JP3245731B2 - Flat panel display inspection system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a test system, and more particularly, to a test system for testing a flat panel display such as a liquid crystal display (LCD).

[0002]

BACKGROUND OF THE INVENTION Test systems currently used to detect defects (e.g., defective pixels) in flat panel display systems such as LCDs generally produce an image on a display and the resulting image. Uses a means to detect errors. One such type of LCD tester is described in U.S. Pat. No. 4,899,105. As described in U.S. Pat. No. 4,899,105, the resulting display images are conventionally evaluated using the naked eye. Obviously, a camera can be used instead of the human eye so that a computer can later analyze the displayed image.

Usually, even if display pixels of a flat panel display are focused on a detector pixel array of a camera, the display pixels and the detector pixels do not correspond exactly one-to-one. Causes moire image interference fringes (or interference fringes), and the display image detected by the camera is distorted. This is called aliasing. Depending on the degree of such distortion of the detected image due to aliasing,
Pixel defects in flat panel displays may be hidden.

[0004] In addition to testing the display for defective pixels, it is also useful to detect whether the brightness of the pixels is uniform throughout the display. Such sensitivity tests could not be performed accurately using known flat panel display testers.

[0005] Other measurements performed on conventional flat panel displays include viewing angle tests. In the viewing angle test, a detector (e.g., a camera or operator's eye) is moved in an xy plane parallel to the display and the
The luminance or darkness level of one or more pixels is measured. This test method requires a considerable amount of time to physically move the detector above the surface of the display, while at the same time analyzing the detected image.

[0006]

There are other inaccurate test methods for prior art display testers, such as chromaticity tests. Therefore, with the increasing resolution of flat panel displays, there is a need for improved test systems for displays that can more quickly and more accurately measure display panel parameters.

[0007] This document proposes an improved test system and method for testing flat panel displays.

[0008]

In this test system,
The operator first inserts a flat panel display to be tested below a conventional high resolution camera, such as a charge injection device (CID) type camera. Since each detector pixel in the camera is not perfectly aligned with the associated pixel in the display, aliasing occurs, moiré image fringes (or fringes) occur, and the detected image is distorted. .

The present invention avoids aliasing errors by incrementally shifting the displayed image relative to the camera optics and detecting the displayed image at various shift positions. The resulting accurate display can be reconstructed using software by first identifying for each shift position the camera detector pixels that were completely superimposed by the image of the signal display pixels. This can be done by identifying the detector pixel that produces the largest signal. A single image can then be reconstructed using only the detected maximum pixel signal. The reconstructed image has not been subjected to the aliasing effect.

[0010] The reconstructed image can then be analyzed electronically using a software program,
Then, the abnormality of the pixels forming the display panel can be accurately detected.

Anomalies due to non-uniform brightness across the display can be accomplished by programming a memory chip for a particular display panel to compensate for the display driver signal for each display pixel to eliminate the anomalies described above. Can be remedied.
Thus, in this case, the display panel can be corrected to always achieve a high performance level.

In an alternative embodiment, a method is provided for electronically detecting a display image formed by a periodic array of display pixels. The method of the invention comprises the step of spatially and periodically positioning the detection means for displaying the display image.
The detection means includes a first spatially periodic array of detector elements. A display image formed by a second spatially periodic array of display pixels is focused on the first spatially periodic array of detector elements. Each of the detection elements generates a signal corresponding to the intensity of light incident on the element. The method of the present invention is generated by the detector element when the detector element is at a first position relative to a displayed image,
Detecting a first signal including a first moiré image interference fringe. Shifting the displayed image to a second position along an axis relative to the detector line is also included. The method further includes detecting a second signal generated by the detector element when the detector element is at a second position relative to the displayed image and including a second moiré image interference pattern. Averaging the intensity levels of the first signal and the second signal generated by the detector element at each sampling point of the display pixel to form a first moire image interference pattern formed by a display image impinging on the detector element; Other steps to reduce the effect of the second moiré image fringes are also used.

[0013] The method of the invention, as well as the previous embodiment, additionally shifts the displayed image with respect to the detector element along a second line of display pixels orthogonal to the first line of display pixels. Including steps. Detecting and averaging the signal generated by the detector element after each shift step until the effect of the moiré image interference fringes on the determination of the relative intensity level of the display pixels is reduced to a desired level is also included.

In LCDs and other types of displays, the drive voltage applied to a display pixel affects the viewing angle of the pixel. Thus, by supplementing the drive voltage to optimize the viewing angle of the pixel and programming the memory chip for the display, the testing system of the present invention can be used to correct the viewing angle of the pixel.

In a preferred embodiment, a single pixel on a flat panel display is activated to detect the viewing angle of the display to determine the required correction,
The pixel is detected by a detection camera in which a detector pixel array is optically positioned directly above the display pixel. A polar plot of brightness versus viewing angle is then generated from the detected intensities of the activated pixels across the camera's pixel array while the camera is stationary. This viewing angle test is preferably
This is done on some representative pixels around the display to sample the viewing angles for the various parts of the display. In that case, the appropriate group of pixels is associated with a correction factor to optimize the overall viewing angle of the display.

