JP2002116741A - Method for adjusting display luminance of liquid crystal display element and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for adjusting display luminance of a liquid crystal display element bringing into little variance, treatable within a short period and being simple and easy. SOLUTION: In relation to driving voltage and transmission luminance, a characteristic curve 14 for a checked mosaic display and a characteristic curve 13, expressing a mean value of a characteristic curve 12 for a black display and a characteristic curve 11 for a white display, are detected with visual examination or with an optical measuring device. An optimal offset value of driving voltage is obtained from the intersection point of the characteristic curves 14, 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of adjusting display luminance of a dot matrix type liquid crystal display element which performs simple matrix driving, and a liquid crystal display device which automatically adjusts display luminance.

[0002]

2. Description of the Related Art Liquid crystal display devices are used as display media for various electronic devices. It is used for various applications such as display devices for OA equipment, display devices for home electric appliances, automotive instruments, measuring instruments, calculators and cameras. In recent years, demand for car navigation, communication devices, portable information terminals, and the like has been increasing. Accordingly, there is a need for a liquid crystal display device having good visibility, high-speed response, and capable of achieving a display with a high contrast ratio.

[0003] When used outdoors, a wider operating temperature range is required than when used indoors.
In the case of an active matrix liquid crystal display element in which an active element is arranged for each pixel, there is little need to correct the display because there are few fluctuation elements of the liquid crystal with respect to temperature.

On the other hand, in the case of a dot matrix type liquid crystal display device employing a simple matrix drive,
It is necessary to adjust the drive voltage according to desired display characteristics.
Among them, Super Twisted Nematic (ST
N) The drive voltage of the liquid crystal display element changes greatly when the temperature changes. The technology of STN liquid crystal display element is US
5194975, US5262881, US55483
02, US Pat.

FIG. 9 is a graph showing the relationship between the ambient temperature and the driving voltage in the STN liquid crystal display device. In the low temperature range, the driving voltage increases because the elastic constant of the liquid crystal increases. Conversely, in a high temperature range, the driving voltage is reduced because the elastic constant of the liquid crystal is reduced. This is because the elastic constant of the liquid crystal is directly affected by the temperature.

Therefore, the display of the STN liquid crystal display element is
If an attempt is made to use a constant drive voltage, the brightness of the displayed image fluctuates with changes in the ambient temperature. In order to solve this problem, a liquid crystal display element used for a large panel such as a notebook personal computer or a portable data display device is provided with a volume for adjusting contrast near the liquid crystal panel. The user uses the liquid crystal display element while manually adjusting the volume to adjust the display contrast ratio and brightness to desired states.

There is also known a liquid crystal display device which automatically adjusts a driving voltage according to a temperature change, instead of a manual operation. The drive voltage of the liquid crystal display element is adjusted using light emitted from a photodiode mounted on the liquid crystal display element instead of external light (JP-A-11-30520).
0).

[0008] Further, a technology for providing an optimum display with respect to an ambient temperature by providing a temperature sensor is also known (Japanese Patent Laid-Open No. 1-1).
67734). FIG. 10 shows an example of a circuit configuration for performing temperature compensation. A temperature sensor 105 such as a thermistor converts the measured temperature data into an analog voltage signal. A / D
Converter 106 converts the analog voltage signal into a digital signal and outputs the digital signal to an address terminal of ROM 107. In the ROM 107, digital data corresponding to a drive voltage corresponding to the operating temperature is prepared.

Digital data corresponding to a predetermined drive voltage is output from the ROM 107 and output to the power supply circuit 108. The power supply circuit 108 outputs a drive voltage to the row electrode driver 102 and the column electrode driver 103. Other components such as the controller 101 and the liquid crystal panel 104 are the same as those usually used. By providing such a function in the liquid crystal display device, it is possible to automatically adjust display according to a change in ambient temperature.

[0010] In addition, overall dispersion may occur in the entire liquid crystal display device including the liquid crystal display element and the peripheral circuits. There is known a method of adjusting an offset voltage of a drive circuit in order to reduce variation among units in a liquid crystal display device. A plurality of parameter values are prepared in advance in the ROM as offset voltages, display brightness is adjusted at the time of shipment of each product, and a parameter is set so that an optimum drive voltage is generated for each product and a good display brightness is exhibited. Select and set a value.

