KR101774559B1 - Liquid Crystal Display Device and Driving Method thereof - Google Patents

Abstract

An embodiment of the present invention is a liquid crystal display device comprising: a liquid crystal panel; A common voltage generator for supplying a common voltage to the liquid crystal panel; And a common voltage tracing unit for periodically analyzing and periodically analyzing the common voltage outputted from the common voltage generating unit and supplying a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generating unit according to the analysis result do.

Description

[0001] The present invention relates to a liquid crystal display device and a driving method thereof,

An embodiment of the present invention relates to a liquid crystal display and a driving method thereof.

As the information technology is developed, the market of display devices, which is a connection medium between users and information, is getting larger. Accordingly, a flat panel display (FPD) such as a liquid crystal display (LCD), an organic light emitting diode (OLED), and a plasma display panel (PDP) Usage is increasing. Among them, liquid crystal display devices capable of realizing high resolution and capable of not only miniaturization but also enlargement are widely used.

The liquid crystal display includes a transistor substrate on which a transistor, a storage capacitor, a pixel electrode, and the like are formed, and a liquid crystal layer disposed between the color filter substrate and the color filter substrate on which the color filter and the black matrix are formed. The liquid crystal display displays images in such a manner that light incident from the backlight unit is emitted by adjusting the arrangement direction of the electric field liquid crystal layer formed on the pixel electrode, the transistor substrate, or the common electrode formed on the color filter substrate.

The liquid crystal display device functions as a voltage for driving the liquid crystal, the difference between the data voltage supplied from the data driver and the common voltage serving as the reference potential. The common voltage varies depending on the position of the liquid crystal panel due to the influence of the wiring resistance and the capacitor formed in the liquid crystal panel. That is, the common voltage is one of the voltages having the greatest influence over the entire liquid crystal panel.

Conventional liquid crystal display devices use only a common voltage initially set by a fixed common voltage. Thus, the common voltage is fixed to have a constant voltage range by the power supply unit. Accordingly, it is generalized that common voltage is set as a driving condition of a model by selecting an appropriate common voltage while setting flicker and gray every time when a new model is developed.

Therefore, in the conventional liquid crystal display device, due to the fixed common voltage setting and the difference of the parasitic capacitors due to the process variation, there may be a large variation in the voltage of DELTA Vp depending on the product and as a result, there is a difference in the average voltage stored in the storage capacitor do. In addition, in the conventional liquid crystal display device, flicker is generated, and a DC (DC) after-image is generated due to occurrence of fluctuation of a common voltage.

According to an embodiment of the present invention for solving the problems of the background art described above, a common voltage tracking unit can be used to automatically control a fluctuation amount in which a common voltage fluctuates according to a process variation and a service life, DC) residual image in a liquid crystal display device.

According to an embodiment of the present invention, there is provided a liquid crystal display device comprising: a liquid crystal panel; A common voltage generator for supplying a common voltage to the liquid crystal panel; And a common voltage tracing unit for periodically analyzing and periodically analyzing the common voltage outputted from the common voltage generating unit and supplying a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generating unit according to the analysis result do.

The common voltage tracking unit includes at least two capacitors for dividing the common voltage output from the common voltage generating unit and a control unit for analyzing the voltage divided by at least two capacitors to find a variation value proportional to the variation of the common voltage, And outputting a constant voltage proportional to the value of the reference voltage.

The at least two capacitors may have a constant ratio of capacitance to the capacitance of the capacitor formed by the common voltage line located in the display region of the liquid crystal panel.

A dummy capacitor for stabilizing a constant voltage output from the common voltage tracking unit and a common voltage supplied to the liquid crystal panel may be further formed outside the display region of the liquid crystal panel.

The common voltage tracing unit can divide the common voltage and analyze it in units of at least one frame and supply a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generating unit according to the analysis result.

The common voltage tracking unit includes a first capacitor and a second capacitor for dividing the common voltage outputted from the common voltage generating unit, a first switch for switching to read the voltage divided by the first and second capacitors, A control unit for analyzing the divided voltage supplied through the converting unit to find a variation value proportional to the variation of the common voltage; A reference voltage generator for outputting a constant voltage proportional to a variation of the common voltage, and a second switch for switching the constant voltage output from the reference voltage generator to be supplied to the output terminal of the common voltage generator.

