KR101818459B1 - Driving circuit of liquid crystal device for a smart tv and method for driving the same - Google Patents

Abstract

The present invention relates to a driving apparatus for a liquid crystal display for a smart TV and a driving method thereof, which can reduce the overall power consumption by adjusting the luminance of light emitted from the backlight unit in accordance with the characteristics of a displayed image, A liquid crystal panel formed with a pixel region; A data driver for driving data lines of the liquid crystal panel; A gate driver for driving gate lines of the liquid crystal panel; A timing controller for aligning image data input from the outside and supplying the data to the data driver and generating a gate and a data control signal to control the gate and the data driver; And an image analyzing unit for controlling light brightness of the backlight unit in response to an analysis result in response to a graphic mode signal supplied from an external system or analyzing image data aligned from the timing controller, And the light luminance is varied in units of at least one frame period in response to the luminance control signal input from the image analysis unit, and the light is irradiated to the liquid crystal panel.

Description

TECHNICAL FIELD [0001] The present invention relates to a driving apparatus for a liquid crystal display device for a smart TV and a driving method thereof. BACKGROUND OF THE INVENTION 1. Field of the Invention [0002]

The present invention relates to a liquid crystal display device, and more particularly, to a driving device for a smart TV liquid crystal display device which can reduce the overall power consumption by adjusting the luminance of light emitted from the backlight unit in accordance with the characteristics of an image to be displayed, Driving method.

2. Description of the Related Art Recently, various types of image display devices have emerged as means for variously touching digital contents. The most commonly used image display devices are flat panel display devices such as a liquid crystal display device, an organic light emitting display device, a field emission display device ) And a plasma display panel (PDP) are mainly used. The liquid crystal display device displays an image by adjusting the light transmittance of each pixel through a plurality of pixels arranged on the display panel.

In the liquid crystal display device, the amount of light transmitted from a backlight unit is controlled by a liquid crystal panel having a plurality of liquid crystal cells arranged in a matrix form to display a desired image on a screen. Specifically, a liquid crystal display device obtains a desired image by forming an electric field in a liquid crystal layer according to an image data signal to adjust the transmittance of light passing through the liquid crystal layer.

In recent years, a liquid crystal display device has been applied to a smart TV, which is a means of accessing a variety of digital contents. In this way, a liquid crystal display device is applied to a smart TV, .

BACKGROUND ART [0002] Since conventional TVs mainly display images on a video basis, backlight units provided in a TV liquid crystal display device must continuously irradiate the liquid crystal panels with a maximum amount of high luminance light during a period of displaying an image. Therefore, the power consumption of the liquid crystal display devices for TV is very large.

However, when a liquid crystal display device is applied to a smart TV, since various types of still images such as an internet screen and an application program can be continuously displayed in addition to moving pictures, the backlight unit also needs to continuously examine only the high- I will not. Therefore, there is a need for a power consumption reduction method of a liquid crystal display device, particularly a backlight unit, applied to a smart TV.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems and it is an object of the present invention to provide a driving apparatus for a smart TV liquid crystal display device capable of reducing the overall power consumption by adjusting the brightness of light emitted from the backlight unit, And a driving method thereof.

According to an aspect of the present invention, there is provided a liquid crystal display device for a smart TV, including: a liquid crystal panel having a plurality of pixel regions; A data driver for driving data lines of the liquid crystal panel; A gate driver for driving gate lines of the liquid crystal panel; A timing controller for aligning image data input from the outside and supplying the data to the data driver and generating a gate and a data control signal to control the gate and the data driver; And an image analyzing unit for controlling light brightness of the backlight unit in response to an analysis result in response to a graphic mode signal supplied from an external system or analyzing image data aligned from the timing controller, And the light luminance is varied in units of at least one frame period in response to the luminance control signal input from the image analysis unit, and the light is irradiated to the liquid crystal panel.

The image analyzing unit generates a luminance control signal including an amplitude control signal when the graphic mode signal is input as a still image mode signal or the analysis result of the aligned image data is analyzed as a still image, And supplies a luminance control signal including a dimming control signal to the backlight unit when the graphic mode signal is input as a moving picture mode signal or the analysis result of the aligned picture data is analyzed as a moving picture .

