Patent Publication Number: US-11043176-B2

Title: Redundant display systems and methods for use thereof in safety critical applications

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 62/812,873 filed Mar. 1, 2019 and U.S. Provisional Application No. 62/834,508 filed Apr. 16, 2019, the contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to display systems using row and column drivers to control an active matrix of transistors to display information, such as an Active Matrix Liquid Crystal Displays (AMLCDs) or simply, Liquid Crystal Displays (LCDs), or Organic Light Emitting Diode (LED) displays. More specifically, the present invention relates to display systems used in safety critical applications where redundancy is desired to maintain functionality under adverse environments. 
     BACKGROUND 
     AMLCDs (also referred to herein as LCDs) are commonly employed for presenting information to a user or users. Typically, an LCD consists of a single display element (i.e., a single large array of colored pixels) for generating static and moving images, for displaying text, for displaying symbols, etc., to a user. 
     For example, in the aerospace industry, an LCD display can replace multiple analog instrumentation displays by dividing the active viewing area into multiple “windows”, with each window displaying a separate piece of information. 
     LCDs are used under extreme environmental conditions, the LCD may suffer damage and become non-useable. Extreme environmental conditions may include intensely hot or cold conditions and/or conditions with extreme vibrations, mechanical shocks or electromagnetic interferences, such as conditions that may occur in a moving aircraft. 
     To mitigate the risk of losing critical data, such as flight critical data in an aircraft, the LCDs need to be designed in a manner that incorporates some internal redundancy. With redundancy, if the LCD is only partly damaged, a portion of the display will remain functional, and critical data can be moved to the remaining functional portion of the LCD. 
     Various techniques have been proposed to incorporate redundancy in LCDs. One well-known technique is to construct the LCD as essentially two side-by-side LCDs with fully independent operation on a single piece of glass. Thus, if the left half LCD is damaged, the right half LCD may still function, and vice-versa. Having completely independent side by side displays requires special considerations to harmonize the LCDs for color and brightness uniformity. If the voltages used to drive the internal transistors vary, then one side may appear brighter or dimmer than the other. 
     Another technique that has been proposed is to construct the LCDs as two independent LCDs front-to-back. Thus, if the front LCD fails, the rear LCD may still work, and vice-versa. 
     While these approaches are somewhat effective in providing redundancy, they require LCDs that can only be used separately. This results in a waste of resources, which is a critical concern particularly in a small area, such as an airplane cockpit. 
     There is thus a need for an LCD that allows for redundancy without requiring two distinct LCDs that can only be used separately. 
     SUMMARY 
     The present embodiments relate to system and method for redundant display using row and column drivers to control an active matrix of transistors to display information. A thin-film-transistor (TFT) layer is arranged in a pixel array and includes a plurality of rows of conductors and TFTs. Each row extends from left to right across the entire pixel array. First and second set of row drivers arranged on respective sides of the pixel array control the voltage across entire rows in tandem. The TFT layer also includes a plurality of columns of conductors and TFTs controlled by a set of column drivers, each column extending from top to bottom across the pixel array, and one or more columns of switching elements extending from the top to the bottom of the pixel array. The column of switching elements is disposed between the conductors and TFTs in a left portion of the pixel array and the conductors and TFTs in a right portion of the pixel array. During normal operation, the column of switching elements connects left row portions with right row portions, such that voltages are applied which cause an image to be displayed across the entire pixel array. Responsive to a malfunction of the first set or the second set of row drivers on one side of the pixel array, the column of switching elements isolates the left row portions from the right row portions, such that voltages from the remaining functional row drivers on the other side of the pixel array are applied to the liquid crystal material on that side of the column of switching elements which cause the image to be displayed only across a left portion or a right portion of the pixel array. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       In order that the manner in which the above-recited and other features and advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawing(s). Understanding that these drawing(s) depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawing(s) in which: 
         FIG. 1A  illustrates a conventional non-redundant AMLCD system including one set of row drivers. 
         FIG. 1B  illustrates a conventional non-redundant AMLCD system including two sets of row drivers. 
         FIG. 1C  illustrates a conventional dual redundant AMLCD system including two independent AMLCDs. 
         FIG. 1D  illustrates a redundant AMLCD system according to an illustrative embodiment. 
         FIG. 2A  illustrates conventional TFT arrays included in a conventional dual redundant AMLCD system. 
         FIG. 2B  illustrates a TFT array including a column of transistors according to an illustrative embodiment. 
         FIG. 3  illustrates a TFT array including a column of fuses according to an illustrative embodiment. 
         FIG. 4  illustrates a TFT array including a column of resistors according to an illustrative embodiment. 
         FIG. 5A  illustrates a redundant AMLCD system according to another illustrative embodiment. 
         FIG. 5B  illustrates a redundant AMLCD system according to another illustrative embodiment. 
         FIG. 6A  illustrates a method for operating a redundant display according to one illustrative embodiment. 
         FIG. 6B  illustrates a method for operating a redundant display according to another illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     According to illustrative embodiments, an AMLCD system includes a single LCD panel that provides redundancy by having two sets of row drivers and two sets of backlights. This is different from a conventional AMLCD system that includes one set of row drivers and one back light. 
     Many details of an LCD that would be understood by those skilled in the art are not repeated here. For purposes of this application, a short description of a conventional AMLCD system is provided below with reference to  FIG. 1A , followed by relevant details of the illustrative embodiments. 
     Referring to  FIG. 1A , a conventional non-redundant AMLCD system  100 A is shown from a top view. As those skilled in the art will appreciate, an LCD contains several layers which work in combination to create a viewable image. Although not shown for simplicity of illustration, the LCD includes a liquid crystal material. The liquid crystal material is located between front and rear transparent plates. The front plate is generally referred to as the “color filter” (CF) layer, and the rear plate is generally referred to as the “thin film transistor” (TFT) layer. In  FIG. 1A , only the TFT layer  110 A is shown for simplicity of illustration. 
     The liquid crystal material may be actively configured to pass or block a certain amount of light which is originating from a backlight  140  in response to an applied voltage/charge from conductors in the TFT layer. The conductors in the TFT layer  110 A can apply specific voltages to the liquid crystal material, causing localized alignment of the liquid crystal material. This alignment affects the transmissibility of light rays of light from the backlight  140  through the LCD, Selective alignment and non-alignment of the liquid crystal material caused by the voltages applied to the conductors in the TFT layer  110 A cause an image to be displayed which is visible through an external face of the LCD. 
     As depicted in  FIG. 1A , a traditional TFT array  110 A includes a plurality of rows of conductors extending from left to right and a plurality of columns of conductors extending from top to bottom (shown as a grid in  FIG. 1A ). The rows and columns of conductors are arranged in an array of regions referred to as pixels. As those skilled in the art will appreciate, a transistor is preferably placed within each pixel. 
     Row drivers  120  and column drivers  130  are in electrical communication with a timing controller  150 . Although not shown, a video source including two driver cards supplies the video data to be displayed, which may be communicated via the timing controller  150 . The driver cards provide drive signals to the row drivers  120  and the column drivers  130 . 
     The timing controller  150  provides the proper timing for displaying the video data, and the row drivers  120  and the column drivers  130  generate the proper charge/voltage to cause the image to be displayed. In particular, the row drivers  120  are used to apply voltages to the rows of conductors from a top row to a bottom row, and the column drivers  130  are used to apply voltages to the columns of conductors, from a left-most column to a right-most column. 
     A power supply  160  may provide power through the timing controller  150  to the row drivers  120  and the column drivers  130 . Each pixel in the assembly can be controlled when a respective row driver activates the row of conductors in which include the pixel, while the respective column driver activates the corresponding column of conductors which include the pixel. 
     The TFT array  110 A requires the operation of the row drivers  120 , the column drivers  130 , the timing controller  150 , the power supply  160 , and the backlight  140  to create an image. If any of these devices were to fail, then the entire LCD would fail to create an image. This is sometimes referred to as a ‘single point failure.’ As discussed above, the failure of the entire LCD is undesirable but has traditionally been a significant risk for LCD displays. 
     On large displays where the length of the rows is long, capacitive loading can lead to propagation delay and voltage differences between the pixels at the start of the row and the end of the row. To alleviate this issue, the rows can be driven with row drivers  120 A and  120 B on the left and right sides, respectively, of a TFT array  110 B in tandem, as in the AMLCD system  100 B shown in  FIG. 1B . 
     An LCD will not function satisfactorily without an appropriate and properly-functioning set of row and column drivers. If, for example, the row drivers fail, the entire LCD may fail to create an image. In configurations with a second row driver, such as that shown in  FIG. 1B , a failure in one row driver may still cause the LCD to fail to function correctly, depending on the nature of the failure. If the failing row driver upsets the voltage on the row, either by creating a short circuit to ground or another voltage source, the improper voltage will propagate across the entire length of one or more rows of pixels causing the entire line to fail. 
     In a dual-redundant AMLCD  100 C with two independent AMLCDs having two TFT arrays  110 A and  110 B on a single master piece of glass as shown in  FIG. 1C , the failure of a row driver  120 A or  120 B results in the loss of that row of information within  110 A or  110 B. This may be further understood with reference to  FIG. 2A  which illustrates a conventional dual AMLCD including two TFT arrays  200 A and  200 B. 
     According to illustrative embodiments, an AMLCD system is provided that provides for continuous display of an image across an entire pixel array during normal operation. Each row is driven from both sides of the pixel array, e.g., the left side and the right side. In normal operation, an intermediate switching element is closed, allowing current to flow through from the left to right side. In the event of a failure of a row driver on one side, when the switching element is open, it may possible to continue to display the image across the entire row of the display if the row driver on the opposite side is capable of maintaining the proper voltage. That is, if the switching element is, for example, a transistor, the row information may be carried across the transistor, as illustrated in  FIG. 2B  described in detail below. 
     This may be understood with reference to  FIG. 1D  which illustrates a redundant AMLCD system  100 D according to an illustrative embodiment. The AMLCD system  100 D includes some components similar to those of a conventional AMLCD system, such as the timing controller  150  and the power supply  160 . Also, although not shown, a video source may supply video data. 
     Instead of the TFT array  110 A, the AMLCD system  100 D includes a TFT array  110 D shown from a top view in  FIG. 1D . Similar to the TFT array  110 A, the TFT array  110 D includes a plurality of rows of conductors and a plurality of columns of conductors arranged in an array of pixels. Also, each pixel includes a TFT (shown in more detail in  FIGS. 2B-4 ). 
     In the AMLCD system  100 D shown in  FIG. 1D , instead of having one set of row drivers, two sets of row drivers  125 A and  125 B are included on respective sides of the TFT array  110 D. Both sets of row drivers  125 A and  125 B are in electrical communication with the timing controller  150 . Both the “left” set of row drivers  125 A and the “right” set of row drivers  125 B apply voltages to each of the entire rows of conductors in tandem. Although shown on the left and right sides of the TFT array  110 D, it should be appreciated that the sets of row drivers  125 A and  125 B may be positioned in other areas relative to the TFT array  110 D. 
     As can be seen from  FIG. 1D , column drivers  130  are also in electrical communication with the timing controller  150  and are used to apply voltages to the columns of conductors across the width of the pixel array. Although column drivers  130  are depicted as controlling the columns of conductors of the TFT array  110 D from the top, it should be appreciated that the column drivers  130  may, instead, control the columns of conductors of the TFT array  110 D from the bottom. 
     The power supply  160  may provide power through the timing controller  150  to the row drivers  125 A,  125 B and the column drivers  130 . 
     During normal operation, the entire LCD is operated in a continuous left-right dual mode. Every column in the pixel array is individually addressed from a top or bottom edge as in a “normal”’ LCD, but each row is addressed from both the left and right sides simultaneously by both sets of row drivers  125 A and  125 B. The dual sets of row drivers cut the propagation delay of the row (scan) line signal by half during normal operation. The display may have no gap or a small gap between the left and right sides and would look and function like one single display until a malfunction occurs. 
     According to illustrative embodiments, the TFT array  110 D includes a “middle” column of switching elements  105  disposed between a left portion of the pixel array and a right portion of the pixel array. It should be appreciated that although the column of switching elements  105  is shown as being in the middle of the pixel array, the column of switching elements may be included anywhere in the pixel array, e.g., to the left of the middle of the pixel array or to the right of the middle of the pixel array. 
     When any portion of the driving system on one side fails, such as if one set of row drivers fails, the column of switching elements  105  is opened, isolating the side of the pixel array driven by the non-failing portion of the drive system from the side of the pixel array driven by the non-failing portion of the drive system, hence maintaining the operation of the non-failing row portion of the drive system. For example, responsive to a malfunction of a set or row drivers on one side of the TFT array  110 D, the column of switching elements  105  isolates the left row portions from the right row portions, such that voltages from the remaining functional row drivers on the other side of the TFT array  110 D are applied to the liquid crystal material on that side of the column of switching elements  105 , which causes the image to be displayed only across a left portion or a right portion of the pixel array. 
     Thus, the LCD may be effectively be operated as a single large display (during normal operation) or as two independent side-by-side displays (during malfunctioning of any portion of the drive system for one side, such as a set or row drivers). The column of switching elements  105  may be implemented with transistors, fuses, or resistors according to various embodiments described below. 
     In addition, while the set of column drivers  130  controls conductors in columns across the entire width of the pixel array during normal operation, the set of column drivers  130  may be configured such that during abnormal operation (e.g., failure of either of the set of row drivers  125 A or  125 B) or responsive to a user command, a portion of the column drivers may output voltages that cause a black screen image to be displayed. For example, if the row drivers  125 A fail, column drivers on the left side of the pixel array may output voltages that cause a black screen image to be displayed. 
     The AMLCD system  100 D also includes a backlight which can operate as a single backlight  140  or as two backlights  145 A and  145 B. Each backlight may contain independent light source such as light emitting diode (LED) strings and LED drivers that have separate control inputs. During normal operation of the AMLCD system  100 C, both backlights  145 A and  145 B are in operation. However, when, for example, row drivers on one side of the pixel array fail, the backlight on that side may be turned off to conserve energy and prevent the display of erroneous information. For example, if the row drivers  125 B driving the rows of conductors from the right side of the TFT array  110 B fail, then the portion of the backlight illustrated as  145 B may be turned off. 
     Referring now to the detailed embodiments, according to a first embodiment, as shown in  FIG. 2B , a TFT array  210  includes a middle column of transistors  205  disposed vertically down the middle of the pixel array, splitting each row of conductors into right and left portions. All the gates of the transistors in the column  205  may be driven together by a common user control signal. This column of transistors  205  may be then operated as a switch to isolate the left or the right side of the pixel array from the side driven by malfunctioning row drivers. During normal operation of the AMLCD system, the transistors are turned on to connect the portions of rows of conductors on the left side of the pixel array with the portions of rows of conductors on the right side of the pixel array. When the transistors are on, they serve to keep the row voltage between the two sides of the pixel array the same, allowing for uniform brightness, thus harmonizing the brightness and contrast of the two sides. If a row driver on one side fails in a state which would allow the opposite side to continue to drive the required voltage levels on the entire line, then the opposite end of the drive lines can continue to supply the voltages to maintain the line&#39;s full or slightly diminished functionality. However, when a row driver fails such that the voltage levels of the entire row would be affected, or other drive system failure occurs, the transistors turn off to isolate the portions of the rows on the left side from the portions of the rows on the right side. 
     According to a second embodiment, as shown in  FIG. 3 , a TFT array  300  includes a column of fuses  305  instead of a column of transistors. During normal operation of the AMLCD system, the fuses are intact or closed, such that the portions of rows of conductors on the left side of the pixel array are connected to the portions of rows of conductors on the right side of the pixel array. When the fuses are active (closed), they serve to keep the voltage between the two sides the same, allowing for uniform brightness. In the event that a set of row drivers develops short-circuits at its outputs, an over-current is created that causes the fuses to open up one by one during a vertical scan to disconnect the left portion of rows from the right portion of rows. 
     According to a third embodiment, as shown in  FIG. 4 , a TFT array  400  includes a column of high impedance resistors  405  instead of fuses or transistors. During normal operation of the AMLCD system, the high impedance resistors operate to connect the left portion of rows of the pixel array to the right portion of rows. Also, during normal operation, the high impedance resistors serve to keep the voltage between the two portions of the pixel array closer, allowing for a more uniform brightness. In the event of a malfunction of a set of row drivers, the high impedance resistors can minimize the current flow between the left portion of rows from the right portion of rows. This approach may be considered a “light” separation of the left portion from the right portion that works well just enough to allow a viewer to extract useful information from one side of the display. During normal operation, the resistors allow some current to pass which improves the harmonization of the right and left halves of the display. The impedance of the resistors must be large enough that the current flow from side to side is small enough such that during a failure, the failure on one side does not change the voltage so much that the other side cannot be driven by its, still functional, driver. 
       FIG. 5A  illustrates a redundant AMLCD system according to another illustrative embodiment. The AMLCD system  500 A shown in  FIG. 5A  includes a thin film transistor (TFT) array  510 A arranged in a pixel array and includes a plurality of rows and columns of conductors and TFTs. 
     The AMLCD system  500 A shown in  FIG. 5A  includes first and second driver cards  530 A and  540 A that receive video signals from a video source (not shown) and provide drive signals to row and column drivers. In addition, although not shown, the AMLCD system  500 A may also include backlights like the backlights  140 ,  145 A and  145 B shown in  FIG. 1D . The backlight may function as a single unit supplying light to the entire pixel array or as a first backlight supplying light to a left portion  513 A of the pixel array, a second backlight supplying light to a middle portion  514 A of the pixel array, and a third backlight supplying light to a right portion  515 A of the pixel array. 
     The AMLCD display system  500 A includes first and second sets of row drivers  550 A and  560 A, respectively. The AMLCD display system  500 A also includes first, second and third set of column drivers  570 A,  580 A, and  590 A, respectively. The first driver card  530 A is connected to the first and second sets row drivers  550 A and  560 A and to the first, second and third sets of column drivers  570 A,  580 A, and  590 A. Similarly, the second driver card  540 A is connected to the first and second sets row drivers  550 A and  560 A and to the first, second and third sets of column drivers  570 A,  580 A, and  590 A. 
     The TFT array  510 A also includes first and second columns of switching elements  511 A and  511 B, respectively, extending from the top to the bottom of the pixel array. The first column of switching elements  511 A is disposed between a left portion  513 A of the pixel array and a middle portion  514 A of the pixel array. The second column of switching elements  512 A is disposed between a right portion  515 A of the pixel array and the middle portion  514 A of the pixel array. 
     During normal operation, the left, middle and right portions  513 A,  514 A and  515 A of the pixel array are interconnected by the first and second columns of switching elements  511 A and  512 A, respectively, such that the same voltages are applied to all of the pixels of the array. A single gamma curve is used to adjust all of the voltages so that there is uniform luminance or intensity across the entire pixel array. 
     During normal operation, the first driver card  530 A delivers drive signals to both sets of row drivers  550 A and  560 A and to all of the column drivers  570 A,  580 A and  590 A such that the entire pixel array, including the left portion  513 A, the middle portion  514 A and the right portion  515 A, is driven by the both sets of row drivers  550 A and  560 A and by their respective column drivers  570 A,  580 A and  590 A. Alternatively, during normal operation, the entire pixel array may be driven by the second driver card  540 A delivering drive signals to all of the row and column drivers. 
     Either the first driver card  530 A or the second driver card  540 A can independently drive the display. Thus, if a failure occurs in the first driver card  530 A or the second driver card  540 A, the failing driver card can be disabled, and the other driver card can drive both sets of row drivers  550 A and  560 A and all the column drivers  570 A,  580 A and  590 A, thereby driving the entire pixel array with no loss of functionality. 
     If a failure occurs in the first set of row drivers  550 A, causing one or more rows of pixels to fail across the entire pixel array, the first set of row drivers  550 A can be disabled, and the left column of switching elements  511 A can be opened to isolate the middle and right portions  514 A and  515 A of the pixel array from the failed row driver  550 A and the left portion  513 A. In this case, the second set of row drivers  560 A continues to drive the rows for the middle and right portions  514 A and  515 A of the pixel array. 
     Likewise, if a failure occurs in the second set of row drivers  560 A, causing one or more rows to fail across the entire display, the second set of row drivers  560 A can be disabled, and the right column of switching elements  511 B can be opened to isolate the middle and left portions  513 A and  514 A of the pixel array from the failed row driver  560 A and the right portion  515 A. In this case, the first set of row drivers  550 A continues to drive the rows for the middle and left portions  513 A and  514 A of the pixel array. 
     A similar type of redundancy may be used for the first, second, and third sets of column drivers  570 A,  580 A, and  590 A. That is, if a failure occurs in one or more of the first, second or third sets of column drivers  570 A,  580 A and  590 A, the failing column drivers can be disabled, and the non-failing column drivers can continue to drive the array of pixels. 
     Although three portions  513 A,  514 A, and  515 A of the pixel array and two columns of switching elements  511 A and  511 B are shown, it should be appreciated that there may be any number of portions of the pixel array with a corresponding number of switching elements. 
       FIG. 5B  illustrates a different embodiment with a similar partitioning of row drivers and pixel array elements but with different driver cards controlling the right row and column drivers. The AMLCD system  500 B shown in  FIG. 5B  includes a thin film transistor (TFT) array  510 B arranged in a pixel array and includes a plurality of rows and columns of conductors and TFTs. 
     The AMLCD system  500 B shown in  FIG. 5B  includes first and second driver cards  530 B and  540 B that receive video signals from a video source (not shown) and provide drive signals to row and column drivers. In addition, although not shown, the AMLCD system  500 B may also include backlights like the backlights  140 ,  145 A and  145 B shown in  FIG. 1D . The backlight may function as a single unit supplying light to the entire pixel array or as a first backlight and a second backlight supplying light to a left portion  513 B of the pixel array and a right portion  514 B of the pixel array, respectively 
     The AMLCD display system  500 B includes first and second sets of row drivers  550 B and  560 B, respectively. The AMLCD display system  500 B also includes first and second sets of column drivers  570 B and  580 B, respectively. The first driver card  530 B is connected to the first set of row drivers  550 B and the first set of column drivers  570 B. The second driver card  540 B is connected to the second set of row drivers  560 B and to second set of column drivers  580 B. 
     The TFT array  510 B also includes a column of switching elements  511 C extending from the top to the bottom of the pixel array. The column of switching elements  511 C is disposed between a left portion  513 B of the pixel array and a right portion  514 B of the pixel array. It should be appreciated that although the column of switching elements  511 C is shown as being in the middle of the pixel array, the column of switching elements may be included anywhere in the pixel array, e.g., to the left of the middle of the pixel array or to the right of the middle of the pixel array. 
