KR20050004080A - A substrate and a display device incorporating the same - Google Patents

Abstract

PURPOSE: A substrate and a display device combining with the same are provided to have a test member mounted on a substrate for discriminating normal operations of switching devices. CONSTITUTION: The test member(18) is arranged along a lower edge of a matrix(6) of pixels. The test member includes plural sensing amplifiers(15) having inputs connected to row electrodes, respectively. The sensing amplifiers is controlled by a control signal from a timing and control circuit(2). The outputs of the sensing amplifiers are provided to an A/D(Analog-Digital) conversion block(16). The outputs of the A/D conversion block are connected to a read-out shift register(17). The serial output data converted by the read-out shift register are provided to an output line(19). The test member(18) obtains information on capacitances of data lines(S1,S2).

Description

Substrate and Display Device Combining the Same {A SUBSTRATE AND A DISPLAY DEVICE INCORPORATING THE SAME}

The present invention relates to a substrate for an active matrix display such as an active matrix liquid crystal display (AMLCD), for example, in which each switching device is provided with a switching device such as polycrystalline silicon thin film transistors (TFTs). More specifically, the present invention relates to a substrate having test means provided on the substrate for determining whether the switching elements operate correctly.

1 illustrates a conventional active matrix liquid crystal display device. The device is formed on a display substrate which is schematically represented by reference numeral 1 and comprises a timing and control circuit 2 connected to an input 3 for receiving timing and control signals together with the image data to be displayed. The circuit 2 supplies appropriate signals to the data signal generator in the form of a display source driver 4 and to the scan signal generator in the form of a gate driver 5.

The display source driver 4 comprises a plurality of column electrodes S ₁ , S ₂ , which act as column data lines (or “source lines”) for the active matrix of picture elements (pixels) indicated by 6. ... have a plurality of outputs connected to S _m ). The column electrodes extend through the height of the active matrix 6 and each is connected to the data inputs of each column of pixels. Similarly, the driver 5 has a plurality of outputs connected to the row electrodes G ₁ , G ₂ ... G _n extending through the width of the matrix 6. Each row electrode acts as a row scan line (or “gate line”) and is connected to the scan inputs of the pixels of each row.

One of the pixels is shown in more detail at 7, which is a standard active matrix liquid crystal type. The pixel comprises, for example, an electronic switch 8 in the form of a polycrystalline-silicon thin film transistor whose source is connected to the _ith column electrode Si and the gate is connected to the jth row electrode G _j . The pixel is therefore labeled P _ij . The drain of the switch 8 is connected to the pill cell electrode 11 forming a part of the liquid crystal pixel image generating element 9, and also to the parallel storage capacitor 10. The image display element 9 comprises a pixel electrode 11, a counter-electrode 13 disposed opposite the pixel electrode, and a liquid crystal layer disposed between the pixel electrode 11 and the counter-electrode 13 ( 12) is formed.

The criteria for rows and columns is not intended to be limited to horizontal rows and vertical columns, but instead refers to the well-known manner of the standard in which image data is input line by line. In a display, although pixel rows are arranged horizontally and pixel columns are arranged vertically, this is not essential, the rows are equally well arranged vertically and the columns are also arranged horizontally.

In use, the image data for display is supplied to the input 3 of that arrangement by any suitable source and displayed by the pixel active matrix 6 in accordance with the operation of the drivers 4, 5. To write data to a particular pixel, an "enable" voltage is applied to a row scan line connected to the switching element of that pixel-thus to write data to that pixel _Pij , The " able " voltage will be applied to the row scan line G _j to turn on the switching element 8 so as to electrically conduct between the source and the drain of the switching element 8. (Applying that enable voltage to the row scan line G _j will also turn on all other switching elements connected to that row scan line G _j .) As a result, the pixel electrode and the storage capacitor have a column the voltage applied to the electrodes (S _i) is electrically connected to the column electrodes (S _i) to be written to the pixel electrode 11 of the liquid crystal pixel image generating device 9, and is also written into the storage capacitor 10. The enable voltage is then removed from the row scan line G _j to turn off the switching element. Which is electrically isolated from the pixel that the column electrodes (Si) so as not to affect the voltage stored in the following changes in the voltages of the column electrodes (S _i) are pixel (P _ij).

In general, the display of the type shown in FIG. 1 is refreshed line by line. The pixel image data is supplied in series as image frames with frame synchronization pulses indicating the start of each frame refresh cycle. Rows of pixel image data are input one after the command in the display source driver 4 and an enable signal is supplied to the appropriate row scan line for enabling the image data to be stored in the appropriate rows of pixels. Therefore, the pixel rows of the matrix 6 are refreshed one row at a time by the gate driver 5, which supplies enable signals, typically one row at a time, starting at the top row and ending at the bottom row when the frame refresh cycle is complete. do.