Wherein the backlight unit generates and outputs an amplitude modulation signal when the luminance control signal input from the image analysis unit includes the amplitude control signal and outputs the pulse width modulation signal when the luminance control signal includes the dimming control signal An inverter for generating and outputting a drive signal in the form of a direct current or an alternating current whose amplitude or pulse width is respectively modulated in response to the amplitude modulation signal or the pulse width modulation signal; And a backlight that includes a plurality of light sources and an optical unit that improves efficiency of light incident from each light source, and generates light in accordance with a driving signal input from the inverter.

Wherein the inverter control unit fixes the duty ratio when the amplitude modulation signal is generated at a fixed rate of 100% per frame and outputs the duty ratio when the amplitude modulation signal is generated, And the amplitude of the amplitude modulated signal is generated so as to have a width smaller than that of the pulse width modulated signal.

Wherein the inverter generates a direct current or alternating current drive signal having a voltage level preset to correspond to a duty ratio of the input pulse width modulation signal when the pulse width modulation signal is input, Each generating a drive signal of a predetermined level of direct current or alternating current so as to respectively correspond to a 100% duty ratio of the modulated signal, wherein the amplitude modulated signal is generated at a lower voltage level than the pulse width modulated signal, The voltage level of the drive signal of the generated direct current or alternating current is generated at a level lower than the voltage level of the drive signal of direct current or alternating current generated according to the pulse width modulation signal.

According to an aspect of the present invention, there is provided a method of driving a liquid crystal display device for a smart TV, including a liquid crystal panel, a gate and a data driver for driving the liquid crystal panel, and a timing controller And a controller for controlling the brightness of the backlight unit in response to an analysis result in response to a graphic mode signal supplied from an external system or analysis of image data aligned from the timing controller, And a step of varying the light luminance in units of at least one frame period in response to the luminance control signal input from the image analysis unit and irradiating the light to the liquid crystal panel.

The step of controlling the optical brightness of the backlight unit may include generating a luminance control signal including an amplitude control signal when the graphic mode signal is input as a still image mode signal or the analysis result of the aligned image data is analyzed as a still image And supplying the luminance control signal including the dimming control signal to the backlight unit when the graphic mode signal is input as a moving picture mode signal or the analysis result of the aligned image data is analyzed as moving picture, And is supplied to the backlight unit.

The step of irradiating light to the liquid crystal panel may include generating and outputting an amplitude modulation signal when the luminance control signal includes the amplitude control signal and generating a pulse width modulation signal when the luminance control signal includes the dimming control signal Generating and outputting a drive signal of a DC or AC type in which the amplitude or the pulse width is respectively modulated in response to the amplitude modulation signal or the pulse width modulation signal; And generating light according to the direct current or alternating current driving signal to irradiate light to the liquid crystal panel.

Wherein the step of generating and outputting the pulse width modulated signal comprises the step of outputting the duty ratio of the amplitude modulated signal at a constant value of 100% for each frame when the amplitude modulated signal is generated, And outputs a signal having a duty ratio that is greater than 30% and less than 100% depending on the characteristics, and the amplitude of the amplitude modulated signal is generated to have a smaller width than the pulse width modulated signal.

The step of generating light according to the direct current or alternating current driving signal may include generating a direct current or alternating current driving signal of a voltage level preset to correspond to the duty ratio of the input pulse width modulated signal when the pulse width modulated signal is inputted And generates a DC or AC drive signal of a predetermined level to correspond to the 100% duty ratio of the input amplitude modulated signal when the amplitude modulated signal is input, wherein the amplitude modulated signal is lower than the pulse width modulated signal The voltage level of the driving signal of the DC or AC generated in accordance with the amplitude modulation signal generated at the voltage level is generated at a level lower than the voltage level of the driving signal of the DC or AC generated in accordance with the pulse width modulation signal .

The apparatus and method for driving a liquid crystal display for a smart TV according to an embodiment of the present invention having the above-described technical features can adjust the brightness of light emitted from a backlight unit according to characteristics of a displayed image, Can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram illustrating a driving apparatus for a smart TV liquid crystal display according to an embodiment of the present invention; FIG.
FIG. 2 is a view showing a luminance control signal output from the image analyzing unit of FIG. 1 according to image display modes; FIG.
3 is a waveform diagram showing driving signals of a backlight unit input / output in a moving image mode;
4 is a waveform diagram showing driving signals of a backlight unit input / output in a still image mode;

Hereinafter, a driving apparatus for a smart TV liquid crystal display device and a driving method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a driving apparatus for a smart TV liquid crystal display according to an embodiment of the present invention.

