Abstract:
An electrically erasable writing surface is provided. The writing surface includes a bistable display layer that responds to electrical and mechanical inputs. A touch pad is located above or below the display layer. The writing surface facilitates writing complex characters and increases accuracy by displaying a user input created by a passive stylus.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to pressure sensitive input devices. More particularly, the invention provides a mechanically and electrically addressable writing surface that incorporates a bistable display layer that retains an optical state until electrically erased.  
         BACKGROUND OF THE INVENTION  
         [0002]    Pressure sensitive touch pads are commonly used with personal digital assistants (PDAs) and other portable electronic devices. Pressure sensitive touch pads convert mechanical pressure, typically applied by a stylus, into an electrical output. The stylus is typically used to enter characters or make menu selections. Many conventional touch pads do not include a display that traces (i.e., shows) the path of the stylus. As a result, it can be difficult for users to accurately use a stylus to input character data. This is particularly a problem with complex characters, such as characters that are a part of oriental languages. As the accuracy of the input data decreases, so does the accuracy of the output electrical data.  
           [0003]    One approach to displaying the path traced by a stylus includes the use of an active stylus. An active stylus generates an electric or magnetic field and changes the state of a display placed over a touch pad. One of the disadvantages of using an active stylus is that an active stylus cannot be interchanged with other styluses. Another disadvantage is that active styluses that include electrical components are expensive, when compared with passive styluses.  
           [0004]    Electrically addressable displays have also been placed over touch pads to display the path traced by a stylus. Information detected by the touch pad is transmitted to a display driver circuit. The display driver circuit energizes patterned display electrodes and causes the display to display the path traced by the stylus. Display driver circuits increase the size and expense of the device. Another drawback to devices that include electrically addressable displays placed over touch pads is that such devices require frequent and inconvenient calibration steps in order to keep the trace generated by the display aligned with the actual position of the stylus.  
           [0005]    Therefore, there exists a need in the art for a pressure sensitive input device that displays the trace of a stylus without the use of an active stylus or complex driver circuits.  
         SUMMARY OF THE INVENTION  
         [0006]    One or more of the above-mentioned needs in the art are satisfied by the disclosed systems and methods that include a mechanically and electrically addressable writing surface that incorporates a bistable display layer that retains an optical state until electrically erased. The writing surface provides immediate feedback to a user and facilitates the writing of characters. The bistable display layer increases efficiency by only consuming electrical power when resetting the state of the display layer.  
           [0007]    A first embodiment of the invention provides a writing surface. The writing surface includes a display layer comprising electrically and mechanically sensitive display material having at least two stable optical states. A touch pad is physically coupled to the display layer. The touch pad is configured to convert a mechanical input into an electrical output.  
           [0008]    In another embodiment, a user interface for use with an electronic device is provided. The user interface includes an optical output section and a mechanical input section. The mechanical input section includes a display layer comprising electrically and mechanically sensitive display material having at least two stable optical states. A touch pad is physically coupled to the display layer. The touch pad is configured to convert a mechanical input into an electrical output. The user interface may be used with a mobile terminal.  
           [0009]    In yet another embodiment of the invention, a method of operating an input device is provided. The input device includes an electrically and mechanically sensitive display layer having at least two stable optical states and physically coupled to a touch pad. The method includes (a) receiving at the display layer and the touch pad a mechanical input. In response to (a) an optical state of the display layer is changed and, at the touch pad, the physical input is converted to an electrical output.  
           [0010]    In other embodiments of the invention, computer-executable instructions for implementing the disclosed methods are stored on computer-readable media. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The present invention is illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which:  
         [0012]    [0012]FIG. 1 shows a portable electronic device that incorporates a writing surface in accordance with an embodiment of the invention;  
         [0013]    [0013]FIG. 2 shows another portable electronic device that incorporates a writing surface in accordance with an embodiment of the invention;  
         [0014]    [0014]FIG. 3 illustrates an operation of a writing surface in accordance with an embodiment of the invention;  
         [0015]    [0015]FIG. 4 illustrates a structure of a writing surface in accordance with an embodiment of the invention;  
         [0016]    [0016]FIG. 5 shows a schematic diagram of an electronic device that incorporates a writing surface in accordance with an embodiment of the invention; and  
         [0017]    [0017]FIG. 6 shows a device having an integrated display and writing surface in accordance with an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    [0018]FIG. 1 illustrates a portable electronic device such as a mobile terminal  100  in accordance with an embodiment of the invention. Mobile terminal  100  includes an optical output section  102  that may be used to display information to a user. Optical output section  102  may be implemented with a liquid crystal display or any other conventional flat-panel display conventionally used with portable electronic devices. A user of mobile terminal  100  may enter information with a mechanical input section  104  and/or a keypad section  108 . Mechanical input section  104  may include a mechanically and electrically addressable writing surface that includes a bistable display layer. U.S. Pat. No. 6,104,448 to Doane et al. discloses an exemplary mechanically and electrically addressable display material that may be used to create a display layer. The bistable display layer is mechanically coupled to and positioned in an overlapping relationship with a touch pad. Keypad  108  may include a variety of alphanumeric keys, function keys or other keys typically found in portable electronic devices. When entering data, a user may utilize mechanical input section  104  or keypad  108 . Because of the increased accuracy provided by mechanical input section  104  when compared to prior art devices, users may find it convenient to use mechanical input section  104  for inputting a greater number of characters. As a result, the number of characters represented by keypad  108  may be reduced and the overall size of mobile terminal may be reduced.  
