CN103096216A - Audio processing circuit and earphone - Google Patents

Abstract

The invention discloses an audio processing circuit, which comprises: an audio input interface, a third resistor, a left channel differential audio processing circuit, and a right channel differential audio processing circuit; wherein, the third resistor is connected to the audio input Between the common end of the interface and the ground end of the audio processing circuit, the resistance value of the third resistor is far greater than the equivalent resistance of the audio signal line; the left channel differential audio processing circuit includes a left differential audio amplifier, a left channel The signal processing circuit, the right channel differential audio processing circuit includes a right differential audio amplifier and a right channel signal processing circuit. Correspondingly, the present invention also discloses an earphone including the above-mentioned audio processing circuit, which can effectively prevent the charging current from interfering with the audio signal, and significantly reduce the noise of the earphone.

Description

A kind of audio processing circuit and earphone

technical field

The invention relates to the technical field of audio processing, in particular to an audio processing circuit and earphones.

Background technique

At present, the application of headphones has become more and more common. Many wireless headphones can not only be used wirelessly, but also have a wired jack at the same time. The earphone can not only play audio information wirelessly, but also can be connected to an audio device with an output function (such as a PC, etc.) through a wired jack, and play audio information in a wired way.

Earphones are generally powered by rechargeable batteries. When the battery is low, the battery needs to be charged, and audio information can be played while charging. When the earphone is connected to the same audio device for audio information playback and charging, under normal conditions, the charging current in the earphone flows back into the audio device through the ground wire (PGND) of its charging circuit, and the audio signal current passes through its audio processing circuit The ground wire (AGND) of the circuit returns to the audio equipment without interfering with each other. However, since the reference potential of the charging circuit in the earphone, PGND, and the reference potential of the audio processing circuit, AGND, are equipotential, a part of the changing charging current will flow back into the audio device through AGND, so that the changing charging current will be It will affect the output voltage of the audio processing circuit, generate humming current noise, and seriously affect the playback effect of audio information.

For example, in the situation shown in Figure 1, the audio input terminal of the earphone is connected to the audio output interface of a computer, and its charging interface is connected to the charging interface (such as a USB interface) of the computer at the same time, and the earphone plays the audio of the computer and passes the The computer is charging. In this case, there will be a continuous humming noise in the audio played in the earphone, and the humming noise will increase with the increase of the volume. When the playback is paused or the playback is switched, the noise will be more and more obvious.

Contents of the invention

The invention provides an audio processing circuit and an earphone to solve the problem of noise existing when the existing earphone is connected to the same audio device to output audio information and charge at the same time.

The present invention provides an audio processing circuit, which includes an audio input interface, a third resistor, a left channel differential audio processing circuit, and a right channel differential audio processing circuit; wherein,

The third resistor is connected between the common end of the audio input interface and the ground end of the audio processing circuit, and the resistance value of the third resistor is much larger than the equivalent resistance of the audio signal line;

The left channel differential audio processing circuit includes: a left differential audio amplifier, a left channel signal processing circuit, a resistor is respectively connected between the input end of the left differential audio amplifier, the audio input interface, and the ground terminal of the audio processing circuit, and the left The output end of the differential audio amplifier is connected to the left channel signal processing circuit;

The right channel differential audio processing circuit includes: a right differential audio amplifier, a right channel signal processing circuit, a resistor is respectively connected between the input end of the right differential audio amplifier, the audio input interface, and the ground terminal of the audio processing circuit, and the right The output end of the differential audio amplifier is connected to the right channel signal processing circuit.

