JPH06214523A - Automatic contrast adjusting device - Google Patents

Abstract

PURPOSE:To provide an automatic contrast adjusting device capable of providing the optimum LCD contrast for the eyes of respective users. CONSTITUTION:By a CPU 23, a characteristic table showing temperature to liquid crystal driving voltage in a RAM 25 according to the temperature data from a thermistor 12 is referred, and a corresponding PWM value (liquid crystal driving voltage V0) is read out, and a PWM pulse 33 with a duty ratio corresponding to the PWM value is outputted. On the other hand, when the contrast adjustment is performed by contrast switches 38, 39 manually, the characteristic data in the RAM 25 are corrected according to the adjusted amount to be written in a REEPROM 31.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a contrast automatic adjustment device capable of automatically adjusting the contrast of a liquid crystal display screen.

[0002]

2. Description of the Related Art In information processing devices such as personal computers, a liquid crystal display device (hereinafter, referred to as LCD) is often used as a display device from the viewpoint of downsizing and power saving. This LCD is generally provided with a contrast volume, which can be manually operated to adjust the contrast to a desired state.

However, since the display density of the LCD is usually dark at low temperature and whitish at high temperature, the contrast must be adjusted by operating the volume according to the temperature rise in use in the above-mentioned device. I have to.

[0004]

In order to solve such a problem, there has been considered a device in which the contrast is automatically adjusted according to the temperature. However, there is an individual difference in whether or not the contrast is appropriate, and when the contrast is adjusted according to a specific adjustment rule (that is, temperature vs. driving voltage characteristic), the contrast is not necessarily optimized for all users. It cannot be adjusted. In addition, the LCD itself has a certain degree of characteristic variation in manufacturing, and there is a problem that the contrast differs between individual LCDs even with the same drive voltage, and there is no means for solving this problem. It was

The present invention has been made to solve the above problems, and an object of the present invention is to obtain an automatic contrast adjusting device capable of providing an optimum LCD contrast to the eyes of each user.

[0006]

According to a first aspect of the present invention, there is provided a liquid crystal display device for displaying various information with a contrast according to a given driving voltage. Storage means for storing a characteristic table associated with the voltage, (ii) operation switch for input setting the drive voltage of the liquid crystal display device, (iii) based on the drive voltage set by this operation switch, Characteristic correcting means for correcting the content of the characteristic table, (iv) temperature measuring means for measuring the temperature of the liquid crystal display device,
(v) Liquid crystal driving means for reading a corresponding driving voltage from the characteristic table based on the temperature data obtained by the temperature measuring means and supplying the driving voltage to the liquid crystal display device.

According to a second aspect of the present invention, there is provided the automatic contrast adjusting apparatus according to the first aspect, wherein the characteristic correction means is responsive to the difference between the value set by the operation switch and the value before the setting. The temperature range to be corrected is changed.

According to a third aspect of the invention, there is provided the automatic contrast adjusting apparatus according to the first aspect, wherein the characteristic correcting means inputs the operation switch again before a predetermined time has elapsed after the input from the operation switch is completed. It is characterized in that the characteristic data is corrected only when there is no such change.

An automatic contrast adjusting device according to a fourth aspect of the present invention is the automatic contrast adjusting device according to the first aspect, further comprising a determining means for determining the type of the liquid crystal display device.
The characteristic table of the storage means is provided for each type of liquid crystal display device, and the corresponding characteristic table is used according to the determination result of the determination means. The automatic contrast adjustment device according to the invention of claim 5 is
In a liquid crystal display device that displays various types of information with a contrast according to a given drive voltage, (i) a storage unit that stores a characteristic table that associates the operating temperature with the drive voltage,
(ii) temperature measuring means for measuring the temperature of the liquid crystal display device, (iii) reading means for reading the corresponding drive voltage from the characteristic table based on the temperature data obtained by the temperature measuring means, and (iv) ) Driving voltage output means for changing and outputting the variation width of the driving voltage applied to the liquid crystal display device according to the difference between the driving voltage read by the reading means and the previous driving voltage. It is a feature.

According to the sixth aspect of the automatic contrast adjusting apparatus, the correction amount of the drive voltage set by the operation switch at the temperature _t is ΔV _t, and the drive voltage at the temperatures (t-n-1) and (t + n + 1) is set. When the correction amounts are ΔV _tn−1 and ΔV _{t + n + 1} and a is a constant, the equation ΔV _tn-1 = ΔV _{t + n + 1} = ΔV _{t + n} −a / ΔV _t (n = 0 ,
It is characterized in that the characteristic table is modified so as to satisfy 1, 2 ,.

