Automatic gain control circuit, audio playing device and audio and video playing device

Abstract

The utility model discloses an automatic gain control circuit, audio playing equipment and audio and video playing equipment. The automatic gain control circuit comprises an amplification unit and a detection switch unit, the positive input end of the amplification unit is connected with an analog signal, and the output end is connected with the input end of the detection switch unit and a load; the output end of the detection switch unit is connected with the negative input end of the amplification unit; the detection switch unit is used for detecting an analog signal value of the output end of the amplification unit, and when a voltage value of an analog signal is greater than a preset threshold value, a path between the output end of the amplification unit and the negative input end of the amplification unit is conducted; the amplification unit is used for amplifying the difference between the positive input end and the negative input end and outputting the amplified difference to a load so as to reduce the output gain. When the voltage value of the output end of the amplification unit is larger than the preset threshold value, the circuit between the output end and the negative input end of the amplification unit is switched on through the detection switch unit, negative feedback adjustment is achieved, the output voltage value of the amplification unit is reduced, and the saturation distortion problem is solved.

Description

TECHNICAL FIELD

[0001] The utility model relates to audio signal processing technical field, especially relate to a kind of automatic gain control circuit, audio playing equipment and audio-video playing equipment. BACKGROUND

[0002] When audio is played, analog audio signal needs to be processed to adjust the volume of audio.

[0003] When small signal input, the conventional analog amplification circuit needs to increase the amplification multiple of the volume knob to meet the hearing requirement, when setting in larger volume output, a big signal comes suddenly, at this time, power amplifier may appear saturation distortion, even super power output leads to power amplifier damage. UTILITY MODEL CONTENTS

[0004] The utility model discloses a kind of automatic gain control circuits, to solve the saturation distortion problem caused by power amplifier output too large.

[0005] To achieve the above object, the automatic gain control circuit provided by the utility model, the automatic gain control circuit includes:

[0006] Amplification unit and detection switch unit;

[0007] The positive input end of amplification unit is used to access analog signal, and the input end of detection switch unit and load are connected to the output end;The output end of detection switch unit is connected to the negative input end of amplification unit;

[0008] Detection switch unit is used to detect the analog signal value of amplification unit output end, when the voltage value of the analog signal is greater than preset threshold, the passage between amplification unit output end and amplification unit negative input end is turned on;

[0009] The amplification unit is used to amplify the difference between the positive input end and the negative input end and then output to load, to reduce output gain.

[0010] The utility model also proposes a kind of audio playing equipment, and the audio playing equipment includes the automatic gain control circuit.

[0011] The utility model also proposes a kind of audio-video playing equipment, and the audio-video playing equipment includes the automatic gain control circuit.

[0012] The utility model discloses an automatic gain control circuit, the automatic gain control circuit includes: amplification unit and detection switch unit, the positive input end of amplification unit is used to access analog signal, and the input end of detection switch unit and load are connected to the output end, the output end of detection switch unit connects the negative input end of amplification unit, and detection switch unit is used to detect the analog signal value of amplification unit output end, when the voltage value of analog signal is greater than the preset threshold value, the passage between amplification unit output end and amplification unit negative input end is conducted, the amplification unit is used to amplify the difference between positive input end and negative input end and then output to load to reduce output gain, the utility model discloses when the voltage value of amplification unit output end is greater than the preset threshold value, the passage between amplification unit output end and negative input end is conducted through detection switch unit, realizes negative feedback regulation, reduces amplification unit output voltage value, and overcomes the saturation distortion problem. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical scheme in the embodiment of the utility model or prior art, the following will briefly introduce the drawing needed to be used in the embodiment or prior art description, and obviously, the drawing in the following description is only some embodiments of the utility model, and for those skilled in the art, other drawings can also be obtained according to the structure shown in these drawings without creating labor.

[0014] Figure 1 It is the structural schematic diagram of an embodiment of the automatic gain control circuit of the utility model,

[0015] Figure 2 It is the structural schematic diagram of another embodiment of the automatic gain control circuit of the utility model,

[0016] Figure 3 It is the structural schematic diagram of still another embodiment of the automatic gain control circuit of the utility model,

[0017] Figure 4 It is the structural schematic diagram of still another embodiment of the automatic gain control circuit of the utility model,

[0018] Figure 5 It is the structural schematic diagram of still another embodiment of the automatic gain control circuit of the utility model.

