Abstract:
A position sensing display integrates a touch sensor with an active matrix LCD panel. X sense electrodes and y sense electrodes in respective layers on a front panel are coupled capacitatively to respective sense circuits on active rear panel. A common electrode is driven, and the resulting signal on the x-sense electrodes and y sense electrodes is measured by the respective sense circuits. Changes in the resulting signal when sensed object approaches are measured to locate the sensed object.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority of U.S. Patent Provisional Application No. 61/016,804, filed on Dec. 26, 2007, and claims the priority of European Patent Application No. EP 08160966.1, filed on Jul. 23, 2008, the entirety of which is incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a position sensing display and a method of operation of such a display. 
         [0004]    2. Description of the Related Art 
         [0005]    Position sensors have been combined with displays in the form of a transparent position sensing overlay which is placed over the display to record touch or pen input. Such sensors may consist of arrays of electrodes which are connected to drive/sense circuits. 
         [0006]    The sensors may be capacitance sensors with sets of electrodes connected to drive and/or sensing circuits. The location of an object such as a stylus or finger is then determined by measuring changes in the capacitances associated with the electrodes which are affected by the object in close vicinity. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The invention provides an active matrix display, comprising: a front panel and a rear panel; wherein the front panel includes: a transparent substrate; a common electrode for cooperating with a rear active substrate for driving the liquid crystal; a plurality of first sense electrodes extending across the display; the rear panel includes: a substrate; and an array of display pixels arranged as rows and columns; a plurality of sense circuits coupled to the respective sense electrodes further comprising coupling capacitors capacitively coupling the sense electrodes to the respective sense circuits for coupling sense signals from the sense electrodes to the sense circuits. 
         [0008]    The invention also provides a front transparent substrate for an active matrix liquid crystal display, for cooperating with a rear active substrate with sense circuits, the front transparent substrate comprising: a common electrode for cooperating with the rear active substrate for driving the liquid crystal; a plurality of first sense electrodes extending across the display in a first direction; and a plurality of second sense electrodes extending across the display in a second direction across the first sense electrodes; coupling electrodes connected to each of the first sense electrodes and second sense electrodes, the coupling electrodes extending beyond the common electrode to a coupling region for capacitively coupling to coupling electrodes on the rear active substrate for coupling capacitance sense signals from the sense electrodes to the sense circuits on the rear active substrate. 
         [0009]    The invention also provides a rear active substrate for an active matrix liquid crystal display, for cooperating with a front transparent substrate with sense electrodes, the rear active substrate comprising: an active matrix array of pixels; a plurality of first sense circuits and second sense circuits; and a plurality of coupling electrodes connected to respective x-sense circuits and y-sense circuits for capacitively coupling with coupling electrodes on the front transparent substrate for coupling capacitance sense signals from the sense electrodes to the sense circuits on the rear active substrate. 
         [0010]    The invention further provides a method of sensing the position of a sensed object with an active matrix liquid crystal display with a transparent front substrate with a common electrode, a plurality of row sense electrodes extending across the display in a first x direction, and a plurality of column sense electrodes extending across the display in a second y direction across the row sense electrodes and an active rear substrate with an array of display pixels and a plurality of row sense circuits and column sense circuits, the method comprising: driving the common electrode with a drive signal; capacitatively coupling the drive signal on the x sense electrodes and y sense electrodes to respective x sense circuits and y sense circuits and detecting the capacitatively coupled drive signal on the x sense circuits and y sense circuits; and detecting the changes in the detected drive signal on particular row sense circuits and column sense circuits caused by the presence of a sensed object adjacent to respective row sense electrodes and column sense electrodes to locate the sensed object. 
         [0011]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0013]      FIG. 1  shows a side view of an active matrix LCD according to an embodiment of the invention; 
           [0014]      FIG. 2  shows the transparent front plate of the arrangement of  FIG. 1 ; 
           [0015]      FIG. 3  shows the active rear plate of the arrangement of  FIG. 1 ; and 
           [0016]      FIG. 4  is a circuit diagram showing the capacitative coupling between various components of the arrangement of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0018]    By integrating the sense circuits with the display the display is simplified compared with prior display modules which potentially reduces cost and improves yield. Further, by avoiding providing a separate touch panel the possibility of dust or other small particles being trapped between the separate touch panel and the display is avoided. 
         [0019]    In addition, a separate touch panel can affect the optical performance of the display by introducing additional surfaces that may cause reflections, which problem is reduced by integrating the touch sensor. 
         [0020]    The inventors have realized that by coupling the front and rear panels the sense circuits can be provided on the active rear panel and coupled to electrodes on the front panel. The use of capacitors to couple the circuits to the electrodes avoids the difficult manufacturing step of providing ohmic contacts. 
         [0021]    Referring to  FIGS. 1 to 4 , an active matrix liquid crystal display has a front panel  2 , a rear panel  4  and liquid crystal  6  between the front and rear panels. 
         [0022]    Referring to  FIGS. 1 and 2 , note that  FIG. 2  shows the front panel  2  viewed from the front. The front panel  2  has a transparent substrate  10  facing forward in the finished device, omitted from  FIG. 2  for clarity. On the transparent substrate is an x-sense electrode layer  12  made up of a plurality of x-sense electrodes  14  extending in the column direction parallel to one another. 
