JPS62131233A - Liquid crystal display - Google Patents

Abstract

PURPOSE:To absorb the fluctuation of halftone display luminance due to the fluctuation of transistor characteristics in a TFT substrate by reading out stored halftone display luminance data and executing interpolating operation between areas to be sampled to find out a necessary control variable. CONSTITUTION:The display luminance of representative points (P11, P12...) In a section obtained when a liquid crystal panel 5 is driven by a fixed driving voltage is measured by a luminance measuring instrument 6 and information indicating the unevenness of the luminance is stored in a frame memory 7. A horizontally/vertically synchronizing signal is impressed from a synchronizing signal detecting circuit 3 to the memory 7 and a reading clock signal is formed and synchronized with a display video signal to read out the uneven luminance information stored in the memory 7. As to points other than the representative points such as P11, P12... interpolating operation is executed by an interpolating operation circuit based on data in the vicinity of these points and the operated result is supplied to a level shift circuit 2 as DC voltage information to display a video with a correct luminance level on a liquid crystal panel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a liquid crystal display device, and particularly relates to means for compensating for variations in driving voltage characteristics (variations in VtA) existing between pixels.

[Background of the invention]

In order to display halftones correctly in an active matrix type liquid crystal display device using thin film transistors (T)'T), it is necessary that there be little variation in the transistor drive pressure characteristics within the liquid crystal panel. However, in reality, for example, the Institute of Electronics and Communication Engineers Technical Research Report VoI 8
2 A 215 (7) Trial production of active matrix 0HLOD using C882-93rα-81 film transistors, there is considerable variation in TFT arrays, and , 1) Even if the problem is reduced by 10% for display complementation, in cases where sub-display between the two is essential, such as in TV images, the variation is one of the major factors in deteriorating the image quality of the reproduced image. Become.

As the area of the TET substrate, that is, the screen size of the liquid crystal panel, increases, this variation also increases.
It is good to reproduce good image quality on a large LCD panel.
)It becomes difficult to absorb the variations in i' F T characteristics.It seems that many studies are being done at the process stage, but it is difficult to absorb the variations between each pixel that remain after the liquid crystal panel is completed. There are no reports on the means to do so.

[Purpose of the invention]

An object of the present invention is to provide a means for absorbing variations in halftone display brightness between pixels caused by variations in transistor characteristics that remain after the above-mentioned liquid crystal panel is completed. ] The present invention is the same as the variation within a general semi-convoluted wafer.
We focused on the fact that even within the TF'T substrate, the variation between adjacent pixel transistors is relatively small, and the wafer as a whole exhibits a large slope variation characteristic.
, a plurality of display brightness sampling areas are set in each of the Y directions, the halftone display brightness data of the sampling areas is read, and the liquid crystal applied pressure is t4jlJ@ so that the display brightness of the area becomes a predetermined brightness, The control amount is stored and stored in a frame memory, and between the sampled areas, mlj@tr in the neighboring sampling area is calculated by means of linear approximation, etc. This method is characterized in that the necessary control amount is determined by using the TF''1' substrate, and variations in the intermediate LL% display brightness caused by variations in transistor characteristics within the T F''1' substrate are absorbed.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG. 1 and will be described in detail. 1st
In the figure, 1 is a video signal input terminal.

2 is a DC voltage level shift circuit, 3 is a circuit for detecting horizontal and vertical synchronizing signals from video 1g to determine the operation timing of the valley block, and 4 is a signal processing and scanning circuit for displaying images on the liquid crystal panel 5. Circuit (LCD panel attendance 1
1), 6 is a brightness measuring device such as a television camera, which measures the brightness on the liquid crystal panel as will be explained in detail later. 7 is a frame memory, and 8 is an interpolation calculation circuit.

As mentioned above, when the liquid crystal panel 5 is composed of a TFT active matrix, within the TFT wafer,
As in the case of general semi-integrated bodies, variations in transistor characteristics occur, and it is extremely difficult to completely eliminate this.
Generally speaking, the difference in characteristics between adjacent pixels is small, but the characteristics of the wafer as a whole exhibit a gradual periodic slope.This variation in transistor characteristics is a factor in deteriorating image quality such as brightness and contrast as a liquid crystal panel. ,
In particular, the threshold voltage of the pixel transistor (0N10F
Variations in the switching voltage (F switching voltage) greatly affect variations in screen brightness during halftone display, resulting in significant image quality deterioration.

Furthermore, even if variations in TFTs are reduced, there are factors that affect display brightness, such as variations in alignment performance of liquid crystal alignment films and variations in liquid crystal filling gap spacing.

In FIG. 1, the panel display brightness when the liquid crystal panel 5 is driven at a constant driving pressure is measured by a brightness measuring device t6 such as a camera, and information on the brightness unevenness is stored in the frame memory 7.
Store in. At this time, it is difficult to measure and store the brightness corresponding to all pixels in the liquid crystal panel in terms of measurement time and memory capacity, so the screen is divided into multiple sections as shown in Figure 2. Divide the area into representative points (pH
, PI3...).

