JPH0887001A - Method for determining driving voltage of liquid crystal panel - Google Patents

Abstract

PURPOSE: To make it possible to easily determine the best driving voltage within a voltage range which can be applied to a liquid crystal panel by plotting the measured values of the contrast and gradation inversion angles at the arbitrary voltage which can be previously applied to liquid crystals. CONSTITUTION: The display signal to be supplied to a signal line is defined as Vs and the counter signal to be supplied to a counter electrode as Vcom. Vs and Vcom are square waves inverting at a specified period and the amplitudes thereof are respectively defined as Vspp, Vcompp. At this time, the max. contrast of the liquid crystal panel when Vs is changed is defined as CMAX and the actual driving voltage of Vspp which is approximately the min. value of Vspp necessary for obtaining the prescribed contrast Cact (where 1<cact <cmax ) with respect to specified Vcom is defined as Vsppact . Next, the actual driving voltage of Vcompp which is approximately the min. value of Vcompp to realize the contrast C>=Cact under the Vspp=Vsppact is determined as Vcomppact .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving voltage determining method for a liquid crystal panel.

[0002]

2. Description of the Related Art In recent years, the image quality of liquid crystal panels has improved and is rapidly approaching the image quality of CRTs. This is a liquid crystal material,
It is no exaggeration to say that it has been achieved by technological innovations such as rubbing technology and driving voltage.

In such a situation, many companies have proposed and adopted liquid crystal drive voltage, and most of them are driven by a voltage as small as possible in view of the requirement of low power consumption. From the results, it has been decided by cut-and-try whether or not it is possible to secure the target performance such as contrast and gradation reversal angle that influence the image quality of the liquid crystal panel. Further, the contrast and the gradation inversion angle are in a trade-off relationship, and there is a cause for making it more difficult to determine the drive voltage.

[0004]

SUMMARY OF THE INVENTION The present invention satisfies the above requirements and does not require cut and try.
It is an object of the present invention to easily determine a drive voltage that can satisfy both a desired contrast Cact and a gradation inversion angle θact with a voltage that can be applied to the liquid crystal in advance.

[0005]

In order to achieve this object, the present invention provides scanning lines and signals arranged in an XY matrix on a main surface of a first substrate, and areas divided by these scanning lines and signals. A thin film transistor arranged in a unit pixel and a pixel electrode electrically connected to the thin film transistor are formed, and liquid crystal is sealed in a facing gap between the first substrate and a second substrate on which a counter electrode is formed. When determining the drive voltage of the liquid crystal panel, the display signal supplied to the signal line is Vs and the counter signal supplied to the counter electrode is Vcom. Vspp, V
In the case of compp, the maximum contrast of the liquid crystal panel when Vs is changed is CMAX, and Vspp is an approximate minimum value of Vspp required to obtain a predetermined contrast Cact (where 1 <Cact <CMAX) for a constant Vcom. Let Vsppact be the actual drive voltage of Vspp = Vspp
Vcom that realizes the contrast C ≧ Cact under ct
The actual driving voltage of Vcompp is Vcom at the approximate minimum value of pp.
It is decided as ppact.

Further, in the present invention, Vspp = Vs
Under ppact, contrast C ≧ Cact and gradation inversion angle θ
V is an approximate minimum value of Vcompp that simultaneously realizes ≧ θact.
The actual drive voltage of compp is determined as Vcomppact.

Further, in the present invention, Vspp = Vs
Under ppact, the actual driving voltage of Vcompp is determined as Vcomppact at the approximate minimum value of Vcompp that simultaneously realizes the contrast Cact ≧ 50 and the gradation inversion angle θact ≧ 5 °.

[0008]

With this configuration, it becomes possible to easily determine the best drive voltage for the liquid crystal panel.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

In the present embodiment, unless otherwise noted, the liquid crystal panel will be described as a normally white display in which the screen brightness decreases as Vspp increases.

FIG. 6 shows the potential relationship between the display signal Vs supplied to the signal line of the 1H inversion drive, the counter signal Vcom supplied to the counter electrode, and the scanning signal Vg, which are generally used in the drive system of the active matrix liquid crystal panel.

