US20060109231A1 - System for correcting display device and method for correcting the same - Google Patents

Abstract

In a display device having a nonvolatile memory device, such as an active matrix type liquid crystal display device, display contents displayed on the display device are obtained by a camera device. The obtained information (corresponding to the display contents) is digital-converted and then processed to detect a defect and a nonuniformity on the display device, so that correction information is produced. The correction information is stored in the nonvolatile memory device of the display device. Display information to be displayed on the display device is processed using the stored correction information, so that display contents are corrected and a defect and a nonuniformity on the display contents are inconspicuous.

Description

BACKGROUND OF THE INVENTION
• The present invention relates to a display correction system for a display device, in particular, a display device having a nonvolatile memory device and a display device correction method.
• As a conventional display device, a cathode ray tube (CRT) device, a plasma display device, a liquid crystal display (LCD) device or the like is used. Recently, an LCD device, in particular, an active matrix type LCD device has been developed.
• Since a dielectric constant of a liquid crystal substance (molecule) in a parallel direction to a molecule axis is different from that in a vertical direction, an LCD device uses this characteristic and displays ON/OFF states, that is, light/dark states by adjusting a transmission quantity or a scattering quantity of a light. In general, a liquid crystal material includes, a twisted nematic (TN) liquid crystal, a super twisted nematic (STN) liquid crystal, a ferroelectric liquid crystal and the like.
• It is said that among display devices using a liquid crystal, an active matrix type LCD device has a superior display characteristic. As shown inFIG. 2, in a conventional active matrix type LCD device,source lines203 to205 connected to asource driver201 are combined withgate lines206 to208 connected to agate driver202 in a matrix form, and thin film transistors (TFTs)209 to212 are arranged in these intersection portions. Gate electrodes in TFTs are connected to thegate lines206 to208, source electrodes in the TFTs are connected to thesource lines203 to205, and drain electrodes in the TFTs are connected to pixel electrodes and retainingcapacitors213 to216.Liquid crystal217 to220 are arranged between the pixel electrodes.
• FIGS. 3A to3C show operation waveforms of the TFT. When signal voltages are applied to the gate electrode and the source electrode of the TFT, the TFT is turned on, so that a voltage on the pixel electrode almost coincides with a source voltage. When the signal voltage is not applied to the gate electrode of the TFT, the TFT is turned off, so that a voltage on the pixel electrode is maintained until the TFT is turned on next.
• Since a voltage is applied from the pixel electrode to the liquid crystal by the above manner, an LCD device having less crosstalk and a large contrast with respect to adjacent pixels can be produced.
• In an active matrix type LCD device described above, since the necessary number of TFTs corresponds to the number of pixels, a defect produces in a TFT element formed in a substrate. If a TFT having a defect is in an open state or a short circuit state, a defect pixel has a desired voltage or a voltage on the defect pixel is unstable, so that the pixel produces as a point defect on a panel. Also, by variations of a threshold value and a mobility in a TFT, a voltage applied to a pixel electrode is varied, so that variations in brightness (gradation) of pixels produce.
• To solve the above problem, as shown inFIG. 4, in a pixel portion havinggate lines401 and402 andsource lines403 and404, a plurality ofTFTs405 and406 are arranged for onepixel electrode407 to obtain redundancy. That is, if the TFT406 is a defective element, a drain terminal is scribed (cut) in a laser scribingportion408 using a laser or the like to remove a defective element.
• A defective element is detected by using a structure as shown inFIG. 5. InFIG. 5, the structure includesgate lines501 and502,source lines503 and504,common electrode line505,TFTs506 to509,retaining capacitors510 and511,switches512 to515,amplifiers516 and517,measurement terminals518 and519 andpower sources520 and521. A voltage by which a TFT is turned on sufficiently is applied to thegate lines501 and502 connected to elements to be examined through theswitches512 and513 and simultaneously a desired voltage is applied to thesource lines503 and504 connected to the elements through theswitches514 and515. Next, a voltage on the gate lines is set to a ground level, to turn off the TFTs.
• Application of the voltage to the source lines is stopped and then the TFTs are leaved for a desired period of time. After that, a voltage is applied to the gate lines again and then a voltage on the source lines is measured. When the TFTs are in a normal state, since a first source voltage is maintained by the retaining capacitors, it is measured. Also, When a drain and a source in each TFT are in a short circuit state, since discharge produces in each TFT through resistors connected to the source lines while leaving the TFTs, a voltage is varied in measurement. Further, when the TFTs are in an open state, even though a voltage is applied to the gate lines, the voltage is not applied to the retaining capacitors. Furthermore, even through the retaining capacitors are charged insufficiently by variations of mobility and threshold of the TFT, a defect element can be distinguished by voltage measurement with high accuracy.
• In a conventional LCD device and a correction method for the device, as described above, the following problems produce. Though a defect of a pixel TFT can be corrected, a nonuniform display due to variation of a liquid crystal material and a band nonuniformity produced by rubbing cannot be corrected, so that an LCD device becomes a defective product in many cases.
