Driving circuit of loudspeaker and method for generating current sampling signal of loudspeaker

A driving circuit of a loudspeaker includes a periodic signal generation circuit, a signal processing circuit, a class-D amplifier circuit, a current sensing circuit, and a sample and hold circuit. The periodic signal generation circuit is arranged to generate a periodic signal and a control signal. The signal processing circuit is coupled to the periodic signal generation circuit, and is arranged to generate a pre-driving signal. The class-D amplifier circuit is coupled to the signal processing circuit, and is arranged to drive the loudspeaker according to the pre-driving signal. The current sensing circuit is coupled to the class-D amplifier circuit, and is arranged to generate a current sensing signal. The sample and hold circuit is coupled to the periodic signal generation circuit and the current sensing circuit, and is arranged to sample and hold the current sensing signal according to the control signal, to generate a current sampling signal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to current sampling, and more particularly, to a driving circuit of a loudspeaker and associated method for generating a current sampling signal of the loudspeaker.

2. Description of the Prior Art

A loudspeaker is a device having a voice coil that moves a diaphragm and converts an electrical signal into an acoustic signal. When the temperature of the voice coil is too high or the displacement of the diaphragm is too large, the loudspeaker may be damaged. For a typical class-D amplifier, it is arranged to drive the loudspeaker to achieve the effect of playing music. However, in order to prevent the loudspeaker from being damaged, a smart amplifier may further need to detect the condition of the loudspeaker (e.g. obtain a current signal flowing through the loudspeaker), to determine a working condition (e.g. temperature) under which the loudspeaker is operated.

For example, a plurality of current sensing resistors (e.g. two current sensing resistors) may be added to a class-D amplifier that is coupled to the loudspeaker to measure the current flowing through the loudspeaker. One current detection architecture may couple the current sensing resistors to both sides of the loudspeaker. Another current detection architecture may couple the current sensing resistors to the ground. Compared with the former, the current detection architecture that couples the current sensing resistors to the ground has a better noise floor. However, if the current sensing resistors are not matching (e.g. resistance values of the current sensing resistors are different), this architecture may have a poor second-order harmonic distortion. In addition, the mismatch of the current sensing resistors may cause the problem of DC offset. As a result, a novel driving circuit of the loudspeaker with this architecture and associated method for generating a current sampling signal of the loudspeaker are urgently needed.

SUMMARY OF THE INVENTION

It is therefore one of the objectives of the present invention to provide a driving circuit of a loudspeaker and associated method for generating a current sampling signal of the loudspeaker, to address the above-mentioned issues.

According to one embodiment of the present invention, a driving circuit of a loudspeaker is provided. The driving circuit may include a periodic signal generation circuit, a signal processing circuit, a class-D amplifier circuit, a current sensing circuit, and a sample and hold circuit. The periodic signal generation circuit may be arranged to generate a periodic signal and a control signal, wherein the control signal is arranged to indicate occurrence timing of a specific extreme value of the periodic signal. The signal processing circuit may be coupled to the periodic signal generation circuit, and may be arranged to receive a first audio input signal, a second audio input signal, and the periodic signal, and generate a pre-driving signal according to the first audio input signal, the second audio input signal, and the periodic signal, wherein the second audio input signal is an inverse of the first audio input signal. The class-D amplifier circuit may be coupled to the signal processing circuit, and may be arranged to drive the loudspeaker according to the pre-driving signal. The current sensing circuit may be coupled to the class-D amplifier circuit, and may be arranged to sense a driving current of the loudspeaker to generate a current sensing signal. The sample and hold circuit may be coupled to the periodic signal generation circuit and the current sensing circuit, and may be arranged to sample and hold the current sensing signal according to the control signal, to generate a current sampling signal of the loudspeaker.

According to one embodiment of the present invention, a method for generating a current sampling signal of a loudspeaker is provided. The method may include: generating a periodic signal and a control signal, wherein the control signal is arranged to indicate occurrence timing of a specific extreme value of the periodic signal; generating a pre-driving signal according to a first audio input signal, a second audio input signal, and the periodic signal, wherein the second audio input signal is an inverse of the first audio input signal; driving the loudspeaker, by a class-D amplifier circuit, according to the pre-driving signal; sensing a driving current of the loudspeaker to generate a current sensing signal; and sampling and holding the current sensing signal according to the control signal, to generate the current sampling signal.