In the above solution, the left channel differential audio processing circuit includes: a fourth resistor, a fifth resistor, a sixth resistor, an eleventh resistor, a left differential audio amplifier, and a left channel signal processing circuit; wherein, the left The first input terminal of the differential audio amplifier is connected in series with the fourth resistor and connected to the left channel signal input interface of the audio input interface, and is also connected to the ground terminal of the audio processing circuit through the eleventh resistor connected in series, and the second input The end of the fifth resistor is connected in series with the common end of the audio input interface, and the output end of the left differential audio amplifier is connected through the sixth resistor, and the output end of the left differential audio amplifier is connected to the left The input terminal of the channel signal processing circuit;

The right channel differential audio processing circuit includes: a seventh resistor, an eighth resistor, a ninth resistor, a twelfth resistor, a right differential audio amplifier, and a right channel signal processing circuit; wherein, the first differential audio amplifier of the right The second input terminal is connected in series with the eighth resistor and connected to the right channel signal input interface of the audio input interface, and connected to the ground terminal of the audio processing circuit through the serial connection of the twelfth resistor, and the first input terminal is connected in series with the The seventh resistor is also connected to the common end of the audio input interface, and is also connected to the output end of the right differential audio amplifier through the ninth resistor, and the output end of the right differential audio amplifier is connected to the right channel signal processing input to the circuit.

In the above scheme, the resistance values of the sixth resistance, the ninth resistance, the eleventh resistance and the twelfth resistance are equal, and the resistance values of the fourth resistance, the fifth resistance, the seventh resistance and the eighth resistance are equal .

In the above solution, the audio processing circuit also includes:

The first capacitor is connected in series with the fourth resistor, and is connected in series between the input terminal of the left differential audio amplifier and the left channel signal input interface of the audio input interface;

And/or, the second capacitor is connected in series with the fifth resistor, and is connected in series between the input terminal of the left differential audio amplifier and the ground terminal of the audio processing circuit of the audio input interface;

And/or, the eleventh capacitor is connected in series between the output terminal of the left differential audio amplifier and the input terminal of the left channel signal processing circuit.

In the above solution, the audio processing circuit also includes:

The third capacitor is connected in series with the eighth resistor, and is connected in series between the input terminal of the right differential audio amplifier and the left channel signal input interface of the audio input interface;

And/or, the fourth capacitor is connected in series with the seventh resistor, and is connected in series between the input terminal of the right differential audio amplifier and the ground terminal of the audio processing circuit of the audio input interface;

And/or, the twelfth capacitor is connected in series between the output end of the right differential audio amplifier and the input end of the right channel signal processing circuit.

The present invention also provides an earphone, the earphone includes a charging circuit, a battery and the above-mentioned audio processing circuit;

The charging circuit is connected to the charging interface of the external audio equipment and the battery to charge the battery; the battery supplies power to the audio processing circuit;

The ground terminal of the charging circuit is at the same potential as the ground terminal of the audio processing circuit.

In the above solution, the earphone is a wireless earphone.

In the above solution, the earphone is an active wired earphone.

The beneficial effects of the embodiments of the present invention are as follows: firstly, a resistor is used to isolate the common terminal of the audio input interface from the ground terminal of the audio processing circuit, so as to prevent the charging current from interfering with the audio signal and effectively reduce the noise of the earphone; An audio amplifier is added to the processing circuit, and the audio signal is processed through differential input to offset the difference in common mode signal between the ground terminal of the audio equipment and the power supply ground terminal, and eliminate the influence of the potential difference of the ground terminal on the audio signal. In this way, the charging current will not affect the audio signal, and the interference signal on the power supply ground terminal will not be picked up into the audio signal, thereby achieving the purpose of eliminating noise.

Description of drawings

FIG. 1 is a schematic diagram of connection between earphones and audio equipment in the prior art;

Figure 2 is a schematic diagram of the principle of current noise generation when the earphone is charged and the audio signal is output through the same audio device;

Fig. 3 is a circuit diagram of an audio processing circuit in an embodiment of the present invention;

Fig. 4 is a schematic diagram of the circuit principle of the earphone and its noise reduction when charging and outputting audio signals through the same audio device in an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

The connection between the earphone and the audio device is shown in Figure 2, wherein the charging circuit of the earphone is connected to the charging interface of the audio device, the audio processing circuit of the earphone is connected to the audio output interface of the audio device, and the earphone is used to output the audio device audio signal while charging through the audio device.