• In general, when an operator watches a display device, two pixels which are sufficiently apart from each other cannot be distinguished even though a brightness (gradation) difference between one pixel and the other pixel is 10% or more. However, adjacent pixels are distinguished each other even though the brightness difference is about 2%. Therefore, it is important to suppress variations of brightness between adjacent pixels.
• An LCD device has a tendency to extend a size of a display portion (screen portion). In accordance with an increase of the size, it is difficult to maintain uniform display, so that a yield of an LCD device is deteriorated. Also, in a personal computer and a work station, since an operator continues to watch a display portion at a near position for a long period of time, nonuniform display is disagreeable for an operator and efficiency of the operator decreases, so that it is a claim subject from a user.
SUMMARY OF THE INVENTION
• The object of the present invention is to solve the above problem. In the present invention, a liquid crystal display (LCD) device includes a memory device for storing correction contents of pixel, and correction is performed by storing into the memory device the correction contents obtained by an external camera device, so that uniform display can be performed.
• According to the present invention, there is provided a correction system comprising: a display device having a nonvolatile memory; and a correction data producing device, wherein the correction data producing device includes, an obtaining circuit for obtaining an image signal displayed on the display device, a converter for converting the image signal into digital data, a signal processor for processing the digital data to obtain correction data, and a writing circuit for writing the correction data into the nonvolatile memory.
• According to the present invention, there is provided a method for operating a correction system including a display device and a correction data producing device, wherein the display device has a nonvolatile memory, and the correction data producing device includes an obtaining circuit for obtaining an image signal displayed on the display device, a converter for converting the image signal into digital data, a signal processor for processing the digital data to obtain correction data, and a writing circuit for writing the correction data into the nonvolatile memory, the method comprising the step of processing the correction data stored in the nonvolatile memory and the image signal to be displayed on the display device, to correct the image signal.
• According to the present invention, there is provided a display device comprising: a display portion for displaying image data; a driver for driving the display portion; a memory for storing correction data for correcting a nonuniform display of the display portion; and a processor for adding the stored correction data to the image data to obtain corrected image data, wherein the corrected image data is displayed on the display portion.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 shows a correction system having a liquid crystal display (LCD) device according to an embodiment of the present invention;
• FIG. 2 is a schematic structure view of a conventional active matrix type LCD device;
• FIGS. 3A to3C are operation waveforms of a thin film transistor (TFT);
• FIG. 4 shows a pixel region of the conventional active matrix type LCD device;
• FIG. 5 shows an active matrix portion including a measurement circuit for examining the conventional active matrix type LCD device;
• FIG. 6 shows a correction system having an LCD device according to another embodiment of the present invention; and
• FIGS.7 to15 show information to be processed or to be displayed in the correction system of the present invention.
DETAILED DESCRIPTION OF THEPREFERRED EMBODIMENTSEmbodiment 1
• FIG. 1 shows a correction system having a liquid crystal display (LCD) device according to an embodiment of the present invention. InFIG. 1, the correction system includes anLCD device110 formed on a glass substrate (not shown) and a correction information (correction data) producingdevice100. TheLCD device110 has anactive matrix portion111, agate driver112, asource driver113, amemory controller114, a memory device (a correction memory115), acorrection processor116, an analog/digital (A/D)converter117, asynchronous divider118, aclock generator119 and a digital/analog (D/A)converter120.
• The correctioninformation producing device100 produces correction information used to correct theLCD device110 and then writes the produced correction information into thecorrection memory115. Thedevice100 has a charge coupled device (CCD)camera device101, anamplifier102, an A/D converter103, asignal processor104, adata write unit105, aclock generator106 and avideo signal generator107. Thedevices100 and110 are connected with each other byconnection terminals108 and109.
• Correction is performed for theLCD device110. After the correction is completed, thedevice100 is disconnected from thedevice110. After that, thedevice100 is connected to another LCD device through theconnection terminals108 and109 and then next correction is performed.
• In the correctioninformation producing device100, a video signal output from thevideo signal generator107 is input to the A/D converter117 through thesynchronous divider118 of theLCD device110, so that the video signal is digital-converted. The digital converted video signal is input to thecorrection processor116. Since in an initial-stage, correction is not performed in thecorrection processor116, the video signal is input to the D/A converter120, so that the video signal is analog-converted. After that, the analog-converted video signal is input to theactive matrix portion111 through thesource driver113, so that a display is performed. Until this stage, the same operation as that of a conventional LCD device is performed.
• Correction information (correction data) is produced as follows.
