PATENT DOCUMENT

Publication Number: US-10541280-B1
Application Number: US-201715706411-A
Country: US
Kind Code: B1

Title: OLED based touch sensing and user identification

Abstract:
A touch screen configured for optical touch sensing and user identification using organic light emitting diodes (OLEDs) is disclosed. In some examples, one or more OLEDs can be used to display one or more images on the device, can be configured to emit light for optical touch sensing, and/or can be configured to detect a reflection of the emitted light. The touch screen can include a spatial filter configured to focus light emitted from the OLEDs and/or reflected light detected by the OLEDs for improved optical touch sensing. Using optical touch sensors, the touch screen can be capable of discerning between water and an object (e.g., finger) and/or noise (e.g., ambient light) and an object. The touch screen can also be capable of identifying (e.g., authenticating) a user using the active area of the device.

Claims:
What is claimed: 
     
       1. A touch screen, comprising:
 a plurality of light emitting diodes (LEDs) configured to emit a first light for displaying one or more images, the plurality of LEDs including first LEDs and second LEDs, the first LEDs configured to emit a second light for optical touch sensing, the second light being a predetermined light different from and independent from the one or more images displayed with the first light, and the second LEDs configured to sense at least a portion of a reflection of the second light and generate one or more signals indicative of the reflection of the second light; 
 a plurality of current sources coupled to the plurality of LEDs; 
 sense circuitry coupled to the second LEDs; 
 a switch configured to electrically couple and decouple the second LEDs to the sense circuitry during a touch sensing mode; and 
 a processor configured to:
 receive the one or more signals generated by the second LEDs, and 
 determine one or more properties of one or more proximate objects based on the one or more signals. 
 
 
     
     
       2. The touch screen of  claim 1 , wherein the plurality of current sources are configured to apply a forward bias across the first LEDs and further configured to apply a reverse bias across the second OLEDs during the touch sensing mode. 
     
     
       3. The touch screen of  claim 1 , wherein the first LEDs are further configured to sense at least a portion of the reflection of the second light, and the second LEDs are further configured to emit the second light. 
     
     
       4. The touch screen of  claim 1 , further comprising an analog to digital converter (ADC) having an input and an output, the input coupled to the one or more signals, and the output coupled to the processor. 
     
     
       5. The touch screen of  claim 1 , wherein the sense circuitry further comprises:
 a function generator configured to produce a ramp function, 
 a plurality of comparators configured to compare the ramp function to the one or more signals and further configured to generate an enable signal when the ramp function matches the one or more signals, each comparator coupled to one of the second LEDs; and 
 a plurality of registers configured to store the ramp function, each register coupled to one of the plurality of comparators. 
 
     
     
       6. The touch screen of  claim 1 , wherein the first LEDs are arranged in first rows, the second LEDs are arranged in second rows, and the first rows are interleaved with the second rows. 
     
     
       7. The touch screen of  claim 6 , wherein at least two of the first rows are adjacent. 
     
     
       8. The touch screen of  claim 1 , wherein the touch screen excludes capacitive touch sensors. 
     
     
       9. The touch screen of  claim 1 , wherein the sense circuitry includes a sense amplifier operatively coupled to a compensation signal, the compensation signal configured to compensate for a leakage current received by the sense amplifier. 
     
     
       10. The touch screen of  claim 1 , further comprising:
 a plurality of touch electrodes configured to sense a capacitance; 
 a second sense circuitry coupled to the plurality of touch electrodes, the second sense circuitry configured to generate one or more second signals indicative of the change in capacitance, wherein the processor is further configured to: 
 receive the one or more second signals generated by the plurality of touch electrodes; and 
 determine one or more properties of the one or more proximate objects based on the one or more second signals. 
 
     
     
       11. The touch screen of  claim 10 , wherein:
 the plurality of touch electrodes comprise a first plurality of touch electrodes configured to receive a first voltage, and a second plurality of touch electrodes configured to capacitively couple to the first plurality of touch electrodes, and 
 the second sense circuitry is coupled to the second plurality of touch electrodes. 
 
     
     
       12. The touch screen of  claim 10 , wherein the processor is further configured to:
 determine one or more locations of one or more proximate objects using the second sense circuitry; and 
 select, from the plurality of LEDs, the first LEDs and the second LEDs that are located at the one or more locations of the one or more proximate objects. 
 
     
     
       13. A method of operating a touch screen, the method comprising:
 applying first currents to a plurality of LEDs included in the touch screen, the first currents indicative of intensities, associated with one or more displayed images, of a first light; 
 applying second currents to first LEDs, the first LEDs included in the plurality of LEDs, wherein the second currents cause the first LEDs to emit a second light, the second light being a predetermined light different from and independent from the one or more images displayed with the first light; 
 applying third currents to second LEDs to detect a reflection of at least a portion of the second light, wherein the second LEDs are included in the plurality of LEDs; 
 generating, with the second LEDs, one or more signals in response to the detected reflected light; and 
 determining, based on the received one or more signals, one or more properties of one or more proximate objects. 
 
     
     
       14. The method of  claim 13 , wherein the second currents apply forward biases to the first LEDs, and the third currents apply reverse biases to the second LEDs. 
     
     
       15. The method of  claim 13 , wherein applying the third currents to the second LEDs occurs a non-zero time delay after applying the second currents to the first LEDs. 
     
     
       16. The method of  claim 13 , wherein applying the third currents to the second LEDs is concurrent with applying the second currents to the first LEDs. 
     
     
       17. The method of  claim 13 , further comprising:
 modulating the second currents with a plurality of waveforms included in an encoding matrix, wherein waveforms associated with adjacent first LEDs are separate and distinct; and 
 demodulating the one or more signals with an inverse of the encoding matrix. 
 
     
     
       18. The method of  claim 13 , wherein the one or more properties includes optical properties, the method further comprising:
 in accordance with a determination that the optical properties of the one or more proximate objects are indicative of one or more objects that are not water, processing one or more locations of the one or more proximate objects as touch locations; and 
 in accordance with a determination that the optical properties of the one or more proximate objects are indicative of water on the touch screen, forgoing processing the one or more locations as touch locations. 
 
     
     
       19. The method of  claim 13 , wherein the LEDs are organic light emitting diodes (OLEDs). 
     
     
       20. The method of  claim 13 , further comprising:
 sensing, with a plurality of touch electrodes, a capacitance; 
 generating, with the plurality of touch electrodes, one or more second signals indicative of the change in capacitance; and 
 determining, based on the received one or more second signals, one or more properties of the one or more proximate objects. 
 
     
     
       21. The method of  claim 20 , wherein sensing the capacitance comprises:
 receiving, with a first plurality of the plurality of touch electrodes, a first voltage; and 
 capacitively coupling, with a second of the plurality of touch electrodes, to the plurality of first plurality of touch electrodes, wherein the second sense circuitry is coupled to the second plurality of touch electrodes. 
 
     
     