If the brightness of a minute area can be measured, a half-tone scale is displayed on the entire surface of the liquid crystal panel 5 so that the brightness meter 6 is not affected by the display brightness of areas other than the sections or representative points to be measured. The position or angle of 1, 1ii and 1 degree meter 6 can be controlled according to each point to be measured using the clock signal for setting the address at the time of grading in memory 7, and the measurement results can be stored in memory 7. The measurement range is wide,
If the influence of the brightness of adjacent sections or adjacent representative points cannot be separated, the signal applied to the video signal input terminal 1 may be devised.
Pt2. It is sufficient to generate a video signal that shifts the position of a bright spot on the liquid crystal panel corresponding to halftone white, such as Pt3, ...P45.The method of generating such a video signal is usually This can be easily realized due to the technological level of However, in this case, only the video information changes and no change occurs in the synchronization signal, so in order to determine which measurement point is lit, the address at the time of data writing to the frame memory 7 is As setting information, it is necessary to supply a signal from the video signal generator 9 to the frame memory 7. An example in this case is shown in FIG.

Through the above operations, brightness unevenness information that integrates the dispersion performance of TFTs, alignment films, liquid crystal layer gaps, etc. can be stored in the frame memory together with address information.

Next, when using the information stored in the memory, in FIG. 1, apply a horizontal and vertical synchronizing signal to the memory 7,
From these, a black signal for bladder evacuation for setting a bladder ejection address is formed, and the memorized luminance unevenness information is generated in synchronization with the video signal for display to each part on the screen.

At this time, for points other than the representative points such as pH, P+2, . . . shown in FIG. 2, interpolation calculations are performed using nearby data to correct brightness unevenness.

The above interpolation calculation methods include, for example, one-edge interpolation (Figure 4 (α)), smooth interpolation using a low-pass filter (Figure 4), and calculation of a cubic curve using four data. There are methods such as interpolation (FIG. 4(C)). This is shown in FIG. 4, and the method of finding a cubic curve and interpolating it is, for example, the correction of the Pt2-Pt3 section in FIG. A 6th order curve passing through each data of Pt4 is obtained, and the Pt2-Pt3 interval is interpolated according to the curve, and the Pt3-Pt4 interval is corrected by P+2. P.I.
3. PI3. This method involves finding a cubic curve passing through each piece of PI3 data and interpolating the B3-Pt4 section according to that curve. Although the circuit configuration for calculation is complicated, it allows for smooth interpolation, and , it is possible to perform correct interpolation without time delay compared to the interpolation using the low-pass filter shown in FIG. 4(b).

The above interpolation calculation is performed by an interpolation calculation circuit 8. The result of interpolation calculation is DC voltage, 'Ki' of video signal, *v
It is supplied as DC voltage information to the level shift circuit 2, which can turn off the L voltage and turn off the signal, and adjusts the @flow pressure level of the video signal to be applied to the liquid crystal panel 5.
Ir1J control to display images at the correct brightness level on the LCD panel.

In the above explanation, a constant level of video (7T) was applied to the liquid crystal panel, 1llf unevenness on the liquid crystal panel was measured, and the measured data was stored in memory. , write and read memory 7 simultaneously (
It is possible to correct the correction more accurately by using a method in which the data is stored in the memory 7 in a state in which the brightness unevenness on the liquid crystal panel can be corrected.

Also, in the above explanation, we have described the means for white luminance correction, but for example, red, green, and evening wavelength selection filters can be installed in sequence on the front of the camera, and white balance correction can be performed from those data. It is also possible to directly measure the color temperature of white and perform white balance correction to obtain a predetermined white color.

The frame memory capacity required to correct uneven brightness of the LCD panel shown in Figures 1 and 2 depends on the number of brightness measurement points on the screen and the accuracy with which brightness correction is to be performed. However, for example, if measurements are made at 16x16 points on the screen, and each point requires an "ibit" monument, it can be realized with a minimum of 1024 bits of memory.

Since the brightness measuring device 6 is needed only during manufacturing adjustment of the liquid crystal display device, the fact that the screen side thereof is high is hardly a problem.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to solve the variations in halftone display brightness of the liquid crystal panel caused by variations in TFTs, alignment films, liquid crystal gaps, etc., and to maintain good image quality. can be displayed.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment according to the present invention;
FIG. 3 is a block diagram of a second embodiment of the present invention, and FIG. 4 is an explanatory diagram showing an example of an interpolation calculation state. 1...Video signal input terminal 2...Variable amplifier 3...Synchronization signal detection circuit 4...Liquid crystal panel drive circuit 5...Liquid crystal Panel, 6...Brightness measurement device 7...Frame memory 8...Interpolation calculation circuit 9...Video signal generation device / Concave 2 flashes

Claims (1)

[Claims] 1. In a TFT active matrix liquid crystal display device consisting of a video signal input terminal, a liquid crystal panel, and a liquid crystal panel drive circuit, means for displaying halftone white on the liquid crystal panel, and dividing the screen into a plurality of sections. , a brightness measuring means for measuring the brightness of each section or the brightness of a representative point of each section;
A memory means for storing the luminance information obtained from the luminance measuring means according to address information indicating the position on the screen of the representative point of each division, and reading out the stored luminance information of the plurality of divisions or the representative point of the division when receiving the video signal. and means for performing interpolation calculations on the plurality of read luminance information according to the state of a clock signal corresponding to a scanning position on the screen, and means for controlling the DC voltage of the input video signal by the output signal of the interpolation calculation means. and applying the controlled video signal to a liquid crystal panel.