Abstract:
A liquid crystal display (LCD) device includes means for selectively connecting at least two data lines together to provide image data to pixels of a defective column due to either a defective column line (e.g., a line break) or a defective column driver. The means preferably includes a plurality of switches for connecting the two data lines together. The switches may either be cross-column switches extending between the two data lines, or may be column test switches used in a column calibration procedure and connecting the two columns each to a common column test line. Registers are preferably also provided for each switch to store therein a data value indicating whether the switch should be opened or closed. The registers may comprise a shift register.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention pertains to the field of image display devices, and more particularly to liquid crystal display devices, and to drive circuitry for such devices.  
           [0003]    2. Description of the Related Art  
           [0004]    Image display devices such as liquid crystal display (LCD) devices are widely unknown. With reference to the following description, familiarity with conventional features of such devices will be assumed, so that only features bearing on the present invention will be described.  
           [0005]    [0005]FIG. 1 shows relevant portions of an exemplary liquid crystal display (LCD) device  100 .  
           [0006]    The LCD device  100  comprises in relevant part: a plurality of pixels  110 ; a plurality of column (data) lines  120  connected to the plurality of pixels  110 ; a plurality of column (data) drivers  130  for supplying data to pixels  110  via the column lines  120 ; a plurality of column driver switches  140 ; a plurality of row (scanning) lines  150  connected to rows of pixels  110 ; and a plurality of row drivers  160  connected to the row lines  120  for selecting a row of pixels  110  to which data from the column drivers  130  is to be applied.  
           [0007]    Typically, each pixel  110  includes a pixel switching device  112  and a storage (pixel capacitor)  114 . The pixel switching device  112 , which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line  150  to switch a data signal applied via the connected column line  120  into the storage device  114 .  
           [0008]    The LCD device  100  may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers  130 , column driver switches  140 , and/or row (scanning) drivers  160  may be integrated onto a same silicon substrate as the liquid crystal pixels  110 .  
           [0009]    Some problems with the prior art LCD device  100  will now be explained.  
           [0010]    Occasionally, a break may occur in the fabrication of one or more column lines  120 . For example, in FIG. 1 a break or line defect  170  is indicated between the points A and A′ in the column line  120  of column  2 . Because of the line defect  170 , it is not possible to provide a data signal to any of the pixels  110  of column  2  from row numbers 3 to N. Accordingly, all pixels  110  of column  2  from row number 3 to row number N fail, and those pixels  110  of the display  100  will be permanently white or black, depending upon whether the device operates in a normally white or normally black mode.  
           [0011]    Also, a column driver  130  for a particular column may be defective and fail to provide a data signal to the column line  120 . For example, in FIG. 1 a failed column driver  130  is indicated for column  4 . In that case, it is not possible to provide a data signal to any of the pixels  110  of column  4 . Accordingly, all pixels  110  of column  4  fail, and the entire column  4  of the display  100  will be permanently white or black, depending upon whether the device operates in a normally white or normally black mode.  
           [0012]    Accordingly, it would be desirable to provide an image display system that can operate despite one or more column line defects, or breaks, and/or failed column drivers. Other and further objects and advantages will appear hereinafter.  
         SUMMARY OF THE INVENTION  
         [0013]    Accordingly, in one aspect, an image display device includes means for selectively connecting at least two data lines together to provide image data to pixels of a defective column due to either a defective column line (e.g., a line break) or a defective column driver. The means preferably includes a plurality of switches for connecting the two data lines together.  
           [0014]    In another aspect, registers are preferably also provided for storing therein a data value indicating whether a switch should be opened or closed to connect two or more column lines together. The registers may comprise a shift register.  