       22. The method of  claim 13 , further comprising:
 producing, with a function generator, a ramp function; 
 comparing, with a plurality of comparators, the ramp function to the one or more signals generated with the second LEDs; 
 generating, with the plurality of comparators, one or more enable signals when the ramp function matches the one or more signals generated with the second LEDs; and 
 in response to detecting the one or more enable signals, storing, with a plurality of registers, the ramp function.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/396,046, filed Sep. 16, 2016, which is hereby incorporated by reference in its entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates to a touch screen and, more particularly, to a touch screen configured for optical touch sensing and user identification using organic light emitting diodes (OLEDs). 
     BACKGROUND OF THE DISCLOSURE 
     Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens, and the like. Touch screens, in particular, are becoming increasingly popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor and a display device positioned partially or fully behind the touch sensor so that the touch-sensitive surface can cover at least a portion of the active area of the display device. The display device can include technologies such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, etc. OLEDs, for example, can provide a flat or flexible display in a relatively thin package that can be suitable for use in a variety of portable electronic devices. In addition, OLED displays can display brighter and more vibrant images in a thinner and lighter package compared to LCD displays, making them suitable for use in compact portable electronic devices. 
     Sensing a proximate object using one or more capacitance-based (e.g., self- and/or mutual capacitance) touch sensors can provide an input modality for an electronic device. Recent advancements in touch sensor technology have allowed capacitance-based touch sensors to perform at higher speeds and at higher touch resolutions than was previously possible. Some applications, such as user identification, may desire a higher sensitivity and/or resolution than capacitance-based touch sensing. 
     SUMMARY OF THE DISCLOSURE 
     This relates to a touch-sensitive display and, more particularly, to a touch screen configured for optical touch sensing and user identification using organic light emitting diodes (OLEDs). In some examples, one or more OLEDs can be used to display one or more images on the device, can be configured to emit light for optical touch sensing, and/or can be configured to detect a reflection of the emitted light. In some examples, an approximate touch location can be determined by optical touch sensors. In some examples, an approximate touch location can be determined by capacitive touch sensors, and one or more finer details can be resolved by optical touch sensors. The touch screen can include a spatial filter configured to focus light emitted from the OLEDs and/or reflected light detected by the OLEDs for improved optical touch sensing. Emitted light can reflect off an object (e.g., a finger) touching or hovering proximate to the touch screen, for example. Using optical touch sensors, the touch screen can be capable of discerning between water and an object (e.g., finger) and/or noise (e.g., ambient light) and an object. The touch screen can also be capable of identifying (e.g., authenticating) a user using the active area of the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an example mobile telephone that includes a touch screen according to examples of the disclosure. 
         FIG. 1B  illustrates an example digital media player that includes a touch screen according to examples of the disclosure. 
         FIG. 1C  illustrates an example personal computer that includes a touch screen according to examples of the disclosure. 
         FIG. 2  illustrates a cross-sectional view of an exemplary touch screen according to examples of the disclosure. 
         FIG. 3A  illustrates a cross-sectional view of an exemplary touch screen configured for optical touch sensing using a plurality of OLEDs according to examples of the disclosure. 
         FIG. 3B  illustrates a top view of an exemplary touch screen configured for optical touch sensing using a plurality of OLEDs according to examples of the disclosure. 
         FIG. 3C  illustrates exemplary circuitry coupled to the plurality of OLEDs according to examples of the disclosure. 
         FIG. 3D  illustrates an exemplary timing diagram for optical touch sensing according to examples of the disclosure. 
         FIG. 3E  illustrates an exemplary method for optical touch sensing according to examples of the disclosure. 
         FIG. 3F  illustrates an exemplary method for displaying an image and optically detecting touch according to examples of the disclosure. 
         FIG. 3G  illustrates an exemplary timing diagram for optical touch sensing according to examples of the disclosure. 
         FIG. 3H  illustrates an exemplary block diagram for processing optical touch information according to examples of the disclosure. 
         FIG. 3I  illustrates an exemplary method for processing optical touch information according to examples of the disclosure. 
         FIG. 3J  illustrates an exemplary method for processing optical touch information according to examples of the disclosure. 
         FIG. 3K  illustrates a top view of an exemplary touch screen configured for displaying and optical touch sensing using a plurality of OLEDs according to examples of the disclosure. 
         FIG. 3L  illustrates a top view of an exemplary touch screen configured for optical touch sensing using a plurality of OLEDs according to examples of the disclosure. 
         FIG. 4A  illustrates an exemplary circuit for optical touch sensing according to examples of the disclosure. 
         FIG. 4B  illustrate an exemplary table of operations for optical touch sensing according to examples of the disclosure. 
         FIG. 5  illustrates a top view of an exemplary touch screen with one or more objects in contact with its surface according to examples of the disclosure. 
         FIG. 6A  illustrates an exemplary matrix for temporally modulating a plurality of OLEDs according to examples of the disclosure. 
         FIG. 6B  illustrates an exemplary sequence of temporally-modulated light for one row of OLEDs according to examples of the disclosure. 
         FIG. 7A  illustrates a cross-sectional view of an exemplary touch screen including touch electrodes configured for capacitive touch sensing and a plurality of OLEDs configured for optical touch sensing according to examples of the disclosure. 
         FIG. 7B  illustrates an exemplary method for capacitive and optical touch sensing according to examples of the disclosure. 
         FIG. 7C  illustrates an exemplary timing diagram for capacitive and optical touch sensing according to examples of the disclosure. 
         FIGS. 8A-8B  illustrate cross-sectional and top view of an exemplary touch screen for user identification according to examples of the disclosure. 
         FIG. 8C  illustrates an exemplary method for user identification according to examples of the disclosure. 
         FIG. 9  illustrates a block diagram of an exemplary computing system that including a touch screen according to examples of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of examples, reference is made to the accompanying drawings 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 various examples. 
     This relates to a touch-sensitive display and, more particularly, to a touch screen configured for optical touch sensing and user identification using organic light emitting diodes (OLEDs). In some examples, one or more OLEDs can be used to display one or more images on the device, can be configured to emit light for optical touch sensing, and/or can be configured to detect a reflection of the emitted light. In some examples, an approximate touch location can be determined by optical touch sensors. In some examples, an approximate touch location can be determined by capacitive touch sensors, and one or more finer details can be resolved by optical touch sensors. The touch screen can include a spatial filter configured to focus light emitted from the OLEDs and/or reflected light detected by the OLEDs for improved optical touch sensing. Emitted light can reflect off an object (e.g., a finger) touching or hovering proximate to the touch screen, for example. Using optical touch sensors, the touch screen can be capable of discerning between water and an object (e.g., finger) and/or noise (e.g., ambient light) and an object. The touch screen can also be capable of identifying (e.g., authenticating) a user using the active area of the device. 
       FIGS. 1A -IC illustrate exemplary systems including a touch screen according to examples of the disclosure. Mobile telephone  136  can include touch screen  124  and home button  134 . In some examples, touch screen  124  can be visible in the viewable area of mobile telephone  136 . Media player  140  can include touch screen  126 . Personal computer  144  (e.g., a tablet computer or desktop computer) can include touch screen  128 . Touch screen  124 , touch screen  126 , and/or touch screen  128  can include one or more components and/or functionality as described below. 
       FIG. 2  illustrates a cross-sectional view of an exemplary touch screen according to examples of the disclosure. Touch screen  200  can include OLED display  230  and touch sensor  240 . OLED display  230  can be configured for displaying one or more images. OLED display  230  can include transistor  210 , metallization  211  and  221 , insulator  204 , planarization  206 , spacer  220 , cathode  235 , OLED material  233 , and anode  231  deposited on substrate  201 . Substrate  201  can be configured for supporting OLED display  230 . For example, substrate  201  can act as a protective layer between transistor  210  and additional components of a host device incorporating touch screen  200 . 
     Transistor  210  can include any type of switch configured for activating (or deactivating) one or more pixels included in OLED display  230 . Transistor  210  can include a gate, a source connected to a source, and a drain connected to cathode  235 . Metallization  211  and  221  can be any type of conductor configured for routing a voltage signal, for example, between transistor  210  and cathode  235 . Insulator  204  and planarization  206  can be configured for insulating transistor  210  and any additional transistors (not shown) included in OLED display  230 , for example. Spacer  220  can be configured to maintain a sufficient distance between cathode  235  and transistor  210  to minimize any damage to OLED display  230  that can be created from external forces (e.g., from a finger or stylus) applied to touch screen  200 . 
     To display an image, transistor  210  can be switched on by applying an appropriate voltage to the gate of the transistor  210 . A voltage can be applied to cathode  235  through the source of transistor  210  and metallization  211  and  221 . Another voltage can be applied to anode  231 . In some examples, the voltage applied to anode  231  can be greater (e.g., more positive) than the voltage applied to cathode  235  (e.g., the OLED can be forward biased). If the voltage difference between cathode  235  and anode  231  is greater than a threshold voltage, OLED material  233  can generate light emitted towards top surface  249  with an intensity based on the applied voltage difference. 
     Although  FIG. 2  illustrates the OLED display as including an anode, OLED material, and a cathode, examples of the disclosure can include additional components. For example, one or more color filters can be included between the OLED material and the cover material (e.g., for displaying a plurality of colors using white OLEDs). Further, although  FIG. 2  illustrates cathode  235  as electrically coupled to transistor  210  with anode  231  disposed on a top side of OLED material  233 , examples of the disclosure can include the polarity of the OLED stack-up as reversed. That is, an anode can be electrically coupled to one or more transistors with a cathode located on the top side (i.e., side closer to top surface  249 ) of the OLED material. 
     In some instances, the display may further comprise touch sensor  240 , which can be configured for detecting an object touching and/or proximate to top surface  249  of touch screen  200 . Touch sensor  240  can include a plurality of touch electrodes (e.g., touch electrode  241  and touch electrode  243 ) deposited on substrate  202 . Touch electrode  241  and touch electrode  243  can be made out of ITO or another suitable conductive material, for example. In some examples, touch electrode  241  and touch electrode  243  can be configured to sense a change in a capacitance relative to one or more of the touch electrodes (e.g., mutual capacitance between touch electrode  241  and touch electrode  243 ) or a change in capacitance (e.g., self-capacitance) relative to ground, where the change in capacitance can be indicative of an object proximate to or contacting top surface  249 . For example, touch electrode  241  and touch electrode  243  can act as two plates of a parallel plate capacitor, and substrate  202  can act as a dielectric, electrically isolating touch electrode  241  and touch electrode  243 . 