According to another embodiment of the present invention, a driving circuit of a loudspeaker is provided. The driving circuit may include a periodic signal generation circuit, a signal processing circuit, a class-D amplifier circuit, a current sensing circuit, a logic control circuit, and a sample and hold circuit. The periodic signal generation circuit may be arranged to generate a periodic signal. The signal processing circuit may be coupled to the periodic signal generation circuit, and may be arranged to receive a first audio input signal, a second audio input signal, and the periodic signal, and generate a pre-driving signal according to the first audio input signal, the second audio input signal, and the periodic signal, wherein the second audio input signal is an inverse of the first audio input signal. The class-D amplifier circuit may be coupled to the signal processing circuit, and may be arranged to drive the loudspeaker according to the pre-driving signal. The current sensing circuit may be coupled to the class-D amplifier circuit, and may be arranged to sense a driving current of the loudspeaker to generate a current sensing signal. The logic control circuit may be coupled to the signal processing circuit, and may be arranged to generate a control signal according to the pre-driving signal. The sample and hold circuit may be coupled to the current sensing circuit and the logic control circuit, and may be arranged to sample and hold the current sensing signal according to the control signal, to generate a first current sampling signal.

According to another embodiment of the present invention, a method for generating a first current sampling signal of a loudspeaker is provided. The method may include: generating a periodic signal; generating a pre-driving signal according to a first audio input signal, a second audio input signal, and the periodic signal, wherein the second audio input signal is an inverse of the first audio input signal; driving the loudspeaker, by a class-D amplifier circuit, according to the pre-driving signal; sensing a driving current of the loudspeaker to generate a current sensing signal; generating a control signal according to the pre-driving signal; and sampling and holding the current sensing signal according to the control signal, to generate a second current sampling signal. In addition, the method may further include: performing computation upon the second current sampling signal, to generate the first current sampling signal.

One of the benefits of the present invention is that, by sampling and holding the current sensing signal at the time the triangle wave signal has the peak value according to the control signal,

the second-order harmonic distortion may be improved and the problem of DC offset may be avoided, wherein the peak value of the triangle wave signal corresponds to a time interval where the current flows through the loudspeaker and all of the current sense resistors at the same time. In addition, the current sensing signal may also be sampled and held only during a period in which the current flows through the loudspeaker and all of the current sense resistors at the same time according to the control signal, to generate a first current sampling signal. Then, average value computation may be performed upon the first current sampling signal, to generate a second current sampling signal of the loudspeaker. In this way, the second-order harmonic distortion may also be improved and the problem of DC offset may also be avoided.

DETAILED DESCRIPTION

FIG.1is a diagram illustrating a driving circuit10of a loudspeaker11according to an embodiment of the present invention. The driving circuit10may include a periodic signal generation circuit (e.g. a triangle wave generation circuit100), a signal processing circuit102, a class-D amplifier circuit104, a current sensing circuit105, and a sample and hold circuit106. It should be noted that, the triangle wave generation circuit100is only for illustrative purposes, and the present invention is not limited thereto. In practice, any other type of the periodic signal (e.g. a sawtooth wave signal) will fall within the scope of the present invention. The triangle wave generation circuit100may be arranged to generate a triangle wave signal TRI and a control signal CS, wherein the control signal CS may be arranged to indicate occurrence timing of a specific extreme value (e.g. a peak value) of the triangle wave signal TRI.