Wherein, the earphone may include: a charging circuit 21, a battery 22 and an audio processing circuit 23, wherein the charging circuit is used to charge the battery, the battery is used to supply power to other parts, and the audio processing circuit is used to process the audio signal of the audio device and output.

The charging circuit 21 includes: a charging processing module 211 , a charging power line VBUS, a charging ground line PGND, and an equivalent resistance first resistor R1 on each signal line (VBUS and PGND) of the charging circuit. Among them, the charging power line VBUS is sequentially connected to the charging terminal U _CHG of the charging interface on the audio equipment, the first resistor R1, the charging processing module and the battery, and the charging ground line PGND is sequentially connected to the charging ground terminals U _{G1 and} the charging interface of the audio equipment. The ground terminal of the charging circuit, the charging processing module 211 and the battery 22 .

The audio processing circuit includes: left channel signal processing circuit A _L , right channel signal processing circuit A _R , left channel speaker L, right channel speaker R, left channel signal line SPK_L, right channel signal line SPK_R, audio The ground wire AGND, the equivalent resistance second resistor R2 on each signal wire (SPK_L, SPK_R and AGND) of the audio processing circuit. Wherein, the left channel signal line SPK_L is sequentially connected to the left channel signal output interface U _L of the audio output interface on the audio equipment, the second resistor R2, the left channel signal processing circuit A _L and the left channel speaker L; The signal line SPK_R is sequentially connected to the right channel signal output interface U _R of the audio output interface on the audio device, the second resistor R2, the right channel signal processing circuit A _R and the right channel speaker R; the audio ground wire AGND is connected to the audio device The ground terminal UG1 of the upper audio output interface, the second resistor R2 and the ground terminal GND2 of the audio processing circuit, the left channel signal processing circuit A _L , the right channel signal processing circuit A _R , the left channel speaker L, and the right channel speaker R Also connected to the ground terminal GND2 of the audio processing circuit respectively.

Among them, the ground terminal of the charging circuit, the ground terminal GND2 of the audio processing circuit, and the common terminal of the audio input interface of the audio processing circuit are all at the same potential, U _G1 is the voltage value on the ground wire of the charging interface and the audio output interface on the audio equipment, The ground terminal of the interface and the ground terminal of the audio output interface are connected together.

The charging current in the charging circuit changes, and there will be periodic changes under the influence of the charging processing module and the battery. Assuming that the constant part of the charging current is I _CHG , and the changing part is Δi, then the relationship of the following formula (1) and formula (2) exists:

I _CHG =I _CHG1 +I _CHG2 (1)

Δi=Δi ₁ +Δi ₂ (2)

Among them, ICHG1 and Δi1 are the return components of the charging current on the charging ground line PGND, I _CHG2 and Δi2 are the return components of the charging current on the audio ground line AGND, I _CHG1 and I _CHG2 and Δi ₁ and Δi ₂ are respectively based on the corresponding signal line The distribution of the impedance relationship.

Assume that the reference potential of the ground terminal GND1 of the audio equipment terminal is 0V.

When the audio device has no audio signal output, only the charging current is provided, assuming that the charging voltage is 5V, at this time: U _L =U _R =0, I _L =I _R =0, U _CHG =5V. Among them, U _L and UR are respectively the audio output voltage of the left channel and the audio output voltage of the right channel on the audio device, and U _CHG is the output voltage of the charging interface on the audio device.