     In some examples, touch electrode  241  can receive a signal (e.g., a drive signal or a stimulation signal) from drive circuitry (not shown). Capacitive coupling between touch electrode  241  and touch electrode  243  can cause touch electrode  243  to carry a signal as a result of the driven signal on touch electrode  241 , for example. When a conductive object (e.g., a finger or a stylus) is touching or proximate to top surface  249 , the object can receive charge due to capacitive coupling. Touch electrode  243  can be electrically coupled to sense circuitry (not shown), which can be configured to measure the capacitively coupled signal at touch electrode  243  (or routing signals electrically coupled to touch electrode  243 ). Based on the measured signal, a touch controller (not shown) can determine how much charge, if any, has been coupled to the object, thereby detecting touch and/or hover events. 
     Although  FIG. 2  illustrates touch screen  200  as including two layers of touch electrodes (e.g., touch electrode  241  and touch electrode  243 ) for detecting a mutual capacitance indicative of a proximate object, in some examples, other types of touch sensors are possible. Accordingly, many different configurations and touch sensing technologies can be employed without departing from or with respect to claimed subject matter scope. For example, a touch sensor configuration can utilize, but is not limited to, touch sensing technologies that employ resistive, surface acoustic, self-capacitance, mutual capacitance, or any combinations thereof. 
     Touch screen  200  can further include one or more of passivation  244 , adhesive  245 , and cover material  247 . Passivation  244  can be configured for insulating touch sensor  240  from OLED display  230 . Adhesive  245  can attach one or more layers of touch screen  200  to cover material  247 . In some examples, adhesive  245  can be an optically clear adhesive (OCA) and/or a pressure sensitive adhesive (PSA). Cover material  247  can be configured for protecting one or more layers included in touch screen  200 , for example. In some examples, cover material  247  can protect the underlying layers of touch screen  200  while allowing a user to view one or more displayed images emitted by OLED display  230  and/or perform an operation and/or action using touch sensor  240 . 
     Due to the touch sensor  240  located between and separating OLED display  230  from top surface  249 , in some examples, display brightness and/or clarity can be reduced. For example, light emitted by OLED material  233  can pass through touch sensor  240 , but may be partially absorbed by one or more components of the touch sensor. A touch screen including a fewer number of components and/or layers in between the OLED display and the top surface  249  of the touch screen can reduce device thickness and manufacturing costs and complexity, for example. 
     In some instances, the touch screen can be configured for optical touch sensing.  FIG. 3A  illustrates a cross-sectional view of an exemplary touch screen including a plurality of OLEDs configured for displaying an image and optical touch sensing according to examples of the disclosure. Touch screen  300  can include OLED stackup  330 , cover material  347 , and adhesive  345 . OLED stackup  330  can include transistor  310 , metallization  311  and  321 , insulator  304 , planarization  306 , spacer  320 , cathode  335 , OLED material  333 , and anode  331  deposited on substrate  301 . Substrate  301  can be configured for supporting OLED stackup  330 . For example, substrate  301  can act as a protective layer between transistor  310  and additional components of a host device incorporating touch screen  300 . 
     Cover material  347  can be configured for protecting one or more layers included in touch screen  300 , for example. In some examples, cover material  347  can protect the underlying layers of touch screen  300  while allowing a user to view one or more displayed images emitted by OLED stackup  330  and to perform an operation and/or action using touch inputs detected by OLED stackup  330 . In some examples, the cover material  347  can be attached to the one or more layers of touch screen  300  using adhesive  345  (e.g., an optically clear adhesive (OCA)). Top surface  349  of touch screen  300  can be accessible to a user of the touch screen to display an image and/or to receive a touch input, for example. 
     Touch screen  300  can include plurality of pixels, where each pixel can include an OLED (e.g., a region of OLED stackup  330 ) and a transistor (e.g., transistor  310 ), for example. In some examples, the plurality of pixels can be individually addressable by way of individually addressable transistors (e.g., transistor  310 ). In some examples, transistor  310  can be a thin-film transistor (TFT). Transistor  310  can include any type of switch configured for activating (or deactivating) a display pixel. Transistor  310  can include a gate, a source connected to a source (e.g., source ICS 1  or source ICS 2  illustrated in  FIG. 3C ), and a drain connected to cathode  335 . Metallization  311  and  321  can be any type of conductive material configured for routing a voltage signal, for example, between transistor  310  and cathode  335 . Insulator  304  and planarization  306  can be configured for insulating transistor  310  and any additional transistors (not shown) included in touch screen  300 , for example. Spacer  320  can be configured to maintain sufficient distance between cathode  335  and transistor  310  to minimize any damage to OLED stackup  330  that can be created from external forces applied to touch screen  300 . 
     Although  FIG. 3A  illustrates an exemplary touch screen  300  including OLED stackup  330 , additional components can be included in an OLED stackup. For example, an OLED stackup can include one or more color filters located between OLED material  333  and cover material  347  (e.g., for delineating light emitted by white OLED elements into a plurality of colors). Although  FIG. 3A  illustrates cathode  335  as electrically coupled to transistor  310  with anode  331  disposed on a top side of OLED material  333 , in some examples, the polarity of the OLED stackup can be reversed. That is, an anode can be electrically coupled to one or more transistors with a cathode located on the top side (e.g., side closer to top surface  349 ) of the OLED material. 
     In some examples, optical touch sensing can include a first plurality of OLEDs configured with a different mode than a second plurality of OLEDs for optical touch sensing.  FIG. 3B  illustrates a top view of an exemplary touch screen including a first plurality of OLEDs interleaved with a second plurality of OLEDs for displaying an image and optical touch sensing according to examples of the disclosure. Touch screen  300  can include a plurality of OLEDs (e.g., plurality of OLEDs  332  and plurality of OLEDs  334 ). Plurality of OLEDs  332  and plurality of OLEDs  334  can include OLED stackup  330  (illustrated in  FIG. 3A ). Each OLED can be configured to operate in one of a plurality of modes: emission mode, sensing mode, or off mode. For example, the plurality of rows of OLEDs configured in the same mode (e.g., emission mode while displaying one or more images on the touch screen). Alternatively, the first plurality of OLEDs (e.g., plurality of OLEDs  334 ) can be configured in a different mode (e.g., emission mode) than the plurality of second OLEDs (e.g., plurality of OLEDs  332 ). Although the figure illustrates plurality of OLEDs  332  interleaved with plurality of OLEDs  334 , examples of the disclosure can include any type of arrangement. Moreover, the arrangement for the modes that the OLEDs are operating in can change dynamically. For example, during a first time period, a row of OLEDs can be configured in the emission mode, but during a second time period, the row of OLEDs can be configured in the sensing mode. In some examples, the mode of each OLED can be determined on a row-by-row basis (e.g., the first two rows can be configured in emission mode, while the next row can be configured in sensing mode). In some examples, touch screen  300  can exclude capacitive touch sensors. Although  FIG. 3B  illustrates OLEDs grouped into rows, examples of the disclosure can include other arrangements. For example, the touch screen can include OLEDs grouped into columns or clusters (e.g., forming a checkerboard pattern, as illustrated in  FIG. 3L ), etc. 
       FIG. 3C  illustrates an exemplary circuit coupled to the plurality of OLEDs according to examples of the disclosure. The circuit can switchably couple one or more OLEDs (e.g., OLED  332 - 1  and/or OLED  334 - 1 ) to drive circuitry (e.g., source ICS 1  and/or source ICS 2 ) and sense circuitry (e.g., amplifier  346 , capacitor  348 , and Vbias  347 ). 
     First switch S 1  and second switch S 2  can be coupled to OLED  334 - 1 ; second switches S 3  and first switch S 4  can be coupled to OLED  332 - 1 . Each OLED (e.g., OLED  332 - 1  and OLED  334 - 1 ) can include the anode (e.g., anode  331 ) coupled to a source (e.g., source ICS 1  or source ICS 2 ) via first switches (e.g., switch or S 1  and switch S 3 ). OLED  334 - 1  and OLED  332 - 1  can also be switchably coupled through second switches switch S 2  and S 4  to amplifier  346 , respectively. The cathode (e.g., cathode  335 ) can be coupled to voltage source Vcathode  335 . While the circuitry is illustrated as electrically coupling (i.e., shared between) OLED  332 - 1  and OLED  334 - 1 , it should be appreciated that each OLED (or group or row of OLEDs) may have their own respective drive and sense circuitry. 
     To configure an OLED to operate under forward bias (e.g., during emission mode), the first switch (e.g., first switch S 1  or first switch S 3 ) can electrically couple the anode (e.g., anode  331 ) of the OLED to an anode source (e.g., source ICS 1  or source ICS 2 ), and the second switch (e.g., second switch S 2  or second switch S 4 ) can electrically decouple the anode of the OLED from sense circuitry (e.g., amplifier  346 , capacitor  348 , and Vbias  347 ). The source line connection may be or may not be shared. 
     The anode source (e.g., source ICS 1  or ICS 2 ) can be configured to provide a current (e.g., a display image-dependent current) to the respective OLED (e.g., OLED  332 - 1  or OLED  334 - 1 ), while the cathode (e.g., cathode  335 ) can be held at a voltage level approximately at GND. V+ can be held at a voltage level high enough to sustain the currents through each respective OLED. In some examples, V+ can be configured with a greater (e.g., more positive) voltage than Vcathode  335 . If the voltage difference between cathode  335  and anode  331  is greater than the threshold voltage of the OLED, OLED material (e.g., OLED material  333  illustrated in  FIG. 3A ) can generate light (e.g., towards top surface  349  illustrated in  FIG. 3A ) with an intensity based on the current through the OLED. 
     To configure the OLED to operate under reverse bias (e.g., during sensing mode), the second switch (e.g., second switch S 2  or second switch S 4 ) can electrically couple the anode (e.g., anode  331 ) of the OLED to sense circuitry (e.g., (e.g., amplifier  346 , capacitor  348 , and Vbias  347 ), and the first switch (e.g., first switch S 1  or first switch S 3 ) can electrically decouple the anode to the anode source (e.g., source ICS 1  or ICS 2 ). Vbias  347  can be configured to provide a lower (e.g., less positive) voltage than cathode source Vcathode  335 . In this manner, the OLED can be configured detect light and generate a photocurrent that can be sensed by the sense circuitry. 
     Plurality of OLEDs  332  and plurality of OLEDs  334  and associated circuitry can be configured to operate in the same modes or in different modes, depending on whether touch screen is configured for display mode or optical touch sensing mode.  FIG. 3D  illustrates an exemplary timing diagram for alternating between displaying an image, optical touch sensing, and calibrating according to examples of the disclosure. Each OLED (e.g., OLED  332 - 1  or OLED  334 - 1 ) can be configured to operate in one or more operation modes: an emission mode, a sensing mode, and an off mode. 
     At a time t 1 , the touch screen can be configured in a display mode by configuring both OLED  332 - 1  and OLED  334 - 1  to operate in the emission mode. At time t 2 , the touch screen can be configured in an optical sensing mode by configuring OLED  334 - 1  to operate in the emission mode and OLED  332 - 1  to operate in the sensing mode. At time t 3 , the touch screen can be configured in a calibration mode. OLED  334 - 1  can be configured in the off mode (e.g., electrically decoupled from both drive and sense circuitry). OLED  332 - 1  can be configured to operate in the sensing mode. The calibration procedure is described in more detail with reference to  FIG. 8C  (below). 
