Abstract:
An inductive touch key switch assembly and circuit are provided. The circuit optimizes signal strength and noise immunity by reducing the number of long paths through the circuit board and localizes the driver circuit to each key switch assembly sensor coil. The key switch assembly optimizes placement of the target to enable the user interfaces on domestic appliances and products having present values of front panel thickness.

Description:
FIELD OF THE INVENTION 
       [0001]    The instant invention relates to an inductive touch key switch and its associated control circuit, wherein the inductive touch key switch user interface is adapted for use with a control circuit having drive elements localized to each key switch. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    Generally, inductive touch key switches and circuits are known. For example, referring now to  FIG. 1 , MICROCHIP TECHNOLOGY INC. (“MICROCHIP”) of Chandler, Ariz. has published an inductive touch key switch assembly design  10  (the “MICROCHIP Design”) that uses a magnetic coupling between a solid metal target  12  and an inductive sensing or sensor coil  14 , separated from one another by a spacer layer  16 . The spacer layer  16  defines a cavity or pocket into which the solid metal target  12  can flex when pressed, thus changing the proximity to, and the field around, the sensor coil  14 , which is mounted to, printed on and/or etched into a printed circuit board PCB  19 . More particularly, pressing the inductive key switch defined on a front panel  18  causes the coupling between the target  12  and sensor coil  14  to change, thus indicating a key press. The front panel  18 , also called the top key switch layer or fascia, can be the outermost skin of the product or domestic appliance of which the keyboard is a part. The MICROCHIP Design suggests that materials of choice for a combined fascia layer/target are copper, aluminum, brass, stainless steel and mild steel, but a target in accordance with the design could also be made from gold and/or silver, so long as the material permits a physical deformation of the target over the sensor coil. Specific target embodiments disclosed in the MICROCHIP Design include a copper lamination and a self-adhesive copper label stuck to the underside of the fascia. The MICROCHIP Design states that, generally, the target  12  should be the size and shape of the sensor coil  14 . 
         [0003]    What is needed is an improved target design for use with an inductive touch key switch system. 
         [0004]    Additionally, in accordance with the MICROCHIP Design, a microcontroller is provided to periodically poll various sensors by measuring the impedance of a sensing coil. If the impedance of the sensing coil has changed, then the microcontroller determines if the shift in impedance is sufficient to qualify as a user&#39;s press. In the MICROCHIP Design, the individual sensing coils (i.e., one for each switch) are connected, by a single common connection, to a “reference coil” that acts as a reference inductor, allowing a ratio-metric measurement which removes several sources of drift. As shown in  FIG. 2 , the inductive touch circuit of the MICROCHIP Design utilizes a single driver circuit to drive each of the sensing coils, each of which is tied through a common connection to the reference coil. 
         [0005]    However, in many applications, the outer material of a key switch (the fascia) is made from a relatively thick piece of stainless steel, for example, 0.032-0.036 inches thick. However, using the calculations taught in the MICROCHIP Design, to produce a 0.010 mm movement of an inductive key switch having a target fascia/target thickness of 0.036 inches under 1.1 lb force key press would require a sensing coil having a diameter of 2.15 inches. Such a sensing coil diameter would be impractical for the landscape of the device keyboard, i.e., requiring a key spacing of more than 2 inches. Also, it was found that, with such materials, a drive current needed to be sufficiently high so as to induce eddy currents in the metal. However, higher drive currents in the large drive loops on the PCB can cause crosstalk and loss of signal strength in the circuit. Additionally, the circuit loops can pick up signals from external fields (i.e., large loops on the PCB layout pick up noise signals). However, the use of “reference coils” in the MICROCHIP Design forces the inclusion of large current loops in the PCB layout, as every sensing coil in the keyboard must pass its current to the reference coil. This increased noise/decreased signal strength problems are even further exacerbated when a keyboard is long, rather than of a small, square shape. 
         [0006]    The MICROCHIP Design suggests that, as an alternative solution, the reference coil can be omitted and software can be provided to compensate for drift. However, the MICROCHIP Design specifically discloses that such software can become complex and can significantly increase the burden on the microcontroller, whereas the inclusion of the reference inductor on the board is minimal and, therefore, the MICROCHIP Design specifically states that omitting the reference coil is not recommended, once the increase in software complexity is considered. 