According to Ohm's law, the voltage U _G2 on the ground terminal GND2 of the audio input circuit can be obtained by the following formula (3):

U _G2 =(I _CHG +Δi)*(R1//R2)=I _CHG *(R1//R2)+Δi*(R1//R2)=I _CHG *(R1//R2)+ΔU(3)

Among them, R1 is the equivalent resistance of each signal line on the charging circuit, R2 is the equivalent resistance of each signal line on the audio processing circuit, ΔU=Δi*(R1//R2) is the voltage change on GND2.

For the speaker, since there is no audio signal output, the voltage variation of the high potential U3 on the left channel speaker L in the audio processing circuit is 0, and the voltage variation of the low potential U4 is ΔU; the right channel of the audio processing circuit The voltage change of the high potential U5 on the speaker R is 0, and the voltage change of the low potential U6 is ΔU; according to the following formula (4) and formula (5), the input voltage U _{SPK_L} and U _{SPK_R} on the two speakers can be obtained The variations of ΔUSPK_L and ΔUSPK_R are both -ΔU. At this time, the variation of the input voltage is -ΔU, which will cause the speaker to generate noise.

ΔU _{SPK_L} = ΔU3-ΔU4=-ΔU≠0 (4)

ΔU _{SPK_R} = ΔU6-ΔU5=-ΔU≠0 (5)

When an audio device outputs an audio signal, there are two speakers whose voltage variation on the low potential is ΔU, the voltage variation on the left channel speaker L’s high potential ΔU3=I _L *R2=ΔU _L , and the right channel speaker R is high The voltage variation on the potential ΔU6=I _R *R2=ΔU _R , ΔU _L and ΔU _R are useful signals.

According to the following equations (6) and (7), the variation of the input voltage on the two speakers can be obtained

ΔU _{SPK_L} and ΔU _{SPK_R} are ΔU _L -ΔU and ΔU _R -ΔU respectively. It can be seen that ΔU will be superimposed on the audio signal, and there will still be noise.

ΔU _{SPK_L} = ΔU3-ΔU4=ΔU _L -ΔU (6)

ΔU _{SPK_R} = ΔU6-ΔU5=ΔU _R -ΔU (7)

In summary, when the earphone is connected to the same audio device for audio signal output and charging, the noise is caused by the changing charging current that interferes with the output of the audio signal when the charging circuit and the audio processing circuit share the same ground.

If the ground wire of the charging circuit is disconnected from the ground wire of the audio processing circuit, it is necessary to use load electrical isolation devices such as audio transformers, photoelectric isolation devices and other circuits, and these circuits will also interfere with the audio signal output by the earphone. And it will increase the area and volume of the whole machine, increase the cost, increase the difficulty of development and debugging, etc.

The basic idea of the present invention is to provide an audio processing circuit and an earphone including the audio processing circuit, a resistor is connected in series between the common end of the audio input interface in the audio processing circuit and the ground end of the audio processing circuit, and at the same time A differential input circuit is added to the audio processing circuit, and the audio signal is processed through differential input, so that the ground terminal of the audio processing circuit (same as the ground terminal of the charging circuit) and the common terminal of the audio input interface are separated by the resistor. Avoid the charging current in the charging circuit from flowing into the audio signal, eliminate the interference of the charging current on the audio signal, and at the same time process the audio signal through differential input to offset the common mode signal between the ground terminal of the audio device and the ground terminal of the earphone Different, eliminate the influence of the potential difference of the ground terminal on the audio signal, and achieve the purpose of eliminating noise.

An audio processing circuit provided by an embodiment of the present invention includes an audio input interface, a third resistor, a left channel differential audio processing circuit, and a right channel differential audio processing circuit; wherein the third resistor is connected to the audio input Between the common end of the interface and the ground end of the audio processing circuit, the resistance of the third resistor is much greater than the equivalent resistance of the audio signal line;

The left channel differential audio processing circuit includes: a left differential audio amplifier, a left channel signal processing circuit, a resistor is respectively connected between the input end of the left differential audio amplifier, the audio input interface, and the ground terminal of the audio processing circuit, and the left The output end of the differential audio amplifier is connected to the left channel signal processing circuit;

The right channel differential audio processing circuit includes: a right differential audio amplifier, a right channel signal processing circuit, a resistor is respectively connected between the input end of the right differential audio amplifier, the audio input interface, and the ground terminal of the audio processing circuit, and the right The output end of the differential audio amplifier is connected to the right channel signal processing circuit.