[0011]

According to the first aspect of the invention, the content of the characteristic table is corrected according to the adjustment amount manually input by the contrast switch, and thereafter, the contrast of the liquid crystal panel is automatically adjusted based on the characteristic table.

According to the second aspect of the invention, the correction amount in other temperature zones of the characteristic table changes according to the magnitude of the adjustment amount by manual input.

According to the third aspect of the invention, the characteristic table is corrected only after a lapse of a fixed time after the operation of the contrast switch.

According to the fourth aspect of the invention, the adjustment is made according to the type of the liquid crystal panel.

According to the fifth aspect of the invention, the contrast is adjusted according to the magnitude of the temperature change amount.

According to the sixth aspect of the invention, the contrast is adjusted according to the magnitude of the constant a.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples.

FIG. 1 shows an automatic contrast adjusting device and a liquid crystal display panel according to an embodiment of the present invention. In this figure, the LCD panel 11 is provided with four control terminals V _DD , V _EE , V _SS and V ₀ , which are (+5 V), (+38 V), GND and liquid crystal drive voltage (2
6V to 38V) is supplied. Then, various information is displayed with a contrast according to the liquid crystal drive voltage V ₀ . Also, on the side of the LCD panel 11,
A thermistor 12 is fixedly installed, one end of which is grounded and the other end of which is connected to a power supply V _CC through a resistor 13. The resistance value of the thermistor 12 decreases / increases as the temperature of the installation site rises / falls, and the potential V _T (hereinafter, referred to as sensor voltage V _T ) at one end 15 thereof is as shown in FIG. It decreases as the temperature rises. The sensor voltage V _T is converted into a digital value by an analog / digital (A / D) converter 22 in the contrast control unit 21,
It is input to the central processing unit (CPU) 23.

Further, a DIP switch 40 for outputting information indicating the LCD type such as STN monochrome / STN color.
Is provided, and the LCD type information 16 is read by the CPU 23 as 2-bit information at the first startup after manufacturing.

In the contrast controller 21, a read only memory (ROM) 24 and a writable / readable memory (R) are available.
AM) 25, and the former stores a characteristic table showing the basic characteristic of the temperature vs. liquid crystal drive voltage V ₀ as shown in FIG. 3 for each LCD type. This characteristic table is actually a correspondence between the sensor voltage V _T corresponding to the temperature data and the PWM (pulse width modulation) value corresponding to the liquid crystal drive voltage, and is stored in the RAM 25 or externally as necessary. Provided electrically rewritable memory (EEPRO
M) 31 is copied.

The CPU 23 refers to the characteristic table in the RAM 25 on the basis of the sensor voltage V _T from the thermistor 12, and reads and outputs the corresponding PWM value. This PWM
The value is a PW output from the CPU 23 with a frequency of 1 KHz.
Count number C _H of the high level period of M pulse 33 (see FIG. 4)
(A)), which is such that C _H decreases as the sensor voltage V _T decreases (that is, the temperature increases). One cycle of this PWM pulse 33 is 250
Corresponding to the count, the count number C _H is shown in FIG.
As shown in (b) and (c), values of "60" to "249" can be taken.

A PWM pulse 33 from the CPU 23 is converted into an analog voltage by a digital / analog (D / A) converter 32, and an M of the liquid crystal drive voltage is converted by an analog adder 34.
The LCD is added with the reference voltage (+ 26V), which is the IN value.
The liquid crystal drive voltage V ₀ is supplied to the panel 11.

Further, contrast switches 38 and 39 are connected to the contrast control section 21 via an encoder 37, and by manually or manually depressing these switches, as shown in FIG. 4 (d). , CPU23
The liquid crystal drive voltage V ₀ can be changed by changing the duty ratio of the PWM pulse 33. Here, the contrast switch 38 is used to increase the liquid crystal drive voltage V ₀ to lighten the contrast, and the contrast switch 39 is used to decrease the liquid crystal drive voltage V ₀ to darken the contrast.

The operation of the automatic contrast adjusting device having the above-mentioned structure will be described with reference to FIGS.