In FIG. 6, Vg (H) and Vg (L) are a high level and a low level of the scanning signal, and are signals which turn on the thin film transistor of the liquid crystal panel at the high level and turn off at the low level. In addition, Vs and Vcom can be changed within the range of Vg (H) and Vg (L). Regarding Vg (H) and Vg (L), the first
It is determined by the potential difference required in the design of the thin film transistor formed on the substrate.

Next, the inversion drive in which Vs and Vcom are inverted at a constant cycle will be described with reference to the conceptual diagram of FIG.

In the variable range of Vs in FIG. 7, VsT is Vs.
It is assumed that the level can be changed to L level and VsL can be changed to VsT level. Further, in the actual image display of the liquid crystal panel, the amplitude Vcompp is constant and the luminance of the liquid crystal panel is changed by the change of Vs. However, in the following description, the amplitude Vspp is constant and Vcompp is changed to perform the measurement. In some cases, the variable range of Vcompp is defined as follows in FIG. The variable range of Vcom is such that VcomH can be changed to the level of VcomL
It is assumed that comL can be changed to the level of VcomH.

The procedure of the driving voltage determining method of the present invention shown in FIG. 1 will be described below.

As the first procedure, Vsppact is obtained from the method described below. In FIG. 7, Vcompp has an amplitude, but Vcompp is determined when Vsppact is determined.
It is easier to think that = 0, so Vcom is VcomC
To be constant.

FIG. 2 shows a drive waveform used in the luminance measurement for determining Vsppact. In FIG. 2, Vcom
C is a voltage given by the following equation.

VcomC = (Vg (H) −Vg (L)) / 2 Further, Vs is assumed to change equally in the plus direction and the minus direction centering on VcomC, and the change amount is | VcomC.
-Vsm |.

Using this drive waveform, Vsm is changed and luminance is measured. Figure 3 shows the measurement result on the X-axis | Vc
omC-Vsm |, the brightness is plotted on the Y-axis, and X-
It is the figure which made Y graph.

Next, since the brightness MAX and the brightness MIN are known from FIG. 3, the maximum contrast CMAX of this liquid crystal panel is known. The required contrast Cact is determined with this CMAX as the maximum value. Next, from FIG. 3, the value of | VcomC-Vsm | at the time of starting to decrease from the brightness MAX is VsW, and the brightness at this time is TW. Required contrast Cac
Brightness of black for obtaining t This is TB. However, TB =
TW / Cact.

| VcomC-Vsm at this brightness TB
| This can be determined as VsB, and Vsppact can be determined as Vsppact = VsB-VsW.

As the second procedure, the gradation reversal voltage at which the luminance decreases and then starts to increase is measured by the method described below. Vspp is fixed to Vsppact while changing the angle θ of the brightness measuring portion up to 90 ° in the direction in which the grayscale inversion of the liquid crystal panel occurs from the normal to the display surface of the liquid crystal panel, and the brightness is measured while changing Vcompp. The angle θ is measured by dividing 90 ° into 10 equal parts to 30 equal parts. More accurate data can be obtained by finely dividing 90 to be measured, but in the present embodiment, in order to simplify the explanation,
It will be described as being divided into 10 equal parts, and θ is from θ0 to θ9.

Next, the change of θ0 to θ9 is plotted with Vcompp on the horizontal axis and the luminance on the vertical axis. The result is shown in FIG.

From FIG. 4, at each of θ0, θ1 ... θ9, Vcompp at a point where the luminance decreases as Vcompp increases and then increases is read. The voltage of Vcompp at the point where the luminance changes from decrease to increase becomes the grayscale inversion voltage at each angle θ, and Vcomppθ0 and Vcomp, respectively.
ppθ1 ... Vcomppθ9.

At this time, Vcomppθ0 to Vcompp
θ0 to θ9 corresponding to each of θ9 are gradation inversion angles.

As the third procedure, the contrast C at each gradation inversion voltage is obtained by the method described below.

