A circuit and audio system for improving the separation of each channel of an analog audio interface

Abstract

The present invention relates to a circuit and an audio system for improving the separation of each channel of an analog audio interface, wherein the circuit comprises: an audio circuit inside a headphone interface chip and an external related interface circuit; wherein the audio circuit inside the headphone interface chip comprises: an amplifier driving circuit and analog switches Rsw1-Rsw8; the reference ground of the amplifier driving circuit and the reference ground of a MICBIAS decoupling capacitor C3 are both connected to an off-chip location near the headphone interface through an analog switch; when the headphone type is determined, a connection relationship is established with an off-chip circuit by configuring the state of the on-chip analog switches Rsw1-Rsw8 according to the headphone type to achieve a correct electrical connection. The present invention can effectively improve the separation between the left and right channels of a speaker and the separation between a speaker and a microphone by optimizing the internal audio circuit of a headphone interface chip and the external related interface circuit, thereby improving sidetone and improving the quality of playback and calls.

Description

Technical Field

[0001] The present invention relates to the technical field of audio transmission, and in particular to a circuit and an audio system for improving the separation degree of each channel of an analog audio interface. Background Art

[0002] The 3.5 mm headphone jack in the prior art can be divided into two standards, OMTP and CTIA, according to the order of pin definition. The two standards have different pin definitions. The specific definitions and differences are as follows: Figure 1 As shown. With the development of electronics and integrated circuits, in order to accommodate headphones of different standards, terminal devices currently mainly use integrated single chips to identify the type of headphones and use internal semiconductor switches to achieve correct electrical connections. The on-chip structure of the existing conventional headphone adapter chip is shown in the figure below. Figure 2 As shown. The semiconductor switch integrated in the chip is not an ideal device and must have on-resistance. Therefore, for 3.5mm interface headphones and their interface circuit interface chips, the common ground path between the left and right channels of the speaker and between the speaker and the microphone is not ideal, which will inevitably lead to a certain amount of crosstalk between them. The crosstalk between the left and right channels is manifested in the stereo headphone output system. It is expected that the a channel has output but the b channel has no output. In fact, the sound that should be emitted from the a channel can also be heard on the b channel. The crosstalk between the speaker and the microphone is manifested in a scenario where a person using a headphone interface chip with a crosstalk problem is talking to someone on the phone. On the one hand, the other party can hear what he says because it is unnecessary and can be called noise. This noise mixed with the voice of the other party will also reduce the clarity of the call, and in serious cases, it will interfere with the normal call.

[0003] Separation is an indicator of the degree of crosstalk suppression of the audio input and output system. For the headphone adapter chip system, separation is an important parameter to measure its audio quality, so it is of great significance to improve this indicator in chip design. Summary of the invention

[0004] In view of this, an object of the present invention is to overcome the deficiencies of the prior art and provide a circuit and an audio system for improving the separation of each channel of an analog audio interface.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a circuit for improving the separation of each channel of an analog audio interface, comprising:

[0006] The internal audio circuit of the headphone interface chip and the external related interface circuit;

[0007] The internal audio circuit of the headphone interface chip includes: a DAC module, a power amplifier driving circuit, an analog switch group, a MICBIAS generating unit, a gain amplifier and an ADC module;

[0008] The output end of the DAC module is connected to the input end of the power amplifier driving circuit through the gain resistors Rg1 and Rg2; the output end of the power amplifier driving circuit is connected to the corresponding interface of the speaker on the earphone through the resistor set Rb1 or Rb2; the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 are both connected to the off-chip near the earphone interface through the analog switch group; the input end of the ADC module is connected to the microphone and the corresponding interface on the earphone through the gain amplifier;

[0009] The analog switch group includes: analog switches Rsw1 to Rsw8;

[0010] After the type of earphone is determined, a connection relationship is established with an off-chip circuit by configuring the states of the on-chip analog switches Rsw1 to Rsw8 according to the type of earphone to achieve a correct electrical connection.

[0011] Optionally, establishing a connection relationship with an off-chip circuit by configuring states of on-chip analog switches Rsw1 to Rsw8 according to the type of earphone includes:

[0012] When the earphone type is a 4-band earphone,

[0013] The analog switches Rsw1 and Rsw6 are closed to select whether Sleeve or Ring2 is connected to MICBIAS via Rbias;

[0014] Close Rsw2 and Rsw5 to connect Sleeve or Ring2 to GND.