[0019] Explanation of the attached drawings:

[0020]

[0021] The realization, functional characteristics and advantages of the utility model will be further explained by combining with the embodiment and referring to the drawings. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only part of the embodiments of the present utility model, rather than all the embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present utility model.

[0023] It should be noted that all the directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present utility model are only used to explain the relative positional relationship, movement condition, etc. between components in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directional indications will also change accordingly.

[0024] In the present utility model, unless otherwise explicitly specified and limited, the terms "connection", "fixation" and the like should be understood in a broad sense, for example, "fixation" can be fixed connection, or detachable connection, or integral; can be mechanical connection, or electrical connection; can be direct connection, or indirect connection through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meanings of the above terms in the present utility model can be understood according to the specific circumstances.

[0025] In addition, in the present utility model, the description such as "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection required by the present utility model.

[0026] The utility model provides a kind of automatic gain control circuit, and the automatic gain control circuit includes:

[0027] Amplification unit and detection switch unit 10;

[0028] The positive input end of the amplification unit is used to input analog signal, and the output end is connected to the input end of the detection switch unit 10 and the load;The output end of the detection switch unit 10 is connected to the negative input end of the amplification unit;

[0029] Detection switch unit 10 is used to sample the analog signal value of the output end of the amplification unit, and when the voltage value of the analog signal is greater than the preset threshold, the path between the output end of the amplification unit and the negative input end of the amplification unit is turned on.

[0030] The amplification unit is used to amplify the voltage difference between the positive input terminal and the negative input terminal and output it to the load to reduce the output gain.

[0031] It should be noted that the automatic gain control circuit proposed in this solution can be applied to audio signal processing. However, it is worth noting that this solution is not limited to the audio field; it can also be applied to scenarios where power amplifiers are used to amplify analog signals, such as wireless communication and ultrasound imaging. When the automatic gain control circuit is applied to audio signal processing, the analog signal can be an audio analog signal.

[0032] The amplification unit is used to amplify the input signal and output it. The amplification unit may include an operational amplifier. The amplification unit has a fixed voltage gain factor. When a small signal is input to the input of the amplification unit, the amplification unit outputs a voltage signal amplified by the voltage gain factor. However, if a large signal is input to the input of the amplification unit, the product of the voltage value of the large signal and the voltage gain factor may exceed the output voltage range of the amplification unit. At this time, saturation distortion will occur, and the amplification unit may even over-power output, causing damage to the power amplifier.

[0033] To avoid the aforementioned saturation distortion, this solution uses the detection switch unit 10 to sample the amplified analog signal voltage value at the output of the amplification unit; it compares this voltage value with a preset threshold, and when the analog signal voltage value is greater than the preset threshold, the path between the output of the amplification unit and the negative input of the amplification unit is opened. It should be noted that in this solution, the amplification unit has a voltage gain, which is determined by the internal circuitry of the amplification unit. The amplification unit may include an amplifier or an amplification circuit.

[0034] To further clarify, when the analog signal value at the output of the amplification unit is less than or equal to a preset threshold, the detection switch unit 10 disconnects the path between the output of the amplification unit and the negative input of the amplification unit. It is easy to understand that at this time, the amplification unit amplifies the analog signal connected to its positive input and outputs the amplified analog signal. The detection switch unit 10 detects the voltage value of the amplified analog signal. If the voltage value of the amplified analog signal is greater than the preset threshold, the detection switch unit 10 reconnects the path between the output of the amplification unit and the negative input of the amplification unit, thereby introducing the voltage at the output of the amplification unit to the negative input of the amplification unit, forming negative feedback. The amplification unit amplifies the voltage difference between the positive and negative inputs and outputs it to the load. The negative feedback reduces the output gain of the analog signal after passing through the amplification unit.

[0035] However, it should be noted that the area between the output terminal and the negative input terminal of the amplification unit may contain not only the detection switch unit 10, but also other electrical / electronic components, such as resistors and capacitors. The detection switch unit 10 may contain more than just switching devices, thereby transforming the voltage of the analog signal at the output terminal of the amplification unit before outputting it back to the amplification unit, thus adjusting the voltage gain of the amplification unit and reducing the output gain of the analog signal.