       FIG. 3E  illustrates an exemplary method for configuring the plurality of OLEDs for optical touch sensing according to examples of the disclosure. A plurality of first OLEDs (e.g., plurality of OLEDs  334 ) can be configured to operate in the emission mode by configuring the anode sources (e.g., anode source ICS 1  or anode source ICS 2  illustrated in  FIG. 3C ) to apply first currents to the anode (e.g., anode  331 ) (step  352  of process  350 ). The plurality of first OLEDs can emit light (step  354  of process  350 ). The emitted light can reflect off an object (e.g., a finger or stylus) located in close proximity to or in contact with the top surface (e.g., surface  349  illustrated in  FIG. 3A ) (step  356  of process  350 ). A plurality of second OLEDs (e.g., plurality of OLEDs  332 ) can be configured to operate in the sensing mode by coupling (e.g., using switch S 3 ) to sense circuitry (e.g., charge amplifier  346 , capacitor  348 , and Vbias  347 ) (step  358  of process  350 ). In some examples, the plurality of second OLEDs can be electrically decoupled from the anode source (e.g., anode source ICS 2  illustrated in  FIG. 3C ) to prevent a forward-bias that could cause the plurality of second OLEDs to emit light. The plurality of second OLEDs can detect light that has reflected off the proximate object and can generate one or more signals (step  360  of process  350 ). The controller (not shown) can receive the one or more signals and can determine one or more touch (and/or hover) information (step  362  of process  350 ). 
     In some examples, OLED stackup  330  can be configured to operate in emission mode during one time period and can be configured to operate in sensing mode during another time period. In some examples, the currents through OLEDs  332  and OLEDs  334  can be the same for emission and sensing modes. In some examples, the currents through OLEDs  332  and OLEDs  334  can be different for emission and sensing modes. 
       FIG. 3F  illustrates an exemplary method for displaying an image and optically detecting touch according to examples of the disclosure. Process  351  can include updating the display in step  353 . In some examples, updating the display can include updating the anode source(s) (e.g., anode source ICS 1  and/or anode source ICS 2 ) according to the intensity levels of the displayed image at the respective locations of the OLEDs (e.g., OLEDs  334  and/or  332 ) (step  355  of process  351 ). During the display update, all switches S 1 , S 2 , S 3 , and S 4  can be configured to electrically decouple (i.e., “open”) circuitry. First switches S 1  and S 3  can be configured for electrically coupling (i.e., “closed”) to enable the OLEDs  332  and OLEDs  334  to operate in the emission mode (step  357  of process  351 ). The touch screen can be configured to switch to touch sensing in step  359 . Anode source(s) (e.g., anode source ICS 1  and/or anode source ICS 2 ) can be updated according to the light intensity levels required for optical touch sensing mode while all switches S 1 , S 2 , S 3 , and S 4  be configured to electrically decouple circuitry (step  361  of process  351 ). OLED  334 - 1  can be configured to operate in the emission mode by configuring first switch S 1  for electrically coupling and second switch S 2  for electrically decoupling. OLED  332 - 1  can be configured to operate in the sensing mode by configuring second switch S 4  for electrical coupling and first switch S 3  for electrical decoupling (step  363  of process  351 ). OLED  332 - 1  can receive reflected light (e.g., light emitted by OLED  334 - 1  and reflected off a user&#39;s finger) and can generate a photocurrent to be sensed by sense circuitry (step  365  of process  351 ). The sensed photocurrent can be digitized by an ADC to obtain a digital representation of the intensity of the reflected light. In some examples, the sensed touch data can be processed in step  367 . Step  367  can include reading and processing the intensity level of the received light associated with one or more OLEDs (e.g., OLED  332 - 1 ) (step  369  of process  351 ). In some examples, the intensity of received light can also be used for fingerprint recognition, as will be described below. 
     In some examples, the optical touch sensing mode can operate with a non-zero delay between light emitted the plurality of first OLEDs and a reflection of the light sensed by the plurality of second OLEDs.  FIG. 3G  illustrates an exemplary timing diagram for optical touch sensing using a non-zero delay between the emission mode of the plurality of first OLEDs and the sensing mode of the plurality of second OLEDs according to examples of the disclosure. Non-zero delay  372  can be included, for example, to account for time for light to be emitted by the OLEDs, reflect off the object, and detected by the OLEDs. For example, the device can prompt the user to touch a portion of the touch screen, where the prompt can include emitting light by the OLEDs. The user can touch the portion of the touch screen, but only after reading the prompt, which may include a non-zero delay. 
       FIGS. 3H-3J  illustrate an exemplary block diagram and exemplary methods for processing optical touch information according to examples of the disclosure. In some examples, plurality of OLEDs  330  can include an array of OLEDs operatively coupled to row driver  312  and circuit  345 . Circuit  345  can be configured to sample one or more signals generated by plurality of OLEDs  330 . Circuit  345  can include, at least in part, analog front end  310 , generator  320 , and plurality of registers  338 . In some examples, plurality of registers  338  can be output registers configured to shift an output to a host processor of a device including circuit  345 . 
     Analog front end  310  can include sample and hold circuit  314  and comparator array  313 . In some examples, sample and hold circuit  314  can also include an array of charge amplifiers. In some examples, sample and hold circuit  314  can sample data from plurality of OLEDs  330 . In some examples, the data can include a signal from the output of sample and hold circuit  314 . Comparator array  313  can be configured for comparing one or more outputs from sample and hold circuit  314  to a ramp function (e.g., generated by generator  320 ). 
     Generator  320  can be configured to provide a ramp function to the comparator array  313 . Generator  320  can include counter  321  and a digital-to-analog converter (DAC)  323 . In some examples, counter  321  can be an N-bit counter configured to generate a digital ramp. DAC  323  can be configured to convert a digital signal to an analog signal. For example, DAC  323  can convert the output signal from counter  321  to an analog signal. Digitized readings from analog front end  310  can be stored in a plurality of registers  338 . The plurality of registers  338  can include registers  331  and registers  333 , for example. In some examples, registers  331  can include a plurality of storage registers, and registers  333  can include a plurality of shift registers. Including storage and shift registers in plurality of registers  338  can give circuit  345  the capability of storing conversion results for a currently sampled ADC conversion, while shifting out conversion results from a previously sampled ADC conversion to a processor for further data processing. Registers  331  and registers  333  may form double buffered registers, where register  331  can be updated with conversion results from a currently sampled ADC conversion, and registers  333  can include conversion results from a previously sampled ADC conversion. The previously sampled ADC conversion can be transmitted to a processor in a parallel fashion for further processing. Comparator array  313 , ramp generator  320  and output register  331  can form a scalable ADC. It should be understood, that other ADC topologies and arrangements are possible. 
     One or more rows included in plurality of OLEDs  330  can be configured (e.g., via row driver  312 ) to detect light reflected off an object in contact with or in close proximity to plurality of OLEDs  330 . Each column of plurality of OLEDs  330  can be coupled to analog front end  310  to receive one or more signals (e.g., photocurrents) indicative of a touch or hover event (step  372  of process  370 ). In some examples, the one or more signals can be received as photocurrents and can be converted to voltage levels by a charge amplifier. DAC  323  can provide a voltage waveform (e.g., analog ramp) to comparator array  313  (step  374  of process  370 ). Comparator array  313  can compare one or more signals from analog front end  310  to the analog ramp (step  376  and step  378  of process  370 ). When the voltage level of the analog ramp is greater than the output voltage level from a given charge amplifier in the charge amplifier array, the associated comparator in the comparator array  313  can enable the associated output register  331  of the plurality of registers  338  to store the digital count value from counter  321  (step  380  of process  370 ). The digital count value can be representative of the sampled voltage level from the charge amplifier array. When registers  331  are enabled (e.g., when the value of the ramp function matches the output from sample and hold circuit  314 ), the one or more signals stored in registers  333  can be transmitted to a processor or controller (not shown) for analysis (step  382  of process  370 ). The value(s) stored in the first registers (e.g., registers  331 ) can be transferred to the second registers (e.g., registers  333 ), and the contents of registers  333  can be read by a host processor for subsequent processing (step  384  of process  370 ). The process can be repeated with one or more signals (e.g., from plurality of OLEDs  330 ) being captured (e.g., by sample and hold circuit  314 ). Although circuit  345  can be configured to sample plurality of OLEDs  330  in a row-by-row process, examples of the disclosure can include sensing each column with column sense amplifiers or other arrangements. 
     One or more OLEDs (e.g., OLED  332 - 1 ) configured to sense touch can receive reflected light (e.g., from a finger or other proximate object) and convert it to a photocurrent (step  373  of process  371 ). Charge amplifiers (e.g., amplifier  346  illustrated in  FIG. 3C ) included in sample and hold circuit  314  can convert a sensed photocurrent into a photo voltage (step  375  of process  371 ). The voltage can be compared to an analog ramp provided by generator  320  via a comparator included in comparator array  313  (step  377  of process  371 ). If the photo voltage is exceeded by the analog ramp level (e.g., from DAC  323 ), the comparator can change states and generate a positive clock edge (step  379  of process  371 ). The clock edge (e.g., generated by the comparator) can cause the digital ramp value to be loaded into a storage register included in the plurality of registers  331  (step  381  of process  371 ). The storage register contents can be transferred to shift registers  333  and the data can be serially shifted to a host processor for touch processing (step  383  of process  371 ). 
     Examples of the disclosure can include other types of arrangements of the plurality of OLEDs. For example, the touch screen can include groups of OLEDs, where each group can be configured to operate in different modes for display and optical touch sensing.  FIG. 3K  illustrates a top view of an exemplary touch screen configured for displaying and optical touch sensing using a plurality of OLEDs according to examples of the disclosure. Touch screen  370  can include plurality of first OLEDs  334 , plurality of second OLEDs  332 , and plurality of third OLEDs  336 . In some examples, touch screen  370  can be configured to operate in display mode and optical touch sensing mode concurrently. 
     A first group (e.g., plurality of OLEDs  334 ) can be configured to operate in emission mode for optical touch sensing. A second group (e.g., plurality of second OLEDs  332 ) can be configured to operate in sensing mode for optical touch sensing. A third group (e.g., plurality of OLEDs  336 ) can be configured to operate in emission mode for displaying one or more images. In some examples, to reduce the likelihood of perception by the user, subpixels (e.g., red subpixel, green subpixel, and blue subpixel) formed from the OLEDs operating in the emission mode can be configured to create a touch screen that can appear gray in color to the user. For example, the red subpixel, green subpixel, and blue subpixel can each be configured to emit 50% intensity. 
     In some examples, touch screen  370  can alternate between display and optical touch sensing modes, where at least one of the groups (e.g., the second group including plurality of OLEDs  332 ) can be configured to operate in sensing mode while touch screen  370  is operating in display mode. At least two adjacent rows can include OLEDs (e.g., plurality of OLEDs  334  and plurality of OLEDs  336 ) configured to operate in emission mode. In some examples, one of the groups of OLEDs (e.g., the first group including plurality of OLEDs  334 ) can alternate between emitting light for display mode and emitting light for optical touch sensing mode. 
     In some examples, the OLEDs can be arranged to form one or more patterns, such as a checkboard pattern, as illustrated in  FIG. 3L . Touch screen  370  can include group  333  and group  337 . Group  333  can include a plurality of OLEDs  332 , and group  337  can include a plurality of OLEDs  334 . In some examples, group  333  can be interleaved (e.g., form a checkerboard pattern) with group  337 . During display mode, group  333  and group  337  can be configured to operate in emission mode. During touch sensing mode, group  333  can be configured to operate in emission mode, and group  337  can be configured to operate in sensing mode. 
     Circuits (e.g., circuit  345  illustrated in  FIG. 3H ) that sense groups (e.g., columns) of OLEDs serially  345  can be associated with multiple steps for processing the plurality of OLEDs across the touch screen. Although serially sampling the one or more signals can reduce the size of the circuitry, the sampling can take a long time. In some examples, the touch screen can include circuits capable of sampling one or more signals from the plurality of OLEDs simultaneously. Although one or more examples described with reference to  FIGS. 3A-3L  relate to a touch screen that may not include a capacitive touch sensor, in some instances, a touch screen including a capacitive touch sensor can include one or more of the systems or methods described with reference to  FIGS. 3A-3L . 
