Patent Publication Number: US-9886143-B2

Title: Multi-function sensing apparatus

Description:
TECHNOLOGICAL FIELD 
     Embodiments of the present invention relate to sensing. 
     BACKGROUND 
     A capacitance touch sensor arrangement may be used to detect a user touch. 
     When a user touches the touch sensor arrangement charge is sourced from or sunk at the user changing the capacitance of the touch sensor arrangement. This enables the touch to be detected. 
     BRIEF SUMMARY 
     According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising: a capacitance touch sensor arrangement configured to have a variable capacitance that varies when a conductive object approaches; and at least one variable impedance sensor configured to have a variable impedance that varies with a sensed parameter; an output node; and at least one switch configured to provide, in a first configuration, an output impedance at the output node that depends upon the variable capacitance and configured to provide, in a second configuration, 
     an output impedance at the output node that depends upon the 
     variable impedance. 
     According to various, but not necessarily all, embodiments of the invention there is provided an apparatus comprising: a first electrode, a second electrode configured to provide an output signal, a switch configured to switch between a first configuration and a second configuration, wherein when the switch switches from the second configuration to the first configuration, it reduces the impedance between the first electrode and the second electrode, 
     wherein, when the switch is in the first configuration, the first and second electrodes form a capacitance touch sensor arrangement configured to have a variable capacitance that varies when a conductive object approaches; 
     and wherein, when the switch is in the second configuration, the first and second electrodes form a variable impedance sensor configured to have a variable impedance that varies with a sensed parameter. 
     According to various, but not necessarily all, embodiments of the invention there is provided a method comprising: performing proximity detection by controlling switching of an apparatus comprising: a capacitance touch sensor arrangement configured to have a variable capacitance that varies when a conductive object approaches; and at least one variable impedance sensor configured to have a variable impedance that varies with a sensed parameter; and an output node, to a first configuration in which an output impedance at the output node depends upon the variable capacitance; and sensing a parameter by controlling switching of the apparatus to a second configuration in which an output impedance at the output node depends upon the variable the variable impedance. 
    
    
     