     During normal operation, the first driver card  530 B controls the set of column drivers  570 B on the left portion  513 B of the pixel array, and the right driver card  540 B controls the set of column drivers on the  580 B on the right portion  514 B of the pixel array. The sets of row drivers  530 B and  540 B are driven from a common clock to ensure that each row is driven simultaneously from both the left side and the right side of the display. 
     In the event of a failure on the first driver card  530 B or a row driver in the set of row drivers  550 B, the first driver card  530 B can be disabled, and the column of switching elements  511 C can be opened to isolate the right portion  514 B of the pixel array from the left portion  513 B. The right portion  514 B of the pixel array may continue to be driven using the second driver card  540 B, the set of row drivers  560 B, and the set of column drivers  580 B. 
     Similarly, in the event of a failure on the second driver card  540 B or a row driver in the set of row drivers  560 B, the second driver card  540 B can be disabled, and the column of switching elements  511 C can be opened to isolate the left portion  513 B of the pixel array from the right portion  514 B. The left portion  513 B of the pixel array may continue to be driven using the first driver card  530 B, the set of row drivers  550 B, and the set of column drivers  570 B. 
     A similar type of redundancy may be used for the first and second sets of column drivers  570 B and  580 B. That is, if a failure occurs in the first or second sets of column drivers  570 B and  580 B, the column of switching elements  511 C can be opened to isolate the left portion  513 B of the pixel array from the right portion  514 B, and the failed side of the display can be turned off while leaving the other side functional. 
     While the various embodiments have been shown and described in example forms of a redundant AMLCD system, it will be apparent to those skilled in the art that a method for providing redundancy in the event of a failure of row drivers may be performed using various components of the system as described above. Further, while the example describes an AMLCD system, the concepts described herein are also applicable to other display systems which use an active matrix of transistors to display information, such as an organic LED (OLED) array. 
       FIG. 6A  illustrates a method  600 A for operating a redundant display according to an illustrative embodiment. At step  610 , a column of switching elements connects left row portions extending across a left portion of a pixel array to right row portions extending across a right portion of a pixel array to cause an image to be displayed across the entire pixel array. At step  620 , if a failure in a driver card occurs, the failed driver card is disabled, and the other driver card is used to drive the row drivers and column drivers at step  630 . 
     At step  640 , if a row driver failure occurs, the column of switching elements isolates the left row portions from the right row portions at step  650 , such that the image is displayed only across a left portion or a right portion of the pixel array. This isolation in response to a failure may be performed in the manner described above with reference to  FIGS. 2, 3, and 4 . 
     At step  660 , if a column driver failure occurs, the failed column driver is disabled, and the non-failing column drivers continue to drive the pixel array at step  670 . 
     If no failure occurs, the method returns to step  610 , and the column of switching elements continues to connect the left row portions to the right row portions. 
       FIG. 6B  illustrates a method  600 B for operating a redundant display according to another illustrative embodiment. At step  610 , a column of switching elements connects left row portions extending across a left portion of a pixel array to right row portions extending across a right portion of a pixel array to cause an image to be displayed across the entire pixel array. At step  625 , if a failure in a driver card or a failure in a row driver occurs, the column of switching elements isolates the left row portions from the right row portions at step  650 , such that the image is displayed only across a left portion or a right portion of the pixel array. This isolation in response to a failure may be performed in the manner described above with reference to  FIGS. 2, 3 , and  4 . 
     At step  660 , if a column driver failure occurs, the failed column driver is disabled, and the non-failing column drivers continue to drive the pixel array at step  670 . 
     If no failure occurs, the method returns to step  610 , and column of switching elements continues to connect the left row portions to the right row portions 
     It should be appreciated that the methods  600 A and  600 B may include additional or alternative steps, e.g., a step for isolating left, middle and right row portions. Further, it should be appreciated that the steps for detecting failures may occur in any order. 
     While the various embodiments have been shown and described in example forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention as defined by the following claims.