[0015] At the same time, one of the two groups of analog switches Rsw3 / Rsw4 and Rsw7 / Rsw8 is selected to be closed and the other is opened according to the type of headphones, so as to connect the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 to the outside of the chip near the headphone interface, so as to reduce the crosstalk between the left and right channels of the speaker and the crosstalk of the speaker to the microphone.

[0016] Optionally, when the headphone type is a 4-segment CTIA type, the analog switches Rsw1, Rsw5, Rsw7 and Rsw8 are opened, and the analog switches Rsw2, Rsw3, Rsw4 and Rsw6 are closed;

[0017] When the earphone type is a 4-band OMTP type, the analog switches Rsw2, Rsw3, Rsw4 and Rsw6 are opened, and the analog switches Rsw1, Rsw5, Rsw7 and Rsw8 are closed.

[0018] Optionally, establishing a connection relationship with an off-chip circuit by configuring states of on-chip analog switches Rsw1 to Rsw8 according to the type of earphone includes:

[0019] When the earphone type is a three-band earphone, the analog switches Rsw1 and Rsw6 are opened, and the analog switches Rsw2 and Rsw5 are closed to select connecting Sleeve and Ring2 to GND at the same time, and the two groups of analog switches Rsw3 / Rsw4 and Rsw7 / Rsw8 are closed.

[0020] Optionally, when routing on the PCB, the impedance of the reference ground of the power amplifier driving circuit is the same as the impedance of the headphone GND routing, and the two routings finally converge at a corresponding solder point of the headphone socket;

[0021] In the PCB routing, keep the two groups of signal lines Ring2_Ref and Ring2, Sleeve_Ref and Sleeve of equal length and width.

[0022] Optionally, depending on the type of the 4-segment earphone, the reference ground of the MICBIAS decoupling capacitor C3 and the reference ground of the MICBIAS generating unit are coupled back to the ground path of the earphone through the analog switch Rsw4 or Rsw8 via Ring2_Ref or Sleeve_Ref.

[0023] Optionally, when the type of the 4-segment earphone is CTIA type, the Sleeve pin is used to connect the microphone of the CTIA type earphone, the Ring2 pin is used to connect the GND of the earphone, and an electrical connection is established between the solder point A corresponding to the Ring2 pin on the earphone socket and the solder point B corresponding to the Sleeve pin through the path (Rb6+Rsw6+Rbias+C3+Rsw4+Rb4).

[0024] Optionally, when the type of the 4-segment earphone is OMTP type, the Ring2 pin is used to connect the microphone of the OMTP type earphone, the Sleeve pin is used to connect the GND of the earphone, and an electrical connection is established between the solder point A corresponding to the Ring2 pin on the earphone socket and the solder point B corresponding to the Sleeve pin through the path (Rb3+Rsw1+Rbias+C3+Rsw8+Rb7).

[0025] The present invention also provides an audio system, comprising:

[0026] A circuit for improving the separation of channels of an analog audio interface as described in any of the above items.

[0027] The present invention adopts the above technical scheme, and the circuit for improving the separation of each channel of the analog audio interface includes: an audio circuit inside the headphone interface chip and an external related interface circuit; wherein the audio circuit inside the headphone interface chip includes: a DAC module, a power amplifier driving circuit, an analog switch group, a MICBIAS generating unit, a gain amplifier and an ADC module; the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 are both connected to the chip near the headphone interface through the analog switch group; the analog switch group includes: analog switches Rsw1~Rsw8; when the headphone type is determined, a connection relationship is established with the off-chip circuit by configuring the state of the on-chip analog switches Rsw1~Rsw8 according to the headphone type to achieve a correct electrical connection. The circuit described in the present invention can effectively improve the separation between the left and right channels of the speaker and the separation between the speaker and the microphone by optimizing the internal audio circuit of the headphone interface chip and the external related interface circuit, improve the side tone, and improve the playback and call quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 It is a schematic diagram of the pin definition of two different standards of headphone plugs in the prior art;

