JP2008216363A - Driving device for liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device for a liquid crystal display that has simplified power source and can lower the breakdown voltage. <P>SOLUTION: A common driver 17 sets the potential of a common electrode OV during positive pole driving. In addition, a source driver 14 sets the potentials V<SB>s(P, n)</SB>, V<SB>s(N, n)</SB>so determined as to satisfy equation: C=(V<SB>s(P, n)</SB>+V<SB>s(N, n)</SB>)/2-ΔV<SB>gd(n)</SB>in source wiring, according to gradation n, and positive pole driving or negative pole driving. C is a constant in the equation, and ΔV<SB>gd(n)</SB>is feed-through voltage corresponding to the gradation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive device for a liquid crystal display device, and more particularly to a drive device for a TFT liquid crystal display device that can prevent an observer from visually recognizing the occurrence of burn-in.

  FIG. 4 is an explanatory diagram showing a configuration example of a TFT (Thin Film Transistor) liquid crystal display device. In the TFT liquid crystal display device, a TFT 1 and a display electrode 2 are provided for each pixel. In FIG. 4, only one TFT 1 and one display electrode 2 are shown, and other TFTs and display electrodes are not shown. The TFT liquid crystal display device is provided with a common electrode 3 facing each display electrode. In this example, a case where there is one common electrode provided in the TFT liquid crystal display device will be described as an example. A liquid crystal layer (not shown) is sandwiched between the common electrode 3 and each display electrode 2.

Display electrode 2 is connected to the drain _{1 b} of the TFT 1. Further, the source 1 _c of the TFT 1 is connected to the source wiring 4, and the gate 1 _a of the TFT 1 is connected to the gate wiring 5. When the potential of the gate 1 _a via the gate line 5 is set to a predetermined ON potential, between the source 1 _c and the drain 1 _b becomes conductive, the display electrodes 2 is set to a potential equal to the source line 4 The When the potential of the gate 1 _a is set to a predetermined OFF voltage, between the source 1 _c and the drain 1 _b becomes nonconductive, between the source line 4 and the display electrodes 2 is also switched to non-conducting state. The predetermined ON potential is a predetermined potential of the gate 1 _a to between the source 1 _c and the drain 1 _b conductive. The predetermined OFF potential is a predetermined potential of the gate 1 _a to between the source 1 _c and the drain 1 _b nonconductive. Hereinafter, the predetermined on potential is represented as V _gH and the predetermined off potential is represented as V _gL . Note that the relationship of V _gL <V _gH is established.

  The alignment state of the liquid crystal between the display electrode 2 and the common electrode 3 is determined according to the potential difference between the display electrode 2 and the common electrode 3. For example, by setting the potential of each display electrode 2 by line sequential driving or the like, it is possible to display an image by controlling the alignment state of the liquid crystal of each pixel.

However, when the potential of the gate _{1 a} is switched from _{V gH} in _{V gL,} the potential of the display electrode 2 is slightly reduced. This amount of potential decrease is called a feedthrough voltage. FIG. 5 is an explanatory diagram showing the feedthrough voltage. A thin solid line shown in FIG. 5 indicates a potential change of the gate wiring 5. A thick solid line shown in FIG. 5 indicates an actual potential change of the display electrode 2. A thin broken line shown in FIG. 5 indicates a potential change of the source wiring 4. The potential of the source wiring at the time of positive polarity driving is represented as V _{s (P),} and the potential of the source wiring at the time of negative polarity driving is represented as V _{s (N)} . The positive drive means driving so that the potential of the display electrode is equal to or higher than the potential of the common electrode. The negative drive means driving so that the potential of the display electrode is equal to or lower than the potential of the common electrode. A thick broken line shown in FIG. 5 indicates an ideal potential change of the display electrode 2.

