio amplification device 30 is in the off stage, and the output terminal voltage V _out drops slowly through the discharge circuit formed by the resistor R2.

The above are only detailed descriptions and drawings of specific embodiments of the present invention, and are not intended to limit the present invention. All scopes of the present invention should be based on the scope of the patent application. Within the field of the present invention, easily conceivable changes or modifications can all be included in the patent scope defined by the present invention.

Claims (19)

1. a message amplifying unit is characterized in that, is applicable to a message Play System, and this message Play System has a message source, an isolated electric capacity and a load, and this message amplifying unit comprises:

One power amplifier circuit, be coupled to this message source, to receive the message that this message source is produced, this power amplification circuit is in order to amplify the power of this message, and by completely cutting off electric capacity, export this message that is exaggerated power to this load, this power amplification circuit comprises a bias circuit unit, and this bias circuit unit is in order to produce the positive and negative Dc bias point of this power amplifier circuit; And

One control unit is coupled to this power amplifier circuit, and this control unit switches the class of operation of this power amplifier circuit according to the bias value of this power amplifier circuit output message;

Wherein when this message amplifying unit starts, when if the bias value of this power amplifier circuit output message is lower than a predetermined potential, this control unit is set at category-A with the class of operation of this power amplifier circuit, when the bias value of this power amplifier circuit output message reached this predetermined potential, this control unit then was set at the AB class with the class of operation of this power amplifier circuit.

2. message amplifying unit as claimed in claim 1 is characterized in that, this power amplification circuit comprises an input stage amplifier, a PMOS transistor and a nmos pass transistor, and this input stage amplifier is coupled to this message source, to import this message.

3. message amplifying unit as claimed in claim 2, it is characterized in that, when this power amplification circuit started, the transistorized gate terminal of this PMOS was accepted the control of this control unit, with the output that is coupled to this input stage amplifier or the positively biased pressure point of this power amplifier circuit.

4. message amplifying unit as claimed in claim 3 is characterized in that, this control unit comprises:

One comparing unit is according to the comparison of the gate terminal potential value of the negative bias pressure point potential value of this power amplification circuit and this nmos pass transistor, to export a controlling signal; And

One switches switch, according to this controlling signal, controls the transistorized gate terminal of this PMOS and is coupled to the output of this input stage amplifier or the positively biased pressure point of this power amplifier circuit.

5. message amplifying unit as claimed in claim 2 is characterized in that, when this power amplification circuit started, the gate terminal of this nmos pass transistor was accepted the control of this control unit, to be coupled to the output of this input stage amplifier.

6. message amplifying unit as claimed in claim 1 is characterized in that, this bias circuit unit comprises a slow current source that rises.

7. message amplifying unit as claimed in claim 6 is characterized in that, this is slow, and to rise current source be a current mirroring circuit.

8. message amplifying unit as claimed in claim 6 is characterized in that, this is slow to rise current source and comprise resistance and an electric capacity, and this resistance and this electric capacity delay the rise time of the output current that rises current source in order to determine this.

9. message amplifying unit as claimed in claim 1 is characterized in that, more comprises a discharge cell, and this discharge cell is coupled to the output of this power amplification circuit.

10. a message Play System is characterized in that, comprising:

One message source is in order to produce a message;

One isolated electric capacity;

One load is coupled to this isolated electric capacity; And

One message amplifying unit comprises:

One power amplifier circuit, be coupled to this message source, to receive the message that this message source is produced, this power amplification circuit is in order to amplify the power of this message, and by completely cutting off electric capacity, export this message that is exaggerated power to this load, this power amplification circuit comprises a bias circuit unit, and this bias circuit unit is in order to produce the positive and negative Dc bias point of this power amplifier circuit; And

One control unit is coupled to this power amplifier circuit, and this control unit switches the class of operation of this power amplifier circuit according to the bias value of this power amplifier circuit output message;

Wherein when this message amplifying unit starts, when if the bias value of this power amplifier circuit output message is lower than a predetermined potential, this control unit is set at category-A with the class of operation of this power amplifier circuit, when the bias value of this power amplifier circuit output message reached this predetermined potential, this control unit then was set at the AB class with the class of operation of this power amplifier circuit.

11. message Play System as claimed in claim 10 is characterized in that, this power amplification circuit comprises an input stage amplifier, a PMOS transistor and a nmos pass transistor, and this input stage amplifier is coupled to this message source.

12. message Play System as claimed in claim 11, it is characterized in that, when this power amplification circuit started, the transistorized gate terminal of this PMOS was accepted the control of this control unit, with the output that is coupled to this input stage amplifier or the positively biased pressure point of this power amplifier circuit.

13. message Play System as claimed in claim 12 is characterized in that, this control unit comprises:

One comparing unit is according to the comparison of the gate terminal potential value of the negative bias pressure point potential value of this power amplification circuit and this nmos pass transistor, to export a controlling signal; And

One switches switch, according to this controlling signal, controls the transistorized gate terminal of this PMOS and is coupled to the output of this input stage amplifier or the positively biased pressure point of this power amplifier circuit.

14. message Play System as claimed in claim 11 is characterized in that, when this power amplification circuit started, the gate terminal of this nmos pass transistor was accepted the control of this control unit, to be coupled to the output of this input stage amplifier.

15. message Play System as claimed in claim 10 is characterized in that, this bias circuit unit comprises a slow current source that rises.

16. message Play System as claimed in claim 15, it is characterized in that, should slow rise current source is an electric current claim the 17 described message Play Systems, it is characterized in that this slow rise current source and comprise resistance and an electric capacity, this resistance and this electric capacity delay the rise time of the output current that rises current source in order to determine this.

17. message Play System as claimed in claim 10 is characterized in that this message amplifying unit more comprises a discharge cell, this discharge cell is coupled to the output of this power amplification circuit.

18. a message amplifying unit prevents the method for sonic boom, is applicable to a message amplifying unit, this message amplifying unit has a power amplification circuit, and wherein this power amplification circuit is characterized in that in order to import and to amplify a message, comprises the following steps:

Start this power amplification circuit, and the class of operation of this power amplifier circuit is set at category-A;

Provide one slow to rise current source, when power amplifier circuit started, the output current of controlling this power amplifier circuit rises to gradually decided electric current;

Whether the bias value of judging this power amplifier circuit output reaches a predetermined potential; And

When if the bias value of this power amplifier circuit output reaches this predetermined potential, the class of operation of this power amplifier circuit is switched to the AB class, to amplify the power of this message.

19. method as claimed in claim 18, it is characterized in that this message amplifying unit more comprises a discharge cell, this discharge cell is coupled to the output of this power amplifier circuit, this method more comprises if this power amplifier circuit is closed, then starts the step of this discharge cell.

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