To analyze the image quality (chromaticity) of the display, pixels of the three primary colors (red, green, blue) are activated one color at a time. Several tuned color filters (tristimulus filters) are sequentially inserted between the camera and the display for each primary color pixel group. Each pixel color (red, green,
A tristimulus value (using the CIE colorimetric system) is generated for each blue color, and the image quality is determined for each display color using the CIE standard.

In a preferred embodiment, a special tester is used to provide easy and reliable contact between the tester electrodes and a number of electrodes arranged at a close pitch around the perimeter of the flat panel display. Na tester /
A display interface connector is used.

[0018]

DETAILED DESCRIPTION FIG. 1 shows a flat panel display test system 10 incorporating various novel features.
Is shown. A flat panel display 11, such as an LCD, to be tested is positioned on a slidable table 12, and then a hinged frame 14 (shown in more detail in FIG. 10) for securing the display panel 11 in place. ) Is lowered. A slidable table 12, usually an xy stage, allows the display panel 11 to be easily positioned below a camera 15, such as a charge injection device (CID) camera. As shown, the table 12 can preferably move in the xy plane via an xy stage, and can also move in the Z plane so that the display can be precisely positioned.

The xy stage may be any suitable base device capable of moving the display panel in the x and / or y directions. This stage is
Continuous movement in the x and / or y directions at a high speed of about 20 mm / sec to about 1.0 mm / sec and a low speed of about 1.0 mm / sec to about 0.5 mm / sec or less is possible. Preferably, the xy stage can also be incremented by a selected dimension in the x and y directions. This incremental dimension ranges from about 400 μm to about 5 μm per display pixel in the x direction and from about 400 μm to about 5 μm in the y direction. The xy stage also requires an accuracy (tracking tolerance) of about ± 5 μm or less in both the x and y directions. Of course, the exact incremental dimensions in the x and y directions will depend on the particular application.

The flexible ribbon wire 16 is connected to the hinged frame 14 from the image drive circuitry in the test system 10.
A drive signal is supplied to the upper conductor. Hinge frame 1
The contact between the conductors on 4 and the electrodes on the display panel 11 is preferably made automatically by the closing of the hinged frame 14, which will be discussed in more detail with respect to FIGS.

The high resolution camera 15 is sealed within an upper body 18 of the test system 10 which is partially cut away to display the camera 15. The camera is preferably
This is an interline transfer CCD having a 1.5K × 1.0K pixel array. Other cameras can be used with camera 15 to achieve the desired resolution and viewing angle. The camera 15, lens 20, and mirror 21 provide a complete image generated on the display panel 11 when the display panel 11 is properly positioned on the table 12 and slid to a predetermined position below the camera 15. Is configured to be detected by the camera.

The camera 15, the lens 20, and the mirror 21 are mounted on a movable support structure 22 for adjusting the height of the camera 15 in the z direction, and thus the viewing angle of the camera 15. The support structure 22 can also be moved in a horizontal direction, such as in the xy direction, as needed for a particular application. The function of the support structure is similar to the xy stage described above.

To test a color display, a number of selectable color filters 23, including red, green, and blue tristimulus filters, on filter wheel 24 are automatically added to lens 20. To a predetermined position between the camera and the camera 15 aperture. Such a filter 23 will be discussed in more detail with respect to FIGS.

The system 10 includes a display panel 1
A second camera 25, for example C
It also includes an ID camera, a charge-coupled device (CCD) camera, and the like. Such tests are discussed in detail with respect to FIGS. The camera 25 is connected to the display panel 1
Mounted on an xy movable support structure 26 to position camera 25 over one selected portion.

The test system 1 allows the operator to identify the characteristics of the display panel via the keyboard 27 and select the particular test to be performed.
0 is a computer (not shown) and keyboard 27
Is also incorporated. A computer may be used to process the image data or compile test data obtained from the test. The computer monitor 28 can display test parameters and / or the operating status of the test system 10.

A light source (not shown) sealed within the lower body 30 of the test system 10 includes a display panel 11
Used to give the necessary back lighting. Examples of such light sources include three-band phosphor cold cathode fluorescent lamps. A schematic diagram of one possible embodiment of the test system is shown in FIG.

In FIG. 2, a high-resolution CID camera 15
Covers the entire area of the display panel 11. Other cameras can be used with camera 15 when testing larger display panels or when higher resolution is needed. The output of camera 15 on line 32 is applied to image processing computer 34,
The image processing computer 34 then processes the camera 15 signals appropriately so that the display image can be evaluated.
The image processing computer 34 is controlled by a computer 36. Computer 36 interfaces with the operator using a monitor and keyboard 38.

As is well known for certain displays,
The brightness of the display panel pixels is strongly affected by the viewing angle. To eliminate the difference in display pixel luminance level due to the different viewing angle of the display pixel with respect to the camera lens 20,
The signal output by the camera detector pixel on line 32 in FIG. 2 is compensated by digital techniques to eliminate the effect of viewing angle on the detected brightness level of the display panel pixel.