[0030] Figure 2 This is the internal structure diagram of the existing conventional headphone adapter chip;

[0031] Figure 3 It is a schematic diagram of the internal structure of a circuit for improving the separation of each channel of an analog audio interface according to the present invention;

[0032] Figure 4 It is a schematic diagram of the internal structure of the DAC left and right channel crosstalk suppression circuit of the present invention;

[0033] Figure 5 This is a structural diagram of an equivalent circuit for the internal connection of a CTIA type earphone adapter chip of the present invention;

[0034] Figure 6 This is a structural diagram of an equivalent circuit for the internal connection of an OMTP type earphone adapter chip of the present invention;

[0035] Figure 7 This is a structural diagram of an equivalent circuit of the internal connection of the adapter chip for three-segment headphones of the present invention;

[0036] Figure 8 It is a circuit structure diagram of the present invention for suppressing crosstalk between DAC output and ADC;

[0037] Fig. 9 This is a circuit structure diagram of the invention for suppressing crosstalk between the DAC output and the ADC of a CTIA type headphone adapter;

[0038] Fig.10 It is a schematic diagram of the principle of suppressing crosstalk between the DAC output and the ADC of a CTIA type headphone adapter according to the present invention;

[0039] Fig.11 This is a circuit structure diagram of the present invention for suppressing crosstalk between the DAC output and the ADC of an OMTP type headphone adapter;

[0040] Fig.12 It is a schematic diagram of the principle of suppressing crosstalk between the DAC output and the ADC of the OMTP type headphone adapter of the present invention. DETAILED DESCRIPTION

[0041] To make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other implementation methods obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention.

[0042] Figure 3 The present invention is a schematic diagram of the internal structure of a circuit for improving the separation of each channel of an analog audio interface.

[0043] like Figure 3 As shown, a circuit for improving the separation of each channel of an analog audio interface according to the present invention comprises:

[0044] The internal audio circuit of the headphone interface chip and the external related interface circuit;

[0045] The internal audio circuit of the headphone interface chip includes: a DAC module, a power amplifier driving circuit, an analog switch group, a MICBIAS generating unit, a gain amplifier and an ADC module;

[0046] The output end of the DAC module is connected to the input end of the power amplifier driving circuit through the gain resistors Rg1 and Rg2; the output end of the power amplifier driving circuit is connected to the corresponding interface of the speaker on the earphone through the resistor set Rb1 or Rb2; the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 are both connected to the off-chip near the earphone interface through the analog switch group; the input end of the ADC module is connected to the microphone and the corresponding interface on the earphone through the gain amplifier;

[0047] The analog switch group includes: analog switches Rsw1 to Rsw8;

[0048] After the type of earphone is determined, a connection relationship is established with an off-chip circuit by configuring the states of the on-chip analog switches Rsw1 to Rsw8 according to the type of earphone to achieve a correct electrical connection.

[0049] Figure 3 In the figure, Rg1 / Rg2 is the gain resistance of the power amplifier driving circuit in the chip; Rb1 / Rb2 / Rb3 / Rb4 / Rb5 / Rb6 / Rb7 represent the resistance of the chip-level on-chip routing, bonding wires, solder joints between the chip and PCB, and PCB board-level routing; Rcon1 / Rcon2 / Rcon3 / Rcon4 are the equivalent contact resistances between the 3.5mm headphone jack and the headphone plug; Rsw1~Rsw8 are the equivalent resistances of the analog switches in the chip; when the type of headphone is determined, a connection relationship is established with the off-chip circuit by configuring the states of the on-chip analog switches Rsw1~Rsw8 according to the type of headphone to achieve a correct electrical connection.

[0050] What needs to be explained about the analog switches on the chip is that

[0051] In the 4-band headphone application scenario: Rsw1 and Rsw6 are closed to select whether to connect Sleeve or Ring2 to Micbias through Rbias; Rsw2 and Rsw5 are closed to select whether to connect Sleeve or Ring2 to GND; Rsw3 / Rsw4 and Rsw7 / Rsw8 are two groups of analog switches, one of which is closed and the other is opened according to the type of headphone, so as to connect the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 to the outside of the chip near the headphone interface, so as to reduce the crosstalk between the left and right channels of the speaker and the crosstalk of the speaker to the microphone.