Specifically, as shown in FIG. 3 , the audio processing circuit in the embodiment of the present invention may mainly include: an audio input interface 31, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a left differential audio amplifier A ₁ , a seventh Resistor R7, eighth resistor R8, ninth resistor R9, eleventh resistor R11, twelfth resistor R12, right differential audio amplifier A ₂ , left channel signal processing circuit A _L , right channel signal processing circuit A _R , The left channel speaker L, the right channel speaker R and the third resistor R3.

Wherein, the audio input interface 31 includes three interfaces, respectively a first interface 1, a second interface 2, and a third interface 3, wherein the third interface 3 is used as a left channel signal input interface, and the first interface 1 is used as an input interface for the left channel signal. The common end GND3 of the audio input interface, the second interface 2 is the right channel signal input interface.

As shown in FIG. 3 , a third resistor R3 is connected in series between the first interface 1 of the audio input interface 31 and the ground terminal GND2 of the audio processing circuit. The resistance of the third resistor R3 is much larger than the equivalent resistance of the charging signal line and the equivalent resistance of the audio signal line. Generally speaking, the equivalent resistance of the charging signal line and the equivalent resistance of the audio signal line have a resistance value of about several milliohms. Therefore, the resistance value of the third resistor R3 is between 100Ω and 100KΩ, and the third resistor R3 is preferably The resistance of R3 is 100Ω. In this way, R3 can isolate GND2 from GND3, prevent the charging current in the charging circuit from flowing into the audio processing circuit, and effectively reduce the noise caused by the charging current interfering with the audio signal.

As shown in Figure 3, the first input terminal of the left differential audio amplifier _A1 is connected in series with the fourth resistor R4 and connected to the third interface 3 of the audio input interface 31, and is also connected to the audio processing circuit through the series connection of the eleventh resistor R11 The ground terminal GND3, the second input terminal is connected in series with the fifth resistor R5 and connected to the first interface 1 of the audio input interface 31, the second input terminal is also connected to the output terminal through the sixth resistor R6, and the output of the left differential audio amplifier _A1 The terminal is connected to the input terminal of the left channel signal processing circuit _AL , and the output terminal of the left channel signal processing circuit _AL is connected to an input terminal of the left channel speaker L.

The first input terminal of the right differential audio amplifier _A2 is connected in series with the seventh resistor R7 and connected to the first interface 1 of the audio input interface 31, and the output terminal is also connected through the ninth resistor R9, and the second input terminal is connected in series with the eighth resistor R8 is also connected to the second interface 2 of the audio input interface 31, and is connected to the ground terminal GND3 of the audio processing circuit through a serial connection of the twelfth resistor R12, and the output terminal of the right differential audio amplifier A2 is connected to the right channel signal processing circuit _AR . The input terminal, the output terminal of the right channel signal processing circuit _AR is connected to an input terminal of the right channel speaker R.

As shown in Figure 3, the voltage on the third interface 3 is U _L , the voltage at the output terminal of the left differential audio amplifier A ₁ is UO1 , the voltage on the second interface 2 is U _R , and the voltage at the output terminal of the right differential audio amplifier A ₂ is UO2, the voltage on the first interface 1, that is, the voltage of GND3 is _UG3 , the voltage of the ground terminal GND2 of the audio processing circuit is UG2, the left channel audio processing is composed of R1, R4, R5, R6 and A1 to form a subtraction circuit; the right channel Audio processing is composed of R2, R7, R8, R9 and A2 to form a subtraction circuit, and the outputs are:

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="u\; o"\; filenames="HDA00002831779000031.png"\; state="\{\{state\}\}">u</figure-callout></span><figure-callout\; id="1"\; label="u\; o"\; filenames="HDA00002831779000031.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 11</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}}{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="u\; G"\; filenames="HDA00002831779000021.png"\; state="\{\{state\}\}">u</figure-callout></span><figure-callout\; id="3"\; label="u\; G"\; filenames="HDA00002831779000021.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}$

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 9</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 12</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 9</span>}}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}}<span\; class="notranslate">\; \&times;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="u\; G"\; filenames="HDA00002831779000021.png"\; state="\{\{state\}\}">u</figure-callout></span><figure-callout\; id="3"\; label="u\; G"\; filenames="HDA00002831779000021.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}$

When R11=R6=R12=R9=Rf, R4=R5=R7=R8=R, there is

${\mathrm{<span\; class="notranslate">\; <figure-callout\; id="1"\; label="u\; o"\; filenames="HDA00002831779000031.png"\; state="\{\{state\}\}">u</figure-callout></span><figure-callout\; id="1"\; label="u\; o"\; filenames="HDA00002831779000031.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; </span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; f</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; G</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>$

Therefore, the gain of the left and right channel processing circuits is:

Here, in practical applications, the gain brought by the subtraction circuit to which A1 belongs can be adjusted by adjusting the resistance values of R11, R4, R5, and R6, and the gain brought by the subtraction circuit to which A2 belongs can be adjusted by adjusting the resistance values of R12, R7, R8, and R9 . But R11=R6=R12=R9, R4=R5=R7=R8 are required to ensure the same gain of the left and right channels. For example, when R11=R6=R4=R5=R12=R9=R7=R8=4.7KΩ, the circuit gain is 1; when R11=R6=R12=R9=10KΩ, R4=R5=R7=R8=5KΩ , the gain of the circuit is 2.

The left differential audio amplifier A ₁ and the right differential audio amplifier A ₂ mainly serve the function of converting differential signals to single-ended signals, in addition to amplifying signals, increasing input impedance, and enhancing load capacity.

In practical applications, the left differential audio amplifier A ₁ , the left channel signal processing circuit A _L , and the other input end of the left channel speaker L are connected to the power supply ground terminal GND2 of the earphone; the right differential audio amplifier A ₂ , the right channel signal processing circuit The other input terminal of the circuit A _R and the right channel speaker R is also connected to the power supply ground terminal GND2 of the earphone.

In addition, a first capacitor C1 can also be connected in series between the first input end of the left differential audio amplifier _A1 and the third interface 3 of the audio input interface 31, and the first capacitor C1 can be connected between the second input end and the first interface 1 of the audio input interface 31. A second capacitor C2 can also be connected in series between the output terminal and the input terminal of the left channel signal processing circuit _AL , and a twelfth capacitor C12 can also be connected in series. A fourth capacitor C4 can also be connected in series between the second input end of the right differential audio amplifier A ₂ and the second interface 2 of the audio input interface 31, and can also be connected between the first input end and the first interface 1 of the audio input interface 31. The third capacitor C3 is connected in series, and an eleventh capacitor C11 may also be connected in series between the output terminal and the input terminal of the right channel signal processing circuit _AR . Among them, the first capacitor C1, the second capacitor C2, the twelfth capacitor C12, the third capacitor C3, the fourth capacitor C4, and the eleventh capacitor C11 are input coupling capacitors, and the capacitor value is preferably 10 μF, which is used to eliminate the DC component of .

The embodiment of the present invention also provides an earphone, which includes the above-mentioned audio processing circuit. Specifically, as shown in FIG. 4 , the earphone may include: a charging circuit 41, a battery 42 and the above-mentioned audio processing circuit 43, Wherein, the charging circuit 41 is connected to the charging interface of the audio equipment and the battery 42 to charge the battery 42; the audio processing circuit 43 is connected to the audio output interface of the audio equipment to process and output the audio signal of the audio equipment; The processing circuit 43 is powered. In particular, the earphone may be a wireless earphone or an active wired earphone.

