System and method of integrating a touchscreen within an lcd

Abstract

A touchscreen liquid crystal display, method for using a liquid crystal display as a user input, and a mobile electronic device are provided. The touchscreen liquid crystal display comprises: a liquid crystal display having a viewing surface and including a plurality of parallel first electrodes located on one side of a liquid crystal containing area and overlapping with a plurality of parallel second electrodes located on an opposite side of the liquid crystal containing area, the first and second electrodes overlapping to form an array of liquid crystal pixel elements, at least some of the first electrodes being displaceable towards the second electrodes in response to external pressure applied to the viewing surface; a driver circuit coupled to the first and second electrodes for driving the electrodes for selectively controlling a display state of the display pixel elements; and a measurement circuit coupled to the electrodes for measuring display pixel element voltages for at least some of the display pixel elements formed by the first electrode, and for each display pixel element for which a display pixel element voltage is measured, comparing the measured voltages to reference voltages and determining a relative force of the external pressure on the viewing surface based on the measured voltages.

1 . A touchscreen liquid crystal display, comprising: 
 a liquid crystal display having a viewing surface and including a plurality of parallel first electrodes located on one side of a liquid crystal containing area and overlapping with a plurality of parallel second electrodes located on an opposite side of the liquid crystal containing area, the first and second electrodes overlapping to form an array of liquid crystal pixel elements, at least some of the first electrodes being displaceable towards the second electrodes in response to external pressure applied to the viewing surface;    a driver circuit coupled to the first and second electrodes for driving the electrodes for selectively controlling a display state of the display pixel elements; and 
 a measurement circuit coupled to the electrodes for measuring display pixel element voltages for at least some of the display pixel elements formed by the first electrode, and for each display pixel element for which a display pixel element voltage is measured, comparing measured voltages to a reference voltage and determining a relative force of the external pressure on the viewing surface based on the measured voltages.  
   
   
   
       2 . The display of  claim 1 , wherein the measurement circuit is configured for determining a type of press causing the external pressure applied to the viewing surface.  
   
   
       3 . The display of  claim 2 , wherein determining a type of press comprises determining whether the determined relative force is associated with a full press or double press on the viewing surface causing the external pressure applied to the viewing surface.  
   
   
       4 . The display of  claim 1 , further comprising: 
 a reference electrode in the liquid crystal display overlapping with the first or second electrodes to form reference pixel elements;    wherein the measurement circuit is configured to measure corresponding reference pixel element voltages at corresponding reference pixel elements to obtain the reference voltage.    
   
   
       5 . The display of  claim 4 , wherein the reference pixel elements are located outside of a viewable area of the liquid crystal display a sufficient distance so as not to be substantially affected by external pressure applied to the viewing surface.  
   
   
       6 . The display of  claim 4 , wherein the measurement circuit is configured to determine in dependence on the measured display pixel element voltages and corresponding reference pixel element voltages a relative displacement between at least some of the first electrodes and the second electrodes in response to external pressure applied to the viewing surface to determine a relative force of the external pressure on the viewing surface based on the measured voltages.  
   
   
       7 . The display of  claim 1 , wherein the measurement circuit is configured for operating in a first mode and in a second mode, wherein in the first mode the measurement circuit measures voltages across a subset of the pixel elements until the measured electrical characteristic indicates that external pressure has been applied to the viewing surface, after which the control circuit automatically operates in the second mode, wherein in the second mode the measurement circuit measures voltages across a larger set of the pixel elements and determines the location of the external pressure based thereon.  
   
   
       8 . The display of  claim 1 , wherein the measurement circuit is configured for determining a location of the external pressure on the viewing surface based on the measured voltages.  
   
   
       9 . The display of  claim 8 , wherein a location of the external pressure is determined based on which measured pixel element voltage varies the greatest from a reference value determined in dependence on the reference voltage.  
   
   
       10 . The display of  claim 4 , wherein each of the first and second electrodes is a substantially transparent strip electrode, the first electrodes being arranged substantially parallel to each other, the second electrodes being arranged substantially parallel to each other and substantially orthogonal to the first electrodes for defining the array of pixel elements, each pixel element being associated with one of the first electrodes and one of the second electrodes, the measuring circuit including a sampling circuit for sampling a voltage across each of the pixel elements and a processing circuit for detecting the displacement and a location thereof based on the sampled voltages, the reference electrode being arranged substantially parallel to either the first or second electrode and substantially orthogonal to the other of the first or second electrode.  
   
