JPH11174416A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain always optimum temperature-compensated control independently of the dispersion of a cell thickness or power supply voltage by previously measuring deviation between an optimum driving condition of a liquid crystal(LC) panel and a temperature compensation table, storing the deviation as an offset value and controlling the driving condition of the LC panel by shifting the table by the offset. SOLUTION: A temperature compensation table in which the combination of driving voltage Vop and one horizontal scanning period 1H to be a proper driving condition is written in accordance with digital data AD corresponding to the temperature of an LC panel 1 is stored in a programmable ROM 6c built in an MPU 6b. In a driving margin inspection to be executed before shipment, a deviation between the table and an optimum driving condition in each LC panel is measured and stored in a memory 6g as an offset value AD3. At the time of temperature-compensated control, the table is shifted by the stored offset AD3 and the optimum driving condition is controlled to minimize the deviation of the optimum driving condition from the table due to dispersion in each LC panel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a temperature compensation control for a liquid crystal display, and more particularly to a temperature compensation control for a liquid crystal display using a ferroelectric liquid crystal.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used as display devices. Among them, ferroelectric liquid crystals are particularly used. (1) High-speed response: fast switching of liquid crystal molecules (2) Memory (The number of scanning lines can be increased): Bistable (3) Wide viewing angle: Molecules switch in the same plane, etc., especially for large-screen, high-definition, high-speed display devices Is the optimal liquid crystal material. The details of the ferroelectric liquid crystal are described in “Structure and Physical Properties of Ferroelectric Liquid Crystal” (Atsuo Fukuda, Hideo Takezoe, published by Corona Co., Ltd.).

In the liquid crystal display device using the ferroelectric liquid crystal, the driving characteristics of the liquid crystal material have a large temperature characteristic in view of the above-mentioned characteristics. Temperature compensation control for controlling the conditions is required. The basic configuration of the temperature compensation control has already been disclosed in Japanese Patent Publication No. 4-46408.

Here, the temperature characteristics of the ferroelectric liquid crystal will be briefly described. FIG. 7 is a graph showing the relationship between the temperature of the ferroelectric liquid crystal material and the applied voltage or pulse width required for switching the liquid crystal. The graph is
This indicates that the liquid crystal switches with a lower voltage or a shorter pulse width as the temperature of the liquid crystal increases.

When the ferroelectric liquid crystal is formed on an XY matrix panel, a driving waveform as shown in FIG. 8 is used. In the figure, a) is a scanning signal (Y side),
b) is an information signal (X side) having a symmetrical waveform of "selection" and "non-selection", and c) is a composite waveform of a scanning signal and an information signal, and this composite waveform is applied to the liquid crystal. White is displayed when selected and black is displayed when not selected.

At this time, if the voltage Von = Vop = | V2 | + | V3 | at the time of selection exceeds the threshold voltage of the liquid crystal material, the liquid crystal switches as well as the voltage Voff at the time of non-selection. = | V2 |-| V4 | Alternatively, when the information signal voltage (V3, V4) exceeds the threshold value of the liquid crystal, the liquid crystal switches even if it is a non-selection signal, that is, crosstalk occurs.

Therefore, for a certain liquid crystal material temperature,
The direction of the vertical axis between the threshold value and the value at which crosstalk occurs is an optimal driving condition, and this is called a driving margin. Conversely, the temperature range in the horizontal axis direction under a certain driving condition is called a temperature margin. Therefore, when performing drive control of the ferroelectric liquid crystal panel, it is necessary to perform temperature compensation control within this margin.

