JP2008070701A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of preventing lowering of display quality is prevented by compensating a counter voltage considering changes of a liquid crystal related to a display time. <P>SOLUTION: When a power supply of the liquid crystal display device is turned on, a display time counter part 13 starts counting, and a temperature detecting part 12 starts detecting ambient temperature of a liquid crystal display part 11. A temperature/time computing part 14 integrates the temperature and the display time only for the time in which the detected temperature exceeds the predetermined temperature. A display control part 16 calculates the counter voltage value based on the temperature of the liquid crystal display part 11 at this moment and the value integrated with the temperature/time computing part 14. A data table of the counter voltage corresponding to the integrated value calculated with the temperature/time computing part 14 is stored in a data store memory 15. The display control part 16 obtains the counter voltage value corresponding to the temperature and the integrated vale of the liquid crystal display part 11 from the data table stored in the data storing memory and drives the liquid crystal display part 11 with the obtained counter voltage value. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device capable of automatically correcting a counter voltage of a liquid crystal panel.

  In recent years, liquid crystal panels have been widely used for television receivers, personal computer monitors, and mobile phones. The liquid crystal changes its characteristics depending on the usage environment such as the ambient temperature, and flickers that cause flickering at a constant cycle occur, which may lower the display quality. These problems are described in detail below.

  In an active matrix liquid crystal panel using TFTs, the drain voltage is affected by pseudo capacitance due to the overlap between the gate and drain of the TFT. When the gate is turned off, the voltage held in the pixel electrode fluctuates due to the influence of the pseudo capacitance. In addition, the difference in film thickness between the alignment films of the TFT substrate and the counter substrate, the difference in the materials of the alignment films of the TFT substrate and the counter substrate, and the electrode material on the TFT substrate side and the counter substrate as in a reflective liquid crystal display device Also due to the asymmetry due to the difference in the materials of the electrodes and alignment film facing each other across the liquid crystal layer, such as the difference between the electrode material on the side (for example, the reflective electrode of aluminum on the TFT side and the transparent electrode of ITO on the counter substrate side) The drain voltage varies. For this reason, the effective voltage applied to the liquid crystal layer changes at a constant period, and the transmitted light (reflected light in the reflection type or the like) changes to cause flicker.

  Further, as is generally known, since the characteristics of the TFT change due to changes in the surrounding environment, there is a problem that the balance of the effective voltage once corrected is lost and the counter voltage must be finely adjusted again. However, it was difficult to actually recalibrate after shipment. Flicker not only makes humans uncomfortable, but the balance of effective voltage breaks down, causing the DC component to continue to be applied to the liquid crystal layer, resulting in shortening the life of the liquid crystal and causing problems such as image sticking. It can also be a cause.

Therefore, Patent Document 1 discloses a display device that corrects the counter voltage according to the ambient temperature of the liquid crystal panel and suppresses the occurrence of flicker and liquid crystal deterioration.
JP 2005-292493 A

  However, in a product that is used for a long time such as a television receiver or a monitor of a personal computer, the characteristics of the liquid crystal change due to the long-time use. In particular, the use of a high-brightness backlight in order to increase the display brightness results in a high liquid crystal ambient temperature for a long time, resulting in a decrease in the voltage holding ratio of the liquid crystal material. Thus, since the characteristics of the liquid crystal itself change, even if correction is performed according to the initial setting value of the counter voltage according to the ambient temperature as in Patent Document 1, the deterioration of display quality (caused by flicker) cannot be suppressed. In addition, there is a possibility of liquid crystal deterioration due to DC application.

  In view of such a situation, the present invention is to provide a liquid crystal display device capable of correcting a counter voltage in consideration of a change in liquid crystal characteristics related to display time and preventing deterioration in display quality.

  The present invention includes a liquid crystal display unit that displays an image on a liquid crystal panel, a temperature detection unit that detects an ambient temperature of the display unit, a display time count unit that counts a display time of the display unit, and the temperature equal to or higher than a predetermined temperature. An integration processing unit that integrates the detected temperature and the display time of the temperature, and a display that corrects the counter voltage value to a value required for a predetermined display quality based on the current detection temperature and the integrated value calculated by the integration processing unit. And a control unit.

  In addition, the present invention further includes storage means for storing a counter voltage value necessary for display quality corresponding to the detected temperature and the integrated value, and the display control unit detects the counter voltage based on the value stored in the storage means. The voltage value is corrected.

  According to the present invention, the ambient temperature of the liquid crystal display unit is detected, the display time is counted, the integrated value of temperature and time is calculated, and based on this, the counter voltage value of the liquid crystal display unit is set to a value that does not cause flicker or the like. Since the correction is made, it is possible to improve the viewability of the user without degrading the display quality even if the characteristics of the liquid crystal change.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a liquid crystal display device according to the present invention. The liquid crystal display device includes a liquid crystal display unit 11 composed of a liquid crystal panel, a temperature detection unit 12 that detects the ambient temperature of the liquid crystal display unit 11, a display time counter unit 13 that counts the display time of the liquid crystal display unit 11, a detected temperature and a display. A temperature / time calculation unit 14 that integrates time, a data storage memory 15 that stores simulation data for setting a counter voltage of the liquid crystal panel, and a display control unit that performs control to display an image on the liquid crystal display unit 11 16.