• Optical display contents displayed on theactive matrix portion111 of theLCD device110 are obtained by theCCD camera device101 of the correctioninformation producing device100. TheCCD camera device101 has a CCD camera and the like. Since a video signal output from thedevice101 is generally a weak signal, it is amplified by theamplifier102. The amplified video signal is digital-converted by the A/D converter103 and then input to thesignal processor104.
• In thesignal processor104, a noise component and a moire component are removed from the video signal, to detect only information with respect to a defect of a pixel and a nonuniformity in theLCD device110. To easily detect a defect and a nonuniformity, it is desired that display contents displayed in theactive matrix portion111 have the same color and the same brightness (gradation).
• To detect a defect and a nonuniformity, three methods as described below can be used. In a first method, a difference between a desired standard level and a level of a signal input to thesignal processor104 is obtained and then used as a correction value. In a second method, a small changing component of a signal (original signal) input to thesignal processor104 is extracted using a median filter and then an extracted result is subtracted from the original signal, to detect a singular point. In a third method, a large changing component of the signal is extracted using a Laplacian filter to detect a singular point. When a singular point is detected using the median filter or the Laplacian filter, since correction information is only information with respect to the singular point, it does not represent a small change of brightness in a display device. However, as described above, no problem produces because an eye of a human is insensitive with respect to a small change.
• An output of thesignal processor104 is written into thecorrection memory115 of theLCD device110 by the data writeunit105. The data writing is performed by a desired method in response to a kind of thecorrection memory115 controlled by thememory controller114. Theclock generator106 controls theCCD camera device101, the A/D converter103, thesignal processor104, the data writeunit105 and thevideo signal generator107. A correction operation is completed after the data writing to thecorrection memory115 is performed.
• After the correction operation is completed, the correctioninformation producing device100 is disconnected from theLCD device110, so that theLCD device110 is connected to a system such as a personal computer body.
• When a video (image) signal output from the system is input to theLCD110 to perform a display, the video signal is digital-converted by the A/D converter117 through thesynchronous divider118. The digital-converted video signal is processed and corrected using correction data stored in thecorrection memory115 by thecorrection processor116. The corrected video signal is input to thesource driver113 through the D/A converter120. Thegate driver112 is controlled by theclock generator119. Theclock generator119 also controls thesource driver113, thememory controller114, thecorrection processor116, the A/D converter117 and thesynchronous divider118. In theactive matrix portion111, the corrected video signal is displayed.
• FIGS.7 to15 show information to be processed or to be displayed in the correction system of the present invention.
• FIG. 7 shows a display result of theactive matrix portion111 before correction is performed. InFIG. 7, though a matrix size of theactive matrix portion111 is 8×8, the size is arbitrary. A symbol x represents a nonuniform portion (pixel). A brightness (gradation) level is within 0 to 100 and brightness to be displayed is uniformly 50.
• FIG. 8 shows display information obtained after the display contents ofFIG. 7 are obtained by theCCD camera device101 and then digital-converted by the A/D converter103. A difference between a brightness value of a portion in which nonuniformity produces and that of surrounding portions is large. In a whole display portion, a brightness value is changed gradually from an upper left to a lower right. However, as described above, no problem produces on visual sensation of a human because a change is small.
• FIG. 9 shows a result representing a difference between brightness (50) to be displayed and display information ofFIG. 8. This result is obtained by thesignal processor104 and used as correction information.
• FIG. 10 shows a result obtained by digital-converting a video signal to be newly displayed after correction information is produced (obtained). This result represents output information of the A/D converter117.
• FIG. 11 shows a result obtained by adding information ofFIG. 9 to information ofFIG. 10 in thecorrection processor116. This result represents output information of thecorrection processor116. When the output information is input to theactive matrix portion111, a nonuniformity of a display portion on theactive matrix portion111 is corrected, so that the information ofFIG. 10 is displayed on theactive matrix portion111.
• FIG. 12 shows a result obtained by processing the display information ofFIG. 8 using an median filter in thesignal processor104, without performing simply subtraction.
• FIG. 13 shows a result obtained by subtracting the result ofFIG. 12 from the display information ofFIG. 8. This result represents correction information. The median filter passes only a small change component of the video signal (display information) and therefore removes nonuniformity information. Original information is subtracted from information obtained after the nonuniformity information is removed, so that the nonuniformity information can be obtained.
• When a Laplacian filter is used, information representing a large change point can be obtained.FIG. 14 shows a result obtained by adding the correction information ofFIG. 13 to the information ofFIG. 10 in thecorrection processor116. This result represents output information of thecorrection processor116.
• FIG. 15 shows display information displayed on theactive matrix portion111. The display information includes a small change component but does not include a large change component, so that nonuniformity on a display portion can be inconspicuous.
• In the embodiment, though an analog gradation type driver is used, a digital gradation type driver may be used. When the digital gradation type driver is used, the D/A converter120 is not required. Also, when thevideo signal generator107 generates a digital signal and when a digital video signal is input to theLCD device110, the A/D converter117 is not also required.
• The data writeunit105 is a read only memory (ROM) writer or the like. Also, thecorrection memory115 is a nonvolatile memory such as an electrically programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), a flash memory or the like. These memory are a semiconductor memory. Thecorrection memory115 may be arranged on a glass substrate of theLCD device110 by a chip on glass (COG) technique, or may be arranged on another substrate other than the glass substrate.
• A driver circuit for driving a pixel TFT may be formed on a glass substrate using TFTs simultaneously in forming an active matrix portion, or a single crystalline chip corresponding to the driver circuit may be arranged by the COG technique or a tape automated bonding (TAB), as similar to thecorrection memory115.
Embodiment 2
• FIG. 6 show a correction system having an LCD device according to another embodiment of the present invention. The embodiment is different fromEmbodiment 1, and obtainment and correction of display information to be displayed are performed a plurality of times.
• InFIG. 6, a correction system of the embodiment includes anLCD device620 formed on a glass substrate (not shown) and a correction information (correction data) producingdevice600. TheLCD device620 has anactive matrix portion621, agate driver622, asource driver623, amemory controller624, a memory device (a correction memory625), acorrection processor626, an A/D converter627, asynchronous divider628, aclock generator629 and a D/A converter630.
• The correctioninformation producing device600 produces correction information used to correct theLCD device620 and then writes the produced correction information into thecorrection memory625. Thedevice600 has aCCD camera device601, anamplifier602, an A/D converter603, asignal processor604, adata write unit605, aclock generator606, avideo signal generator607,memories608 and609,adders610 and611 and aswitch612. Thedevices600 and620 are connected with each other byconnection terminals613 and614.
• Correction is performed for theLCD device620. After the correction is completed, thedevice600 is disconnected from thedevice620. After that, thedevice600 is connected to another LCD device through theconnection terminals613 and614 and then next correction is performed.
• In the correctioninformation producing device600, a video signal output from thevideo signal generator607 is input to the A/D converter627 through thesynchronous divider628 of theLCD device620, so that the video signal is digital-converted. The digital converted video signal is input to thecorrection processor626. Since in an initial stage, correction is not performed in thecorrection processor626, the video signal is input to the D/A converter630, so that the video signal is analog-converted. After that, the analog-converted video signal is input to theactive matrix portion621 through thesource driver623, so that a display is performed. Until this stage, the same operation as that of a conventional LCD device is performed.
• Correction information (correction data) is produced as follows.
• Optical display contents displayed on theactive matrix portion621 of theLCD device620 are obtained by theCCD camera device601 of the correctioninformation producing device600. TheCCD camera device601 has a CCD camera and the like. Since a video signal output from thedevice601 is generally a weak signal, it is amplified by theamplifier602. The amplified video signal is digital-converted by the A/D converter603 and then input to thesignal processor604.
• In obtaining first display contents, correction information obtained by thesignal processor604 is stored in thememory608. The correction information is also stored in thecorrection memory625 through theswitch612 and data writeunit605. After correction is performed similar toEmbodiment 1, a display is performed again and then second display contents are obtained. Correction information (with respect to the second display contents) obtained by thesignal processor604 is added to the correction information (with respect to the first display contents) stored in thememory608 by theadder610, so that the added correction information is stored in thememory609 and thecorrection memory625. TheLCD device620 is corrected again. After that, a display is performed and then third display contents are obtained. Output information of thesignal processor604 is added to the correction information (with respect to the second display contents) stored in thememory609 by theadder611 and then stored in thecorrection memory625 through theswitch612 and the data writeunit605.
• By repeating obtainment and correction of display information a plurality of times, further high precise correction can be performed. In the embodiment, though correction is performed three times, correction may be performed two times, four times or more.
• In driving the correction memory and the active matrix portion, the same operation asEmbodiment 1 is performed.
• The present invention is not different from a conventional correction method using a pixel TFT having redundancy. By combining the correction method of the present invention with the conventional correction method, further improved effect can be obtained.
• As described above, in the present invention, information with respect to a defect and a nonuniformity is stored in a memory device incorporated in an LCD device, a video signal input to the LCD device is processed using the stored information, and then a defect and a nonuniformity on a display portion of the LCD device is corrected, so that high quality display can be performed.