As can be seen from above, the correct operation of the active matrix display device depends on the switching elements functioning correctly to disconnect the pixel electrode from or connect the pixel electrode to the column electrode associated with the desired pixel electrode. do. If the switching element does not function properly, it is not possible to address the associated pixel in the desired manner. The two largest common fault modes of the switching element are permanently open circuitry so that (a) the pixel electrode is permanently disconnected from its associated column electrode regardless of whether or not the enable voltage is applied to the associated row scan line. (b) permanently short-circuit such that the pixel electrode is permanently connected to its associated column, whether or not the enable voltage is applied to its associated row scan line or not. Goes. In the case of (a), it is impossible to write fresh data to the pixel, whereas in (b) the data stored in that pixel changes each time the voltage of its associated column data line changes.

Defects in the switching elements can occur during the manufacture of the active matrix display device. It is desirable to detect faulty switching elements at an early stage of manufacture of the display device, since the display must be discarded if a repair operation has to be made or even if there are too many defects. The cost savings are made by repairing other defective displays in the former case and eliminating additional manufacturing steps on the defect displays in the latter case.

A conventional method of detecting defective switching elements during the manufacture of an active matrix display device is to use external testing equipment to write a fixed charge to each pixel. This charge is stored in the pixel storage capacitor and read back after a set period of time. By comparing the amount of charge read back with that written, the integrity of each pixel switch in its active matrix can be ascertained. External equipment used to detect faults is expensive and time consuming to use and must be reset for each different design of the display. Examples of such conventional methods are provided in US-A-5 377 030.

WO 92/11560 discloses an active matrix device in which a test circuit is mounted on its substrate. Two test circuits are connected to each scanning line or data line, one at each end of the line. In operation, one test circuit applies a voltage to a data line or a scanning line connected thereto, and the test circuit on the other side of the scanning line or data line measures the resulting voltage at which the current flowing through the line can be determined. . The current flowing through a particular line provides an indication as to whether the line has a short circuit or breakage therein.

US-A-5 774 100 discloses an active matrix liquid crystal display provided with a "test section" in which a row of test transistors are formed. In operation, the driver circuit supplies a signal to the scanning line or data line, and the resulting output voltage level on that scanning / data line, and the time taken for that voltage level for adjustment are determined.

US-A-5 576 730 relates to an active matrix substrate provided with terminals used for testing the active matrix substrate. However, no test circuit is provided for the active matrix substrate. An "inspection signal" is provided by an external source, and the results are read by a computer external to the substrate separated from the analog / digital converter and the active matrix substrate.

1 is a schematic diagram of a typical active matrix display.

2 is a block schematic diagram of an active matrix substrate in accordance with an embodiment of the present invention.

3A is an illustration of the active matrix substrate of FIG.

3B is a schematic diagram of a liquid crystal display device incorporating the active matrix substrate of FIG. 3A.

4 is a block flow diagram illustrating a first method of the present invention.

5 is a block flow diagram illustrating a second method of the present invention.

<Explanation of symbols for the main parts of the drawings>

1: display board

2: timing and control circuit

4: display source driver

5: display gate driver

6: active matrix

15: Sense Amplifier

16: analog-to-digital conversion block

17: read shift register

18: self-testing circuit

A first aspect of the invention provides a display picture element electrode; Switching element-The switching element receives a first terminal connected to a picture element electrode, a second terminal connected to a data line, and an enable signal for selectively enabling the switching element to receive the second terminal at the second terminal. Having a third terminal for connecting one terminal; Test means for obtaining information about the operation of said switching element, said test means obtaining information on the capacitance of said data line for two presumably different states of said switching element in use.

Since the test means are integrated on the substrate, expensive external testing equipment is not required. The correct operation of the switching elements can be confirmed at an early stage of the manufacture of the substrate, for example immediately after the switching elements are manufactured. It is not necessary to integrate the substrate into a complete device before testing the switching elements.

The substrate may further comprise control means for controlling the test means to obtain information about the operation of the switching element.

In a first period, the control means inhibits the application of the enable signal to the second terminal of the switching element and the test means obtains second information about the value of the capacitance of the data line and the Application is suppressed.

In a second period, the control means permits the application of an enable signal to the second terminal of the switching means such that the test means obtains second information about the value of the capacitance of the data line and the enable signal. Is applied to the second terminal of the switching element.

The test means can be adjusted to determine the difference between the capacitance of the data line and the capacitance of the reference capacitor.

The test means may comprise a sense amplifier.

The test means may comprise analysis means for obtaining information on the operation of the switching element from the obtained information on the capacitance of the data line.

The analyzing means may be adjusted to compare the first information on the capacitance value of the data line with the second information on the capacitance value of the data line.