The reference voltage generating unit may vary the output level of the constant voltage according to the variation value supplied from the control unit.

The common voltage tracing unit may further include an output buffer unit formed between the reference voltage generating unit and the second switch.

According to another aspect of the present invention, there is provided a method of driving a liquid crystal display device, comprising: dividing a common voltage output from a common voltage generating unit for supplying a common voltage to a liquid crystal panel; Converting the divided voltage into a digital signal; Analyzing the divided voltage to find a variation value proportional to the variation of the common voltage; And outputting a constant voltage proportional to a variation of the common voltage based on the variation value.

The driving method of the liquid crystal display device can divide the common voltage and analyze it in units of at least one frame and supply a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generating part according to the analysis result.

The embodiment of the present invention provides an effect of providing a liquid crystal display device capable of automatically compensating for fluctuations in which the common voltage fluctuates in accordance with process variation and lifetime by using the common voltage tracing unit to compensate for flicker and residual afterglow have. In addition, the present invention solves the problem of life span and image quality while minimizing the additional cost due to the device configuration by additionally providing at least two capacitors outside the liquid crystal panel and including the function of the common voltage tracer in one IC There is provided an advantageous effect of providing a liquid crystal display device.

1 is a block diagram of a liquid crystal display according to an embodiment of the present invention;
2 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention;
FIG. 3 is a flow chart for explaining the operation of the common voltage tracking unit shown in FIG. 2. FIG.
4 is a configuration diagram of a liquid crystal display device according to another embodiment of the present invention.
5 is a plan view of a liquid crystal panel showing an example of a position where the dummy capacitors shown in FIG. 4 are formed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a liquid crystal display device according to an embodiment of the present invention.

1, a liquid crystal display according to an exemplary embodiment of the present invention includes a timing controller TCN, a liquid crystal panel PNL, a gate driver SDRV, a data driver DDRV, a backlight unit BLU, A power supply unit PWR and a common voltage tracking unit TRC.

The timing control unit TCN receives a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, a clock signal CLK and a data signal DATA from the outside. The timing controller TCN controls the data driver DDRV and the data driver DDRV using timing signals such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, and a clock signal CLK. And controls the operation timing of the driving unit SDRV. Also, the timing control unit TCN varies the level of the common voltage output from the programmable power supply unit PWR by the position of the liquid crystal panel PNL using the power supply control signal PSC. The timing control unit TCN can determine the frame period by counting the data enable signal DE in one horizontal period so that the vertical synchronization signal Vsync and the horizontal synchronization signal Hsync supplied from the outside can be omitted. The control signals generated by the timing controller TCN include a gate timing control signal GDC for controlling the operation timing of the gate driver SDRV and a data timing control signal DDC for controlling the operation timing of the data driver DDRV. ) May be included. The gate timing control signal GDC includes a gate start pulse GSP, a gate shift clock GSC and a gate output enable signal GOE. The gate start pulse GSP is supplied to a gate drive IC (Integrated Circuit) generating the first gate signal. The gate shift clock GSC is a clock signal commonly input to the gate drive ICs, and is a clock signal for shifting the gate start pulse GSP. The gate output enable signal GOE controls the output of the gate drive ICs. The data timing control signal DDC includes source start pulses (Source, Start Pulse, SSP), Source Sampling Clock (SSC), Source Output Enable (SOE), and the like. The source start pulse SSP controls the data sampling start timing of the data driver DDRV. The source sampling clock SSC is a clock signal for controlling the sampling operation of data in the data driver DDRV based on the rising or falling edge. The source output enable signal SOE controls the output of the data driver DDRV. On the other hand, the source start pulse SSP supplied to the data driver DDRV may be omitted depending on the data transfer method.