  Since the effective voltage of the liquid crystal changes depending on the temperature, the liquid crystal needs to be corrected and corrected to a counter voltage suitable for maintaining high display quality. FIG. 2 is a graph showing the display time and the shift amount (correction amount) of the counter voltage for each temperature around the liquid crystal panel. As shown in the figure, the counter voltage value is increased as the temperature rises based on the counter voltage value in a normal temperature environment (25 ° C.). In this way, deterioration of display quality due to flicker or the like is suppressed.

  In addition, the liquid crystal changes its characteristics when used for a long time, but the degree of the characteristic change varies depending on the temperature. In particular, in a liquid crystal panel of a television receiver, in order to ensure high luminance, the temperature increases due to the use of a high luminance backlight. Since the liquid crystal causes characteristic deterioration (decrease in voltage holding ratio) as the display time becomes longer, it is necessary to increase the amount of shift of the counter voltage. FIG. 3 shows the relationship between the counter voltage shift amount and the display time of the liquid crystal panel at each temperature.

  For example, according to FIG. 3, when the temperature is lower than 25 ° C., the characteristic change hardly progresses, and the shift of the counter voltage is hardly required. On the other hand, the characteristic change of the liquid crystal proceeds from a temperature of 25 ° C. or higher, and the counter voltage needs to be corrected. Therefore, in FIG. 3, when the temperature of the counter voltage is 60 ° C. with respect to the normal temperature of 25 ° C., the characteristic change is remarkably advanced, and it is necessary to increase the counter voltage shift amount with the display time. When the predetermined time (about 300 hours) is reached, the characteristic change does not proceed and the counter voltage may be constant.

  Next, the counter voltage correction processing of the liquid crystal display device based on the relationship between the display time and the liquid crystal characteristic change will be described. FIG. 4 is a flowchart showing the counter voltage correction process of the liquid crystal display device based on the relationship between the display time and the liquid crystal characteristic change.

  When the power supply of the liquid crystal display device is turned on (step S1), the display time counter unit 13 starts counting, and the temperature detection unit 12 starts detecting the ambient temperature of the liquid crystal display unit 11 (step S2). The temperature / time calculation unit 14 performs an integration calculation of the temperature and the display time only when the detected temperature exceeds a predetermined temperature. FIG. 5 is a graph showing the ambient temperature and display time of the liquid crystal display unit. The predetermined temperature is set to 25 ° C. at which the liquid crystal characteristic starts to change, and an integration process with time is performed for a temperature exceeding the predetermined temperature. In FIG. 5, the display time exceeds 25 ° C. for about 200 hours to 450 hours. The integration process during this period is performed, and the area of the hatched portion in FIG. 5 is the integrated value of temperature and time.

  Therefore, the display control unit 16 obtains the counter voltage value based on the current ambient temperature of the liquid crystal display unit 11 and the integrated value calculated by the temperature / time calculation unit 14. The counter voltage corresponding to the integrated value calculated by the temperature / time calculation unit 14 is obtained in advance by simulation, and this data table is stored in the data storage memory 15. The liquid crystal display unit 16 obtains the counter voltage value corresponding to the temperature of the liquid crystal display unit 11 and the integrated value calculated by the temperature / time calculation unit 14 from the data table stored in the data storage memory, and obtains the liquid crystal display unit 11. Is driven with the obtained counter voltage value (step S4).

  Thus, by correcting the counter voltage value of the liquid crystal so as not to reduce the display quality according to the display time of the liquid crystal display unit 16, it is possible to prevent the deterioration of the liquid crystal characteristics due to flicker or the like and DC application.

It is a block diagram which shows the liquid crystal display device which concerns on this invention. It is a graph which shows the shift amount (correction amount) of display time and counter voltage for every temperature around a liquid crystal panel. It is a graph which shows the relationship between the amount of counter voltage shifts, and the display time of the liquid crystal panel in each temperature. It is a flowchart which shows the opposing voltage correction process of a liquid crystal display device based on the relationship between a display time and the characteristic change of a liquid crystal. It is a graph which shows the ambient temperature and display time of a liquid crystal display part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Liquid crystal display part 12 Temperature detection part 13 Display time counter part 14 Temperature / time calculating part 15 Data storage memory 16 Display control part

Claims (2)

A liquid crystal display for displaying images on the liquid crystal panel;
A temperature detection unit for detecting an ambient temperature of the display unit;
A display time counting unit for counting the display time of the display unit;
An integration processing unit that integrates the detected temperature equal to or higher than a predetermined temperature and a display time of the temperature;
A liquid crystal display device comprising: a display control unit for correcting a counter voltage value to a value necessary for a predetermined display quality based on a current detected temperature and an integrated value calculated by the integration processing unit. Storage means for storing a counter voltage value necessary for display quality corresponding to the detected temperature and the integrated value;
The liquid crystal display device according to claim 1, wherein the display control unit corrects the counter voltage value based on a value stored in the storage unit.

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