JPH0312633A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate variance in brightness by controlling the driving conditions of the frequency of a signal voltage applied to a picture element, a common voltage applied to the counter electrode of the picture element, etc., according to a condition setting means where the conditions are set in advance. CONSTITUTION:The driving conditions are set by the condition setting means 6 in advance and a control circuit 2 makes a display on a liquid crystal panel 1. Then an in-panel detecting means 4 or external factor detecting means 5 detects the internal and internal states of the liquid crystal panel 1 and its detection output is inputted to the control circuit 2 to set the best driving conditions corresponding to the detection output again. Namely, the signal voltage, common voltage, a frame frequency, and the brightness of backlighting are controlled corresponding to information obtained by the detecting means 4 to set the best driving condition for various kinds of environment. Consequently, the variance in brightness is eliminated to obtain invariably excellent picture quality.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive device in a liquid crystal active matrix display.

[Conventional technology]

FIG. 2 shows the driving voltage waveform of the TPT-driven liquid crystal active matrix display. The source voltage Vs directly applied to the liquid crystal 8 is determined by the characteristics of the TFT 7 and the liquid crystal 8. The main ones include TPT threshold Vth (TF
T) is the mobility μ, the off-state current I ox1□, and the liquid crystal threshold V th (L(R) and the resistivity ρ. These characteristics are determined by the ambient temperature and brightness.

and varies depending on usage time. For this reason, there were variations in display due to differences in environment and changes over time.

Regarding temperature compensation of liquid crystal panels, for example,
JP-A-56-1997 and the like can be mentioned.

[Problem to be solved by the invention]

The above-mentioned conventional technology did not take into account environmental conditions such as ambient temperature and brightness, and variations in TPT and various properties of liquid crystal caused by long-term use, resulting in the problem of image quality variation6. The purpose is to eliminate such variations in brightness and always provide good image quality.

[Means to solve the problem]

In order to achieve the above purpose, we installed an external factor detection section that detects ambient temperature, brightness, etc., or an in-panel detection section that detects the characteristics of test cells installed in the panel, and each detection section From the information detected by , the signal voltage V s
i g , frame frequency JF + common voltage V co
s and the brightness of the backlight.

[Effect]

Corresponding to the information obtained by the detection means, the signal voltage,
By controlling the common voltage, frame frequency, and backlight brightness, the optimal driving conditions can be set for various environments. This makes it possible to always obtain good image quality.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. The device includes a liquid crystal panel 1. Control circuit 2° system 3.
Panel internal detection means 4. It is composed of external factor detection means 52 and condition setting means 6.

Driving conditions are set in advance by the condition setting means 6, and the liquid crystal panel 1 is caused to display by the control circuit 2. Next, the internal and external conditions of the liquid crystal panel are detected by the panel internal detection means 4 or the external factor detection means, and the detected output is inputted to the control circuit 2, and the optimum driving conditions corresponding to the detected output are re-established. This is what you set. By repeating feedback using the closed loop described above, a good display can always be obtained.

FIG. 3 shows a specific example of the embodiment. A detection means for detecting the brightness of the liquid crystal panel 1, such as an optical sensor 11, is provided in a part of the liquid crystal panel 1. The output detected by this detection means is input to the control circuit 2. Here, the optimum brightness is set in advance using condition setting means such as a ROM or a microprocessor. In this way, the control circuit 2 controls the signal voltage Vs so that the output of the detection means and the value set by the condition setting means 13 are equal.
+g, the brightness of the liquid crystal panel 1 is optimized by controlling the frame frequency and repeating feedback.

FIG. 4 shows the signal voltage V s *-brightness B characteristic of the liquid crystal. This Vssg B characteristic is determined by characteristics such as the threshold value, mobility, off-resistance of TPT, resistance of liquid crystal, and threshold value. However, these characteristics vary greatly depending on the ambient temperature. In addition, there are other problems such as a decrease in TPT's off-resistance depending on the intensity of the surrounding brightness, and a drift in the TPT's threshold value due to long-term use.
7 and the liquid crystal 8 are unavoidable. This variation in characteristics changes the effective value of the source voltage Vs directly applied to the liquid crystal, causing a variation in the brightness of the liquid crystal.

For this reason, variations in the Vs□-B characteristics occur as shown in FIG.

In addition to such brightness fluctuations, flickering on one display screen is another problem. Figure 5 shows the principle of flicker. Flicker is caused by the asymmetry of the source voltages between odd and even frames. When the source voltage is asymmetrical, there is a problem that not only flicker occurs but also DC voltage components are superimposed and the liquid crystal deteriorates.

In order to prevent this flicker, it is necessary to optimize the common voltage applied to the opposing electrodes.

Therefore, the brightness of the panel detected by the aforementioned optical sensor 21 is input to the flicker amplitude detection section 20, and the amplitude of the flicker is detected. The common voltage is changed by the control circuit 2 so that the amplitude of this flicker is reduced. By repeating such feedback, flicker can be prevented.

As described above, the brightness and flicker of the liquid crystal are detected, and the signal voltage VsIg+ corresponding to each from both points of view is detected.
By optimizing the frame frequency fF and common voltage Vcom, good display can always be obtained.
Furthermore, it is possible to eliminate direct current components that cause deterioration of liquid crystals.

FIG. 6 shows an optical sensor provided outside the panel. This light sensor detects the brightness around the panel. Driving conditions such as signal voltage Vs+g and frame frequency are set in accordance with the detected brightness around the panel. That is, when the brightness around the panel is bright, the display on the panel is also brightened, and when the around the panel is dark, the display on the panel is also darkened. Such setting conditions are set in advance by the condition setting means 13 as in the previous embodiment, so that the brightness can be set to be easy to see depending on the surrounding brightness. Furthermore, this embodiment can be combined with the embodiment shown in FIG. 3, thereby making it possible to control driving conditions more effectively.