[0011]

However, in the case of the prior art, the occurrence of underexposure or overexposure in gray scale display is determined by visual inspection. Therefore, the drive voltage is detected for each unit of the liquid crystal display element,
Even if the offset value of the drive voltage is set, the drive voltage is not always the optimum value. In addition, in the pre-shipment inspection in the production process, even if the drive voltage was adjusted for a group of liquid crystal display elements, considerable variation occurred as a whole group.

In order to achieve good production efficiency in a factory, high throughput is required. However, in the prior art, the results of adjusting the driving voltage vary and the process of adjusting the display luminance is complicated. Therefore, there is a problem that a long man-hour is required. When the drive voltage was adjusted using an optical measuring device, the display luminance could be measured with high precision. However, two levels (white level and adjacent gray level) on the low luminance side and two levels on the high luminance side were obtained. (A gray level adjacent to a black level) was required. Further, it is necessary to adjust the display by repeatedly measuring each luminance until a desired luminance distribution is obtained for a predetermined gray scale. This task was complicated and time-consuming.

The present invention has been made to solve such a problem, and it is an object of the present invention to easily adjust the display luminance of a liquid crystal display element which performs dot matrix display with gradation. That is, the present invention provides a display adjustment method that can perform adjustment in a short time, can be easily incorporated into an automatic production process of a factory, and has a small variation in a set driving voltage. Also, the present invention provides a method of adjusting display brightness, in which even if a visual inspection is performed, the variation in the adjustment result is extremely small as compared with the related art, and the processing can be performed in a short time. Further, the present invention provides a liquid crystal display device capable of constantly adjusting the drive voltage automatically.

[0014]

According to the present invention, a liquid crystal layer is disposed between a row electrode and a column electrode, and an intersection between the row electrode and the column electrode arranged in a matrix is defined as a pixel. In the method of adjusting the display luminance of the liquid crystal display element in which a drive voltage is applied between the column electrode and the column electrode, low-luminance display, medium-luminance display, high-luminance display, the low-luminance display and the high-luminance display are performed. The present invention provides a method for adjusting the display luminance of a liquid crystal display element, in which a drive voltage is set so that the average display luminance of the liquid crystal display and the display luminance of the medium luminance display substantially match each other.

The low-luminance display, the medium-luminance display,
A drive voltage is prepared by preparing a low gradation level, a middle gradation level, and a high gradation level of a driving voltage corresponding to the high luminance display, preparing a plurality of offset voltages for shifting the driving voltage, and selecting an offset voltage. Is provided. Further, the present invention provides the above-described adjustment method for simultaneously performing the low-luminance display and the high-luminance display. Further, the present invention provides the above-described adjustment method for simultaneously performing the low-luminance display, the high-luminance display, and the medium-luminance display. In addition, the present invention provides the above-described adjustment method in which any one of the low-luminance display, the medium-luminance display, and the high-luminance display or the average display luminance is detected by an optical measurement device. Further, assuming that the display luminances of the low luminance display, the medium luminance display, and the high luminance display are B _L , B _m , and B _H , respectively, B _m is within ± 5% of (B _L + B _H ) / 2. Is provided. Preferably, it sets the B _m to _{(B L + B H) /} 2 of within ± 1%.

Further, a liquid crystal layer is sandwiched between the row electrode and the column electrode, the intersection of the row electrode and the column electrode arranged in a dot matrix form a pixel, and a driving voltage is applied between the row electrode and the column electrode. Is applied to a liquid crystal display device provided with a liquid crystal display element and a drive circuit, low-luminance display is performed, medium-luminance display is performed, high-luminance display is performed, and the low-luminance display and the high-luminance display are performed. The average display luminance of the display is detected, the display luminance of the medium luminance display is compared with the average display luminance,
Provided is a liquid crystal display device in which a driving voltage is automatically adjusted.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows general characteristics of transmission luminance versus driving voltage of a liquid crystal display device. Hereinafter, the driving voltage is 2 V
Also called _r . Further, the dynamic V-T curve representing a relationship between the transmission luminance and 2V _r is referred to as a characteristic curve. This is a display in which a predetermined gradation is displayed on a liquid crystal display element, and the display luminance is measured by an optical measuring device. In the present invention, the liquid crystal display element displays at least three displays having different brightnesses, that is, a low-luminance display, a medium-luminance display, and a high-luminance display. Then, an optimal drive voltage is set so that the average display luminance of the low luminance display and the high luminance display substantially matches the display luminance of the medium luminance display.