In the case of positive polarity driving, when the potential of the gate line 5 is switched from V _gL to V _gH , the source 1 _c and the drain 1 _b are in a conductive state, and the potential V _{s of the} display electrode 2 is equal to the source line 4. It rises to _(P) . Thereafter, when the potential of the gate wiring 5 is switched from V _gH to V _gL , the potential of the display electrode is lowered as the gate potential is lowered. This amount of potential decrease is the feedthrough voltage. The feedthrough voltage is represented as ΔV _gd . The liquid crystal between the display electrode and the common electrode is aligned according to the potential difference between the display electrode potential and the common electrode potential, which is lower by ΔV _gd than the potential V _{s (P)} of the source wiring. Even when the potential of the gate wiring 5 is switched from V _gH to V _gL , it is ideal that the display electrode potential does not change as shown by a thick broken line in FIG. 5, but the display electrode potential actually decreases by ΔV _gd . .

In the case of negative polarity driving, when the potential of the gate line 5 is switched from V _gL to V _gH , the source 1 _c and the drain 1 _b are in a conductive state, and the potential V _{s of the} display electrode 2 is equal to the source line 4. _(N) . Thereafter, when the potential of the gate wiring 5 is switched from V _gH to V _gL , the potential of the display electrode is lowered as the gate potential is lowered. The liquid crystal between the display electrode and the common electrode is in an alignment state corresponding to the potential difference between the display electrode potential and the common electrode potential, which is lower by ΔV _gd than the potential V _{s (N)} of the source wiring.

  It is known that when a DC voltage is continuously applied to the liquid crystal disposed between the display electrode and the common electrode, ion impurities gather on the electrode to form a layer. This phenomenon is called burn-in. When burn-in occurs, the displayed image is recognized by the observer even after the display is stopped due to the difference in the degree of burn-in for each pixel.

  When driving a TFT liquid crystal display device, in order to prevent the occurrence of image sticking, a positive voltage drive and a negative polarity drive are alternately performed so that a DC voltage is not applied to the liquid crystal. However, since a feedthrough voltage is generated when the gate wiring potential is switched, not only the positive polarity driving and the negative polarity driving are performed alternately, but also the average of the common electrode potential during the positive polarity driving and the common electrode potential during the negative polarity driving. The value (center of amplitude of the common electrode potential) had to be determined in consideration of the feedthrough voltage.

FIG. 6 is an explanatory diagram showing a conventional method for determining the average value of the common electrode potential during positive polarity driving and the common electrode potential during negative polarity driving (the amplitude center of the common electrode potential). The potential set to the common electrode during positive polarity driving is denoted as V _COML . At the time of positive polarity driving, the potential of the display electrode after switching the potential of the gate wiring 5 from V _gH to V _gL is denoted as V _{pixel (P)} . V _{pixel (P)} is a potential that is lowered from the source wiring potential by the feedthrough voltage. Therefore, V _{pixel (P)} = V _{s (P)} −ΔV _gd . A potential set to the common electrode during negative polarity driving is denoted as V _COMH . At the time of negative polarity driving, the potential of the display electrode after switching the potential of the gate wiring 5 from V _gH to V _gL is denoted as V _{pixel (N)} . V _{pixel (N)} is a potential lowered by the feedthrough voltage from the source wiring potential, and V _{pixel (N)} = V _{s (N)} −ΔV _gd .

Further, when the amplitude center of the common electrode potential is V _COMC , V _COMC = (V _COMH + V _COML ) / 2.

The voltage applied to the liquid crystal during positive polarity driving _{(denoted as} V _{lcd (P)} ) is expressed by the following formula 1.

V _{lcd (P)} = V _{pixel (P)} −V _COML
= Vs _(P)-[ Delta] _Vgd - _VCOML (Equation 1)

Further, the voltage applied to the liquid crystal during negative polarity driving (denoted as V _{lcd (N)} ) is expressed by the following formula 2.

V _{lcd (N)} = V _{pixel (N)} −V _COMH
= V _{s (N)} -ΔV _gd -V _COMH (Formula 2)

Therefore, when the average voltage applied to the liquid crystal is V _DC , V _DC is expressed by the following Equation 3.

V _DC = (V _{lcd (P)} + V _{lcd (N)} ) / 2
_{= (V s (P) +} V s (N)) / 2-ΔV gd -V COMC ( Equation 3)

If V _DC ≠ 0 V, a DC voltage is continuously applied to the liquid crystal even when the positive polarity driving and the negative polarity driving are alternately switched. Therefore, in order to prevent burn-in, V _COMC is determined so that V _DC = 0V. That is, V _COMC is determined so as to satisfy the following Expression 4.