         [0023]    An insulating layer  16  covers the x-sense electrode layer  12 . A y-sense electrode layer  18  is provided on the insulating layer, the y-sense electrodes extending in the row direction parallel to one another. 
         [0024]    For clarity, only three x-sense electrodes  14  and y-sense electrodes  20  are shown in  FIG. 2  but in reality there may be many more. For example, there may be tens or hundreds of electrodes depending on the resolution required. 
         [0025]    A filter layer  21  is provided on the y-sense electrode layer, the filter layer including red, green and blue filters for providing a colour display. 
         [0026]    A common electrode  22  is provided across the panel  2  on filter layer  21 . 
         [0027]    Each of the x-sense electrodes  14  includes a coupling region  24  which will be described further below. The y sense electrodes  20  include coupling regions  28 . A contact region  26  for providing a direct contact to the common electrode  22  is also provided. 
         [0028]    The electrodes  14 ,  20 ,  22  are conveniently transparent and may be made of transparent conducting material such as indium tin oxide. Likewise the substrate  10  is also transparent, and may be of glass or plastics for example. 
         [0029]    As for the rear panel, referring to  FIGS. 1 and 3 , this includes a rear substrate  30  and an active circuit layer  32  on the rear substrate. The active circuit layer  32  includes an active matrix pixel array  34  made up of a plurality of pixels  36  arranged in rows and columns. This may be any type of active matrix array as is well known in the art and so will not be described further. 
         [0030]    Row drive circuit  38  is provided along one edge of the pixel array  34  to drive the rows of pixels and column drive circuit  40  is provided along an adjacent edge of the pixel array  34  to drive the columns. Any convenient drive circuit may be used. 
         [0031]    X-sense circuits  42  are provided along the opposite edge of the pixel array  34  to the column drive circuit  40 , arranged in a row. Each x-sense circuit  42  is connected to a respective coupling electrode  46  which is arranged in registration with a corresponding coupling region  24  of a respective x-sense electrode  14  on the passive substrate. 
         [0032]    Similarly, y-sense circuits  44  are provided along the opposite edge of the pixel array  34  to the row drive circuit  38 . Each y-sense circuit  44  is connected to a respective coupling electrode  48  which is arranged in registration with a corresponding coupling region  28  of a respective y-sense electrode. 
         [0033]    A common electrode drive circuit  50  is arranged in direct (ohmic) contact with the contact region  26  to drive common electrode  22 . 
         [0034]    Note that the unlike the connection between common electrode drive circuit  50  and the contact region  26 , the coupling regions  24 , 28  of the sense electrodes are not directly connected to the corresponding coupling electrodes  46 ,  48 ; instead they are capacitatively coupled. In the embodiment, the liquid crystal acts as the dielectric though since the coupling regions and coupling electrodes are arranged outside the pixel array in other embodiments a solid dielectric support structure or spacer may act as the dielectric. 
         [0035]    This sets up a circuit as illustrated in  FIG. 4  wherein the common electrode drive circuit  50  drives the common electrode  22  which is capacitatively coupled to sense electrodes  14 ,  20  by a sense-common coupling capacitance  52 . The capacitance between coupling regions  24 ,  28  and coupling electrodes  46 ,  48  is represented schematically as coupling capacitor  54  between the sense electrodes  14 ,  20  and sense circuits  42 ,  44 . 
         [0036]    In use, the common electrode drive circuit  50  drives the common electrode  22  and this is coupled to the sense electrodes  14 ,  20  by the sense-common coupling capacitance  52 . The signal on the sense electrodes  14 ,  20  is transmitted across coupling capacitor  54  to the sense circuits  42 ,  44 . 
         [0037]    When a stylus or finger  60  as sensed object is arranged near to the screen, this acts as an effective grounded capacitor coupled to the sense circuits  42 ,  44  through capacitor  56  which affects the signals detected on sense circuits  42 ,  44  and hence allows the position of the stylus or finger  60  to be determined by identifying which of the x-sense circuits  42  and y-sense circuits  44  have a change in the detected signal. 
         [0038]    It will be appreciated that the common electrode  22  and pixel array  34  may be driven at the same time by drive circuits  38 ,  40 ,  50  to display an image or a sequence of images on the display. 
         [0039]    The integration of sensing with an active matrix liquid crystal display enhances the ease of manufacture of a touch sensitive display. Further, the embodiment avoids the use of ohmic contacts, avoiding significant unreliability. 
         [0040]    By coupling the sense electrodes  14 ,  20  to the sense circuits  42 ,  44  by capacitances formed between the active and passive substrate there is no need to provide a row of contacts to connect the sense circuits  42 ,  44  to the electrodes  14 ,  20  on the other substrate. Therefore, in this way all the active circuitry can be provided on the active rear panel  4  and the front panel  2  remains passive. The only direct contact in the embodiment described is that between the drive circuit  50  and contact region  26 . 
         [0041]    Although a specific embodiment has been described, this is by way of example only and those skilled in the art will realise that modifications can be made to the embodiment. 
         [0042]    In particular, the invention may be used with active matrix organic light emitting diodes (AMOLED) devices. 
         [0043]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.