The driving apparatus for a smart TV liquid crystal display shown in FIG. 1 includes a liquid crystal panel 2 formed with a plurality of pixel regions; A data driver 4 for driving the data lines DL1 to DLm of the liquid crystal panel 2; A gate driver 6 for driving the gate lines GL1 to GLn of the liquid crystal panel 2; A timing controller 8 for controlling the gate and data drivers 6 and 4 by generating gate and data control signals GCS and GCS while supplying image data RGB inputted from the outside to the data driver 4 ); And controlling the light luminance of the backlight unit 18 in response to the analysis result of analyzing the image data (MData) aligned from the timing controller 8 or in response to the graphic mode signals DM and SM supplied from the external system And an image analyzing unit 11 for analyzing the image. The backlight unit 18 changes the light luminance in units of at least one frame period in response to the luminance control signal input from the image analysis unit 11 and irradiates the liquid crystal panel 2 with the light luminance.

The liquid crystal panel 2 includes a thin film transistor (TFT) formed in each pixel region defined by a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm, and a liquid crystal capacitor (Clc). The liquid crystal capacitor Clc is composed of a pixel electrode connected to the TFT, and a common electrode facing the pixel electrode and the liquid crystal. The TFT supplies a video signal from each of the data lines DL1 to DLm to the pixel electrode in response to a scan pulse from each of the gate lines GL1 to GLn. The liquid crystal capacitor Clc charges the difference voltage between the video signal supplied to the pixel electrode and the common voltage supplied to the common electrode, and adjusts the light transmittance by varying the arrangement of the liquid crystal molecules according to the difference voltage. The storage capacitor Cst is connected in parallel to the liquid crystal capacitor Clc so that the voltage charged in the liquid crystal capacitor Clc is maintained until the next data signal is supplied. The storage capacitor Cst is formed by overlapping the pixel electrode with the previous gate line and the insulating film interposed therebetween. Alternatively, the storage capacitor Cst may be formed by overlapping the pixel electrode with the storage line and the insulating film interposed therebetween.

The gate driver 6 outputs a gate control signal GCS from the timing controller 8, for example, a gate start pulse GSP, a gate shift clock GSC, a gate output enable Sequentially generates a scan pulse in response to a Gate Output Enable (GOE) signal, and sequentially supplies the scan pulse to the gate lines GL1 to GLn. In other words, the gate driver 6 shifts the GSP from the timing controller 8 according to the GSC to sequentially supply a scan pulse, for example, a gate-on voltage to the gate lines GL1 to GLn. Then, the gate-off voltage is supplied during the period when the gate-on voltage is not supplied to the gate lines GL1 to GLn. Here, the gate driver 6 controls the pulse width of the scan pulse in accordance with the GOE signal.

The data driver 4 receives a data control signal DCS from the timing controller 8, for example, a source start pulse SSP, a source shift clock SSC, a source output enable SOE (Source Output Enable) signal from the timing controller 8 to an analog voltage, that is, a video signal. Specifically, the data driver 4 latches the data (Data) subjected to the gamma conversion through the timing controller 8 in accordance with the SSC, and supplies a scan pulse to each of the gate lines GL1 to GLn in response to the SOE signal And supplies a video signal for one horizontal line to each of the data lines DL1 to DLm for every one horizontal period to be supplied. At this time, the data driver 4 selects a positive or negative gamma voltage having a predetermined level according to the gradation value of the aligned data Data, and outputs the selected gamma voltage to each of the data lines DL1 to DLm Supply.

The timing controller 8 arranges image data (RGB) input from an external system, for example, a TV system or a video card, so as to be suitable for driving the liquid crystal panel 2, and supplies the image data to the data driver 4. The gate and data control signals GCS and DCS are generated using at least one of a synchronizing signal input from the outside, that is, a dot clock DCLK, a data enable signal DE, and horizontal and vertical synchronizing signals Hsync and Vsync. And controls the gate and data drivers 6 and 4 by supplying them to the gate and data drivers 6 and 4, respectively.