         [0007]    What is needed is an inductive touch key switch and circuit that improves noise immunity and signal strength, without requiring the addition of the complex software described in connection with the MICROCHIP Design. 
       SUMMARY OF THE INVENTION 
       [0008]    It is accordingly an object of this invention to provide an inductive touch key switch and circuit that overcomes the disadvantages of the prior art. In one particular embodiment of the invention, an improved inductive touch key switch is provided. In another embodiment of the invention, an inductive touch key switch circuit that does away with the reference inductor without requiring the addition of complex software is provided. 
         [0009]    Although the invention is illustrated and described herein as embodied in an inductive touch key switch assembly and circuit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims. 
         [0010]    The construction of the invention, however, together with the additional objects and advantages thereof will be best understood from the following description of the specific embodiments when read in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which: 
           [0012]      FIG. 1  is a cross-sectional view of an inductive touch sensor assembly in accordance with the prior art; 
           [0013]      FIG. 2  is a block diagram of an inductive touch circuit in accordance with the prior art; 
           [0014]      FIG. 3  is a circuit diagram of an inductive touch key switch circuit in accordance with one particular embodiment of the present invention; 
           [0015]      FIG. 4  is a cross-sectional view of an inductive touch key switch assembly in accordance with one particular embodiment of the instant invention; 
           [0016]      FIGS. 5-7  are cross-sectional views of inductive touch key switch assembly in accordance with other particular embodiments of the instant invention; 
           [0017]      FIG. 8A  is an isometric view of a disc used as a target in accordance with one particular embodiment of the instant invention; 
           [0018]      FIG. 8B  is a side plan view of the disc of  FIG. 8A ; 
           [0019]      FIG. 9A  is an isometric view of a legged disc used as a target in accordance with one particular embodiment of the instant invention; 
           [0020]      FIG. 9B  is a side plan view of the legged disc of  FIG. 9A ; 
           [0021]      FIG. 10  is a view of a dome or cap shaped target in accordance with another embodiment of the instant invention; 
           [0022]      FIG. 11  is an isometric view of a rectangular target in accordance with another embodiment of the present invention; 
           [0023]      FIGS. 12-15  are cross-sectional views of inductive touch key switch assembly in accordance with further particular embodiments of the instant invention; 
           [0024]      FIG. 16  is a top plan view of one particular embodiment of a multi-leaf target in accordance with another embodiment of the instant invention; 
           [0025]      FIG. 17  is a top plan view of the metal deposition layer of a sensor coil in accordance with one particular embodiment of the present invention; 
           [0026]      FIG. 18  is a perspective, exploded view of the metal deposition layers of a multi-level coil in accordance with one particular embodiment of the present invention; 
           [0027]      FIG. 19A  is a partial, cut-away, side plan view of an inductive touch keyboard in accordance with one particular embodiment of the invention; 
           [0028]      FIG. 19B  is a partial, exploded view of a portion of the keyboard of  FIG. 19A ; 
           [0029]      FIG. 20A  is a perspective view taken from the top of one particular embodiment of a frame for use in the keyboard of  FIG. 19A ; 
           [0030]      FIG. 20B  is an enlarged partial top plan view of a frame including key switch members in accordance with one particular embodiment of the invention; 
           [0031]      FIG. 21A  is a top plan view of a key switch member in accordance with one particular embodiment of the invention; 
           [0032]      FIG. 21B  is a perspective view, taken from the top, of the key switch member of  FIG. 21A ; and; 
           [0033]      FIG. 21C  is a perspective view, taken from the bottom, of the key switch member of  FIGS. 21A and 21B ; 
           [0034]      FIG. 22  is a top plan view of one possible PCB layout for each inductive touch key switch assembly in accordance with one particular embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    An inductive touch key switch assembly and circuit are provided herein, which, under certain circumstances, can be used to improve both the signal strength and the noise immunity of the instant invention over that of the MICROCHIP Design. 
         [0036]    Referring more particularly to  FIG. 2 , there is shown a block diagram of a prior art inductive touch key switch system  20  in accordance with the teachings of the MICROCHIP Design. In order to measure the impedance of an individual sensor or sensing coil  26 , the system  20  produces a pulse at the pulse width modulator (PWM)  22 , which is converted into a drive pulse by the driver  24  that is used to excite, in turn, each individual sensor coil  26 . This produces a pulsed voltage across the excited sensor coil  26  that is proportional to both the current and the impedance of the coil  26 . The pulsed voltage from the sensor coil  26  is further processed and analyzed to determine whether a shift in impedance has occurred, indicating a user&#39;s touch. As shown in  FIG. 2 , each of the sensor coils  26  are connected at one end to a single common connection with a reference coil  28 . As described hereinabove, the connection to such a reference coil forces the creation of long paths in the PCB layout that pick up noise and decrease signal strength, especially in long keyboards. 
         [0037]    Referring now to  FIG. 3 , there is shown one particular embodiment of an inductive touch key switch circuit  100  of the present invention that provides improved noise immunity and signal strength transmission. In particular, the number of long, noisy paths inherent in the prior art system are greatly reduced. As can be seen from the circuit of  FIG. 3 , each of the sensor coils  110  of the system  100  is tied at the common connection directly to ground  112  (i.e., and not through any other serially connected circuit element), and not to a reference coil, thus obviating the need to extend a path from each sensor coil to a common reference coil. Thus, no energy goes to the reference coil, thereby reducing the ratio change when a key press is detected. If desired, in one particular embodiment of the invention software filtering is added to compensate for drift, in place of the omitted reference coil. 
         [0038]    Further, the circuit  100  also eliminates long paths from a common driver circuit to each sensor coil  110  by providing individual drive or driver circuits  120  for exciting each coil  110 . More particularly, each of the driver circuits  120  are provided local to (i.e., in close proximity to) the sensor coil  110  that it drives. For example, the driver circuit  120   a  is located on the PCB near the sensor coil  110   a . Similarly, the remaining individual driver circuits  120  are located on the PCB near the respectively connected sensor coil  110 , driven by the individual driver circuit  120 . For example,  FIG. 22  shows a representative metal layer  160  of a PCB layout in accordance with one particular embodiment of the present invention. In the metal layer  162 , the metal forming the sensor coil  162  is laid on the PCB proximal to the metal tracks  166  and contacts or pads  164  for the elements of the drive circuit (i.e., a drive transistor, input resistor(s), output resistor(s), etc.). In particular, for each sensor coil  162  of a keyboard, the metallization for the contacts for the drive circuit associated with that sensor coil  162  is located, at most, a few millimeters away from the outermost winding of the sensor coil  162 , and thus, can shorten the lead lengths between a drive circuit and the sensor coil  162  that it drives. 
         [0039]    As illustrated in  FIG. 3 , each of the plurality of driver circuits  120  includes its own drive transistor T 1  and resistor and capacitor elements used to define the drive current. In one particular embodiment of the invention, each of the drive circuits  120  includes at least a drive transistor T 1 , a first input resistor Rin 1 , connected between the base of the transistor T 1  and a clock input for the respective driver circuit  120 , a second input resistor Rin 2 , connected between the base of T 1  and a DC power supply, an output resistor Rout and a capacitor C 1 . For purposes of example only, in one particular embodiment of the invention, Rin 1  is 470 ohms, Rin 2  is 100 ohms, Rout is 270 ohms, C 1  is 1 μF and the power supply is 5 Volts DC. The value of the inductors  110  are chosen based on a number of factors, including the outer radius of the coil, the number of turns in the coil and the depth of the coil. Each sensor coil  110  is periodically sampled, via a sampling output shown in  FIG. 3 , by a microcontroller or microprocessor (not shown). Note that, although the transistor T 1  is illustrated as being a pnp transistor, this is not meant to be limiting, as the circuit can be adapted to use an npn transistor. 
         [0040]    As shown in  FIG. 3 , each sensor coil  110  of the instant embodiment is driven by only one driver circuit  120 , and conversely, each driver circuit  120  drives only one associated sensor coil  110 . This prevents the need for routing higher currents around the PCB (i.e., from a central, common driver circuit to each individual sensor coil). The localization of each of a plurality of driver circuits to its one associated sensor coil results in a small current loop through the sensor coil of each key assembly, without much current/noise radiating outside of the coil. Thus, the less current/noise radiated outside the coil, the less can be picked up by other sensor coils. Eliminating the reference coil and moving the driver circuit local to each coil/key assembly allows for better use of the sensing current and energy, as well as making the loop area smaller to reduce the pick-up from external noise fields (as each coil can act as an antenna to external fields). These circuit changes also result in less connections being routed across the PCB. Since keyboards for appliances tend to be narrow, this also helps to reduce their complexity and permits the fabrication of the assembly using fewer layers in the PCB design than traditional assemblies. This, resultantly, reduces the cost for producing the assembly. 
         [0041]    Since, in the above-described embodiment of the present invention, nearly all external fields will form a uniform field localized to the individual coil/key assembly, noise pick-up by the coil can be further reduced by adding a shorted turn outside of the coil in the PCB foil. This will tend to reduce some of the signal strength, but since it is outside of the coil area and the coil induced field is concentrated near the coil pattern, it does not make a large reduction in signal strength. The shorted turn, however, will reduce uniform external fields, since they come from outside of the coil pattern. 
         [0042]    Additionally, if desired, noise pick-up by the sensor coil can be further reduced by adding turns outside of the sensor coil, as an extension of the sensor coil, but of reverse direction. See, for example,  FIG. 17 , wherein the turns  510  of the sensor coil  500  turn in a first direction, but reverse at the turn portion  515  to include a plurality of turns  520  in the reverse direction. The use of such extra turns  520  will reduce field strength such that, to external fields, the loop area of the sensor coil minus the loop area of the reverse direction turns results in pick-up by (N coils—x reverse turns) 2 . Note that only a few large reverse turns will equal the same loop area of many small turns in the coil. 
         [0043]    Referring now to  FIG. 18 , there is shown a further embodiment of a multi-level or multi-layer sensor coil  530  that can be used as the sensor coil in a system in accordance with the instant invention. In particular, the multi-layer sensor coil  530  includes two individual sensor coils  540 ,  550  that overlay one another on the surface of the PCB (not shown), and which share commonly connected input  542 ,  552  and output contacts  544 ,  554 . In particular, the coil  550  is wound in an opposite direction to that of the coil  540 , and overlays the coil  540  on the PCB. Both input contacts  542  are connected to a sense input (shown, for example, in  FIG. 3 ) of a microcontroller or microprocessor (not shown), which is programmed to evaluate the measurements taken across the sensor coil  530 . The output contacts  544  and  554  are connected to a common reference potential such as ground The multi-layer coil provides for a greater field strength and better eddy currents, which result in a better signal back when movement of the target occurs. The PCB can further include offset vias to avoid blind vias and to help keep down the cost down. Note that, although two coils are shown in the exemplary illustration of  FIG. 18 , this is not meant to be limiting, as even more layers of coils can be provided, if desired. However, it should be understood that increasing the number of layers of coil in the sensor coil  530  correspondingly decreases the spacing between the uppermost surface of the sensor coil  530  and the target portion of the key switch, due to the increased thickness of the layers on the PCB. A corresponding adjustment to the spacing between the uppermost coil layer and the target can be made to accommodate for the increased layer height on the PCB, if desired. 
         [0044]    Another benefit of localizing the driver circuits is that, if desired, the driver circuits  120  can be configured to permit key to key variations in drive strength. For example, differently sized keys (and their associated coils) may need different levels of signal strength. The driver voltage can be varied from one sensor coil/key assembly to another by a fixed value. Alternately, if desired, the driver voltage can be varied from one sensor to another as a software variable using an adaptive algorithm. 
         [0045]    A further advantage to the localization of the driver  120  to the location of the associated sensor coil  110  is that the delay of the drive pulse can be optimized to get all useful signals into the detector, as compared to a synchronous detector system. In particular, the delay can be much improved by moving the drive transistor and sense resistor to the coil location, as previous drive pulse delay times were affected by temperature and part variation. 
         [0046]    Additionally, in one particular embodiment of the invention, noise was further reduced by adding coil layers in the PCB design. For example, in accordance with the present embodiment, coils can be stacked in double sided PCBs. In one very particular embodiment, four layers of coils were stacked in a four layer PCB by offsetting the via, to avoid hidden vias. 
         [0047]    Referring now to  FIG. 4 , there will be described an inductive touch key switch assembly  200  providing improved signal strength and mechanical stability in an inductive touch key switch system in accordance with one particular embodiment of the present invention. The key switch assembly  200  of the instant embodiment is disposed below a portion of the front panel or fascia  218  (i.e., the front panel of the keyboard, product and/or domestic appliance) defining a key switch of the user interface. In one particular example, the front panel  218  and thus the user interface, is a thin stainless steel plate. However, in contrast to the prior art key switch assembly illustrated in  FIG. 1 , the target  212  of the key switch assembly  200  is not adhered to the underside of the fascia  218 , but rather, is supported by a frame  216  disposed between the fascia  218  and the PCB  219 . 
         [0048]    The frame  216  is formed as a bracket or pocket defining a space or cavity  217  around the sensor coil  214 . Most preferably, the frame  216  is a separate, stand-alone piece made of plastic and includes a support bracket  216  surrounding the sensor coil  214 , at the top of which is a bridging section  216   a  that passes over the sensor coil  214  and under the fascia  218 , adjacent to, and in contact with, the underside of the fascia  218  at a location defining a key switch on the user interface of the front panel  218 . A metallic target  212  of the instant embodiment is adhered to the underside of the bridging section  216   a , in the cavity  217 , above the sensor coil  214 . The support bracket  216  can be made as a frame (i.e., four legs or four walls, etc.) or can be in the shape of a ring covered by the bridging section  216   a . This frame can be connected to the PCB  216  by screws, heat staked connectors, or other known connection methods. In the instant embodiment, the bridging section  216   a  is designed to be very thin plastic, so that flexure of the fascia  218  will result in flexure of the bridging section  216   a . In one particular example, the thickness “A” of the bridging section  216   a  is 0.8 mm. 
         [0049]    Upon flexure of the fascia  218  and, resultantly, the bridging section  216   a , the metallic target  212  on the underside of the bridging portion is additionally flexed, thus changing between the target  212  and the sensing coil  214 , indicating a key switch press. Thus, in the instant embodiment, the target  212  is supported by a structure disposed between the front panel fascia  218  and the PCB  219 , and is not directly adhered to the underside of the front panel fascia  218 . 
         [0050]    Rather, as noted above, the target  212  of the key switch assembly  200  is adhered to the underside of the bridging section  216   a , to bring the target  212  into the desired relationship to the sensor coil  214 . In one particular embodiment of the instant invention, the target  212  is applied to the underside of the bridging section as part of a heat stamping process. Alternatively, if desired, the target  212  can be applied to the underside of the bridging section  216   a  by printing the target directly on the backside of the fascia to create a metal surface above the sensor coil. For example, in accordance with the instant embodiment, a heat stamped foil or a conductive printing material can be applied to the frame  216  by an appropriate process (i.e., heat stamping, printing, etc.). The heat stamping or printing of the target  212  on a surface of the frame  216 , rather than the fascia  218 , can be especially useful in applications where adjacent lighting is needed and/or curved surfaces are used. 
         [0051]    In one particular embodiment of the invention, a portion of the front panel  218  defines a user interface or keyboard for a product or domestic appliance. Using a heat stamping process, a metal foil is stamped onto the internal surface of the plastic bracket or pocket. In the instant embodiment, the foil is desirably between 0.05 mm and 0.1 mm in thickness. Thus, in the instant embodiment, the traditional PCB based keypads are replaced by a heat stamped foil or printed conductive layer supported by a separate bracket. 
         [0052]    Alternately, as described above, a printing process can be used to print a conductive material onto the underside of the bridging section  216   a . The thickness of the printed material would be similar to that for the heat-stamped foil, i.e., most preferably between 0.05 mm and 0.1 mm. 
         [0053]    Referring now to  FIG. 5 , there is shown another embodiment of a key switch assembly  220  in accordance with the present invention. The key switch assembly  220  is similar to the key switch assembly  200  of  FIG. 4 , but is directed towards a user interface including key switches having some kind of lighted indicia, such as words, light rings and/or other lighted indicators, but which include an opaque plate. The key switch assembly  220  includes a target  212  mounted to the bridging section  226   a  of a frame  226  in a particular plane relative to a sensor coil  214 . As with the previous embodiment, flexure of the key switch fascia  228  results in the flexing of the bridge section  226   a , which changes the coupling between the target  212  and the sensor coil  214 , indicating a key press of the key switch fascia  228 . However, in the instant embodiment, the frame  226  of the instant embodiment is made of a clear or other light transmissive plastic, so that light emitted from a light source can be transmitted to the ring, words or indicia on the user interface. Although any suitable type of light source may be used (i.e., incandescent, electroluminescent, etc.) in connection with the present invention, in one preferred embodiment the light source includes light emitting diodes (LEDs)  230  mounted to the underside of the PCB  229 . 
         [0054]    In one particular embodiment of the invention shown in  FIG. 5 , the plastic frame includes a light transmissive ring portion  226   b , which surrounds an opaque key switch fascia  228 . Alternately, or in addition thereto, the key switch fascia  228 , itself, can have cutout portions, such as words or other indicia, that are intended to be lighted. Light emitted by the LEDs  230  are used to illuminate the ring and/or indicia, as follows. Light from the LEDs  230  pass through the PCB  229  via holes  222  in the PCB  229  located adjacent to the light emitting face of the LEDs. The holes  222  open into the cavity  227  formed in the frame between the target  212  and the sensor coil  214 . The light emitted directly into the cavity  227 , as well as that light reflected from the metal target  212 , is transmitted by the frame  226  to the light ring portions  226   b  of the frame  226 , and/or to any indicia or words on the fascia  228  and/or the front panel  218 ′. If desired, the frame  226  can optionally include facets  226   c  particularly located to direct and concentrate light emitted by the LEDs  230  into the cavity  227  onto the light ring portions  226   b . Additionally, if desired, the frame  226  can include opaque or non-light transmissive portions  224 , to block the light emitted in connection with one key switch assembly from being transmitted to another key switch assembly. In one particular embodiment of the instant invention, the PCB  226  located in the cavity  227  has an applied white coating, to even further reflect light from the cavity  227  into the light transmissive frame  226 . 
         [0055]    As with the key switch assembly  200 , the target  212  of the key switch assembly  220  can be applied to the frame  226  in a variety of ways including, but not limited, heat stamping the target  212  to the frame  226  and/or printing the target  212  to the frame  226  using a conductive ink. Note that, if desired, the target  212  can also be made as a metal disc or foil that is adhesively applied to the underside of the bridging section  226   a , without deviating from the spirit of the instant invention. 
         [0056]    Referring now to  FIG. 6 , there is shown a further embodiment of a key switch assembly  300  for an inductive touch key switch in accordance with the present invention. The key switch assembly  300  includes a frame  310  disposed between the PCB  302  and the front panel  318  of the user interface of an appliance, similar to the frame  216  described in connection with  FIG. 4 . The frame  310  of the assembly  300  includes a bridging section  310   a , located adjacent to, and in contact with, the underside of the front panel  318  at a location defining a key switch on the front panel  318 . The bridging section is preferably made of a thin plastic material, having a thickness “B” that permits it to flex in response to flexure of the front panel  318 . In one particular embodiment, the dimension “B” is 0.8 mm. 
         [0057]    The frame  310  additionally includes a push pin or boss  310   b  extending from the middle of the bridging portion  310   a , towards the sensor coil  320 . In the instant embodiment of the invention, the target  330  is in communication with the distal end of the boss  310   b  and has a circumference that is greater than the circumference of the sensor coil  320 , thus circumscribing the sensor coil  320 . As can be seen, flexure of the front panel  318  above the bridging section  310   a  will cause the push pin  310   b  to push a portion of the target  330 , thus flexing the target  330  and, resultantly, changing the coupling between the target  330  and the sensor coil  320 , indicating a key switch press. In the present embodiment of  FIG. 6 , the target  330  is formed as a dome-shaped cap, as shown more particularly in  FIG. 10 . 
         [0058]    Note that other shapes of target can be used in connection with the frame  310  to achieve the same results. For example,  FIGS. 9A-9B  show a legged “disc”  332  that can be surface mounted (via the extending leg portions) on the PCB  302 , in place of the target  330  of  FIG. 6 , wherein flexure of the front panel  318  over the frame  310  causes the boss  310   b  to flex the legged disc  332 , thus changing the coupling between the target  332  and the sensor coil  320 , indicating a key switch press has occurred. The legged disc  332  of  FIGS. 9A and 9B  can be formed by chemically etching and/or stamping of the metal to be used as the target. 
         [0059]    Similarly, referring now to  FIGS. 6 and 11 , instead of the dome or cap shaped target  330 , a target  334  in the shape of a square or rectangle (i.e., “box-shaped”) can be placed over the sensor coil  320  and activated by the boss  310   b  upon flexure of the front panel  318  over the frame  310 . 
         [0060]    Referring now to  FIG. 7 , there is shown a further embodiment of a key switch assembly  340  utilizing a frame  350  having a boss  350   a  to transmit the flexure of the key switch fascia  228  to the PCB board mounted target  330 , wherein light from a light source, LEDs  230  in the current embodiment, pass through holes  222  in the PCB  355 . In the instant embodiment, the frame  350  is made from a light-transmitting material, such as a clear plastic. The frame  350  is, therefore, aligned with the holes  222 , to cause light to show from the ring portions  350   b , as well as through any words or indicia cut into the key switch fascia  228 . Note this is not meant to be limiting, as other arrangements of the LEDs, holes  222  and frame  350  can be implemented in accordance with the present invention. For example, the LEDs  230  and holes  222  can be arranged to illuminate the central cavity  317  of the frame  350 , and through this, the frame  350  and ring portions  350   b , in the same manner as described in connection with the frame  226  of  FIG. 5 . 
         [0061]    Additionally, if desired, the LEDs  330  can be replaced with LEDs mounted on the front side of the PCB  355 . Referring now to  FIGS. 12 and 13 , there are shown two further lighted key switch assemblies  400 ,  430 , respectively, in accordance with additional embodiments of the instant invention. More particularly,  FIG. 12  shows an key switch assembly  400  wherein the LEDs  410  are mounted on the front side of the PCB  415 , with their light emitting faces pointed towards the sidewalls of the frame  420 . In  FIG. 13 , the LEDs  450  are surface mounted on the PCB  445  within the cavity  447  of the frame  440 , with their light emitting faces being directed towards the front panel  457 . It can be seen from the foregoing that other configurations of a lighted key switch assembly can be made using a light transmissive frame in communication with a target in accordance with the present invention. 
         [0062]    Referring now to  FIG. 14 , there is shown another embodiment of a key switch assembly  500  in accordance with the present invention. The key switch assembly  500  is similar, in many respects, to the key switch assembly  300  of  FIG. 6 . However, instead of using a surface mounted target sandwiched between the boss and the PCB, as with the key switch assembly  200 , the instant embodiment uses a floating target  510  secured to the boss  310   b . As such, flexure of the bridging portion  310   a , rather than causing flexure of the target  510 , brings the target closer to the sensor coil  214 , thus changing the field of the sensor coil  214  and indicating a key press. Although any of the targets described herein in connection can be used as the target  510 , in one particularly preferred embodiment, the target  510  is a cut or stamped disc, such as the disc  338  illustrated in  FIGS. 8A and 8B , herein. The diameter of the disc  338 ,  510  can be chosen, as desired, but is preferably equal to or greater than the diameter of the sensor coil  320 . It can also be seen that the floating target  510  of  FIG. 14  can be used in a lighted key assembly, in accordance with the teachings herein. For example, the floating target  510  can replace the surface mounted target  330  in the key switch assembly  340  of  FIG. 7 , or in any other embodiment described herein. 
         [0063]    Additionally, in accordance with the teachings made in connection with  FIG. 14 , multiple floating targets of multiple key switch assemblies can be implemented using a single, multi-leaf floating target, such as that shown in  FIG. 16 , if desired. 