         [0019]    One skilled in the art will appreciate that aspects of the present invention, including the disclosed writing surfaces, may be used with a variety of electronic devices. FIG. 2, for example, shows a personal digital assistant  200  that incorporates a mechanically and electrically addressable writing surface  202  that includes a bistable display layer. Moreover, personal digital assistant  200  shows that in some embodiments, the disclosed writing surface may be incorporated into devices that do not include a keypad. In other embodiments of the invention, a mechanically and electrically addressable writing surface that includes a bistable display layer may be used to create a scratch pad or whiteboard.  
         [0020]    An example of the operation of mobile terminal  100  and personal digital assistant  200  is illustrated in FIG. 3. FIG. 3 shows a device that prompts a user to enter a character. In a first state  302 , the device electrically erases any information on the contents of a writing surface  300   a  and displays information to the user on display  300   b . As described below, writing surface  300   b  may be erased by applying an electric or magnetic field to a bistable display layer. In a second state  304 , a user enters a character  308  on writing surface  300   a  with a stylus  310 . The entered character is displayed on writing surface  300   a  in response to mechanical pressure applied by stylus  310 . The bistable display layer displays the character without any further mechanical or electrical input. That is, the state of writing surface  300   b  is stable. The device may use a handwriting recognition module to recognize the character written on writing surface  300   a.    
         [0021]    The final device state  306 , shows that the device has recognized the written character, displayed the character on display  300   b  and erased writing surface  300   a . The bistable display layer provides flexibility to developers and users and allows writing surface  300   a  to be erased at a variety of different times. For example, writing surface  300   a  may be erased after the character is recognized by a handwriting recognition module, after a predetermined time period, after a command from the user or at any other time.  
         [0022]    [0022]FIG. 4 illustrates a writing surface, in accordance with an embodiment of the invention. [Question to inventors—Please let us know if you have any particularly preferred materials, thickness, etc. for the elements of the writing surface that have not been included] A display layer  402  is held between two substrates  404  and  406 . Display layer  402  includes an electrically and mechanically sensitive display material having at least two stable optical states. A display material is electrically and mechanically sensitive when the display layer can change optical states in response to both an electrical field and to a mechanical input, such as a pressure source. As used herein, an optical state is stable when the display material maintains the optical state without the application of an excitation source for at least several seconds. Optical states may include transparent, blocking and reflective. Examples of electrically and mechanically sensitive display materials having at least two stable optical states include: cholesteric liquid crystal material, twisted nematic liquid crystal material and suspended particle display materials. Display layer  402  may include a polymer dispersed throughout the display layer to aid in stabilizing the optical states.  
         [0023]    The embodiment of display layer  402  shown in FIG. 4 includes cholesteric liquid crystal material. Region  408  includes cholesteric liquid crystal material having helical axes aligned at random angles. When helical axes are aligned at random angles, the material is in a transparent optical state. Region  410 , corresponding to a region that has been mechanically stimulated by stylus  428 , includes cholesteric liquid crystal material having helical axes aligned essentially orthogonal to substrates  404  and  406 . The material in region  410  reflects incident light having a predetermined wavelength. As is well known in the art, the wavelength λ of the light reflected light is determined by λ=np, where n=the refractive index of the liquid crystal material and p=the pitch length of the liquid crystal material.  
         [0024]    Substrate  404  may be a transparent and flexible material, such as glass or plastic. In one embodiment, substrate  406  is also transparent and flexible. In embodiments in which a touch pad is formed above substrate  404 , substrate  406  need not be flexible.  