           [0015]    In yet another aspect, defective columns may be repaired by selectively closing column test switches used in a display calibration procedure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 shows a prior art liquid crystal display (LCD) device;  
         [0017]    [0017]FIG. 2 shows a first embodiment of an image display device capable of operating with a column line or column driver defect;  
         [0018]    [0018]FIG. 3 shows a second embodiment of an image display device capable of operating with a column line or column driver defect;  
         [0019]    [0019]FIG. 4 shows a third embodiment of an image display device capable of operating with a column line or column driver defect; and  
         [0020]    [0020]FIG. 5 shows a fourth embodiment of an image display device capable of operating with a column line or column driver defect. 
     
    
     DETAILED DESCRIPTION  
       [0021]    [0021]FIG. 2 shows a first embodiment of an image display device in accordance with one or more aspects of the invention. The first embodiment is described with respect to a liquid crystal display (LCD) device  200 . For clarity and simplicity, those portions of the LCD device  200  relating to the present invention are illustrated.  
         [0022]    The LCD device  200  comprises in relevant part: a plurality of pixels  210 ; a plurality (M) of column (data) lines  220  connected to the plurality of pixels  210 ; a plurality of column (data) drivers  230  for supplying data to the pixels  210  via the column lines  220 ; a plurality of column driver switches  240 ; a plurality (M) of column driver switch registers  245 ; a plurality (N) of row (scanning) lines  250  connected to N rows of pixels  210 ; a plurality of row drivers  260  connected to the row lines  250  for selecting a row of pixels  210  to which data from the column drivers  230  is to be applied; a plurality (M−1) of cross-column switches  280  each extending between two adjacent column lines  220 ; and a plurality (M−1) of cross-column switch registers  290  each having an output connected to a control terminal of a corresponding one of the cross-column switches  280 . Beneficially, the column driver switch registers  245  and/or the cross-column switch registers  290  may be configured as shift registers.  
         [0023]    Typically, each pixel  210  includes a pixel switching device  212 , having first and second terminals and a control terminal, and a storage device (pixel capacitor)  214  connected to the first terminal of the pixel switching device  212 . However, a two terminal switch such as a diode may be used. The second terminal of the pixel switching device  212  is connected to one of the column lines  220 . The pixel switching device  212 , which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line  250  to selectively connect the column line  220  to the storage device  214  and thereby to store a data signal applied via the column line  220  into the storage device  214 .  
         [0024]    The LCD device  200  may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers  230  and/or row (scanning) drivers  260  may be integrated onto a same silicon substrate as the liquid crystal pixels  210 . Also, the column driver switches  240 , the column driver switch registers  245 , the cross-column switches  280  and/or the cross-column switch registers  290  may be integrated onto the same substrate.  
         [0025]    The operation of various pertinent elements of the first preferred embodiment LCD device  200  in the case of a defective column will now be explained.  
         [0026]    In FIG. 2, a break or line defect  270  is indicated between the points A and A′ in the column line  220  of column  2 . Because of the line defect  270 , it is not possible to provide a data signal from the column driver  230  for column  2  to any of the pixels  210  for row numbers  3  to N. Accordingly, during a test of the LCD device  200 , it will be determined that those pixels  210  of the LCD device  200  are permanently white or black, depending upon whether the device operates in a normally white or normally black mode.  
         [0027]    In that case, a data value (e.g., “1” or “0”) is stored into a cross-column switch register  290  connected to the control terminal of the cross-column switch  280  between columns  2  and  3 , such that a control signal output by the cross-column switch register  290  causes the cross-column switch  280  between columns  2  and  3  to close. In other words, the data value stored in each cross-column switch register  290  indicates whether the corresponding cross-column switch  280  should be opened or closed. With the cross-column switch  280  between columns  2  and  3  closed, the pixels  210  for rows  3  to N of column  2  are connected to the column line  220  for column  3 . Accordingly, in response to a scanning (gate) signal of the corresponding row (scanning) line  250 , the pixels  210  for rows  3  to N of column  2  are driven by the data signal of column  3  to store and display image data.  