[0052] In the 3-band headphone application scenario: Rsw1 and Rsw6 are both disconnected; Rsw2 and Rsw5 are both closed, which is used to select to connect Sleeve and Ring2 to GND at the same time, and to close the two sets of analog switches Rsw3 / Rsw4 and Rsw7 / Rsw8 at the same time.

[0053] Specifically, the connection relationship of each analog switch is described as follows according to the headphone type:

[0054] When the headset is of 4-band CTIA type: open the analog switches Rsw1, Rsw5, Rsw7 and Rsw8, and close the analog switches Rsw2, Rsw3, Rsw4 and Rsw6;

[0055] When the headset is of 4-band OMTP type: open the analog switches Rsw2, Rsw3, Rsw4 and Rsw6, and close the analog switches Rsw1, Rsw5, Rsw7 and Rsw8;

[0056] When the earphone is of the 3-band type: open the analog switches Rsw1 and Rsw6, and close the analog switches Rsw2, Rsw3, Rsw4, Rsw5, Rsw7, and Rsw8.

[0057] The two suppression circuits are introduced below.

[0058] (1) Circuit for suppressing crosstalk between left and right channels of DAC output

[0059] With respect to the crosstalk between the left and right channels output by the DAC, the invention is innovative in that: Figure 4 The reference GND (i.e. point C, denoted as Ref_GND) of the DAC power amplifier driver (i.e. Driver) module shown in the figure is not directly connected to GND inside the chip (e.g. Figure 2 As shown in FIG. 1 , instead, a connection relationship is established between the chip switch state and the off-chip circuit according to the identified headphone type (CTIA / OMTP), such as Figure 4 Indicated by the dotted line.

[0060] Furthermore, when routing on the PCB, the impedance of the routing of Ref_GND (RING2_Ref for CTIA type headphones and Sleeve_Ref for OMTP type headphones) and the impedance of the routing of the headphone GND (RING2 for CTIA type headphones and SLEEVE for OMTP type headphones) are set to the same value as much as possible, and the two routings finally converge at the corresponding solder points of the headphone socket, namely point A and point B.

[0061] As a headphone adapter chip, it is uncertain what type of headphones will be inserted in the application scenario. It may be a 3-band headphone, or it may be a CTIA or OMTP in a 4-band headphone. According to the above impedance requirements, the two groups of signal lines Ring2_Ref and Ring2, Sleeve_Ref and Sleeve should be kept as equal in length and width as possible in the PCB routing, and the routing should be as short as possible.

[0062] When the headset is of 4-band CTIA type, such as Figure 5 In the dotted line portion, the reference ground of the power amplifier driving circuit is connected to point A through the analog switches Rsw3 and Rb4;

[0063] When the headset is of 4-band OMTP type, such as Figure 6 In the dot-dash line portion, the reference ground of the power amplifier driving circuit is connected to point A through the analog switches Rsw7 and Rb7;

[0064] When the earphone is of 3-band type, such as Figure 7 In the dotted line portion in FIG. 1 , the reference ground of the power amplifier driving circuit is connected to point A through the analog switches Rsw3 and Rb4, and is connected to point B through the analog switches Rsw7 and Rb7.

[0065] (2) Circuit for suppressing crosstalk between DAC output and microphone

[0066] With regard to the crosstalk between the DAC output and the ADC, the invention is innovative in that: Figure 8 As shown, the reference GND of the MICBIAS decoupling capacitor C3 and the reference GND of the MICBIAS generating unit are not directly connected to GND, but are coupled back to the ground path (Ring2 / Sleeve) of the earphone via the on-chip switch Rsw4 or Rsw8 through Ring2_Ref or Sleeve_Ref.

[0067] for Figure 2 In the circuit structure shown, even if a headphone adapter chip that does not use this design is used, the input of the ADC can be understood as the signal difference between points A and B. Due to the non-ideality of the ground path Ring2 / Sleeve, the residual signal difference generated at points AB at the DAC output can be re-coupled to the ADC.