The first mode of the average display luminance is that the two display patterns of low luminance display and high luminance display are spatially mixed or displayed alternately with time. This is a case where the display luminance is almost uniform. The two displays may be combined spatially and / or temporally.

At this time, the average display luminance can be detected by an optical measuring device or can be detected by visual inspection. Further, in order to compare the display luminance of the medium luminance display with the display luminance, if an optical measuring device is used, the processing can be performed in a temporally separated manner. Moreover, the average display luminance and the display luminance of the medium luminance display can be measured in order by one optical measuring device. When the visual inspection is used, it is preferable to perform the three displays of the low-luminance display, the medium-luminance display, and the high-luminance display separately on the same display surface at the same time to adjust the drive voltage.

The second mode of the average display luminance is mainly for the case where each display luminance of the high luminance display and the low luminance display is detected by the optical measuring device. That is, the display luminances of the low luminance display and the high luminance display are detected substantially separately. The average display luminance is obtained from the detected display luminances, and the average display luminance and the display luminance of the medium luminance display can be compared. Then, the drive voltage is adjusted so that the two substantially match. When detecting with an optical measuring device, the display brightness can be compared in an analog or digital manner.

The low-luminance display, the medium-luminance display, and the high-luminance display have relatively different luminance levels, and the respective luminances are B _L , B _M , and B _H , and the maximum luminance is 100%. In this case, it is preferable that B _M −B _L ≧ 30%. Also, B _H −
B _M ≧ 30% is preferred.

Usually, B_MIs 40-60%, B_LIs 0-1
0%, B_HIs preferably set to 90-100%
No. When adjusting display brightness easily and with higher precision
Is B _L0-5%, B_M45-55%, B_HFrom 95 to
Preferably, it is set to 100%. Mainly specific color display
Liquids that often display specific images
In the case of crystal display devices, the adjustment criteria for display brightness
Shift and B_MDisplay brightness by setting to about 40% or 60%
Can be adjusted.

Next, a method of creating a data conversion table of an ambient temperature versus a driving voltage called a lookup table will be described. Hereinafter, this data conversion table is called a characteristic table. FIG. 11 is a schematic diagram of a display adjustment pattern corresponding to eight gradations. In the drawing, the higher the hatching density, the lower the display luminance, and the lower the black display.

From the gray level 0 (white level) at the left end to the gray level 7 (black level) at the right end, the brightness of each stripe of the display adjustment pattern gradually decreases.
This display adjustment pattern may be displayed on a part or substantially the entire panel surface of the liquid crystal display element. An independent display surface for adjusting the display luminance may be formed and used in addition to the normally used panel surface.

The display adjustment pattern is displayed on the panel surface, and the driving voltage is adjusted while observing the change in the display luminance of each stripe. At this time, adjustment is performed so that the luminance difference between gray level 0 and gray level 7 is large, and the luminance difference between gray level 0 and gray level 1 and the luminance difference between gray level 6 and gray level 7 are large.

That is, a setting is made so as to avoid a darkened state in which the adjacent luminance pattern cannot be recognized in the bright left area, and to avoid a darkened state in which the adjacent luminance pattern cannot be recognized in the dark right area. . As a whole, the display brightness is adjusted so that a gray scale display with a large contrast ratio is obtained.

Then, a desired operating temperature range, for example,
A characteristic table of the ambient temperature versus the driving voltage is determined in a temperature range of -10 ° C to + 70 ° C. To do so, the measurement of the drive voltage for the main ambient temperature is performed in the manner described above. Further, the drive voltage at a temperature other than the main ambient temperature is determined by performing data interpolation. In this way, a characteristic table of the ambient temperature versus the drive voltage is created.