The signal processing circuit102may be coupled to the triangle wave generation circuit100, and may be arranged to receive two audio input signals A_IN andA_INand the triangle wave signal TRI, and generate a pre-driving signal PDRV according to the audio input signals A_IN andA_INand the triangle wave signal TRI, wherein the pre-driving signal PDRV includes a first switch pre-driving signal F_SW and a second switch pre-driving signal S_SW, and the audio input signalA_INis an inverse of the audio input signal A_IN (i.e. the phase difference between the audio input signal A_IN and the audio input signalA_INis 180 degrees). The signal processing circuit102may include two comparator circuits108and110and two pre-driver circuits112and114. The comparator circuit108may be coupled to the triangle wave generation circuit100, and may be arranged to compare the audio input signal A_IN with the triangle wave signal TRI, to generate a first comparator result signal F_COM. The comparator circuit110may be coupled to the triangle wave generation circuit100, and may be arranged to compare the audio input signalA_INwith the triangle wave signal TRI, to generate a second comparison result signal S_COM. The pre-driver circuit112may be coupled to the comparator circuit108, and may be arranged to generate the first switch pre-driving signal F_SW according to the first comparator result signal F_COM. The pre-driver circuit114may be coupled to the comparator circuit110, and may be arranged to generate the second switch pre-driving signal S_SW according to the second comparison result signal S_COM.

The loudspeaker11acts as a load of the class-D amplifier circuit104. The class-D amplifier circuit104may be coupled to the signal processing circuit102, and may be arranged to drive the loudspeaker11according to the pre-driving signal PDRV (i.e. the first switch pre-driving signal F_SW and the second switch pre-driving signal S_SW). The class-D amplifier circuit104may include four switch circuits116,118,120, and122. The switch circuit116has a first end coupled to a first reference voltage (e.g. a power voltage VDD). The switch circuit118has a first end coupled to the first reference voltage (e.g. the power voltage VDD), wherein the loudspeaker11is coupled between a second end of the switch circuit116and a second end of the switch circuit118. The switch circuit120has a first end coupled to the second end of the switch circuit116, and the switch circuit122has a first end coupled to the second end of the switch circuit118. In addition, the first switch pre-driving signal F_SW may be arranged to conduct one of the switch circuit116and the switch circuit120, and the second switch pre-driving signal S_SW may be arranged to conduct one of the switch circuit118and the switch circuit122.

It should be noted that, the modulation method of the class-D amplifier circuit104is BD modulation. That is, there are 4 directions of current flowing through the loudspeaker11in the class-D amplifier circuit104. According to the first switch pre-driving signal F_SW and the second switch pre-driving signal S_SW, 4 switch timings a, b, c, d of the 4 switch circuits116,118,120, and122may be obtained. It is assumed that a voltage at a node between the switch circuit116and the switch circuit120is VOUTA, and a voltage at a node between the switch circuit118and the switch circuit122is VOUTB.

For the positive half cycle of the audio input signal A_IN, in the switch timing a, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit116, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit122(i.e. the level of the voltage VOUTA is high, and the level of the voltage VOUTB is low). In the switch timing b, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit116, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit118(i.e. both of the levels of the voltages VOUTA and VOUTB are high). In the switch timing c, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit116, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit122(i.e. the level of the voltage VOUTA is high, and the level of the voltage VOUTB is low). In the switch timing d, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit120, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit122(i.e. both of the levels of the voltages VOUTA and VOUTB are low).

For the negative half cycle of the audio input signal A_IN, in the switch timing a, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit120, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit118(i.e. the level of the voltage VOUTA is low, and the level of the voltage VOUTB is high). In the switch timing b, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit116, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit118(i.e. both of the levels of the voltages VOUTA and VOUTB are high). In the switch timing c, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit120, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit118(i.e. the level of the voltage VOUTA is low, and the level of the voltage VOUTB is high). In the switch timing d, the first switch pre-driving signal F_SW may be arranged to conduct the switch circuit120, and the second switch pre-driving signal S_SW may be arranged to conduct the switch circuit122(i.e. both of the levels of the voltages VOUTA and VOUTB are low).

The current sensing circuit105may be coupled to the class-D amplifier circuit104, and may be arranged to sense a driving current of the loudspeaker11to generate a current sensing signal Isen. The current sensing circuit105may include two current sensing resistors124and126, wherein the current sensing resistor124may be coupled between a second end of the switch circuit120and a second reference voltage (e.g. a ground voltage GND), and the current sensing resistor126may be coupled between a second end of the switch circuit122and the second reference voltage (e.g. the ground voltage GND).

