Patent Publication Number: US-9851853-B2

Title: Low power scan for device wake up and unlock

Description:
FIELD OF THE DISCLOSURE 
     This relates generally to touch sensitive devices, and in particular, to a low power scan mode for waking up and unlocking touch sensitive devices. 
     BACKGROUND OF THE DISCLOSURE 
     Portable electronic devices, such as mobile telephones, media players and wearable devices can operate using a battery as a source of power. The battery can have a limited amount of power and lifetime before recharging. Therefore, portable electronic devices can have stringent power consumption requirements to make sure that they are able to power the device for an adequate amount of time, without requiring big and heavy batteries to do so. To conserve battery power, it may be beneficial to reduce the power consumption of applications, reduce computing complexity and provide full functionality (and a resultant increase in power consumption) only when necessary. 
     SUMMARY 
     This relates to a low power scan for device wake up and unlock. The low power scan can include one or more algorithms used to detect a sequence and/or one or more gestures to wake up a processor and unlock the device for user interaction. A sequence and/or one or more gestures can be determined by a microcontroller and/or by a separate hardware component. The microcontroller can send a notification or a wake signal to the processor. The notification can wake the processor, and the processor can unlock the device and/or power on one or more components. By determining whether to unlock the device and/or switch the device from an idle state to an active state in the microcontroller before powering on or waking up the processor, the amount of power consumed can be reduced, and the battery life can be extended. In some examples, the one or more algorithms can include logic to prevent false wake ups from artifacts, such as a water splash, a water film, or noise, generating a touch signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1C  illustrate systems in which examples of the disclosure can be implemented. 
         FIG. 2A  illustrates an exemplary block diagram of a computing system for detecting or scanning a touch surface for a sequence and/or one or more gestures. 
         FIG. 2B  illustrates an exemplary process for detecting or scanning a touch surface for a sequence and/or one or more gestures. 
         FIG. 3  illustrates an exemplary process for unlocking a device according to examples of the disclosure. 
         FIG. 4A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor for unlocking a device by detecting a presence of a touch using a low power scan according to examples of the disclosure. 
         FIGS. 4B-4C  illustrate exemplary values for unlocking a device by detecting a presence of a touch using a low power scan according to examples of the disclosure. 
         FIG. 4D  illustrates an exemplary process for unlocking a device by detecting a presence of a touch using a low power scan according to examples of the disclosure. 
         FIG. 5A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor for unlocking a device by rejecting a presence of an object covering the device surface using a low power scan according to examples of the disclosure. 
         FIGS. 5B-5D  illustrate exemplary values for unlocking a device by rejecting a presence of an object covering the device surface using a low power scan according to examples of the disclosure. 
         FIG. 5E  illustrates an exemplary process for unlocking a device by rejecting a presence of an object covering the device surface using a low power scan according to examples of the disclosure. 
         FIG. 6A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor for unlocking a device by detecting a presence of a finger using a low power scan according to examples of the disclosure. 
         FIGS. 6B-6D  illustrate exemplary values for unlocking a device by detecting a presence of a finger using a low power scan according to examples of the disclosure. 
         FIG. 6E  illustrates an exemplary process for unlocking a device by detecting a presence of a finger using a low power scan according to examples of the disclosure. 
         FIG. 6F  illustrates an exemplary process for detecting a presence of a finger based on area and density using a low power scan according to examples of the disclosure. 
         FIG. 7  illustrates an exemplary process for unlocking a device by detecting a presence of a tap using a low power scan according to examples of the disclosure. 
         FIG. 8A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor for unlocking a device by detecting a presence of a two or multiple fingers tap according to examples of the disclosure. 
         FIG. 8B  illustrates an exemplary process for unlocking a device by detecting a presence of a two or multiple fingers tap according to examples of the disclosure. 
         FIG. 8C  illustrates an exemplary process for unlocking a device by detecting a presence of a two fingers tap and hold using a lower power scan according to examples of the disclosure. 
         FIG. 9  illustrates an exemplary process for unlocking a device by detecting a presence of a finger swipe according to examples of the disclosure. 
         FIG. 10A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor with a water splash located on the touch screen generating a false wake up according to examples of the disclosure. 
         FIG. 10B  illustrates exemplary values for a water splash located on a touch screen according to examples of the disclosure. 
         FIG. 10C  illustrates an exemplary process for rejecting water splashes according to examples of the disclosure. 
         FIG. 10D  illustrates an exemplary scatter plot of centroid positions for real touches and water splashes according to examples of the disclosure. 
         FIG. 10E  illustrates an exemplary scatter plot of the radii of real touches and water splashes according to examples of the disclosure. 
         FIG. 10F  illustrates a three-dimensional plot of corrected values and a shape for an exemplary finger touch image according to examples of the disclosure. 
         FIG. 10G  illustrates a three-dimensional plot of corrected values and a shape of an exemplary water splash located on a touch screen according to examples of the disclosure. 
         FIG. 10H  illustrates an exemplary scatter plot of the relative shape for real touches and water splashes according to examples of the disclosure. 
         FIG. 11  illustrates an exemplary state machine for recognizing a tap gesture according to examples of the disclosure. 
         FIG. 12  illustrates an exemplary computing system that can utilize sensing device according to various examples of the disclosure. 
         FIG. 13  illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific examples that can be practiced. It is to be understood that other examples can be used and structural changes can be made without departing from the scope of the disclosed examples. 
     Various techniques and process flow steps will be described in detail with reference to examples as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects and/or features described or referenced herein. It will be apparent, however, to one skilled in the art, that one or more aspects and/or features described or referenced herein may be practiced without some or all of these specific details. In other instances, well-known process steps and/or structures have not been described in detail in order to not obscure some of the aspects and/or features described or referenced herein. 
     Further, although process steps or method steps can be described in a sequential order, such processes and methods can be configured to work in any suitable order. In other words, any sequence or order of steps that can be described in the disclosure does not, in and of itself, indicate a requirement that the steps be performed in that order. Further, some steps may be performed simultaneously despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modification thereto, does not imply that the illustrated process or any of its steps are necessary to one or more of the examples, and does not imply that the illustrated process is preferred. 
     Touch-sensitive screens (“touch screens” or “touchscreens”) can be used in many electronic devices to display graphics and text, and to provide a user interface through which a user may interact with the devices. A touch screen can detect and respond to contact on the touch screen. A device can display one or more soft keys, menus, and other user-interface objects on the touch screen. A user may interact with the device by contacting the touch screen at locations corresponding to the user-interface object with which the user wishes to interact. 
     Touch screens can be included in portable electronic devices, such as laptops, tablet computing devices, cellular telephones, media players, gaming devices, handheld devices, miniature devices, wearable devices, etc. In recent years, these electronics devices have become small, light, powerful, and more user-friendly. These electronic devices generally operate using some form of battery power. Batteries, however, can only provide a limited amount of power for a limited amount of time before being drained. Therefore, portable electronic devices can have stringent power requirements to make sure that they are able to power the device for an adequate amount of time, without requiring big and heavy batteries to do so. 
     To conserve battery power, the device can have several operating states. Each state can be associated with a level of availability of the computing device, and each state can have a related amount of power consumed. For example, the device can be in an active state with a relatively higher power consumption. Other states can include, but are not limited to, a sleep state and a standby state, with lower power consumption. 