Claims (18)

1. A method for operating an active matrix type display device, wherein the active matrix type display device comprising:

an active matrix type display portion;

a source driver;

a nonvolatile memory for storing a correction information; and

a correction processor,

wherein the method comprising:

inputting a video signal to the correction processor;

inputting the correction information from the nonvolatile memory to the correction processor;

correcting the video signal by the correction information;

inputting the corrected video signal to the source driver; and

displaying an image on the active matrix type display portion by the corrected video signal inputted to the source driver.

2. A method for operating an active matrix type display device, wherein the active matrix type display device comprising:

an active matrix type display portion;

a source driver;

a nonvolatile memory for storing a correction information;

a correction processor; and

an A/D converter,

wherein the method comprising:

inputting an analog video signal to the A/D converter;

converting the analog video signal to a digital video signal;

inputting the digital video signal to the correction processor;

inputting the correction information from the nonvolatile memory to the correction processor;

correcting the digital video signal by the correction information;

inputting the corrected digital video signal to the source driver; and

displaying an image on the active matrix type display portion by the corrected digital video signal inputted to the source driver.

3. A method for operating an active matrix type display device, wherein the active matrix type display device comprising:

an active matrix type display portion;

a source driver;

a nonvolatile memory for storing a correction information;

a correction processor;

an A/D converter; and

a D/A converter,

wherein the method comprising:

inputting an analog video signal to the A/D converter;

converting the analog video signal to a digital video signal;

inputting the digital video signal to the correction processor;

inputting the correction information from the nonvolatile memory to the correction processor;

correcting the digital video signal by the correction information;

inputting the corrected digital video signal to the D/A converter;

converting the corrected digital video signal to a corrected analog video signal; and

displaying an image on the active matrix type display portion by the corrected analog video signal inputted to the source driver.

4. A method for operating an active matrix type display device according toclaim 1, wherein the active matrix type display device is a liquid crystal display device.

5. A method for operating an active matrix type display device according toclaim 2, wherein the active matrix type display device is a liquid crystal display device.

6. A method for operating an active matrix type display device according toclaim 3, wherein the active matrix type display device is a liquid crystal display device.

7. A method for operating an active matrix type display device according toclaim 1, wherein the active matrix type display device further comprises a gate driver and a synchronous divider.

8. A method for operating an active matrix type display device according toclaim 2, wherein the active matrix type display device further comprises a gate driver and a synchronous divider.

9. A method for operating an active matrix type display device according toclaim 3, wherein the active matrix type display device further comprises a gate driver and a synchronous divider.

10. A method for operating an active matrix type display device according toclaim 1, wherein the display portion comprises a thin film transistor.

11. A method for operating an active matrix type display device according toclaim 2, wherein the display portion comprises a thin film transistor.

12. A method for operating an active matrix type display device according toclaim 3, wherein the display portion comprises a thin film transistor.

13. A method for operating an active matrix type display device according toclaim 1, wherein the source driver comprises a thin film transistor formed over the same substrate as the display portion.

14. A method for operating an active matrix type display device according toclaim 2, wherein the source driver comprises a thin film transistor formed over the same substrate as the display portion.

15. A method for operating an active matrix type display device according toclaim 3, wherein the source driver comprises a thin film transistor formed over the same substrate as the display portion.

16. A method for operating an active matrix type display device according toclaim 1, wherein the nonvolatile memory is a flash memory.

17. A method for operating an active matrix type display device according toclaim 2, wherein the nonvolatile memory is a flash memory.

18. A method for operating an active matrix type display device according toclaim 3, wherein the nonvolatile memory is a flash memory.

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