The image analyzing unit 11 receives the graphic mode signals DM and SM supplied from the external system, for example, a still picture mode signal SM such as an internet screen or an application program screen, a moving picture mode signal (Dim, Aim) for controlling the light luminance of the backlight unit 18 in response to each of the luminance control signals DM. At this time, the generated luminance control signals (Dim, Aim) are supplied to the backlight unit (18).

On the other hand, the image analyzing unit 11 analyzes the supplied image data (MData) supplied from the timing controller 8 to receive the aligned image data (MData) A moving picture such as a movie or a TV program screen can be analyzed. A luminance control signal (Dim, Aim) for controlling the light luminance of the backlight unit (18) can be generated and supplied to the backlight unit (18) according to the analysis result. Specifically, the image analyzing unit 11 stores image data (MData) arranged in units of at least one frame and compares them with each other in at least one frame unit, thereby counting the same number of frames, Or at least one frame. The luminance control signal (Dim, Aim) is generated according to the analysis result. Here, the luminance control signal (Dim, Aim) is a control signal for controlling the luminance of light generated by controlling the light generation method of the backlight unit. The luminance control signals Dim and Aim may include a dimming control signal or an amplitude control signal.

FIG. 2 is a diagram showing a luminance control signal output from the image analysis unit of FIG. 1 according to image display modes.

Referring to FIG. 2, the image analyzer 11 receives the graphic mode signals DM and SM as a still image mode signal SM or analyzes the result of the aligned image data MData as a still image (Static Mode), the luminance control signal Aim including the amplitude control signal is supplied to the backlight unit 18 in at least one frame unit.

When the graphic mode signal is input as the moving picture mode signal DM or the analysis result of the aligned picture data MData is analyzed as a moving picture (Dynamic Mode), the luminance control signal Dim including the dimming control signal And supplies it to the backlight unit 18.

2, the luminance control signal Dim may further include an address and a size of the liquid crystal panel 2 in addition to the amplitude control signal and the pulse width control signal. The amplitude control signal and the pulse width control signal .

The backlight unit 18 varies the light luminance in units of at least one frame period in response to the luminance control signal (Dim, Aim) input from the image analysis unit 11, and irradiates the liquid crystal panel 2 with the light luminance. The backlight unit 18 generates pulse width modulation (PWM) signals and amplitude modulation (PAM) signals in response to the luminance control signals (Dim, Aim) input from the image analysis unit 11 do. And generates light corresponding to the PWM signal or the PAM signal.

More specifically, the backlight unit 18 shown in FIG. 1 generates and outputs an amplitude modulation (PAM) signal when the luminance control signal (Dim, Aim) input from the image analysis unit 11 includes an amplitude control signal An inverter control section 14 for generating and outputting a pulse width modulation (PWM) signal when the luminance control signal (Dim, Aim) includes a dimming control signal, an amplitude modulation (PAM) signal or a pulse width modulation An inverter 16 for generating and outputting a drive signal ADS of a DC or AC (AC / DC) type modulated in amplitude or pulse width in response to the drive signal ADS; And a backlight 12 having a plurality of light sources and an optical unit for improving efficiency of light incident from each light source and generating light in accordance with a driving signal ADS input from the inverter 16. [

FIG. 3 is a waveform diagram showing driving signals of a backlight unit input / output in a moving picture mode, and FIG. 4 is a waveform diagram showing driving signals of a backlight unit input / output in a still picture mode.

The driving method of the backlight unit will be described in detail with reference to FIG. 1 and FIG. 3 and FIG. 4, respectively.

The inverter control unit 14 includes an inverter control IC and switching circuits which are not shown and controls an amplitude modulation (PAM) signal or a pulse width modulation (PWM) signal according to a luminance control signal (Dim, Aim) (PWM) signal.