     In an idle state (e.g., sleep state or standby state), some or all of the components (such as a processor) can be powered down, and the device can be idle. To unlock the device or to switch the device from an idle state to an active state, any number of unlocking procedures, such as pressing a sequence of on-screen buttons or performing one or more gestures (simultaneously or sequentially), can be used. The sequence and/or gestures can be detected by using a series of processing steps including a watershed algorithm to determine the boundaries of one or more touch regions, calculating the centroid of each region, transferring the information to the processor, and then performing tap and event gesturing parsing. However, these series of processing steps can be complex and can involve a significant amount of processing power and hence, can consume a significant amount of battery life. 
     This disclosure relates to a low power scan for device wake up and unlock. The low power scan can include one or more algorithms used to detect a sequence and/or one or more gestures to wake up the processor and unlock the device for user interaction. A sequence and/or one or more gestures can be determined by a controller, such as a microcontroller or touch controller, and/or by a separate hardware component. The controller can send a notification or a wake signal to the processor. The notification can wake the processor, and the processor can unlock the device and/or power on one or more components. By making the determination whether to unlock the device and/or switch the device from an idle state to an active state in the controller before powering on or waking up the processor, the amount of power consumed can be reduced, and the battery life can be extended. 
     Representative applications of methods and apparatus according to the present disclosure are described in this section. These examples are being provided solely to add context and aid in the understanding of the described examples. It will thus be apparent to one skilled in the art that the described examples may be practiced without some or all of the specific details. In other instances, well-known process steps have been described in detail in order to avoid unnecessarily obscuring the described examples. Other applications are possible, such that the following examples should not be taken as limiting. 
       FIGS. 1A-1C  illustrate systems in which examples of the disclosure can be implemented.  FIG. 1A  illustrates an exemplary mobile telephone  136  that can include a touch screen  124 .  FIG. 1B  illustrates an exemplary media player  140  that can include a touch screen  126 .  FIG. 1C  illustrates an exemplary wearable device  144  that can include a touch screen  128  and can be attached to a user using a strap  146 . The systems of  FIGS. 1A-1C  can utilize the one or more low power scan and detection mechanisms for device wake up and unlock as will be disclosed. 
     The one or more devices as illustrated in  FIGS. 1A-1C  can have several operating states that can range from fully on (e.g., active state) when a central processing unit (CPU) can be powered on and operational, to a CPU stop state where the CPU can be powered off but a software state can be saved in random access memory (RAM), to a very low power state (e.g., sleep state) where the software state can be saved in a non-volatile memory (such as a hard drive) and then the memory and CPU can be powered off, though the disclosure is not limited to just these states. Some operating states can consume relatively more power than others can. Often times, to help conserve energy (and battery life for portable electronic devices), the portable electronic devices can switch to a lower powered state, such as a standby state or a sleep state, when user interaction is reduced or temporarily absent. In some examples, a standby state can consume more power than a sleep state. In a sleep state, substantially all of the device components can be powered down. In a standby state, one or more components can be powered down, while one or more components can be fully or partially on. For example, in a standby state, a touch panel and display can be powered down while a wireless transceiver can be fully on. The device can continue to receive messages or data through the Internet while the user is not interacting with the device. 
     When a device is in an active state and user interaction is reduced or temporarily absent, the device can include a timer. The timer can monitor or track the amount of time until a user interaction is received. If a certain amount of time has elapsed since a user interaction has been received, the device can automatically switch to an idle state. In some examples, the user can force the device to enter the idle state. When the user wishes to interact with the device and/or switch the device from an idle state to an active state, the user can “unlock” the device by pressing a sequence of one or more buttons or performing one or more gestures (simultaneously or sequentially). 
       FIG. 2A  illustrates an exemplary block diagram of a computing system, and  FIG. 2B  illustrates an exemplary process for detecting or scanning a touch surface for a sequence or one or more gestures. Computing system  200  can correspond to any of the computing devices illustrated in  FIGS. 1A-1C . Additionally, computing system  200  can also correspond to public computer systems such as information kiosks, automated teller machines (ATM), point of sale machines (POS), industrial machines, gaming machines, arcade machines, vending machines, airline e-ticket terminals, restaurant reservation terminals, customer service stations, library terminals, learning devices, and the like. 
     Computing system  200  can include a processor  210  configured to execute instructions and to carry out operations associated with computing system  200 . For example, using instructions retrieved from memory, processor  210  can control the reception and manipulation of input and output data between components of the computing system  200 . Processor  210  can be a single-chip processor or can be implemented with multiple components. 
     In some examples, processor  210  together with an operating system can operate to execute computer code and produce and use data. The computer code and data can reside within a program storage block  202  that can be operatively coupled to the processor  210 . Program storage block  202  can generally provide a place to hold data that is being used by the computing system  200 . By way of example, the program storage block  202  can include Read-Only Memory (ROM)  204 , Random-Access Memory (RAM)  206 , hard disk drive  208  and/or the like. The computer code and data could also reside on a removable storage medium and loaded or installed onto the computing system  200  when needed. Removable storage mediums include, for example, CD-ROM, DVD-ROM, Universal Serial Bus (USB), Secure Digital (SD), Compact Flash (CF), Memory Stick, Multi-Media Card (MMC) and a network component. 
     Computing system  200  can also include an input/output (I/O) controller  212  that can be operatively coupled to processor  210  or it may be a separate component as shown. The I/O controller  212  can be configured to control interactions with one or more I/O devices. The I/O controller  212  can operate by exchanging data between the processor  210  and the I/O devices that desire to communicate with the processor  210 . The I/O devices and the I/O controller  212  typically communicate through a data link. The data link may be a one way link or a two way link. In some cases, I/O devices can be connected to the I/O controller  212  through wireless connections. By way of example, a data link can correspond to PS/2, USB, Firewire, IR, RF, Bluetooth or the like. 
     Computing system  200  can include a display device  220  that can be operatively coupled to processor  210 . Display device  220  can be a separate component (peripheral device) or may be integrated with the processor  210  and program storage block  202  to form a desktop computer (all in one machine), a laptop, handheld or tablet computing device or the like. Display device  220  can be configured to display a graphical user interface (GUI) including perhaps a pointer or cursor as well as other information to the user. By way of example, display device  220  can be any type of display including liquid crystal displays (LCDs), electroluminescent displays (ELDs), field emission displays (FEDs), light emitting diode displays (LEDs), organic light emitting diode displays (OLEDs) or the like. 
     Computing system  200  can also include a touch screen  230  that can be operatively coupled to processor  210 . Touch screen  230  can be the combination of sensing device  232  and display device  220 , where the sensing device  232  can be a transparent panel that is positioned in front of the display device  220  or integrated with the display device. In some cases, touch screen  230  can recognize touches and the position and magnitude of touches on its surface. Touch screen  230  can report the touches to processor  210 , and the processor can interpret the touches in accordance with its programming. For example, processor  210  can perform tap and event gesture parsing and can initiate a wake of the device or powering on one or more components in accordance with a particular touch. 
     In some examples, the touch screen  230  can be capable of tracking multiple objects, which rest on, tap on, or move across the touch sensitive surface of the touch screen. The touch screen  230  can include a sensing device  232  configured to detect an object in close proximity thereto and/or the pressure exerted thereon. The sensing device  232  can be divided into several independent and spatially distinct sensing electrodes, nodes or intersections  234  that are positioned throughout. Sensing electrodes  234  can be dispersed about the touch screen  230  with each sensing electrode  234  representing a different position on the surface of the touch screen  230  (or touch screen plane). The sensing electrodes  234  can be positioned in a grid or a pixel array where each pixilated sensing electrode  234  can be capable of generating a signal at a same time. In the simplest case, a signal can be produced each time an object is positioned over a sensing electrode  234 . When an object is placed over multiple sensing electrodes  234  or when the object is moved between or over multiple sensing electrodes  234 , multiple signals can be generated. 