A test program for a particular type of display panel is programmed into the computer 36 and automatically controls the test procedure, including applying signals to the display panel driver 40. Conductor 4
1 (shown as a flexible ribbon 16 in FIG. 1) couples the driver output signal to the hinged cover 14 shown in FIG.
1 to the upper electrode.

The test results for each display panel are recorded in a test data file 42. This allows defects or non-uniformity trends to be detected and corrected in the manufacturing process.

In a light-shielded LCD display panel placed on the table 12, a back light source 44 is used.
Displays in which the display pixels themselves emit photons do not require backlighting.

The display panel 11 placed on the table 12 in FIG. 1 or 2 can be a completed display before it is connected to a laptop computer or the like.
Unfinished panels may be used. This allows the display manufacturer to save on subsequent manufacturing costs if the display panel fails to meet specifications and to compensate for certain defects in the display panel. Testing for such imperfect displays can also confirm specifications at various points in display panel manufacturing.

As a first test, the automatic test system 10 performs a display pixel luminance uniformity test, and calculates a necessary adjustment for each pixel drive voltage to correct the luminance uniformity. can do. In the test, first, the relative luminance of each pixel of the display panel is obtained.
In such a test, test system 10 applies a voltage to the electrodes on the display panel to activate the pixels,
The image to be detected must be displayed. However, in order to be able to accurately inspect a high resolution display with an easily obtained electronic camera, it is necessary to eliminate the image distortion effect of aliasing. Aliasing occurs when display pixels are imaged on a camera detection array that has detector pixels that are not uniformly aligned with each pixel of the display panel.

Aliasing is a well-known phenomenon that occurs as moire image fringes (or fringes), ie, periodic modulation of the image voltage signal provided by the camera array. Moiré image interference fringes occur because display pixels are not mapped to camera detection pixels exactly in a one-to-one correspondence. If the mapping is not exactly one-to-one, then the photons associated with a certain display pixel
Hits on the non-responsive part (if any) of the array,
"Street" and "Ally" (all
ey) "is imaged on the sensitive area of the camera array. As a result of this non-optimal pixel relationship, moire image interference fringes as shown in FIG. 3 occur, distorting the true relative luminance level of the display pixels.

The test system 10 uses special multi-frame image conversion techniques to eliminate inaccuracies in the detected image due to aliasing.

FIG. 3 shows one example of a moiré image interference fringe that occurs because a focused display panel pixel 50 is not mapped in a one-to-one correspondence with a smaller and more closely spaced camera detector pixel 52. Here are two examples. As can be seen from FIG. 3, one of the camera detector pixels 52, such as pixel 54, completely overlaps a single display panel pixel image 56. Therefore, these display panel pixels 5 that completely overlap with a single camera detector pixel 54
6 is detected by the camera detector pixels as being brighter than a display panel pixel, such as pixel 58, where the image partially falls on a non-sensitive area between two adjacent camera detector pixels 52. When evaluating only a single display image due to the moire image fringes of FIG. 3, the brightness of one display panel pixel is incorrectly detected as being higher than the brightness of another display panel pixel. .

In a particular embodiment used by the test system 10 to determine display panel luminance uniformity, the first inspection of display panel pixels is performed using a method such as the alignment shown in FIG. , During the first alignment of the display panel image with the camera pixel array. The luminance level (ie, intensity) signal generated by each camera detector pixel 52 during this first alignment is cross-referenced to the particular display pixel that generated the luminance level signal, and then the computer 36 ( 2). Suitable mapping techniques will be known to those skilled in the art.

In the second step of detecting the brightness uniformity of the display panel, the display image is changed by physically shifting the display panel or the camera optical system or changing the angle of the reflecting mirror 21 (FIG. 1). Is slightly shifted with respect to the camera detector pixel 52. After this shift, another image of the display panel is detected and mapped to memory. The moiré image interference fringes are slightly different from those shown in FIG.

Next, the display panel image is again shifted relative to the camera detector pixels. This process is repeated until all display panel pixels overlap with the camera detector pixels during any of the detection stages. A camera detector pixel located entirely within the display pixel image (ie, completely overlapping the display pixel image) detects the exact relative luminance level of the display pixel.

As can be seen with reference to FIG. 3, before the Moire image fringes in FIG. 3 are repeated, the required number of shifts of the display panel image relative to the camera detector pixels is four small left-right incremental shifts and four Includes two small up and down incremental shifts. In a further preferred embodiment, the camera is displaced by a distance x1 in a _first x-direction, by a distance x2 in a _second x-direction and by a distance x1 in a first y-direction with respect to a zero on the display panel. only y ₁ is displaced, is displaced to the second y-direction by a distance y _2. The distance x ₂ is approximately the distance equal to (-x ₁₎ or 2x _1, the distance y ₂ is approximately equal to the distance (-y ₁₎ or 2y _1. Of course, the required number of shifts and the magnitude of the shift are determined by the number of shifts and the magnitude of the shift required to enable each display pixel to be detected by a camera detector pixel located entirely within the projected image of the display pixel. It is. Then, a single mapping is constructed from only the maximum intensity signal for each display pixel. The entire display is then analyzed using this information.