       FIGS. 4A-4B  illustrate an exemplary circuit and an exemplary table for optical touch sensing according to examples of the disclosure. Pixel  411  can include OLED  434  coupled to a gate driver  438 . Gate driver  438  can include a plurality of sources (e.g., voltage sources), storage capacitor C ST    435 , and a plurality of transistors. OLED  434  can be switchably operable to emit and detect light, for example. OLED  434  can operate similarly to OLED  332 - 1  and/or OLED  334 - 1  described with reference to  FIGS. 3A-3J . The plurality of sources can include source  443 , source  445 , and source  447 . In some examples, the plurality of sources can be voltage sources. Storage capacitor C ST    435  can be configured to store a charge. The plurality of transistors can include transistor  411 , transistor  413 , transistor  415 , and transistor  417 . In some examples, transistor  411 , transistor  413 , and/or transistor  415  can be PMOS transistors. In some examples, transistor  417  can be a NMOS transistor. The plurality of transistors can be configured to couple one or more lines together. For example, the gate of transistor  411  can be coupled to pixel enable PEN  401 ; the source of transistor  411  can be coupled to source  443 ; and the drain of transistor  411  can be coupled to the drain of transistor  417 . The gate of transistor  417  and the drain of transistor  413  can be coupled to C ST    435 . The drain of transistor  417  and the source of transistor  415  can be coupled to the anode of OLED  434 . The gate of transistor  413  can be coupled to gate enable GEN  403 , and the source of transistor  413  can be coupled to source  447 . The gate of transistor  415  can be coupled to data enable DEN  405 , and the drain of transistor  415  can be coupled to line  436 . 
     Although  FIG. 4A  illustrates transistor  411 , transistor  413 , and transistor  415  as PMOS transistors and transistor  417  as a NMOS transistor, examples of the disclosure can include any type of switch configured with any orientation. For example, transistor  411 , transistor  413 , transistor  415 , and transistor  417  can be MOSFETS with reversed polarities. For example, one or more PMOS (e.g., transistor  411 , transistor  413 , and transistor  415 ) transistors can replace one or more NMOS transistors, one or more NMOS transistors (e.g., transistor  417 ) can replace one or more PMOS transistors, and/or the control signals can be switched accordingly. In some examples, non-transistor switches can be used. 
     In some examples, OLED  434  can be coupled to analog front end  410  to optically sense touch. Analog front end  410  can include multiplexer  427 , buffer  431 , amplifier  433 , iDAC  460 , comparator  437 , and register  439 . In some examples, register  439  can be a multi-bit (e.g., “N” bit) storage register. In some examples, each analog front end  410  can be coupled to one pixel  411  or one column of pixels. 
     OLED  434  can be configured to operate in any number of modes including, but not limited to, display mode, emission mode (for optical touch sensing), and sensing mode.  FIG. 4B  illustrates exemplary functions associated with the OLED modes. The mode can be selected based on the signal lines (e.g., pixel enable PEN  401 , gate enable GEN  403 , data enable DEN  405 , and data select DSEL  407 ). 
     During a display mode, the OLEDs can be updated by configuring pixel enable PEN  401  high, gate enable GEN  403  low, data enable DEN  405  low, and data select DSEL  407  low. Transistor  411  can decouple V+ source  443  from transistor  417 , allowing source  447  to update C ST    435 , and the anode of OLED  434  can receive charge from C ST    435 . Transistors  413  and  415  can be enabled, allowing storage capacitor C ST  to be charged to a voltage VGS equivalent to the difference between V DATA  and V GATE . In some examples, V CATHODE    445  may have a low enough value to ensure OLED  434  is not forward biased. V DATA  can be propagated from buffer  431  through multiplexer  427  to line  436 . Display mode can be similar to the emission mode for optical touch sensing. That is, all switches can be off, except transistor  411 , which can allow transistor  417  to generate a current through the OLED  434  that is set by the gate to source voltage of transistor  417  equivalent to the voltage across C ST . 
     During the emission mode for optical touch sensing, the OLEDs  434  can be driven such that light with an intensity based on the current through the OLED can be emitted. The current through the OLED can be generated by transistor  417  and storage capacitor C ST    435 . In some examples, pixel enable PEN  401  can be low, and data enable DEN  405  can be high. Transistor  411  can electrically couple source V+  443  to the source of transistor  417 . The drain of transistor  417  can be coupled to the anode of OLED  434 . The cathode of OLED  434  can be coupled to the cathode source  445 . Source  443  and cathode source  445  can be configured such that OLED  434  can be forward biased (e.g., for optical touch sensing as described with reference to  FIGS. 3A-3J  and  FIGS. 7A-7B ). Transistor  415  can electrically decouple the anode of OLED  434  from line  436 , thereby preventing analog front end  410  from receiving one or more signals from OLED  434 , for example. 
     During the sensing mode for optical touch sensing, pixel enable PEN  401  can be high, gate enable GEN  403  can be high, data enable DEN  405  can be low, and data select DSEL  407  can be high. Transistor  411  and transistor  413  can electrically decouple source V+  443  and source V GATE    447 , respectively, from the circuit. Transistor  415  can electrically couple the anode of OLED  434  to analog front end  410  via line  436 . OLED  434  can detect light and can generate one or more signals, which can be transmitted on line  436 . In some examples, OLED  434  can generate a photocurrent that can be a function of the intensity of the received light. The photocurrent can be propagated via line  436  through multiplexer  427  to a charge amplifier. The charge amplifier can comprise amplifier  433 , CFB  432 , and Vbias  431 . Charge amplifier can convert the signal (e.g., a photocurrent) to a voltage. iDAC  460  can be used to compensate for any leakage or offset currents into the inverting terminal of amplifier  433  in order to improve dynamic range, for example. In some examples, leakage or offset currents can be induced by disabled transistors  415  along line  436 . Capacitor C SH    436  can sample and hold the one or more signals. 
     Analog front end  410  can receive signal  451  and signal  453  from generator  420 . In some examples, generator  420  can be a ramp generator, and signal  451  and signal  453  can include a ramp function. In some examples, comparator  437  can receive signal  451  and an input from amplifier  433  (and/or capacitor C SH    441 ). Comparator  437  can compare signal  451  and one or more signals from amplifier  433  (and/or capacitor C SH    441 ). When signal  451  matches the one or more signals from C SH    441 , comparator  437  can enable signal  453  to be stored in register  439 . In some examples, signal  453  can be indicative of the one or more signals sampled from the plurality of OLEDs. Controller  440  can receive the output from register  439  and can perform analysis. 
     In some examples, optical touch sensing can identify an object in contact with a touch screen based on its optical properties.  FIG. 5  illustrates an exemplary touch screen with one or more objects in contact with its surface according to examples of the disclosure. In some examples, one or more objects, such as water  501  and object  502 , can be touching a surface of touch screen  500 . In some examples, a touch screen  500  can be capable of differentiating between water  501  from object  502 . In this manner, touch screen  500  can accurately reject signals associated with water  501  while accepting signals associated with object  502 . This may be unlike some capacitive touch sensors (e.g., mutual capacitance based touch sensors), which may erroneously mistake water  501  as user input due to the conductive properties of water  501 , for example. 
     In addition to or instead of discerning water from objects based on the differences in footprint (e.g., a finger object may have an oval shaped footprint), touch screen  500  can discern different objects based on differences in one or more optical properties. For example, water can have an absorption band around 1700 nm, whereas a finger object can have an absorption band around 1000-1500 nm. In some examples, water  501  and object  502  can have different spectral “fingerprints.” A spectral fingerprint can include the absorbance (or reflectance) values across a spectrum of wavelength (e.g., visible range). Water  501  and object  502  can include different types of materials, which may lead to differences in spectral “fingerprints.” Based on the frequency of the reflected light or spectral “fingerprint” detected by the plurality of OLEDs, a processor or controller can determine the type of object. 
     In some examples, water can be distinguished from a finger object by performing one or more optical touch scans with emitting light having object-specific frequencies (e.g., a scan outside of 1700 nm may not detect water or a scan outside of 1000-1500 nm may not detect a finger). Additionally or alternatively, one or more narrowband filters can be applied, where the narrowband filter can include or exclude one or more object-specific frequencies. 
     In some examples, light reflected off water  501  can have a different level of transparency (e.g., percent reflectance) and/or heterogeneity properties than object  502 . For example, object  502  can be a finger, which can be opaque and can have heterogeneous optical properties, while a drop of water may be more transparent and can have homogeneous optical properties. 
     The touch screen can determine the location(s) of water  501  and/or object  502  using optical touch sensing or capacitive touch sensing (discussed below [shs31] ). In some examples, capacitive touch sensors can be employed to determine the location of the object(s), and optical touch sensing can be employed to determine whether the contact is from water or another object (e.g., a finger). In some examples, determining whether the contact is from water or another object can include utilizing only those touch sensors positioned at the determined location(s). In some examples, a processor or controller can ignore any contacts from water. 
     In addition to water rejection, examples of the disclosure can include configuring OLEDs for noise rejection. In some examples, noise can include ambient light, stray light from other OLEDs or other sensors, and/or light from multiple reflections off the object (e.g., finger) and/or device stackup. The OLEDs can be temporally and/or spatially modulated for noise rejection.  FIG. 6A  illustrates an exemplary matrix for temporally modulating a plurality of OLEDs according to examples of the disclosure. Matrix  600  can include plurality of rows  620  and plurality of columns  622 . In some examples, the number of columns  622  can be equivalent to the number of OLEDs in each row. For example, each OLED can be associated with a pixel, where a pixel can include a red display sub-pixel, a green display sub-pixel, and a blue display sub-pixel. The number of rows  620  can be equal to the number of frames for optical touch sensing, for example. In some examples, the number of columns  622  can be equal to the number of rows such that matrix  600  can be a square matrix. One or more rows of OLED pixels (e.g., including OLEDs  334  illustrated in  FIGS. 3B-3D, 3G, 3K, and 3L ) can be configured to operate in the emission mode and can be spatially modulated with a spreading code represented by matrix  600  at a given time. One or more rows of OLEDs (e.g., OLEDs  332  illustrated in  FIGS. 3B-3D, 3G, 3K, and 3L ) can be configured to operate in sensing mode and can be demodulated with another matrix. In some examples, the other matrix can be the inverse of matrix  600 . In some examples, demodulation of the OLEDs can be performed after charge amplification and before the one or more signals pass through analog-to-digital circuits. 
     In some examples, matrix  600  can be a Walsh-Hadamard matrix. Other types of encoding are possible. In some examples, matrix  600  can be a rectangular matrix, and other methods of demodulation can be used. In some examples, spatial modulation can be used to differentiate light emitted by one or more OLEDs. For example, at a first time, the first row of OLEDs can be configured to operate in display mode with modulated intensities represented by the first row  620  of the matrix  600  (e.g., I(1,1), I(1,2), . . . I(1,N)). 