     The number and configuration of the sensing electrodes  234  can be widely varied. The number of sensing electrodes  234  can depend on the desired sensitivity as well as the desired transparency of the touch screen  230 . More nodes or sensing electrodes  234  generally increases sensitivity, but reduces transparency (and vice versa). With regard to configuration, the sensing electrodes  234  can map the touch screen plane into a coordinate system such as a Cartesian coordinate system, a Polar coordinate system or some other coordinate system. When a Cartesian coordinate system is used (as shown), the sensing electrodes  234  can correspond to x and y coordinates. When a Polar coordinate system is used, the sensing electrodes can correspond to radial (r) and angular coordinates (θ). 
     Touch screen  230  can be coupled to a touch controller or sensing circuit  240  that can acquire data from the touch screen and can supply the acquired data to the processor  210 . In some cases, the sensing circuit  240  can be configured to send raw data to the processor  210  so that the processor  210  processes the raw data. For example, the processor  210  can receive data from the sensing circuit  240  and can determine how to interpret the data. The data can include the coordinates in each sensing electrode  234  as well as the pressure exerted on each sensing electrode  234 . In some examples, sensing circuit  240  can be configured to process the raw data itself. That is, the sensing circuit  240  can read the signals from the sensing electrodes  234  and turn them into data that the processor  210  can understand. Sensing circuit  240  can perform filtering and/or conversion processes. Filtering processes can be implemented to reduce a busy data stream to prevent the processor  210  from being overloaded with redundant or non-essential data. The conversion processes can be implemented to adjust the raw data before sending or reporting them to the processor  210 . The conversion can include determining the center point for each touch region (e.g., centroid). 
     The sensing circuit  240  can include one or more microcontrollers, each of which monitors one or more sensing electrodes  234 . The microcontrollers can, for example, correspond to an application specific integrated circuit (ASIC), which works with firmware to monitor the signals from the sensing device  232  and to process the monitored signals and to report this information to the processor  210 . 
     In some examples, sensing device  232  is based on capacitance. When two electrically conductive members come close to one another without actually touching, their electric fields can interact to form a capacitance. The first electrically conductive member can be a sensing electrode  234  and the second electrically conductive member can be an object  290  such as a finger. As the object  290  approaches the surface of the touch screen  230 , a capacitance can form between the object  290  and the sensing electrodes  234  in close proximity to object  290 . By detecting changes in capacitance at each of the sensing electrodes  234  and noting the position of the sensing electrodes  234 , the sensing circuit  240  can recognize multiple objects, and determine the location, pressure, direction, speed and acceleration of the objects  290  as they move across the touch screen  230 . For example, the sensing circuit  240  can determine whether the sensed touch is a finger, tap, or an object covering the surface. 
     The sensing device  232  can be based on self-capacitance or mutual capacitance. In self-capacitance, each of the sensing electrodes  234  can be provided by an individual charged electrode. As an object approaches the surface of the touch screen  230 , the object capacitively couples to those electrodes in close proximity to the object, thereby stealing charge away from the electrodes. The amount of charge in each of the electrodes can be measured by the sensing circuit  240  to determine the positions of multiple objects when they touch the touch screen  230 . In mutual capacitance, the sensing device  232  can include a two layer grid of spatially separated lines or wires, although other configurations are possible. The upper layer can include lines in rows while the lower layer can include lines in columns (e.g., orthogonal). The sensing electrodes  234  can be provided at the intersections of the rows and columns. During operation, the rows can be charged, and the charge can be capacitively coupled from the rows to the columns. As an object approaches the surface of the touch screen  230 , the object capacitively couples to the rows in close proximity to the object, thereby reducing the charge coupling between the rows and columns. The amount of charge in each of the columns can be measured by the sensing circuit  240  to determine the position of multiple objects when they touch the touch screen  230 . 
       FIG. 2B  illustrates an exemplary process for unlocking a device by detecting a sequence or one or more gestures. Process  250  can include scanning sensing device  232  in step  252 . Object  290  can touch the touch surface, and sensing device  232  can form a touch “image.” The microcontroller  242  in the sensing circuit  240  can receive the signals or capacitance values from the sensing device  232 , and can perform a baseline subtraction on the signals in step  254 . In step  256 , the microcontroller can determine the boundaries of the touch image using a watershed algorithm. Generally speaking, the watershed algorithm can perform image segmentation, which can partition the image into distinct regions as, for example, the regions of multiple objects come in contact with the touch screen. In some examples, step  256  can include image filtering and/or smoothing. 
     In step  258 , the microcontroller can determine the coordinates for each of the calculated touch regions using a centroid calculation with the raw data associated with each touch region. The centroid can include the central coordinate of the touch region. In some examples, the microcontroller can compute features associated with each touch region, such as second and higher moments, area, density, major and minor axes and orientation for a best fit ellipse, wavelet and other types of region shape and density features. In step  260 , the microcontroller (located in the sensing circuit  240 ) can send the processed information to the processor  210 . The processor  210  can then perform tap and event gesture parsing in step  262 . Based on the results from the tap and event gesture parsing, processor  210  can determine if the touch matches the unlock sequence or gesture. 
     While the process exemplified in  FIG. 2B  can be used to detect a sequence and/or one or more gestures for unlocking a device, the calculations performed in steps  256  and  258  can consume a significant amount of processing power. Additionally, transmitting the calculated touch information from the microcontroller to the processor  210  can consume additional power and can require the processor to wake (thereby requiring more power) before determining whether or not to unlock the device. A detection mechanism that is simpler, faster, and consumes less power can be desired. 
       FIG. 3  illustrates an exemplary process for unlocking a device according to examples of the disclosure. Process  350  can include scanning the touch screen using selected drive lines and selected touch lines or sensing electrodes (step  352 ). To conserve power, one or more drive lines and/or one or more sense lines can be activated, while the other drive and sense lines can be powered down. In some examples, multiple drive lines and/or multiple sense lines can be switched to the same circuitry to reduce power consumption. In some examples, drive and sense lines can be activated in some areas of the screen and deactivated in other areas. For example, drive and sense lines whose intersection occurs in the center of the screen can be activated, while other drive and sense lines can be deactivated. In some examples, all of the drive and sense lines can be activated, and the low power scan can include a full scan of the touch screen. 
     In step  354 , a baseline subtraction can be performed by the microcontroller. In step  356 , the microcontroller can detect the presence of a touch, finger, tap, or swipe using any one of the examples described below. In some examples, step  356  can be performed by a separate hardware component. In some examples, step  356  can be performed in firmware. In step  358 , the microcontroller can send a notification or a wake signal to the processor  210 . The notification can wake the processor  210 , and the processor  210  can unlock the device and/or power on one or more components in step  360 . By determining whether to unlock the device and/or switch the device from an idle state to an active state before powering on or waking up the processor, the amount of power consumed can be reduced, and the battery life can be extended. In some examples, the processor can consume a greater amount of power in the active state than the controller consumes in the active state. 
       FIGS. 4A-4D  illustrate an exemplary block diagram, exemplary values, and an exemplary process for unlocking a device by detecting a presence of a touch using a low power scan according to examples of the disclosure. Process  450  can include scanning the sensing device  432  of touch screen  430  in step  452 . As illustrated in  FIG. 4A , sensing device  432  can include a plurality of sensing electrodes such as sensing point  434 . Touch screen  430  can be operatively coupled to a sensing circuit  440 . Sensing circuit  440  can include a microcontroller  442  and can be operatively coupled to a processor  410 . In some examples, the scan can be limited to a certain area. For example, scanning the sensing device  432  can be limited to activating only those sensing points  434  located in the center of the sensing device  432 . Although sensing device  432  is illustrated in  FIG. 4A  as a mutual capacitive touch sensing device, examples of the disclosure can include a self-capacitive touch sensing device. 