More specifically, when the luminance control signal (Dim, Aim) input from the image analysis unit 11 includes the amplitude control signal, the inverter control unit 14 generates an amplitude modulation (PAM) signal Respectively. When the luminance control signals (Dim, Aim) include a dimming control signal, a pulse width modulation (PWM) signal is generated and outputted as shown in Fig. here,

The inverter control unit 14 outputs a fixed duty ratio (Duty Ratio) of 100% for every frame when generating an amplitude modulation (PAM) signal and outputs the fixed image data (Duty Ratio) of more than 30% and less than 100% according to the brightness characteristic of the MData. Here, the amplitude of the amplitude modulation (PAM) signal may be generated to have a smaller width than the pulse width modulation (PWM) signal. On the other hand, at the time of generation of the pulse width modulation (PWM) signal, the duty ratio of the dark image is smaller and the duty ratio of the bright image is larger according to the brightness characteristics of the aligned image data (MData) .

The inverter 16 generates a DC or AC drive signal DC / AC_ADS for driving the plurality of lamps in response to the amplitude modulation (PAM) signal or the pulse width modulation (PWM) signal, , The inverter 16 generates driving signals ADS each of which has an amplitude or a pulse width modulated in accordance with the amplitude modulation (PAM) signal or the pulse width modulation (PWM) signal.

3, when the pulse width modulation (PWM) signal is inputted, the inverter 16 generates a direct current or alternating current (AC) of a predetermined voltage level corresponding to the duty ratio of the input pulse width modulation (DC / AC_ADS), respectively. 4, when the amplitude modulation (PAM) signal is inputted, a DC or AC drive signal DC / AC_ADS of a preset level corresponding to 100% of the inputted amplitude modulation (PAM) Respectively. At this time, the amplitude modulation signal is generated at a lower voltage level than the pulse width modulation signal, and the voltage level of the DC or AC drive signal (DC / AC_ADS) generated in accordance with the amplitude modulation (PAM) Is generated at a level lower than the voltage level (e.g., 65mA) of the DC or AC drive signal DC / AC_ADS generated according to the pulse width modulation (PWM) signal. Accordingly, when a still image is displayed, the driving signal voltage level of the lamps is set to be low, so that the power consumption can be reduced more than in the moving image display mode.

The backlight 12 includes a plurality of light sources and an optical unit for improving the efficiency of light incident from each light source to generate light in accordance with a direct current or AC drive signal AC / DC_ADS from the inverter 16. [ Here, a plurality of fluorescent lamps may be used as a plurality of light sources, but at present, a light emitting diode is mainly used. These light sources are driven by the AC drive signal AC_ADS or the DC drive signal DC_ADS from the inverter 16 to generate light. The backlight 12 simultaneously or sequentially turns on / off the plurality of light sources according to the DC or AC drive signals DC / AC_ADS to generate light. In addition, the optical unit diffuses and condenses the incident light from the light source to improve the light efficiency.

As described above, the driving apparatus and the driving method of a liquid crystal display for a smart TV according to an embodiment of the present invention are applied to a backlight unit in real time in accordance with the characteristics of a displayed image, Thereby adjusting the luminance of the light. In particular, when a still image such as an internet display screen or an application program screen is displayed rather than a moving picture such as a movie or a TV image, the power consumption of the backlight unit 18 can be reduced.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Will be apparent to those of ordinary skill in the art.

Claims (10)