       BRIEF DESCRIPTION 
       For a better understanding of various examples that are useful for understanding the brief description, reference will now be made by way of example only to the accompanying drawings in which: 
         FIG. 1  illustrates an example of an multi-function sensing apparatus; 
         FIG. 2  illustrates an example of an multi-function sensing apparatus; 
         FIG. 3A  illustrates schematically the apparatus of  FIG. 2  when the switch is in the first configuration; 
         FIG. 3B  illustrates schematically the apparatus of  FIG. 2  when the switch is in the second configuration; 
         FIG. 4  illustrates an example of an multi-function sensing apparatus; 
         FIG. 5  illustrates an example of an multi-function sensing apparatus; 
         FIG. 6  illustrates an example of the multi-function sensing apparatus illustrated in  FIG. 5 ; 
         FIG. 7A  illustrates an equivalent circuit for the multi-function sensing apparatus of  FIG. 5  when the switch is in the second configuration and a conductive object  2  is not near; 
         FIG. 7B  illustrates an equivalent circuit for the multi-function sensing apparatus of  FIG. 5  when the switch is in the second configuration and a conductive object  2  is near; 
         FIG. 8A  illustrates the an example of the multi-function sensing apparatus of  FIG. 7  that has a planar configuration; 
         FIG. 8B  illustrates the an example of the multi-function sensing apparatus of  FIG. 7  that has a stacked configuration; 
         FIG. 9  illustrates an example of a detector; 
         FIG. 10  illustrates an example of a multi-function sensing apparatus; and 
         FIG. 11  illustrates an example of the multi-function sensing apparatus of  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     The Figures illustrate a sensing apparatus  10  comprising: a capacitance touch sensor arrangement  20  configured to have a variable capacitance  22  that varies when a conductive object  2  approaches; and at least one variable impedance sensor  30  configured to have a variable impedance  32  that varies with a sensed parameter p; an output node  50 ; and at least one switch  40  configured to provide, in a first configuration, an output impedance at the output node  50  that depends upon the variable capacitance  22  and configured to provide, in a second configuration, an output impedance at the output node  50  that depends upon the variable impedance  32 . 
       FIG. 1  illustrates one of many possible examples of an apparatus  10 . 
     In this example, the apparatus  10  comprises a capacitance touch sensor arrangement  20 , a variable impedance sensor  30 , a switch  40  and an output node  50 . 
     The capacitance touch sensor arrangement  20  is configured to have a variable capacitance  22  that varies when a conductive object  2  approaches. 
     The capacitance touch sensor arrangement  20  therefore has an electrical characteristic (capacitance) that varies as the object  2  approaches. This electrical characteristic may be measured by a detector  100  attached to the output node  50 . The detector  100  is configured to use this measurement to detect when the object  2  is close to or touching the apparatus  10 . 
     The variable impedance sensor  30  is configured to have a variable impedance  32  that varies with a sensed parameter p. The variable impedance sensor  30  therefore has an electrical characteristic (impedance) that is dependent upon the presence of the sensed parameter p. This electrical characteristic may be measured by a detector  100  attached to the output node  50 . The detector  100  is configured to use this measurement to detect the presence of the sensed parameter p. 
     The switch  40  is configured to switch between a first configuration  41  and a second configuration  42 . 
     In the first configuration  41 , the detector  100  is able to detect the variable capacitance  22  and in the second configuration the detector  100  is able to detect the variable impedance  32 . 
     The switch  40 , in the first configuration  41 , provides an output impedance at the output node  50  that depends upon the variable capacitance  22 . 
     The switch  40 , in the second configuration  42 , provides an output impedance at the output node  50  that depends upon the variable impedance  32 . 
     In some but not necessarily all examples, the output impedance at the output node  50 , when the switch  40  is in the first configuration  41 , depends predominantly or solely upon the variable capacitance  22 . 
     In some but not necessarily all example, the output impedance at the output node  50 , when the switch  40  is in the second configuration  42 , depends predominantly or solely upon the variable impedance  32 . 
       FIG. 2  illustrates one of many possible examples of the apparatus  10 . 
     In this example, as in the example of  FIG. 1 , the apparatus  10  comprises a capacitance touch sensor arrangement  20 , a variable impedance sensor  30 , a switch  40  and an output node  50 . The description of these components and their operation given with respect to  FIG. 1  is also applicable to  FIG. 2 . 
     In  FIG. 2 , the capacitance touch sensor arrangement  20  comprises a first electrode  61  arranged to provide at least some of the variable capacitance  22  with respect to the conductive object  2 . 
       FIG. 3A , illustrates schematically the apparatus  10  when the switch  40  is in the first configuration  41 . The first electrode  61  is connected to the output node  50  via a low impedance path  63 . 
       FIG. 3B , illustrates schematically the apparatus  10  when the switch  40  is in the second configuration  42 . The variable impedance  32  is, instead, connected to the output node  50 . 
     In the apparatus  10 , illustrated in  FIG. 2 , a second electrode  62  is connected between the switch  40  and the output node  50 . 
       FIG. 4  illustrates one of many possible examples of the apparatus  10 . In this example, as in the example of  FIGS. 1 and 2 , the apparatus  10  comprises a capacitance touch sensor arrangement  20 , a variable impedance sensor  30 , a switch  40  and an output node  50 . In this example, as in the example of  FIG. 2 , the apparatus  10  comprises a first electrode  61  and a second electrode  62 . The description of these components and their operation given with respect to  FIG. 1 ,  FIG. 2  and  FIGS. 3A and 3B  is also applicable to  FIG. 4 . 