     Values at the sensing points  434  can be determined. As shown in  FIG. 4B , a user touching the surface of touch screen  430  can be sensed by sensing point  434  located at the intersection of drive line D 2  and sense line S 2  and can generate a value of 25, for example. In step  454 , the microcontroller  442  can perform a baseline subtraction (or division) on the generated value using a predetermined baseline value. For example, the predetermined baseline value can be 5, resulting in a corrected value of 20, as shown in  FIG. 4C . In some examples, the predetermined baseline value can be indicative of a noise level in the absence of a touch. In step  456 , the corrected value can be compared to a touch detection threshold. If the corrected value is greater than or equal to the touch detection threshold, microcontroller  442  can send a wake notification to processor  410  in step  458 . In step  460 , processor  410  can wake up in response to the received notification and can unlock the device. Otherwise, the device can remain locked (step  462 ). 
     To conserve power and extend battery life, the device should not wake when sensing a large body contact, such as being covered by a palm, crossed arms, the device placed in a pocket, etc.  FIGS. 5A-5E  illustrate an exemplary block diagram, exemplary values, and an exemplary process for preventing the unlocking of a device by rejecting the presence of an object covering the device surface using a low power scan according to examples of the disclosure. As illustrated in  FIG. 5E , process  550  can include scanning the sensing device  532  of touch screen  530  in step  552 . As illustrated in  FIG. 5A , sensing device  532  can include a sensing points  534 . Touch screen  530  can be operatively coupled to sensing circuit  540 , and sensing circuit  540  can include a microcontroller  542 . Sensing circuit can be operatively coupled to a processor  510 . Although sensing device  532  is illustrated in  FIG. 5A  as a mutual capacitive touch sensing device, examples of the disclosure can include a self-capacitive touch sensing device. 
     An object (e.g., a large body contact) can be covering the surface of the touch screen  530  (i.e., a cover touch), and can lead to a plurality of sensing points  534  detecting the presence of the object. As shown in  FIGS. 5A-5B , the presence of the object covering the surface of the touch screen  530  can cause a change in capacitance (as described earlier). The change in capacitance can be sensed at those sensing points  534 . In step  554 , microcontroller  542  can perform a baseline subtraction (or division) on the touch values using a predetermined baseline value or noise threshold. For example, the predetermined baseline value can be 5, and performing a baseline subtraction can lead to the corrected values shown in  FIG. 5C . In step  556 , the corrected values can be sorted in ascending (or descending) order, as shown in  FIG. 5D . 
     In step  558 , microcontroller  542  can sum together a certain number (e.g., N number) of sensing electrodes with the lowest corrected values (compared to all or a subset of all of the corrected values). In step  560 , microcontroller  542  can sum together a certain number (e.g., M number) of sensing electrodes with the highest corrected values (compared to all or a subset of all of the corrected values). For example, N can be 6, and M can be 4. The sum of the N sensing electrodes with the lowest corrected values (i.e., sum of the lowest) can be 150, and the sum of the M sensing electrodes with the highest corrected values (i.e., sum of the highest) can be 300. In step  562 , microcontroller  542  can compare the sum of the lowest to a first threshold value and can compare the sum of the highest to a second threshold value. If sum of the lowest is greater than the first threshold value (i.e., the touch is not a finger touch or touch from a small object) and sum of the highest is greater than the second threshold value (i.e., the touch is a hovering object), then the touch detected is a large body contact or a cover touch. As a result, the device can remain locked in step  572 . If the touch detected is not a large body contact or a cover touch, the microcontroller  542  can send a wake notification to processor  510  (step  564 ), and processor  510  can unlock the device (step  566 ). In some examples, the microcontroller  542  can check for other conditions before sending the wake notification to processor  510 . 
       FIGS. 6A-6E  illustrate an exemplary block diagram, exemplary values, and an exemplary process for unlocking a device by detecting a presence of a finger using a low power scan according to examples of the disclosure.  FIG. 6A  illustrates a touch screen  630  including sensing device  632  and coupled to a sensing circuit  640 . Sensing circuit  640  can include a microcontroller  642  and can be coupled to a processor  610 . Sensing device  632  can include a plurality of sensing points  634 . 
     As shown in  FIG. 6E , process  650  can include scanning the scanning device  632  of touch screen  630  in step  652 . A finger can be present at the surface of the touch screen  630  leading to a change in touch values at the corresponding sensing points  634  (e.g., sensing points at (D 1 ,S 2 ), (D 2 ,S 1 ), (D 2 ,S 2 ), (D 2 ,S 3 ), and (D 3 ,S 2 ) intersections) as shown in  FIG. 6B . In step  654 , microcontroller  642  can perform a baseline subtraction on the values using a predetermined baseline value. For example, a predetermined baseline value of 5 can be subtracted from the values resulting in the corrected values shown in  FIG. 6C . 
     The microcontroller  642  can determine if the touch is a finger (or another object) by looking at the area of the touch image. In step  656 , microcontroller  642  can determine a touch detection threshold. The touch detection threshold can be, for example, a value calculated from a certain percentage of full coverage (e.g., the value when the touch screen surface is fully covered). In some examples, full coverage can have a value of 1024, and the touch detection threshold can be equal to 20% full coverage or 204. In some examples, the touch detection threshold can be predetermined. For example, the touch detection threshold can have a predetermined value of 50. In step  658 , for each sensing electrode, microcontroller  642  can compare the corrected value to the touch detection threshold. Microcontroller  642  can discard any corrected values that are less than the touch detection threshold, as shown in  FIG. 6D . The microcontroller  642  can count the number of sensing electrodes with a corrected value greater than or equal to the touch detection threshold (i.e., number of peak pixels) in step  660 . For example, the number of peak pixels can be 5. In step  662 , microcontroller  642  can determine if the finger is a small finger (e.g., number of peak pixels is between 1 and 5), large finger (e.g., number of peak pixels is between 5 and 10) or a flat finger or thumb (e.g., number of peak pixels is greater than 10, but not a large body contact). If the number of peak pixels corresponds to a small finger, large finger, or flat finger or thumb, then microcontroller  642  can send a wake notification to processor  610  (step  664 ). In step  666 , processor  610  can unlock the device. If the number of peak pixels does not correspond to a small finger, large finger, or flat finger or thumb, then the device can remain locked in step  672 . 
     In some examples, both an area and density can be used as an indication of a presence of a finger.  FIG. 6F  illustrates an exemplary process for detecting a presence of a finger based on area and density according to examples of the disclosure. Similar to process  650  in  FIG. 6E , process  680  for detecting a presence of a finger based on area and density can include steps  652 - 662  for comparing the area of the touch image to an area of a finger. Process  680  can also include summing the corrected values of those sensing electrodes  634  that have a corrected value greater than or equal to a touch detection threshold and calculating a density in step  682 . For example, the sum of the corrected values of the sensing electrodes can be 375 and the density can be 75. In step  684 , microcontroller  642  can compare the density to a finger density threshold and a palm density threshold. If the density of the touch image is greater than the finger density threshold, but less than the palm density threshold, then the microcontroller  642  can send a wake notification to processor  610  (step  686 ), and processor  610  can unlock the device (step  688 ). If the density of the touch image is less than the finger density threshold or the density of the touch image is greater than the palm density threshold, the device can remain locked (step  690 ). The finger density threshold can be a value representative of a finger touch, and palm density threshold can be a value representative of a palm touch. 
       FIG. 7  illustrates an exemplary process for unlocking a device by detecting a presence of a tap using a low power scan according to examples of the disclosure. Detecting a presence of a tap can include the microcontroller rejecting any touches that are large body contacts (as illustrated in  FIGS. 5A-5E , for example) and determining if the touch is a finger touch (as illustrated in  FIGS. 6A-6F , for example). Process  750  for detecting a tap can further include capturing corrected values for the plurality of sensing electrodes in frames (step  752 ), and storing the result of each frame in a local memory or frame history (step  754 ). In step  756 , the microcontroller can compare the results from a frame history. Based on the results from the frame history, the microcontroller can determine if the touch is a tap (step  758 ). In some examples, determining the touch is a tap can include a finger touch detected in one frame and no finger touch detected in a following frame. In some examples, the touch can be rejected as a tap if the duration of the touch exceeds a predetermined number of frames or a predetermined duration. In some examples, the touch can be rejected as a tap if its centroid position is not substantially near a center of the touch screen as determined by exceeding a predetermined distance threshold. The microcontroller can send a wake notification to the processor (step  760 ), and the processor can unlock the device (step  762 ) if the touch is a tap. If the touch is not a tap, the device can remain locked (step  772 ). 