The luminance at each gradation inversion voltage is read from FIG. Luminance at Vcompp θ0 This is T0. Vc
Luminance at ompp θ1 This is T1. ... Vco
Luminance at mpp θ9 This is T9.

Next, by using T0 to T9 and the TW, the contrast at each gradation inversion voltage is represented by Cθ0, Cθ1, ... C.
Obtained as θ9.

TW / T0 = Cθ0, TW / T1 = Cθ
1, ... TW / T9 = Cθ9 As the fourth procedure, the drive voltage of the liquid crystal panel is determined.

The relationship between Vcompp, the gradation inversion angle, and the contrast is obtained by the method described below. Vcompp on the horizontal axis
, The vertical axis has two axes, one vertical axis has the gradation inversion angle,
The contrast is plotted on the other vertical axis, and Vcomppθ
The gradation inversion angles θ0 to θ9 and the contrasts Cθ0 to Cθ9 at 0 to Vcompp θ9 are plotted. The result is shown in FIG. Since the relationship between Vcompp, the gradation inversion angle, and the contrast can be easily confirmed from FIG. 5, Vc in the range where the desired contrast Cact and the gradation inversion angle θact can be obtained.
Optimum drive voltage Vsppact by reading omppact
And Vcomppact can be determined.

In order to obtain a good image on the liquid crystal panel,
It was found that a contrast C ≧ 50 and a gradation inversion angle ≧ 5 ° were required.

[0032]

As described above, the present invention is extremely useful in practice for easily determining the best drive voltage within the voltage range that can be applied to the liquid crystal panel.

[Brief description of drawings]

FIG. 1 is a flowchart showing a driving voltage determination method for a liquid crystal panel of the present invention.

FIG. 2 is a voltage waveform diagram of Vs and Vcom when performing luminance measurement.

FIG. 3 is a characteristic diagram showing the relationship between the brightness of a liquid crystal panel and | VcomC-Vsm |.

FIG. 4 is a characteristic diagram showing a relationship between a grayscale inversion angle of a liquid crystal panel and Vcompp.

FIG. 5 is a characteristic diagram showing the relationship between Vcompp, contrast, and gradation inversion angle of the present invention.

FIG. 6 is a waveform diagram showing a potential relationship of 1H inversion drive of a general liquid crystal panel.

FIG. 7 is a voltage waveform diagram when Vs and Vcom are inversely driven.

Front page continuation (72) Inventor Tetsu Ogawa, 1006, Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. A scanning line and signals arranged in an XY matrix on a main surface of a first substrate, a thin film transistor arranged in a unit pixel in a region partitioned by these signals, and electrically connected to the thin film transistor. Signal line when determining a drive voltage of a liquid crystal panel in which liquid crystal is sealed in a facing gap between a first substrate and a second substrate on which a counter electrode is formed. Vs is a display signal supplied to the counter electrode, and Vcom is a counter signal supplied to the counter electrode. Vs and Vcom are rectangular waves that are inverted at a constant period, and their amplitudes are Vspp and Vspp, respectively.
When Vcompp is set, the maximum contrast of the liquid crystal panel when Vs is changed is CMAX, and a predetermined contrast Cact (where 1 <Cact <CMAX) for a constant Vcom.
Vsppact is the actual driving voltage of Vspp at the approximate minimum value of Vspp required to obtain Vspp = Vsp
Vco that realizes the contrast C ≧ Cact under pact
The actual drive voltage of Vcompp is Vco at the minimum value of mpp.
A method for determining a drive voltage of a liquid crystal panel, characterized by determining as mppact. 2. Under Vspp = Vsppact, the actual driving voltage of Vcompp is determined as Vcomppact at an approximate minimum value of Vcompp that simultaneously realizes the contrast C ≧ Cact and the gradation inversion angle θ ≧ θact. Item 2. A method for determining a driving voltage of a liquid crystal panel according to item 1. 3. An actual drive voltage of Vcompp is determined as Vcomppact at an approximate minimum value of Vcompp that simultaneously realizes a contrast Cact ≧ 50 and a gradation inversion angle θact ≧ 5 ° under Vspp = Vsppact. The method for determining a drive voltage of a liquid crystal panel according to claim 1.