A liquid crystal panel formed with a plurality of pixel regions;
A data driver for driving data lines of the liquid crystal panel;
A gate driver for driving gate lines of the liquid crystal panel;
A timing controller for aligning image data input from the outside and supplying the data to the data driver and generating a gate and a data control signal to control the gate and the data driver; And
And an image analysis unit for controlling the light luminance of the backlight unit in response to the analysis result obtained by analyzing the image data sorted by the timing controller or in response to the graphic mode signal supplied from the external system,
Wherein the backlight unit varies light luminance in units of at least one frame period in response to a luminance control signal input from the image analysis unit and irradiates the liquid crystal panel to the liquid crystal panel. As a result,
The image analysis unit
When the graphic mode signal is input as a still image mode signal or the analysis result of the aligned image data is analyzed as a still image, a luminance control signal including an amplitude control signal for amplitude modulation is generated, Light unit,
And a luminance control signal including a dimming control signal for pulse width modulation is supplied to the backlight unit when the graphic mode signal is input as a moving picture mode signal or the analysis result of the aligned picture data is analyzed as a moving picture And a driving device for the liquid crystal display device for smart TV. delete The method according to claim 1,
The backlight unit
An inverter for generating and outputting an amplitude modulation signal when the luminance control signal input from the image analysis unit includes the amplitude control signal and generating and outputting a pulse width modulation signal when the luminance control signal includes the dimming control signal, The control unit,
An inverter for generating and outputting a driving signal of a DC or AC type in which the amplitude or the pulse width is respectively modulated in response to the amplitude modulation signal or the pulse width modulation signal; And
And a backlight which includes a plurality of light sources and an optical unit for improving the efficiency of light incident from each light source and generates light according to a driving signal input from the inverter. The method of claim 3,
The inverter control unit
Wherein the duty ratio of the amplitude modulation signal is fixed to 100% of every frame, and when the amplitude modulation signal is generated, the duty ratio is greater than 30% and less than 100% So that the duty ratio is set to a predetermined value,
And the amplitude of the amplitude modulation signal is generated to have a smaller width than the pulse width modulation signal. 5. The method of claim 4,
The inverter
When the pulse width modulation signal is input, generating a direct current or alternating current drive signal having a preset voltage level corresponding to the duty ratio of the input pulse width modulation signal,
When the amplitude modulation signal is input, generates a direct current or alternating current drive signal of a predetermined level corresponding to the 100% duty ratio of the input amplitude modulated signal,
Wherein the amplitude modulation signal is generated at a lower voltage level than the pulse width modulation signal so that the voltage level of the drive signal of the direct current or alternating current generated in accordance with the amplitude modulation signal is driven by a direct current or alternating current generated according to the pulse width modulation signal Signal is generated at a level lower than the voltage level of the signal. A method of driving a liquid crystal display device for a smart TV having a liquid crystal panel, a gate and a data driver for driving the liquid crystal panel, and a timing controller for controlling the gate and the data driver,
Controlling light brightness of the backlight unit in response to an analysis result in response to a graphic mode signal supplied from an external system or analyzing image data aligned from the timing controller,
And a step of varying the light luminance in units of at least one frame period and irradiating the light to the liquid crystal panel in response to an input luminance control signal from the image analysis unit,
The step of controlling the light luminance of the backlight unit
When the graphic mode signal is input as a still image mode signal or the analysis result of the aligned image data is analyzed as a still image, a luminance control signal including an amplitude control signal for amplitude modulation is generated, Light unit,
And a luminance control signal including a dimming control signal for pulse width modulation is supplied to the backlight unit when the graphic mode signal is input as a moving picture mode signal or the analysis result of the aligned picture data is analyzed as a moving picture And a driving method of the liquid crystal display device for a smart TV. delete The method according to claim 6,
The step of irradiating light to the liquid crystal panel
Generating and outputting an amplitude modulation signal when the luminance control signal includes the amplitude control signal, generating and outputting a pulse width modulation signal when the luminance control signal includes the dimming control signal,
Generating and outputting a driving signal of a DC or AC type in which the amplitude or the pulse width is respectively modulated in response to the amplitude modulation signal or the pulse width modulation signal; And
And generating light according to the direct current or alternating current driving signal to irradiate light to the liquid crystal panel. 9. The method of claim 8,
The step of generating and outputting the pulse width modulated signal
Wherein the duty ratio of the amplitude modulation signal is fixed to 100% of every frame, and when the amplitude modulation signal is generated, the duty ratio is greater than 30% and less than 100% So that the duty ratio is set to a predetermined value,
Wherein the amplitude of the amplitude modulated signal is generated to have a smaller width than the pulse width modulated signal. 10. The method of claim 9,
The step of generating light in accordance with the direct current or alternating current driving signal
When the pulse width modulation signal is input, generating a direct current or alternating current drive signal having a preset voltage level corresponding to the duty ratio of the input pulse width modulation signal,
When the amplitude modulation signal is input, generates a direct current or alternating current drive signal of a predetermined level corresponding to the 100% duty ratio of the input amplitude modulated signal,
Wherein the amplitude modulation signal is generated at a lower voltage level than the pulse width modulation signal so that the voltage level of the drive signal of the direct current or alternating current generated in accordance with the amplitude modulation signal is driven by a direct current or alternating current generated according to the pulse width modulation signal Signal is generated at a level lower than the voltage level of the signal.

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