         [0064]    Referring now to  FIG. 15 , there is shown a further embodiment of an inductive touch key switch assembly  550  in accordance with the present invention. In the present embodiment, instead of being disposed between, and in communication with, the PCB  555  and the front panel  318 , the frame  560  is disposed between a ground plane PCB  565  and the front panel  318 , which is disposed above the PCB  555  supporting the sensor coil  320 . The ground plane PCB  565  is separated from the PCB  555  by a spacer  570 , which includes a circular cut-out above the sensor coil  320 , thus creating a cavity or chamber above the sensor coil  320 . The frame  560  is supported on the ground plane PCB  565  by its outer wall portions over solid portions of the spacer layer, thus supporting the frame  560  when a key switch indicated on the front panel  318  above the assembly  550  is pressed. The frame additionally includes, extending from the middle portion thereof, a boss  560   a , in contact with a portion of the ground plane PCB  565 . Flexure of the front panel  318  over the boss  560   a  causes the boss  560   a  to flex the PCB  565 . The portion of the PCB  565  disposed below the boss  560   a  includes a metal target  570  disposed on the bottom side thereof, adjacent the sensor coil  320 . Thus, flexure of the front panel  318  is transmitted, by the frame  560  to the target  570 , which changes the coupling between the target  570  and the sensor coil  320 , indicating a key switch located above the assembly on the user interface has been pressed. In one particularly preferred embodiment, the target  570  is either printed or heat-stamped onto the undersurface of the PCB  565 . Note that other methods of depositing the target  570  onto the PCB  565  can be used, including all known methods for providing metallization of a PCB. 
         [0065]    Referring now to  FIGS. 19A-21C , there is shown another particular embodiment of an inductive touch key switch and assembly that can be used in connection with the inductive touch key switch system of the instant invention. In particular, the keyboard  600  includes a plurality of lighted key switches  640 , wherein the key switch member  640  acts as both the light pipe for transmitting the light through the fascia or front panel  610 , as well as the force translator for moving the target relative to the sensor coil. In particular, a back-lit key switch  640  is provided that includes lighted protrusions  640   a , which form a light ring, and which pass through openings  610   a  in the opaque front panel  610 . The key switch members  640  are held in place in a frame  620  disposed between the front panel  610  and a PCB  630 . The frame  620  can be secured in place by the adhesive layers  615  located between the frame  620  and the PCB  630  and the frame  620  and the front panel  610 . As with the prior embodiments, each key switch will be disposed in the frame over a corresponding sensor coil located on the PCB  630 . The frame  620  can be aligned relative to the front panel  610  using the alignment pins  622 , if desired. 
         [0066]    Each key switch member  640  is designed to mate with an opening  620   a  of the frame  620 , with the light transmitting protrusions  640  passing through the front panel  610  of the assembly  600 . A planar face  640   c  of the key switch member  640  is provided to support an adhesive layer and/or the front panel  610 . The key switch member  640  is maintained in the frame (as shown in  FIG. 20B ) by the lugs  640   b  and notch  640   e , which engage the back side of the frame  620 , i.e., the side distal from the front face  610 . A target (not shown in  FIGS. 19-21 ) can be disposed directly on the rear face  640   d  of the key switch member  640  by heat stamping, adhesive and/or conductive printing. In one particular embodiment, the target is a piece of metallic foil adhered to the rear face  640   d.    
         [0067]    Upon assembly, each key switch member  640  is supported above a sensor coil by the frame  620  and/or an adhesive layer  612  (which does not pass under the portion of the key switch member including the target). The target on the rear face  640   d  of each key switch member  640  is disposed in the desired relationship with a sensor coil, as described elsewhere herein. As such, pressing the front face or fascia located over a key switch member  640  will result in flexure of the key switch member  640 , thus changing the coupling between a target on the bottom face  640   d  of the key switch member  640  and the target. 
         [0068]    It is important to note that the key switch assemblies described in connection with  FIGS. 4-7 ,  12 - 15  and  19 - 20  can be used with the circuit shown in  FIG. 3 , but is not limited thereto. In particular, the improved inductive touch key switches described herein in connection with  FIGS. 4-7 ,  12 - 15  and  19 - 20  can also be used with other inductive touch key switch driver circuits, including, but not limited to, the prior art driver circuit described in connection with  FIG. 2 . 
         [0069]    Although the invention is illustrated and described herein as embodied in an inductive touch key switch, circuit and method, it is nevertheless not intended to be limited to only these details shown. For example, if desired, the inductive touch circuit of the instant invention can be modified to include a reference coil implemented in one key position of the keyboard. In such a configuration, the reference coil is used to aid in drift compensation as a standard reference with no key movement permitted. As can be seen, various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.