[0068] Taking the CTIA type headset application scenario as an example, the connection relationship of the on-chip switch is as follows: Fig. 9 The Sleeve pin is used to connect the microphone of the CTIA type headset, the Ring2 pin is used to connect the GND of the headset, and the actual electrical connection relationship is established between the A / B points through the following path (Rb6+Rsw6+Rbias+C3+Rsw4+Rb4) (as shown in Figure 1). Fig.10 ), rather than Figure 2 are independent of each other as described in .

[0069] by Fig.10 The CTIA type headphones in the example are used as an example to explain the suppression principle: Due to the imperfect grounding, the residual voltage of the DAC output signal at point S is recorded as V S , V AYes V S At a voltage divider point on the branch Rcon3+Rb3+Rsw2+Rb5, there are two parallel branches between point S and point A: 1. Rcon3; 2. Rmicphone+Rcon4+Rb6+Rsw6+Rbias+RC3+Rsw4+Rb4. B is the voltage divider point of branch 2. Based on the above information, it is easy to conclude that the ADC input V AB Yes V SA The voltage divider, while V SA Depends on Rcon3. By optimizing the interface Rcon3, very low impedance can be achieved, that is, V SA can be very small, so theoretically the ADC input V AB It can also be very small.

[0070] Similarly, for OMTP type headphones, the connection relationship of the on-chip switches is as follows: Fig.11 The Ring2 pin is used to connect the microphone of the OMTP type headset, and the Sleeve pin is used to connect the GND of the headset. The solder point A corresponding to the Ring2 pin on the headset socket and the solder point B corresponding to the Sleeve pin establish an actual electrical connection relationship through the path (Rb3+Rsw1+Rbias+C3+Rsw8+Rb7) (as shown in Figure 1). Fig.12 shown).

[0071] Use existing Figure 2 In the circuit structure shown, the left and right channels of the earphone speaker and the speaker and the micphone share a common ground path Rcom (Rcon3+Rb3+Rsw2+Rb5 for CTIA type and Rcon4+Rb6+Rsw5+Rb5 for OMTP type).

[0072] According to the test results, the crosstalk between the left and right channels of the speaker is about -52dB when the speaker load is 32ohm; and the crosstalk between the speaker and the microphone can be understood as the difference between the speaker output voltage at point A and point B. According to the actual measurement results, the crosstalk between the speaker and the microphone is about -40dB when the speaker load is 32ohm.

[0073] according to Figure 4 After the structure shown is connected, according to the laboratory test results, the crosstalk between the left and right channels of the speaker is about -69dB, which is Figure 2 The existing solution described above improves the sound quality by 17 dB, and the crosstalk between the left and right channels of the loudspeaker is significantly reduced.

[0074] according to Figure 8After the structure shown is connected, according to the laboratory test results, the crosstalk between the speaker and the microphone is about -55dB, which is better than Figure 2 The existing solution described above improves the performance by 15 dB, and the crosstalk between the speaker and the microphone is significantly reduced.

[0075] According to the measured results, the two improved means of the present invention can effectively improve the crosstalk between the left and right channels of the speaker, and the crosstalk between the speaker and the microphone, respectively. The circuit has good practical application significance.

[0076] The circuit described in the present invention can effectively improve the separation between the left and right channels of the speaker and the separation between the speaker and the microphone by optimizing the internal audio circuit of the headphone interface chip and the external related interface circuit, thereby improving the side tone and enhancing the playback and call quality.

[0077] In addition, the present invention also provides an audio system, comprising: Figures 3 to 12 A circuit for improving the separation of channels of an analog audio interface as described in any one of the items.

[0078] It can be understood that the same or similar parts of the above embodiments can be referenced to each other, and the contents not described in detail in some embodiments can refer to the same or similar contents in other embodiments.

[0079] It should be noted that, in the description of the present invention, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. In addition, in the description of the present invention, unless otherwise specified, the meaning of "plurality" refers to at least two.