The operation of the conventional temperature compensation control will be briefly described. FIG. 9 is a block diagram showing a conventional example, in which a driving means 102 is connected and fixed to a liquid crystal panel 101, and a bus board 103 for supplying a power supply and a control signal to the driving means 102 is connected. Here, at a position avoiding the liquid crystal filling port 104 of the liquid crystal panel 101, a temperature detecting means 105 constituted by, for example, a thermistor is fixed as a means for detecting the temperature of the liquid crystal panel 101. Here, the temperature data detected by the temperature detecting means 105 is converted into analog data corresponding to the resistance-temperature characteristics of the thermistor, and then converted into analog data.
6 analog / digital converters (A / D converters) 1
06a and converted into digital data AD corresponding to the detected temperature. The MPU 106b, which controls the display operation and temperature compensation of the liquid crystal panel 101, outputs A
The digital data AD from the / D converter 106a is received. By the way, the MPU 106b is a liquid crystal panel 101
A temperature compensation table in which a combination of a driving voltage (hereinafter referred to as Vop) and one horizontal scanning period (hereinafter referred to as 1H) which are appropriate driving conditions corresponding to the digital data AD corresponding to the temperature is stored. The MPU 106b is provided with a ROM 106c, and the MPU 106b converts the digital data AD corresponding to the detected temperature and the digital data D1 for determining the proper driving condition Vop based on the temperature compensation table into a digital / analog converter (D / A).
/ A converter) 106d via the drive voltage generation circuit 1
06H, and outputs digital data D2 for determining 1H to the 1H generation circuit 106f.

The drive voltage generation circuit 106e generates a power supply voltage necessary for generating the drive voltage Vop in accordance with the D / A converted voltage signal from the MPU 106b, and the 1H generation circuit 106f outputs the power supply voltage from the MPU 106b. A signal for determining the frame frequency corresponding to the digital data D2 corresponding to 1H is output to the driving means 102 via the bus board 103. Thereafter, the driving means 102 outputs a signal for generating these Vop and 1H and the host 1
Based on the address-added image data received from step 08 and other control signals and power supply voltages (not shown), a drive waveform for driving the liquid crystal as shown in FIG. 8 is generated and applied to the liquid crystal panel 101.

The liquid crystal panel is formed so that two transparent substrates face each other at equal intervals so as to have a constant cell thickness. The cell thickness is usually within a range of a designed value ± 5 to 10%. Is formed. Drive voltage Vop applied to liquid crystal
Even if is constant, if the cell thickness varies due to variations, the electric field strength of the voltage actually applied to the liquid crystal will differ.For example, as the cell thickness increases, the electric field strength decreases and the liquid crystal becomes difficult to operate. The liquid crystal panel operates so that Vop is low or 1H is short.
In addition, the accuracy of the voltage generated by the drive voltage generation circuit is ± 3 to
Since it is about 5%, the driving voltage further varies depending on the combination with the panel.

In the temperature compensation control, the driving condition is controlled with respect to the temperature detected by the temperature detecting means. Is provided with an adjustment trimmer 107 that can adjust the resistance-temperature characteristics of the thermistor using a variable resistor so that the digital data AD for referring to the temperature compensation table can be adjusted to obtain an optimum driving condition. It is adjustable so that it can be adjusted.

However, if the cell thickness varies greatly between the liquid crystal panels and the deviation of the optimum driving conditions is large, the adjustment trimmer variable width provided for the user to adjust must be increased, and the adjustment trimmer is driven. If the margin is set to a large value, an image may not be displayed uniformly on the screen of the liquid crystal panel.

[0013]

As described above, in the conventional example, the driving of the temperature compensation table corresponding to the temperature detected by the temperature detecting means due to the variation in the cell thickness of the liquid crystal panel and the variation in the driving voltage. The conditions are not always the optimal driving conditions for the liquid crystal panel,
A deviation occurs between the temperature compensation table and the optimal driving conditions, and it becomes necessary to adjust the driving conditions with an adjusting trimmer.

If the displacement is large, the variable width of the adjustment trimmer must be increased, and the driving margin can be set to a large value, so that an image cannot be displayed uniformly on the liquid crystal panel screen. Such settings can be made.

The present invention has been made in view of the above-described problems in the conventional example, and has a liquid crystal display device capable of always performing optimal temperature compensation control regardless of variations in cell thickness or power supply voltage between liquid crystal panels. The purpose is to provide. Another object of the present invention is to provide a liquid crystal display device that minimizes the variable width of an adjustment trimmer that is adjusted by a user to optimally drive a liquid crystal and that does not display an uneven image even when the adjustment trimmer is improperly set. I do.