[0036] Additionally, it should be noted that the purpose of this application is to solve the problem of saturation distortion caused by excessive power amplifier output. Saturation distortion occurs when the amplifier output reaches its maximum positive voltage, at which point the positive half of the signal is clipped. Specifically, when the input signal is too large, causing the transistor to enter the saturation region, the amplifier cannot provide a larger voltage at the output, and the amplitude of the output signal reaches its maximum value and cannot increase further, at which point saturation distortion occurs. The preset threshold can be determined by the researchers themselves; it is easy to understand that the preset threshold is less than or equal to the maximum output voltage value of the amplification unit.

[0037] Furthermore, the negative input terminal of the amplification unit is not only connected to the output terminal of the detection switch unit 10, but can also be connected to the circuit components inside the amplification unit.

[0038] This invention discloses an automatic gain control circuit, comprising an amplification unit and a detection switch unit 10. The positive input terminal of the amplification unit is used to receive an analog signal, and its output terminal is connected to the input terminal of the detection switch unit 10 and a load. The output terminal of the detection switch unit 10 is connected to the negative input terminal of the amplification unit. The detection switch unit 10 detects the analog signal value at the output terminal of the amplification unit. When the voltage value of the analog signal is greater than a preset threshold, it opens the path between the output terminal and the negative input terminal of the amplification unit. The amplification unit amplifies the difference between the positive and negative input terminals and outputs it to the load to reduce the output gain. This invention achieves negative feedback regulation by opening the path between the output terminal and the negative input terminal of the amplification unit when the voltage value at the output terminal of the amplification unit is greater than a preset threshold, thereby reducing the output voltage value of the amplification unit and overcoming saturation distortion.

[0039] In one embodiment, the amplification unit includes:

[0040] First operational amplifier U1, first resistor R1, and second resistor R2;

[0041] One end of the first resistor R1 is connected to an analog signal, and the other end is connected to the positive input terminal of the first operational amplifier U1; one end of the second resistor R2 is connected to the output terminal of the first operational amplifier U1, and the other end is connected to the negative input terminal of the first operational amplifier U1. The output terminal of the first operational amplifier U1 is connected to a load.

[0042] like Figure 1 As shown, the amplification unit uses a first operational amplifier U1 to amplify the voltage; the analog signal reaches the positive input terminal of the first operational amplifier U1 via the first resistor R1, and one end of the second resistor R2 is connected to the output terminal of the first operational amplifier U1, and the other end is connected to the negative input terminal of the first operational amplifier U1. The first operational amplifier U1, the first resistor R1, and the second resistor R2 constitute a positive-inverting negative feedback amplifier circuit with a voltage gain of [value missing]. Where A is the voltage gain of the positive feedback amplifier circuit. The value of the first resistor R1, This is the value of the second resistor R2.

[0043] It should be noted that the first operational amplifier U1 can be powered by either a dual power supply or a single power supply. This solution does not impose any restrictions.

[0044] Reference Figure 2 In this embodiment, the input terminal of the detection switch unit 10 is connected to the output terminal of the first operational amplifier U1, and the output terminal of the detection switch unit 10 is connected to the negative input terminal of the first operational amplifier U1. The detection switch unit 10 and the second resistor R2 are connected in parallel. It should be noted that the overall impedance after parallel connection is less than the impedance value of any single device in the parallel structure. Therefore, after the detection switch unit 10 turns on the output terminal and the negative input terminal of the first operational amplifier U1, the equivalent impedance between the output terminal and the negative input terminal decreases; this can be equivalent to the resistance value of the second resistor R2 decreasing, as calculated by the formula... It can be seen that the voltage gain of the positive feedback amplifier circuit decreases, thereby reducing the analog signal voltage value output by the first operational amplifier U1 to the load, thus overcoming the saturation distortion problem.