First, when a power switch (not shown) is turned on, in the case of the first activation after manufacturing (FIG. 5, step S101;
Y), the CPU 23 fetches the LCD type information 16 to determine the LCD type (step S102), reads the corresponding LCD characteristic table from the ROM 24, and outputs the characteristic table.
Write to EPROM 31 and RAM 25 (step S
103). On the other hand, if it is not the first activation (step S101; N), the characteristic table in the EEPROM 31 is read and written in the RAM 25 (step S10).
7).

The ROM 24 stores revision numbers (revisions) together with the default values of the characteristic table, and these are written in the EEPROM 31. Therefore, RO
By determining whether or not the revisions of M and the EEPROM 31 match, it is possible to determine whether or not it is the first activation after manufacturing.

Next, the CPU 23 takes in the sensor voltage V _T from the thermistor 12 and performs A / D conversion, and sets this value in the variable X (step S104). Then, based on the value of the variable X, the corresponding PWM value is read by referring to the characteristic table of the RAM 25, and the PWM determined by this value is set.
The pulse 33 is output (step S105). This PW
The M pulse 33 is converted into an analog voltage by the D / A converter 32, and the reference voltage (+ 26V) is added by the adder 34 to become the liquid crystal drive voltage V ₀ of the LCD panel 11. Then C
The PU 23 sets “0” to the counter C and the accumulated variable Y (step S111 in FIG. 6), and then according to the following steps S113 to S118, four times per second for four seconds in total for 16 temperature data (sensor voltage V _T ) and take the average. That is, first, it is checked whether or not the contrast switch 38 or 39 is pressed (step S112), and if not pressed (same; N), one sensor voltage V _T is taken in and A / D is acquired.
It is converted to obtain the digital value T (step S113).
Then, this digital value T is added to the accumulation variable Y (step S114), and if the counter C does not reach "15" (step S115; N), C is incremented (step S116) and the process returns to step S112. . Hereinafter, this process is repeated until the counter C reaches "15" (step S115; Y), and a total of 16 data is obtained, and the average value A is obtained (step S11).
7).

Next, the average value A thus obtained is compared with the variable X (previous PWM value), and when A is larger than X (step S118; Y, step S119;
N), X is incremented by "1", and when A is equal to X (step S118; Y, step S119;
Y) and X are not changed. On the other hand, when A is smaller than X (step S118; N), the magnitudes of A and (X-3) are further compared, and the value of X is changed according to the result. That is, when A is smaller than (X-3) (step S121; Y), X is decremented by "1", and when not (step S121; N), the value of X is not changed. Then, the CPU 23 refers to the characteristic table of the RAM 25 on the basis of the value of the variable X and sets the corresponding PW.
The M value is read, and the PWM pulse 33 determined by this value is output (step S105).

Such processing (steps S118 to S1)
By performing 22), the value of the variable X (sensor voltage V _T ) when referring to the characteristic table changes by 1 even when the difference between the previous temperature data and the previous temperature data greatly changes. The liquid crystal drive voltage V ₀ also changes by the minimum step. Particularly, when the temperature rises and the sensor voltage V _T decreases, the liquid crystal drive voltage V ₀ is not changed unless the sensor voltage V _T decreases by 3 or more. As a result, it is possible to effectively suppress the fluctuation of the contrast due to the automatic adjustment when the temperature fluctuation is large. In the above example, the value of the sensor voltage V _T , which is the temperature data, is corrected, but in addition to this, the PWM value obtained by referring to the characteristic table may be corrected by increment or decrement. Of course, the same effect can be obtained.

When it is detected in step S112 that the contrast switch has been pressed (step S112; Y in FIG. 6), the manual input value from the contrast switch is fetched (step S131 in FIG. 7), and based on this, the time The PWM value at step S1 is corrected (step S1
32). Specifically, as shown in FIG. 4D, every time the contrast switch 38 is pressed, the count number C _{H in} the high level period of the PWM pulse 33 is incremented by 1 and the liquid crystal drive voltage V ₀ is increased. Increases, L
The display on the CD panel 11 becomes faint. Conversely, each time the contrast switch 39 is pressed once, the count number C _H is decremented by one count, the liquid crystal drive voltage V ₀ is reduced, and the display on the LCD panel 11 is darkened. When the contrast switch is continuously pressed, the CPU2
No. 3 polls at a constant cycle until the pressing of the contrast switch 38 or 39 is completed (step S133; Y), and the count number C _H is incremented by 1 until the initial 4th count and up to the 8th count. Change by 2 counts and then by 4 counts.

Next, when the CPU 23 detects that the contrast switch 38 or 39 is released (step S133; Y), it resets the timer (step S13).
4) If the switch is not pressed again before 5 seconds have elapsed (step S135; N, step S136;
N, step S135; Y), based on the PWM value obtained in step S132, the characteristic table in the RAM 25 is corrected (the correction method will be described later) (step S138) and is written in the EEPROM 31 (step S138). (S139), and returns to step S111.
On the other hand, if the switch is pressed again within 5 seconds after detecting that the contrast switch is off (step S13).
6; Y), reset the timer (step S13)
7) and returns to step S111.

By such processing, even when the contrast switch is manually operated by trial and error to perform the manual adjustment, the characteristic table is corrected only when the final contrast state is reached, and rewriting is performed. This is effective in that the life of the EEPROM, which has a limited number of times, can be extended.

Next, referring to FIG. 8, step S of FIG.
A method of correcting the characteristic table in 138 will be described.

Now, the initial characteristic table is the solid line 4 in FIG.
1 and the current temperature is t. If the contrast switch 39 is operated to lower the liquid crystal drive voltage V ₀ by ΔV _t , the temperatures (t−n−1) and (t +) on both sides of the liquid crystal drive voltage V ₀ are reduced.
The correction amount ΔV of the liquid crystal drive voltage in (n + 1) is calculated from the following equation (1). However, n = 0, 1, 2, ...

ΔV _tn−1 = ΔV _{t + n + 1} = ΔV _{t + n} −a / ΔV _t (1) where “a” is the temperature range to be corrected, that is, the correction at a certain temperature. It is a constant indicating the degree of influence on other temperature regions and is written in the EEPROM.
The setting can be changed.

In this equation (1), n is 0 to 1,
The temperature (t-n-
Correction amount ΔV _tn-1 of liquid crystal drive voltage in 1) and correction amount ΔV of liquid crystal drive voltage at temperature (t + n + 1)
_{When t + n + 1} is calculated, for example, it becomes as follows.

N = 0: ΔV _t−1 = ΔV _{t + 1} = ΔV _t −a / ΔV _t (2) n = 1: ΔV _t-2 = ΔV _{t + 2} = ΔV _{t + 1} −2 a / ΔV _t (3) n = 2: ΔV _t−3 = ΔV _{t + 3} = ΔV _{t + 2} −3 a / ΔV _t (4) ... And, the (temperature vs. drive voltage) characteristic curve data of the characteristic table The data is sequentially changed to the data obtained from the above equations (2) and (3), and such processing is performed until a new characteristic curve intersects with the original characteristic curve. This allows
When the user changes the liquid crystal drive voltage by ΔV _t by operating the switch at a certain temperature t, not only the liquid crystal drive voltage correction amounts (ΔV _t-1 , ΔV _{t + 1} ) on both sides of the voltage change, but
Further, the amount of voltage correction around it will also be changed.

As can be seen from the equation (1), if a is made extremely large, the influence on other temperature zones of the table is reduced. On the other hand, when a is reduced, the influence is exerted over a wide temperature range, and for example, when a = 0 is extremely set, the characteristic curve is translated.

By performing the characteristic table correction process as described above, for example, new characteristic data as shown by the broken line 42 in FIG. 8 can be obtained. Then, by performing such a manual adjustment at several temperatures, the initial characteristic table matches the characteristics of the liquid crystal panel and is sequentially learned and modified to a characteristic table that the user likes. Will be done.

When the value ΔV _{t to} be manually adjusted is large, as shown in FIG. 9 (a), the effect of the adjustment at one temperature on the other temperature zones is large, and conversely when it is small. As shown in FIG. 9B, the influence is small.

[0041]

As described above, according to the first aspect of the present invention, the contents of the characteristic table are corrected according to the adjustment amount manually input by the contrast switch, and thereafter, based on this characteristic table. The contrast of the LCD panel is automatically adjusted. As a result, even if there are variations in the characteristics of individual liquid crystal display panels or individual differences among users,
There is an effect that the optimum contrast adjustment can be automatically performed according to the user's preference.