[0016]

According to a first aspect of the present invention, a driving means for sandwiching a liquid crystal between two substrates and applying a voltage to the liquid crystal is connected. A liquid crystal panel, a temperature detecting means for detecting a temperature of the liquid crystal panel and outputting temperature data, an analog / digital converter for converting the temperature data to digital data, and a temperature data converted to the digital data. A liquid crystal display device comprising: control means for changing the driving conditions of the liquid crystal panel based on a table in which driving conditions including combinations of temperature data, pulse widths, and voltage values previously stored in the first storage means are associated. In order to adjust the dispersion of the optimal driving conditions for each liquid crystal panel, the deviation between the table and the optimal driving conditions is measured in advance for each liquid crystal panel, and the The amount of shift is stored as an offset value of digital data in the second storage means, and when performing the temperature compensation control, the table is shifted by the stored offset value to control the optimum driving condition. The deviation from the temperature compensation table due to the variation in is made to be the minimum.

According to a second aspect of the present invention, there is provided a liquid crystal panel comprising a liquid crystal sandwiched between two substrates and connected to a driving means for applying a voltage to the liquid crystal; Temperature detecting means for outputting data, an analog / digital converter for converting the temperature data into digital data, and temperature data and pulses previously stored in the first storage means in accordance with the temperature data converted into the digital data. Control means for changing the driving conditions of the liquid crystal panel based on a table corresponding to driving conditions comprising a combination of a width and a voltage value; and adjustment capable of increasing or decreasing temperature data in order to adjust the variation of the driving conditions for each liquid crystal panel. In order to adjust the variation of the driving conditions for each liquid crystal panel, a deviation between the table and the optimum driving conditions is adjusted in advance for each liquid crystal panel. In the liquid crystal display device, the shift amount is stored as an offset value in the second storage means, and when the temperature compensation control is performed, the table is shifted by the stored offset value to control the optimal driving condition. When measuring the deviation between the table and the optimum driving condition, the variable width of the adjustment trimmer is set wide, and when the deviation is stored in the second storage means as the offset value, the adjustment trimmer variable The second to set the width narrow
The deviation from the temperature compensation table due to the variation of each liquid crystal panel is minimized, and after the measurement, the variable width of the adjustment trimmer is set to be narrow to allow the user to deviate from the driving margin. To prevent settings from being made.

In the present invention, the temperature detecting means is, for example, a thermistor. Further, the liquid crystal is particularly preferably a ferroelectric liquid crystal.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram showing one embodiment of the present invention. A driving means 2 is connected and fixed to the liquid crystal panel 1, and a bus board 3 for supplying a power supply, a control signal and the like to the driving means is connected.

Here, at a position avoiding the liquid crystal injection port 4 of the liquid crystal panel 1, a temperature detecting means 5 composed of, for example, a thermistor is fixed as a means for detecting the temperature of the liquid crystal panel 1. The temperature data detected by the temperature detecting means 5 is converted into analog data according to the resistance-temperature characteristics of the thermistor, and then input to an analog / digital converter (A / D converter) 6a of the control circuit board 6. It is converted into digital data AD1 corresponding to the detected temperature.
In this embodiment, the digital data AD1 is 0-255.
(8 bits). The MPU 6b, which controls the display operation and temperature compensation of the liquid crystal panel, receives the digital data AD1 from the A / D converter at regular intervals.
Receive.

An adjustment trimmer 7 is provided for adjusting the digital data AD1. The adjustment trimmer 7 is an analog signal using a variable resistor in the conventional example. However, in this embodiment, the adjustment trimmer 7 is a tact switch for directly inputting the count number AD2 of how many AD1 are to be changed to the MPU 6b. , AD1 can be increased or decreased. The variable width of the adjustment trimmer 7 with respect to AD1 can be adjusted by the programmable RO inside the MPU 6b.
It can be stored in M6c or stored in memory 6g, and is controlled by firmware stored in MPU 6b. In this embodiment, it is ± 42.