   
       11 . The display of  claim 10 , wherein the reference electrode forms the reference liquid crystal pixel elements with the first electrodes, and the second electrodes are each individually sampled to acquire the measured voltages, the reference electrode being driven with the same data as the second electrode being sampled.  
   
   
       12 . The display of  claim 10 , wherein a plurality of scanable electrodes are included among at least one of the first electrodes and the second electrodes, each scanable electrode being connected by an associated switch to the driver circuit, the sampling circuit including a controller for individually controlling each switch, the controller being configured for opening the switch associated with a selected one of the scanable electrodes and causing the voltage across the pixel elements associated with the selected one of the scanable electrodes to be sampled when the switch associated with the selected one of the scanable electrodes is open.  
   
   
       13 . The display of  claim 10 , wherein the electrodes are Indium-Tin Oxide (ITO).  
   
   
       14 . A method for using a liquid crystal display as a user input, the liquid crystal display having a viewing surface and including a plurality of parallel first electrodes located on one side of a liquid crystal containing area and overlapping with a plurality of parallel second electrodes located on an opposite side of the liquid crystal containing area, the first and second electrodes overlapping to form an array of liquid crystal pixel elements, at least some of the first electrodes being displaceable towards the second electrodes in response to external pressure applied to the viewing surface, the method comprising: 
 (a) selectively driving the first and second electrodes to cause the pixel elements to display an image visible on the viewing surface;    (b) sampling voltages between the first and second electrodes;    (c) comparing the measured voltages to a reference voltage; and    (d) determining a relative force of the external pressure on the viewing surface based on the measured voltages.    
   
   
       15 . The method of  claim 14 , further comprising: 
 determining a type of press associated with the external pressure applied to the viewing surface in accordance with the determined relative force.    
   
   
       16 . The method of  claim 15 , wherein determining a type of press comprises determining whether the external pressure applied to the viewing surface relative force is associated with a full press or double press on the viewing surface.  
   
   
       17 . The method of  claim 14 , further comprising: 
 sampling voltages between a reference electrode in the liquid crystal display and a plurality of first electrodes or second electrodes that the reference electrode overlaps for use as the reference voltage.    
   
   
       18 . The method of  claim 14 , further comprising: 
 determining based on the sampled voltages if any of the first electrodes have been displaced towards the second electrodes.    
   
   
       19 . The method of  claim 18 , wherein the sampling step (b) includes sampling voltages at a sub-set of pixel element locations until a determination is made that a displacement of first electrodes has occurred and then sampling voltages at a larger set of pixel element locations and determining based on the sampled voltages from the larger set a relative location of the displacement.  
   
   
       20 . The method of  claim 19 , wherein sampling of the sub-set is carried out at a lower rate than sampling of the larger set.  
   
   
       21 . The method of  claim 19 , wherein based on the measured voltages from the sub-set a general location of the displacement is determined, and the larger set is selected to include the general location.  
   
   
       22 . The method of  claim 18 , further comprising determining the center of deflection of the displaced first electrodes by determining, based on the measured voltages, a weighted average of the deflection at a plurality of the pixel locations and determining a centroid of the deflection based on the weighted average.  
   
   
       23 . A mobile electronic device, comprising: 
 a processor for controlling the operation of the device;    a touchscreen liquid crystal display for display an image visible from a viewing surface, comprising: 
 a liquid crystal display including a plurality of parallel first electrodes located on one side of a liquid crystal containing area and overlapping with a plurality of parallel second electrodes located on an opposite side of the liquid crystal containing area, the first and second electrodes overlapping to form an array of liquid crystal pixel elements, at least some of the first electrodes being displaceable towards the second electrodes in response to external pressure applied to the viewing surface;  
 a driver circuit coupled to the first and second electrodes for driving the electrodes for selectively controlling a display state of the display pixel elements; and  
 a measurement circuit coupled to the electrodes for measuring display pixel element voltages for at least some of the display pixel elements formed by the first electrode, and for each display pixel element for which a display pixel element voltage is measured, comparing the measured voltages to a reference voltage and determining a relative force of the external pressure on the viewing surface based on the measured voltages.