     In the apparatus  10 , illustrated in  FIG. 4  the first electrode  61  is a first electrode of the variable capacitance  22  and also a first electrode of the variable impedance  32 . The second electrode  62 , connected in electrical series to the output node  50 , is a second electrode of the variable capacitance  22  and also a second electrode  62  of the variable impedance  32 . The variable impedance  32  is the impedance between the first electrode  61  and the second electrode  62 . 
     The switch  40 , when it changes from the second configuration  42  to the first configuration  41 , creates a low impedance current path in parallel to the variable impedance  32  between the first electrode  61  and the second electrode  62 . 
     In the illustrated example, the switch  40  is used to open/close a bypass circuit that is in electrical parallel to the variable impedance sensor  30  and between the first and second electrodes  61 ,  62 . 
     In the first configuration  41 , the switch is closed to interconnect the first electrode  61  and the second electrode in electrical series via a low impedance current path through the switch  40 . This current path provides an alternative lower impedance current path compared to the current path through the variable impedance  32 . The lowest impedance path is therefore via the switch  40  rather than through the variable impedance sensor  30  and the impedance between the first electrode  61  and the second electrode  62  is reduced when the switch switches to the first configuration  41 . 
     The first electrode  61  and the second electrode  62  together provide the variable capacitance  22  with respect to a proximal conductive object  2 . The first electrode  61  forms a first capacitor with the conductive object  2  and the second electrode  62  forms a second capacitor with the second electrode. The first capacitor and the second capacitor are in parallel, so if the first capacitor has a variable capacitance C 1  and the second capacitor has a variable capacitance C 2 , then the variable capacitance  22  is the sum of C 1  and C 2 . 
     In the second configuration  42 , the switch  40  is open disconnecting the low impedance current path between the first electrode  61  and the second electrode  62 . The lowest impedance path between the first electrode  61  and the second electrode is now via the variable impedance sensor  30 . 
     The switch  40  in the second configuration  42  may connect the first electrode  61  to a reference node  64  (e.g. earth) via a low impedance current path. 
     The output node  50  sees as its output impedance the variable impedance  32   
     (if a conductive object  2  is not close) or (if a conductive object  2  is close) it sees the variable impedance  32  in parallel with the second capacitor formed between the second electrode  62  and the conductive object  2 . 
     It may therefore be preferable for the variable capacitance C 2  of the second capacitor to be small, so that the output impedance at the output node  50 , when the switch  40  is in the second configuration, is dominated by the variable impedance  22  and is not strongly dependent upon the presence or location of a conductive object  2 . The second electrode  62  may, for example, have a small area. 
       FIG. 5  illustrates one of many possible examples of the apparatus  10 . In this example, as in the example of  FIG. 4 , the apparatus  10  comprises a capacitance touch sensor arrangement  20 , a variable impedance sensor  30 , a switch  40  and an output node  50 . In this example, as in the example of  FIG. 4 , the apparatus  10  comprises a first electrode  61  and a second electrode  62 . The description of these components and their operation given with respect to  FIG. 1 ,  FIG. 2 ,  FIGS. 3A and 3B  and  FIG. 4  is also applicable to  FIG. 5 . 
     In the apparatus  10 , illustrated in  FIG. 5  the variable impedance sensor  30  is a capacitor  72  formed between the first electrode  61  and the second electrode  62 . 
     A capacitor dielectric  70  is positioned between the first electrode  61  and the second electrode  62   
     The variable impedance  32  may be a variable capacitance dependent upon the capacitor dielectric  70 . 
     The relative permittivity of the dielectric  70  is dependent upon a sensed parameter p. Presence of the sensed parameter changes the relative permittivity of the dielectric  70 , which changes the capacitance of the capacitor  72 . 
     For example, the sensed parameter p may be humidity. The capacitor dielectric  70  is formed from a material whose dielectric constant changes with relative humidity. Suitable materials include polymers such as polyimide. A route for the humidity to reach the capacitor dielectric  70  should also be provided. 
     For example, the sensed parameter p may be temperature. The capacitor dielectric  70  is formed from a material whose dielectric constant changes with temperature. Suitable materials include polytetrafluoroethylene (PTFE). 
     Alternatively, or in addition, the variable impedance  32  may be a variable capacitance dependent upon a variable separation between the first electrode  61  and the second electrode  62 . The variable separation is dependent upon a sensed parameter p. Presence of the sensed parameter p changes the separation, which changes the capacitance of the capacitor  72 . 
     For example, the sensed parameter p may be pressure, force, strain, or displacement. The material used for the capacitor dielectric  70  may have an elasticity (Young&#39;s modulus) suitable for its purpose. 
       FIGS. 7A and 7B  illustrate equivalent circuits for the apparatus  10  of  FIG. 5  when the switch is in the second configuration and when a conductive object  2  is not close ( FIG. 7A ) and when a conductive object  2  (e.g. a user&#39;s finger) is close ( FIG. 7B ). 
     When a conductive object  2  is not close ( FIG. 7A ). the output node  50  sees as its output impedance the variable impedance  32   