According to the second aspect of the present invention, the correction amount in other temperature zones of the characteristic table changes according to the magnitude of the adjustment amount by manual input.

According to the third aspect of the present invention, since the characteristic table is corrected only after a lapse of a certain time after the operation of the contrast switch, the contrast switch is operated carelessly or by trial and error. Even in this case, only the final adjustment amount is adopted and the characteristic table is modified.

According to the fourth aspect of the invention, since the contrast is adjusted according to the type of the liquid crystal panel, there is an effect that a circuit for contrast adjustment can be shared.

According to the fifth aspect of the present invention, since the contrast adjustment width is changed according to the magnitude of the temperature change amount, it is possible to avoid the contrast fluctuation.

According to the sixth aspect of the invention, it is possible to arbitrarily set the degree of the influence of the correction at a certain temperature on the correction amount at another temperature zone, depending on the magnitude of the value of the constant a.

[Brief description of drawings]

FIG. 1 is a block diagram showing an automatic contrast adjustment apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing temperature characteristics of the thermistor in FIG.

FIG. 3 is a characteristic diagram showing contents of a characteristic table stored in a ROM shown in FIG.

FIG. 4 is an explanatory diagram showing a waveform of a PWM pulse output from the CPU in FIG.

FIG. 5 is a CP in the automatic contrast adjustment device of FIG.
It is a flowchart which shows the processing content of U.

FIG. 6 is a CP in the automatic contrast adjustment device of FIG.
It is a flowchart which shows the processing content of U.

FIG. 7 is a CP in the automatic contrast adjustment device of FIG.
It is a flowchart which shows the processing content of U.

FIG. 8 is an explanatory diagram illustrating a method of correcting a characteristic table.

FIG. 9 is an explanatory diagram illustrating a method of correcting a characteristic table.

[Explanation of symbols]

 11 LCD Panel 12 Thermistor 21 Contrast Control Unit 23 CPU 24 ROM 25 RAM 31 EEPROM 38, 39 Contrast Switch

Claims (6)

[Claims] 1. A liquid crystal display device for displaying various kinds of information with a contrast according to a given drive voltage, a storage means for storing a characteristic table in which an operating temperature and a drive voltage are associated with each other, and a drive voltage for the liquid crystal display device. An operation switch for input setting, a characteristic correction means for correcting the contents of the characteristic table based on the drive voltage set by the operation switch, and a temperature measurement means for measuring the temperature of the liquid crystal display device. And a liquid crystal driving means for reading a corresponding driving voltage from the characteristic table based on the temperature data obtained by the temperature measuring means and supplying the driving voltage to the liquid crystal display device. 2. The characteristic correcting means according to claim 1, wherein the temperature range to be corrected is changed according to the magnitude of the difference between the value set by the operation switch and the value before the setting. Characteristic automatic contrast adjustment device. 3. The characteristic correction means according to claim 1, wherein the characteristic correction means corrects the characteristic data only when an input from the operation switch is not made again before a predetermined time has elapsed after the input from the operation switch is completed. An automatic contrast adjustment device characterized by the above. 4. The method according to claim 1, further comprising a determining means for determining the type of liquid crystal display device,
An automatic contrast adjustment device, wherein a characteristic table of the storage means is provided for each type of liquid crystal display device, and a corresponding characteristic table is used according to the determination result of the determination means. 5. A liquid crystal display device for displaying various kinds of information with a contrast according to a given drive voltage, a storage means for storing a characteristic table in which an operating temperature and a drive voltage are associated with each other, and a temperature of the liquid crystal display device. Temperature reading means for reading the corresponding driving voltage from the characteristic table based on the temperature data obtained by the temperature measuring means, and the driving voltage read by the reading means An automatic contrast adjustment device, comprising: a drive voltage output unit that changes and outputs a variation range of a drive voltage applied to a liquid crystal display device according to a difference with the drive voltage. 6. The characteristic correction means according to claim 2, wherein the correction amount of the drive voltage set by the operation switch at the temperature _t is ΔV _t, and the drive is performed at temperatures (t−n−1) and (t + n + 1). The amount of voltage correction is Δ
_Vtn-1 and ΔVt _{+ n + 1} , where a is a constant, the characteristic table is modified so as to satisfy the following equation: _ΔVtn-1 = ΔVt _{+ n + 1} = ΔV _{t + n} −a / ΔV _t (n = 0,
1,2, ...)