Further, in the memory 6g, the optimal driving conditions of the liquid crystal panel and the deviation amount of the temperature compensation table are measured in advance, and the deviation amount measured as the offset value AD3 how many AD1 should be shifted is stored. In the programmable ROM 6c of the MPU 6b, a combination of a drive voltage (hereinafter, referred to as Vop) and one horizontal scanning period (hereinafter, referred to as 1H), which are appropriate drive conditions, is written in accordance with the digital data AD corresponding to the temperature of the liquid crystal panel 1. The MPU 6b calculates the digital data AD1 corresponding to the detected temperature, the AD increase / decrease value AD2 received from the adjustment trimmer 7, and the offset value AD3 stored in the memory 6g. Referring to the temperature compensation table based on the obtained digital data AD4, the digital data D1 for determining the appropriate driving condition Vop is transmitted to the driving voltage generation circuit 6e via the digital / analog converter (D / A converter) 6d for 1H. Is output to the 1H generation circuit 6f.

Then, the driving voltage generation circuit 6e
A power supply voltage (V1, V2, V3, V4, V5, VC, etc. shown in FIG. 8) required to generate the drive voltage Vop in accordance with the voltage signal from the MPU 6b subjected to the / A conversion is generated, and a 1H generation circuit is generated. 6f outputs a signal for determining a frame frequency according to the digital data D2 corresponding to 1H from the MPU 6b to the driving means 2 via the bus board 3. Thereafter, the driving means 2 generates a signal Vop or 1H, the image data with an address received from the host 8, and other control signals (not shown), a power supply voltage, and the like. A driving waveform for driving the liquid crystal as shown in FIG. 1 is generated and applied to the liquid crystal panel 1.

In this description, the A / D converter 6a and the D / A converter 6d are configured separately from the MPU 6b. For example, the A / D converter 6a and the D / A converter 6d are integrated in the MPU 6b. Even if it is formed, there is no problem in operation. Conversely, the programmable ROM 6c and the memory 6g are formed integrally with the MPU 6b. However, even if these memories are mounted on the control circuit board 6 separately from the MPU 6b, the operation does not hinder at all.

Now, a description will be given of a method for measuring a deviation between the temperature compensation table and the optimum driving condition for each liquid crystal panel and storing an offset value of the temperature compensation table in the temperature compensation control having such a configuration. Various inspections are usually performed on the liquid crystal display device during its manufacturing process. In a liquid crystal display device using a ferroelectric liquid crystal, a drive margin is inspected before shipment. In the present embodiment, in the driving margin inspection, a deviation between the temperature compensation table and the optimal driving condition for each liquid crystal panel is measured according to the configuration shown in FIG. 1 and the flow shown in FIG. To memorize.

In FIG. 1, a host 8 is a dedicated drive margin inspection device or a normal personal computer on which software for driving margin inspection and offset value measurement is installed, and is dedicated to the control circuit board 6 of the liquid crystal display device. Connected by an interface. The dedicated interface includes a serial communication line, and the host 8 transmits digital data D1, D2 or AD (AD1 to AD1) representing the driving conditions 1H and Vop from the liquid crystal display device through the serial communication line.
4) After directly obtaining and calculating the offset value AD3,
The offset value AD3 is written to the memory 6g.

FIG. 2 is a diagram showing a measurement flow for determining an offset value. In order to measure the difference between the temperature compensation table and the optimal driving condition of the liquid crystal panel and determine the offset value, it is necessary to measure the temperature compensation table of the liquid crystal panel and the driving margin of the panel as shown in FIG. By operating the adjustment trimmer 7, the measurement is performed. At this time, for example, the + side of the adjustment trimmer 7 is set as the crosstalk, the − side as the threshold, the variable widths on the + side and the − side are set to be the same, and set wider than the drive margin of the liquid crystal panel. In this embodiment, the variable width is ± 42 as described above.

As a method of measuring AD, there is a method of directly obtaining AD from the MPU 6b of the liquid crystal display device. However, the programmable R in the MPU 6b of the liquid crystal display device is provided in the host 8.
Digital data D1, D having the same temperature compensation table stored in OM6c and representing Vop, 1H
2 is obtained from the MPU 6b, and a combination of D1 and D2 is referred to on the temperature compensation table to obtain a matching AD.