         [0028]    Also, a column driver  230  for a particular column may be defective and fail to provide a data signal to a column line  220 . For example, in FIG. 2 a failed column driver  230  is indicated for column  4 . Because of the defective column driver  230 , it is not possible to provide a desired data signal from the column driver  230  for column  4  to any of the pixels  210  of column  4 . Accordingly, during a test of the LCD device  200 , it will be determined that the pixels  210  of column  4  of the LCD device  200  are permanently white or black, depending upon whether the device operates in a normally white or normally black mode.  
         [0029]    In that case, a data value (e.g., “1” or “0”) is stored into a cross-column switch register  290  connected to the control terminal of the cross-column switch  280  between columns  3  and  4  such that a control signal output by the cross-column switch register  290  causes the cross-column switch  280  between columns  3  and  4  to close. Also, a data value is stored into a column driver switch register  245  for column  4  such that a control signal output by the column driver switch register  245  for column  4  connected to the control terminal of column driver switch  240  for column  4  causes the column driver switch  240  for column  4  to open. In other words, the data value stored in each column driver switch register  245  indicates whether the corresponding column driver switch  240  should be opened or closed. With the cross-column switch  280  between columns  3  and  4  closed, and the column driver switch  240  for column  4  opened, the pixels  210  of column  4  are connected to the column line  220  for column  3 . Accordingly, in response to a scanning (gate) signal of the corresponding row (scanning) line  250 , the pixels  210  for column  4  are driven by the data signal of column  3  to store and display image data.  
         [0030]    It should be understood that, although in the above example with the line defect  270  the pixels  210  for rows  3  to N of column  2  were connected to column  3 , it is possible instead to connect the pixels  210  for rows  3  to N of column  2  to column  1 . Similarly, in the above example where the column driver for column  4  is defective, the pixels  210  of column  4  may be connected to column  5  instead of to column  3 . Indeed, multiple columns may be connected in a variety of configurations to account for multiple defective column lines  220  and/or column drivers  230 .  
         [0031]    Beneficially, when the column driver switch registers  245  and/or the cross-column switch registers  290  are configured as shift registers, data values may be supplied for the column driver switch registers  245  and cross-column switch registers  290  of the LCD device  200  by shifting them into place using a shift enable or clock signal. Also, it is possible to either store the data permanently in the registers  245  and  290  after performing a test of the LCD device  200 , or the data may be reloaded into the registers periodically, such as upon powering up the LCD device  200 .  
         [0032]    It is also possible to dynamically change the contents of the registers  290 . In that case, for example, with the line defect  270 , the pixels  210  for rows  3  to N of column  2  may be alternately connected to column  3  and to column  1 , say, in alternating frames. This may allow for an improved display, as the human eye will tend to average the video data displayed by the pixels  210  for rows  3  to N of column  2 . Similarly, in the case where the column driver for column  4  is defective, the pixels  210  of column  4  may be alternately connected to column  3  and to column  5 , say, in alternating frames.  
         [0033]    Many LCD devices employ a column (data) driver layout wherein the column (data) drivers are disposed on two sides (e.g., top and bottom) of the pixel area. Typically, in such a layout column lines are alternatingly connected to column drivers on opposite sides of the pixel area. That is, odd-numbered column lines are all connected to column drivers on one side (e.g., the top) of the pixel area, and even-numbered column lines are all connected to column drivers on the opposite side (e.g., the bottom) of the pixel area. By employing such an interleaved column driver layout, the frequency of the data signal that must be communicated to and processed by each column (data) driver can be reduced by ½.  
         [0034]    [0034]FIG. 3 shows a second preferred embodiment of an image display device in accordance with one or more aspects of the invention. The second embodiment is described with respect to a liquid crystal display (LCD) device  300  having column (data) drivers disposed on two sides (top and bottom) of the pixel area, i.e., the so-called interleaved column (data) driver layout. For clarity and simplicity, those portions of the LCD device  300  relating to the present invention are illustrated.  