[0045] In one embodiment, the detection switch unit 10 includes: a voltage divider detection circuit 110 and a voltage comparison circuit 120;

[0046] The input terminal of the voltage divider detection circuit 110 is connected to the output terminal of the first operational amplifier U1, and the output terminal is connected to the input terminal of the voltage comparison circuit 120. The voltage divider detection circuit 110 is used to sample the voltage value at the output terminal of the first operational amplifier U1, divide the voltage value, and output it to the voltage comparison circuit 120.

[0047] The output terminal of the voltage comparison circuit is connected to the negative input terminal of the first operational amplifier U1; the voltage comparison circuit 120 is used to compare the voltage value after voltage division with a voltage threshold, and when the voltage value after voltage division is greater than the voltage threshold, the path between the output terminal of the voltage divider detection circuit 110 and the negative input terminal of the first operational amplifier U1 is opened.

[0048] It should be noted that the voltage value of the analog signal output from the amplification unit may be too large, which is not conducive to voltage comparison. In this embodiment, the voltage divider detection circuit 110 uses the voltage value from the output of the first operational amplifier U1, divides the voltage value, and then outputs it to the voltage comparison circuit 120 for comparison. The voltage comparison circuit 120 compares the divided voltage with a voltage threshold and, based on the comparison result, turns on / off the path between the output and negative input of the first operational amplifier U1. Specifically, it turns on the path between the output of the voltage divider detection circuit 110 and the negative input of the first operational amplifier U1. It is easy to understand that after the path between the output and negative input of the first operational amplifier U1 is turned on, the voltage comparison circuit 120 outputs the voltage value divided by the voltage divider detection circuit 110 to the negative input of the first operational amplifier U1.

[0049] Therefore, the voltage gain of the voltage divider detection circuit 110 will determine the voltage value at the negative input terminal of the first operational amplifier U1, thereby changing the voltage value of the analog signal output from the first operational amplifier U1 to the load. The voltage divider detection circuit 110 can be a resistor voltage divider circuit.

[0050] The voltage comparison circuit 120 is used to compare the divided voltage value with a voltage threshold. When the divided voltage value is greater than the voltage threshold, the path between the output terminal of the voltage divider detection circuit 110 and the negative input terminal of the first operational amplifier U1 is opened. When the divided voltage value is greater than or equal to the voltage threshold, the voltage comparison circuit 120 closes the path between the output terminal of the voltage divider detection circuit 110 and the negative input terminal of the first operational amplifier U1. The voltage comparison circuit 120 may include a switching device, and the voltage threshold can be determined by the researchers. In particular, the voltage threshold can be the turn-on voltage value of the switching device, and the researchers can select the corresponding switching device after determining the voltage threshold.

[0051] In one example, the voltage divider detection circuit 110 includes: a third resistor R3 and a fourth resistor R4;

[0052] like Figure 3As shown, the third resistor R3 and the fourth resistor R4 are connected in series between the output terminal of the first operational amplifier U1 and ground, and one end of the third resistor R3 and the fourth resistor R4 connected to each other is connected to the input terminal of the voltage comparator circuit 120.

[0053] It is easy to understand that the voltage divider circuit composed of the third resistor R3 and the fourth resistor R4 divides the voltage at the output terminal of the first operational amplifier U1 and outputs it to the voltage comparator circuit 120. The voltage divider detection circuit 110 also includes a fifth capacitor C5. The fifth capacitor C5 is connected in parallel with the grounded resistor in the voltage divider detection circuit 110.

[0054] The voltage comparison circuit 120 includes: a first diode D1 and a second diode D2;

[0055] The first diode D1 and the second diode D2 are connected in reverse parallel. The first end of the first diode D1 is connected to the end where the third resistor R3 and the fourth resistor R4 are connected, and the second end is connected to the negative input terminal of the first operational amplifier U1.

[0056] It is readily understood that, in this example, the voltage threshold can be the conduction voltage value of the first diode D1 and the second diode D2 connected in reverse parallel. When the voltage value output by the voltage divider detection circuit 110 is less than or equal to the voltage threshold, the diode is turned off; when the voltage value output by the voltage divider detection circuit 110 is greater than the voltage threshold, the diode is turned on.

[0057] It should be noted that the voltage value output by the voltage divider detection circuit 110 depends on the voltage value output by the first operational amplifier U1 to the load. When the voltage value of the analog signal connected to the positive input terminal of the first operational amplifier U1 is too large, the voltage value output by the voltage divider detection circuit 110 will be greater than the voltage threshold, causing the diode to conduct and opening the path between the output terminal of the voltage divider detection circuit 110 and the negative input terminal of the first operational amplifier U1. The voltage gain of the positive-inverting negative feedback amplifier circuit can be changed by adjusting the resistance values ​​of the third resistor R3 and the fourth resistor R4.

[0058] Reference Figure 4 The automatic gain control circuit further includes a first capacitor C1, a second capacitor C2, and a third capacitor C3.

[0059] The first capacitor C1 is disposed in the path between the first resistor R1 and the positive input terminal of the first operational amplifier U1; the second capacitor C2 is disposed in parallel with the second resistor R2; the first terminal of the third capacitor C3 is connected to the output terminal of the first operational amplifier U1, and the second terminal is connected to the input terminal of the voltage divider detection circuit 110.

[0060] The first capacitor C1, the second capacitor C2, and the third capacitor C3 are filter capacitors. The first capacitor C1 filters the high-frequency components of the analog signal introduced at the positive input terminal of the first operational amplifier U1. The second capacitor C2 is connected in parallel with the first operational amplifier U1 to filter the high-frequency components reaching the negative input terminal of the first operational amplifier U1 via the second resistor R2; additionally, it can perform phase compensation to improve circuit stability. The third capacitor C3 is located between the output terminal of the first operational amplifier U1 and the load to filter the high-frequency components in the analog signal output by the first operational amplifier U1.

[0061] The detection switch unit 10 further includes: a voltage follower;

[0062] The input terminal of the voltage follower is connected to the output terminal of the voltage comparator circuit 120, and the output terminal is connected to the negative input terminal of the first operational amplifier U1.

[0063] In this example, the voltage follower provides a circuit node with high input impedance and low output impedance. This means it can effectively isolate the preceding and following stages in the circuit, preventing mutual interference between them. Using a voltage follower in the circuit can reduce signal loss and distortion, acting as a buffer. The voltage follower can accurately transmit the voltage value at the output of the first voltage comparator circuit 120 to the negative input of the first operational amplifier U1, ensuring that the voltages before and after are almost equal.

[0064] In addition, voltage followers achieve impedance matching in circuits by providing high input impedance and low output impedance, thus protecting the stability of signals during transmission.

[0065] Reference Figure 5 The voltage follower includes: a second operational amplifier U2;

[0066] The positive input terminal of the second operational amplifier U2 is connected to the output terminal of the voltage comparator circuit, and the negative input terminal is connected to the output terminal of the second operational amplifier U2; the output terminal of the second operational amplifier U2 is also connected to the negative input terminal of the first operational amplifier U1.

[0067] The voltage comparison circuit 120 further includes a sixth capacitor C6. The sixth capacitor C6 is connected in series between the second terminal of the first diode D1 and the positive input terminal of the second operational amplifier U2.

[0068] The detection switch unit 10 further includes: a fifth resistor R5 and a fourth capacitor C4;

[0069] The first end of the fifth resistor R5 is connected to the output terminal of the second operational amplifier U2, and the second end is connected to the negative input terminal of the first operational amplifier U1 and the first end of the sixth capacitor C6; the second end of the fourth capacitor C4 is grounded.

[0070] It should be noted that the fourth capacitor C4 can filter the voltage output from the second operational amplifier U2. The RC circuit composed of the fifth resistor R5 and the fourth capacitor C4 can also perform phase compensation on the voltage signal output from the second operational amplifier U2.

[0071] This utility model also proposes an audio playback device, which includes the aforementioned automatic gain control circuit.

[0072] The audio playback device may include devices capable of playing audio, such as MP3 players, recorders, mobile phones, iPads, or computers.

[0073] This utility model also proposes an audio and video playback device, which includes the aforementioned automatic gain control circuit.

[0074] The audio and video playback devices may include televisions, computers, mobile phones, or other devices capable of playing audio and video.

[0075] The specific structure of the automatic gain control circuit is as described in the above embodiments. Since the audio playback device and the audio / video playback device adopt all the technical solutions of all the above embodiments, they at least have all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be repeated here. The above descriptions are only optional embodiments of this utility model and do not limit the patent scope of this utility model. All equivalent structural transformations made under the inventive concept of this utility model using the content of this utility model specification and drawings, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this utility model.

Claims

1. An automatic gain control circuit, characterized in that, The automatic gain control circuit includes: Amplification unit and detection switch unit; The positive input terminal of the amplifier unit is used to input analog signals, and the output terminal is connected to the input terminal of the detection switch unit and the load; the output terminal of the detection switch unit is connected to the negative input terminal of the amplifier unit. The detection switch unit is used to detect the analog signal value at the output of the amplifier unit. When the voltage value of the analog signal is greater than a preset threshold, the path between the output of the amplifier unit and the negative input of the amplifier unit is opened. The amplification unit is used to amplify the difference between the positive input terminal and the negative input terminal and output it to the load to reduce the output gain.

2. The automatic gain control circuit as described in claim 1, characterized in that, The amplification unit includes: First operational amplifier, first resistor, and second resistor; One end of the first resistor is connected to an analog signal, and the other end is connected to the positive input terminal of the first operational amplifier; one end of the second resistor is connected to the output terminal of the first operational amplifier, and the other end is connected to the negative input terminal of the first operational amplifier.

3. The automatic gain control circuit as described in claim 2, characterized in that, The detection switch unit includes: a voltage divider detection circuit and a voltage comparison circuit; The input terminal of the voltage divider detection circuit is connected to the output terminal of the first operational amplifier, and the output terminal is connected to the input terminal of the voltage comparator circuit. The voltage divider detection circuit is used to sample the voltage value at the output terminal of the first operational amplifier, divide the voltage value, and output it to the voltage comparator circuit. The output terminal of the voltage comparison circuit is connected to the negative input terminal of the first operational amplifier; the voltage comparison circuit is used to compare the voltage value after voltage division with a voltage threshold, and when the voltage value after voltage division is greater than the voltage threshold, the path between the output terminal of the voltage division detection circuit and the negative input terminal of the first operational amplifier is opened.

4. The automatic gain control circuit as described in claim 3, characterized in that, The voltage divider detection circuit includes: a third resistor and a fourth resistor; The third resistor and the fourth resistor are connected in series between the output terminal of the first operational amplifier and ground. The voltage comparison circuit includes: a first diode and a second diode; The first diode and the second diode are connected in reverse parallel. The first end of the first diode is connected to the end where the third resistor and the fourth resistor are connected, and the second end is connected to the negative input terminal of the first operational amplifier.

5. The automatic gain control circuit as described in any one of claims 3 to 4, characterized in that, The automatic gain control circuit further includes: a first capacitor, a second capacitor, and a third capacitor; The first capacitor is disposed in the path between the first resistor and the positive input terminal of the first operational amplifier; the second capacitor is disposed in parallel with the second resistor; the first terminal of the third capacitor is connected to the output terminal of the first operational amplifier, and the second terminal is connected to the input terminal of the voltage divider detection circuit.

6. The automatic gain control circuit as described in any one of claims 3 to 4, characterized in that, The detection switch unit further includes: a voltage follower; The input terminal of the voltage follower is connected to the output terminal of the voltage comparator circuit, and the output terminal is connected to the negative input terminal of the first operational amplifier.

7. The automatic gain control circuit as described in claim 6, characterized in that, The voltage follower includes: a second operational amplifier; The positive input terminal of the second operational amplifier is connected to the output terminal of the voltage comparator circuit, and the negative input terminal is connected to the output terminal of the second operational amplifier; the output terminal of the second operational amplifier is also connected to the negative input terminal of the first operational amplifier.

8. The automatic gain control circuit as described in claim 7, characterized in that, The detection switch unit further includes: a fifth resistor and a fourth capacitor; The first end of the fifth resistor is connected to the output terminal of the second operational amplifier, and the second end is connected to the negative input terminal of the first operational amplifier and the first end of the fourth capacitor; the second end of the fourth capacitor is grounded.

9. An audio playback device, characterized in that, The audio playback device includes the automatic gain control circuit as described in any one of claims 1 to 8.

10. An audio / video playback device, characterized in that, The audio / video playback device includes the automatic gain control circuit as described in any one of claims 1 to 8.

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