         [0025]    A pair of electrodes  414  and  416  may be used to apply an electric or magnetic field to display layer  402 . Top electrode  414  may be formed of a transparent material, such as indium-tin oxide. Bottom electrode  416  may also be formed of a transparent material. In reflective embodiments (not shown), electrode  416  may be formed of a reflective material, such as silver or aluminum. Alternatively, in reflective embodiments, an additional reflective layer may be included. Electrodes  414  and  416  may be sheet electrodes used to apply a field to the entire display layer and need not be patterned electrodes used to address individual pixels. Of course, patterned electrodes may be used and the patterned electrodes may be addressed at the same time.  
         [0026]    A pigment layer  418  may be attached to substrate  406 . Pigment layer  418  may be implemented with a black layer or a colored material. In one embodiment, pigment layer  418  has a color complimentary to the color of light reflected by display layer  402 . A touch pad  420  may be coupled below substrate  406  or above substrate  404 . Touch pad  420  may be implemented with a conventional grid of electrodes that convert a mechanical input into an electrical output. Touch pad  412  generates an electrical output from a mechanical input and may transmit an electrical output signal to a processor  422 . Of course, when touch pad  412  is positioned above substrate  404 , touch pad  420  may be transparent and flexible.  
         [0027]    The operation of the writing surface shown in FIG. 4 will now be described. A reset module  424  applies an electric field to display layer  402 . The application of an electric field causes the helical axes of the cholesteric liquid crystal material display layer  402  to align at random angles and assume a transparent state. Light ray  426 , for example, travels through the transparent material and is reflected by pigment layer  418 . Light ray  426  then leaves pigment layer  418  and is transmitted back to a user. When pressure is applied to display layer  402 , such as by pressing on substrate  404  with a stylus  428 , the mechanical pressure causes the helical axes of the depressed portions of the cholesteric liquid crystal material to become aligned essentially orthogonal to substrates  404  and  406 . Regions of display layer  402  that have helical axes aligned essentially orthogonal with substrates  404  and  406  reflect light having the wavelength describe above.  
         [0028]    After the removal of the mechanical pressure applied by stylus  428 , the optical state of display layer  402  remains stable. The entire display layer may be reset to a transparent state by applying an electric or magnetic field with reset module  424 .  
         [0029]    One skilled in the art will appreciate that several other display materials and configurations may be used to implement aspects of the pressure invention. For example, a writing surface may have stable light blocking and transparent states. Moreover, a display material that selectively rotates light in response to an electrical or mechanical stimulus may be used in connection with one or more linear polarizers. Other conventional layers and films may also be added without departing from the inventive principals.  
         [0030]    [0030]FIG. 5 illustrates a schematic diagram of a mobile terminal, personal digital assistant or other electronic device that incorporates the disclosed writing surface. A bistable display layer  502  is mechanically coupled to a touch pad  504  in the manner described above. Touch pad  504  may be electrically coupled to a processor  506 . Processor  506  may be coupled to a memory module  508  that may be used to store computer executable instructions or other data. In one embodiment, memory module  508  stores a handwriting recognition module that may be used by processor  506  to recognize characters written on touch pad  504 . A keypad  510  and/or other conventional input device, such as a microphone or pointing device, may also be coupled to processor  506 . Processor  506  may also be used to control a display driver  512  that is used to control the state of a display  514 . Display  514  may correspond to display  102  shown in FIG. 1. Bistable display layer  502  may be controlled by driver circuit  516  that is coupled to processor  506 . One skilled in the art will appreciate the differences between driver circuit  512  and driver circuit  516 . In particular, driver circuit  516  may be much simpler and include fewer components because bistable display layer  502  does not require patterned electrodes. In one embodiment, the output of driver circuit  516  includes two terminals that may be coupled to two electrodes of bistable display layer  502 .  
         [0031]    While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention. For example, FIG. 6 illustrates a device that includes an integrated display  602  and writing surface  604 . Display  602  may be used to display information to a user in a conventional manner. Writing surface  604  may operate as described above. Display  602  and writing surface  604  may share a common upper substrate  606 , lower substrate  608 , pigment layer  610  and display layer  612 . Display  602  utilizes electrodes  608   a  and  608   b . Electrodes  608   a  and  608   b  may be patterned to address individual pixels in a conventional manner. In contrast to electrodes  608   a  and  608   b , electrodes  610   a  and  610   b  may be sheet electrodes that are used to reset an entire writing surface section. Writing surface  604  may include a touch pad  614  positioned above substrate  606  or below substrate  608 .