The above method is considered a particular embodiment. First, an alternative to determining the maximum intensity ratio for each display pixel after every incremental shift and mapping these maximum intensity ratios as a single mapping is a camera detector that receives a portion of the corresponding display pixel image. A simple averaging of the pixel's luminance level output signal over all incremental shifts. In that case, this average intensity level for each display pixel over all incremental shifts is mapped such that each display pixel is associated with the correct relative intensity level.

In a preferred alternative embodiment, the method of the present invention also uses several images to average the periodic variation of the moire fringes. The method of the present invention includes capturing a first image including a periodic change from a display panel. The first image is captured, such as via a CCD-type camera, and stored in memory, preferably via standard mapping techniques.

Next, the step of displacing the CCD camera with respect to the display panel is performed. The display panel is displaced in the x and / or y directions with respect to the CCD camera array. CC
The D camera is also displaced in the x and / or y directions with respect to the panel. Also, both the CCD camera and the panel are displaced in the x and / or y directions to provide a relative spatial displacement between them. The relative displacement between the CCD camera and the panel is preferably about half the panel display pixel period in the x direction when the displacement in the x direction is made. Also, the relative displacement between the CCD camera and the display panel is preferably about half the panel display pixel period in the y-direction when the displacement in the y-direction is made. The relative spatial displacement between the CCD camera and the display panel is half the panel display pixel period in the x or y direction.

This preferred embodiment uses a display
Capturing (or obtaining) a second image of the panel and storing such a second image in memory, again via standard mapping techniques. The second image also includes the same periodic changes having the same period as the first image. But,
The arrangement of the periodic changes of the second image is displaced by a half period in the x or y direction with respect to the first image via a displacement step. Of course, in the arrangement of periodic changes, the first
It is not possible to position another display pixel at the same relative position as the display pixel in the image capturing step.

Next, the step of mutually adding the first image and the second image is performed by using standard image processing techniques. The periodic patterns effectively cancel each other out, preserving the "real" changes in the panel.
Several images can be added as long as the following criteria are satisfied. Preferably, the number of images is at least two, more preferably the number of images is two or more, and more preferably the number of images is four or more. In a further preferred embodiment, the camera is displaced by a distance x _{1 in a first} x direction with respect to a zero on the display panel and a second x
It is displaced in a direction by a distance x _2, the distance y ₁ to a first y-direction
Is only displaced, it is displaced to the second y-direction by a distance y _2. The distance x ₂ is approximately the distance equal to (-x ₁₎ or 2x _1, the distance y ₂ is approximately equal to the distance (-y ₁₎ or 2y _1. Each resulting image must have a matching image (or complementary image) with a relative displacement of half a panel pixel period in the x and / or y directions. The camera may be displaced in the y direction before the x direction, or may be displaced in a combination of the x and y directions.

In certain alternative embodiments, the present invention provides a method for reducing, and possibly eliminating, periodic variations from a display panel image signal by filtering. The method of the present invention includes filtering the change signal from the display panel image signal with a spatial filter. The cycle of the change signal is determined by the cycle of the display panel pixels and the cycle of the CCD pixels in the spatial region. The image processor (and computer) implements a spatial filter on the display panel image signal by convolving the CCD signal with a filter whose width is designed to eliminate the periodic variations. Alternatively, the CCD signal can be mapped from the spatial domain to the frequency domain using a technique such as a Fourier transform.
The frequency of the moiré image interference fringes can be calculated from the cycle of the CCD pixels and the FPD pixels. Techniques such as bandpass filtering can be used to eliminate selected frequencies that contain moiré image fringes.

With the exact relative intensity for each display pixel mapped to memory using any of the techniques described above, the preferred next step is to analyze the luminance uniformity across the display panel, and then And correcting the brightness non-uniformity. In one embodiment, this is done by detecting a minimum display pixel luminance level and using that minimum luminance to correct for all other display pixel luminance. Next, a compensation coefficient is calculated for each display pixel drive voltage.

This compensation factor is then loaded into a look-up table in memory located at computer 36 in FIG. This coefficient in the look-up table is then applied to the display driver via the compensation control circuit 64 in FIG. 2 to drive the pixels whose luminance level needs to be attenuated to match the luminance level of the minimum luminance pixel. Voltage can be reduced. The displayed image is detected again using the same process as described above, and the luminance level is measured again to determine the non-uniformity.

It will be appreciated by those skilled in the art that other techniques may be substituted for the above-described method involving reducing the luminance level of all pixels to match the minimum luminance level. One alternative technique is to determine an average display pixel brightness level and then increase or decrease individual display pixel brightness levels to match this average brightness level. Such an alternative using the average brightness level as a reference is desirable where there is a pixel defect (ie, one or more pixels have a zero brightness level).