In the following Examples 1 to 3, light is transmitted when the driving voltage is low, and light is blocked when the driving voltage is high.
A simple matrix drive transmission type STN liquid crystal display element which performs so-called normally white display is used. It is also assumed that 16 types of gray levels can be displayed, white having the highest transmittance is gray level 0, black having the lowest transmittance is gray level 15, and gray levels are gray levels in descending order of luminance (transmittance). Call them 1-14.

FIG. 1 shows a characteristic curve 11 for a gray level 15 (black), a characteristic curve 12 for a gray level 0 (white), and a characteristic curve 13 for a gray level 7.
Then, a checkered black-and-white image is adopted as a display adjustment pattern, a high-luminance display and a low-luminance display are spatially arranged, and the display luminances of both are averaged to become the average display luminance. Then, to detect the average display brightness in the optical measuring device, shows the characteristic curve 14 relative to 2V _r of the horizontal axis.

From the graph of FIG. 1, it can be seen that there is a drive voltage value where the characteristic curve 14 and the characteristic curve 13 for the gray level 7 intersect. Hereinafter, the average display luminance of the high luminance display and the low luminance display and the gray level n (n is 1 to 1)
A drive voltage value at which the display luminance of the medium luminance display is equal to (an integer of 4) is called Vgrayn. In the case of 16 gradations, for example,
Set n = 7. Set near the middle point of the gradation value. At this time, Vgray 7 can be measured by visual inspection or an optical measuring device.

Next, a method of measuring Vgray 7 by visual inspection will be described. FIG. 2 shows an example of a display adjustment pattern that can be used in the present invention. A checkerboard mosaic display unit 21 and a halftone display unit 22 exhibiting a single display luminance level of halftone are provided. The checkerboard display image only needs to be arranged such that pixels set to low luminance and high luminance are arranged and averaged spatially or temporally or temporally and spatially. It is sufficient that the display can be perceived by human eyes as a display having a substantially uniform display luminance. Instead of a checkered pattern, black and white pixels may be arranged in a spot pattern, or a random pattern of black and white pixels may be employed.

For example, as shown in FIG. 2, an image in which white pixels and black pixels are arranged in a checkered pattern for each dot may be displayed, or white and black may be alternately displayed in time. The display image of the checkered pattern shown in FIG. 2 and the display image obtained by exchanging the black and white state may be alternately displayed in time.

When a human adjusts the display luminance, the drive voltage may be finely adjusted so that the luminance of the mosaic display unit 21 and the luminance of the halftone display unit 21 become equal. In the visual inspection, the mosaic display unit is sensed as a constant display luminance, and the value on the characteristic curve 14 in FIG. 1 can be observed. As shown in FIG. 1, there is always a state where the display luminances of the two displays are equal, and this can be sensed accurately.

Basically, when n = 7, the ratio of the black and white area of the mosaic display section 21 is set to 1: 1. Further, the spatial ratio and / or the temporal ratio of the low-luminance display and the high-luminance display may be set to be distributed at a constant ratio according to the value of n to be set. Also, pixels for high-luminance display and pixels for low-luminance display may be randomly arranged spatially or temporally.

In the example shown in FIG. 2, the mosaic display section 21 and the halftone display section 22 are arranged adjacent to each other so that the display can be easily compared. Further, although they are arranged in the vertical direction, they may be arranged in the horizontal direction. Alternatively, the mosaic display unit 21 and the halftone display unit 22 may be arranged in three or more areas.

The mosaic display section 21 may be arranged so that the averaged luminance can be perceived when viewed by a human or measured by an optical measuring device. When counting is performed using a pair of each of the high-brightness display and the low-brightness display in the whole region as a unit, if the density is high, the display screen can be visually recognized from a nearby position or can be measured. Normally,
It is preferable to display a checkered pattern in units of each pixel of the dot matrix. This display adjustment pattern is
It may be displayed on the entire panel surface, or may be set to a size that is easy for humans to see, for example, an area of 10 cm × 10 cm.

Next, the procedure for determining Vgray 7 by visual inspection will be described. 3 shows, in panel surface to display the display adjustment pattern shown in FIG. 2, when changing the 2V _r, a change in the display state on the panel surface shown schematically. In the figure, the denser the diagonal lines, the lower the luminance (dark state), and the coarser the diagonal lines, the higher the luminance (bright state).

In the case 2V _r is smaller than Vgray7, (a)
Lower than the luminance of the luminance halftone display unit 22 of the mosaic display unit 21 for displaying the checkered pattern as, 2V _r is Vgra
If it is larger than y7, the mosaic display unit 2 as shown in (c)
1 is higher than the luminance of the halftone display unit 22.

[0039] In the case 2V _r is equal to Vgray7 is, (b)
The luminance of the mosaic display unit 21 and the halftone display unit 22
A state where the luminance of the image becomes equal to that of the image is observed. This (b)
As shown in the above condition, the state where the brightness of the two regions is equal is accurately sensed, and the drive voltage at that time is measured.
Can be determined.

Next, the principle that Vgray 7 becomes equal to the optimum driving voltage will be described. In the graph of FIG. 4, the characteristic curve 41 indicates white (gray level 0), the characteristic curve 45 indicates black (gray level 15), the characteristic curve 42 indicates gray level 4,
The characteristic curve 43 plots the gray level 7, the characteristic curve 44 plots the gray level 11, and the characteristic curve 46 plots the checkered pattern. The straight line 47 is Vgray7
And the straight line 48 is Vgra, which is 1% smaller than Vgray7.
The line 49 schematically indicates y7-1%, and the straight line 49 indicates Vgray7 + 1% which is a voltage 1% larger than Vgray7.

FIG. 5 shows the relationship between the gray scale values on the horizontal axis and the brightness on the vertical axis. Curve 5
1 is 2V _r Vgray7, the curve 53 is 2V _r Vgray7-1%,
Curve 52 is intended to 2V _r is the case of Vgray7 + 1%, were plotted luminance change. Gray level 0 represents a bright high luminance display, and gray level 15 represents a dark low luminance display. These curves show the dynamic range of display luminance.

The slope of the curve in the vicinity of both ends of the gray level from 5 (gray levels 11 to 15 and gray level 0-4) It can be seen that differs by the value of 2V _r which a parameter. If the slope of the curve is steep, the brightness difference between gray levels is large, and if the slope is gentle, the brightness difference between gray levels is small.

FIG. 6 shows the luminance difference between the gray levels (gray levels 11 to 15, 7 to 11, 4 to 7, 0 to 4) by two.
V _r is shown as a parameter. Curve 61 shows the relative relationship in three cases of Vgray7, curve 63 shows Vgray7-1%, and curve 62 shows Vgray7 + 1%. There is a tendency that the luminance difference is large near the center of the gray level, and the luminance difference is small on both sides of the gray level.

In the case of Vgray7 + 1% shown by the curve 62 in FIG. 6, the luminance difference between the gray level 11 and the gray level 15 (1
1 to 15) are smaller than the case of Vgray7 shown by the curve 61. In other words, it can be seen that gray levels close to black (for example, gray levels 11 to 15) are difficult to identify, and that blackening has occurred.

In the case of Vgray7-1% shown by a curve 63 in FIG.
The luminance difference (0 to 4) between the gray level 0 and the gray level 4 is smaller than that in the case of Vgray7 indicated by the curve 61, and a gray level close to white (for example, gray levels 0 to 4) is difficult to discriminate, and white loss occurs. You can see that it is. Therefore, in the case of Vgray7 indicated by the curve 61, it can be seen that the luminance of all gray levels is distributed most uniformly, and that the gray levels are easy to identify as a whole. Therefore, it can be determined that Vgray7 is the optimum drive voltage.

Next, the measurement accuracy of display luminance when the present invention is used will be described. In the graph of FIG. 1, it is attempted to measure a point where the characteristic curve 14 corresponding to the checkered pattern and the characteristic curve 13 corresponding to the halftone display intersect and the drive voltages of the two become equal. As shown in this graph, the two characteristic curves intersect with a significant difference, and the optimum drive voltage can be accurately determined, so that measurement with a small error can be performed.

As described above, the optimum driving voltage can be easily and accurately determined by measuring the Vgray 7 using the visual inspection or the optical measuring device at each ambient temperature.
Then, a characteristic table of ambient temperature vs. drive voltage, which can be incorporated in an actual liquid crystal display element, can be created.

[0048]

EXAMPLE 1 The display brightness of a 480 × 240 dot matrix STN liquid crystal display element was adjusted using the display adjustment pattern shown in FIG. The multi-line addressing method was driven. The cell gap of the liquid crystal display element is 5 μm, and the driving voltage of the driving IC used is 35.0 V
And A 16-gradation display was performed, n was set to 7, and the optimal driving voltage was measured by visual inspection at room temperature.

First, two areas of 5 cm × 5 cm are provided adjacent to the left and right near the center of the panel surface of the liquid crystal display element.
A mosaic display unit that presents a monochrome display for each dot is arranged on the left side, and a halftone display of gray level 7 is arranged on the right side,
Displayed. The drive voltage was continuously changed while visually observing the change in the display luminance of both. In order to perform this inspection, a predetermined inspection circuit was connected to the liquid crystal display device.

Then, a state in which the display luminances of the checkered mosaic display section and the halftone display section of the gray scale 7 were substantially equal was visually detected, and the drive voltage at that time was obtained.
The value of the drive voltage for the liquid crystal display element was 26.2V.

Next, the ambient temperature of the liquid crystal display device is set to -20.
° C, -10 ° C, 0 ° C, + 10 ° C, + 20 ° C, + 40 ° C,
The temperature was changed to + 60 ° C. and + 85 ° C., and the optimum drive voltage at each temperature was similarly detected to determine the characteristic table. In addition, various images were displayed using the data of the characteristic table, a good contrast ratio and a predetermined display luminance were exhibited over the entire temperature range, and the predetermined display characteristics could be achieved over the entire temperature range.

Further, instead of the visual inspection, the display luminance was adjusted using an optical measuring device (BM-7, manufactured by Topcom). The display adjustment pattern and procedure were the same as in the visual inspection. The display luminance of each of the mosaic display unit and the halftone display unit was detected by using one optical measuring device.
As a result, almost the same drive voltage was obtained, and it was confirmed that there was no significant difference between the visual inspection and the adjustment of the display luminance by the optical measurement device. Note that the mosaic display unit and the halftone display unit can be simultaneously detected using two optical measurement devices. Regardless of the method used, the variation in drive voltage over the entire temperature range was about ± 0.5% or less, and the optimum voltage could be determined with high accuracy.

(Example 2) FIG. 7 is a block diagram of a liquid crystal display device provided with a function of automatically adjusting a drive voltage with respect to temperature. A controller 701, a row electrode driver 702, a column electrode driver 703, a liquid crystal panel 704 as an STN liquid crystal display element, a backlight 712, a temperature sensor 705,
The functions of the A / D converter 706 and the ROM 707 are the same as in the related art.

The EEPROM 709 outputs digital data corresponding to a preset drive voltage offset value. ROM 707 and EEPROM 709
Indicating the voltage value output from the adder 71
The value is added by 0, converted to data corresponding to a predetermined drive voltage value, and output to the power supply circuit 708. From the power supply circuit 708, the output given drive voltage 2V _r is sent to the row electrode driver 702 and the column electrode driver 703, the liquid crystal panel 704 are driven.

Next, a method of adjusting the display luminance in the liquid crystal display device will be described. Even if a characteristic table of ambient temperature versus drive voltage is created for one liquid crystal display element using the method of Example 1, there is a unit difference in the optimal drive voltage for each liquid crystal display element. Therefore, a drive voltage characteristic table created by adjusting one liquid crystal display element cannot be directly applied to another liquid crystal display element. This is because the drive voltage varies among the units of the liquid crystal display device due to the overall dispersion of the individual liquid crystal display elements, the drive ICs used in combination, and other circuit elements.

Therefore, it is necessary to adjust the drive voltage before shipping the liquid crystal display device in order to correct the unit difference between the products. Adjustment of voltage before shipment is performed at room temperature
On the other hand, a display adjustment pattern as shown in FIG. 2 is displayed so that the drive voltage matches Vgray7, that is, the luminance of the checkered mosaic display unit 21 and the luminance of the halftone display unit 22 become substantially equal. Select the offset value of the drive voltage. Then, the correction value is stored in the EEPROM 70 of each product.
9 is performed. By using this method, it is possible to accurately and easily adjust the drive voltage for each product before shipping the liquid crystal display device.

