Abstract:
A device includes a substrate, a top touch panel, and an electrode supported by the substrate including a conductive compressible material extending from the substrate to the top touch panel. Another electrode is supported by the substrate and arranged to form an electric field coupling with the electrode including the compressible material. A touch sensitive region is transferred from the substrate to the top touch panel by the compressible material.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C.  119 (e) of U.S. Provisional Patent Application Ser. No. 61/102,830, filed on Oct. 4, 2008, which is incorporated herein by reference in it entirety. 
     
    
     BACKGROUND 
       [0002]    Using a charge transfer capacitive measurement approach, such as that described in U.S. Pat. No. 6,452,514, it is possible to create touch sensing regions that can detect human touch through several millimeters of a plastic or glass front panel. In prior devices, the electrodes are formed on a separate substrate that is glued or held in contact with the front panel, and this panel is then electrically interconnected to a main printed circuit board (PCB) using wires in the form of a connector, or wiring loom. The interconnect can also be somewhat problematic because it can move, causing changes in capacitance and it also introduces some fixed amount of stray capacitance that acts to desensitize the touch control. 
         [0003]    In the above charge transfer capacitive measurement approach, a transmit-receive process is used to induce charge across the gap between an emitting electrode and a collecting electrode (the transmitter and the receiver respectively, also referred to as X and Y). As a finger touch interacts with the resulting electric field between the transmitter and receiver electrodes, the amount of charge coupled from transmitter to receiver is changed. A particular feature of the above approach is that most of the electric charge tends to concentrate near sharp corners and edges (a well known effect in electrostatics). The fringing fields between transmitter and receiver electrodes dominate the charge coupling. Compatible electrode design therefore tends to focus on the edges and the gaps between neighboring transmitter and receiver electrodes in order to maximize coupling and also to maximize the ability of a touch to interrupt the electric field between the two, hence giving the biggest relative change in measured charge. Large changes are desirable as they equate to higher resolution and equally to better signal to noise ratio. 
         [0004]    A specially designed control chip can detect these changes in charge. It is convenient to think of these changes in charge as changes in measured coupling capacitance between transmitter and receiver electrodes (charge is rather harder to visualize). The chip processes the relative amounts of capacitive change from various places around the sensor and uses this to detect the presence of a touch on a touch button. Commonly, these electrodes are required to be transparent so that light can pass through the touch sensor to provide aesthetic and/or functional illumination effects. 
         [0005]    An advantage of the charge transfer capacitive measurement approach is that many touch sensors can be formed at a lower “cost per sensor” than other techniques. This is because the intersection between every X and Y electrode can form a touch sensor. For example, a system that has 10 X electrodes and 8 Y electrodes can be used to form 80 touch sensors. This requires only 18 pins on a control chip, whereas an equivalent open-circuit sensing scheme would need 80. 
         [0006]    The charge transfer capacitive measurement approach is a transmit-receive architecture that uses a two-part electrode design. A typical prior-art electrode design is show in  FIG. 1 . Here a transmit  100  and receive  101  element are shown that serve to couple an electric field  102  between the two. 
         [0007]    In  FIG. 2 , the prior art electrode design is shown in cross section with the transmit  200  and receive  201  elements bonded or pushed against an insulating front panel  202 . The electric field  203  coupled between the two elements can be disrupted  204  by the presence of a finger or other touching object  205 . This serves to decrease the mutual capacitance from transmit to receive element, this change being sensed by a control circuit  206  to register an output  207  to indicate the presence (or not) of the touch  205 . 
       SUMMARY 
       [0008]    A touch sensitive device includes transmit and receive electrodes separating a substrate and a touch panel. Selected electrodes may be formed of conductive compressible material compressed between the substrate and the touch panel. Some electrodes are supported by the substrate and are arranged to form an electrical field coupling with the conductive compressible electrodes. The electrical field coupling is configured to change in response to a touch event of the touch panel near a conductive compressible electrode. In some embodiments, electrodes may be transparent to allow illumination through the electrode. In some embodiments, electrodes may include holes to allow illumination through the touch panel from light sources supported by the substrate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a top view of a prior art layout of electrodes for a capacitive based touch sensor. 
           [0010]      FIG. 2  is cross section of the prior art layout of  FIG. 1 . 
           [0011]      FIG. 3  is a cross section of an electrode configuration using springs between the electrodes and a front panel according to an example embodiment. 
           [0012]      FIG. 4  is a cross section of an example electrode configuration using springs between the electrodes and a front panel according to an example embodiment. 
           [0013]      FIG. 5A  is a cross section of an electrode configuration using springs between electrodes and a front panel according to an example embodiment. 
           [0014]      FIG. 5B  is a cross section of an electrode pair with a spring showing a touch according to an example embodiment. 
           [0015]      FIG. 6A  is cross section of a further electrode configuration using springs between electrodes and a front panel according to an example embodiment. 
           [0016]      FIG. 6B  is a perspective representation of a spring with electrodes according to an example embodiment. 
           [0017]      FIG. 7A  is a cross section of an electrode configuration using springs between electrodes and a front panel according to an example embodiment. 