The liquid crystal panel PNL includes sub-pixels SP arranged in a matrix form including a liquid crystal layer positioned between a thin film transistor substrate (hereinafter abbreviated as TFT substrate) and a color filter substrate. Data lines DL, gate lines GL, TFTs, storage capacitors, and the like are formed on the TFT substrate, and black matrices, color filters, and the like are formed on the color filter substrate. One subpixel SP is defined by a data line D1 and a gate line G1 intersecting with each other. One subpixel SP includes a TFT driven by a gate signal supplied through a gate line G1, a storage capacitor Cst for storing a data signal supplied through a data line D1 as a data voltage, And a liquid crystal cell Clc driven by the data voltage stored in the data line Cst. The liquid crystal cell Clc is driven by the data voltage supplied to the pixel electrode 1 and the common voltage supplied to the common electrode 2. [ The common electrode 2 is formed on a color filter substrate in a vertical field driving mode such as a TN (Twisted Nematic) mode and a VA (Vertical Alignment) mode. Is formed on the TFT substrate together with the pixel electrode 1 in the same horizontal electric field driving system. The common electrode 2 is supplied with a common voltage from the common voltage line VCOM. A polarizing plate is attached to the TFT substrate of the liquid crystal panel (PNL) and the color filter substrate, and an alignment film for setting a pre-tilt angle of the liquid crystal is formed. The liquid crystal mode of the liquid crystal panel PNL can be implemented in any liquid crystal mode as well as the TN mode, VA mode, IPS mode, and FFS mode described above.

The gate driver SDRV is responsive to the gate timing control signal GDC supplied from the timing controller TCN to switch the gate driver control voltage GDC in accordance with the swing width of the gate drive voltage at which the TFTs of the subpixels SP included in the liquid crystal panel PNL are operable And sequentially generates the gate signal while shifting the level of the signal. The gate driver SDRV supplies the gate signal generated through the gate lines GL to the sub-pixels SP included in the liquid crystal panel PNL. The gate driver SDRV may be mounted on the liquid crystal panel PNL in the form of an integrated circuit (IC) or may be formed on the liquid crystal panel PNL in the form of a gate in panel (GIP).

The data driver DDRV samples and latches the data signal DATA supplied from the timing control unit TCN in response to the data timing control signal DDC supplied from the timing control unit TCN and converts the sampled data signal into data of a parallel data system . The data driver DDRV converts the data signal DATA into a gamma reference voltage when converting into data of a parallel data system. The data driver DDRV supplies the data signal DATA converted through the data lines DL to the sub-pixels SP included in the liquid crystal panel PNL. The data driver DDRV may be mounted on the liquid crystal panel PNL in the form of an IC or may be formed on the liquid crystal panel PNL in the form of a gate in panel (GIP).

The backlight unit (BLU) provides light to the liquid crystal panel (PNL). The backlight unit BLU includes a light source for emitting light, a light guide plate for guiding light to the liquid crystal panel PNL, an optical sheet for condensing and diffusing light, and the like.

The power supply unit PWR includes a gamma unit GMA that converts an input power supply Vin supplied from the outside to a DC power supply and outputs gamma voltages GMA0 through GMA7 and a common voltage generator Vcom that outputs a common voltage Vcom. ). The gamma voltages GMA0 to GMA7 output from the gamma unit GMA are supplied to the data driver DDRV and the common voltage Vcom output from the common voltage generator Vcom is supplied to the common voltage line VCOM. In addition, the power supply unit PWR may output a driving voltage for driving the gate driving unit SDRV and the data driving unit DDRV.

The common voltage tracing unit TRC divides and periodically analyzes the common voltage output from the common voltage generating unit Vcom and periodically analyzes a constant voltage proportional to the variation of the common voltage according to the analysis result to the output terminal of the common voltage generating unit Vcom Or the common voltage line VCOM. The common voltage tracking unit TRC supplies a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generation unit Vcom or the common voltage line VCOM to compensate for the fluctuated common voltage.

Hereinafter, the compensation of the common voltage using the common voltage tracking unit TRC will be described in more detail.

FIG. 2 is a configuration diagram of a liquid crystal display device according to an embodiment of the present invention, and FIG. 3 is a flowchart for explaining an operation of the common voltage tracking unit shown in FIG.

As shown in FIGS. 1 and 2, the common voltage tracking unit TRC includes at least two capacitors Ccom and Cload for dividing a common voltage output from the common voltage generating unit Vcom, and at least two capacitors And a reference voltage generator 130 for outputting a constant voltage proportional to the variation value. The reference voltage generator 130 generates a constant voltage proportional to the variation value. The control unit 120 determines a variation value proportional to the variation of the common voltage.

The common voltage tracing unit TRC divides the common voltage and analyzes it in units of at least one frame and outputs a constant voltage proportional to the variation of the common voltage to the output terminal of the common voltage generating unit Vcom or the common voltage line VCOM, .

The common voltage tracking unit TRC includes a first capacitor Ccom and a second capacitor Cload, a first switch SW1, a conversion unit 110, a control unit 120, a reference voltage generation unit 130, Part 140 and a second switch SW2.

The first capacitor Ccom and the second capacitor Cload serve to divide the common voltage output from the common voltage generating unit Vcom. The first capacitor Ccom and the second capacitor Cload may have a constant ratio of capacitance to the capacitance of the capacitor Cvcom formed by the common voltage line VCOM located in the display region of the liquid crystal panel PNL .

The first switch SW1 switches to read the voltage divided by the first capacitor Ccom and the second capacitor Cload. The first switch SW1 may be switched on / off by a control signal output from the timing control unit TCN or on / off switched by a control signal output from the control unit 120. [

The conversion unit 110 converts the divided voltage of the analog signal type read through the first switch SW1 into a digital signal. The conversion unit 110 converts an analog voltage to a DC voltage so that the controller 120 can analyze the voltage using the divided voltage read through the first switch SW1.

The control unit 120 analyzes the divided voltage of the digital signal supplied through the conversion unit 110 and finds a variation value proportional to a variation of the common voltage.

The reference voltage generator 130 outputs a constant voltage proportional to the variation of the common voltage based on the variation value supplied from the controller 120. The reference voltage generator 130 varies the output level of the constant voltage to be the compensation voltage according to the variation value supplied from the controller 120.

The output buffer unit 140 is formed between the reference voltage generator 130 and the second switch SW2 and serves as a buffer for controlling the output of a constant voltage output from the reference voltage generator 130. [

The second switch SW2 switches the constant voltage output from the reference voltage generator 130 to be supplied to the output terminal of the common voltage generator Vcom or the common voltage line VCOM. The second switch SW2 may be switched on / off by a control signal output from the timing control unit TCN or on / off switched by a control signal output from the control unit 120. [

As shown in FIGS. 1 to 3, the common voltage tracking unit TRC can operate in the following flow.

(S111) converts the divided voltage into a digital signal (S113). The divided voltage is supplied to the liquid crystal panel PNL. The divided voltage is divided by the common voltage output from the common voltage generating unit Vcom to supply the common voltage to the liquid crystal panel PNL. (S115) and outputs a constant voltage proportional to the variation of the common voltage based on the variation value (S117).

The common voltage tracing unit TRC divides the common voltage by at least one frame and analyzes a predetermined voltage proportional to the variation of the common voltage according to the analysis result to the output terminal of the common voltage generating unit Vcom or the output terminal of the common voltage generating unit Vcom And supplies it to the voltage line VCOM.

As described above, the common voltage tracking unit TRC reads a voltage divided by a predetermined time from the first capacitor Ccom and the second capacitor Cload connected to the output terminal of the common voltage generating unit Vcom, And to update it.

When the common voltage is varied in accordance with the process variation and the lifetime, the divided voltage of the analog form corresponding to the ratio of the first capacitor Ccom and the second capacitor Cload is turned on by the ON of the first switch SW1, (110). The divided voltage in the form of an analog signal input to the converter 110 is converted into a divided voltage in the form of a digital signal. The controller 120 analyzes the divided voltages in the form of a digital signal, finds a variation value proportional to the variation of the common voltage, and transmits the variation to the reference voltage generator 130. The reference voltage generator 130 changes the reference voltage based on the variation value and outputs a constant voltage based on the reference voltage. The constant voltage output from the reference voltage generator 130 is supplied to the output terminal of the common voltage generator Vcom or the common voltage line VCOM through the output buffer 140 and the second switch SW2.

In the embodiment, "Cvcom" means the capacitance of the capacitor Cvcom formed by the common voltage line VCOM located in the liquid crystal panel PNL. The degree of the capacitor Cvcom of the liquid crystal panel (PNL) is generally known at the time of designing. Since the output terminal of the common voltage generating unit Vcom has a characteristic of operating with a constant frequency, it can be regarded as having one large impedance. Accordingly, the first capacitor Ccom and the second capacitor Cload can be formed outside the liquid crystal panel PNL by using the characteristic having a constant frequency.

The capacitance of the capacitor Cvcom of the liquid crystal panel PNL is preferably not affected by the capacitances of the first capacitor Ccom and the second capacitor Cload. More specifically, since the first capacitor Ccom and the second capacitor Cload are connected in parallel, the capacitance of the capacitor Cvcom of the liquid crystal panel PNL in terms of the voltage of the output terminal of the total common voltage generator Vcom It is preferable to form it smaller. One of the first capacitor Ccom and the second capacitor Cload has a capacitance of 0.1 times the capacitance of the capacitor Cvcom of the liquid crystal panel PNL and the other of the capacitors Ccom and Cload is 10 times the capacitance of the capacitor Cvcom of the liquid crystal panel PNL . Then, since the capacitances of the first capacitor Ccom and the second capacitor Cload are reduced, the capacitance of the capacitor Cvcom of the liquid crystal panel PNL is not affected. Therefore, the capacitances of the first capacitor Ccom and the second capacitor Cload are set to 0.1 to 10 times the capacitance of the capacitor Cvcom of the liquid crystal panel PNL based on the above description.

Meanwhile, in the embodiment, the capacity can be set so that a large voltage is applied to both ends of the first capacitor Ccom due to voltage distribution in the impedance connection, and a small voltage is applied to both ends of the second capacitor Cload.

For example, assuming that the "CVcom" capacitance is 100 nF and the operating frequency is 100 KHz, the impedance of the "CVcom" capacitance is calculated to be approximately 159 ohms. If the capacitance of "CLoad" is the same as the capacity of "CVcom" and the impedance of "Ccom" is set to 10 times of the capacity of "CLoad", the value of "Ccom" capacity is calculated to be about 10nF do. Therefore, assuming that the voltage of "Vcom" is changed by 0.1 V, the voltage distribution of "Ccom" and the capacity of "CLoad" is 10: 1, so the voltage of "Vcom" is 90% 0.09V.

Therefore, by using the common voltage tracking unit (TRC), it is possible to predict how much the voltage changed by the ratio between the "Ccom" capacity and the "CLoad" capacity can be estimated. . The common voltage tracing unit TRC controls the ON / OFF time of the first switch SW1 and the second switch SW2 so that the voltage of the output voltage of the common voltage generator Vcom Can be determined.

FIG. 4 is a configuration diagram of a liquid crystal display device according to another embodiment of the present invention, and FIG. 5 is a plan view of a liquid crystal panel showing an example of a position where the dummy capacitors shown in FIG. 4 are formed.

4 and 5, the liquid crystal display according to another embodiment of the present invention includes a common voltage tracking unit (TRC) included in one embodiment. The common voltage tracking unit TRC includes a first capacitor Ccom and a second capacitor Cload, a first switch SW1, a conversion unit 110, a control unit 120, a reference voltage generation unit 130, Part 140 and a second switch SW2.

In the case of the common voltage tracking unit (TRC), it operates in the same manner and in the same manner as in the embodiment. However, the liquid crystal display according to another embodiment of the present invention further includes a dummy capacitor Cvc formed in a non-display area NA which is an outer edge of the display area AA of the liquid crystal panel. The dummy capacitor Cvc stabilizes the constant voltage output from the common voltage tracing unit TRC and the common voltage supplied to the liquid crystal panel PNL.

The dummy capacitor Cvc compensates for a problem due to the small capacitance of the first capacitor Ccom and the second capacitor Cload included in the common voltage tracing unit TRC. The output terminal of the voltage Vcom and the common voltage line Vcom are provided in parallel to prevent the voltage from being shaken. On the other hand, the common voltage output from the output terminal of the common voltage generating unit Vcom can be supplied to either or both of the liquid crystal panel PNL, such as Vcom1 and Vcom2. Here, "Cvcom" means the capacitance of the capacitor Cvcom formed by the common voltage line VCOM located in the liquid crystal panel PNL.

The present invention described above can be applied to a liquid crystal display device capable of compensating for a flicker and a DC afterglow by allowing a common voltage follower (TRC) to automatically follow a fluctuation amount in which a common voltage fluctuates according to process variation and lifetime . In addition, the present invention is characterized in that at least two capacitors are additionally provided outside the liquid crystal panel and the function of the common voltage tracking unit is included in one integrated circuit (IC) to minimize the additional cost due to the device configuration, There is an effect of providing a liquid crystal display device capable of solving the problem of the liquid crystal display device.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood that the invention may be practiced. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. In addition, the scope of the present invention is indicated by the following claims rather than the detailed description. Also, all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

TCN: Timing control part PNL: liquid crystal panel
SDRV: Gate driver DDRV: Data driver
BLU: Backlight unit PWR: Power supply unit
TRC: common voltage trace unit Ccom: first capacitor
Cload: second capacitor SW1: first switch
SW2: second switching 110: conversion section
120: control unit 130: reference voltage generating unit
140: Output buffer section

Claims (10)

A liquid crystal panel;
A common voltage generator for supplying a common voltage to the liquid crystal panel; And
Wherein the common voltage output from the common voltage generator is divided through at least two capacitors, a voltage divided by the at least two capacitors is analyzed, and a constant voltage proportional to the variation of the common voltage And a common voltage tracking unit for supplying the common voltage to an output terminal of the common voltage generator. The method according to claim 1,
The common voltage-
A controller for periodically analyzing a voltage divided by the at least two capacitors to find a variation value proportional to a variation of the common voltage;
And a reference voltage generator for outputting a constant voltage proportional to the variation value. The method according to claim 1,
Wherein the at least two capacitors comprise:
And a capacitor having a constant ratio to a capacity of a capacitor formed by a common voltage line located in a display region of the liquid crystal panel. The method of claim 3,
In the outside of the display region of the liquid crystal panel,
And a dummy capacitor for stabilizing the constant voltage output from the common voltage tracking unit and a common voltage supplied to the liquid crystal panel. The method according to claim 1,
The common voltage-
Wherein the common voltage is divided into at least one frame and analyzed and the predetermined voltage proportional to the variation of the common voltage is supplied to the output terminal of the common voltage generator according to the analysis result. The method according to claim 1,
The common voltage-
A first capacitor and a second capacitor for dividing the common voltage outputted from the common voltage generator,
A first switch for switching to read a voltage divided by the first and second capacitors,
A converter for converting the divided voltage read through the first switch into a digital signal;
A control unit for analyzing the divided voltage supplied through the converting unit to find a variation value proportional to a variation of the common voltage;
A reference voltage generator for outputting a constant voltage proportional to a variation of the common voltage based on the variation value supplied from the controller,
And a second switch for switching the constant voltage output from the reference voltage generator to be supplied to the output terminal of the common voltage generator. The method according to claim 6,
Wherein the reference voltage generator comprises:
Wherein an output level of the constant voltage is varied according to a variation value supplied from the controller. The method according to claim 6,
The common voltage-
And an output buffer unit formed between the reference voltage generating unit and the second switch. Dividing the common voltage output from the common voltage generator for supplying a common voltage to the liquid crystal panel through at least two capacitors and reading the voltage divided by the at least two capacitors;
Converting the divided voltage into a digital signal;
Analyzing the divided voltage to find a variation value proportional to the variation of the common voltage; And
And outputting a constant voltage proportional to a variation of the common voltage based on the variation value. 10. The method of claim 9,
A method of driving a liquid crystal display device,
Wherein the common voltage is divided into at least one frame and analyzed, and a constant voltage proportional to a variation of the common voltage is supplied to an output terminal of the common voltage generator according to an analysis result.

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