         [0035]    The LCD device  300  comprises in relevant part: a plurality of pixels  310 ; a plurality (M) of column (data) lines  320  connected to the plurality of pixels  310 ; a plurality of column (data) drivers  330  disposed on opposite sides of the pixels  310  for supplying data to the pixels  310  via the column lines  320 ; a plurality of column driver switches  340 ; a plurality (M) of column driver switch registers (not shown); a plurality (N) of row (scanning) lines  350  connected to N rows of pixels  310 ; a plurality of row drivers  360  connected to the row lines  350  for selecting a row of pixels  310  to which data from the column drivers  330  is to be applied; a plurality of cross-column switches  380  each extending between two column lines  320 ; and a plurality of cross-column switch registers  390  each having an output connected to a control terminal of a corresponding one of the cross-column switches  380 . Beneficially, the column driver switch registers and/or the cross-column switch registers  390  may be configured as shift registers.  
         [0036]    Typically, each pixel  310  includes a pixel switching device  312 , having first and second terminals and a control terminal, and a storage device (pixel capacitor)  314  connected to the first terminal of the pixel switching device  312 . The second terminal of the pixel switching device  312  is connected to one of the column lines  320 . The pixel switching device  312 , which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line  350  to selectively connect the column line  320  to the storage device  314  and thereby to store a data signal applied via the column line  320  into the storage device  314 .  
         [0037]    The LCD device  300  may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers  330  and/or row (scanning) drivers  360  may be integrated onto a same silicon substrate as the liquid crystal pixels  310 . Also, the column driver switches  340 , the column driver switch registers, the cross-column switches  380  and/or the cross-column switch registers  390  may be integrated onto the same substrate.  
         [0038]    The operation of various pertinent elements of the second preferred embodiment LCD device  300  in the case of a defective column will now be explained.  
         [0039]    The second embodiment of the LCD device  300  operates similarly to the first embodiment of the LCD device  200 , except that the second embodiment of the LCD device  300  has column drivers  330 , cross-column switches  380 , and cross-column switch registers  390  located on two opposite sides of the pixel area.  
         [0040]    Accordingly, for example, when a line defect  370  indicated between the points A and A′ in the column line  320  of column  2  occurs, the pixels for rows  3  to N of column  2  are still connected to the column driver  330  for column  3 , located on a first (bottom) side of the pixel area. However, the pixels for rows  1  and  2  are disconnected from the column driver  330  for column  2 . In that case, a data value (e.g., “1” or “0”) is loaded into the cross-column switch register  390  connected to the control terminal of the cross-column switch  380  between columns  2  and  3  located on the opposite (top) side of the pixel area from the column driver  330  for column  2 , such that a control signal output by the cross-column switch register  390  causes the cross-column switch  380  between columns  2  and  3  to close. In other words, the data value stored in each cross-column switch register  390  indicates whether the corresponding cross-column switch  380  should be opened or closed.  
         [0041]    With the cross-column switch  380  between columns  2  and  3  closed, the pixels  310  for rows  1  and  2  of column  2  are connected to the column line  320  for column  3 . Accordingly, in response to a scanning (gate) signal of the corresponding row (scanning) line  350 , the pixels  310  for rows  1  and  2  of column  2  are driven by the data signal of column  3  to store and display image data. It should be understood that it is possible to connect the pixels  310  for rows  1  and  2  of column  2  to column  1  instead of to column  3 .  