The analyzing means may be adjusted to compare the first and / or second information about the capacitance value of the data line with a predetermined threshold.

The substrate includes a plurality of display picture element electrodes arranged in rows and columns; A plurality of data lines, each data line associated with a respective column of picture element electrodes; And a plurality of switching elements, each switching element having a first terminal connected to a respective one of the picture element electrodes, a second terminal connected to the data line associated with a respective one of the picture electrodes, and And a third terminal for receiving an enable signal for selectively enabling a switching element and for connecting said first terminal to said second terminal, said control means being in use each of said switching elements. It can be adjusted to control the test means to obtain information about the operation.

The invention also provides a combination comprising a substrate as defined above and analysis means for receiving output from said test means and obtaining information on said or each switching element from the output from said test means. Since the output from the test means is passed to an analysis means separate from the substrate, the analysis means need not be integrated on the substrate.

A second aspect of the invention provides a display device comprising a substrate as defined in the first aspect of the invention.

The display device includes a substrate defined in the first aspect of the present invention; A counter substrate disposed opposite the substrate; And a liquid crystal material disposed between the substrate and the counter substrate.

A third aspect of the invention provides a method for testing a switching element of a substrate, wherein the switching element comprises a first terminal connected to a picture element electrode, a second terminal connected to a data line, and the switching element. And a third terminal for receiving an enable signal for selectively enabling the third terminal to connect the first terminal to the second terminal, wherein the method of testing the switching element is a state in which two measurements of the switching element are different. Acquiring information about the capacitance of the data line for each of the two data lines.

The principle of the testing method of the present invention is that by applying the enable signal to the switching element, when the switching element operates correctly, the capacitance of the column electrode (data line) must be changed. When all switching elements connected to a column electrode are opened, the measurement of the capacitance of that column electrode will only measure the capacitance of that column electrode. However, when the switching element of a pixel associated with that column electrode is closed, the measurement of the capacitance of that column electrode not only measures the capacitance of that column electrode, but also the pixel capacitance (ie, the capacitance of the storage capacitor and the pixel electrode). will be. Therefore, measuring the capacitance of the column electrode provides a quick and simple way to check, for example, that the switching element of the active matrix substrate is operating correctly.

The method may further comprise acquiring first information about the capacitance value of the data line when no enable voltage is applied to the second terminal of the switching element.

The method may further comprise obtaining second information about the capacitance value of the data line when the enable voltage is applied to the second terminal of the switching element.

The method may further comprise comparing the first information for the capacitance value of the data line with the second information for the capacitance value of the data line.

The method may further comprise comparing the first and / or second information about the capacitance value of the data line with a predetermined threshold.

The method may determine the first and second information for the capacitance value of the data line if the first information for the capacitance value of the data line is substantially similar to the second information for the capacitance value of the data line. The method may further include comparing with.

The method may further include determining a difference between the capacitance of the data line and the capacitance of the reference capacitor as information on the capacitance value of the data line.

The method may further comprise generating a voltage having a magnitude proportional to the difference between the capacitance of the data line and the capacitance of the reference capacitor.

A fourth aspect of the invention provides a method for testing an active matrix substrate, the active matrix substrate comprising: a plurality of display picture element electrodes arranged in rows and columns; A plurality of data lines, each data line associated with a respective column of picture element electrodes; And a plurality of switching elements, each switching element selectively selecting a first terminal connected to each of the picture element electrodes, a second terminal connected to the data line associated with each of the picture element electrodes, and the switching element. And a third terminal for receiving an enable signal for enabling and connecting the first terminal to the second terminal, wherein the method does not enable any enable signal to any of the switching elements. Acquiring first information for each capacitance of each data line if not applied; Applying an enable signal to each switching element in the selected first row while not applying the enable signal to the switching elements in the other rows; Acquiring second information for each capacitance of each data line when the enable signal is applied to the switching elements in the selected first row; Obtaining information about the switching elements in the selected first row from the first and second information for the respective capacitance of each data line.

The present invention includes applying an enable signal to each switching element in a selected second row while not applying the enable signal to switching elements in other rows; Acquiring third information for each capacitance of each data line when the enable signal is applied to the switching elements in the selected second row; And obtaining information about switching elements in the selected second row from the first and third information for each capacitance of each data line.

Alternatively, the present invention includes the steps of: obtaining third information for each capacitance of each data line when any enable signal is applied to any of the switching elements; Applying an enable signal to each switching element in the selected second row while not applying the enable signal to the switching elements in the other rows; When the enable signal is applied to the switching elements in the selected second row, obtaining information about the switching elements in the selected second row from the third and fourth information for each capacitance of each data line; It may further comprise a step.

The invention will be further described by way of example with reference to the accompanying drawings.

Like reference numerals refer to like elements throughout.

<Example>

The invention will be described in particular with reference to an active matrix substrate comprising a matrix of picture element electrodes, but the invention is in principle not limited thereto.

2 is a block schematic diagram of an active matrix substrate 14 according to an embodiment of the present invention. The active matrix substrate 14 includes a source driver 4, a gate driver 5, and an active matrix 6 of picture element electrodes formed on the substrate 1. Each picture element electrode is controlled by an associated switching element. If the substrate is integrated into a fully display device, each picture element electrode will correspond to a pixel (picture element) of the device.

The active matrix substrate 14 of FIG. 2 further comprises test means 18 for testing whether the switching elements of the active matrix 6 operate correctly. The test means 18 may comprise circuits provided on the substrate 1 and for example integrated on the substrate 1.

FIG. 3A illustrates the components of the active matrix substrate 14 of FIG. 2 in more detail. The components of the active matrix substrate 14 are formed on the substrate labeled 1 and are to be displayed for receiving timing and control signals (and also once the active matrix substrate 14 is integrated into a complete display device). And a timing and control circuit 2 connected to the input 3). The timing and control circuit 2 supplies the appropriate signals to the data signal generator in the form of a source driver 4 and to the scan signal generator in the form of a gate driver 5. The display source driver 4 and the scan driver 5 may be of any suitable type, such as standard or conventional types, and will not be described further. The display source driver 4 is connected to a plurality of column electrodes S ₁ , S ₂ ... S _m which act as column data lines for the matrix of picture elements (pixels) indicated by 6. Has the outputs of The timing and control circuit 2 controls whether the outputs of the display source driver 4 are electrically connected to or disconnected from the data lines. The display source driver can only be connected to its data lines, for example when the display source driver 4 is enabled by the control circuit 2. The data lines extend through the entire height of the active matrix 6 and each data line is connected to the data inputs of a column of respective pixels. Similarly, the gate driver 5 has a plurality of outputs connected to the row electrodes G ₁ , G ₂ ,... G _n extending through the entire width of the matrix 6. Each row electrode acts as a row scan line and is connected to the scan inputs of the pixels of each row.

One of the pixels is shown in more detail at 7. It will be shown that the pixel 7 of FIG. 3A generally corresponds to the pixel 7 of FIG. 1, and the description will not be repeated here. However, it should be noted that since FIG. 3A shows the active matrix substrate 14 rather than a complete display device, the liquid crystal layer 12 and the counter electrode 13 of FIG. 1 do not exist and so are not shown in FIG. 3A. .

In the embodiment of FIG. 3A, the test means 18 is arranged along the lower edge of the matrix 6 of pixels. The test means 18 comprises a plurality of sense amplifiers 15 whose inputs are connected to each of the column electrodes. The sense amplifiers are controlled, eg enabled, by a control signal from the timing and control circuit 2. The outputs of the sense amplifiers are fed to an analog-to-digital conversion block 16, which converts the analog values sensed by the sense amplifiers 15 into parallel digital outputs. The outputs of the conversion block 16 are connected to a read-out shift register 17, which converts the parallel output data from the conversion block 16 into serial output data and outputs it to the output line 19. To feed.

The test means 18 can obtain information about the capacitance of the data lines S ₁ , S ₂ ... S _m . Information as to whether the switching elements 8 operate correctly can be obtained from the measured capacitance of the data lines. In a particularly preferred embodiment, the information about the operation of the switching elements can be obtained by making two measurements of the capacitance of the data line, and when these two measurements are made, the switching element connected to the data line is estimated in two presumptions. Are in different states.

The principle of the test method will now be described below with reference to the pixel _Pij associated with the data line _Si and the row electrode G _j .

Initially, its timing and control circuitry that enables the sense amplifier 15 that the data line sense amplifier 15 in the first cycle to the measurement of the capacitance of the (S _i). During this first cycle, the timing and control circuit ensures that electrically disconnected from the data line (S _i), the display source driver 4. The timing and control circuit 2 also suppresses the gate driver 5 from applying the enable voltage to the row scan line G _j . In practice, the timing and control circuit 2 inhibits the gate driver 5 from applying the enable voltage to any of the row scan lines G _j . Therefore, the measurement of the capacitance during the first period is _i , which is estimated to be an open circuit, so that the data line Si is disconnected from the storage capacitance 10 and pixel electrode 11 of all pixels of the i-th pixel column in measurement. Consisting of all switching elements 8 connected to the first column data line-that is, the switching element will be an open circuit if it works correctly. The data line (S _i) is also disconnected from the display source driver 4. Consequently, if the capacitance measured in the first cycle, the switching devices are operating correctly connected to the data line, to be an intrinsic capacitance of the data line (S _i).

In the second period, the timing and control circuits instruct the gate driver 5 to apply the enable voltage to the row scan line Gj while not applying the enable voltage to any other row scan line. The timing and control circuit is to keep the display source driver 4 is disconnected from the source line (S _i), and also in continuing the sense amplifier 15 to measure the capacitance of the source line (S _i) enable. Since the pixel (P _ij) the switching elements are now the source line (S _i) is closed onto the estimate so that the connection with the estimation to a pixel (P _ij) in, - that a switching element of a pixel (P _ij) that it is operating correctly, If it is, the capacitance measured in the second period should be the sum of the capacitance of the pixel Pi _j and the inherent capacitance of its source line Si. The predominant contribution to that pixel capacitance will be the storage capacitance. Therefore, if the switching element is tested at one point in the manufacturing processes, for example, after its storage capacitance 10 has been manufactured, the capacitance measured in the second period is determined by the storage capacitance 10 and its to be the sum of the intrinsic capacitance of the source line (S _i).

Information about the operation of the switching element of that pixel can be obtained by comparing the capacitance obtained in the first period with the capacitance measured in the second period. Since the capacitance measured in the second period to be stored including the capacitance as well as the capacitance inherent of the data line (S _i), the capacitance measured in the second period is greater than the measured capacitance at the first cycle. Therefore, if the comparison shows that the capacitance measured in the second period is actually greater than the capacitance measured in the first period, this suggests that the switching element is operating correctly. However, if the comparison shows that the capacitance measured in the first period is approximately the same as the capacitance measured in the second period, this indicates that the switching element is defective. Which the switching element (two measurements only the data line (S such that they measure the inherent capacitance of the _i)), or indicate that the permanently open circuit, or that the switching device is (a data line measured at the first cycle (S _i ), in addition to the capacitance of _i ), so that it is permanently closed (to be a measure of the total capacitance of the storage capacitor 10). These two fault conditions can be distinguished from each other by comparing the capacitances measured in the first and second periods with a predetermined threshold. The threshold is set at a level greater than the expected capacitance of the data line Si, but it is lower than the capacitance of the storage capacitor 10. Therefore, if the capacitance measured in the first period is substantially the same as the capacitance measured in the second period, and lower than a predetermined threshold, then either measurement of the capacitance will cause the switching capacitor to open permanently. It does not contain. Conversely, if the capacitance measured in the first period is substantially the same as the capacitance measured in the second period and both are greater than the threshold, this means that the switching element is permanently closed-the measurements of both capacitances of the storage capacitor It includes.

Therefore, the measurement of capacitance in this manner provides a simple technique for determining whether the switching element is operating correctly. Moreover, it not only provides information on whether the switching element works correctly but also provides information on the defect nature of whether the switching element is found to be defective.

The test technique of the present invention can be performed on an active matrix substrate during the measurement of the substrate. The method does not require a liquid crystal layer to be present, so the substrate can be tested before integrating into a fully display device. The test method of the present invention may be performed at any stage in the manufacture of an active matrix substrate after its switching elements and storage capacitors have been fabricated on the substrate. Therefore, defects can be detected at a relatively early stage of the manufacturing process-which allows the defect to be repaired, or alternatively, the substrate discards if too many defect switching elements are present.

The testing method of the present invention does not require critical equipment outside the active matrix substrate. Only required external equipment receives the output from the shift register 17 and converts the output from the shift register to provide a useful output such as a "pass / fail" indication or the location of any defective switching elements. Means (indicated by 44 in FIG. 3A). (Although this is less efficient than using external means due to the area of the substrate to be currently employed, the means for generating a "pass / fail" indication or the position of any defective switching elements from the output of the shift register 17 is in principle Can be integrated onto the substrate.)

In principle, the analog-to-digital conversion block 16 and the shift register 17 can be integrated into external testing equipment rather than integrated on the active matrix substrate 14. This will reduce the space taken up by the testing equipment on the active matrix substrate, even though it has the disadvantage of requiring many special connections between the external testing equipment and a panel with columns in the pixel matrix.

The description refers to a sense amplifier measuring the capacitance of the source line in the first and second periods. Although this can be done in principle, in a preferred embodiment the sense amplifier measures the difference between the capacitance of the source line and the capacitance of the reference capacitor integrated on the active matrix substrate. In this embodiment, the sense amplifier outputs a voltage signal that is proportional to the difference between the capacitance of the reference capacitor and the capacitance of the source line. The analog-digital conversion block generates a binary word that is proportional to this voltage signal. The reference capacitor is manufactured to have the same capacitance as the inherent capacitance of the source line. Therefore, its output binary word from the analog-to-digital conversion block in the first period is zero (assuming no switching element connected to the source line is permanently closed).

The above description refers to testing a switching element of a single pixel of an active matrix substrate. Indeed, of course, it would be desirable to test all the switching elements on the active matrix substrate, and FIG. 4 shows one way to do this.

Initially, in FIG. 20, the capacitance of each data line (source line) is measured. For each data line, its capacitance is usually measured with all switching elements connected to that data line in the OFF state. Step 20 is, for example, a display source driver that inhibits the gate driver applying an enable voltage to any row scan line and enabling the sense amplifier 15 to measure the capacitance of their respective data lines. Timing and control circuit 2 for disconnecting all data lines from (4).

In step 20, each sense amplifier will generate a voltage signal that is proportional to the difference between the capacitance of the associated data line and the capacitance of the reference capacitor. In a preferred embodiment of the substrate of the present invention, a plurality of reference capacitors are integrated on the substrate, one for each sense amplifier. In this case, each sense amplifier generates a first voltage signal proportional to the difference between the capacitance of its associated data line and the capacitance of each reference capacitor in step 20. In principle, however, the substrate may be provided with a single reference capacitor. The first voltage signal generated by each sense amplifier is stored in a calibration data file, indicated at 22 in step 21.

In principle, the method includes measuring the capacitance of each data line in succession, wherein measurements obtained from one data line are stored before the capacitance of the next data line is measured. In principle, however, it may be desirable to simultaneously measure the capacitance of each data line in step 20 and to simultaneously store each measurement in step 21, which may reduce the time taken. The value for the capacitance of the data line obtained in step 20 should be equal to the inherent capacitance of that data line if all switching elements connected to that data line are operating correctly, and considered as a correction value for that data line. Can be.

In step 23, the first row scan line may be made active. This is done by the timing and control circuit 2 instructing its gate driver to apply its " enable " voltage to its first row scan line, for example row scan line G ₁ . Therefore, the "enable" voltage is applied to the gate electrodes of all switching elements connected to the first row scan line, so that each switching element in the first row is turned on (assuming it is operating correctly). ON). The other row scan lines remain inactive at step 23, and the timing and control circuitry inhibits gate driver 5 from applying its " enabled " voltage to the other row scan lines.

In step 24, the capacitance of each data line is measured again by the sense amplifier 15. Step 24 provides a second capacitance measurement for each data line. Step 24 may include measuring the capacitance of each data line in succession, or it may include simultaneously measuring the capacitance of each data line.

In step 25, the values of the first capacitance for each data line are retrieved from the correction data file 22. For each data line, the capacitance measured in step 21 and retrieved in step 24 is subtracted from the capacitance measured in step 24. The result of each subtraction is stored in pixel state map file 27 in step 26. Each subtraction is stored for each row scan line (G ₁ in this example) and for each data line.

As described above, if the switching element is functioning correctly, the result of the subtraction in step 25 is that the capacitance measured in step 24 should include the storage capacitance, whereas the capacitance measured in step 20 should not include the storage capacitance. It must be a positive value. Therefore, the result obtained in step 26 indicates whether the switching element (in the first row) is operating correctly (positive value is obtained) or the switching element is not operating correctly (zero fast value will be obtained). Provide immediate orders regarding

In step 28 it is determined whether the test procedure has been performed for all row scan lines. If step 28 does not produce a "no" decision, then the current active row scan line is inactive and the next row scan line becomes active at step 29. For example, if gate line G ₁ is currently the active row scan line, step 29 removes the "enable" voltage from row scan line G ₁ and that "enable" to row scan line G ₂ . Timing and control circuit 2 that instructs gate driver 5 to apply a voltage. Step 24, step 25, and step 26 are then repeated for the next row scan line. If no "no" decision is still obtained in step 28, then step 29, step 24, step 25, step 26 are repeated until the "yes" decision is obtained in step 28.

The pixel state file map 27 generated by the method of FIG. 4 includes an indication for each pixel of the active matrix substrate 14 as to whether the switching element is operating correctly or is defective. If it is desired to obtain more information about the defective pixel, this can be done, for example, by searching for the capacitance measured in step 20 for its associated data line and comparing it with a threshold as described above. (Comparing its capacitance with a threshold is only effective if the substrate has a few defective switching elements. For example, the comparison with the threshold may have more than one permanently closed switching element, or It may not be efficient if it has at least one permanently closed switching element and at least one permanently open switching element, but the substrate has a large number of defective switching elements and is generally not cost-effective to repair the switching elements. In this case, the substrate can simply be discarded.)

In the method of FIG. 4, the capacitance of each data line measured in step 20 is used every time step 25 is performed in the testing procedure. Testing the actual active matrix substrate will typically take approximately 10 ms or so, and it is possible that the accuracy of the test process can be achieved, for example, by variations in temperature or supply voltages during the test process. . Therefore, Figure 5 of the present invention shows a second method of testing an active matrix substrate, and this disadvantage is overcome.

