JPH0229718A - Contrast adjusting device for liquid crystal - Google Patents

Abstract

PURPOSE:To obtain an optimum contrast of a liquid crystal independently of a dispersion of constants, etc., of a liquid crystal cell by sensing the quantity of light of a lighting part and an unlighting part of a liquid crystal display device and adjusting a driving electric voltage of the liquid crystal display device so as to result the maximum value of the difference of the quantity of light. CONSTITUTION:Each level of a lighting level sensing cell 6 and an unlighting level sensing cell 5 of a liquid crystal display panel 1 functioning as display part is sensed with a photoelectric conversion element CDS 1 and CDS 2 respectively, and a difference of its output is amplified with a differential amplifier OP1. A peak of a difference between the photoelectric conversion element CDS 1 and CDS 2 is sensed with a peak sensing circuit 2, and a driving voltage of the liquid crystal display device is controlled by feeding back the difference from the peak sensing circuit 2 to a driving power source 3 so as to obtain the maximum value of an output voltage of the differential amplifier OP1. By this method, the driving voltage of the liquid crystal display device is controlled automatically so that a liquid crystal display panel constituted of a cell having an optional contrast characteristic may produce an optimum contrast.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a device for adjusting the contrast of a liquid crystal display device, and particularly to a device for adjusting the contrast of a liquid crystal display device, and in particular, the contrast of a liquid crystal display device that automatically obtains the optimum contrast: I! This relates to J adjustment equipment.

[Prior Art] An active matrix drive method is adopted as a liquid crystal display device. In this driving method, each pixel of a liquid crystal device is provided with a switch device and, if necessary, a signal storage fortress, and the liquid crystal is driven with an integrated configuration.

′! Figure J3 shows a thin film transistor (hereinafter abbreviated as TPT).

) is a switch element and a signal storage element is provided. FIG. In the figure, the active matrix display device includes a scanning circuit 102 connected to a gate bus 101, a hold circuit 104 connected to a source bus 103 for supplying signals, and a gate bus and a source bus. It includes a TFT 105 serving as a switch device provided at each intersection of the matrix, a signal storage capacitor 106 for holding a signal, and a liquid crystal display device 107 (hereinafter abbreviated as cell). The active matrix liquid crystal display device sequentially operates the operation electrodes of the gate bus 101 in a fully sequential manner, and all T, FT1 on one gate bus 101
05 is temporarily rendered conductive, and a signal is supplied from the hold circuit 104 to each signal storage capacitor 106 via the source bus 103. The supplied signal can excite the liquid crystal until the next frame is operated.

FIG. 4 is a schematic cross-sectional view of a conventional active matrix liquid crystal display device. Referring to FIG. 4, the conventional active matrix liquid crystal display device has a polarizing plate 22.3 on the outside.
8 and a glass substrate 1.36
surrounded by a picture element electrode 10.32 formed inside, a liquid crystal alignment film 24 for aligning the molecular axes of the liquid crystal formed thereon, two glass substrates 9.36, and a frame 30. and a liquid crystal 26 sealed within the space. The picture element electrode 10 on the side owned by the backlight 39 is connected to a TPT as a switching device.

Referring to FIGS. 3 and 4, the liquid crystal display device receives an operation signal from the gate bus 101, drives the TPT 105, and receives an image signal from the source bus 103, so that each pixel electrode 10 is connected to the liquid crystal display device. The liquid crystal is driven through the corresponding cell 107.

FIG. 5 is a diagram showing the temperature characteristics of the optimum contrast of each cell constituting the liquid crystal display device.

The temperature characteristics of three cells A and BSC are shown in the figure. It can be seen that cells A, B, and C each have their own drive voltage characteristics with respect to temperature.

Conventionally, in order to correct this variation, a thermistor was used to compensate for temperature changes, a volume or the like was used to compensate for variations in the cell itself, and the drive voltage was changed to approximate the optimum contrast. FIG. 6 is a diagram on which FIG. 5 is based, and is a diagram showing the driving voltage and contrast ratio at each temperature for one cell. Referring to FIG. 6, the driving voltage at which the contrast becomes maximum varies depending on the temperature, and the peak value of the contrast ratio also varies depending on the temperature. Therefore, it is inappropriate to control the drive voltage based on the absolute value of the contrast ratio.