_VCOMC = (Vs _(P) + Vs _(N) ) / 2- [Delta] _Vgd (Formula 4)

  Also in Cited Document 1, it is described that the amplitude center of the counter electrode potential is made lower by about the feedthrough voltage than the center potential of the signal wiring potential.

Note that the feedthrough voltage ΔV _gd changes for each gradation, and the source wiring potentials V _{s (P)} and V _{s (N)} are also determined for each gradation. However, in the TFT liquid crystal display device, V _COML is constant regardless of the gradation. Therefore, V _COMC is determined from V _{s (P)} , V _{s (N)} , and ΔV _gd in the intermediate gradation between the maximum gradation and the minimum gradation, and the DC voltage is minimized. For example, in a TFT liquid crystal display device that displays all 64 gradations from the 0th gradation to the 63rd gradation, Equation 4 is obtained from V _{s (P)} , V _{s (N)} , and ΔV _gd in the 32nd gradation. To determine V _COMC .

FIG. 7 shows examples of a feedthrough voltage ΔV _gd that changes for each gradation, source wiring potentials V _{s (P)} and V _{s (N)} that are determined for each gradation, and V _COMC that is determined by a conventional method. Indicates.

JP 2006-3512 (paragraphs 0023, 0024)

The determination method of the conventional _{V COMC,} determines the _{V COMC} from the equation shown in Equation 4. As can be seen from Equation 4, subtraction is performed with the feedthrough voltage ΔV _gd . This subtraction results in V _COMC being lower than the ideal V _COMC without a feedthrough voltage. When V _COMC is determined to be low by subtraction of ΔV _gd , the common electrode potential V _COML at the time of positive polarity driving is also low, and V _COML is lower than the ground voltage (0 V, hereinafter referred to as GND). .

FIG. 8 is a driving waveform showing a change in the conventional common electrode potential. As shown in FIG. 8, when a V _COML lower than GND is applied to the common electrode, the configuration of the power supply circuit that supplies such a negative voltage V _COML becomes complicated.

In addition, the withstand voltage of the driving device of the liquid crystal display device is preferably low. For example, when the driving device is configured as an IC, the withstand voltage of the IC is preferably low. The breakdown voltage is, for example, AVDD-V _COML . If V _COML <GND, the breakdown voltage of the driving device also increases. Note that AVDD is a voltage boosted to a value higher than the highest potential set in the source wiring. By supplying AVDD to the source driver that sets the potential of each source wiring, the source driver can set the potential of the source wiring to a potential corresponding to each gradation.

  In addition, it is preferable that driving conditions such as a potential set in the source wiring can be more easily determined in accordance with the gradation.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a driving device for a liquid crystal display device that can simplify the power source and reduce the withstand voltage. It is another object of the present invention to prevent the observer from recognizing the occurrence of image sticking and to easily determine the potential set to the source wiring and the potential of the common electrode in accordance with the gradation.

A driving device for a liquid crystal display device according to the present invention includes a liquid crystal between a plurality of display electrodes arranged in a matrix and a common electrode facing the display electrode, and a TFT is provided for each display electrode. A driving device for a liquid crystal display device in which a source wiring connected to a display electrode via a TFT is provided for each column, and includes a source driver for setting the potential of the source wiring of each column, according to one gradation The potential that the source driver sets for the source wiring during positive polarity driving is V _{s (P, n),} and the potential that the source driver sets for the source wiring during negative polarity driving is V _{s (N, n). ),} And when the feedthrough voltage at that gradation is ΔV _{gd (n)} and C is a constant, C = (V _{s (P, n)} + V _{s (N, n)} ) / 2−ΔV _{gd (n)} the relationship that, most of the minimum gradation Characterized in that it holds in each tone to tone.

  It is preferable to provide a common driver that sets the potential of the common electrode depending on whether it is during positive polarity driving or negative polarity driving, and the common driver sets the potential of the common electrode to 0 V or more during positive polarity driving. .

  It is preferable that a control unit that instructs the source driver and the common driver to perform positive polarity driving or negative polarity driving is provided, and the control unit switches between positive polarity driving and negative polarity driving for each frame. According to such a configuration, occurrence of flicker can be prevented.

  According to the present invention, the power source for setting the potential of the common electrode can be simplified, and the withstand voltage of the driving device can be lowered. In addition, the occurrence of burn-in can be prevented from being recognized by an observer, and the potential set to the source wiring and the potential of the common electrode can be easily determined according to the gradation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory diagram showing a configuration example of a driving apparatus according to the present invention. The driving device 11 of the present invention drives the TFT liquid crystal display device 20. As illustrated in FIG. 4, the TFT liquid crystal display device 20 includes a TFT 1 and a display electrode 2 for each pixel, and also includes a common electrode 3 facing each display electrode 2. Liquid crystal is sandwiched between each display electrode 2 and the common electrode 3. As already explained, the display electrode 2 is connected to the drain _{1 b} of the TFT 1. Further, the combinations of the TFT 1 and the display electrode 2 are arranged in a matrix.

  The drive device 11 includes a control unit 12, a source driver 14, a gate driver 15, and a power supply 16. The driving device 11 of the present invention is configured as an IC, for example, but may not be configured as an IC.

Each gate line 5 in (see FIG. 4.) Each row is connected to the gate _{1 a} of each of TFT1 in one line. Each gate line 5 is connected to a gate driver 15 (see FIG. 1). Each source line 4 (see FIG. 4.) Is in each column is connected to the source _{1 c} each TFT1 in a row. Each source line 4 is connected to a source driver 14 (see FIG. 1).

The gate driver 15 sequentially selects display electrodes for each row. Specifically, the gate driver 15 performs scanning while sequentially selecting the gate wiring, sets the potential of the selected gate wiring to V _gH, and sets the potential of the unselected gate wiring to V _gL . While the row (gate wiring) is selected by the gate driver 15, the source driver 14 sets the potential of each source wiring according to the image data for one row corresponding to the selected row. As a result, each display electrode in the selected row is set to a potential corresponding to the image data in the selected row by the source driver 14, and each display electrode 2 and common electrode 3 (see FIG. The voltage corresponding to the image data is applied to the liquid crystal between them. In addition, charges are accumulated between the display electrodes 2 and the common electrode 3. Thereafter, by sequentially selecting the gate wiring in the same manner, an image for one screen is displayed on the liquid crystal display panel 1.

When the potential of the gate wiring in the row selected by the gate driver 15 is switched from V _gH to V _gL , the potential of the display electrode in that row drops by the feedthrough voltage.

The power supply 16 supplies voltages V _gH and V _gL to the gate driver 15. The power supply 16 supplies the source driver 14 with a voltage AVDD (a voltage boosted to a value higher than the highest potential set in the source wiring). The source driver 14 sets the potential of the source wiring to a potential corresponding to each gradation, but the potential corresponding to each gradation is a value lower than AVDD.

The power source 16 includes a common driver 17 that sets the potential of a common electrode provided in the TFT liquid crystal display device 20. The power supply 16 uses the common driver 17 to set the common electrode potential to V _COML during positive polarity driving and to set the common electrode potential to V _COMH during negative polarity driving. Note that V _COML <V _COMH .

The potential that the source driver 14 sets to the source wiring during positive polarity driving according to the gradation indicated by the image data is denoted as V _{s (P, n)} . Similarly, the potential that the source driver 14 sets in the source wiring during negative polarity driving according to the gradation indicated by the image data is denoted as V _{s (N, n)} . Here, n is a value representing gradation. For example, the potential of the source wiring set according to the third gradation during positive polarity driving is V _{s (P, 3)} . If the values of n are equal, V _{s (P, n)} and V _{s (N, n)} are different in terms of whether the potential is set during positive polarity driving or the potential set during negative polarity driving. Both are potentials set according to the same gradation. For example, V _{s (P, 3)} and V _{s (N, 3)} are both potentials set according to the third gradation.

The potentials V _{s (P, n)} and V _{s (N, n)} set to the source wiring in accordance with each gradation are determined in advance so as to satisfy a predetermined condition. A method for determining V _{s (P, n)} and V _{s (N, n)} will be described later.

  The control unit 12 outputs a control signal (hereinafter referred to as a row switching signal) instructing switching of the selected row to the source driver 14 and the gate driver 15. Further, the control unit 12 outputs a control signal (hereinafter referred to as a polarity signal) indicating whether to perform positive polarity driving or negative polarity driving to the source driver 14 and the common driver 17. The control unit 12 switches the polarity signal for each frame. That is, the control unit 12 switches between positive polarity driving and negative polarity driving for each frame. The frame is a period from when the gate driver 15 starts selecting the first row gate wiring to when the gate driver 15 starts selecting the first row gate wiring.

Next, a method for determining V _{s (P, n)} and V _{s (N, n)} will be described. In this determination method, V _{s (P, n)} and V _{s (N, n)} are determined so as to satisfy Equation 5 shown below. In the following description, the case where the TFT liquid crystal display device 20 has 64 gradations from the 0th gradation to the 63rd gradation will be described as an example.

C = (V _{s (P, n)} + V _{s (N, n)} ) / 2−ΔV _{gd (n)} Equation 5

C in Equation 5 is a constant. Hereinafter, a method for determining V _{s (P, n)} and V _{s (N, n)} will be described in detail. A method for determining the common electrode potentials V _COML and V _COMH will also be described.

First, the voltage applied to the liquid crystal is specified according to each gradation, and the feedthrough voltage in each gradation is specified. As already described, since the feedthrough voltage differs depending on the gradation, first, the feedthrough voltage in each gradation is specified. ΔV _{gd (n)} in Equation 5 is a feedthrough voltage corresponding to each gradation. n is a value representing a gradation, and represents the same gradation as n in V _{s (P, n)} and V _{s (N, n)} . For example, the feedthrough voltage at the third gradation is ΔV _{gd (3)} . The feedthrough voltage ΔV _{gd (n)} corresponding to each gradation may be specified from the specification of the manufacturer of the TFT liquid crystal display device 20, for example. Alternatively, the feedthrough voltage of the TFT liquid crystal display device 20 may actually be measured for each gradation.

After specifying the feedthrough voltage ΔV _{gd (n)} at each gradation, either the amplitude of the common electrode potential (hereinafter referred to as V _COM amplitude) or so as to satisfy the contrast required for the TFT liquid crystal display device 20. The set potentials V _{s (P, k)} and V _{s (N, k)} of the source wiring in one gradation (referred to as the k-th gradation ₎ are determined. Here, k is one of the gradations. For example, when the TFT liquid crystal display device 20 is a positive type, V _{s (P, 0)} and V _{s in} the 0th gradation (when black is displayed). _What is necessary is just to determine _{(N, 0)} and a _VCOM amplitude. For example, when the TFT liquid crystal display device 20 is a negative type, V _{s (P, 63)} , V _{s (N, 63)} and V _COM amplitude at the 63rd gradation (when white is displayed) are determined. do it. The 0th gradation and the 63rd gradation exemplified here are examples, and V _{s (P, k)} and V _{s (N, k)} in other gradations may be determined. Here, it is assumed that V _{s (P, 0)} , V _{s (N, 0)} and the V _COM amplitude in the 0th gradation are determined. The V _COM amplitude is the absolute value of the difference between V _COMH and V _COML .

Subsequently, the determined V _{s (P, 0)} and V _{s (N, 0)} and the feedthrough voltage ΔV _{gd (0)} at the gradation (the 0th gradation in this example) are substituted into Equation 5. The constant C is calculated. The resulting C is determined as a constant in Equation 5.

Further, the common electrode potential V _COML at the time of positive polarity driving is determined as a value of 0 V or more. In particular, V _COML = 0V is preferable. A value obtained by adding V _COM amplitude to V _COML is determined as a common electrode potential V _COMH during negative polarity driving. As described above, V _COML and V _COMH are determined from the condition of V _COML ≧ 0 (particularly V _COMML = 0 is preferable) and the V _COM amplitude, and V _COML and V _COMH can be _{simply calculated} without using Equation 5 _. Can be determined. Further, V _COMMC (= (V _COML + V _COMH ) / 2), which is the amplitude center of the common electrode potential, is usually a value larger than the above constant C when V _COML = 0V.

After the constant C is determined, the set potentials V _{s (P, n)} and V _{s (N, n)} of the source wiring in each gradation are determined using the constant C so as to satisfy Expression 5.

When Vs _{(P, n)} and Vs _{(N, n)} are determined, the voltage applied to the liquid crystal belongs to a voltage range in which the transmittance in the VT characteristic of the liquid crystal display device changes. Each V _{s (P, n)} and V _{s (N, n)} are determined as follows. The VT characteristic is a characteristic indicating the relationship between the voltage applied to the liquid crystal and the transmittance of the liquid crystal display device. FIG. 2 is an explanatory diagram illustrating an example of the VT characteristic. In the example shown in FIG. 2, when the applied voltage to the liquid crystal is in the range of V _{1 to} V ₂ , the transmittance of the liquid crystal display device changes with the change of the applied voltage. On the other hand, the applied voltage V ₁ lower than or V ₂ is greater than the range of the liquid crystal, even the applied voltage is changed is not the transmittance change.

The voltage applied to the liquid crystal is | V _{s (P, n)} −ΔV _{gd (n)} −V _COML | in the case of positive polarity driving. In the case of negative polarity driving, | V _{s (N, n)} −ΔV _{gd (n)} −V _COMH |. Therefore, Expression 5 is satisfied, and | V _{s (P, n)} −ΔV _{gd (n)} −V _COML | and | V _{s (N, n)} −ΔV _{gd (n)} −V _COMH | Each V _{s (P, n)} and V _{s (N, n)} is determined so as to belong to a voltage range in which the transmittance changes (in the example shown in FIG. 2, a range of V _{1 to} V ₂ ).

The drive device 11 of the present invention drives the TFT liquid crystal display device 20 using V _{s (P, n)} , V _{s (N, n)} , V _COML , and V _{COMH determined} as described above. In the above description, the case where the number of gradations is 64 in all is taken as an example, but the number of all gradations may not be 64.

Next, the operation will be described. The control unit 12 outputs a polarity signal that instructs the source driver 14 and the common driver 17 to drive positive polarity at the start of the frame. The common driver 17 sets the potential of the common electrode to V _COML according to the polarity signal. Further, the control unit 12 outputs a row switching signal to the source driver 14 and the gate driver 15 at regular time intervals. The gate driver 15 switches a selected row (gate wiring) every time a row switching signal is input.

When the row switching signal is input, the source driver 14 sets the potential of each source wiring according to the gradation of each pixel indicated by the image data of the selected row and the polarity signal from the control unit 12. Here, since the polarity signal indicates positive polarity driving, the source driver 14 sets the potential of each source wiring to V _{s (P, n)} according to the gradation of each pixel indicated by the image data of the selected row. Set.

At the start of the next frame, the control unit 2 outputs a polarity signal instructing the source driver 14 and the common driver 17 to perform negative polarity driving. The common driver 17 sets the potential of the common electrode to V _COMH according to the polarity signal. As in the case of positive polarity driving, the control unit 12 outputs a row switching signal to the source driver 14 and the gate driver 15 at regular intervals, and the gate driver 15 selects a row to be selected every time the row switching signal is input. Switch.

In addition, since the polarity signal indicates positive polarity driving, the source driver 14 sets the potential of each source wiring to V _{s (N, n)} according to the gradation of each pixel indicated by the image data of the selected row. To do.

Next, the effect of the present invention will be described. According to the present invention, the TFT liquid crystal display device 20 is driven using the potentials V _COML and V _COMH determined without depending on the equation (5). That is, V _COML and V _COMH determined without depending on the potential set for the source wiring are set for the common electrode. As described above, V _COML and V _COMH are determined without depending on Formula 5, so that V _COML can be determined as a potential of 0 V or more without being less than 0 V. Therefore, since the power supply 16 does not need to supply a negative voltage, the configuration of the power supply 16 can be simplified. In particular, when V _{COML is set} to 0 V (GND), the configuration of the power supply 16 can be further simplified.