In FIG. 5, the counter is initialized to N = 1 in step 30. As will be described below, this counter indicates the index of the row scan line.

In step 31, the capacitance of each data line (source line) is measured inactive for every row scan line. The results are stored in the correction data file 33 in step 32. Steps 31 and 31 of FIG. 5 correspond to steps 20 and 21 of FIG. 4 and will not be described further.

In step 34, the Nth row scan becomes active. Since N is currently 1, step 34 applies gate driver 5 to apply its " enable " voltage to row scan line G ₁ while not applying its " enable " voltage to other row scan lines. And a timing and control circuit 2 for commanding.

In step 35 the capacitance of each column data line is measured again. In step 36, for each data line, the value of the capacitance measured in step 31 is retrieved and subtracted from the value obtained in step 35, and in step 37 the results are stored in the pixel state map file 38. Step 35, step 36, and step 37 of FIG. 5 correspond to step 24, step 25, and step 26 of FIG. 4 and will not be further described.

In step 39 it is determined whether the test process has been performed for all row scan lines. If no "no" decision is obtained, then the current active row scan line is inactive at step 40. In this example, step 40 will include timing and control circuitry to instruct gate drive 5 to stop the application of the " enable " voltage to row scan line G ₁ .

In step 41, the counter N is incremented by one. In this case, the new head of the counter will be N = 2.

Steps 31 to 37 are then repeated for row scan line G ₂ . Then incrementing the counter N and repeating steps 31 to 37 for each value of N are repeated until a "yes" decision is obtained in step 39.

In the embodiment of Figure 5, step 31 is repeated before each row scan line becomes active. Therefore, the "correction data" used in step 36 is data obtained just before step 35 was performed. This minimizes errors resulting from variations in quantities such as temperature or supply voltage.

The active matrix substrate of the present invention can be integrated into a liquid crystal device when it is determined that the number of defective switching elements is sufficiently small, or when the switching elements in which a defect is found are repaired or replaced. FIG. 3B is a schematic cross-sectional view through a liquid crystal display device incorporating the active matrix substrate 14 of FIG. 3A, and it will be shown that the structure of the liquid crystal display device is entirely separated from the use of the active matrix substrate of the present invention. The counter substrate 42 is disposed opposite the active matrix substrate 14. As is well known, one or more counter electrodes 13 are provided on the counter substrate (only one counter electrode 13 is shown in FIG. 3B). The liquid crystal layer 12 is disposed between the counter substrate and the active matrix substrate and sealed by sealing means 43. The counter substrate, sealing means and liquid crystal layer can be of any suitable type, such as standard or conventional type, and will not be described herein. The substrates are arranged such that the pixel electrodes 11 of the active matrix substrate and the counter electrode of the counter substrate are adjacent to the liquid crystal layer. (Actually, layers such as alignment layers for aligning the liquid crystal layer (not shown in FIG. 3B) will be provided through the pixel electrodes 11 of the active matrix substrate and the counter electrode of the counter substrate.)

The present invention has been described above with reference to an active matrix substrate comprising picture element electrodes disposed in a matrix of rows and columns. However, the present invention is not limited thereto.

According to the invention, since the test means are integrated on the substrate, expensive external testing equipment is not required. The correct operation of the switching elements can be confirmed at an early stage of the manufacture of the substrate, for example immediately after the switching elements are manufactured. It also provides a quick and simple way to verify that the switching elements of an active matrix substrate are operating correctly.

Claims (26)