     Although  FIG. 7  illustrates an exemplary process for unlocking a device by detecting a presence of a tap, examples of the disclosure can include detecting a presence of a double tap, detecting a presence of a finger hold, and detecting a presence of a tap followed by a finger hold. Detecting a presence of a double tap or a presence of a finger hold can include comparing the results from the frame history (step  756 ). 
     Determining if the touch is a double tap can include at least four frames. The four frames can include a finger touch detected in one frame and no finger touch detected in a following frame, followed by a finger touch detected a second time and no finger touch detected a second time. 
     Determining the touch is a finger hold can include multiple frames where the finger touch is detected. In some examples, the number of frames can be higher and/or can be based on a sampling rate. In some examples, determining a presence of a tap can include determining whether the touch is located within a certain region. 
     In some examples, the finger touch detected can be in substantially the same location. In some examples, the finger touch detected can have substantially the same area. In some examples, the frames can be consecutive. 
     Detecting a presence of a tap followed by a finger hold can include at least four frames. The four frames can include a finger touch detected in one frame, no finger touch detected in a following frame, followed by a finger touch detected a second time for multiple frames. 
       FIGS. 8A-8B  illustrate an exemplary block diagram and an exemplary process for unlocking a device by detecting a presence of a two or multiple fingers tap according to examples of the disclosure. Detecting a presence of a two fingers tap can include the microcontroller scanning the sensing device  832  and rejecting any touches that are large body contacts or cover touches in step  852  of process  850 . Sensing device  832  can be segmented into regions such as region  1  and region  2  (step  854 ). Sensing device  832  can determine for each region if a touch in that region is a finger. 
     Determining if a touch in a region is a finger can include, for each sensing point  834 , a baseline subtraction (step  856 ) to result in a plurality of corrected values, comparing each corrected value to a touch detection threshold (step  858 ), counting the number of sensing electrodes  834  in a region (e.g., region  1  or region  2 ) with a corrected value greater than the touch detection threshold (step  860 ), and determining if a touch in the region is a finger touch (step  862 ). The process can be repeated for each region (step  864 ). In step  868 , the microcontroller can determine if the number of regions with a finger tap is equal to two. If a two fingers tap is present, the microcontroller can send a wake notification to the processor (step  870 ), and the processor can unlock the device (step  872 ). Otherwise, the device can remain locked (step  882 ). 
       FIG. 8C  illustrates an exemplary process for unlocking a device by detecting a presence of a two fingers tap and hold using a lower power scan according to examples of the disclosure. Process  880  can include capturing two fingers tap results in frames in step  882 , and storing the result of each frame in a frame history in step  884 . In step  886 , the microcontroller can compare the results from the frame history. Based on the results from the frame history, the microcontroller can determine if the touch is a two fingers tap (step  888 ). In some examples, determining if the touch is a two fingers tap can include a two fingers touch detected in one frame and no finger (or less than or greater than two fingers) touch detected in a following frame. In step  890 , microcontroller can determine if a two fingers hold is detected following detection of a two fingers tap. Detection of a two fingers hold can include multiple frames where a touch using two fingers is detected. If a two fingers tap or two fingers hold is not detected, the device can remain locked (step  898 ). Otherwise, the microcontroller can send a wake notification to the device (step  892 ), and the processor can unlock the device (step  894 ). 
       FIG. 9  illustrates an exemplary process for unlocking a device by detecting a presence of a finger swipe according to examples of the disclosure. Process  950  can include the microcontroller rejecting any touches that are large body contacts or cover touches (as illustrated in  FIGS. 5A-5E , for example), and determining if the touch is a finger touch (as illustrated in  FIGS. 6A-6F , for example). In step  952 , corrected values for the plurality of sensing electrodes can be captured into frames. In step  954 , the result of each frame can be stored in a frame history. In step  956 , the microcontroller can track the pattern of the finger touch. If the pattern of the finger touch over the course of several frames is similar or closely matches a finger swipe, the microcontroller can determine that a finger swipe is present (step  958 ). In some examples, determination of a finger swipe can include determining whether a line path is followed over a predetermined number of frames, determining whether a predetermined speed threshold has been exceeded, and/or determining whether the pattern of finger touch is located within a certain region or follows a certain direction. In some examples, an active region centroid location can be determined. In some examples, an active region size metric and/or active region orientation metric can be used. In some examples, frame-to-frame region correlation metric and/or frame-to-frame region velocity region can be used. In some examples, the microcontroller can limit the detection of the finger swipe to one or more designated regions on the touch screen surface. If a finger swipe is present, the microcontroller can send a wake notification to the processor (step  960 ), and the processor can unlock the device (step  962 ). If a finger swipe is not present and/or if the location of the finger swipe is not in the designated areas, the device can remain locked (step  972 ). 
     In some examples, the one or more examples described above can be sampled at a lower rate than compared to an active touch mode scan rate. In some examples, to prevent false detection, the touch, finger, tap, and/or swipe detection can be limited to a center of the touch screen. The portable electronic device can include a housing surrounding the touch screen. The housing can be made of a conductive material that can surround a peripheral area of the touch screen. Touches detected in the peripheral area of the touch screen may be from the coupled housing, and as a result, may be a false detection. 
     In some examples, the device can waste power due to false wake ups. The false wake ups can be caused by water droplets, water splashes, a water film, or noise, for example. A device that can distinguish a normal touch from a touch caused by artifacts can help eliminate or reduce the false wake ups.  FIG. 10A  illustrates an exemplary block diagram of a touch screen, sensing circuit, and processor with a water splash located on the touch screen generating a false wake up according to examples of the disclosure. Sensing device  1032  can include a plurality of sensing points  1034 . Touch screen  1030  can include sensing device  1032  housed in casing  1002  and can be operatively coupled to sensing circuit  1040 . Sensing circuit  1040  can include a microcontroller  1042  and can be operatively coupled to a processor  1010 . Water splash  1036  can be touching the surface of touch screen  1030 , and can lead to a plurality of sensing points  1034  detecting the presence of the water splash  1036  as a touch. The change in capacitance due to the water splash  1036  touching the surface of touch screen  1030  and the casing  1002  can lead to non-zero touch values detected at the corresponding sensing points  1034 . The microcontroller  1042  can perform touch detection using any one of the exemplary processes illustrated above, but can also generate a false wake up. That is, the water splash  1036  can cause the microcontroller  1042  to mistakenly believe that the non-zero touch values represent a real touch (i.e., a touch from the user&#39;s finger) indicative of the user&#39;s desire to wake up the device, and microcontroller  1042  can generate a false wake up in response to the detected touch. The microcontroller  1042  may have to perform additional computing in order to prevent false wake ups. 
       FIG. 10B  illustrates exemplary values for a water splash located on a touch screen according to examples of the disclosure. The water splash  1036  on touch screen  1030  of  FIG. 10A  can be detected by the microcontroller  1042 . Microcontroller  1042  can determine if the sensed touch is a cover touch, and cover touches can be rejected. Determination and rejection of a cover touch can include one or more of the examples described earlier. The sorted, corrected values for each of the sensing points  1034  are shown in  FIG. 10B . 
       FIG. 10C  illustrates an exemplary process flow for rejecting water splashes according to examples of the disclosure. In step  1052  of process  1050 , cover touches can be rejected (as described above). In step  1054 , microcontroller  1042  can define a centroid for the pixels whose corrected value is greater than a pre-determined threshold. The x-coordinate value for the centroid can be determined as: 
                     C   x     =         ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢           ⁢       x   i     ⁢     CV   ij               ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢     CV   ij                   (   1   )               
where x i  is the x-coordinate value of the pixel location, CV ij  is the corrected value at that location, D is the number of rows (or drive lines) and S is the number of columns (or sense lines).
 
The y-coordinate value for the centroid can be determined as:
 
                     C   y     =         ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢       y   i     ⁢     CV   ij               ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢     CV   ij                   (   2   )               
where y i  is the y-coordinate value of the pixel location.
 
       FIG. 10D  illustrates an exemplary scatter plot of centroid positions for real touches and water splashes according to examples of the disclosure. The small, solid circles can represent the centroid position for multiple real touches, and the large, open circles can represent the centroid position for multiple water splashes. The figure is illustrative of how the centroid position can be confined to the middle area of the touch screen  1030  (i.e., the centroid position of a real touch can be located within Bounded Region  1031 ). The centroid position for water, on the other hand, may not be confined to the middle area and instead, can be located throughout the touch screen  1030 , such as in peripheral areas of the touch screen (e.g., outer areas of the touch screen that are away from the center and close to the housing). Linear decision boundaries can be set for a touch to eliminate or reduce false positives for water splashes, a water film, or noise and false negatives for touch. 
     Referring again to  FIG. 10C , in step  1056 , microcontroller  1042  can reject the touches whose centroid position is not located in the center or substantially in the center position CP x , CP y . That is,
 
∥ C   x −CP x   ∥&lt;CD   (3)
 
∥ C   y −CP y   ∥&lt;CD   (4)
 
where CD can be a pre-determined distance threshold representative of the distance from the center where touches are accepted. For example, CD can be 5 mm or the size of one pixel.
 
     In step  1058 , the standard deviation in the horizontal and vertical dimensions can be computed to determine the radii R x  and R y  of the water splash  1036  in the x and y directions. 
                     R   x     =     SF   ⁢           ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢         (       x   i     -     C   x       )     2     ⁢     CV   ij               ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢     CV   ij                       (   3   )                 R   y     =     SF   ⁢           ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢         (       y   i     -     C   y       )     2     ⁢     CV   ij               ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢     CV   ij                       (   4   )               
where SF is a scale factor that can convert pixels to mm units. In some examples, the radii R x  and R y  can be calibrated using a 10 mm diameter standard probe or a size of a typical finger.
 
       FIG. 10E  illustrates an exemplary scatter plot of the radii along the x-direction and the y-direction for real touch touches and water splashes according to examples of the disclosure. As illustrated in the figure, the radii for real touches can be bounded between a certain range of radii values along the x-direction and along the y-direction (i.e., the combined radii along the x-direction and along the y-direction of a real touch can be located within Bounded Region  1033 ), whereas the radii for water splashes can be scattered throughout. Boundaries can be set to represent a user&#39;s finger touch or multiple finger touches. In some examples, the boundaries can be set during a calibration procedure. The boundaries can help eliminate or reduce false positives for water splashes and false negatives for touch. 
     In step  1060 , microcontroller  1042  can determine if the touch is within an allowed range of radii.
 
 LR&lt;R   x   &lt;UR   (5)
 
 LR&lt;R   y   &lt;UR   (6)
 
where LR and UR can be indicative of lower and upper bounds of the radii. For example, UR can be 5 mm, and water splash  1036  can have a radius R x  larger than 5 mm (or a diameter larger than 10 mm). As a result, the touch from water splash  1036  can be rejected.
 