The measuring method is to measure each AD when the trimmer is fully filled on the + side upper limit and on the − side lower limit fully, and the center of the variable width of the trimmer is set as the AD of the temperature compensation table. Next, the drive margins on the crosstalk side and the threshold side are measured to obtain respective ADs, and the center thereof is obtained as the AD under the optimum drive conditions of the liquid crystal panel. The difference between the temperature compensation table thus calculated and the AD of the optimum driving condition is calculated, and the obtained AD is set as an offset value AD3. The offset value AD thus obtained
3 is sent from the host 8 to the control circuit board 6 of the liquid crystal display device via the serial communication line, and is written into the memory 6g provided in the MPU 6b.

The order of measurement of the variable width of the adjustment trimmer and the upper and lower limits of the drive margin can be set arbitrarily. In this embodiment, the upper and lower limits of the variable width of the adjustment trimmer are measured to determine the center of the temperature compensation table, and the center is set as the center of the temperature compensation table.
If a means for adjusting the adjustment trimmer to the midpoint is prepared (for example, a program that adjusts the adjustment trimmer to the midpoint of ± 0 by pressing + and-of the adjustment trimmer simultaneously for a few seconds is prepared in the firmware. If the center of the temperature compensation table can be measured in that state or the digital data AD1 corresponding to the detected temperature can be directly stored in the memory 6g and the data can be obtained, the measurement procedure and the calculation procedure are omitted. Time can be shortened.

(Second Embodiment) FIG. 3 is a view for explaining a second embodiment of the present invention, and a graph showing the outline of the temperature compensation table is indicated by a thick line. It also shows that the amount of deviation between the temperature compensation table and the optimal driving condition may differ depending on the temperature.

As described above, the ferroelectric liquid crystal material has a temperature characteristic, and its driving margin varies depending on the temperature as shown in FIG. 7, and therefore, as shown in FIG. Since the deviation from the driving conditions may differ depending on the temperature, using only the offset value measured at a specific temperature may cause the offset to be too large or too small at other temperatures, and instead, the deviation may be large. May also occur.

As described in the first embodiment, the liquid crystal display device using the ferroelectric liquid crystal is provided with the step of inspecting the drive margin in the manufacturing process. Immediately after the liquid crystal panel is turned on (when the liquid crystal panel temperature is low), when the temperature inside the liquid crystal display device is saturated in a low temperature environment (when the liquid crystal panel temperature is around room temperature and the temperature margin is reduced), and when the liquid crystal display device is in a high temperature environment. Are measured (when the temperature of the liquid crystal panel is high and the temperature margin is reduced).

The host 8 stores each offset value measured at the three temperatures of the drive margin measurement,
The average value of the offset values at these three temperatures is represented by the offset value A.
By setting D3 in the memory 6g, the amount of deviation at each temperature can be made as small as possible in consideration of the temperature characteristics of the driving margin of the liquid crystal panel.

(Third Embodiment) FIG. 4 is a block diagram showing a configuration of a third embodiment of the present invention. In this embodiment, since the offset value is measured by operating the adjustment trimmer, it is better that the adjustment trimmer variable width is wide at the time of measurement, but after storing the offset value, the deviation amount from the temperature compensation table should be as small as possible. Therefore, the adjustment trimmer does not need to be largely varied, and it is preferable that the adjustment trimmer be as narrow as possible so that the user does not set the driving margin.

Since the variable width of the adjustment trimmer is set in the memory 6g of the MPU 6b, a wide value (for example, ± 42) is set as an initial value at the time of measurement.
After the offset value is measured, the variable width of the adjustment trimmer is set to a small value (for example, ± 16) when it is set in the memory 6g.

FIG. 5 is a flowchart showing a measurement procedure for setting the adjustment trimmer variable width, and is different from FIG. 2 only in the part where the adjustment trimmer variable width is set after calculating the offset value.

As described above, when the offset value is measured, the adjustment trimmer variable width is set wide, and after the offset value is stored, the adjustment trimmer variable width is set as narrow as possible. After setting the offset value and setting the amount of deviation from the temperature compensation table to be the minimum, it is possible to prevent the setting that deviates from the drive margin by the adjustment trimmer, so that the display always has uniform image quality. Will be able to do it.

(Fourth Embodiment) FIG. 6 is a block diagram showing a fourth embodiment of the present invention.

In the above-described embodiments, all the offset values are measured in the host 8 and set in the memory 6g. However, the offset value is determined only by the firmware inside the MPU 6b regardless of the external host 8. It is also possible to measure the value.