As an alternative to the iterative process described above, instead, it may be desirable to continuously increment the display pixel drive voltage for selected pixels in the display while simultaneously measuring luminance uniformity across the display. . This alternative process of determining brightness uniformity is performed for each shift position of the display image relative to the camera detector pixels. In order to eliminate the effects of the moiré image fringe phenomenon shown in FIG. 3, the selected pixel in the display to be adjusted for each image shift has an image that completely overlaps a single camera detector pixel Only the pixels identified as After every image shift, all display pixels should have the same predetermined brightness level.

It will be appreciated that the pixel darkness level can substitute for the pixel brightness level, depending on whether the display pixels scatter light or whether the display pixels themselves emit light.

After the final compensation coefficients for each display pixel are stored in a look-up table, these compensation coefficients can be downloaded to the EPROM chip 66 (FIG. 2) for the particular display panel under test. EPROM 66
Is then disconnected from the test system 10 and installed in the drive system for that particular display panel to constantly control the compensation of the display driver signal to obtain uniform brightness across the display panel.

Some types of displays such as LCD panels
In a panel, the activation pixel voltage also affects at which angles the pixel elements appear brightest (darkest). Thus, by using the foregoing techniques for compensating for pixel drive voltages, the activation voltage for each pixel can be adjusted to set the angle at which the image on the display panel looks brightest. This is desirable in certain applications, such as in the cockpit of an airplane, where the intended viewer is not directly facing the display panel.

Using the above-described luminance uniformity test, the display pixels are not merely set to the luminance level to the reference level, but to the most uniform contrast ratio (ratio of luminance to darkness). You can also. To achieve such a uniform contrast ratio across the display panel, both the maximum luminance and maximum darkness of the pixel are measured, and a compensation factor for both luminance uniformity and darkness uniformity is generated. There must be.

All image processing and other analysis can be performed using digital techniques, and the signal can be characterized using a Fourier transform as needed.

Pixel defects and other defects in the display panel (eg, shorts or breaks in conductors) can be easily detected by detecting pixels with a luminance level below a threshold. Such defects can be identified and repaired by the test system 10, or the display panel can be discarded. To enable such defects to be repaired, the display device must be mounted during the manufacturing process where the pixel elements and conductors are exposed.
The panel should be tested.

The test system 10 can include a special camera and / or zoom lens, or both, that can be automatically directed by the test system 10 to the defective display portion to photograph the defective portion. It can assist in correcting defects. display·
A method for correcting panel defects is described in related U.S. patent application Ser. No. 07 / 716,592, assigned to the present assignee.

The color display detects the luminance level and chromaticity of the red, green, and blue display panel pixels using the color filter 23 in FIG.

As shown in FIG. 4, luminance uniformity across a color display panel having red (R), green (G), and blue (B) pixels that can be individually activated is shown. To detect, a single color pixel is activated at a time. For example, as can be seen with reference to FIG. 4, initially only red pixel 70 is activated on display panel 72.

The filter wheel 24 in FIG. 1 is shown in more detail in FIG. When detecting the brightness (not the chromaticity) of the red pixel 70 in FIG.
A narrow bandwidth red filter 74 is positioned to be inserted between the camera lens 20 and the aperture for the camera 15. Images across the display are detected using the incremental shifting technique described above to eliminate aliasing effects. In a color display, each display pixel imaged on a camera detector pixel array is typically
Since it is smaller than a single detector pixel, the signal-to-noise (S / N) ratio of each color display pixel is relatively small. To increase the signal-to-noise ratio and at the same time eliminate aliasing effects, the average intensity value output by the camera detector pixel is obtained after a predetermined number of incremental shifts (this is a single (As opposed to mapping only the minimum pixel intensity to the shift). This average is then:
It is mapped into memory and accurately reflects the relative speed of the red pixels in the color display.

The brightness non-uniformity can be corrected using the method described above for FIG. Pixel defects can also be identified.

In the next step, all green pixels are activated and the displayed image is filtered by the narrow bandwidth green filter 76 shown in FIG. The brightness level detection process is repeated as described above for the red pixel.

This process is then repeated for the blue pixels filtered by the blue filter 78 in FIG.

Thus, the luminance levels of the red, green and blue pixels in a color display can be accurately measured without the effects of aliasing and corrected using the test system 10 as needed.

In a monochromatic display, the filter wheel 24 in FIG. 5 is set so that the opening 80 is located between the lens 20 and the aperture of the camera 15.

To attenuate light from a high brightness display panel, a neutral filter (eg,
A second filter wheel consisting of (gray density) can be arranged in front of the filter wheel 24.

To test the chromaticity of a color display panel, the three color stimulus value filters 82, 84, 86, 8
8 using the four primary color stimulus value curves x shown in FIG.
(Λ) 90, 92, y (λ) 94, z (λ) 96 (x, y, z of x (λ), y (λ), z (λ) above each have a bar above, Modify the spectral response of camera 15 to match the CIE colorimetric system trichromatic stimulus value spectral response for each The trichromatic stimulus value spectral response shown in FIG. 6 takes into account the sensitivity of the human eye to various wavelengths of light.

For more information on the CIE colorimetric system and the spectral trichromatic stimulus curve shown in FIG.
Science: Concepts and Meth
ods, Quantitative Data and
Formulae "Wyszekki et al., Chapter 3,
Wiley, Canada, 1982.

The chromaticity test performed by the test system 10 results in the red, green, and blue pixels emitted by the red, green, and blue pixels in the color display panel.
Green or blue image quality or purity is determined. Using the color filters 82, 84, 86, 88, respectively,
The tri-color stimulus value responses 90, 92, 94, 96 shown in FIG. 6 can be obtained to define the displayed color by the detected tri-color stimulus values. As an example of applying the trichromatic stimulus value spectral response of FIG. 6 to determine the image quality of a color display panel image when only red pixels are activated, the output of camera 15 is x (λ) Filter 8
2 is used, the tristimulus value is 0.5 when the y (λ) filter 86 is used, and the tristimulus value is 0.2 when the y (λ) filter 86 is used.
When the (λ) filter 84 and the z (λ) filter 88 are used, the value corresponds to zero.

After the three color stimulus values are obtained, the coordinates x, y, z
Is calculated, and these values are plotted on the xyCIE chromaticity diagram of FIG. The values of x, y, z are calculated as follows.

(Equation 1)

Using the aforementioned three-color stimulus values, x is calculated to be about 0.71, y is calculated to be about 0.28, and z is calculated to be zero.

Next, these chromaticity coordinates are represented by x-
It can be plotted as a point 97 on the y CIE chromaticity diagram to indicate that the red image displayed by one or more pixels in the color display panel under test is substantially pure red.

Those skilled in the art will readily recognize the background information provided for the aforementioned three-color stimulus values. Detail is,
It can be obtained from the above-mentioned book such as Wyszekki.

In a practical application, a range of wavelengths is emitted by a color display panel pixel. The range can be shown as a small circle or ellipse when plotted on the diagram of FIG. The display quality is determined based on the position and size of the circle or ellipse. Determining tricolor stimulus values and plotting the coordinates on the diagram of FIG. 7 has been described with respect to mental arithmetic and manual plotting, but determination of these values and their characteristics is performed by software in test system 10. Can be. If desired, the plot shown in FIG. 7 can be actually printed by test system 10 on a single pixel or on the entire display panel. The test system 10 can also provide a simple rating of the color display.

The above method used to determine the purity of the red light emitted by the red pixels in the display under test is then performed on the green and blue pixels in the color display panel, and An analysis is performed to determine the green and blue display qualities of the color display panel.

The image quality of the color output of each individual pixel in the color display panel can be mapped into the memory of computer 36 (FIG. 2). The mapped data can be compared to the manufacturer's specifications for color to determine the quality of each pixel in the color display panel.
Such a determination of image quality can be made for each pixel, or for a selected portion of the display, or for the entire display.

In a preferred embodiment, the trichromatic stimulus filters 82, 84, 86, 88 are of the absorption type, and the filter material is optical quality glass. The filters were manufactured using optical manufacturing technique tolerances. To very accurately match the standard theoretical trichromatic stimulus spectral response shown in FIG.
Each of 2, 84, 86, 88 is a stack of several different filter glasses, each having a different thickness and spectral transmission. For light rays passing through the filter at non-standard angles of incidence, the transmittance of the absorption filter changes as the optical path length increases.
However, if the change in transmittance is the same for each filter (and because the rays are incident on each filter at the same angle), then because the chromaticity coordinates are a normalization function of the chromatic coordinates, It was found by modeling that there was no error in the chromaticity coordinates. This is important because the optical system must capture light at a large angle of incidence in order to image a large area. Using such techniques, 70
A colorimeter capable of performing chromaticity measurement over a large area of 000 mm ² or more was obtained.

The aberrations of the optical system are minimized by placing the filters closely in front of the camera 15. Minimizing aberrations increases the resolution of the optical system.

The test system 10 can perform L
Another test for a CD panel is a viewing angle characteristic determination test.
As is well known, the effective viewing angle of an image displayed on an LCD panel is relatively limited and can affect the usefulness of the LCD panel.

A conventional electronic method for detecting the viewing angle of a display panel is to move the angle of a detector (which may be the human eye) with respect to the display panel and to determine where the brightness level of the image is at the maximum brightness. Is to detect whether it decreases to a certain ratio.

FIG. 8 shows an improved method of determining the viewing angle characteristics which is performed by the automatic test system 10 of FIG.

In FIG. 8, a single pixel 100 in the display panel 102 has been activated. Using the lens 104 on the camera 25 in FIG. 1, almost all light emitted from the pixel 100 is focused on the camera pixel array 108.

Preferably, the lens 104 is
Are provided with two infinitely corrected microscope objectives positioned back-to-back so that the image can be located closer to the camera pixel array 108. Panel 102 is reflective L
If it is a CD, use the lens 104 to
The effective darkness "emitted" from the LCD is focused and the light source is LCD
Information or attached below. Using the field stop 110, the field of view is limited to an angle that is sufficient to measure the viewing angle of the pixel 100.