     In addition to centroid and radii, a finger touch can resemble a specific shape, such as an ellipsoid.  FIG. 10F  illustrates a three-dimensional plot of correct values and a shape for an exemplary finger touch image according to examples of the disclosure. PeakPixel (PP) can represent the largest corrected value of the finger touch.  FIG. 10G  illustrates a three-dimensional plot of corrected values and a shape of an exemplary water splash located on a touch screen according to examples of the disclosure. In step  1062 , the volume of the touch shape can be determined. For example, the volume of an ellipsoid can be: 
                     V   ellipsoid     =       4   3     ⁢   π   ⁢           ⁢     R   x     ⁢     R   y     ⁢   PP             (   7   )               
In step  1064 , the volume of the touch can be compared to an ellipsoidal shape to determine a relative shape or an amount of discrepancy from a real touch. PeakPixelValue ij  is defined to be equal to CV ij  whenever CV ij &gt;T, or equal to zero otherwise. T can be a predetermined threshold. In some examples, T can be a fixed percentage of the sensor full scale.
 
                   LD   &lt;       V   ellipsoid         ∑     i   =   1     D     ⁢           ⁢       ∑     j   =   1     S     ⁢     PeakPixelValue   ij           &lt;   UD           (   8   )               
where DL can be a lower bounds and DH can be an upper bounds on the amount of discrepancy. The microcontroller  1042  can determine if the relative shape or amount of discrepancy is within an allowed range (step  1066 ).
 