[0057] In the above description, it is assumed to match the optimal 2V _r a Vgray7, the display feels that the optimum individual differences and, there may be a difference due to the application. Therefore, the setting of the offset value of the driving voltage to be performed before the shipment of the liquid crystal display device can be easily used depending on individual differences and applications.

[0058] The display darker than that in the case of Vgray7, ie if there even if a high 2V _r than Vgray7 such as Vgray6 and Vgray5 are preferred, display brighter than in the case of Vgray7, that is, than Vgray7 such as Vgray8 and Vgray9 In some cases, a lower 2V _r is preferred. Thus, in order to correspond to the difference due to individual differences and applications, rather than Vgray7 adjusting the drive voltage of the factory may be set 2V _r to fit such Vgray6 and Vgray8.

[0059] (Example 3) Next, a liquid crystal display device is described which can perform automatic adjustment of 2V _r with respect to temperature. Figure 8 shows a block diagram of an automatic adjusting circuit of 2V _r.
A mosaic display unit 807 presents an image such as a checkered pattern, and an optical sensor 805 installed thereon and a halftone display unit 808.
The difference between the output voltage values of the optical sensors 806 installed above the comparator 809 is calculated by the comparator 809, and is taken into the MPU 810.
The halftone display unit 808 displays a halftone image of gray level 7.

A signal indicating a drive voltage is output from MPU 810 and sent to power supply circuit 812. Power supply circuit 812
In outputting the specified 2V _r, the liquid crystal panel 804 is driven. The backlight 813 irradiates not only a display area but also a portion where the optical sensors 805 and 806 are installed. In this example, a display adjustment area is provided outside the normally used display area. Controller 80
1, row electrode driver 802, column electrode driver 803, S
The structure and function of the liquid crystal panel 804 as a TN liquid crystal display element are the same as those of a normal liquid crystal display device.

The mosaic display section 807 and the halftone display section 80
Since 8 is arranged outside the display area, the display image in the display area is not restricted at all. Further, the mosaic display unit 807 and the halftone display unit 808 may be driven by electrodes common to the display area, or may be driven independently by electrodes separated from the display area.

Next, a description will be given of a method for automatic adjustment of 2V _r. The output of the MPU 810 is configured to change so that the output from the comparator 809 approaches 0, and a feedback loop is formed. The mechanism of the automatic adjustment, the optimal 2V _r for the liquid crystal display device
Can be automatically detected. Further, even if the optimum 2V _r of the liquid crystal display element due to secular change of use environment and the electronic components is changed, it automatically compensates for the change. Adopting this method has the following advantages.

(1) There is no need to create a characteristic table of ambient temperature versus drive voltage in advance. (2) It is less susceptible to unit differences in liquid crystal display devices and aging. (3) No temperature measurement circuit is required. (4) By selecting a frequently used gray level in the halftone display section 808, settings for dark display or bright display can be easily made according to the application and customer preference. (5) Offset adjustment of the liquid crystal display element before shipment becomes unnecessary.

In general, liquid crystal display elements have variations in gaps between column electrodes and row electrodes, alignment film thicknesses, and the like. In addition, the characteristics of other electronic components and the like used change over time, and the optimal 2 V when viewed as a whole liquid crystal display device.
_r may change. However, if the method of the present example is used, the optimum 2V _r (Vgray7) can always be detected, so that the influence of the above problem can be suppressed.

Depending on the use of the liquid crystal display device, it may be necessary to perform stable display continuously and not to perform fine adjustment by manual operation. This is because the user is engaged in operating other devices and cannot afford to adjust the liquid crystal display device. Such characteristics are required for display devices of factories and production lines, and for meters of automobiles. It is important to be able to always provide a display with a constant contrast ratio. In addition, the present invention can be applied to color adjustment when performing color display.

[0066]

According to the present invention, it is possible to easily set the driving voltage of the liquid crystal display element and to drastically reduce the variation between the product units. The display can be adjusted while suppressing individual differences between the measurers. In addition, in the display adjustment before shipment at the factory, the processing can be performed in a short time, and the display brightness can be adjusted by overcoming the unit difference of each product and setting the optimum drive voltage in the liquid crystal display element. .