           [0018]      FIG. 7B  is a cross section of an electrode pair with a spring showing a touch and electric field fringe lines according to an example embodiment. 
           [0019]      FIG. 8  is a cross section of an electrode configuration having a hole and spring according to an example embodiment. 
           [0020]      FIG. 9  is a cross section of an electrode configuration having electroluminescent light generation and a spring according to an example embodiment. 
           [0021]      FIG. 10  is a perspective representation of an electrode configuration having a light diffuser and a spring according to an example embodiment. 
           [0022]      FIG. 11  is a cross section representation of an electrode configuration with a light emitting diode and spring according to an example embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    A structure for a touch control uses a compressible conductive material to form a touch sensitive region at some distance from a control circuit. Using traditional capacitive sensing methods that rely on an open-circuit electrode arrangement, it is easy to use a conductive spring or other compressible material to transfer the touch sensitive region from a substrate, such as a control printed circuit board (PCB) up to a front panel. In some embodiments, no special interconnection is required at the front panel; the “spring” simply pushes up against the front panel and has sufficient surface area when compressed to form a touch control. As a result, significant cost savings can be realized during assembly because the whole sensor PCB becomes self contained with the “springs” installed onto conductive traces on the PCB. The PCB itself is then fixed in place relative to the front panel with the “springs” held in compression to ensure a mechanically stable system (import for capacitive touch controls as any movement can cause fluctuations in the signals measured from the sensor). 
         [0024]    A charge transfer capacitive measurement approach, such as described in U.S. Pat. No. 6,452,514, (or other transmit receive method) may be used with a touch sensitive device having a mechanical “spring” arrangement between a control printed circuit board (PCB) and a front panel. It should be understood that any compressible conductive material could be used to form this “spring”. So long as the electrical resistivity of the spring is moderately low, such as for example, below 100K ohms in one embodiment, then any compressible conductive material, such as metal or plastic springs, open or closed cell foam or further such materials may be used. In some embodiments, the resistivity may be 10K ohms, or 1K ohms or less. 
         [0025]    It should be noted that the examples cited place the transmit and receive elements on the same plane and hence require only one layer to implement on a substrate. It is equally possible to form a charge transfer capacitive measurement touch sensor across two layers i.e. with X below Y. 
         [0026]    One way to use springs to transfer the “intersection” of X and Y up to a front panel includes the use of two concentric or side-by-side springs on a substrate such as the control board, or any other type of substrate, such as a piece of plastic sheet such as PET or polycarbonate, a glass layer, or other material suitable for supporting electrodes. The substrate may provide a mechanical support with electrical connections to the electrodes by use of discrete wiring. This example embodiment is shown in  FIG. 3 . Here a first X spring  300  and a first Y spring  301  are placed next to each other and pressed in contact with a front panel  302 . A second X/Y pair is shown alongside the arrangement, using the same X line interconnected by a wire or track  303  connected to a second X spring  304  and a second Y spring  305 . In this embodiment, the electric field  306  coupling from the first X spring  300  to the first Y spring  301  also tends to couple  307  to the second Y spring  305 . This may result in touch sensitivity of the second spring pair when touching over the first spring pair. This embodiment uses two springs per touch key. 
         [0027]    In a further embodiment as shown in  FIG. 4 , a common Y spring  400  is shared by two X springs  401  and  402 . Two touch keys are placed physically next to each other for this to function. The use of more than one Y line may result in some lack of key discrimination. 
         [0028]    A further embodiment is shown in  FIG. 5A . A substrate such as control PCB  500  is used to form all the X and Y electrode wiring  501 . A control chip  502  may or may not be present on this control board, but is used to measure capacitive changes in the touch keys. The Y electrodes shown, Y 1   503  and Y 2   504  are connected to a set of Y electrode springs  505 ,  506 ,  507 , and  508 , and  509 ,  510 ,  511 , and  512 , the first group being electrically connected to Y 1  and the second group to Y 2 , using traces on the PCB  500  to affect this interconnection. On the PCB  500  are formed a series of emitter X electrodes called X 1  to X 4   513 ,  514 ,  515 ,  516 ,  517 ,  518 ,  519  and  520 . These electrodes are formed purely as conductive shapes on the surface of the PCB  500 . In one embodiment, the X electrodes may be designed to substantially or completely surround the base of the Y springs  505 ,  506 ,  507 ,  508 ,  509 ,  510 ,  511 , and  512 . As can be seen, eight logical touch keys are so formed  532 ,  533 ,  534 ,  355 ,  536 ,  537 ,  528  and  539 ; X 1 Y 1 , X 2 Y 1 , X 3 Y 1 , X 4 Y 1  and X 1 Y 2 , X 2 Y 2 , X 3 Y 2 , X 4 Y 2 . Hence a total of eight springs are used ( 505 ,  506 ,  507 ,  508 ,  509 ,  510 ,  511  and  512 . The X electrodes, in one embodiment, have sufficient proximity to their neighboring Y spring to keep the electric fields well coupled locally. In  FIG. 5B , a touching object  528  onto the front panel  529  now influences the coupled local X to Y field for predominantly the touch-adjacent touch key. Hence the key discrimination is good. The electric field for a single touch key is shown as  530  and its interaction with the touching object  528  is also shown at  531 . 