       FIG. 10H  illustrates an exemplary scatter plot of the relative shape for a real touch and water according to examples of the disclosure. The relative shape can be indicative of the discrepancy calculated from equation (8). As illustrated in the figure, the relative shape of a real touch can be located between a lower bound (LD) and an upper bound (UD) of the amount of discrepancy, whereas the relative shape for water splashes can be scattered throughout. 
     If a touch is not a cover touch and meets the criteria for at least one of the centroid, radii, and volume of a finger touch, then the microcontroller can send a wake notification to the processor (step  1068 ), and the processor can unlock the device (step  1070 ). Otherwise, the device can remain locked (step  1072 ). 
       FIG. 11  illustrates an exemplary state machine for recognizing a tap gesture according to examples of the disclosure. The lower bound and the upper bound for the allowed times can be adjusted. In some examples, the lower bound for allowed time can be 16 ms, and the upper bound for the allowed time can be 125 ms. In some examples, the scatter plots (as illustrated above) of real touches and water splashes (or water film) can be adjusted using the lower and upper bounds for allowed time. 
     With a user finger touching down in the middle of the touch screen, the timestamp can be recorded. Cover touches can be ignored. The microcontroller can loop as long as there is a touch. When the finger is lifted, the duration can be recorded. The microcontroller can determine if the duration is within the time bounds for a tap gesture. 
       FIG. 12  illustrates an exemplary computing system  1200  that can utilize sensing device  1232  according to various examples of the disclosure. Sensing circuit  1240  can be a single application specific integrated circuit (ASIC) that can include one or more microcontrollers  1242 , which can include, for example, one or more main processors, such as ARM968 processors, ARM CortexM3 processors, or other processors with similar functionality and capabilities. However, in other examples, some of the processor functionality can be implemented instead by dedicated logic, such as a state machine. Microcontroller  1242  can also include, for example, peripherals such as random access memory (RAM)  1212  or other types of memory or storage, watchdog timers (not shown), and the like. Sensing circuit  1240  can also include, for example, receive section  1207  for receiving signals, such as touch sense signals  1203 , from the sense lines of the sensing device  1232  and other signals from other sensors such as sensor  1211 , etc. Sensing circuit  1240  can also include, for example, a demodulation section such as multistage vector demod engine  1209 , panel scan logic  1211 , and a drive system including, for example, transmit section  1214 . Panel scan logic  1212  can access RAM  1212 , autonomously read data from sense channels, and provide control for the sense channels. In addition, panel scan logic  1211  can control transmit section  1214  to generate stimulation signals  1216  at various frequencies and phases that can be selectively applied to the drive lines of the sensing device  1232 . 
     Charge pump  1215  can be used to generate the supply voltage for the transmit section. Stimulation signals  1216  (Vstim) can have amplitudes higher than the maximum voltage the ASIC process can tolerate by cascading transistors. Therefore, using charge pump  1215 , the stimulus voltage can be higher (e.g., 6V) than the voltage level a single transistor can handle (e.g., 3.6 V). Although  FIG. 12  shows charge pump  1215  separate from transmit section  1214 , the charge pump can be part of the transmit section. 
     Sensing device  1232  can include a capacitive sensing medium having a plurality of drive lines and a plurality of sense lines. The drive and sense lines can be formed from a transparent conductive medium such as Indium Tin Oxide (ITO) or Antimony Tin Oxide (ATO), although other transparent and non-transparent materials such as copper can also be used. In some examples, the drive and sense lines can be perpendicular to each other, although in other examples other non-Cartesian orientations are possible. For example, in a polar coordinate system, the sensing lines can be concentric circles and the driving lines can be radially extending lines (or vice versa). It should be understood, therefore, that the terms “drive lines” and “sense lines” as used herein are intended to encompass not only orthogonal grids, but the intersecting traces or other geometric configurations having first and second dimensions (e.g., the concentric and radial lines of a polar-coordinate arrangement). The drive and sense lines can be formed on, for example, a single side of a substantially transparent substrate. 
     At the “intersections” of the traces, where the drive and sense lines can pass adjacent to and above and below (cross) each other (but without making direct electrical contact with each other), the drive and sense lines can essentially form two electrodes (although more than two traces could intersect as well). Each intersection of drive and sense lines can represent a capacitive sensing node and can be viewed as pixel, node, or sensing electrode  1234 , which can be particularly useful when sensing device  1232  is viewed as capturing an “image” of touch. (In other words, after sensing circuit  1240  has determined whether a touch event has been detected at each sensing electrode  1234  in the sensing device  1232 , the pattern of sensing electrodes  1234  in the multi-touch panel at which a touch event occurred can be viewed as an “image” of touch (e.g. a pattern of fingers touching the panel.) The capacitance between drive and sense electrodes can appear as a stray capacitance when the given row is held at direct current (DC) voltage levels and as a mutual signal capacitance Csig when the given row is stimulated with an alternating current (AC) signal. The presence of a finger or other object near or on the touch sensor panel can be detected by measuring changes to a signal charge Qsig present at the pixels being touched, which is a function of Csig. 
     Although sensing device  1232  is illustrated as a mutual capacitive touch sensing device, examples of the disclosure can include a self-capacitive touch sensing device. For a self-capacitive touch sensing device, sensing device  1232  can have a plurality of touch pixel electrodes with an inherent self-capacitance to ground associated with it, and also an additional self-capacitance to ground that can be formed when an object is in proximity to or touching one or more touch pixel electrodes. The one or more touch pixel electrodes can be coupled to a sensing circuit. Sensing circuit can include an operational amplifier, a feedback resistor, a feedback capacitor and an input voltage source, although other configurations can be employed. For example, the feedback resistor can be replaced by a switch capacitor resistor. The touch pixel electrodes can be coupled to an inverting input of an operational amplifier. An AC voltage source can be coupled to the non-inverting input of the operational amplifier. The sensing circuit can be configured to sense changes in the total self-capacitance of a touch pixel electrode induced by the object touching (or in proximity to) the touch sensor panel. The output can be used by a processor to determine a presence of a proximity or touch event, or the output can be inputted into a discreet logic network to determine the presence of a touch or proximity event. 
     Computing system  1200  can also include processor  1210  for receiving outputs from microcontroller  1242  and performing actions based on the outputs that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Processor  1210  can perform additional functions that may not be related to panel processing, and can be coupled to program storage  1233  and display  1220 , such as an LCD display, for providing a user interface to a user of the device. In some examples, processor  1210  can be a separate component for sensing circuit  1240 , as shown. In other examples, processor  1210  can be included as part of sensing circuit  1240 . In other examples, the functions of processor  1210  can be performed by microcontroller  1242  and/or distributed among other components of sensing circuit  1240 . Display device  1220  together with sensing device  1232 , when located partially or entirely under the sensing device  1232 , can form touch screen  1230 . 
     Note that one or more of the functions described above can be performed, for example, by firmware stored in memory (e.g. one of the peripherals) and executed by processor subsystem  1202 , or stored in program storage  1232  and executed by processor  1210 . The firmware can also be stored and/or transported within any non-transitory computer-readable storage medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “non-transitory computer-readable storage medium” can be any medium (excluding a signal) that can contain or store the program for use by or in connection with the instruction execution system, apparatus, or device. The non-transitory computer readable storage medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, a portable computer diskette (magnetic), a random access memory (RAM) (magnetic), a read-only memory (ROM) (magnetic), an erasable programmable read-only memory (EPROM) (magnetic), a portable optical disc such as a CD, CD-R, CD-RW, DVD, DVD-R, or DVD-RW, or flash memory such as compact flash cards, secured digital cards, USB memory devices, memory sticks and the like. 
     The firmware can also be propagated within any transport medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. In the context of this document, a “transport medium” can be any medium that can communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The transport readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, or infrared wired or wireless propagation medium. 
     In some examples, the microcontroller can receive the touch values and can determine the sequence and one or more gestures. Processing of the touch values, determining the sequence and gestures, and rejecting cover touches and water splashes. In some examples, processing of the touch values and the determination need not be performed on the device itself.  FIG. 13  illustrates an exemplary configuration in which a device is connected to a host according to examples of the disclosure. Host  1310  can be any device external to device  1300  including, but not limited to, any of the systems illustrated in  FIGS. 1A-1C  or a server. Device  1300  can be connected to host  1310  through communications link  1320 . Communications link  1320  can be any connection including, but not limited to, a wireless connection and a wired connection. Exemplary wireless connections include Wi-Fi, Bluetooth, Wireless Direct, and Infrared. Exemplary wired connections include Universal Serial Bus (USB), FireWire, Thunderbolt, or any connection requiring a physical cable. 
     In operation, instead of processing light information from the light sensors on the device  1300  itself, device  1300  can send raw data  1330  measured from the light sensors over communications link  1320  to host  1310 . Host  1310  can receive raw data  1330 , and host  1310  can process the touch values. Processing the touch values can include determining the sequence and gestures and rejecting cover touches and water splashes. Host  1310  can include algorithms or calibration procedures to adjust the minimum and maximum allowed times for a tap gesture. Additionally, host  1310  can include storage or memory for recording the timestamp, pre-determined thresholds, and upper and lower bounds. Host  1310  can send the processed result  1340  or related information back to device  1300 . Based on the processed result  1340 , device  1300  can notify the user or adjust its operation accordingly. By offloading the processing and/or storage of the light information, device  1300  can conserve space and power enabling device  1300  to remain small and portable, as space that could otherwise be required for processing logic can be freed up on the device. 
     A touch sensor panel is disclosed. The touch sensor panel may comprise: a touch controller configured to: capture a touch image when the touch sensor panel is in an idle state; and determine if the touch image exhibits one or more characteristics of a false touch; and a processor configured to: remain in the idle state while the touch controller is capturing a touch image; remain in the idle state while the touch controller is determining if the touch image exhibits the one or more characteristics of the false touch, wherein the processor consumes a greater amount of power in an active state than the touch controller. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch comprises: determining a centroid of the touch image; comparing the centroid with a center of the touch sensor panel; and comparing a difference of the centroid with the center of the touch sensor panel to a pre-determined distance value. Additionally or alternatively to one or more examples disclosed above, in other examples, the pre-determined distance value is equal to a size of one touch pixel. Additionally or alternatively to one or more examples disclosed above, in other examples, the size of one touch pixel is equal to 5 mm. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes determining a radii of the touch image. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes calibrating the radii to a 10 mm diameter. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch further includes comparing the radii to an upper radius value and a lower radius value. Additionally or alternatively to one or more examples disclosed above, in other examples, the upper radius value is equal to 5 mm. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes determining at least one of a shape and a volume of the touch image. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes rejecting the touch image when the shape or volume of the touch image is representative of a shape or volume excluding an ellipsoid. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes generating at least one scatter plot. Additionally or alternatively to one or more examples disclosed above, in other examples, the at least one scatter plot is representative of a centroid position, a radii, or a relative shape of the touch image. Additionally or alternatively to one or more examples disclosed above, in other examples, the touch controller is further configured to reject the touch image when one or more touch values associated with the touch image is located outside one or more bounds of the scatter plot. Additionally or alternatively to one or more examples disclosed above, in other examples, the one or more bounds is determined by a calibration procedure. Additionally or alternatively to one or more examples disclosed above, in other examples, determining if the touch image exhibits one or more characteristics of a false touch includes: determining a time associated with the touch image; determining a difference between the time and a timestamp; and rejecting the touch image when the difference is greater than a pre-determined value. Additionally or alternatively to one or more examples disclosed above, in other examples, the false touch is generated by water. 
     A method for switching a device from an idle state to an active state is disclosed. The method may comprise: capturing a touch image using a controller, while maintaining a processor in the idle state, wherein the processor consumes a lower amount of power in the active state than the controller consumes in the active state; determining if the touch image exhibits one or more characteristics of a false touch using the controller, while keeping the processor in the idle state; and maintaining the processor in the idle state when the controller determines that the touch image exhibits the one or more characteristics of the false touch. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining a centroid of the touch image; comparing the centroid to the center of the device; and comparing a difference of the centroid with the center of the device to a pre-determined distance value. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining a radii of the touch image; and comparing the radii to an upper radius value and a lower radius value. Additionally or alternatively to one or more examples disclosed above, in other examples, the method further comprises: determining at least one of a shape and a volume of the touch image; and comparing the shape to an ellipsoid. 
     Although the disclosed examples have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed examples as defined by the appended claims.