[0080] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0081] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A circuit for improving the separation of channels of an analog audio interface, characterized in that: include: The internal audio circuit of the headphone interface chip and the external related interface circuit; The internal audio circuit of the headphone interface chip includes: a DAC module, a power amplifier driving circuit, an analog switch group, a MICBIAS generating unit, a gain amplifier and an ADC module; The output end of the DAC module is connected to the input end of the power amplifier driving circuit through the gain resistors Rg1 and Rg2; the output end of the power amplifier driving circuit is connected to the corresponding interface of the speaker on the earphone through the resistor set Rb1 or Rb2; the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 are both connected to the off-chip near the earphone interface through the analog switch group; the input end of the ADC module is connected to the microphone and the corresponding interface on the earphone through the gain amplifier; The analog switch group includes: analog switches Rsw1 to Rsw8; After the type of the earphone is determined, a connection relationship is established with an off-chip circuit by configuring the states of the on-chip analog switches Rsw1 to Rsw8 according to the type of the earphone, so as to achieve a correct electrical connection; wherein the establishing a connection relationship with an off-chip circuit by configuring the states of the on-chip analog switches Rsw1 to Rsw8 according to the type of the earphone includes: When the earphone type is a 4-band earphone, The analog switches Rsw1 and Rsw6 are closed to select whether Sleeve or Ring2 is connected to MICBIAS via Rbias; Close Rsw2 and Rsw5 to connect Sleeve or Ring2 to GND. At the same time, one of the two groups of analog switches Rsw3 / Rsw4 and Rsw7 / Rsw8 is selected to be closed and the other is opened according to the type of headphones, so as to connect the reference ground of the power amplifier driving circuit and the reference ground of the MICBIAS decoupling capacitor C3 to the outside of the chip near the headphone interface, so as to reduce the crosstalk between the left and right channels of the speaker and the crosstalk of the speaker to the microphone.

2. The circuit according to claim 1, characterized in that When the headphone type is a 4-band CTIA type, the analog switches Rsw1, Rsw5, Rsw7 and Rsw8 are opened, and the analog switches Rsw2, Rsw3, Rsw4 and Rsw6 are closed; When the earphone type is a 4-band OMTP type, the analog switches Rsw2, Rsw3, Rsw4 and Rsw6 are opened, and the analog switches Rsw1, Rsw5, Rsw7 and Rsw8 are closed.

3. The circuit according to claim 2, characterized in that The method of establishing a connection relationship with an off-chip circuit by configuring the states of on-chip analog switches Rsw1 to Rsw8 according to the type of earphone includes: When the earphone type is a three-band earphone, the analog switches Rsw1 and Rsw6 are opened, and the analog switches Rsw2 and Rsw5 are closed to select connecting Sleeve and Ring2 to GND at the same time, and the two groups of analog switches Rsw3 / Rsw4 and Rsw7 / Rsw8 are closed.

4. The circuit according to claim 3, characterized in that When routing on the PCB, the impedance of the reference ground of the power amplifier driving circuit is the same as the impedance of the headphone GND routing, and the two routings finally converge at the corresponding soldering point of the headphone socket; In the PCB routing, keep the two groups of signal lines Ring2_Ref and Ring2, Sleeve_Ref and Sleeve of equal length and width.

5. The circuit according to any one of claims 1 to 4, characterized in that: Depending on the type of the 4-band earphone, the reference ground of the MICBIAS decoupling capacitor C3 and the reference ground of the MICBIAS generating unit are coupled back to the ground path of the earphone via Ring2_Ref or Sleeve_Ref through the analog switch Rsw4 or Rsw8.

6. The circuit according to claim 5, characterized in that When the type of the 4-segment earphone is CTIA type, the Sleeve pin is used to connect the microphone of the CTIA type earphone, the Ring2 pin is used to connect the GND of the earphone, and an electrical connection is established between the solder point A corresponding to the Ring2 pin on the earphone socket and the solder point B corresponding to the Sleeve pin through the path Rb6+Rsw6+Rbias+C3+Rsw4+Rb4.

7. The circuit according to claim 5, characterized in that When the type of the 4-segment earphone is OMTP type, the Ring2 pin is used to connect the microphone of the OMTP type earphone, the Sleeve pin is used to connect the GND of the earphone, and an electrical connection is established between the solder point A corresponding to the Ring2 pin on the earphone socket and the solder point B corresponding to the Sleeve pin through the path Rb3+Rsw1+Rbias+C3+Rsw8+Rb7.

8. An audio system, characterized in that: include: A circuit for improving the separation of channels of an analog audio interface as claimed in any one of claims 1 to 7.

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