[Problem 8 to be solved by the invention] As described above, variations in the cells themselves have conventionally been corrected using a thermistor or the like. However, the above method had the following problems.

(1) It is necessary to perform complicated operations such as experimentally determining the voltage that provides the optimal contrast of the cell, and determining the range of the cell driving voltage while taking into account variations in the device.

(2) The voltage at which optimal contrast can be obtained varies depending on variations in the liquid crystal unit itself.

It was not known in advance what voltage should be used for driving to account for these variations.

(3) When temperature correction is performed using a thermistor circuit, it is difficult to match the temperature characteristics of each individual liquid crystal cell. This is because the temperature characteristic curve of the drive voltage is actually not linear but a curve, and correction along the curve is difficult.

Also. Different types of cells have different temperature characteristics, so
A new correction is required.

(4) In order to adjust the characteristic variations of individual cells,
- A volume is added to Boat Fishing that allows the user to adjust the display contrast. However, if the device is designed to cover the optimum drive voltages for cells A and C shown in FIG. 5, the volume adjustment stroke for each cell becomes small, making adjustment difficult. To improve this, a separate level shift circuit or the like is required.

This invention was made in order to solve the above-mentioned problems, and it provides a liquid crystal contrast adjustment device that can determine the drive voltage that provides the optimum contrast, no matter what kind of cell is used. be.

[Means for Solving the Problems] A contrast adjustment device for a liquid crystal display device according to the present invention detects the amount of light in a lighting section and a lighting section of a liquid crystal display device,
The driving voltage of the liquid crystal display device is controlled upwardly so that the difference in light amount is maximized.

[Operation of the Invention] The contrast of a liquid crystal display is determined by the ratio of the brightness of the white level and the black level. Therefore, you can visually decide where it is best. Therefore, the optical sensor feeds back the liquid crystal driver to the voltage that provides the best contrast.

The subject of feedback is the difference between brightness and darkness, and is not related to variations in the constants of the constituent circuits.

[Embodiments of the Invention] FIG. 1 is a block diagram of a contrast adjustment device according to the present invention. Referring to FIG. 1, the contrast adjustment device according to the present invention includes a liquid crystal display panel 1 serving as a display section, a photoelectric conversion device CD51 for detecting the level of a light-off level detection cell 5 of the liquid crystal display panel 1, A photoelectric conversion device CD52 for detecting the level of the lighting level detection cell 6 of the liquid crystal display panel 1, a gain adjustment 4 for adjusting display contrast, and photoelectric conversion devices CD51 and CD5.
a differential amplifier OPI for amplifying the difference in output between the two;
The photoelectric conversion devices CD51 and C are connected to the differential amplifier OPI.
It includes a peak detection circuit 2 for detecting the peak of the difference with D52, and a driving power source 3 for driving the liquid crystal of the liquid crystal display panel 1.

Feedback is applied from the peak detection circuit 2 to the drive power supply 3 so that the output voltage of the differential amplifier OPI is maximized.

Next, individual operations will be explained. When the drive voltage of the drive power supply 3 is increased to increase the output of the differential amplifier OPI, the drive voltage is further increased.

When the drive voltage is increased and the output of the differential amplifier OPI becomes smaller, the drive voltage is lowered. When the output of the differential amplifier OPI increases by reducing the drive voltage, the drive voltage is further reduced. Differential amplifier OP with lower drive voltage
When the output of I becomes small, increase the drive voltage. As mentioned above, drive type 1! By feedback and controlling the voltage of i, 3 by the 1-resistance detection circuit 2, an arbitrary ? A liquid crystal panel constructed of cells having contrast characteristics is automatically adjusted to have optimal contrast.