         [0029]    An alternative scheme is shown in  FIG. 6A  where the springs  601 ,  602 ,  603 ,  604 ,  605 ,  606 ,  607 , and  608  are now connected to X 1  to X 4  emitters and the PCB  600  electrodes  609 ,  610 ,  611 ,  612 ,  613 ,  614 ,  615  and  616  are connected to Y.  FIG. 6B  illustrates a perspective view of spring  601  coupled to an X emitter electrode  621 . This alternate scheme may have an advantage in some applications where an improvement in key discrimination can be affected by virtue of the fact that the Y lines are rather more shielded by the X springs. Another potential advantage is that the Y electrode area can be reduced and hence help minimize noise injected into the Y line during touch. Attaining maximal signal to noise ratio in capacitive sensing systems helps to ensure reliable operation under electrically noisy conditions. 
         [0030]    In some embodiments shown, the springs compress in such a way that the top of the spring forms a flat “spiral” disc. This lends itself well to coupling with the touching object and allowing an interaction with the electric field below the spiral. 
         [0031]    In  FIG. 6B , the X and Y electrodes  621  and  609  are shown as a disk  621  and concentric ring  609  physically separated from each other. Many other configurations of electrodes may be used in further embodiments. Further embodiments may feature increased shared electrode edges where field lines concentrate. 
         [0032]    An alternative arrangement uses a substantially coaxial arrangement, where the springs are connected to X and surround simple Y receiver electrodes on the PCB. This is shown in  FIGS. 7A and 7B  for a pair of touch keys. The PCB  700  uses conductive electrodes for the two Y 1  receivers  701  and  702 . The X 1  emitter is formed from two springs  703  and  704 . The front panel  705  and touching object  706  are shown together with an approximate field distribution  707  and touch interaction  708 . As can be seen, the field is displaced away from the Y receiver in favor of the touching object  706 . This causes a drop in capacitance between X and Y as with the other embodiments. This method has a distinct advantage that the springs can be very simple in design, with no special flat-top arrangement. The touching object  706  effectively touches “inside” the coils of the spring influencing the field  707  and  708 . The spring can be driven from the PCB connection  700  using a contact formed by any conductive means e.g. solder, mechanical clip, glue or simple restraint against a conductive opposing pad on the PCB. Other methods will be obvious to those of normal skill in the art. This embodiment shares the advantage of  FIGS. 6A and 6B  in that the X spring acts to partly shield the Y receiver and the area of the Y receiver can be made relatively small to aid noise immunity. 
         [0033]    Not shown is another embodiment, similar to  FIGS. 7A and 7B  where the springs are connected to Y and the PCB electrodes to X. In a similar way as described in the previous examples, this is equally valid but may show degraded key discrimination and noise immunity in some applications. 
         [0034]    In  FIGS. 7A and 7B  it should be understood that the Y electrode shape can take various forms. Importantly, as shown in  FIG. 8 , this can include a hole  801  in the electrode  802  formed on the PCB  800 . This is very useful to facilitate the placement of a light emitting device, shown in two alternative positions  803  and  804 . There are many configurations of electrode and hole that can be devised. It is also possible to form the PCB electrode from a conductive material that is substantially transparent to allow light to shine through from below. It is also possible to combine the electrode with some form electroluminescent light generation local to the centre of each spring. This is shown in  FIG. 9 . The PCB  900  and spring  901  are shown, and in the middle of the spring  901  is shown an electrode structure where a transparent Y electrode  902  is formed on top of a phosphor  903  layer and a second electrode  904  that may be either grounded or actively driven. A control chip  905  time multiplexes capacitive measurements with electroluminescent high voltage drive  906  periods. This arrangement permits the light emitting layer to be created directly beneath the touch key active area with a very low profile and uniform illumination. 
         [0035]    A similar light emission method can also be conceived where rather than an electroluminescent layer being used, instead a light diffuser sheet is placed below the PCB electrodes (again, being of substantially transparent material to allow the light to pass upwards towards the panel). The light diffuser sheet is well known in the art and typically is illuminated from the edges, uses total-internal-reflection (TIR) to guide the light to chosen areas where is then allowed to escape using a variety of techniques to disrupt the TIR process (mechanical stress, small ridges on the surfaces, refractive index mismatches etc). 
         [0036]    Another illumination method is shown in  FIG. 11 . Here, a coaxially mounted light emitting device  1100  in the centre of the spring  1101 , uses a reflective sleeve  1102  running up the inside of the spring  1101  and stopping just before the inner surface  1103  of the front panel  1104 . The sleeve may be made of any reflective material. 
         [0037]    The spring used in  FIG. 7  can also utilize an inward compressible spiral that flattens on compression. This is shown in  FIG. 10 . An advantage of this method is that it helps to even more completely shield the electrode below  1001 . This may provide noise suppression advantages. The coil of the spring that spirals inwards  1005  may have a moderately open structure to allow the touching object  1002  to interact with the electric field  1003  formed between the spring  1004  and the electrode  1001  on the PCB  1000 .