As shown in FIG. 4 , the charging circuit 41 includes a charging processing module 411 and an equivalent resistance first resistor R1 on each signal line (VBUS and PGND) of the charging circuit. Wherein, the input terminal of the charging processing module 411 is connected to the charging interface U _CHG of the audio equipment through the charging power line VBUS, the output terminal is connected to the battery 42, the ground terminal of the battery 42 is used as the power supply ground terminal GND2, and the ground terminal of the audio equipment is connected to the audio equipment through the charging ground wire PGND terminal GND1, and the power supply ground terminal GND2 is the ground terminal of the charging circuit 41 . Wherein, the charging processing module 411 may specifically be a chip used for charging processing, for example, it may be a chip of Texas Instruments model number BQ24040.

In the audio processing circuit 43, the left differential audio amplifier A ₁ in the left channel processing, the left channel signal processing circuit A _L , and the left channel speaker L are connected through the left channel signal line SPK_L and connected to the audio output interface on the audio device. The left channel output interface U _L , the right differential audio amplifier A ₂ in the right channel processing, the right channel signal processing circuit A _R , and the right channel speaker R are connected through the right channel signal line SPK_R, and connected to the audio on the audio equipment The right channel output interface U _R of the output interface; the left differential audio amplifier A ₁ and the right differential audio amplifier A ₂ are also connected to the ground terminal GND3 of the audio processing circuit 43; the left channel signal processing circuit A _L , the left channel speaker L, The right channel signal processing circuit A _R and the right channel speaker R are also connected to the power supply ground terminal GND2; the ground terminal GND3 of the audio processing circuit 43 is connected to the ground terminal GND1 of the audio equipment through the audio ground wire AGND, and connected to the ground terminal GND1 through the third resistor R3 Power supply ground terminal GND2. The equivalent resistance on each signal line (SPK_L, SPK_R and AGND) of the audio processing circuit is the second resistance R2.

In the embodiment of the present invention, R3 is much larger than R1. Therefore: R3+R2>>R1, according to Ohm's law, the amount of change in charging current flowing back into the audio processing circuit Δi ₂ =R1/(R1+R2+R3)*Δi≈0, Δi is the change in charging current in the charging circuit Therefore, the variation of the reference voltage U _G3 on the ground terminal GND3 of the audio processing circuit ΔU _G3 =R2*Δi ₂ ≈0, so that the variation of the speaker input voltage due to the change of the charging current is almost zero, and the charging The interference of the current on the audio signal in the audio processing circuit is almost zero. When the earphone is connected to the same audio device for audio signal output and charging, it is difficult for the human ear to distinguish the current noise.

In the embodiment of the present invention, first, a resistor is used to isolate the common end of the audio input interface from the ground end of the audio input circuit, that is, the common end of the audio input interface is isolated from the ground end of the charging circuit through a resistor , to prevent the charging current from flowing back into the audio processing circuit to interfere with the audio signal, effectively reducing the noise of the earphone; secondly, adding an audio amplifier to the audio processing circuit to process the audio signal through differential input to offset the grounding terminal of the audio device Unlike the common mode signal between the power supply grounds, the influence of the ground potential difference on the audio signal is eliminated. In this way, the charging current will not affect the audio signal, and the interference signal on the ground terminal of the earphone will not be picked up into the audio signal, thereby achieving the purpose of eliminating noise.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims (8)