         [0042]    Also, for example, a column driver  330  for column  4  may be defective and fail to provide a data signal to a column line  320  of column  4 . In that case, a data value (e.g., “1” or “0”) is stored into a cross-column switch register  390  connected to one of the cross-column switches  380  (top or bottom) between columns  3  and  4 , such that a control signal output by the cross-column switch register  390  causes the cross-column switch  380  between columns  3  and  4  to close. Also, a data value (e.g., “1” or “0”) is stored into a column driver switch register for column  4  such that a control signal output by the column driver switch register  390  for column  4  causes the column driver switch  340  for column  4  to open. In other words, the data value stored in the column driver switch register  390  indicates whether the corresponding column driver switch  340  should be opened or closed. With one of the cross-column switches  380  between columns  3  and  4  closed, and the column driver switch  340  for column  4  opened, the pixels  310  of column  4  are connected to the column line  320  for column  3 . Accordingly, in response to a scanning (gate) signal of the corresponding row (scanning) line  350 , the pixels  310  for column  4  are driven by the data signal of column  3  to store and display image data.  
         [0043]    It should be understood that, in the above example where the column driver  330  for column  4  is defective, the pixels  310  of column  4  can be connected to column  5  instead of to column  3 .  
         [0044]    [0044]FIG. 4 shows a third embodiment of an image display device in accordance with one or more aspects of the invention. The third embodiment is described with respect to a liquid crystal display (LCD) device  400 . For clarity and simplicity, those portions of the LCD device  400  relating to the present invention are illustrated.  
         [0045]    The LCD device  400  comprises in relevant part: a plurality of pixels  410 ; a plurality (M) of column (data) lines  420  connected to the plurality of pixels  410 ; a plurality of column (data) drivers  430  for supplying data to the pixels  410  via the column lines  420 ; a plurality of column driver switches  440 ; a plurality (M) of column driver switch registers  445 ; a plurality (N) of row (scanning) lines  450  connected to N rows of pixels  410 ; a plurality of row drivers  460  connected to the row lines  450  for selecting a row of pixels  410  to which data from the column drivers  430  is to be applied; a plurality (M) of column test switches  480  each connected with a corresponding one of the column lines  420 ; a common test line  486  connected to each of the column test switches  480 ; a buffer  488  connected to the common test line  486 ; and a plurality (M) of column test switch registers  490  each having an output connected to a control terminal of a corresponding one of the column test switches  480 . Beneficially, the column driver switch registers  445  and/or the column test switch registers  490  may be configured as shift registers.  
         [0046]    Typically, each pixel  410  includes a pixel switching device  412 , having first and second terminals and a control terminal, and a storage device pixel capacitor)  414  connected to the first terminal of the pixel switching device  412 . The second terminal of the pixel switching device  412  is connected to one of the column lines  420 . The pixel switching device  412 , which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line  450  to selectively connect the column line  420  to the storage device  414  and thereby to store a data signal applied via the column line  420  into the storage device  414 .  
         [0047]    The LCD device  400  may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers  430  and/or row (scanning) drivers  460  may be integrated onto a same silicon substrate as the liquid crystal pixels  410 . Also, the column driver switches  440 , the column driver switch registers  445 , the column test switches  480 , the buffer  488 , and/or the column test switch registers  490  may be integrated onto the same substrate.  
         [0048]    The operation of various pertinent elements of the third preferred embodiment LCD device  400  in the case of a defective column will now be explained.  
         [0049]    The third embodiment of the LCD device  400  operates similarly to the first embodiment of the LCD device  200 , except that instead of the cross-column switches extending between pairs of adjacent columns, the third embodiment includes the column test switches  480  each connecting a corresponding column line  420  to the common test line  486 . Accordingly, when a defect of a column line  420  or a column driver  430  is detected, then a data value is stored in the corresponding column test switch register  490  so as to output a control signal to cause the corresponding column test switch  480  to close, thereby connecting pixels of the defective column to the common test line  486 . Also, a data value is stored in a column test switch register  490  for another properly working column, preferably an adjacent column, so as to output a control signal to cause the corresponding column test switch  480  to close, thereby also connecting the properly working column line  420  to the common test line  486 . In other words, the data value stored in each cross-column switch register  490  indicates whether the corresponding cross-column switch  480  should be opened or closed. As a result, the pixels of the defective column are driven, via the common test line  486 , by the data signal of a properly working (preferably adjacent) column line  420  to store and display image data.  