       FIG. 6B  illustrates an exemplary sequence of temporally-modulated light for one row of OLEDs according to examples of the disclosure. A row of OLEDs can be configured to operate in display mode by emitting temporally modulated light. That is, during N frames, a modulation sequence (e.g., one or more waveforms) can be applied to row  650  of OLEDs. During a first frame, the modulation sequence can have a first set of N intensity values I(1,1), I(1,2), . . . I(1,N), respectively. During a second frame  653 , the modulation sequence of row  650  can have a second set of N intensity values I(2,1), I(2,2), . . . I(2,N), respectively. During the last frame  655 , the modulation sequence can have a nth set of N intensity values I(N,1), I(N,2), . . . I(N,N), respectively. In this manner, each OLED can be modulated with a unique spreading code across N frames. 
     The spreading code for each of the N OLEDs can be orthogonal to the spreading code of the other OLEDs. In some examples, the modulated reflected light from N OLEDs configured to operate in emission mode can be received by N OLEDs configured to operate in sensing mode. The modulated signal from the OLEDs configured to operate in sensing mode can be demodulated with a de-spreading code, which can be derived by inverting matrix  600 . Matrix  600  can be configured such that the spreading code for each OLED configured to operate in emission mode (and associated de-spreading code for the optically coupled OLED configured to operate in sensing mode) can be orthogonal to that of other OLEDs configured to operate in emission mode, therefore minimizing crosstalk between optically coupled OLEDs. 
     In some examples, modulation of the OLEDs can include both temporal and spatial modulation. For example, the OLEDs in one row can be modulated by a first row  620  of matrix  600 , while the OLEDs in another row can be modulated by a different row  620  of matrix  600  during one frame. In the next frame, for example, each row of OLEDs can be modulated by a different row  620  of matrix  600  than the last frame, such that one or more OLEDs can be modulated with a unique, but predictable pattern. Due to the pattern being predictable and unique, a processor or controller can differentiate between light emitted by the OLEDs and light from noise sources (e.g., ambient light, stray light from other sensors, and/or light due to multiple reflections from the object and/or device stackup). In some examples, each waveform included in matrix  600  can be different from neighboring waveforms to improve pixel separation, which can make it easier to separate neighboring pixels and to determine which OLED the reflected light originated from. 
       FIG. 7A  illustrates a cross-sectional view of an exemplary touch screen configured for capacitive touch sensing with a touch sensor and optical touch sensing using a plurality of OLEDs according to examples of the disclosure. Touch screen  700  can include cover material  747 , OLED display  730 , touch sensor  740 , filter  744 , and encapsulation  746 . Cover material  747  can be configured for protecting one or more layers included in touch screen  700  while allowing a user of the touch screen to view a displayed image and/or perform an operation and/or action by touching a surface of the touch screen. In some examples, cover material  747  can be attached to the one or more layers of touch screen  700  using adhesive  745  (e.g., an optically clear adhesive (OCA)). 
     OLED display  730  can be configured for displaying one or more images and/or optical touch sensing. OLED display  730  can include transistor  710 , metallization  711  and  721 , insulator  704 , planarization  706 , spacer  720 , cathode  735 , OLED material  733 , and anode  731  deposited on substrate  701 . Substrate  701  can be configured for supporting OLED display  730 . 
     Transistors  710  can be included in a plurality of individually addressable transistors, where each transistor  710  can be coupled to a pixel. In some examples, transistor  710  can be a thin-film transistor (TFT). Transistor  710  can include any type of switch configured for activating (or deactivating) a pixel. Transistor  710  can include a gate, a source connected to a voltage source, and a drain connected to cathode  735 . Metallization  711  and  721  can be any type of conductor configured for routing a voltage signal, for example, between transistor  710  and cathode  735 . Insulator  704  and planarization  706  can be configured for insulating transistor  710  and any additional transistors (not shown) included in touch screen  700 , for example. Spacer  720  can be configured to maintain sufficient distance between cathode  735  and transistor  710  to minimize any damage to OLED display  730  that can be created from external forces applied to touch screen  700 . 
     Further, although  FIG. 7A  illustrates an exemplary touch screen  700  including OLED stackup  730 , additional components can be included in an OLED stackup according to examples of the disclosure. For example, an OLED stackup can include one or more color filters located between OLED material  733  and cover material  747  (e.g., for displaying a plurality of colors using white OLED elements). Although  FIG. 7A  illustrates cathode  735  as electrically coupled to transistor  710  with anode  731  disposed on a top side of OLED material  733 , in some examples, the polarity of the OLED stackup can be reversed. That is, an anode can be electrically coupled to one or more transistors with a cathode located on the top side of the OLED material. 
     Touch sensor  740  can include passivation  743 , touch electrode  740 , and touch electrode  743  deposited on substrate  702 . In some examples, touch electrode  741  and touch electrode  743  can be configured as a capacitive touch sensor to sense a self- or mutual capacitance indicative of an object proximate to or touching the touch screen. In some examples, touch electrode  741  and touch electrode  743  can be made of ITO or another suitable conductive material. 
     Touch screen  700  can further include filter  744 . Filter  744  may be needed to enhance the accuracy of the optical touch sensing measurements. Cover material  747  may be designed for a wide viewing angle. While the wide viewing angle may enhance the user&#39;s viewing experience, it may lead to light emitted by the OLEDs causing multiple reflections at one or more interfaces of the device&#39;s stackup. The multiple reflections can be sensed by other sensors, which can lead to erroneous measurements and the inability to resolve fine features. 
     Filter  744  can be any type of filter configured to change one or more optical properties of light emitted from OLED material  733 . For example, filter  744  can focus light emitted from OLED display  730 . In some examples, filter  744  can focus the light to certain locations (e.g., predicted spots where one or more undulations may be located). In some examples, filter  744  can be configured to reduce stray light from other sensors and/or the reflections from the device stackup. In some examples, filter  744  can change one or more properties (e.g., angle of incidence, beam size, and/or intensity) of light such that a finer resolution (than capacitive touch sensing) can be achieved. One or more properties (e.g., material, thickness, refractive index, number of layers) of filter  744  can be selected based on pixel dimensions, pixel pitch, optical properties of the stackup, number of layers in the stackup, the properties of the OLED material, touch feature resolution size (e.g., undulation in a fingerprint), conversion time per row, object size, and/or a frame rate of touch screen  700 . In some examples, the filter can include a plurality of layers, where each layer can be separated from another layer by at least a substrate (e.g., substrate  702 ), a layer included in the stackup of touch sensor  740 , and/or a layer included in the stackup of OLED display  730 . 
     In some examples, OLED display  730  can be configured for displaying one or more images during one time period and can be configured for touch sensing during another time period. To display an image, a current can be passed through the OLED, where the current is a function of the intensity level of the displayed image at the location of the OLED. In some examples, the current through OLED can be the same during display and optical touch modes. In some examples, the current through OLED can be the different during display and optical touch modes. For example, the currents passed through the OLEDs during the display mode can be based on the intensity of one or more display images, whereas the currents passed through the OLEDs during the optical touch mode can be based on the intensity values in matrix  600 . 
     For touch sensing, touch screen  700  can be configured for capacitive touch sensing and/or optical touch sensing. In some examples, touch screen  700  can be configured for capacitive touch sensing for coarse determination (e.g., location) of an object in close proximity or touching touch screen  700  and optical touch sensing for fine determination (e.g., fingerprint resolution).  FIG. 7B  illustrates an exemplary timing diagram for capacitive and optical touch sensing according to examples of the disclosure. 
     At a time t 1 , the touch screen can be configured to in a display mode by configuring both OLED  732  and OLED  734  to operate in the emission mode. At time t 2 , the touch screen can be configured in capacitive sensing mode by configuring touch sensor  740  to capacitively couple to the touch object using, for example, drive circuitry supplying one or more drive signals. At time t 3 , the touch screen can be configured in an optical sensing mode by configuring OLED  732  to operate in the emission mode and OLED  734  to operate in the sensing mode. At time t 5 , the touch screen can be configured in a calibration mode. OLED  734  can be configured in the off mode (e.g., electrically decoupled from both drive and sense circuitry). OLED  732  can be configured to operate in the sensing mode. The calibration procedure is described in more detail with reference to  FIG. 8C  (below). 
     For mutual capacitive touch sensing (e.g., when the touch screen is in capacitive sensing mode shown between time t 2  and time t 3  illustrated in  FIG. 7C ), the sensing device can include two layers (e.g., touch electrode  741  and touch electrode  743  illustrated in  FIG. 7A ) of spatially separated conductive sections. One layer can include sections arranged as rows, while the other layer can include sections arranged as columns (e.g., orthogonal). Sensing nodes can be formed at intersections of the rows and columns. 
     In some examples, capacitive sensing mode can include self-capacitive touch sensing, the layers (e.g., touch electrode  741  and touch electrode  743 ) of spatially separate conductive sections can each be driven and have its self-capacitance sensed. In other examples, a touch screen can include pixelated self-capacitance electrodes in one layer. Each pixelated electrode can correspond to a unique part of the touch screen and be driven and have its self-capacitance sensed. 
       FIG. 7C  illustrates an exemplary timing diagram for capacitive and optical touch sensing according to examples of the disclosure. For capacitive touch sensing, a first one or more touch electrodes can be stimulated and charged (step  752  of process  750 ). In a mutual capacitance touch screen, the charge can capacitively couple to a second one or more touch electrodes at the sensing nodes. As an object (e.g. a finger) approaches the surface of touch screen  700 , the object can shunt some of the electric field to reduce the charge of the electrodes (step  754  of process  750 ). The reduction of charge can be sensed as a change in mutual or self-capacitance. The amount of charge (or change in coupled charge) in each of the columns can be measured by a sense circuitry, coupled to one or more touch electrodes, to determine the location(s) of one or more objects when touching (or hovering over) the surface of touch screen  700  (step  756  of process  750 ). 
     Although touch screen  700  includes two touch electrode layers, each including touch electrode  741  and touch electrode  743 , for example, touch screen  700  can include any number of layers. In some examples, other types of touch sensors can be included. Accordingly, many different configurations and touch sensing technologies can be employed without departing from or with respect to claimed subject matter scope. For example, a touch sensor configuration can utilize, but is not limited to, touch sensing technologies that employ resistive, surface acoustic, self-capacitance, mutual capacitance, or any combinations thereof. 
     For optical touch sensing, a first plurality of OLEDs (e.g., plurality of OLEDs  334  illustrated in  FIG. 3B ) can be configured for emitting light towards the cover material (e.g., cover material  747 ). Current sources (e.g., ICS 1  and ICS 2  illustrated in  FIG. 3C ) can inject currents into the plurality of first OLEDs (step  758  of process  750 ). In some examples, currents can be injected to OLEDs at only those locations determined from the capacitive touch measurement (e.g., steps  752 - 756 ). The plurality of first OLEDs (e.g., OLEDs  334 ) can emit light (step  760  of process  750 ). In some examples, the plurality of second OLEDs (e.g., OLED  332 - 1 ) can be deactivated, while the plurality of first OLEDs are configured to operate in emission mode. Deactivating the plurality of second OLEDs can include decoupled the second OLEDs (e.g., using second switch S 4  illustrated in  FIG. 3C ) from sense circuitry (e.g., amplifier  346 , Vbias  347 , and capacitor  348  illustrated in  FIG. 3C ). In some examples, the plurality of second OLEDs can be activated, but signals measured from the plurality of second OLEDs can be ignored. 
     The emitted light (e.g., from OLEDs  334 ) can reflect off one or more undulations (e.g., ridges of a finger) of the object located in close proximity to or in contact with a surface of cover material (e.g., cover material  747  illustrated in  FIG. 7A ) (step  762  of process  750 ). 
     A reverse bias can be applied to a plurality of second OLEDs (step  764  of process  750 ) by closing a switch (e.g., first switch S 3  illustrated in  FIG. 3C ) to couple the second OLED to sense circuitry (e.g., amplifier  346 , Vbias  347 , and capacitor  348  illustrated in  FIG. 3C ). By applying a reverse bias to the plurality of second OLEDs (e.g., OLEDs  332 ), the second OLED can be configured to detect the reflected light and can generate one or more signals (step  766  of process  750 ). The controller (not shown) can receive the one or more signals and can determine one or more touch (and/or hover) information (step  768  of process  750 ). In some examples, the controller can generate a 2-D image of the object(s), where the image can include the detected undulations (step  770  of process  750 ). 
     In some examples, a calibration (i.e., baseline) procedure (discussed below) can be performed at any time (e.g., at time t 3  illustrated in  FIG. 3D  or at time t 5  illustrated in  FIG. 7B ). By time multiplexing the display mode, capacitive sensing mode, optical touch sensing mode, and calibration mode, the touch screen can perform one or more operations with limited interference. For example, the touch screen can be in the calibration mode at a different time than in the optical touch sensing mode, such that the touch screen&#39;s determination of baseline values can be unaffected by stray light from other sensors and/or light due to multiple reflections from the object and/or device stackup. In some examples, the mode can be different in different regions of the touch screen. For example, the touch screen can be configured to sense a touch in one region of the active area, while being simultaneously configured to display one or more images in a different region of the active area. In some examples, one or more first operations can be repeated before performing a second operation. For example, a display operation and a touch sensing operation can be repeated multiple times before performing a calibration procedure. 
     Capacitive touch sensing can be suitable for detecting the location of one or more touch objects, but the resolution of capacitive touch sensing may not be suitable for resolving fine features (e.g., undulations in a finger). For example, a finger may have undulations that are less than 100 μm in size and may be detected using a sensor including a specific high dielectric constant material. The high dielectric constant material may be able to focus the electric fields to resolve the fine features. However, the high dielectric constant material may have limited applicability (e.g., fingerprint detection), limiting the size (e.g., size of home button  134  illustrated in  FIG. 1A ) and/or location (e.g., outside of the active area) of the sensor. Furthermore, in some examples, fidelity of an acquired optical touch image for finger print recognition can be compromised by stray reflections either from a proximate object (e.g., the finger) to be imaged or stray reflections that occur inside the optical medium (e.g. touch sensor, etc.). Since the OLED emitter can have light diffusion characteristics, it can emit light in various angles, for example. Light that is not directed toward the object (e.g., finger) above the touch sensor can illuminate unintended areas of the object and induce secondary (multi-path) reflections. These secondary reflections can wash out or reduce the contrast of the image, for example. In some examples, to provide a touch screen with provisions for mitigating stray OLED light. 
       FIGS. 8A-8B  illustrate cross-sectional and top views of an exemplary touch screen, and  FIG. 8C  illustrates an exemplary method for user identification according to examples of the disclosure. Touch screen  800  can be configured for displaying one or more images during one time period and can be configured for touch sensing during another time period. For touch sensing, touch screen  800  can be configured for capacitive touch sensing and/or optical touch sensing (discussed above). By using capacitive and optical touch sensing, fine features can be resolved with higher resolution touch sensing. Furthermore, resolving fine features and higher resolution touch sensing can be expanded to large areas, such as the active area of the touch screen (e.g., active area of touch screen  124  illustrated in  FIG. 1A ). 
     Touch screen  800  can include diffuser  874 , touch sensor  840 , collimation  870 , and OLED display  830 . Collimation  870  can be disposed between the OLED display  830  and touch sensor  840  as to direct the OLED light emission toward one or more specific areas of top surface of the touch screen (e.g., towards an object (e.g., finger) located at the top surface of the touch screen). In some examples, the collimation function can be integrated into the OLED display  830  and/or touch sensor  840  by adjusting the structure and composition of the OLED material. In addition to the collimation  870 , a diffuser  874  can be added to the top side (e.g., in the light path of OLED display  830  to the user) of the touch sensor  840 . The diffuser  874  can serve multiple purposes, such as to diffuse the collimated light (e.g., in order to improve the viewing angle of the displayed image) and to collimate the reflected light from the object to be imaged toward the OLEDs included in touch sensor  840 . Accordingly, a high resolution optical touch image can be obtained. 
     Touch screen  800  can include plurality of OLEDs  832  and plurality of OLEDs  834  grouped in rows (e.g., plurality of rows  821  and plurality of rows  823 ). Although  FIG. 8B  illustrates the OLEDs as being grouped in rows, in some examples, other group shapes are possible (e.g., checkerboard-shaped group patterns illustrated in  FIG. 3K ). Object  802 , object  804 , object  806 , and object  808  can be in contact with touch screen  800 . In some examples, object  802 , object  804 , object  806 , and object  808  can be a user&#39;s fingers. For example, object  802  can be a thumb; object  804  can be an index finger; object  806  can be a middle finger; and object  808  can be a ring finger. 
     The user identification process can begin by having the user place fingers (e.g., thumb, index finger, middle finger, and ring finger) in close proximity to or touching a surface of touch screen  800 . Touch screen  800  can detect the location(s) of the touch (step  852  of process  850 ). In some examples, detecting the location(s) of the touch can include measuring a mutual or self capacitance. A controller can identify a plurality of first groups (e.g., rows as illustrated in  FIGS. 3K and 8B  or in a checkerboard pattern as illustrated in  FIG. 3L ) of OLEDs associated with touch boundaries (step  854  of process  850 ). In some examples, groups of OLEDs associated with touch boundaries can be groups of OLEDs for which at least one OLED in the group overlaps with a location on the touch screen  800  for which a touch of a predetermined threshold is detected. In some examples, the boundaries can be extended by a predetermined amount beyond the detected boundaries of a proximate or touching object. For example, the controller can identify the first groups as plurality of rows  821  and plurality of rows  823 . Similarly, in some examples, the controller can identify groups of OLEDs in other shapes, such as the checkerboard-shaped groups illustrated in  FIG. 3L . 
     A plurality of second groups (e.g., rows) of OLEDs can be measured to obtain a baseline (i.e., calibration) image (step  856  of process  850 ). The baseline group image can be indicative of noise from the OLED sensors, AFEs, and/or any external noise induced by ambient light, for example. In some examples, the OLEDs included in the plurality of second groups can be decoupled from current sources and/or deactivated when the baseline image is obtained. In some examples, the plurality of second groups (e.g., the second groups of OLEDs that were measured to obtain a baseline) can include the plurality of first groups (e.g., the first groups of OLEDs corresponding to the touch location(s)). In some examples, the plurality of second groups can be offset from the plurality of first groups of OLEDs. In some examples, the baseline image can be obtained prior to having the user touch (or hover over) the surface of touch screen  800 . In some examples, multiple (e.g., two) group scans can be performed. A baseline scan can acquire a baseline group image with the associated OLED emitters disabled, and a touch scan can acquire touch data by performing a scan while the associated OLED emitters can be active with intensity levels set according to the spreading code in matrix  600 , for example, as will be described. 
     The plurality of first rows of OLEDs can be stimulated and measured to obtain a touch image (step  858  of process  850 ). For a given approximate touch location, a processor can identify a first row and last display row associated with the boundaries of the associated touch. In some examples, the touch image acquisition can include scanning rows from the first row to the last row in sequence, as controlled by a processor. Each row scan can involve a row of OLEDs to be configured as OLED emitters and a row of OLEDs to be configured as OLED sensors. In some examples, all other rows (e.g., rows excluding plurality of rows  821  and plurality of rows  823 ) of OLEDs may be decoupled or deactivated. In some examples, the stimulation and measurement can be performed using optical touch sensing. In some examples, touch screen  800  can be configured for high resolution touch sensing. Obtaining the touch image (step  858  of process  800 ) using the plurality of first rows can include configuring a plurality of first OLEDs to emit light towards the object (e.g., steps  758 - 760  of process  750  illustrated in  FIG. 7C ) and configuring a plurality of second OLEDs to detect a reflection of the emitted light (e.g., steps  764 - 766  of process  750  illustrated in  FIG. 7B ). 
     The baseline image obtained in step  858  can be subtracted from the touch image obtained in step  860 . The touch row image, besides internal and external noise, can also include a reading of reflected light (e.g., light reflected from a proximate object, such as a finger). By subtracting baseline from uncompensated touch image, internal/external noise can be largely subtracted from the uncompensated touch image, therefore improving the fidelity and thus dynamic range of the touch image, for example. In some examples, this process can be similar to correlated double sampling. Different patterns of rows can be measured (step  868  of process  850 ) until all patterns of rows have been measured (step  862  of process  850 ). Once all row scans are completed, baseline row image can be subtracted from the touch row image to obtain a full touch image for the first frame. The whole procedure can be repeated for following N−1 touch frames, but for each subsequent touch frame, the intensity levels for the N OLEDs can be varied according to matrix  600 . After all touch frames are acquired, the N touch frames can be demodulated with the inverse of matrix  600  (e.g., a de-spreading code) to acquire the final touch image for further processing by processor (step  864  of process  850 ). A controller can perform image processing (step  868  of process  850 ), and the image can be matched to one or more stored images for user identification. If the image is matched to the one or more stored images, then the touch screen can perform an action (e.g., unlock the touch screen). Although some examples involve OLEDs grouped by row, in some examples, the groups can have different shapes, such as a checkerboard arrangement. 
       FIG. 9  illustrates a block diagram of an exemplary computing system that illustrates one implementation of an example touch screen according to examples of the disclosure. Computing system  900  could be included in, for example, mobile telephone  936 , digital media player  940 , personal computer  944 , or any mobile or non-mobile computing device that includes a touch screen. Computing system  900  can include a touch sensing system including one or more touch processors  902 , peripherals  904 , a touch controller  906 , and touch sense circuitry (described in more detail below). Peripherals  904  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  906  can include, but is not limited to, one or more sense channels  908 , channel scan logic  910  and driver logic  914 . Channel scan logic  910  can access RAM  912 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  910  can control driver logic  914  to generate stimulation signals  916  at various frequencies and/or modes that can be selectively applied to drive regions of the touch sense circuitry of touch screen  920 , as described in more detail below. In some examples, touch controller  906 , touch processor  902  and peripherals  904  can be integrated into a single application specific integrated circuit (ASIC). 