     When a conductive object is close ( FIG. 7B ), the first electrode  61  forms a first capacitor with the conductive object  2  and the second electrode  62  forms a second capacitor with the second electrode. The first capacitor has a variable capacitance C 1 , the second capacitor has a variable capacitance C 2 , and the capacitor  72  has a variable capacitance C 3 . 
     If the switch  40  connects to a reference node  64 , then the first electrode  61  is grounded and the output node  50  sees as its output impedance the capacitance C 3  in parallel with the capacitance C 2 . 
     It may therefore be preferable for the variable capacitance C 2  of the second capacitor to be small, so that the output impedance at the output node  50 , when the switch  40  is in the second configuration  42 , is dominated by the capacitance C 3  and is not strongly dependent upon the presence or location of a conductive object  2 . The second electrode  62  may, for example, have a small area or be positioned further from where the conductive object  2  may be located. 
     If the switch  40  is free floating and does not connect to a reference node  64 , then the first electrode  61  is not grounded and the output node  50  sees as its output impedance the capacitance C 2  in parallel with the series capacitances C 1  and C 3 . 
     It may therefore be preferable for the variable capacitance C 1  of the first capacitor and the capacitance C 2  of the second capacitor to both be significantly smaller, for example at least one or two orders of magnitude smaller, than the capacitance C 3  of the capacitor  72 . 
       FIG. 6  illustrates an example of the apparatus  10  illustrated in  FIG. 5 . 
     The first electrode  61  opposes the second electrode  62  across a gap occupied by dielectric  70 . 
     The switch  40  when in the first configuration  41  connects the first electrode  61  to the second electrode  62 . 
     The switch  40  when in the second configuration  42  connects the first electrode  61  to a reference node or leaves it floating. 
       FIG. 8A  illustrates the apparatus  10  of  FIG. 7  in a planar configuration. 
     The first electrode  6 , the dielectric  70  and the second electrode  62  extend over the same plane. The area of the second electrode  62  adjacent the dielectric  70  is significantly smaller than the area of the first electrode  61  adjacent the dielectric  70 . 
     In the illustrated example, the second electrode  62  is centrally located with the first electrode  61  arranged as a circumscribing ring electrode. 
       FIG. 8B  illustrates the apparatus  10  of  FIG. 7  in a stacked configuration. 
     The first electrode  6 , the dielectric  70  and the second electrode  62  extend over different planes. 
     In this example, the second electrode  62  is at the bottom of the stack and the first electrode  61  is at the top of the stack. The first electrode  61  will therefore couple more strongly with proximal conductive objects  2 . 
       FIG. 9  illustrates an example of a detector  100  suitable for use with the apparatus  10  illustrated in  FIG. 5, 7 or 8 . 
     A reference voltage  106  is applied to both the inverting and non-inverting inputs of an operational amplifier  102 . 
     The input node  104  is connected to the output node  50  of the apparatus  10 . The input node  104  provides the voltage associated with the variable capacitance being sensed (C 1 +C 2  in the first configuration, C 3  in the second configuration) to the non-inverting input of the operational amplifier. The output of the operational amplifier  102  is therefore indicative of the voltage input at the input node  104  which is dependent upon the sensed capacitance. 
       FIG. 10  illustrates an apparatus  10  similar to any of the previously described apparatus  10 . 
     The apparatus  10  in  FIG. 10  is similar to the apparatus  10  in  FIGS. 5 and 6 , and the description provided above in relation to  FIGS. 5 and 6  is also relevant to the apparatus  10  illustrated in  FIG. 10 . 
     The apparatus  10  illustrated in  FIG. 10 , however, comprises a plurality of first electrodes  61  each of which is associated with its own switch  40  configured to switch  40  between a first configuration  41  and a second configuration  42 . 
     The apparatus  10  comprises a single second electrode  62  configured to provide an output signal at an output node  50 . 
     When a switch  40  switches from the second configuration  42  to the first configuration, it provides a lower impedance current path between the first electrode  61  associated with the switch  40  and the second electrode  62  by interconnecting that first electrode  61  and the second electrode  62 . 
     When the switch  40  is in the first configuration  41 , the first electrode  61  associated with that switch  40  and the second electrode  62  form a capacitance touch sensor arrangement  20  configured to have a variable capacitance  22  that varies when a conductive object  2  approaches. 
     When the switch  40  is in the second configuration  42 , the first electrode  61  associated with that switch  40  and the second electrode  62  form a variable impedance sensor  30  configured to have a variable impedance  32  that varies with a sensed parameter p. 
     Each first electrode  61  and the second electrode  62  form a variable impedance  32  that varies with a particular parameter p. In the illustrated example, each first electrode  61  and the second electrode  62  form a capacitor with a dielectric with a relative permittivity that varies with a particular parameter p. 
     Each pairing of second electrode  62  and particular first electrode  61 , forms a particular arrangement comprising: a capacitance touch sensor arrangement  20  configured to have a variable capacitance  22  that varies when a user finger touches the capacitance touch sensor arrangement  20 ; and a variable impedance sensor  30  configured to have a variable impedance  32  that varies with a sensed parameter p; and an associated switch  40  configured to provide, in a first configuration, an output impedance that depends upon the variable capacitance  22  and configured to provide, in a second configuration, an output impedance that depends upon the variable impedance  32 . 
     The arrangements are connected in parallel—the second electrode  62  being common to all arrangements. Each of the switches  40  in the first configuration  41  connect their associated first electrodes  61  to the second electrode  62  which operates as a common output node  50 . 
     When all of the switches  40  are in the first configuration  41 , the apparatus  10  is optimized for detection of a proximal object  2 . To read a particular impedance sensor  30 , the switch  40  associated with that particular impedance sensor  30  is changed from the first configuration  41  to the second configuration  42 . One impedance sensor  30  may be read at a time or alternatively multiple impedance sensors  30  may be read at the same time. 
     In some but not necessarily all embodiments, different ones of the plurality of arrangements comprise different variable impedance sensors  30  each configured to have a variable impedance  32  that varies with a different sensed parameter p. The apparatus  10  is configured to sense a particular parameter p by switching the one or more switches associated with the one or more variable impedance sensors  30  for that parameter p to a second configuration  42 . 
       FIG. 11  illustrates the apparatus  10  of  FIG. 10  in a planar configuration. 
     The first electrodes  61 , the dielectric  70  and the common second electrode  62  extend over the same plane. Each of the first electrodes  61  has its own dielectric  70 . The area of the second electrode  62  adjacent a dielectric  70  is significantly smaller than the area of the first electrode  61  adjacent the dielectric  70 . 
     In the illustrated example, the second electrode  62  is centrally located with the first electrodes  61  arranged as a group of separate electrodes that in combination surround the second electrode  62 . 
     In some but not necessarily all embodiments, each of the first electrodes may be associated with the same dielectric. The variable impedance sensors  30  therefore sense the same parameter p but at different locations. This may allow the sensing of a stimulus location or orientation (e.g. axis of strain). 
     In some but not necessarily all embodiments, each of the first electrodes may be associated with a different dielectric. The variable impedance sensors  30  therefore sense the different parameters p. 
     In the foregoing description reference has been made to the switching of switch(es)  40  between a first configuration  41  and a second configuration  42 . 
     Circuitry may be provided as part of the apparatus  10  or separately to the apparatus  10 , that is configured to provide control signals that control the configuration of the switch(es)  40 . For example, the detector  100  may be configured to provide switch control signals that control the configuration of the switch(es)  40 . 
     In the preceding embodiments, the switches  30  have a first configuration  41  and a second configuration  42 . 
     In the first configuration  41 , the first electrode  61  and second electrode  62  are interconnected, short-circuiting the variable impedance  32 . Either the first electrode  61  or the second electrode  62  may be used as an output node  50 . 
     In the second configuration  42 , the first electrode  61  is connected to a reference node  64  via the switch  40  and the second electrode  62  is used as an output node  50 . 
     In the following embodiment, the switch(es)  30  have an additional third configuration. 
     The third configuration is similar to the second configuration. However, in the third configuration, the second electrode  62  (not the first electrode  61 ) is connected to a reference node via the switch  40  and the first electrode  61  (not the second electrode  62 ) is used as an output node. 
     A measurement of only the variable impedance  32  may be determined by:
     a) measuring the output impedance Z 1  at the first or second electrode  61 ,  62  when the switch  40  is in the first configuration,   b) measuring the output impedance Z 22  at the second electrode  62  when the switch  40  is in the second configuration (and the first electrode is connected to a reference node); and   c) measuring the output impedance Z 21  at the first electrode  61  when the switch  40  is in the third configuration similar to the second configuration except that the second electrode  62 , not the first electrode  61 , is connected to a reference node.   

     The variable impedance  32  is given by [½(Z 21   −1 +Z 22   −1 −Z 1   −1 )] −1 . 
     If first capacitor formed by the first electrode  61  has impedance z1, the second capacitor formed by the second electrode  62  has impedance z2 and the variable impedance  32  has impedance z3, then 
     
       
         
           
             
               
                 
                   
                     
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     However, in a typical arrangement z3&lt;&lt;z1, z3&lt;&lt;z2, so Z 21  approximates to z3. 
     As used here ‘module’ refers to a unit or apparatus that excludes certain parts/components that would be added by an end manufacturer or a user. The apparatus  10  may be a module. 
     The term ‘comprise’ is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use ‘comprise’ with an exclusive meaning then it will be made clear in the context by referring to “comprising only one . . . ” or by using “consisting”. 
     In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term ‘example’ or ‘for example’ or ‘may’ in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus ‘example’, ‘for example’ or ‘may’ refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a sub-class of the class that includes some but not all of the instances in the class. 
     Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed. 
     Features described in the preceding description may be used in combinations other than the combinations explicitly described. 
     Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not. 
     Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not. 
     Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.