In light of the above, in the switch timing a, for the positive half cycle of the audio input signal A_IN, the current will flow through the switch circuit116, the loudspeaker11, the switch circuit122, and the current sensing resistor126in sequence. As a result, the current sensing signal Isen is generated according to the current sensing resistor126. For the negative half cycle of the audio input signal A_IN, the current will flow through the switch circuit118, the loudspeaker11, the switch circuit120, and the current sensing resistor124in sequence. As a result, the current sensing signal Isen is generated according to the current sensing resistor124. However, if the current sensing resistors124and126are not matching (e.g. resistance values of the current sensing resistors124and126are different), the current sensing signal Isen generated by current sensing circuit105will not be the same. In the switch timing b, for the positive half cycle or the negative half cycle of the audio input signal A_IN, the current will flow through the switch circuit116, the loudspeaker11, and the switch circuit118in sequence (i.e. will not flow through either the current sensing resistor124or the current sensing resistor126). As a result, the current sensing signal Isen is equal to 0 in the switch timing b. The current direction in the switch timing c is the same as that in the switch circuit a. For brevity, similar descriptions are not repeated in detail here.

On the other hand, in the switch timing d, for the positive half cycle or the negative half cycle of the audio input signal A_IN, the current will flow through the current sensing resistor124, the switch circuit120, the loudspeaker11, the switch circuit122, and the current sensing resistor126in sequence (the current direction is labeled as dashed line inFIG.1), and the current sensing signal Isen is generated according to the current sensing resistors124and126. No matter whether the resistance values of the current sensing resistors124and126are matching, the current sensing signal Isen generated by current sensing circuit105will be the same. In addition, please note that at the occurrence timing of the peak value of the triangle wave signal TRI, the 4 switch circuits116,118,120, and122has the switch timing d. As a result, the sample and hold circuit106may be coupled to the triangle wave generation circuit100and the current sensing circuit105, and may be arranged to sample and hold the current sensing signal Isen at the time the triangle wave signal TRI has the peak value according to the control signal CS, to generate a current sampling signal Isam of the loudspeaker11. In this way, the second-order harmonic distortion and the DC offset that are caused by mismatch of the current sensing resistors124and126may be improved.

FIG.2is a diagram illustrating associated signals of the driving circuit shown inFIG.1according to an embodiment of the present invention. In this embodiment, the triangle wave signal TRI may be compared with the positive half cycle of the audio input signal A_IN and the corresponding audio input signalA_IN, to generate the 4 switch timings a, b, c, and d, wherein the 4 switch timings a, b, c, and d correspond to 4 time intervals A, B, C, and D, respectively. In addition, as shown inFIG.2, the peak value of the triangle wave signal TRI corresponds to the time interval D (both of the levels of the voltages VOUA and VOUTB are low in the time interval D), and the current sensing signal Isen may be sampled and held at the time the triangle wave signal TRI has the peak value according to the control signal CS, to generate the current sampling signal Isam. For brevity, similar descriptions for this embodiment are not repeated in detail here.

FIG.3is a flow chart illustrating a method for generating a current sampling signal of a loudspeaker according to an embodiment of the present invention. Provided that the result is substantially the same, the steps are not required to be executed in the exact order shown inFIG.3. For example, the method shown inFIG.3may be employed by the driving circuit10shown inFIG.1.

In Step S300, the triangle wave signal TRI and the control signal CS are generated, wherein the control signal CS is arranged to indicate occurrence timing of the peak value of the triangle wave signal TRI.

In Step S302, the pre-driving signal PDRV is generated according to the audio input signals A_IN andA_INand the triangle wave signal TRI, wherein the audio input signalA_INis an inverse of the audio input signal A_IN.

In Step S304, the loudspeaker11is driven by the class-D amplifier circuit104, according to the pre-driving signal PDRV.

In Step S306, the driving current of the loudspeaker11is sensed to generate the current sensing signal Isen.

In Step S308, the current sensing signal Isen is sampled and held according to the control signal CS, to generate the current sampling signal Isam of the loudspeaker11.

Since a person skilled in the pertinent art can readily understand details of the steps after reading above paragraphs directed to the driving circuit10shown inFIG.1, further description is omitted here for brevity.

FIG.4is a diagram illustrating a driving circuit40of a loudspeaker41according to another embodiment of the present invention. The driving circuit40may include a periodic signal generation circuit (e.g. a triangle wave generation circuit400), a signal processing circuit402, a class-D amplifier circuit404, a logic control circuit406, a sample and hold circuit408, and a computation circuit (e.g. an average circuit410). It should be noted that, the triangle wave generation circuit400and the average circuit410are only for illustrative purposes, and the present invention is not limited thereto. In practice, any other type of the periodic signal (e.g. a sawtooth wave signal) and any other type of the computation circuit will fall within the scope of the present invention.

The difference between the driving circuit10shown inFIG.1and the driving circuit40shown inFIG.4is that the driving circuit40further includes the logic control circuit406and the average circuit410, and the triangle wave generation circuit402is arranged to generate the triangle wave signal TRI without an accompanying signal that indicates occurrence timing of a specific extreme value of a periodic signal (e.g. a peak value of the triangle wave signal TRI). The logic control circuit406may be coupled to the signal processing circuit402, and may be arranged to generate a control signal CS' according to the pre-driving signal PDRV (i.e. the first switch pre-driving signal F_SW and the second switch pre-driving signal S_SW). The sample and hold circuit408may be coupled to the current sensing circuit405and the logic control circuit406, and may be arranged to sample and hold the current sensing signal Isen according to the control signal CS′, to generate a first current sampling signal F_Isam. In this embodiment, the first current sampling signal F_Isam is a collection of consecutive sample values of the current sensing signal Isen. The average circuit410may be coupled to the sample and hold circuit408, and may be arranged to perform average value computation upon the first current sampling signal F_Isam, to generate a second current sampling signal S Isam of the loudspeaker41. For brevity, similar descriptions for this embodiment are not repeated in detail here.

It should be noted that, the logic control circuit406may be arranged to generate the control signal CS' according to a first logic value L1and a second logic value L2, wherein the first logic value L1may be generated according to the first switch pre-driving signal F_SW, and the second logic value L2may be generated according to the second switch pre-driving signal S_SW. For example, the logic control circuit406may be a NOR gate circuit, wherein the NOR gate circuit has a first input terminal coupled to the pre-driver circuit416, a second input terminal coupled to the pre-driver circuit418, and an output terminal coupled to the sample and hold circuit408, and may be arranged to receive the first logic value L1and the second logic value L2, to generate the control signal CS′, but the present invention is not limited thereto.

When the switch circuit420is turned on according to the first switch pre-driving signal F_SW (i.e. the level of the voltage VOUTA is high), the first logic value L1is equal to 1. When the switch circuit424is turned on according to the first switch pre-driving signal F_SW (i.e. the level of the voltage VOUTA is low), the first logic value L1is equal to 0. On the other hand, when the switch circuit422is turned on according to the second switch pre-driving signal S_SW (i.e. the level of the voltage VOUTB is high), the second logic value L2is equal to 1. When the switch circuit426is turned on according to the second switch pre-driving signal S_SW (i.e. the level of the voltage VOUTB is low), the second logic value L2is equal to 0. The control signal CS' may be arranged to control the sample and hold circuit408to sample and hold the current sensing signal Isen only during a period in which the switch circuit424and the switch circuit426are turned on by the first switch pre-driving signal F_SW and the second switch pre-driving signal S_SW, respectively (i.e. both of the levels of the voltages VOUTA and VOUTB are low, and both of the first logic value L1and the second logic value L2are 0). That is, only when the control signal CS' is equal to 1 (i.e. a result of NORing the first logic value L1(L1=0) and the second logic value L2(L2=0) is equal to 1), the current sensing signal Isen is sampled and held by the sample and hold circuit408, to generate the first current sampling signal F_Isam.

FIG.5is a diagram illustrating associated signals of the driving circuit40shown inFIG.4according to an embodiment of the present invention. The triangle wave signal TRI may be compared with the positive half cycle of the audio input signal A_IN and the corresponding audio input signalA_IN, and the logic combinations of the first logic value L1and the second logic value L2(i.e. 10, 11, 10, 00) correspond to 4 time intervals A, B, C, and D, respectively. In the time interval A, the level of the voltage VOUTA is high and the level of the voltage VOUTB is low (i.e. the combination of the first logic value L1and the second logic value L2is 10). In the time interval B, both of the levels of the voltages VOUTA and VOUTB are high (i.e. the combination of the first logic value L1and the second logic value L2is 11). In the time interval C, the level of the voltage VOUTA is high and the level of the voltage VOUTB is low (i.e. the combination of the first logic value L1and the second logic value L2is 10). In the time interval D, both of the levels of the voltages VOUTA and VOUTB are low (i.e. the combination of the first logic value L1and the second logic value L2is 00). In addition, as shown inFIG.5, the current sensing signal Isen are sampled and held only during the time interval D according to the control signal CS′. For brevity, similar descriptions for this embodiment are not repeated in detail here.

FIG.6is a flow chart illustrating a method for generating a current sampling signal of a loudspeaker according to another embodiment of the present invention. Provided that the result is substantially the same, the steps are not required to be executed in the exact order shown inFIG.6. For example, the method shown inFIG.6may be employed by the driving circuit40shown inFIG.4.

In Step S600, the triangle wave signal TRI is generated.

In Step S602, the pre-driving signal PDRV is generated according to the audio input signals A_IN andA_INand the triangle wave signal TRI, wherein the audio input signalA_INis an inverse of the audio input signal A_IN.

In Step S604, the loudspeaker41is driven by the class-D amplifier circuit404, according to the pre-driving signal PDRV.

In Step S606, the driving current of the loudspeaker41is sensed to generate the current sensing signal Isen.

In Step S608, the control signal CS′ is generated according to the pre-driving signal PDRV.

In Step S610, the current sensing signal Isen is sampled and held according to the control signal CS′, to generate the first current sampling signal F_Isam.

In Step S612, the second current sampling signal S Isam of the loudspeaker41is generated by performing average value computation upon the first current sampling signal F_Isam.

Since a person skilled in the pertinent art can readily understand details of the steps after reading above paragraphs directed to the driving circuit40shown inFIG.4, further description is omitted here for brevity.

FIG.7is a diagram illustrating frequency-domain analysis for a sensing voltage signal V_AB, a sampling voltage signal V_ABS generated by the driving circuit10shown inFIG.1, and a voltage signal VAB_LP generated by a low pass filter. It is assumed that a voltage at a node between the switch circuit120and the current sensing resistor124is a sensing voltage VSENSEA, and a voltage at a node between the switch circuit122and the current sensing resistor126is a sensing voltage VSENSEB. The sensing voltage signal V_AB is a voltage difference between the sensing voltage VSENSEA and the sensing voltage VSENSEB. In addition, the sensing voltage signal V_AB is generated under a condition that the current sensing resistor124and the current sensing resistor126are matching (i.e. resistance values of the current sensing resistors124and126are the same).

The sampling voltage signal V_ABS may be generated by the driving circuit10shown inFIG.1, and may correspond to the current sampling signal Isam. The current sensing circuit105shown inFIG.1may be modified to be coupled to a low pass filter, instead of the sampling and hold circuit106, such that the voltage signal VAB_LP may be generated by directly low pass filtering the current sensing signal Isen. It should be noted that the sampling voltage signal V_ABS and the voltage signal VAB_LP are generated under a condition that the current sensing resistor124and the current sensing resistor126are not matching (i.e. resistance values of the current sensing resistors124and126are different; for example, the resistance value of the current sensing resistor124is 0.1 ohm, and the resistance value of the current sensing resistor126is 0.2 ohm). As shown inFIG.7, since the current sensing resistor124and the current sensing resistor126are matching, the sensing voltage signal V_AB has a better second-order harmonic distortion at 2000 Hz. On the other hand, due to the resistor mismatch, the voltage signal VAB_LP has a poor harmonic distortion at 2000 Hz. However, despite the resistor mismatch, the sampling voltage signal V_ABS still has a better second-order harmonic distortion at 2000 Hz. As a result, the driving circuit10provided by the present invention may improve the second-order harmonic distortion.