Force sensing using capacitive touch surfaces

In one general aspect, a method can include identifying contact with a surface of a touch-sensitive input device, identifying a location of the contact on the surface of the touch-sensitive input device, and calculating a change in a mutual capacitance between a first electrode and a second electrode included in a sensor module disposed below the surface of the touch-sensitive input device. The first electrode can be adjacent to the second electrode. The first electrode and the second electrode can be located approximate to the identified location of the contact on the surface of the touch-sensitive input device. The method can include estimating a contact-coupled capacitance based on the calculated change in a mutual capacitance between the first electrode and the second electrode, and calculating a force applied to the surface of the touch-sensitive input device at the identified location.

TECHNICAL FIELD

This document relates, generally, to computing devices that include touch-sensitive input devices.

BACKGROUND

Computing devices can provide a user with multiple ways to control the operations of and to input data to a computing device. A computing device can include, for example, a touchscreen display device, a keyboard, a mouse, a trackpad, a touchpad, a pointing stick, one or more mouse buttons, a trackball, a joystick, and other types of input devices. A user of the computing device can interact with one or more of these input devices when providing input to and/or otherwise controlling the operation of an application running on the computing device. For example, the user can interact with the computing device by making direct contact with (e.g., touching with one or more fingers, touching with a stylus) the touchscreen display device.

A touchpad, which may also be referred to as a trackpad, can be included in a computing device and can be used as a pointing device to facilitate user interaction with the computing device. For example, a user can interact with the touchpad by making direct contact with the touchpad (e.g., touching with one or more fingers, touching with a stylus). In some cases, the touchpad can be used in place of or in addition to a mouse to maneuver a cursor on a display device included in the computing device, or to trigger one or more functions of the computing device.

SUMMARY

In one general aspect, a method can include identifying, by a computing device, contact with a surface of a touch-sensitive input device, identifying, by the computing device, a location of the contact on the surface of the touch-sensitive input device, calculating a change in a mutual capacitance between a first electrode and a second electrode included in a sensor module disposed below the surface of the touch-sensitive input device, the first electrode being adjacent to the second electrode, the first electrode and the second electrode located approximate to the identified location of the contact on the surface of the touch-sensitive input device, estimating a contact-coupled capacitance based on the calculated change in a mutual capacitance between the first electrode and the second electrode, and calculating a force applied to the surface of the touch-sensitive input device at the identified location based on a change in self-capacitance of the first electrode and the second electrode and based on the estimated contact-coupled capacitance.

Implementations can include one or more of the following features, alone or in combination with one or more other features. For example, the method can further include calculating a change in a mutual capacitance between a third electrode and the second electrode included in the sensor module, the third electrode being adjacent to the second electrode and located closer to the identified location of the contact on the surface of the touch-sensitive input device than the first electrode. Estimating a contact-coupled capacitance can be further based on the calculated change in a mutual capacitance between the third electrode and the second electrode. Calculating the applied force can be further based on a change in self-capacitance of the third electrode. The touch-sensitive input device can be a touchpad. The touch-sensitive input device can be a touchscreen. The surface of the touch-sensitive input device can be a surface of a cover glass. The method can further include providing the calculated applied force to an application executing on the computing device. The method can further include controlling a function of the application based on a value of the calculated applied force. The identified contact with the surface of the touch-sensitive input device can be provided by a finger of a user of the computing device contacting the surface of the touch-sensitive input device at the identified location. The identified contact with the surface of the touch-sensitive input device can be provided by a stylus contacting the surface of the touch-sensitive input device at the identified location.

In another general aspect, a touch-sensitive input device can include a glass-plus-sensor module. The glass-plus-sensor module can include a cover glass including a top surface and a bottom surface, and at least two electrodes attached to the bottom surface of the cover glass. The at least two electrodes can have an associated self-capacitance. The touch-sensitive input device can include an optically clear adhesive layer (OCA) layer, a display device having a top surface and a bottom surface, and a ground plane attached to the bottom surface of the display device. The OCA layer can attach the bottom surface of the cover glass to the top surface of the display device. The glass-plus-sensor module can bend towards the display device at a point of contact of a conductive element with the top surface of the cover glass, the bending changing, for each of the at least two electrodes, the self-capacitance associated with the electrode, and a calculation of a force applied by the contact of the conductive element with the top surface of the cover glass being based on the change in self-capacitance for each electrode.

Implementations can include one or more of the following features, alone or in combination with one or more other features. For example, the OCA layer can have a thickness. The calculation of a force applied by the contact of the conductive element with the top surface of the cover glass can be further based on the thickness of the OCA layer. The self-capacitance associated with the electrode can be a capacitance as measured between the electrode and the ground plane. The at least two electrodes can be adjacent to one another. The calculation of a force applied by the contact of the conductive element with the top surface of the cover glass can be further based on a mutual capacitance between the at least two electrodes. The conductive element can be one of a finger of a user and a stylist.

In yet another general aspect, a computing device can include at least one controller, and a touch-sensitive input device configured to facilitate interaction by a user with a graphical user interface (GUI). The touch-sensitive input device can include a glass-plus-sensor module including a cover glass including a top surface and a bottom surface, and at least two electrodes attached to the bottom surface of the cover glass, the at least two electrodes having an associated self-capacitance. The touch-sensitive input device can further include a display device having a top surface and a bottom surface, the computing device being configured to render the GUI on the display device, an optically clear adhesive layer (OCA) layer attaching the bottom surface of the cover glass to the top surface of the display device, and a ground plane attached to the bottom surface of the display device. The at least one controller and the touch-sensitive input device can be collectively configured to detect contact of a conductive element with the top surface of the cover glass, and based on the detected contact, determine, for each of the at least two electrodes, a self-capacitance associated with the electrode, and calculate a force applied by the contact of the conductive element with the top surface of the cover glass based on the determined self-capacitance associated with each of the at least two electrodes.

Implementations can include one or more of the following features, alone or in combination with one or more other features. For example, the at least one controller can be configured to execute an application on the computing device, and provide the calculated applied force as input to the application. The conductive element can be one of a finger of a user and a stylist. The self-capacitance associated with the electrode can be a capacitance as measured between the electrode and the ground plane. The at least one controller and the touch-sensitive input device can be collectively configured to determine, for each of the at least two electrodes, a mutual capacitance between the at least two electrodes. Calculating a force applied by the contact of the conductive element with the top surface of the cover glass can be further based on the determined mutual capacitance between the at least two electrodes.

DETAILED DESCRIPTION

A trackpad, a touchpad, and a touchscreen display device can be considered (referred to as) touch-sensitive input devices. One or more touch-sensitive input devices can be included in a computing device. Each touch-sensitive input device can include a tactile sensing surface (e.g., a capacitive sensing surface, a resistive and capacitive sensing surface). The touch-sensitive input device can be configured to facilitate interaction by a user with a graphical user interface (GUI) displayed on a display device (e.g., a touchscreen display device) included in the computing device. In some implementations, the touch-sensitive input device can detect a position and a motion of one or more fingers of a user as the one or more fingers contact the tactile sensing surface of the touch-sensitive input device.

In some cases, the computing device can use the detected motion and/or the detected position of the one or more fingers of the user with the tactile sensing surface of the touch-sensitive input device to determine a relative position on the display device (and in relation to the GUI displayed on the display device) that corresponds with the position of the one or more fingers of the user. In some cases, the computing device can use the detected motion and/or the detected position of the one or more fingers of the user with the tactile sensing surface of the touch-sensitive input device to affect movement of a cursor displayed in the GUI. In some cases, the computing device can use a detected motion and/or a detected position of the one or more fingers of the user with the tactile sensing surface in combination with a detected force exerted by the one or more fingers of the user on the tactile sensing surface of the touch-sensitive input device when controlling a position and/or movement of a cursor displayed in the GUI.

In some implementations, a contact with the touch-sensitive input device can be provided by a stylus. A user can use and manipulate the stylus as they would one or more fingers of the user when contacting the tactile sensing surface of the touch-sensitive input device.

Computing devices can include one or more touch-sensitive input devices that include a touch-sensitive surface (e.g., a touchscreen, a trackpad, a touchpad). The touch-sensitive surface can determine when a user is touching (making contact with) the surface. In some implementations, the contact can be one or more fingers of a user that are touching (are in contact with) the touch-sensitive surface. In some implementations, the contact can be made by a stylus as manipulated and used by a user on the touch-sensitive surface of the touch-sensitive input device. As described herein, processes and methods for determining a position, a location, and/or a force of a detected contact with a touch-sensitive surface can be the same for one or more fingers of a user touching or contacting the touch-sensitive surface and for a stylus contacting the touch-sensitive surface.

In addition to determining when a user is making contact with the touch-sensitive surface of the touch-sensitive input device, the computing device can determine the location of the contact on the surface of the touch-sensitive input device (e.g., a location of a contact of a finger of the user on the surface of the touch-sensitive input device). In addition, in some cases, the computing device can measure a force exerted by the finger of the user while touching (contacting) the touch-sensitive surface of the touch-sensitive input device at the determined location.

In some implementations, a touch-sensitive input device can include one or more force sensors that can be used to measure a force exerted by the user (exerted by one or more fingers of the user) when contacting the surface of the touch-sensitive input device. In some cases, force sensors may be expensive and may be difficult to integrate into a touch-sensitive input device included in a computing device that may have size and thickness limitations (e.g., a mobile phone, a tablet device).

In some implementations, a touch-sensitive input device can include a capacitive touch sensor that a computing device can use to determine when a user is contacting the surface of the touch-sensitive input device (e.g., when one or more fingers of a user are touching (contacting) the surface of the touch-sensitive input device). In addition, in some cases, the computing device can use the capacitive touch sensor to calculate an estimate of a force applied by the user to the surface of the touch-sensitive input device (e.g., a force applied by (exerted by) one or more fingers of the user when contacting (touching) the surface of the touch-sensitive input device). In doing so, the computing device may not need any additional components and/or instrumentation to measure the force exerted (applied) by the user (e.g., one or more fingers of the user) when touching (contacting) the touch-sensitive surface of the touch-sensitive input device.

For example, in some implementations, a computing device can include a touchscreen display device that can be considered a touch-sensitive input device. The touchscreen display device can include a plurality of layers that can be stacked and adhered to each other. A first layer (at the top of the stack of layers) can be a cover glass. The cover glass can be flexible, bending when a force is applied to a surface of the cover glass. A touch sensor (e.g., a capacitive touch sensor) can be adhered to a bottom surface of the cover glass. The cover glass and touch sensor can be considered a glass-plus-sensor module. The glass-plus-sensor module can be adhered to (laminated to) a display device (e.g., a Liquid Crystal Display (LCD), an organic light-emitting diode (OLED)) using an optically clear adhesive (OCA). The display device can include a ground plane and can be referred to as the display device-plus-ground plane. In an example where the display device is an LCD, the display device and ground plane can be referred to as the LCD/GND plane.

When a force is applied to the touchscreen display device, the cover glass can bend towards the display device-plus-ground plane (e.g., the LCD/GND plane). The degree to which the cover glass can bend can be a function of the applied force. Because the touch sensor (e.g., a capacitive touch sensor) is physically adhered to (connected to) the cover glass, it follows that electrodes included in the touch sensor are also physically adhered to (connected to) the cover glass and, as such, will bend and be displaced based on the applied force. The self-capacitance of each electrode can vary as a function of the deformation of the cover glass, which is based on the applied force to the cover glass. In some implementations, an estimate of the applied force to a touchscreen display device can be estimated by measuring a change in a self-capacitance of the electrodes included in the touch sensor. When estimating the applied force based on the change in a self-capacitance of the electrodes, the effect of a finger-coupled capacitance can be compensated.

In some implementations, only the changes in the self-capacitances of electrodes located farthest away from the determined location of the contact of a finger of a user on the surface of the touchscreen display device are considered when estimating the applied force. The electrodes located farthest away from the determined location of the contact of the finger of the user on the surface of the touchscreen display device are used because the effect of the finger-coupled capacitance decays exponentially as the distance between an electrode and a location of contact of the finger of the user on the surface of the touchscreen increases. In some implementations, a change in mutual capacitance between adjacent electrodes at the determined location of the contact of the finger of the user on the surface of the touchscreen display device can be used to estimate a finger-coupled capacitance. The computing device can use the determined finger-coupled capacitance to calculate and estimate the applied force.

FIG. 1is a diagram that illustrates an example computing device102that includes touch-sensitive input devices, such as a touchscreen display device120and a touchpad114. As included herein, the terms trackpad, trackpad device, trackpad apparatus, touchpad, touchpad device and touchpad apparatus may be used interchangeably. In addition, as included herein, the terms touchscreen, touchscreen display, touchscreen display device, and touchscreen apparatus may be used interchangeably.

The touchscreen display device120and touchpad114can be pressure-sensitive, touch-sensitive input devices, such as those described herein. A user can interact with the touchscreen display device120and the touchpad114to facilitate interaction with the computing device102. A user can interact with the touchscreen display device120and the touchpad114to facilitate interaction with an application executing on the computing device102. For example, the application can provide (display) a graphical user interface (GUI) on the touchscreen display device120. A user can interact with the touchscreen display device120and/or the touchpad114to control cursor movements in the GUI displayed on the touchscreen display device120.

In the example shown inFIG. 1, the computing device102includes a lid portion104and a base portion106. The base portion106includes an input area122. The input area122includes a keyboard108, the touchpad114, a pointer button110, and mouse buttons112a-d. The lid portion104includes the touchscreen display device120that is part of (housed within/mounted on) the lid portion104of the computing device102.

In the example shown inFIG. 1, the computing device102may take the form of a laptop computer, a notebook computer or a netbook computer. In some implementations, the computing device102may be a tablet computer (as shown inFIG. 2), a desktop computer, a server computer, or a number of other computing or electronics devices. For example, implementations of a desktop computer and/or implementations of a server computer may not include a touchpad (e.g., the touchpad114) as part of a computing device. In these implementations, a touchpad can be included in a pressure-sensitive, touch-sensitive trackpad apparatus external to (and connected to) the computing device. In addition or in the alternative, for example, implementations of a desktop computer and/or implementations of a server computer may not include a touchscreen (e.g., the touchscreen display device120) as part of a computing device. In these implementations, a touchscreen can be included in a display device that is external to (and connected to) the computing device.

For example, the computing device102can be considered in a laptop mode of operation. In a laptop operating mode, a user of the computing device102can interact with the keyboard108, the touchpad114, the pointer button110, and the mouse buttons112a-dincluded in the input area122while viewing/interacting with content rendered on the touchscreen display device120. The touchscreen display device120(e.g., in conjunction with other elements of the computing device102) can render (display) a GUI that allows a user to interact with the computing device102to, for example, execute (run) applications and programs, surf the Internet or World Wide Web, or draft documents using a word processing application. In some cases, a user of the computing device102can interact with the GUI using the keyboard108alone or in conjunction with the pointer button110and/or the mouse buttons112a-dto enter text or commands into an application running (executing) on the computing device102. The keyboard108can take a number of forms, and the particular arrangement of the keyboard108can depend on the particular implementation.

In some cases, a user can also interact with the GUI using the touchpad114alone or in conjunction with the pointer button110and/or the mouse buttons112a-d. For example, the GUI interaction can move a cursor, select objects, launch programs from icons, and/or move objects in the GUI. The particular configuration of the touchpad114can vary dependent on a specific implementation of the computing device102. In some implementations, a trackpad can be larger than the touchpad114. In some implementations, a trackpad can be smaller than the touchpad114. In some implementations, a trackpad can be disposed in (replace and/or include) the area that includes the keyboard108. In these implementations, a trackpad can be disposed over, or included in, the input area122(e.g., a top surface of the base portion106, substantially the entire input area122) included in the base portion106of the computing device102. The input area122can be the same size (e.g., area (e.g., surface area), width and length) or substantially the same size as the base portion106, thus functioning as a touch-sensitive surface (e.g., a touch-sensitive trackpad) that covers (is incorporated in) the base portion106of the computing device102.

FIG. 2is a diagram that illustrates an example computing device202that includes a touchscreen display device220. The touchscreen display device220can be configured to operate as a display device that can, for example, display a GUI. The touchscreen display device220can be configured to operate as a pressure-sensitive, touch-sensitive input device. A user can interact with the touchscreen display device220in the same manner as interactions with touchscreen display devices described herein, in order to provide input to the computing device202. For example, the computing device202can be a tablet computer, a smartphone, a personal digital assistant, a mobile phone, or another type of mobile computing device.

FIG. 3is a diagram that illustrates an example implementation of a touch-sensitive input device300. In some implementations, the touch-sensitive input device300can be configured to determine (sense) a force applied by a user when contacting a surface302of the touch-sensitive input device300. For example, referring toFIG. 1, the touch-sensitive input device300can be (can be included in) the touchscreen display device120. For example, referring toFIG. 1, the touch-sensitive input device300can be (can be included in) the touchpad114. In this example, the touch-sensitive input device300as included in the touchpad114may not include a display device320. For example, referring toFIG. 2, the touch-sensitive input device300can be (can be included in) the touchscreen display device220.

The touch-sensitive input device300can detect (determine) when a user is touching (making contact with) the surface302(e.g., one or more fingers of the user are in contact with the surface302). In addition to detecting when a user is making contact with the surface302of the touch-sensitive input device300, a location of the contact on the surface302of the touch-sensitive input device300(e.g., a location of a contact of a finger of the user on the surface302of the touch-sensitive input device300) can be determined. In addition, in some cases, a force exerted by a finger of a user while touching (contacting) the surface302of the touch-sensitive input device300at the determined location can be measured.

In some implementations, the touch-sensitive input device300can include circuitry (e.g., electronic components, controllers, drivers, memory) that can be configured to detect when a user is touching (making contact with) the surface302, determine a location of the detected contact on the surface302, and determine (measure) a force exerted by a finger of a user while touching (contacting) the surface302. In some implementations, a computing device that includes the touch-sensitive input device300can include circuitry (e.g., electronic components, controllers, drivers, memory) for use with the touch-sensitive input device300. For example, the circuitry can be configured to detect when a user is touching (making contact with) the surface302, determine a location of the detected contact on the surface302, and determine (measure) a force exerted by a finger of a user while touching (contacting) the surface302. In some cases, the circuitry for use with the touch-sensitive input device300can be the same circuitry used for other functions of the computing device.

Referring toFIG. 3, the touch-sensitive input device300includes a plurality of layers that are adhered to (attached to) one another to form a stack. A cover glass304comprises a top layer of the stack. The cover glass304includes a cover glass top surface306aand a cover glass bottom surface306b. In the example shown inFIG. 3, the cover glass top surface306acan be the surface302. One or more electrodes308a-fare attached (e.g., adhered) to the cover glass bottom surface306b. The cover glass304including the one or more attached electrodes308a-fcan be referred to, in general, as a glass-plus-sensor module310. The glass-plus-sensor module310can be laminated to (e.g., attached to, adhered to) the display device320. In implementations where the touch-sensitive input device300is included in a trackpad (e.g., the touchpad114as shown inFIG. 1), the glass-plus-sensor module310can be laminated to (e.g., attached to, adhered to) a ground plane322.

In the example shown inFIG. 3, without any force applied to the surface302of the touch-sensitive input device300, a height334of the cover glass304is essentially the same across a length332of the cover glass304.

FIG. 3illustrates an example implementation of a touch-sensitive input device (e.g., the touch-sensitive input device300) configured to determine (sense) a force applied by a user when contacting a surface of the touch-sensitive input device. The touch-sensitive input device300includes a plurality of layers, described herein, that can be referred to as a touch sensor stack. In some cases, a touch-sensitive input device configured to determine (sense) a force applied by a user when contacting a surface of the touch-sensitive input device can be implemented using other touch sensor stacks. The other touch sensor stacks can include, but are not limited to, a glass-film-film (GFF) stack, a one glass solution (OGS) stack, a G1F stack, a GF1 stack, a GF2 stack, a GG stack, an on-cell stack, a true in-cell stack, and a hybrid in-cell stack.

For example a sensor film can be transparent and conductive. For example, a GFF stack includes two sensor films laminated to (e.g., attached to, adhered to) glass. For example, a OGS stack includes a single sensor film laminated to (e.g., attached to, adhered to) glass. For example, a G1F stack includes a single sensor film with a sensor layer included on one side of the film where the single sensor film is laminated to (e.g., attached to, adhered to) glass. A GF1 stack includes a single sensor film with two sensor layers included on one side of the film where the single sensor film is laminated to (e.g., attached to, adhered to) glass. A GF2 stack includes a single sensor film with a sensor layer included on each side of the film where the single sensor film is laminated to (e.g., attached to, adhered to) glass. For example, a GG stack includes a cover glass and a single sensor glass. For example, an on-cell stack can include a separate layer for touch “receive” (RX) and a separate layer for touch “transmit” (TX) functions where each of the separate layers are placed/located on top of (above) a color filter and a display device. For example, an in-cell stack can include a separate layer for touch “receive” (RX) and a separate layer for touch “transmit” (TX) functions where at least one of the separate layers is placed/located under (below) a color filter and on top of (above) a display device. For example, in a true (one sided) in-cell stack both the touch RX layer and the touch TX layer are placed/located under (below) a color filter and on top of (above) a display device. For example, in a hybrid (two sided) in-cell stack only one layer (e.g., the touch TX layer) is placed/located under (below) a color filter and on top of (above) a display device. The use of each touch sensor stack in a touch-sensitive input device can include appropriate changes to the measurement techniques discussed herein for the touch sensor stack included in the touch-sensitive input device300.

In some implementations, a cover glass can be replaced with a touch surface that includes a plastic or polymers (e.g., a Poly(methyl methacrylate) (PMMA)). In some implementations, a plastic or polymer touch surface can be an integral part of a display stack that incorporates a display device. For example, the plastic or polymer touch surface can be considered a top polarizer for the display device.

Referring toFIG. 3, the glass-plus-sensor module310can be laminated to (e.g., attached to, adhered to) the display device-plus-ground plane314using an optically clear adhesive (e.g., shown in general as an optically clear adhesive layer (OCA) layer312). Specifically, the cover glass bottom surface306bof the glass-plus-sensor module310(that includes the attached one or more electrodes308a-f) can be laminated to (e.g., attached to, adhered to) the display device top surface324a(which is essentially a top surface of the display device-plus-ground plane314). An electrode (e.g., the electrode308a-f) can be located (placed at) a respective distance326a-ffrom the ground plane322. The OCA layer312can have a thickness toca328.

A mutual capacitance between adjacent electrodes can be represented by capacitors330a-e. The mutual capacitance can be established by electric fields that propagate through the cover glass304and the OCA layer312due to a potential difference between adjacent electrodes.

In some implementations, the touch-sensitive input device300can be configured to detect (determine) when a user is touching and/or otherwise making contact with the surface302. For example, the touch-sensitive input device300can be configured to detect (determine) when one or more fingers of the user are in contact with the surface302by monitoring a change in a self-capacitance (represented by capacitors316a-f) of each of the electrodes308a-f, respectively. Referring to the example implementation of the touch-sensitive input device300shown inFIG. 3, a measured value for a self-capacitance (e.g., the measured value of the capacitance of the capacitor316a) of an associated electrode (e.g., the electrode308a) can be primarily a measured capacitance (e.g., the value of the representative capacitor316a) between the electrode (e.g., the electrode308a) and a ground plane (e.g., the ground plane322). In addition, the measured value of a self-capacitance (e.g., the measured value of the capacitance of the capacitor316a) of an associated electrode (e.g., the electrode308a) can be a function of (associated with) a size of the electrode (e.g., a size of the electrode308a), a dielectric constant associated with the optically clear adhesive included in the OCA layer312, and a distance between an electrode and the ground plane (e.g., the distance326a).

For example, it can be assumed that the thickness toca328of the OCA layer312can vary based on an applied pressure to the surface302of the touch-sensitive input device300. The variation in the thickness toca328of the OCA layer312can effect a measured value of a self-capacitance of an electrode. This relationship can be represented by Equation 1.
Cn∝toca,  Equation 1:
where Cnis a measured capacitance of an associated electrode and n=1 to n=6 (referring toFIG. 3).

FIG. 4is a diagram that illustrates an example implementation of the touch-sensitive input device300when a force (shown by the downward arrow440) is applied by a user (e.g., one or more fingers of a user, a stylus controlled by a user) at a point of contact434. The touch-sensitive input device300can detect (determine) when a user is touching (making contact with) the surface302(e.g., a finger of the user can contact (touch) the surface302at the point of contact434, a tip or point of a stylus can contact (touch) the surface302at the point of contact434). The contact and applied force can be shown in general by a conductive element432contacting (touching) the surface302of the touch-sensitive input device300at the point of contact434. In addition to detecting when a user is making contact with the surface302of the touch-sensitive input device300, a location of the contact on the surface302of the touch-sensitive input device300(e.g., the point of contact434) can be determined.

In addition, in some cases, a force exerted by a finger of a user (or by a stylus) while touching (contacting) the surface302of the touch-sensitive input device300at the determined location can be measured. As shown inFIG. 4, for example, a finger of the user can touch (make contact with) the surface302at the point of contact434and press the cover glass304(which can be flexible) in a downward direction as shown by arrow440. The magnitude of the downward applied force can cause the cover glass304and the glass-plus-sensor module310to bend towards the display device320(towards the display device-plus-ground plane314). The magnitude of the bending can be a function of one or more of the magnitude of the applied force, the material properties of the cover glass304(e.g., how easily the cover glass304can bend, how much force is needed to bend the cover glass304a particular amount), the material properties of the OCA, and the location of the point of contact on the surface302of the touch-sensitive input device300.

The bending of the cover glass304changes the geometry of the cover glass304from having the height334that was essentially the same along the length332of the cover glass304when no pressure was applied to the surface302(e.g., as shown inFIG. 3), to having multiple different heights (e.g., heights440a-f) along the length332of the cover glass304when a force is applied at on the surface302at the point of contact434. The bending of the cover glass304because of the force (pressure) applied to the cover glass304at the point of contact434changes a geometry of the cover glass304. A change in the geometry of the cover glass304along the length332of the cover glass304can decrease a distance (e.g., distances426a-f) from one or more of the electrodes308a-fto the ground plane322. For example, referring toFIG. 3andFIG. 4, a distance426cof the electrode308cfrom the ground plane322is less than a distance326cof the electrode308cfrom the ground plane322. For example, a distance426aof the electrode308afrom the ground plane322is substantially the same as a distance326aof the electrode308afrom the ground plane322.

In general, a distance from an electrode to the ground plane322decreases the closer an electrode is to the point of contact434. The farther from the location of the point of contact an electrode is located, the larger (greater) the distance between the electrode and the ground plane322. Equation 2 can represent this relationship.
Δtoca∝F,Equation 2:
where Δtocais a change in the thickness of the OCA and F is the applied force. In some implementation, the applied force F can change a thickness t of any combination of a heterogeneous stack of materials, the thickness t being a distance between an electrode and a reference ground against which a capacitance of the electrode is being measured.

In addition, the existence of the contact of the conductive element432(e.g., a finger of a user, a stylus) with the surface302of the touch-sensitive input device300introduces additional capacitances (e.g., represented by capacitors436a-f) between the electrodes308a-f, respectively, and the conductive element432. Each of the capacitors436a-frepresent capacitances between the electrodes308a-f, respectively, and a ground442provided by (through) the conductive element432at the point of contact434. In the example shown inFIG. 4, a self-capacitance of each of the electrodes308a-fcan be a function of (e.g., the sum of) the capacitors416a-fand the capacitors436a-f. In some implementations, an estimate of an applied force by the conductive element432at the point of contact434can be calculated using the additional capacitances (e.g., represented by capacitors436a-f) between the electrodes308a-f.

In a first implementation, when calculating an estimate of the force applied by the conductive element432at the point of contact434, the changes in the self-capacitance of electrodes located at distances that are farther from the point of contact434can be considered and changes in the self-capacitance of electrodes located at distances that are closer to the point of contact434can be ignored because the effect on the self-capacitance of an electrode due to the presence of the conductive element432at the point of contact434decreases exponentially the further away from the point of contact434the electrode is located. For example, referring toFIG. 4, the self-capacitance of electrodes308a,308b,308e, and308fcan be used to calculate an estimate of the force applied by the conductive element432at the point of contact434.

When using the first implementation to calculate an estimate of the force applied by the conductive element432at the point of contact434, the bending of the cover glass304due to the force applied by the conductive element432at the point of contact434may not be significant enough to result in the additional capacitances (e.g., represented by capacitors436a-f) between the electrodes308a-f, respectively, and the conductive element432having a measurable impact on the self-capacitances of each of the electrodes308a-f.

In a second implementation, a change in a mutual capacitance between adjacent electrodes (e.g., represented by capacitors430a-e) can be calculated and used to estimate a capacitance introduced by the conductive element432at the point of contact434. The capacitance introduced by the conductive element432at the point of contact434can be referred to as a contact-coupled capacitance. The change in the mutual capacitance is the difference between a mutual capacitance between two adjacent electrodes when no contact is detected with the surface302of the touch-sensitive input device300and a mutual capacitance between the two adjacent electrodes when contact is detected with the surface302of the touch-sensitive input device300. The change (difference) in the mutual capacitance between adjacent electrodes can be used to estimate a capacitance between an electrode and the conductive element432at the point of contact434. The estimated capacitance between the electrode and the conductive element432at the point of contact434can be used to calculate an estimate of the force applied by the conductive element432at the point of contact434. In this second implementation, referring toFIG. 4, information provided by and obtained from all of the electrodes308a-fcan be used in calculating an estimate of the force applied by the conductive element432at the point of contact434.

As described, changes in mutual capacitance between adjacent electrodes and changes in the self-capacitance of electrodes located at distances that are farther from a point of contact can be used when calculating an estimate of a force applied by a conductive element432at a point of contact on a surface of a touch-sensitive input device. Equation 3 shows a representation of a calculation for determining an estimate of a force applied by a conductive element432at the point of contact434on the surface302of the touch-sensitive input device300.
{circumflex over (F)}=f(Cn,C′n,ΔCm),  Equation 3:
where, referring toFIG. 3andFIG. 4, n=1-6, and m=1-5, and Cnis the self-capacitance (represented by capacitors316a-f(C1to C6, respectively)) of each of the electrodes308a-fwhen no contact is made with the surface302of the touch-sensitive input device300, C′nis the self-capacitance (represented by capacitors416a-f(C′1to C′6, respectively)) of each of the electrodes308a-fwhen contact is detected with the surface302of the touch-sensitive input device300at the point contact434, and ΔCm=|Cm-C′m| is the change in the mutual capacitance between two electrodes. Referring toFIG. 3, capacitors330a-e(CM1to CM5, respectively) are representative of a mutual capacitance between adjacent electrodes308a-fwhen no contact is detected with the surface302of the touch-sensitive input device300. Referring toFIG. 4, capacitors430a-e(C′M1to C′M5, respectively) are representative of a mutual capacitance between adjacent electrodes308a-fwhen contact is detected with the surface302of the touch-sensitive input device300at the point of contact434.

In some implementations, a contact of a conductive element432(e.g., a finger of a user, a stylus) with the surface302of the touch-sensitive input device300can be detected when a measured capacitance for the contact meets or exceeds a particular threshold value. The use of a threshold value can eliminate possible false contact detections.

Referring toFIG. 4, the farther away from the point of contact434a capacitance is measured, the smaller the measured value of the capacitance will be. For example, the value of the measured capacitance represented by capacitor436cwill be greater than the value of the measured capacitance represented by capacitor436b. In another example, the value of the measured capacitance represented by capacitor436dwill be greater than the value of the measured capacitance represented by capacitor436e.

In the example shown inFIG. 4, the point of contact434is located in approximately a center of the touch-sensitive input device300. In some cases, the point of contact can be located closer to a first end438aof the touch-sensitive input device300. In some cases, the point of contact can be located closer to a second end438bof the touch-sensitive input device300. The closer the point of contact is to an end of the touch-sensitive input device300, the less bend the cover glass304may exhibit.

FIG. 5is a block diagram illustrating example modules included in a computing device500. For example, the computing device500can be the computing device102as shown inFIG. 1or the computing device202as shown inFIG. 2. In the example ofFIG. 5, the computing device500includes a processor520and a memory530. In some implementations, the processor520can be at least one controller or other type of semiconductor computing device. The computing device500can be operatively coupled to input devices540. The computing device500can be operatively coupled to a touchscreen550. In some implementations, the touchscreen550can be included in (can be part of and integrated with) the computing device500. In some implementations, one or more (or all of) the input devices540can be included in (can be part of and integrated with) the computing device500.

The computing device500can receive input data from one or more of the input devices540. A user of the computing device500may interact with one or more of the input devices540to provide input to an application running on the computing device500. For example, the processor520can execute the application that may be stored in the memory530. The application can display a user interface on the touchscreen550. The user can interact with one or more of the input devices540in order to interact with and/or provide input to the application. Referring also toFIG. 1, the input devices540can include, but are not limited to, a keyboard552(e.g., the keyboard108), a pointing device556(e.g., the pointer button110), and mouse buttons558(e.g., mouse buttons118a-d). In some implementations, the touchscreen550(e.g., the touchscreen display device120) can be considered a display device and an input device.

In some implementations, each input device (e.g., input devices552,554,556, and558) can be configured to include circuitry and logic to process a physical input received by the respective input device into data that the input device can provide to the computing device500. For example, the keyboard552can detect a user pressing the “a” key on the keyboard and can provide the input of the letter “a” (e.g., a binary representation of the letter “a”) to the computing device500. For example, the pointing device556and/or the mouse buttons558can detect user interactions and contact and can provide data representative of the interactions to the computing device500for input to an application running on the computing device500.

The trackpad554includes a trackpad controller560, a pressure detection module562, and a location detection module564. Referring toFIG. 1, the trackpad554can operate in a manner similar to the operation of the touchpad114and the touch-sensitive input device300as disclosed herein. For example, the trackpad554can detect contact with a surface of the trackpad554using the trackpad controller560. The location detection module564can determine that the contact with the surface of the trackpad554is at a particular area (e.g., x-y location, a point of contact) on the trackpad554. The pressure detection module562can determine (calculate using the trackpad controller560) pressure (a force) at the area (e.g., x-y location, a point of contact) on the trackpad554as input to an application running on the computing device500. The trackpad554can provide the determined point of contact on the trackpad554and the calculated pressure of the contact to the computing device500. The computing device500can provide the received location of the point of contact on the trackpad554and the calculated pressure of the contact as input to an application running on the computing device500.

The touchscreen550includes a touchscreen controller570, a pressure detection module572, a location detection module574, and a display576. Referring toFIG. 1, the touchscreen550can operate in a manner similar to the operation of the touchscreen display device120and the touch-sensitive input device300as disclosed herein. For example, the touchscreen550can detect contact with a surface of the touchscreen550using the touchscreen controller570. The location detection module574can determine that the contact with the surface of the touchscreen550is at a particular area (e.g., x-y location, a point of contact) on the touchscreen550. The pressure detection module572can determine (calculate using the touchscreen controller570) pressure at the area (e.g., x-y location, a point of contact) on the touchscreen550as input to an application running on the computing device500. The display576can provide (show) a graphical user interface (GUI) to a user interacting with the touchscreen550. For example, an application executing on the computing device500can display a GUI that allows the user to enter and manipulate text and/or images in a document displayed by the application in the GUI. The touchscreen550can provide the determined point of contact on the touchscreen550and the calculated pressure of the contact to the computing device500. The computing device500can provide the received location of the point of contact on the touchscreen550and the calculated pressure of the contact as input to an application running on the computing device500.

Though shown as separate devices in the example inFIG. 5, in some implementations, for example when the touchscreen550and the input devices540are part of (integrated in) the computing device500, the touchscreen controller570and the trackpad controller560can be the same device. In these implementations, in some cases, the processor520can perform the function of one or both of the trackpad controller560and the touchscreen controller570, eliminating the need for the discrete devices. In some implementations, for example when the touchscreen550and the input devices540are part of (integrated in) the computing device500, the pressure detection module562and the pressure detection module572may be the same module. In addition or in the alternative, the location detection module574and the location detection module564may be the same module.

FIG. 6is a flowchart that illustrates a method600for identifying contact with a surface of a touch-sensitive input device. In some implementations, the systems, methods, and processes described herein can implement the method600. For example, the method600can be described referring toFIGS. 1-5

Contact with a surface of a touch-sensitive input device is identified by a computing device (block602). For example, referring toFIG. 4, the touch-sensitive input device300can detect (determine or identify) when a user is touching (making contact with) the surface302of the touch-sensitive input device300. For example, a finger of the user contacts (touches) the surface302at the point of contact434. In another example, a tip or point of a stylus contacts (touches) the surface302at the point of contact434. The contact and applied force can be shown in general by a conductive element432contacting (touching) the surface302of the touch-sensitive input device300at the point of contact434.

A location of the contact on the surface of the touch-sensitive input device is identified by the computing device (block604). For example, in addition to detecting when a user is making contact with the surface302of the touch-sensitive input device300, a location of the contact on the surface302of the touch-sensitive input device300(e.g., the point of contact434) can be identified or determined.

A change in a mutual capacitance between a first electrode and a second electrode included in a sensor module disposed below the surface of the touch-sensitive input device is calculated (block606). The first electrode can be adjacent to the second electrode. The first electrode and the second electrode can be located approximate to the identified location of the contact on the surface of the touch-sensitive input device. For example, referring toFIG. 3andFIG. 4, the change in the mutual capacitance can be the difference between the mutual capacitance between the first electrode and the second electrode when no contact is detected with the surface302of the touch-sensitive input device300(mutual capacitance330b) and a mutual capacitance between the first electrode and the second electrode when contact is detected with the surface302of the touch-sensitive input device300(mutual capacitance430b).

A contact-coupled capacitance based on the calculated change in a mutual capacitance between the first electrode and the second electrode can be estimated (block608). For example, referring toFIG. 3andFIG. 4, a change (difference) in the mutual capacitance between the first electrode (e.g., electrode308b) and the second electrode (e.g., electrode308c) can be used to estimate a capacitance between the first electrode and the conductive element432at the point of contact434(e.g., the capacitor436b).

A force applied to the surface of the touch-sensitive input device at the identified location can be calculated based on a change in self-capacitance of the first electrode and the second electrode and based on the estimated contact-coupled capacitance (block610). For example, equation 3 above shows a representation of a calculation for determining an estimate of a force applied by a conductive element432at the point of contact434on the surface302of the touch-sensitive input device300.

The memory704stores information within the computing device700. In one implementation, the memory704is a volatile memory unit or units. In another implementation, the memory704is a non-volatile memory unit or units. The memory704may also be another form of computer-readable medium, such as a magnetic or optical disk.

The computing device700may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a standard server720, or multiple times in a group of such servers. It may also be implemented as part of a rack server system724. In addition, it may be implemented in a personal computer such as a laptop computer722. Alternatively, components from computing device700may be combined with other components in a mobile device (not shown), such as device750. Each of such devices may contain one or more of computing device700,750, and an entire system may be made up of multiple computing devices700,750communicating with each other.

The processor752can execute instructions within the computing device750, including instructions stored in the memory764. The processor may be implemented as a chipset of chips that include separate and multiple analog and digital processors. The processor may provide, for example, for coordination of the other components of the device750, such as control of user interfaces, applications run by device750, and wireless communication by device750.

Processor752may communicate with a user through control interface758and display interface756coupled to a display754. The display754may be, for example, a TFT LCD (Thin-Film-Transistor Liquid Crystal Display) or an OLED (Organic Light Emitting Diode) display, or other appropriate display technology. The display interface756may comprise appropriate circuitry for driving the display754to present graphical and other information to a user. The control interface758may receive commands from a user and convert them for submission to the processor752. In addition, an external interface762may be provide in communication with processor752, so as to enable near area communication of device750with other devices. External interface762may provide, for example, for wired communication in some implementations, or for wireless communication in other implementations, and multiple interfaces may also be used.

The computing device750may be implemented in a number of different forms, as shown in the figure. For example, it may be implemented as a cellular telephone780. It may also be implemented as part of a smart phone782, personal digital assistant, or other similar mobile device.