Further, since V _COML can be determined as a potential of 0 V or higher, the withstand voltage of the driving device can be reduced. FIG. 3 is a drive waveform showing a change in the common electrode potential when V _COML is determined to be 0V. It can be seen that the withstand voltage (AVDD−V _COML ) can be reduced by setting V _COML to 0 V or higher as compared with the conventional case shown in FIG.

Further, in the present invention, the set potentials V _{s (P, n)} and V _{s (N, n)} of the source wiring in each gradation are determined by using the constant C so as to satisfy Expression 5. This means that a DC voltage is applied to the liquid crystal even when the positive polarity drive and the negative polarity drive are alternately switched. However, since V _{s (P, n)} and V _{s (N, n)} in each gradation are determined so as to satisfy Equation 5 with C as a constant, DC is used regardless of which gradation is displayed. The voltage value is constant. Therefore, a constant DC voltage is applied to each pixel regardless of which gradation is displayed. As a result, image sticking occurs in each pixel, but the degree of image sticking in each pixel becomes equal. Conventionally, since the difference in the degree of image sticking for each pixel is different, the image displayed even after the display is stopped has been recognized by the observer. However, in the present invention, the degree of image burn-in in each pixel can be made equal. It is possible to prevent the observer from recognizing the occurrence of burn-in.

  In the present invention, since a DC voltage may be applied to the liquid crystal, the potential to be set for the source wiring and the potential of the common electrode are removed from the condition that the DC voltage applied to the liquid crystal is 0 V as in the prior art. Can be determined. For this reason, even when contrast, γ characteristics, and the like are taken into consideration, the potential set for the source wiring and the potential of the common electrode can be easily determined under few restrictions.

  In addition, since the control unit 12 alternately switches between positive polarity driving and negative polarity driving at a high frequency for each frame, it is possible to prevent occurrence of flicker.

  The present invention is suitably applied to a driving device for a TFT liquid crystal display device.

Explanatory drawing which shows the structural example of the drive device of this invention. Explanatory drawing which shows the example of VT characteristic. The drive waveform which shows the change of the common electrode potential when _VCOML is determined to 0V. Explanatory drawing which shows the structural example of a TFT liquid crystal display device. Explanatory drawing which shows a feedthrough voltage. Explanatory drawing which shows the determination method of the amplitude center of the conventional common electrode potential. Explanatory drawing which shows the example of source wiring electric potential Vs _(P) , Vs _(N) defined for every gradation, and _VCOMC defined by the conventional method. A driving waveform showing a change in the conventional common electrode potential.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Drive apparatus 12 Control part 14 Source driver 15 Gate driver 16 Power supply 17 Common driver 20 TFT liquid crystal display device

Claims (3)

A liquid crystal is provided between a plurality of display electrodes arranged in a matrix and a common electrode facing the display electrode, a TFT is provided for each display electrode, and a display electrode is provided via a TFT for each column of display electrodes. A driving device of a liquid crystal display device provided with a source wiring to be connected,
It has a source driver that sets the potential of the source wiring of each column,
The potential that the source driver sets to the source wiring during positive polarity driving according to one gradation is V _{s (P, n),} and the potential that the source driver sets to the source wiring during negative polarity driving according to the gray level. When V _{s (N, n)} is set, the feedthrough voltage at the gradation is ΔV _{gd (n),} and C is a constant,
C = (Vs _{(P, n)} + Vs _{(N, n)} ) / 2- [Delta] _{Vgd (n)}
The above-mentioned relationship is established for each gradation from the minimum gradation to the maximum gradation. A common driver that sets the potential of the common electrode according to whether it is during positive polarity driving or negative polarity driving,
The driving device for a liquid crystal display device according to claim 1, wherein the common driver sets the potential of the common electrode to 0 V or more during positive polarity driving. Provided with a control unit that instructs the source driver and the common driver to be positive polarity driving or negative polarity driving,
The driving device for a liquid crystal display device according to claim 2, wherein the control unit switches between positive polarity driving and negative polarity driving for each frame.

Images