1. The audio processing circuit is characterized by comprising an audio input interface, a third resistor, a left channel differential audio processing circuit and a right channel differential audio processing circuit; wherein,

the third resistor is connected between the common end of the audio input interface and the grounding end of the audio processing circuit, and the resistance value of the third resistor is far greater than the equivalent resistor of the audio signal line;

the left channel differential audio processing circuit includes: the left audio amplifier comprises a left differential audio amplifier and a left sound channel signal processing circuit, wherein resistors are respectively connected between the input end of the left differential audio amplifier and the grounding ends of the audio input interface and the audio processing circuit, and the output end of the left differential audio amplifier is connected with the left sound channel signal processing circuit;

the right channel differential audio processing circuit comprises: the audio amplifier comprises a right differential audio amplifier and a right sound channel signal processing circuit, wherein resistors are respectively connected between the input end of the right differential audio amplifier and the grounding ends of the audio input interface and the audio processing circuit, and the output end of the right differential audio amplifier is connected with the right sound channel signal processing circuit.

2. The audio processing circuit of claim 1,

the left channel differential audio processing circuit includes: the audio amplifier comprises a fourth resistor, a fifth resistor, a sixth resistor, an eleventh resistor, a left differential audio amplifier and a left sound channel signal processing circuit; the first input end of the left differential audio amplifier is connected in series with the fourth resistor and is connected to a left channel signal input interface of the audio input interface, and is also connected with the grounding end of an audio processing circuit by being connected in series with an eleventh resistor, the second input end of the left differential audio amplifier is connected in series with the fifth resistor and is connected to the common end of the audio input interface, and is also connected with the output end of the left differential audio amplifier by the sixth resistor, and the output end of the left differential audio amplifier is connected with the input end of the left channel signal processing circuit;

the right channel differential audio processing circuit comprises: the audio amplifier comprises a seventh resistor, an eighth resistor, a ninth resistor, a twelfth resistor, a right differential audio amplifier and a right sound channel signal processing circuit; the second input end of the right differential audio amplifier is connected in series with the eighth resistor and is connected to the right channel signal input interface of the audio input interface, and is also connected with the grounding end of the audio processing circuit by being connected in series with the twelfth resistor, the first input end is connected in series with the seventh resistor and is connected to the common end of the audio input interface, and is also connected with the output end of the right differential audio amplifier by the ninth resistor, and the output end of the right differential audio amplifier is connected with the input end of the right channel signal processing circuit.

3. The audio processing circuit of claim 2, wherein the sixth resistor, the ninth resistor, the eleventh resistor and the twelfth resistor have the same resistance value, and the fourth resistor, the fifth resistor, the seventh resistor and the eighth resistor have the same resistance value.

4. The audio processing circuit of claim 2, further comprising:

the first capacitor is connected with the fourth resistor in series and is connected between the input end of the left differential audio amplifier and a left channel signal input interface of the audio input interface in series;

and/or a second capacitor, which is connected in series with the fifth resistor and is connected in series between the input end of the left differential audio amplifier and the audio processing circuit ground end of the audio input interface;

and/or the eleventh capacitor is connected between the output end of the left differential audio amplifier and the input end of the left channel signal processing circuit in series.

5. The audio processing circuit of claim 2, further comprising:

the third capacitor is connected in series with the eighth resistor and is connected in series between the input end of the right differential audio amplifier and the left channel signal input interface of the audio input interface;

and/or a fourth capacitor, which is connected in series with the seventh resistor and is connected in series between the input end of the right differential audio amplifier and the audio processing circuit ground end of the audio input interface;

and/or a twelfth capacitor connected in series between the output end of the right differential audio amplifier and the input end of the right channel signal processing circuit.

6. An earphone, characterized in that the earphone comprises a charging circuit, a battery and an audio processing circuit according to any one of claims 1 to 5;

the charging circuit is connected with a charging interface of external audio equipment and the battery to charge the battery; the battery supplies power to the audio processing circuit;

the ground terminal of the charging circuit has the same potential as the ground terminal of the audio processing circuit.

7. The headset of claim 6, wherein the headset is a wireless headset.

8. The headset of claim 6, wherein the headset is an active wired headset.

Images