Another embodiment is shown in FIG. 7, in which a monitor element 14 is built into a part of the liquid crystal panel 1.

This monitoring element 14 is capable of detecting a source voltage Vs directly applied to the liquid crystal. The source voltage Vs extracted from the monitoring element is input to an effective value detection section 15 and a DC voltage component detection section 16. The signal voltage Vstgy frame frequency fF is controlled by the control circuit 2 so that the effective value of Vs detected by the effective value detection section 15 becomes equal to the value set in advance by the condition setting means 13. This ensures that the source voltage V
The effective value of s can be constant.

On the other hand, the DC voltage component detection section 16 detects the DC voltage component of the source voltage, and the control circuit 2 detects the DC voltage component of the source voltage.
A common voltage that is equal to or corresponds to the DC voltage component of the source voltage Vs is generated. As a result, the source voltage Vg is always symmetrical about the common voltage, and DC voltage components can be eliminated, thereby preventing flicker.

Incidentally, the brightness of the liquid crystal panel is determined by a combination of the source voltage Vs, the threshold value of the liquid crystal, and the brightness of the backlight.

That is, even if the effective value of the source voltage Vs is constant,
When the temperature changes, the threshold value of the liquid crystal changes, causing the transmittance of the liquid crystal to fluctuate.

FIG. 8 shows the embodiment of FIG. 7 provided with a temperature sensor. A temperature sensor 17 detects the temperature around the panel. Data regarding fluctuations in the threshold value of the liquid crystal due to the panel ambient temperature is inputted in advance by the 1-condition setting means 13, and the effective value of the source voltage Vs is controlled to vary depending on the ambient temperature so that the transmittance is always constant. The circuit 2 changes the signal voltage Vsig and frame frequency. This example does not focus on the brightness of the panel.

Feedback is applied to keep the transmittance constant. Therefore, it is particularly effective when displaying halftones.

FIG. 9 shows a backlight provided with a light sensor. The brightness of the backlight changes depending on the ambient temperature and usage time. The detection output of the optical sensor is input to the backlight power control circuit 19. The backlight power control circuit 19 responds to the detection output of the optical sensor, and changes the power supply voltage or power frequency to brighten the backlight 18 when the backlight 18 becomes darker than a preset brightness.

When the light becomes bright, the opposite operation is performed.

In FIG. 10, a light sensor is provided outside the backlight 18. The light sensor detects the ambient brightness and inputs the output to the backlight power control circuit 19.

If the surroundings are bright, backlight control circuit 1
9, change the power supply voltage or power frequency so that the backlight becomes brighter. Furthermore, when the surroundings become dark, the reverse operation is performed, thereby making it possible to control the backlight 18 to a brightness that is easier to see in accordance with the surrounding brightness.

The control of the brightness of the backlight 18 shown in FIGS. 9 and 10 can be performed by controlling the transmittance of the liquid crystal panel 1 and the brightness of the backlight 18 independently when combined with the embodiments shown in FIGS. 7 and 8. can be controlled. Therefore, it is possible not only to maintain brightness for easy viewing, but also to display a display with good color reproducibility when displaying halftones.

〔Effect of the invention〕

According to the present invention, it is possible not only to prevent a decline in the display image quality due to changes in the external environment, but also to extend the life of the panel by setting the optimal driving conditions to prevent panel deterioration due to long-term use. be.

Also, depending on the brightness around the LCD panel,
You can also control the brightness to make it easier to see.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing an embodiment of the present invention.
LCD driving waveform diagrams, Figures 3 and 6 to 10 are diagrams showing other embodiments, and Figure 4 is a diagram showing the signal voltage vs. of the liquid crystal panel.
The Ig-brightness B characteristic diagram and FIG. 5 are diagrams showing the principle of flicker. 1...Liquid crystal panel, 2...Control circuit, 3.
...System, 4... Panel internal detection means, 5...
External factors Figure 2 Figure 1 In V □m Figure 3 Figure 6 Figure 4 Figure 7 Figure 8 q Figure 9 Figure 10

Claims (1)

[Claims] 1. A liquid crystal display panel in which each pixel is composed of a switching element and a liquid crystal, and the pixels are arranged in a matrix at the intersections of a large number of scanning electrodes and signal electrodes, and means for displaying an image on the display panel. In the liquid crystal display device, there is provided panel internal detection means for detecting characteristics of the liquid crystal display panel, and external factor detection means for detecting conditions outside the liquid crystal display panel,
Driving conditions such as the signal voltage applied to the pixel, the frequency of the signal voltage, and the common voltage applied to the opposing electrode of the pixel are set according to the condition setting means, which sets conditions in advance in accordance with the detection output of the detection means. A liquid crystal display device characterized by controlling. 2. The liquid crystal display device according to claim 1, wherein the panel internal detection means comprises a photosensor for detecting brightness of the liquid crystal display panel. 3. The liquid crystal display device according to claim 1, wherein the panel internal detection means is a monitoring element and can directly detect the effective value of the voltage applied to the liquid crystal. 4. The liquid crystal display device according to claim 1, wherein the external factor detection means is a temperature sensor and detects the temperature around the panel. 5. The liquid crystal display device according to claim 1, wherein the external factor detection means is an optical sensor and detects brightness around the panel. 6. The liquid crystal display device according to claim 1, wherein the condition setting means is comprised of a ROM, a microprocessor, or the like. 7. A detection means for detecting the brightness of the backlight or a detection means for detecting the brightness outside the backlight is provided on the backlight provided on the back of the liquid crystal display panel, and the detection means corresponds to the detection output of the detection means. 2. The liquid crystal display device according to claim 1, wherein the brightness of a backlight is controlled.