Further, it is possible to provide an easy-to-use liquid crystal display device which can set an optimum display image according to the use or the user's preference, and can always provide it. Further, when the method for adjusting a liquid crystal display device of the present invention is adopted, a temperature measurement circuit is basically unnecessary. Further, in the continuous use state of the liquid crystal display device, it is possible to continuously provide an optimum display image according to the surrounding environment.

[Brief description of the drawings]

FIG. 1 is a graph showing characteristics of a liquid crystal used in the adjustment method of the present invention.

FIG. 2 is a schematic diagram of a mosaic display unit and a halftone display unit for comparison.

FIG. 3 is a schematic diagram for performing comparative adjustment.

FIG. 4 is a graph showing a characteristic curve of drive voltage and transmittance used in the present invention.

FIG. 5 is a graph showing a characteristic curve of Vgray7 of the present invention.

FIG. 6 is a graph comparing halftone display before and after Vgray7.

FIG. 7 is a block diagram of a liquid crystal module.

FIG. 8 is a block diagram of a liquid crystal module including the automatic voltage adjustment circuit according to the present invention.

FIG. 9 is a graph showing a relationship between a driving voltage of a liquid crystal and an ambient temperature.

FIG. 10 is a block diagram of a conventional liquid crystal display device.

FIG. 11 is a schematic diagram showing a grayscale display adjustment pattern.

[Description of Signs] 11, 12, 13, 14, 15: Characteristic curves (VT curves) 21: Mosaic display unit 22: Halftone display unit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Isshiki 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term in Asahi Glass Co., Ltd. 2H093 NA06 NA53 NC16 NC53 NC54 NC59 NC62 NC63 ND07 5C006 AA16 AC02 AF46 AF51 AF52 AF53 AF81 BB12 BF08 BF14 BF15 BF28 BF38 EB01 FA21 5C080 AA10 BB05 DD03 DD15 DD28 EE28 JJ02 JJ05

Claims (7)

[Claims] A liquid crystal layer is disposed between a row electrode and a column electrode, an intersection of the row electrode and the column electrode arranged in a matrix is formed as a pixel, and a driving voltage is applied between the row electrode and the column electrode. In the method of adjusting the display luminance of the liquid crystal display element to which is applied, low luminance display, medium luminance display, high luminance display, the average display luminance of the low luminance display and the high luminance display, and A method for adjusting the display luminance of a liquid crystal display element in which a drive voltage is set so as to substantially match the display luminance of the luminance display. 2. A low gradation level of a drive voltage corresponding to each of the low luminance display, the medium luminance display, and the high luminance display,
2. The adjustment method according to claim 1, wherein a medium gray level and a high gray level are prepared, a plurality of offset voltages for shifting the driving voltage are prepared, and the driving voltage is set by selecting the offset voltage. 3. The adjustment method according to claim 1, wherein the low luminance display and the high luminance display are performed simultaneously. 4. The adjustment method according to claim 1, wherein the low luminance display, the high luminance display, and the middle luminance display are performed simultaneously. 5. The adjustment according to claim 1, wherein the display luminance of the low luminance display, the medium luminance display and the high luminance display or the average display luminance is detected by an optical measuring device. Method. 6. The display luminance of the low-luminance display, the medium-luminance display, and the high-luminance display are represented by B _L , B _m , and B _H , respectively.
When, adjustment method according to claim 1, 2, 3, 4 or 5 B _m is set to _{(B L + B H) /} 2 of ± 5% driving voltage to be within. 7. A liquid crystal layer is sandwiched between a row electrode and a column electrode, and an intersection of a row electrode and a column electrode arranged in a dot matrix form a pixel, and a driving voltage is applied between the row electrode and the column electrode. Is applied to a liquid crystal display device provided with a liquid crystal display element and a drive circuit, low-luminance display is performed, medium-luminance display is performed, high-luminance display is performed, and the low-luminance display and the high-luminance display are performed. A liquid crystal display device in which an average display luminance of a display is detected, a display luminance of the medium luminance display is compared with the average display luminance, and a drive voltage is automatically adjusted.