Next, the pixel image is stored in the camera pixel array 10.
Each pixel in the array 108 is focused on 8 and outputs a signal corresponding to the detected luminance of the pixel image. While the pixel array 108 is fixed relative to the pixel 100, substantially the entire area of the pixel array 108 is used to directly map the brightness level versus viewing angle of a single display pixel 100. There is no need to generate interference fringes using this method. Comparing the maximum brightness level, typically located at the center of the array 108, with other brightness levels detected around the array 108,
It can be determined where the brightness level of the array 108 drops, for example, to 50% of the maximum brightness. Next, a computer such as the computer 36 in FIG.
Together with the image processor 34, it effectively produces a polar plot as shown in FIG. 9 of the brightness level of a single pixel 100 versus the viewing angle. The polar plot can then be stored in test data file 42 or printed for visual inspection of brightness level versus viewing angle.

The computer can compare a predetermined criterion for the viewing angle to an internally generated polar plot, or simply identify the viewing angle to the operator as a pass / fail.

Preferably, the display panel 102
To obtain a representative viewing angle of the selected area throughout, several individual pixels 100 around the display panel 102 in FIG. 8 are measured. This is used to approximate the viewing angle of the entire display panel 102,
A polar plot of the entire display can be generated.

The lens 104 and other structures, rather than the arrangement of FIGS. 1 and 8, may be used to eliminate the need for the lens 104, such as placing the camera array 108 close enough to the pixel 100, or a refractive optical system. Instead, a reflective optical system can be used. Other optical structures will be apparent to those skilled in the art.

In a preferred embodiment, the test system 10
Includes a novel display panel connector 120 (FIG. 10) that can quickly and reliably press electrical contacts against the electrodes of the display panel during testing.
It has already been found that it is very difficult to quickly and reliably connect a large number of thin metallized contacts arranged at a close pitch around the periphery of the display panel to the electrodes of the test system.

FIG. 10 shows an LCD array 122 having metallized electrodes 124 arranged at a close pitch around the perimeter to couple electrical signals to the various pixel elements that form the LCD array itself. LCD 122 in circle 126
The metallized electrode 124 is shown in greater detail in the enlarged view of the edge of FIG. In general, pixels in LCD array 122 are activated by activating specific row and column lines in array 122 that terminate at an associated electrode 124. Typically, in LCDs, the electrodes 124 are formed on glass, and the pitch of such electrodes 124 (the distance between the centers of adjacent electrodes) is 1 / 10,000 of an inch. In conventional test systems, the alignment of the LCD electrodes with the test system connectors is typically performed manually.

To more quickly and more reliably electrically couple the display panel 122 to the test system 10 in FIG. 1, a connector 120 is provided on the underside of the hinged frame 14 (also shown in FIG. 1). . One embodiment of connector 120 is shown in more detail in circle 130 of FIG. 10, where flexible tape 132 includes circle 126
Metal traces 134 are formed corresponding to the group of thin film electrodes 124 shown therein. Such flexible tape 132 may be formed of a polymer tape, such as Kapton ^™ , having traces 134 formed using a conventional metallization and photolithographic etching process. Trace 134 is connected to a flexible wire 138 that leads to a display driver 40 for LCD panel 122 (FIG. 2).

The traces 134 on the connector 120 correspond to the electrode 134 patterns configured for the particular display panel 122 to be tested.

In one embodiment, LCD panel 122 includes:
The position of the LCD panel itself and the position of the electrodes 124 are positioned relative to a block 140 or other reference position formed on the table 12 of the test system 10 such that the position is predetermined. Connector 120 is pre-positioned with respect to block 140 such that flexible circuit traces 134 align with respective electrodes 124 on LCD panel 122, or is positioned automatically or manually with respect to block 140. You. Tape 132
Due to the elasticity of the electrodes, an appropriate pressure is applied to each electrode 124.

If the alignment of the block 140 with respect to the trace 132 is not deemed to be reliable and reproducible enough to accurately align the connector 120 with the electrode 124, the table 12 shown in FIG.
Can include a photodetector 144 that detects the overlap between the first electrode 124 on the LCD panel 122 and each trace 134 of the flexible tape 132. Table 12 below transparent LCD panel 122
The light emitting diode 146 is located at Flexible tape 1
32 is transparent or translucent to maximize the amount of light received by the photodetector 144 when the trace 134 and the electrode 124 overlap. in this case,
Using the conductivity of the photodetector 144, the block 140 in FIG.
22 can be shifted with respect to the connector 120, and the maximum output signal can be obtained from the photodetector 144. In another embodiment, the position of the photodetector 144 and the LED
The position of 146 is reversed.

Accordingly, there is an improved flat panel display for detecting and correcting luminance uniformity, image quality, and viewing angle for flat panel displays that eliminates problems due to aliasing and moiré image interference fringes. An automatic test system has been described.

Those skilled in the art will be aware that “Method and A”
pparatus for Automatical
y Inspecting and Repairin
gan Active Matrix LCD Pan
No. 07 / 716,592 entitled "el".
Combining any type of display panel repair system and test system 10 as described in
It will be obvious that the identified defective pixels will be repaired automatically. Accordingly, an automatic test and repair system is also envisioned by the present disclosure.