         [0050]    The third embodiment is particularly useful where the LCD device includes self-calibrating circuitry to compensate for brightness variations between pixels or columns of the LCD device, including the plurality of column test switches  480 . Such an LCD device is described in co-pending U.S. patent application Ser. No. ______ (Docket No. US010349) filed on ______ in the name of inventors Peter J. Janssen and Remus L. Albu and entitled “Self-Calibrating Liquid Crystal Display” the entirety of which is hereby incorporated by reference for all purposes as if fully set forth herein.  
         [0051]    [0051]FIG. 5 shows a fourth embodiment of an image display device in accordance with one or more aspects of the invention. The fourth embodiment is described with respect to a liquid crystal display (LCD) device  500 . For clarity and simplicity, those portions of the LCD device  500  relating to the present invention are illustrated.  
         [0052]    The LCD device  500  comprises in relevant part: a plurality of pixels  510 ; a plurality (M) of column (data) lines  520  connected to the plurality of pixels  510 ; a plurality of column (data) drivers  530  for supplying data to the pixels  510  via the column lines  520 ; a plurality of column driver switches  540 ; a plurality (M) of column driver switch registers  545 ; a plurality (N) of row (scanning) lines  550  connected to N rows of pixels  510 ; a plurality of row drivers  560  connected to the row lines  550  for selecting a row of pixels  510  to which data from the column drivers  530  is to be applied; a plurality (M) of column test switches  580  each connected with a corresponding one of the column lines  520 ; a plurality (≈M/2) of column pair selection switches  582 ; a plurality of column pair selection switch registers  584  each having an output connected to a control terminal of a corresponding one of the column pair selection switches  582 ; a common test line  586  connected to the column pair selection switches  582 ; a buffer  588  connected to the common test line  586 ; and a plurality (M) of column test switch registers  590  each having an output connected to a control terminal of a corresponding one of the column test switches  580 . Beneficially, the column driver switch registers  545  and/or the column test switch registers  590  and column pair selection switch registers  584  may be configured as shift registers.  
         [0053]    Typically, each pixel  510  includes a pixel switching device  512 , having first and second terminals and a control terminal, and a storage device (pixel capacitor)  514  connected to the first terminal of the pixel switching device  512 . The second terminal of the pixel switching device  512  is connected to one of the column lines  520 . The pixel switching device  512 , which may be a thin film transistor (TFT), is responsive to a scanning signal on the connected row line  550  to selectively connect the column line  520  to the storage device  514  and thereby to store a data signal applied via the column line  520  into the storage device  514 .  
         [0054]    The LCD device  500  may be a liquid crystal on silicon (LCOS) type LCD device. In that case, the column (data) drivers  530  and/or row (scanning) drivers  560  may be integrated onto a same silicon substrate as the liquid crystal pixels  510 . Also, the column driver switches  540 , the column driver switch registers  545 , the column test switches  580  and/or the column test switch registers  590  may be integrated onto the same substrate.  
         [0055]    The operation of various pertinent elements of the fourth preferred embodiment LCD device  500  in the case of a defective column will now be explained.  
         [0056]    The fourth embodiment of the LCD device  500  operates similarly to the third embodiment of the LCD device  400 , except that it includes the column pair selection switches  582  and column pair selection switch registers  584 . Unlike the third embodiment, wherein only a single column in each group can be repaired, in the fourth embodiment, multiple defects of column lines  520  and column drivers  530  within a group may be repaired, because each pair of column lines  520  has its own column pair selection switch  582  which can be opened to isolate the column pair from all other columns of the LCD device  500 . As in the first to third embodiments, a data value is stored in each cross-column switch register  590  to indicate whether the corresponding cross-column switch  580  should be opened or closed.  
         [0057]    While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. Accordingly, the invention therefore is not to be restricted except within the spirit and scope of the appended claims.