     Computing system  900  can also include a host processor  928  for receiving outputs from touch processor  902  and performing actions based on the outputs. For example, host processor  928  can be connected to program storage  932  and a display controller, such as a driver  934 . Host processor  928  can use driver  934  to generate an image on touch screen  920 , such as an image of a user interface (UI), and can use touch processor  902  and touch controller  906  to detect a touch on or near touch screen  920 , such as a touch input to the displayed UI. In some examples, host processor  928  can use driver  934  to perform optical touch sensing. The touch input can be used by computer programs stored in program storage  932  to perform actions 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 a document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating 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. Host processor  928  can also perform additional functions that may not be related to touch processing. 
     Touch screen  920  can include touch sense circuitry that can include a capacitive sensing medium having a plurality of drive lines  922  and a plurality of sense lines  923 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  922  can be driven by stimulation signals  916  from driver logic  914  through a drive interface  924 , and resulting sense signals  917  generated in sense lines  923  can be transmitted through a sense interface  925  to sense channels  908  (also referred to as an event detection and demodulation circuit) in touch controller  906 . In this way, drive lines and sense lines can be part of the touch sense circuitry that can interact to form capacitive sensing nodes, which can be thought of as touch picture elements (touch pixels), such as touch pixels  926  and  927 . This way of understanding can be particularly useful when touch screen  920  is viewed as capturing an “image” of touch. In other words, after touch controller  906  has determined whether a touch has been detected at each touch pixel in the touch screen, the pattern of touch pixels in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g., a pattern of fingers touching the touch screen). In some examples, optical touch sensing can be used in addition to or as an alternative to capacitive (e.g., self and/or mutual capacitance) touch sensing. 
     Therefore, according to the above, some examples of the disclosure are directed to a touch screen, comprising: a plurality of light emitting diodes (LEDs) configured to emit a first light for displaying one or more images, the plurality of LEDs including first LEDs and second LEDs, the first LEDs configured to emit a second light for optical touch sensing, and the second LEDs configured to sense at least a portion of a reflection of the second light and generate one or more signals indicative of the reflection of the second light; a plurality of current sources coupled to the plurality of LEDs; sense circuitry coupled to the second LEDs; a switch configured to electrically couple and decouple the plurality of current sources to the sense circuitry during a touch sensing mode; and a processor configured to: receive the one or more signals generated by the second LEDs, and determine one or more properties of one or more proximate objects based on the one or more signals. Additionally or alternatively, in some examples, the plurality of current sources are configured to apply a forward bias across the first LEDs and further configured to apply a reverse bias across the second OLEDs during the touch sensing mode. Additionally or alternatively, in some examples, the first LEDs are further configured to sense at least a portion of the reflection of the second light, and the second LEDs are further configured to emit the second light. Additionally or alternatively, in some examples, the touch screen further comprises an analog to digital converter (ADC) having an input and an output, the input coupled to the one or more signals, and the output coupled to the processor. Additionally or alternatively, in some examples, the sense circuitry further comprises: a function generator configured to produce a ramp function, a plurality of comparators configured to compare the ramp function to the one or more signals and further configured to generate an enable signal when the ramp function matches the one or more signals, each comparator coupled to one of the second LEDs; and a plurality of registers configured to store the ramp function, each register coupled to one of the plurality of comparators. Additionally or alternatively, in some examples, the first LEDs are arranged in first rows, the second LEDs are arranged in second rows, and the first rows are interleaved with the second rows. Additionally or alternatively, in some examples, at least two of the first rows are adjacent. Additionally or alternatively, in some examples, the touch screen excludes capacitive touch sensors. Additionally or alternatively, in some examples, the sense circuitry includes a sense amplifier operatively coupled to a compensation signal, the compensation signal configured to compensate for a leakage current received by the sense amplifier. 
     According to the above, some examples of the disclosure are directed to a method of operating a touch screen, the method comprising: applying first currents to a plurality of LEDs included in the touch screen, the first currents indicative of intensities, associated with one or more displayed images, of a first light; applying second currents to first LEDs, the first LEDs included in the plurality of LEDs, wherein the second currents cause the first LEDs to emit a second light; applying third currents to second LEDs to detect a reflection of at least a portion of the second light, wherein the second LEDs are included in the plurality of LEDs; generating, with the second LEDs, one or more signals in response to the detected reflected light; and determining, based on the received one or more signals, one or more properties of one or more proximate objects. Additionally or alternatively, in some examples, the second currents apply forward biases to the first LEDs, and the third currents apply reverse biases to the second LEDs. Additionally or alternatively, in some examples, applying the third currents to the second LEDs occurs a non-zero time delay after applying the second voltages to the first LEDs. Additionally or alternatively, in some examples, applying the third currents to the second LEDs is concurrent with applying the second voltages to the first LEDs. Additionally or alternatively, in some examples, the method further comprises: modulating the second voltages with a plurality of waveforms included in an encoding matrix, wherein waveforms associated with adjacent first LEDs are separate and distinct; and demodulating the one or more signals with an inverse of the encoding matrix. Additionally or alternatively, in some examples, the one or more properties includes optical properties, the method further comprising: determining, based on the optical properties, whether at least one of the one or more proximate objects is water; and rejecting the one or more signals associated with the at least one of the one or more proximate objects that is water. Additionally or alternatively, in some examples, the LEDs are organic light emitting diodes (OLEDs). 
     According to the above, some examples of the disclosure are directed to a touch screen, comprising: a plurality of light emitting diodes (LEDs) configured to emit a first light for displaying one or more images, the plurality of LEDs including first LEDs and second LEDs, the first LEDs configured to emit a second light for optical touch sensing, and the second LEDs configured to sense at least a portion of a reflection of the second light and generate one or more signals first indicative of the reflection of the second light; a plurality of current sources coupled to the plurality of LEDs; a first sense circuitry coupled to the second LEDs; a switch configured to electrically couple and decouple the plurality of current sources to the first sense circuitry during a touch sensing mode; a plurality of first touch electrodes configured to receive a first voltage; a plurality of second touch electrodes configured to capacitively couple to the plurality of first touch electrodes; a second sense circuitry coupled to the plurality of second touch electrodes, the sense circuitry configured to sense a change in capacitance and generate one or more second signals indicative of the change in capacitance; and a processor configured to: receive the one or more first signals generated by the second OLEDs, receive the one or more second signals generated by the plurality of second touch electrodes, and determine one or properties of one or more proximate objects based one or more of the one or more first signals and the one or more second signals. Additionally or alternatively, in some examples, the plurality of first and second touch electrodes are configured to capacitively sense the one or more proximate objects during a first time, and the plurality of LEDs are configured to optically sense the one or more proximate objects during a second time, the second time following the first time. Additionally or alternatively, in some examples, the touch screen further comprises a spatial filter configured to focus the second light and resolve one or more features included in one or more objects. Additionally or alternatively, in some examples, the spatial filter includes a plurality of layers, each layer separated from another layer by at least a substrate. Additionally or alternatively, in some examples, the touch screen further comprises a collimation layer and a diffuser layer. Additionally or alternatively, in some examples, the collimation layer is disposed between the plurality of OLEDs and a touch electrode layer, the touch electrode layer including the first and second plurality of touch electrodes, and the diffuser layer is disposed on top of the touch electrode layer, the collimation layer, and the plurality of OLEDs. Additionally or alternatively, in some examples, the LEDs are organic light emitting diodes (OLEDs). 
     According to the above, some examples of the disclosure are directed to a method of operating a touch screen, the method comprising: stimulating a plurality of first touch electrodes with a first voltage; sensing a change in capacitance at a plurality of second touch electrodes, the plurality of second touch electrodes capacitively coupled to the plurality of first touch electrodes; generating, with the plurality of second touch electrodes, one or more first signals in response to the change in capacitance; applying first currents to a plurality of light emitting diodes (LEDs) included in the touch screen, the first currents indicative of intensities, associated with one or more displayed images, of a first light; applying second currents to first LEDs, the first LEDs included in the plurality of LEDs, wherein the second currents cause the first LEDs to emit a second light; applying third currents to second LEDs to detect a reflection of at least a portion of the second light, wherein the second LEDs are included in the plurality of LEDs; generating, with the second LEDs, one or more second signals in response to the reflected light; and determining, based on one or more of the one or more first signals and the one or more second signals, one or more properties of one or more proximate objects. Additionally or alternatively, in some examples, the one or more properties of the one or more proximate objects include one or more locations associated with the one or more first signals. Additionally or alternatively, in some examples, the one or more locations are associated with a plurality of rows, and further wherein the first OLEDs and second OLEDs are located in the plurality of rows, the method further comprising: deactivating OLEDs located in rows, excluding the plurality of rows, of the touch screen. Additionally or alternatively, in some examples, the one or more properties of the one or more proximate objects includes one or more features included in the one or more proximate objects, the method further comprising: resolving the one or more features based on the one or more second signals. Additionally or alternatively, in some examples, the method further comprises identifying, based on the one or more second signals, one or more fingerprints; determining whether the one or more fingerprints match a stored one or more fingerprints; and unlocking the touch screen when the one or more fingerprints match the stored one or more fingerprints. 
     Although 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 various examples as defined by the appended claims.

Metadata:
Filing Date: 20170915
Publication Date: 20200121
Grant Date: 20200121
Priority Date: 20160916
Inventors: KRAH, CHRISTOPH H.
BRAHMA, KINGSUK
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04108", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04106", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0445", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/042", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5221", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/323", "inventive": true, "first": true, "tree": "[]"}, {"code": "G06F1/1643", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/042", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0416", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/5206", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/82", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/041661", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/81", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0421", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/04186", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/65", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 69167218