Next, a case where the user wants to change the contrast of the display device will be described. The gain adjustment 4 is attached with an adjustment volume VRI for the user to operate. Photoelectric conversion device CD51 by contrast adjustment volume VR1
The output gain of is adjusted as shown in FIG. The upper part of FIG. 2 shows the contrast ratio detected by the peak detection circuit 1, and the lower part shows the photoelectric conversion device CD5l that is input to the differential amplifier OPI from which the contrast ratio in the upper part is obtained.
, and is a diagram showing the output level of each CD52. Actual contrast adjustment is performed by changing the voltage at which the output level difference between the photoelectric conversion devices CD5I and CD52 with respect to the drive voltage reaches its peak.

FIG. 2 is a diagram showing the relationship between the drive voltage and the contrast ratio when the contrast adjustment volume VR1 is adjusted. In the figure, (a) shows a case where the entire display panel is pale, and shows a case where the gain of the output of the photoelectric conversion device CD51 is adjusted so that the contrast ratio reaches a peak at the drive voltage Va (<V+). In the figure, 21 indicates the peak contrast ratio after gain adjustment. In the figure, 12 indicates the difference between the output of the photoelectric conversion device CD5I and the output of the CD52 corresponding to the peak value after gain adjustment. Gain: Photoelectric conversion device CD after Aa
The output of 5I is 13, and the photoelectric conversion device CD after gain adjustment
The output of 52 is shown at 14.

(b) is a diagram showing a case where the actual contrast is maximum, and shows a state where the gain of the photoelectric conversion device CD51 is not adjusted. In this case, the driving voltage is V.

(c) shows a case where the entire display panel is dark, the drive voltage is V (>V, ), and the gain of the output of the photoelectric conversion device CD51 is adjusted so that the contrast ratio is at its peak. In (a) and (C), the driving voltage VaSV
The output curve of the photoelectric conversion device CJ)Sl is adjusted so that the peak value after gain adjustment is obtained at .

[Effects of the Invention] As described above, according to the second invention, the amount of light between the on part and the off part of the liquid crystal display device is detected, and the drive voltage of the liquid crystal display device is controlled by feedback so that the difference in the amount of light is maximized. do. Therefore, the subject of feedback is the difference in brightness of the display panel, and variations in constants and the like of the constituent liquid crystal cells can be ignored. As a result, there is an effect that a liquid crystal display panel configured of cells having arbitrary contrast characteristics is automatically adjusted to have the optimum contrast.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a liquid crystal contrast adjustment device according to the present invention, FIG. 2 is a diagram showing the relationship between drive voltage and contrast ratio when adjusting the contrast adjustment volume, and FIG. FIG. 4 is a schematic cross-sectional view of the conventional active matrix liquid crystal display device, and FIG. 5 is a diagram illustrating the operating principle of a conventional active matrix liquid crystal display device, and FIG. FIG. 6 is a diagram showing the temperature characteristics of contrast;
The figure is a diagram showing changes in liquid crystal driving voltage and contrast ratio depending on temperature. In the figure, 1 is a liquid crystal display panel, 2 is a beak detection circuit, 3 is a drive power supply, 4 is a gain adjustment, 5 is a cell for detecting a light-off level, 6 is a cell for detecting a light-on level, and CDS 1 is for detecting a light-on level. A photoelectric conversion device, CD52 is a photoelectric device for detecting the light-off level, OPI is a differential amplifier, VRI is a display contrast adjustment volume, and 12 is a photoelectric conversion device CD5.
Output difference between 1 and CD52, 13 is CD5 after gain adjustment
14 is the output of the photoelectric conversion device CD52, and 21 is the peak contrast ratio after gain adjustment. In each figure, the same reference numerals indicate the same or corresponding parts. No. 30 Gateba people's meal meal, So people, people, - Rudo time ○ 5: TPT o6゛ Change of code'' Mayuzumi Pacita 07゛ LCD surface water line?

Claims (1)

[Scope of Claims] A liquid crystal display device having a lighting brightness level and a lighting-off brightness level, a lighting brightness level and a lighting-off brightness level detecting means for detecting the brightness of the lighting brightness level and the lighting brightness level, respectively, and the lighting brightness level and the lighting brightness level. output difference detection means for detecting the output difference between the respective brightness levels obtained by the brightness level and off-light brightness level detection means; A liquid crystal contrast adjustment device including a driving power source for driving the device.