In the substrate, Switching element-The switching element receives a first terminal for connection to a picture element electrode, a second terminal connected to a data line, and an enable signal for selectively enabling the switching element to receive the first terminal. A third terminal for connecting to said second terminal; And Test means for obtaining information on the operation of the switching device, And wherein said test means obtains information on the capacitance of said data line for two presumably different states of said switching element in use. The method of claim 1, And control means for controlling the test means to obtain information about the operation of the switching element. The method of claim 2, In a first period, the control means suppresses the application of the enable signal to the second terminal of the switching element, and the test means is adapted to the first value of the capacitance value of the data while the application of the enable signal is suppressed. Substrates for obtaining information. The method of claim 3, In a second period, the control means permits application of an enable signal to the second terminal of the switching element, and the test means is adapted to apply the data while the enable signal is applied to the second terminal of the switching element. And obtain second information about the capacitance value of the line. The method of claim 1, The test means is adjusted to determine a difference between the capacitance of the data line and the capacitance of a reference capacitor. The method of claim 1, Said test means comprising a sense amplifier. The method of claim 1, Said testing means comprising analyzing means for obtaining information on the operation of said switching element from the obtained information on the capacitance of said data line. The method of claim 3, In a second period, the control means permits application of the enable signal to the second terminal of the switching element, such that the test means is configured to perform the operation while the enable signal is applied to the second terminal of the switching element. Obtain second information about a capacitance value of a data line, wherein said testing means further comprises an analyzing means, said analyzing means for obtaining said first information about a capacitance value of said data line with respect to a capacitance value of said data line; A substrate adjusted to compare with the second information. The method of claim 3, The testing means includes analyzing means for obtaining information on the operation of the switching element from the obtained information on the capacitance of the data line, wherein the analyzing means is further configured to obtain the first information on the capacitance value of the data line. A substrate adjusted to compare with a predetermined threshold. The method of claim 4, wherein The testing means includes analyzing means for obtaining information on the operation of the switching element from the obtained information on the capacitance of the data line, wherein the analyzing means is further configured to obtain the second information on the capacitance value of the data line. A substrate adjusted to compare with a predetermined threshold. The method of claim 1, A plurality of display picture element electrodes arranged in rows and columns; A plurality of data lines, each data line associated with a respective column of picture element electrodes; And a plurality of switching elements, each switching element having a first terminal connected to a respective one of the picture element electrodes, a second terminal connected to the data line associated with each one of the picture electrodes And a third terminal for receiving an enable signal for selectively enabling the switching element and for connecting the first terminal to the second terminal, wherein the control means operates each of the switching elements in use. A substrate adapted to control the test means to obtain information about the substrate. As a combination, The substrate of Claim 1; And Analysis means for receiving an output from said test means and obtaining information for said or each switching element from an output from said test means. A display device comprising the substrate of claim 1. In a display device, A substrate according to claim 1; A counter substrate disposed opposite the substrate; And And a liquid crystal material disposed between the substrate and the counter substrate. In a method for testing a switching element of a substrate, The switching element receives a first terminal for connection to a picture element electrode, a second terminal connected to a data line, and an enable signal for selectively enabling the switching element to receive the first terminal at the second terminal. A third terminal for connecting the terminal; The method of testing the switching device comprises obtaining information about the capacitance of the data line for two presumably different states of the switching device. The method of claim 15, Obtaining first information about a capacitance value of the data line when no enable voltage is applied to the second terminal of the switching element. The method of claim 15, Acquiring second information about a capacitance value of the data line when an enable voltage is applied to the second terminal of the switching element. The method of claim 15, Acquiring first information about a capacitance value of the data line when no enable voltage is applied to the second terminal of the switching element; Obtaining second information on a capacitance value of the data line when an enable voltage is applied to the second terminal of the switching element; And comparing the first information about the value of the capacitance of the data line with the second information about the capacitance value of the data line. The method of claim 16, Comparing the first information about a capacitance value of the data line with a predetermined threshold. The method of claim 17, Further comparing the second information for a capacitance value of the data line with a predetermined threshold. 19. The method of claim 18, wherein if the first information for a capacitance value of the data line is substantially similar to the second information for a capacitance value of the data line, the first and second for the capacitance value of the data line. 2 further comprising comparing the information with a predetermined threshold. The method of claim 14, Determining information of a capacitance value of the data line, the difference between the capacitance of the data line and the capacitance of a reference capacitor. The method of claim 22, Generating a voltage having a magnitude proportional to the difference between the capacitance of the data line and the capacitance of the reference capacitor. In a method of testing an active matrix substrate, The active matrix substrate comprises: a plurality of display picture element electrodes arranged in rows and columns; A plurality of data lines, each data line associated with a respective column of picture element electrodes; And A plurality of switching elements, each switching element selectively enabling a first terminal connected to each of the picture element electrodes, a second terminal connected to the data line associated with each of the picture element electrodes, and the switching element And a third terminal for receiving an enable signal for connecting the first terminal to the second terminal, The method, Acquiring first information for each capacitance of each data line when no enable signal is applied to any of the switching elements; Applying an enable signal to each switching element in the selected first row while not applying the enable signal to the switching elements in the other rows; Acquiring second information for each capacitance of each data line when the enable signal is applied to the switching elements in the selected first row; And Obtaining information about the switching elements in the selected first row from the first and second information for the respective capacitance of each data line. The method of claim 24, Applying an enable signal to each switching element in the selected second row while not applying the enable signal to the switching elements in the other rows; Obtaining third information for the respective capacitance of each data line when the enable signal is applied to the switching elements in the selected second row; And obtaining information about the switching elements in the selected second row from the first and third information for the respective capacitance of each data line. The method of claim 24, Acquiring third information for the respective capacitance of each data line when no enable signal is applied to any of the switching elements; Applying an enable signal to each switching element in the selected second row while not applying the enable signal to the switching elements in the other rows; Acquiring fourth information about the respective capacitance of each data line when the enable signal is applied to the switching elements in the selected second row; And obtaining information about the switching elements in the selected second row from the third and fourth information for the respective capacitance of each data line.