While the preferred embodiment of the invention has been illustrated and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broad aspects of the invention, and the appended claims are intended to cover the invention that is claimed. It is self-evident that all such changes and modifications within the true spirit and scope of the invention are included within the scope.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of a flat panel display test system according to the present invention.

FIG. 2 is a schematic view of a configuration of a camera and a processing device incorporated in a test system.

FIG. 3 is a diagram illustrating moire image interference fringes that normally occur when a display pixel is detected by a camera incorporating a detector pixel array.

FIG. 4 shows red, green, and blue pixels in a color display panel where one color pixel in each pixel group is activated at a time during a test for luminance level and chromaticity of the color display panel. It is a figure which shows the pixel group consisting of.

FIG. 5 shows a color filter wheel incorporated into a test system to detect the luminance level and chromaticity of a color display panel.

FIG. 6 is a graph of CIE spectral trichromatic stimulus values versus wavelength used to determine chromaticity.

FIG. 7 is a CIE chromaticity diagram used to plot tricolor stimulus values to identify the resulting color.

FIG. 8 is a schematic diagram of a configuration for performing a viewing angle characterization test.

FIG. 9 is a polar plot that can be generated in a viewing angle characterization test.

FIG. 10 is a perspective view of an improved display panel connector mounted on a hinged frame in the test system of FIG. 1 to interface the display panel with the test system.

FIG. 11 shows an enlarged edge of the display panel and the connector when the hinged frame is closed, showing an alignment circuit that aligns the connector with the electrodes on the display panel.

DESCRIPTION OF SYMBOLS 10 Flat panel display test system 11 Flat panel display 12 Slidable table 14 Hinge frame 15 Camera 16 Flexible ribbon wire 18 Upper body 20 Lens 21 Mirror 22 Movable support structure 23 Color Filter 24 Filter Wheel 25 Second Camera 27 Keyboard 32 Line 34 Image Processing Computer 36 Computer 40 Display Panel Driver 41 Conductor 42 Test Data File 44 Back Light 52 Camera Detector Pixel 54 Pixel 56 Display Panel Pixel

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Daniel H. Scott United States 95131 San Jose Hapland Court, California 1341 (72) Inventor Robert E Cummins United States 94108 El Granada, California Valencia Avenue 315 (72) Inventor Peter Jay Vikowski United States 94024 California Los Altos Springer Road 952 (56) References International Publication 93/19453 (WO, A1) (58) Field (Int.Cl. ⁷ , DB name) G01M 11/00-11/02

Claims (3)

(57) [Claims] 1. A method for electronically detecting a display image formed by a periodic array of display pixels, the method comprising: positioning periodic detection means for observing the display image, the detection means comprising: The first of the detector elements
And a second array of display pixels in the array .
Focusing the display image formed by the periodic array of light sources to generate a signal corresponding to the intensity of light incident on each of the detector elements; Detecting a first signal generated by the detector element when the detector element is at a position and including a first moiré image interference fringe; a second signal along an axis relative to a line of the detector element. Shifting to approximately a half of a display pixel to a position, wherein the detector element is generated by the detector element when the detector element is at the second position with respect to the display image and includes a second moiré image interference fringe. detecting a second signal, and adding said first and second signal, each of the display pixels
Averaging the intensity levels of the first signal and the second signal generated by the detector element at a footing point, the first moiré formed by the display image incident on the detector element; Reducing the effects of image interference fringes and said second moiré image interference fringes. 2. The display pixel of a display panel, comprising:
A test system for detecting a display image generated by a periodic array of a detector element positioned to observe the display image and detecting the intensity of light from the incident display image .
A detector means comprising a second periodic array; and said image such that a first moiré image interference fringe appears in a first signal and a second moiré image interference fringe appears in a second signal.
Image shifting means for shifting from a first position to a second position along a first line of display pixels by approximately half of the display pixels along an axis associated with the first line of detector elements; the image signal generated by the detector element for each shift of the image by adding and processing from the first position relative to the detector element to the second position, the shift over the array of display pixels Averaging said first signal and said second signal at a toing point;
Formed by the display image incident on the detector element
The first moiré image interference pattern and the second moiré
Means for reducing the effect of image interference fringes . 3. A method for electronically detecting a display image formed by a periodic array of display pixels, comprising: positioning a periodic detection means comprising a CCD camera for observing the display image; The detection means includes a first periodic array of detector elements comprising camera pixels, the array being focused on a display image formed by a second periodic array of display pixels , each of which has a detector element. Generating a signal corresponding to the intensity of light incident on the first image, the first moire image interference pattern generated by the detector element when the detector element is at a first position with respect to the display image; Detecting a first signal comprising: moving the display image along the axis of the detector element relative to a first line by about one-half of a display pixel to a second position hesif. And detecting a second signal generated by the detector element when the detector element is at the second position with respect to the display image and including a second moiré image interference fringe. the first, by adding the second signal, each of the display pixels
Averaging the intensity levels of the first signal and the second signal generated by the detector element at a footing point, the first moiré formed by the display image incident on the detector element; Reducing the effects of image interference fringes and said second moiré image interference fringes.