Programmable ROM 6 inside MPU 6b
The offset value measurement routine is provided by providing a program routine for measuring the offset value in the firmware stored in the memory c, and performing a specific operation (for example, turning on the power while simultaneously pressing + and-of the adjustment trimmer). If a firmware program is created so that is valid, the measurement of the offset value and the setting of the offset value in the memory 6g can be performed by the main body of the liquid crystal display device regardless of the specific host 8.

[0042]

As described above, according to the present invention,
Variations in the optimal driving conditions caused by variations in cell thickness for each liquid crystal panel and variations in power supply voltage can be individually adjusted for each product, so deviations from the temperature compensation table can be minimized, so optimal temperature compensation control is always possible In addition, there is almost no need to adjust the adjustment trimmer provided to adjust the deviation from the temperature compensation table.

Also, the variable width of the adjustment trimmer can be minimized, so that non-uniform image display outside the drive margin when operating the adjustment trimmer can be prevented, and good image quality can always be maintained. Become like

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an overall configuration of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a method of measuring an offset value in the apparatus of FIG.

FIG. 3 is a diagram illustrating a second embodiment according to the present invention.

FIG. 4 is a block diagram showing an overall configuration of a third embodiment according to the present invention.

FIG. 5 is a diagram illustrating a measuring method according to a third embodiment of the present invention.

FIG. 6 is a block diagram showing an overall configuration of a fourth embodiment according to the present invention.

FIG. 7 is a diagram illustrating driving temperature characteristics of a ferroelectric liquid crystal.

FIG. 8 is a diagram illustrating an example of a driving waveform of a ferroelectric liquid crystal.

FIG. 9 is a block diagram showing the entire configuration of a conventional example.

[Explanation of symbols]

1: liquid crystal panel, 2: driving means, 3: bus board, 4: liquid crystal inlet, 5: temperature detecting means, 6: control circuit board, 6
a: analog / digital converter, 6b: MPU, 6c:
Programmable ROM, 6d: digital / analog converter, 6e: drive voltage generation circuit, 6f: 1H generation circuit, 6
g: memory, 7: adjustment trimmer, 8: host.

Claims (4)

[Claims] 1. A liquid crystal panel comprising driving means for sandwiching liquid crystal between two substrates and applying a voltage to the liquid crystal, a temperature detecting means for detecting a temperature of the liquid crystal panel and outputting temperature data, An analog / digital converter for converting temperature data into digital data; and a driving condition comprising a combination of temperature data, pulse width and voltage value stored in advance in the first storage means in accordance with the temperature data converted into digital data. Control means for changing the driving conditions of the liquid crystal panel based on a table corresponding to the above. In order to adjust the variation of the optimum driving conditions for each liquid crystal panel, A deviation between the condition and the table is measured, and the deviation is stored in a second storage unit as an offset value of digital data. A liquid crystal display device that controls driving conditions of the liquid crystal panel by shifting the liquid crystal panel by an offset value. 2. A liquid crystal panel comprising driving means for sandwiching liquid crystal between two substrates and applying a voltage to the liquid crystal, a temperature detecting means for detecting a temperature of the liquid crystal panel and outputting temperature data, An analog / digital converter for converting temperature data into digital data; and a driving condition comprising a combination of temperature data, pulse width and voltage value stored in advance in the first storage means in accordance with the temperature data converted into digital data. A control means for changing the driving conditions of the liquid crystal panel according to a table corresponding to the table, and an adjusting trimmer for increasing or decreasing the temperature data. Measure the optimal driving conditions of the panel and the deviation from the table,
In a liquid crystal display device in which the shift amount is stored in a second storage unit as an offset value and the table is shifted by the stored offset value to control the optimum drive condition, the shift between the optimum drive condition and the table is controlled. When measuring the adjustment trimmer, the variable width of the adjustment trimmer is set to be wide, and when the shift amount is stored as an offset value in the second storage means, the second width of the adjustment trimmer is set to be narrow. A liquid crystal display device stored in a storage means. 3. The liquid crystal display device according to claim 1, wherein said temperature detecting means is a thermistor. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal.