Touch detection using common electrodes of display device

This application is directed to detecting touch events using a display pixel array. The display pixel array includes display pixels each of which is disposed between a display electrode and a common electrode. For touch sensing, a processing device drives the subset of common electrodes with an integration voltage that varies by a voltage variation at a predetermined slew rate. The processing device also drives a subset of display electrodes corresponding to the subset of common electrodes in a synchronous manner, thereby reducing an impact of parasitic capacitance associated with the subset of common electrodes. Each of the subset of display electrodes is driven with an adjusted display voltage that varies by the voltage variation at the predetermined slew rate. While driving the subsets of common and display electrodes, a capacitive sense signal associated with the subset of common electrodes is measured at an output of a capacitance sense circuit.

TECHNICAL FIELD

The disclosed implementations relate generally to touch detection in a display device, including but not limited to methods and systems for configuring common electrodes of the display device for both driving display pixels and sensing touch events, thereby avoiding introduction of a separate touch sensing array in the display device.

BACKGROUND

Touch screens that utilize capacitive sense arrays are widely applied in today's industrial and consumer product markets. Capacitive sense arrays can be found in cellular phones, GPS devices, set-top boxes, cameras, computer screens, MP3 players, digital tablets, and the like, replacing mechanical buttons, knobs, and other conventional user interface controls. A capacitive sense array is often disposed below a touch sensing surface of a touch screen, and includes an array of capacitive sense elements. Capacitances of these capacitive sense elements vary when an object (e.g., a finger, a hand, a stylus, or another object) comes into contact with or hovers above the touch sensing surface. A processing device coupled to the capacitive sense array then measures the capacitances of the capacitive sense elements and/or identifies capacitance variations of the capacitive sense elements for determining a touch or presence of the object associated with the touch sensing surface. The use of the capacitive sense array has offered a convenient and reliable user interface solution that is feasible under many harsh conditions.

Although capacitive sense arrays made of capacitive sense elements have been widely used in many industrial and consumer products, they oftentimes involve one or more dedicated touch sensing layers that are separate from other layers of materials used for display functions of a touch screen. It would be beneficial to integrate touch detection into existing display related infrastructure of a conventional touch screen without causing any detrimental impact on the display functions of the touch screen.

SUMMARY

Touch detection is integrated with a display screen that includes a display pixel array. The display screen normally includes a common electrode layer for providing a bias voltage or a reference voltage to each display pixel in the display pixel array. Accordingly, in various implementations of the application, the common electrode layer of the display screen is configured to use capacitive sense elements for detecting touch events on the display pixel array during a first set of time durations allocated for touch detection, while providing the bias or reference voltages to the display pixels of the display pixel array during a second set of time durations allocated for displaying. Specifically, during the first set of time durations allocated for touch detection, a set of common electrodes is driven with an integration voltage that varies by a predetermined voltage variation at a predetermined slew rate. One or more electrical nodes capacitively coupled to the set of common electrodes are also driven at the same slew rate and have the same voltage variation as the set of driven common electrodes, thereby reducing the impact of parasitic capacitance between the one or more electrical nodes and the set of common electrodes on touch detection implemented via the set of common electrodes. Further, in some implementations, the predetermined slew rate is predetermined to be less than a predetermined slew rate threshold such that the capacitive sense signal does not overshoot to cause current saturation in corresponding capacitance sense circuit.

In accordance with one aspect of the application, a method of detecting touch events using a display pixel array is implemented at a processing device coupled to the display pixel array. The display pixel array includes a plurality of display pixels, a plurality of display electrodes and a plurality of common electrodes, and each display pixel is disposed between a display electrode and a common electrode. The method includes at a touch sensing state, electrically coupling a first subset of the plurality of common electrodes to a capacitance sense circuit for touch detection, and driving the first subset of common electrodes with an integration voltage that varies by a first voltage variation at a predetermined slew rate. The method further includes driving a first subset of display electrodes corresponding to the first subset of common electrodes in a synchronous manner with the first subset of common electrodes, thereby reducing an impact of parasitic capacitance associated with the first subset of common electrodes. Each of the first subset of display electrodes is driven with an adjusted display voltage that varies by the first voltage variation at the predetermined slew rate. The method further includes while driving the first subset of common electrodes and the first subset of display electrodes, measuring a capacitive sense signal associated with the first subset of common electrodes at an output of the capacitance sense circuit.

In yet another aspect of the application, a touch sensing system includes a display pixel array and a processing device. The display pixel array includes a plurality of display pixels, a plurality of display electrodes and a plurality of common electrodes, and each display pixel is disposed between a display electrode and a common electrode. The processing device is coupled to the display pixel array and further includes a processing core, a memory coupled to the processing core, and a capacitive sense circuit coupled to the processing core. The memory stores one or more programs configured for execution by the processing core to control a touch sensing state and a display driving state of the touch sensing system. The capacitive sense circuit is configured to implement the method described herein for detecting touch events.

Thus, devices, storage media, and systems are provided with methods for detecting touches using a display pixel array, thereby reducing an impact of parasitic capacitance associated with the display pixel array and increasing the effectiveness, efficiency, and user satisfaction with such systems. Such methods may complement or replace conventional methods for detecting touches on touch-sensitive surfaces using dedicated touch sensing layers. More importantly, the methods, systems and devices described herein integrate touch detection into existing display related infrastructure in a conventional touch screen without causing any detrimental impact on the display functions of the touch screen.

DESCRIPTION OF IMPLEMENTATIONS

In accordance with various embodiments of this application, touch detection is not implemented using one or more dedicated touch sensing layers. Rather, touch detection is integrated into existing display related infrastructure (e.g., common electrodes of display pixels and related processing circuit) in a conventional touch screen without causing any detrimental impact on display functions of a touch screen. The touch screen normally includes a display pixel array that further includes a common electrode layer for providing a bias voltage or a reference voltage to each display pixel in the display pixel array. In a touch sensing state, the common electrode layer of the touch screen is reconfigured to capacitive sense elements for detecting touch events on the display pixel array during a first set of time durations allocated for touch detection, while in a display driving state, the same common electrode layer provides the bias or reference voltages to the display pixels of the display pixel array during a second set of time durations allocated for displaying. Specifically, during the first set of time durations allocated for touch detection, a set of common electrodes is driven with an integration voltage, and one or more electrical nodes are driven in a synchronous manner with the set of common electrodes. Both the set of common electrodes and the one or more electrical nodes are driven at the same slew rate and have the same voltage variation, thereby reducing the impact of parasitic capacitance between the one or more electrical nodes and the set of common electrodes on touch detection implemented via the common electrodes. As such, touch detection based on the common electrodes used for display driving does not cause any detrimental impact on display functions of the touch screen, and complements/replaces conventional touch detection methods that have to use additional and dedicated touch sensing layers.

FIG. 1is a block diagram illustrating an electronic system100having a processing device110that display driving signals and processes capacitive sense signals in accordance with some implementations. The processing device110is electrically coupled to a display device125including a display pixel array. The display pixel array125further includes a plurality of display pixels, a plurality of display electrodes and a plurality of common electrodes128. Each display pixel is disposed between a display electrode and a common electrode128. More details of the display device125are explained below with reference toFIGS. 2A-2B and 3A-3B. The processing device110operates in two states including a display driving state and a touch sensing state. In the display driving state, a voltage bias is generated and applied between the display and common electrodes of each display pixel to enable display of a color on the respective display pixel. In the touch sensing state, the plurality of common electrodes128are reconfigured to operate as a capacitive sense array128, and the processing device110is configured to measure capacitance variations at the plurality of common electrodes128and detect one or more touches proximate to a surface of the display device125. In some implementations, the processing device125alternates between the display driving state and the touch sensing state according to a predetermined duty cycle (e.g., 80%) for the display driving state, and detects a contact with or a proximity to a touch sensing surface associated with the display pixel array without interfering with current display operations of the display pixel array125.

The processing device110can detect conductive objects, such as touch objects140(e.g., a finger), a passive or active stylus130, or any combination thereof when operating in the touch sensing state. The capacitance sense circuit101can measure touch data created by a touch using the capacitive sense array128reconfigured from the plurality of common electrodes128. The touch may be detected by a single or multiple sensing cells, each cell representing an isolated sense element or an intersection of sense elements (e.g., electrodes) of the reconfigured capacitive sense array128. In some implementations, when the capacitance sense circuit101measures mutual capacitance of the reconfigured capacitive sense array128, the processing device110acquires a two dimensional capacitive image of the touch sensing object and processes the capacitive image data for peaks and positional information. In some implementations, the processing device110is coupled to a microcontroller (e.g., an external host device150) that obtains a capacitance touch signal data set from the reconfigured capacitive sense array128. In some implementations, finger detection firmware executing on the microcontroller identifies data set areas that indicate touches, detects and processes peaks, calculates the coordinates, or any combination thereof. The microcontroller can report the precise coordinates and other information to an application processor.

In some implementations, the electronic system100includes one or more of a processing device110, a display device125(i.e., a display pixel array), a stylus130, and a host150. The common electrodes128may include electrodes made of conductive material, such as copper, and are reconfigured to capacitive sense array128including capacitive sense elements that are electrodes made of the same conductive material. The common electrodes and sense elements may also be part of an indium-tin-oxide (ITO) panel. In the display driving state, the common electrodes128provide a bias voltage or a reference voltage to each display pixel of the display pixel array125, thereby enabling display of a color on the respective display pixel. In the depicted embodiment, the electronic system100includes the common electrodes128coupled to the processing device110via a bus124, and the common electrodes128are configured to receive display driving signals from the processing device110via the bus124. More specifically, the display driving signals are generated by a pixel drive circuit102of the processing device110. Alternatively, in the touch sensing state, the capacitive sense elements of the reconfigured capacitive sense array128can be used to allow the capacitance sense circuit101to measure self-capacitance, mutual capacitance, or any combination thereof. In the depicted embodiment, the electronic system100includes the reconfigured capacitive sense array128coupled to the processing device110via a bus122, and the reconfigured capacitive sense array128is configured to provide capacitive sense signals to a capacitance sense circuit101of the processing device110via the bus122. The reconfigured capacitive sense array128may include a multi-dimension capacitive sense array. In some implementations, the multi-dimension sense array includes multiple sense elements, organized as rows and columns. In some implementations, the reconfigured capacitive sense array128has a flat surface profile. In some implementations, the capacitive sense array128may have a non-flat surface profile. In some implementations, other configurations of capacitive sense arrays can be used. For example, instead of vertical columns and horizontal rows, the capacitive sense array128may have a hexagonal arrangement, or the like, as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. More details on a capacitive sense array128are explained below with reference toFIGS. 2A-2B and 3A-3B.

In some implementations, the electronic system100further includes one or more force electrodes (not shown inFIG. 1) that are disposed below the reconfigured capacitive sense array128and separated from the reconfigured capacitive sense array128. The one or more force electrodes are electrically coupled to the processing device110, and are configured to provide force signals to the processing device110for determining force associated with candidate touches detected from the reconfigured capacitive sense array128. In some implementations, the force signals are measured from capacitance variation associated with the one or more force electrodes, and used to improve accuracy of touch detection based on the capacitive sensing signals.

The operations and configurations of the processing device110and the reconfigured capacitive sense array128for detecting and tracking a touch object140or a stylus130are described herein. In short, the processing device110is configurable to detect a presence of a touch object140, a presence of a stylus130on the reconfigured capacitive sense array128, or any combination thereof. If the touching object is an active stylus, the active stylus130is configured to operate as the timing “master,” and the processing device110adjusts the timing of the reconfigured capacitive sense array128to match that of the active stylus130. In some implementations, the reconfigured capacitive sense array128capacitively couples with the active stylus130, as opposed to conventional inductive stylus applications. It should also be noted that the same assembly (e.g., the processing device110) used for the reconfigured capacitive sense array128, which is configured to detect touch objects140, is also used to detect and track the stylus130without an additional PCB layer for inductively tracking the active stylus130.

In some implementations, the processing device110includes analog and/or digital general purpose input/output (“GPIO”) ports107. GPIO ports107may be programmable. GPIO ports107may be coupled to a Programmable Interconnect and Logic (“PIL”), which acts as an interconnect between GPIO ports107and a digital block array of the processing device110(not shown). In some implementations, the digital block array is configured to implement a variety of digital logic circuits (e.g., DACs, digital filters, or digital control systems) using configurable user modules (“UMs”). The digital block array may be coupled to a system bus. The processing device110may also include memory, such as random access memory (“RAM”)105and non-volatile memory (“NVM”)104. RAM105may be static RAM (“SRAM”). The non-volatile memory104may be a flash memory, which may be used to store firmware (e.g., control algorithms executable by processing core109to implement operations described herein). The processing device110may also include a memory controller unit (“MCU”)103coupled to memory and the processing core109. The processing core109is a processing element configured to execute instructions or perform operations. The processing device110may include other processing elements as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure. It should also be noted that the memory may be internal to the processing device110or external to it. In the case of the memory being internal, the memory may be coupled to a processing element, such as the processing core109. In the case of the memory being external to the processing device110, the processing device110is coupled to the other device in which the memory resides as would be appreciated by one of ordinary skill in the art having the benefit of this disclosure.

Some or all of the operations of the processing core109may be implemented in firmware, hardware, software, or some combination thereof. The processing core109may receive signals from the capacitance sense circuit101, determine the state of the reconfigured capacitive sense array128(e.g., determining whether an object is detected on or in proximity to the touch sensing surface), resolve where the object is on the sense array (e.g., determining the location of the object), track the motion of the object, or generate other information related to an object detected at the touch sensor. In some implementations, the processing core109includes the capacitance sense circuit101. In some implementations, the processing core109performs some or all the functions of capacitance sense circuit101. Additionally, in some implementations, the processing core109provides display information to the pixel drive circuit102, such that the pixel drive circuit102can be configured to drive individual display pixels in the display device125to display images or videos based on the display information. In some implementations, the processing core109includes some or all functions of the pixel drive circuit102, i.e., part or all of the pixel drive circuit102is integrated in the processing core109.

In some implementations, the processing core109generates a touch detection enable signal120and a display driving enable signal121that are synchronized to control the capacitance sensing circuit101and the pixel drive circuit102to detect touch locations and drive individual display pixels, respectively. The touch detection enable signal120is used to enable a touch sensing state. In the touch sensing state, the common electrodes128are decoupled from the pixel drive circuit102and reconfigured to the capacitive sense array128coupled to the capacitance sense circuit102. Self or mutual capacitance of sense elements of the reconfigured capacitive sense array128is scanned by the capacitance sense circuit102. One or more touch locations are thereby detected if one or more objects touch the touch sensing surface of the electronic system100. Alternatively, in some implementations, the display driving enable signal121is used to enable a display driving state (e.g., decouple the capacitance sense circuit101from the reconfigured capacitive sense array128and couple the pixel drive circuit102to the common electrodes128). In such a display driving state, the pixel drive circuit102enables a bias voltage and a reference voltage corresponding to an intended color on each display pixel of the display pixel array. The display pixel displays the intended color when the bias voltage and the reference voltage are applied on the display and common electrodes of the respective display pixel. It is noted that the touch detection enable signal120and the display driving enable signal121can be enabled sequentially and share operation time of the common electrodes/capacitive sense array128.

The processing device110may also include an analog block array (not shown) (e.g., field-programmable analog array). The analog block array is also coupled to the system bus. An analog block array may be configured to implement a variety of analog circuits (e.g., ADCs or analog filters) using, in some implementations, configurable UMs. The analog block array may also be coupled to the GPIO107.

In some implementations, the capacitance sense circuit101is integrated into the processing device110. The capacitance sense circuit101includes analog I/O for coupling to an external component, such as a touch-sensor pad (not shown), a reconfigured capacitive sense array128, a touch-sensor slider (not shown), a touch-sensor buttons (not shown), and/or other devices. The capacitance sense circuit101may be configured to measure capacitance using mutual-capacitance sensing techniques, self-capacitance sensing technique, charge-coupling techniques, charge balancing techniques, or the like. In some implementations, the capacitance sense circuit101operates using a charge accumulation circuit, a capacitance modulation circuit, or other capacitance sensing methods known by those skilled in the art. In some implementations, other capacitance sensing circuits may be used. The mutual capacitive sense arrays, or touch screens, as described herein, may include a transparent, conductive sense array disposed on, in, or under either a visual display itself (e.g. LCD monitor), or a transparent substrate in front of the display.

A reconfigured capacitive sense array128includes a plurality of sense elements. When a touch object, such as a finger140or stylus130, approaches the reconfigured capacitive sense array128, the object causes a decrease in mutual capacitance between some of the sense elements. In some implementations, the presence of a finger increases the capacitance of the electrodes to the environment (Earth) ground, typically referred to as self-capacitance change. In some implementations, the plurality of sense elements of the reconfigured capacitive sense array128are configured to operate as transmit (TX) electrodes and receive (RX) electrodes of a mutual capacitive sense array in a first mode to detect touch objects, and to operate as electrodes of a coupled-charge receiver in a second mode to detect a stylus on the same electrodes of the sense array. Specifically, in the first mode, a mutual capacitance is measured at an intersection of a RX electrode and a TX electrode when a transmit signal provided at the RX electrode is coupled to the TX electrode. Utilizing the change in mutual capacitance, the location of the finger on the reconfigured capacitive sense array128is determined by identifying an RX electrode having a decreased coupling capacitance with a TX electrode whose signal was applied at the time the decreased capacitance is measured on the RX electrode. Therefore, the locations of one or more touch objects can be determined by sequentially scanning the capacitances associated with the intersection of electrodes. In some implementations, in the second mode, the stylus130is activated to generate a stylus transmit signal, which is then coupled to a subset of sense elements of the reconfigured capacitive sense array128that is located below the stylus130.

In some implementations, the processing device110calibrates the sense elements (intersections of RX and TX electrodes) by determining baselines for the sense elements. In some implementations, interpolation is used to detect finger position at better resolutions than a spatial pitch of the sense elements of the reconfigured capacitive sense array128, and various types of coordinate interpolation algorithms are optionally used to detect a center location of a touch.

The processing device110may include internal oscillator/clocks106and a communication block (“COM”)108. In some implementations, the processing device110includes a spread-spectrum clock (not shown). The oscillator/clocks106provides clock signals to one or more of the components of processing device110. The communication block108may be used to communicate with an external component, such as an application processor150, via an application interface (“I/F”) line151. In some implementations, the processing device110may also be coupled to an embedded controller154to communicate with the external components, such as a host150. In some implementations, the processing device110is configured to communicate with the embedded controller154or the host150to send and/or receive data.

The processing device110may reside on a common carrier substrate such as, for example, an integrated circuit (“IC”) die substrate, a multi-chip module substrate, or the like. In some implementations, the components of the processing device110may be one or more separate integrated circuits and/or discrete components. In some implementations, the processing device110may be one or more other processing devices known by those of ordinary skill in the art, such as a microprocessor or central processing unit, a controller, a special-purpose processor, a digital signal processor (“DSP”), an application specific integrated circuit (“ASIC”), a field programmable gate array (“FPGA”), or the like.

It is also noted that the implementations described herein are not limited to having a configuration of a processing device coupled to an application processor, but may include a system that measures the capacitance on the capacitive sense array and sends the raw data to a host computer150where it is analyzed by an application. In effect, the processing that is done by the processing device110may also be done in the application processor. Specifically, in some implementations, instead of performing the operations of the processing core109in the processing device110, the processing device110may send the raw data or partially-processed data to the host150. The host150, as illustrated inFIG. 1, may include decision logic153that performs some or all of the operations of the processing core109. Operations of the decision logic153may be implemented in firmware, hardware, software, or a combination thereof. The host150may include a high-level Application Programming Interface (API) in applications152that perform routines on the received data, such as compensating for sensitivity differences, other compensation algorithms, baseline update routines, start-up and/or initialization routines, interpolation operations, or scaling operations. The operations described with respect to the processing core109may be implemented in the decision logic153, the applications152, or in other hardware, software, and/or firmware external to the processing device110. In some other embodiments, the processing device110is the host150.

The capacitance sense circuit101may be integrated into the IC of the processing device110, or in a separate IC. In some implementations, descriptions of capacitance sense circuit101may be generated and compiled for incorporation into other integrated circuits. For example, behavioral level code describing the capacitance sense circuit101, or portions thereof, may be generated using a hardware descriptive language, such as VHDL or Verilog, and stored to a machine-accessible medium (e.g., CD-ROM, hard disk, floppy disk, or flash memory). Furthermore, the behavioral level code can be compiled into register transfer level (“RTL”) code, a netlist, or a circuit layout and stored to a machine-accessible medium. The behavioral level code, the RTL code, the netlist, and the circuit layout may represent various levels of abstraction to describe the capacitance sense circuit101.

It is noted that the components of the electronic system100may include all the components described above. In some implementations, the electronic system100includes fewer than all of the components described above.

In some implementations, the electronic system100is used in a tablet computer. In some implementations, the electronic device is used in other applications, such as a notebook computer, a mobile handset, a personal data assistant (“PDA”), a keyboard, a television, a remote control, a monitor, a handheld multi-media device, a handheld media (audio and/or video) player, a handheld gaming device, a signature input device for point of sale transactions, an eBook reader, a global position system (“GPS”), or a control panel. The embodiments described herein are not limited to touch screens or touch-sensor pads for notebook implementations. Implementations can be used in other capacitive sensing devices, such as a touch-sensor slider (not shown) or touch-sensor buttons (e.g., capacitance sensing buttons). In some implementations, these sensing devices include one or more capacitive sensors or other types of capacitance-sensing circuitry. The operations described herein are not limited to notebook pointer operations, but can include other operations, such as lighting control (dimmer), volume control, graphic equalizer control, speed control, or other control operations requiring gradual or discrete adjustments. It should also be noted that these capacitive sensing implementations may be used in conjunction with non-capacitive sensing elements, including but not limited to pick buttons, sliders (e.g., display brightness and contrast), scroll-wheels, multi-media control (e.g., volume, track advance), handwriting recognition, and numeric keypad operation.

In some implementations, the electronic system100further includes one or more alternative sense elements156configured to communicate with the processing device110via a bus157. Each alternative sense element156is optionally a capacitance based sensor or a non-capacitance sensor. Example alternative sense elements156include, but are not limited to, an ambient light sensor, a capacitive touch button, and a side touch sensor.

FIG. 2Aillustrates an example touch screen assembly200(e.g., a liquid crystal display screen) including a common electrode array that is reconfigured to a capacitive sense array128in accordance with some implementations. The touch screen assembly200includes a liquid crystal display (LCD)202overlaid by the glass204. A display pattern206is constructed on a surface of the glass204to form a footprint of a display pixel array. Optionally, as shown inFIG. 2A, the display pattern206is constructed on a top surface of the glass204that faces away from the LCD202or on a bottom surface of the glass204that faces the LCD202. The display pattern206includes a plurality of display electrodes for driving a plurality of display pixels made of LCD molecules of the LCD202. Optically clear adhesive (OCA)208is used to bond a top glass210to the surface of the glass204on which the display pattern206is constructed, thus protecting the display pattern206. The touch screen assembly200further includes a common electrode array128opposing the plurality of display electrodes formed on display pattern206. Stated another way, the common electrode array128is formed on a glass212disposed under the LCD202and oppose the glass204. As such, each display pixel of the LCD202is disposed between a respective display electrode and a respective common electrode that are formed on the display pattern206and the common electrode layer128, respectively.

In some implementations not shown inFIG. 2A, the display pattern206is constructed on a surface of the glass204to form a footprint of a display pixel array125, and the glass204is disposed under the LCD202. The common electrode array128is formed on the glass212, and the glass212is disposed above the LCD202and oppose the glass204. The top glass210is bonded to the glass212using OCA208for protecting the common electrode layer128. Each display pixel of the LCD202is still disposed between a respective display electrode and a respective common electrode that are formed on the display pattern206and the common electrode layer128, respectively.

In some implementations, a first thin film transistor (TFT) array is formed on the glass204to drive the display electrodes formed on the display pattern206. More specifically, a gate layer, a semiconductor layer, a source/drain layer, one or more conductive layers and one or more intervening insulating layers are deposited on the glass204. These material layers are lithographically patterned on the glass204to form functional part (e.g., gate, source and drain) of the TFTs as well as the row and column lines of the first TFT array. For each individual display pixel of the LCD202, the respective display electrode is electrically coupled to a respective TFT of the first TFT array. The first TFT array is configured to receive display driving signals from the processing device110(more specifically, the pixel drive circuit102of the processing device110), and generates a first electrical voltage or current to drive the display electrode of each display pixel. As the first electrical voltage or current is applied to the liquid crystal molecules corresponding to each display pixel, the molecules tend to untwist from its original twisted form, and cause a change in the angle of an incident light. Stated another way, the first TFT array includes a two dimensional (2D) array of TFTs, row lines and column lines. As shown inFIG. 2B, each TFT of the first TFT array is connected between a respective row line and a respective column line, and configured to provide the first electrical voltage or current to drive the corresponding liquid crystal molecules of the corresponding display pixel. In some implementations, the entire common electrode layer128is electrically coupled to a reference voltage (sometimes referred to as VCOM). In some implementations, the common electrodes128corresponding to the display pixels are driven individually or in group as explained below.

It is noted that in some implementations, a second thin film transistor (TFT) array is formed on the glass212to drive the common electrodes128. More specifically, a gate layer, a semiconductor layer, a source/drain layer, one or more conductive layers and one or more intervening insulating layers are deposited on the glass212. These material layers are lithographically patterned on the glass212to form functional part (e.g., gate, source and drain) of the second TFTs as well as the row and column lines of the second TFT array. For each individual display pixel of the LCD202, the respective common electrode is electrically coupled to a respective TFT of the second TFT array. The TFT array is configured to receive display driving signals from the processing device110, and generates a second electrical voltage or current to drive the common electrode corresponding to each display pixel. As the first and second electrical voltages/currents are applied to the liquid crystal molecules corresponding to each display pixel, the molecules tend to untwist from its original twisted form, and cause a change in the angle of an incident light. Stated another way, the second TFT array includes a two dimensional (2D) array of TFTs, row lines and column lines. Each TFT of the second TFT array is connected between a respective row line and a respective column line, and configured to provide the second electrical voltage or current to drive the corresponding liquid crystal molecules of the corresponding display pixel in conjunction with the first electrical voltage or current. In some implementations, the common electrodes128, the display electrodes, the first TFT array and the second TFT array (if used) are made of transparent material (e.g., indium-tin oxide (ITO)) to allow light to pass through from the side or the back of the touch screen assembly200.

Optionally, the common electrode array128has a diamond pattern, a row-column pattern or a two-dimensional (2D) array of common electrodes (as shown inFIG. 3A). In some implementations related to the row-column pattern, the capacitive sense array128reconfigured from the common electrode array128includes row and column sense elements that can be expressed as a matrix of the intersections between row and column electrodes. In some implementations, the row and column sense elements are formed on two conductive layers that are electrically insulated from each other, and both of the conductive layers are formed on one of the top or bottom surfaces of the glass212. In some implementations related to the 2D array of common electrodes, the 2D array of common electrodes includes a plurality of square or rectangular electrodes, and when reconfigured to the capacitive sense array128, a set of adjacent common electrodes (e.g., a 2D array of 64×60 common electrodes) is grouped into a unit sense element for touch detection. The resolution of the common electrodes128is represented as the product of the number of rows and the number of columns associated with the common electrodes128. The resolution of the reconfigured capacitive sense array128is represented as the product of the number of rows and the number of columns associated with the capacitive sense elements. The resolutions of the common electrodes128and the reconfigured capacitive sense array128could be identical or distinct.

FIG. 2Billustrates an example display pixel250driven by a display electrode214and a common electrode218in a display driving state in accordance with some implementations. As explained above, the display pixel250is disposed between the display and common electrodes. A first TFT216is connected between a respective row line218and a respective column line220, and configured to provide the first electrical signal to drive the display electrode214of the corresponding display pixel250. In the case of LCD display pixels, the first electrical signal and another second electrical signal are applied onto the display and common electrodes, respectively, and therefore to the liquid crystal molecules corresponding to the display pixel250. The molecules tend to untwist from their original twisted form, and cause a change in the angle of an incident light, thereby causing display of a color at a location corresponding to the display pixel250.

The first TFT216is formed on the glass204to drive the display electrode214that is formed on the same glass substrate. More specifically, a gate layer, a semiconductor layer, a source/drain layer, one or more conductive layers and one or more intervening insulating layers are deposited on the glass204. These material layers are lithographically patterned on the glass204to form functional part (e.g., gate, source and drain) of the first TFT216as well as the row (gate) line218and the column (source) line220of the first TFT216. The first TFT216is configured to receive display driving signals from the processing device110(more specifically, the pixel drive circuit102of the processing device110), and generates the first electrical signal to drive the display electrode214of the display pixel250.

In some implementations (not shown inFIG. 2B), the display pixel250includes a second TFT to generate the second electrical signal to drive the common electrode128. The second TFT is formed on the glass218to drive the common electrode128that is formed on the same glass substrate. A gate layer, a semiconductor layer, a source/drain layer, one or more conductive layers and one or more intervening insulating layers are deposited on the glass212. These material layers are lithographically patterned on the glass204to form functional part (e.g., gate, source and drain) of the second TFT as well as a row (gate) line and a column (source) line of the second TFT. The first TFT is configured to receive the display driving signals from the processing device110(more specifically, the pixel drive circuit102of the processing device110), and generates the second electrical signal to drive the common electrode128of the display pixel250.

In an example, in the display driving state, the common electrode128is coupled to the ground (e.g., 0V) or another reference voltage (e.g., 2V and −2V). The gate line218is coupled to a TFT turn-on voltage VGH(e.g., 13V) to turn on the first TFT216, such that the display electrode214is electrically driven by an electrical signal delivered to the source220of the first TFT216. Optionally, the electrical signal of the source220has a magnitude of +5V or −5V, and the first electrical signal applied on the display electrode214tracks the electrical signal of the source. In another example, the common electrode128is coupled to the ground (e.g., 0V). The gate line218is coupled to a TFT turn-off voltage VGL(e.g., −10V) to turn off the first TFT216, such that the display electrode214is electrically decoupled from the electrical signal delivered to the source220of the TFT216. Regardless of the magnitude of the electrical signal the source220has, the first electrical signal at the display electrode214does not track the electrical signal of the source220.

FIG. 3Ais an example display pixel array125that is reconfigured to a capacitive sense array128in accordance with some implementations, andFIG. 3Bis an example capacitive sense element that is reconfigured from a set of common electrodes128of the display pixel array125shown inFIG. 3Ain accordance with some implementations. The display pixel array125has a first resolution (e.g., 1920×1080), and the capacitive sense array128reconfigured from the display pixel array has a second resolution (e.g., 30×18). The display pixel array125includes a plurality of display pixels (e.g., approximately 2M pixels arranged on the LCD202), a plurality of display electrodes (e.g., approximately 2M display electrodes arranged on the glass204), and a plurality of common electrodes. Each display pixel250is disposed between a display electrode214and a common electrode128. Each display pixel250is accessed by a column line (also called a source line220) and a row line (also called a gate line218). The column and row lines are configured to control the respective TFT216associated with each display pixel250to drive the display electrode214. In an example, the display pixel array125has a first number (e.g., approximately 2M) of display pixels arranged to 1920 rows and 1080 columns.

In some implementations, the common electrodes128of the display pixel array125are reconfigured to operate as the capacitive sense array128having a second resolution, such that the capacitive sense array128includes a second number (e.g., 540) of capacitive sense elements. In a specific example as shown inFIG. 3B, each sense element includes 64 rows and 60 columns of common electrodes128, and therefore, the entire capacitive sense array128has the second resolution of 30×18. Stated another way, the display pixel array125includes an array of 1920×1080 display pixels and is divided into 30×18 pixel sets, and each pixel set includes 64×60 display pixels. The common electrodes128corresponding to each pixel set are grouped into one capacitive sense element of the capacitive sense array128. The pixel set corresponding to each sense element of the capacitive sense array128is driven by 64 gate lines and 60 source lines. In some implementations, the pixel set corresponding to each sense element of the capacitive sense array128includes a single common electrode, i.e., 64×60 display electrodes share the single common electrode. In some implementations, the pixel set corresponding to each sense element of the capacitive sense array128includes a third number (e.g., 64×60 or less) of common electrodes. Optionally, each of the third number of common electrodes corresponds to one or more display pixels in the pixel set. Optionally, the third number of common electrodes are electrically coupled to each other to form the corresponding sense element of the capacitive sense array128.

Referring toFIG. 3A, in the touch sensing state, the second number of sense elements of the reconfigured capacitive sense array128are scanned for detecting a contact with or a proximity to a touch sensing surface associated with the display pixel array125. Further, referring toFIG. 3B, in each sense element of the reconfigured capacitive sense array128, the common electrodes128are grouped to one or more touch sense signals that are measured by the capacitive sense circuit101of the processing device110for touch detection in the touch sensing state. However, the common electrodes128in each sense element are at least capacitively coupled to the display electrodes214via the display pixels125corresponding to the respective sense element, and to the gate lines218and the source lines220via the TFTs216corresponding to the respective sense element. In addition, the common electrodes128in each sense element are also capacitively coupled to touch sense signals302of other sense elements when the touch sense signals302are routed via the respective sense element to an edge of the display device125to gain access to the processing device110. As such, when the common electrodes128of the display pixel array125are reconfigured to operate as the capacitive sense array128, parasitic capacitance is created for each sense element of the capacitive sense array128because of existence of the corresponding display electrode250, gate lines218, source lines220, and signal lines connected to common electrodes of other sense elements.

FIG. 4is an example capacitive sense element128A that is reconfigured from a first subset of common electrodes of a display device125and impacted by parasitic capacitance in accordance with some implementations. In an example, the sense element128A has approximate parasitic capacitances of 67 nF and 10 nF with respect to a set of gate lines218and a set of source lines220corresponding to the common electrodes128reconfigured into the sense element128A, respectively, while the set of gate lines218A and the set of source lines220A have parasitic capacitance of 44 nF between each other. The sense element128A has substantially small capacitance (e.g., less than 1 nF) with respect to one or more alternative sense elements128B that are distinct from the sense element128A.

In accordance with some implementations of this application, in a touch sensing state, the sense element128A is electrically coupled to and driven by an attenuator driver402that provides an integration voltage VYthat varies by a first voltage variation at a predetermined slew rate. The set of gate lines218A corresponding to the common electrodes128A reconfigured into the sense element128A are electrically coupled to and driven by a gate driver404. The set of source lines220A corresponding to the common electrodes128reconfigured into the sense element128are electrically coupled to and driven by a source driver406. The one or more alternative sense elements128B that are distinct from and forms parasitic capacitance with the sense element128A are electrically coupled to and driven by a shield driver408. In some implementations, the set of gate lines218and the set of source lines220are driven in a synchronous manner with the sense element128A (i.e., the first subset of common electrodes corresponding to the sense element128A), thereby reducing an impact of parasitic capacitance associated with the first subset of common electrodes218. In some implementations, the one or more alternative sense elements128B (i.e., a second subset of common electrodes corresponding to the sense element(s)128B) are driven in a synchronous manner with the sense element128A.

When the set of gate lines218A and the set of source lines220A are driven in the synchronous manner with the first subset of common electrodes, a first subset of display electrodes214A corresponding to the first subset of common electrodes is effectively driven in a synchronous manner with the first subset of common electrodes corresponding to the sense element128A. Each of the first subset of display electrodes214A is therefore driven by an adjusted display voltage VADPthat varies by the first voltage variation at the predetermined slew rate, which is consistent with the integration voltage VYdriving the sense element128A.

In addition, in some implementations, the predetermined slew rate is predetermined to be less than a predetermined slew rate threshold such that capacitive sense signal does not overshoot to cause current saturation in corresponding capacitance sense circuit101. The overshoot is associated with transient charge that not only causes a longer settling time on an integration capacitance of the capacitance sense circuit101but also compromises a linear range of the attenuator driver402, which impacts noise suppression and power consumption for touch detection. In some implementations, the predetermined slew rate of the integration voltage is not greater than 2 V/μsec.

FIG. 5Ais a circuit diagram500for an example capacitance sense circuit101configured to sense self capacitance of a sense element128A of a capacitive sense array128in accordance with some implementations. The sense element128A of capacitive sense array128includes a first subset of common electrodes, and forms a self capacitor (Cs)502with respect to a ground. The self capacitor502is coupled to a switching network504and a self capacitance sensing channel506both of which are part of the capacitance sense circuit101. An output of the self capacitance sensing channel506is further processed in the processing device110to detect a touch event on a touch sensing surface of the display device125. The self capacitance sensing channel506further includes a charge integration amplifier508followed by an analog-to-digital converter (ADC)510. The charge integration amplifier508receives a reference voltage VREF, and is coupled to an integration capacitor CINT512and a switch SW3to form a charge integrator.

The switching network504includes at least two switches SW1and SW2. The switches SW1, SW2and SW3are synchronized to alternate the self capacitance sensing channel506and the self capacitor502between a reset cycle and a capacitance measurement cycle. At the reset cycle, the self capacitor502is electrically coupled to a supply voltage VDDwhile the integration capacitor512is short circuited to remove charge accumulated thereon. At the capacitance measurement cycle, the self capacitor502is gradually pulled to the reference voltage VREFwhile charge on the self capacitor502is redistributed to the integration capacitor512. As such, to measure capacitance of the self capacitor502, the voltage level driving the sense element128A varies between the supply voltage VDDand the reference voltage VREF, and an output signal measured at the output of the self capacitance sensing channel506indicates a capacitance variation of the self capacitor502and whether the self capacitor502is associated with a touch event.

In some implementations, at a touch sensing state, the supply voltage is 3.2V, and the reference voltage is 1.2V. The voltage level at the sense element128A varies between 3.2V and 1.2V, and therefore, has a first voltage variation of 2V.

FIG. 5Bis a circuit diagram for an example attenuator driver402configured to drive a sense element of a capacitive sense array128for touch detection in accordance with some implementations. The attenuator driver402includes a two-stage class AB amplifier552coupled as a buffer and a cascoded output stage554, and has an output swing at an output of the cascoded output stage554. The output swing is limited by headroom requirements of the cascoded output stage552of the attenuator driver402. When transistors P2and N2are squeezed, linearity of the attenuator driver402is compromised, and a ratio A between a first charge integrated on an integration capacitor Cint and a second charge integrated on an input capacitor Cp is not constant. In some implementations, the ratio A between the first and second charges is defined by sizes of transistors P1, P2, N1and N2as follows:

A=SP⁢⁢1SN⁢⁢1/SP⁢⁢2SN⁢⁢2
where SP1, SN1, SP2, and SN2are the sizes of transistors P1, P2, N1and N2, respectively, and in some implementations, a transistor size is represented by a ratio between a width and a length of a corresponding transistor. It is noted that the input voltage VYand the output voltage VZhas a ratio of A as well. In an example, capacitance of the integration capacitor Cint is set to 10 pF, and the input voltage VYvaries by 1V (e.g., from 2.7V to 1.7V) at a slew rate of 1 V/μsec. The output swing at the output of the attenuator driver402reaches 3.3V before the linearity of the attenuator driver402is compromised (i.e., the ratio A varies with the output voltage VZ).

FIG. 6Ais an electronic system600that compensates for parasitic capacitance associated with a sense element128A of an example capacitive sense array128reconfigured from common electrodes128of a display device125in accordance with some implementations. At a touch sensing state, the sense element128A is electrically coupled to and driven by an attenuator driver402A that provides an integration voltage VYthat varies by a first voltage variation (e.g., 2V) at a predetermined slew rate (e.g., 2 V/μsec). The sense element128A is reconfigured from a first subset of common electrodes that corresponds to a first subset of display electrodes214A, and the first subset of display electrodes214A is capacitively coupled to the sense element128A. Each of the first subset of display electrodes214A is therefore driven by an adjusted display voltage VADAthat varies by the first voltage variation at the predetermined slew rate, which is consistent with the integration voltage driving the sense element128A. By these means, an impact of parasitic capacitance associated with the first subset of common electrodes can be reduced.

The adjusted display voltage VADPapplied on the first subset of display electrodes214A is created by a first subset of TFTs216A that is electrically coupled to the first subset of display electrodes214. The set of gate lines218A coupled to the TFTs216A are electrically coupled to and driven by a gate driver404A. The set of source lines220A coupled to the TFTs216A are electrically coupled to and driven by a source driver406A. The one or more alternative sense elements128B that are distinct from and forms parasitic capacitance with the sense element128A are electrically coupled to and driven by a shield driver408. In some implementations, the set of gate lines218and the set of source lines220are driven in a synchronous manner with the sense element128A (i.e., a first subset of common electrodes corresponding to the sense element128A). In some implementations, the one or more alternative sense elements128B (i.e., a second subset of common electrodes corresponding to the sense element(s)128B) are driven in a synchronous manner with the sense element128A.

In some implementations, the display device125includes one or more subsets of common electrodes128B reconfigured to the one or more alternative sense elements128B that are distinct from the sense element128A. The display electrodes214B of the alternative sense elements128B are distinct from the first subset of display electrodes214A, and are not disposed oppose the sense element128B. The gate lines218B and source lines220B corresponding to the other sense elements128may not pass the sense element128A. The display electrodes214B, gate lines218B and source lines220B corresponding to the alternative sense elements128B have substantially smaller parasitic impact on the sense element128A than the display electrodes214A, gate lines218A and source lines220A. Optionally, the electronic system600further includes one or more gate drivers404B and source drivers406B to drive the gate lines218B and source lines220B, respectively. In some implementations, the one or more gate drivers404B are distinct from the gate driver404A, and the one or more source drivers406B are distinct from the source driver406A. Stated another way, in some implementations, a second subset of display electrodes214B is driven in a synchronous manner with the first subset of common electrodes128A. The second subset of display electrodes214B are distinct from the first subset of display electrodes214A, and correspond to a distinct subset of display pixels250B from those corresponding to the first subset of display electrodes214A and the first subset of common electrodes128A.

FIG. 6Billustrates an example display pixel250driven by a display electrode214and a common electrode218at a touch sensing state in accordance with some implementations. At the touch sensing state, the common electrode128is reconfigured as part of a sense element as shown inFIG. 3B, and electrically coupled to a capacitance sense circuit101for touch detection at a location corresponding to the common electrode128. The common electrode128is driven with an integration voltage VYthat varies by a first voltage variation at a predetermined slew rate. In an example, at a display driving state, the common electrode128is driven by a ground voltage, and at the touch sensing state, the common electrode128is driven by the integration voltage VYthat alternates between 3.2V and 1.2V with the first voltage variation of 2V. The display electrode214corresponding to the common electrode128is also driven in a synchronous manner with the common electrode128, thereby reducing an impact of parasitic capacitance associated with the common electrode. Stated another way, the display electrode214is driven with an adjusted display voltage VADPthat varies by the first voltage variation at the predetermined slew rate. While driving the common electrode and the display electrode, a capacitive sense signal associated with the common electrode128is then measured at an output of the capacitance sense circuit101(e.g., at an output of a self capacitance sensing channel506).

In light of the above principle explained with reference to a single display pixel250shown inFIG. 6B, a display pixel array125includes a plurality of display pixels250, a plurality of display electrodes214and a plurality of common electrodes128. At a touch sensing state, a first subset of the plurality of common electrodes128A is electrically coupled to a capacitance sense circuit101for touch detection. The first subset of common electrodes128A is driven with an integration voltage VYthat varies by a first voltage variation at a predetermined slew rate, and a first subset of display electrodes214A corresponding to the first subset of common electrodes128A is driven in a synchronous manner with the first subset of common electrodes, thereby reducing an impact of parasitic capacitance associated with the first subset of common electrodes. Each of the first subset of display electrodes214A is driven with an adjusted display voltage VADPthat varies by the first voltage variation at the predetermined slew rate. While driving the first subset of common electrodes128A and the first subset of display electrodes214A, the processing device110measures a capacitive sense signal associated with the first subset of common electrodes128A at an output of the capacitance sense circuit101. In addition, in some implementations, a second subset of display electrodes214B is driven in a synchronous manner with the first subset of common electrodes128A. The second subset of display electrodes214B are distinct from the first subset of display electrodes214A, and correspond to a distinct subset of display pixels250B from those corresponding to the first subset of display electrodes214A and the first subset of common electrodes128A.

It is noted that each display pixel250A is configured to enable display of a color when a display voltage VDPis applied between the display electrode214A and the common electrode128A corresponding to the respective display pixel250A at a display driving state. While operating at the display driving state, the processing device110generates a touch detection enable signal for initiating a touch sensing state on the processing device, and disables the display driving state at a pixel drive circuit102that is configured to drive the display electrodes214A and the common electrodes128A of the display pixel array128at the display driving state. In some implementations, the processing device110and the display device125alternate between the display driving state and the touch sensing state according to a predetermined duty cycle for the display driving state, such that a contact with or a proximity to a touch sensing surface associated with the display pixel array is detected without interfering with current display operations of the display pixel array125. As an example, the predetermined duty cycle for the display driving state is 80%.

Referring toFIG. 6B, each of the first subset of display electrodes214A is driven by a thin film transistor (TFT) that is coupled to a gate electrode (i.e., a gate line218A) and a source electrode (i.e., a source line220A). To drive the first subset of display electrodes214A, for each of the first subset of display electrodes, driving both the gate electrode and the source electrode in a synchronous manner with the first subset of common electrodes128A. The gate electrode and the source electrode are driven by a gate voltage and a source voltage, respectively, and both the gate and source voltages vary by the first voltage variation at the predetermined slew rate.

In some implementations, the first subset of display electrodes214A includes a first display electrode that is driven by a first TFT coupled to a first gate electrode and a first source electrode. In accordance with the display driving state, the first gate electrode is driven by a first gate voltage (e.g., VGHor VGL). In accordance with the touch sensing state, the first gate electrode is driven in a synchronous manner with the first subset of common electrodes, and the first gate electrode is driven by a second gate voltage that is substantially equal to the first gate voltage superimposed with the integration voltage, and varies by the first voltage variation at the predetermined slew rate. In some implementations, the capacitance sense circuit101includes a gate voltage generator configured to generate the second gate voltage. The gate voltage generator is selected from one of a resistive level shifter, a capacitive level shifter, and a ground kicker driver. The gate voltage generator receives the integration voltage VY, is biased under a TFT turn-on voltage VGHor a TFT turn-off voltage VGL, and generates the second gate voltage that varies by the first variation at the predetermined slew rate. More details on the gate voltage generator are explained below with reference toFIGS. 7A-7B, 8A-8B and 9A-9B.

Referring toFIG. 6B, in some implementations, in accordance with the display driving state, the first gate voltage is substantially equal to a TFT turn-on voltage VGH(e.g., 13V) that turns on the first TFT216for electrically coupling the first source electrode220and the first display electrode214. At the display driving state, both the first source electrode220and the first display electrode214are driven by a display voltage VDP, and at the touch sensing state that is subsequent to the display driving state, the display voltage VDPis adjusted according to the integration voltage VY. The adjusted display voltage VADPis substantially equal to the display voltage VDPsuperimposed with the integration voltage VY, and varies by the first voltage variation at the predetermined slew rate. Alternatively, in some implementations, in accordance with the display driving state, the first gate electrode was driven by a TFT turn-off voltage VGL(e.g., −10V) that turns off the first TFT for electrically decoupling the first source electrode and the first display electrode. At the display driving state, the first source electrode is maintained at the same voltage level (e.g., the ground) of the first subset of common electrodes, and at the touch sensing state that is subsequent to the display driving state, the first source electrode is driven with a source voltage that tracks and is substantially equal to the integration voltage VYdriving the first subset of common electrodes128A.

Referring toFIG. 3A, in some implementations, a second subset of common electrodes128B is driven in a synchronous manner with the first subset of common electrodes128A, and the second subset of common electrodes128B is distinct from the first subset of common electrodes128A. Further, in some implementations, the second subset of common electrodes128B is located in the same row or column of the first subset of common electrodes128A. The second subset of common electrodes128B can be driven with a common electrode voltage that tracks and is substantially equal to the integration voltage driving the first subset of common electrodes128A.

FIGS. 7A and 7Bare block diagrams of gate voltage generators700and750that are constructed based on resistive level shifters and configured to make a TFT turn-on voltage VGHand a TFT turn-off voltage VGLtrack a change of an integration voltage VYin a touch sensing state in accordance with some implementations, respectively.FIGS. 8A and 8Bare block diagrams of gate voltage generators800and850that are constructed based on capacitive level shifters and configured to make a TFT turn-on voltage VGHand a TFT turn-off voltage VGLtrack a change of an integration voltage VYin a touch sensing state in accordance with some implementations, respectively.FIGS. 9A and 9Bare block diagrams of gate voltage generators900and950that are constructed based on groundkicker level shifters and configured to make a TFT turn-on voltage VGHand a TFT turn-off voltage VGLtrack a change of an integration voltage VYin a touch sensing state in accordance with some implementations, respectively. Each of the gate voltage generators700,750,800,850,900and950is coupled to receive the integration voltage VYand biased under one of a TFT turn-on voltage VGHand a TFT turn-off voltage VGL. The integration voltage VYvaries by a first variation at a predetermined slew rate. Each of the gate voltage generators700,750,800,850,900and950generates a respective second gate voltage that varies by the first variation at the predetermined slew rate. In some implementations, the gate voltage generator700,800or900generates a second gate voltage that is substantially equal to the TFT turn-on voltage VGHsuperimposed with the integration voltage VY, and the gate voltage generator750,850or950generates a second gate voltage that is substantially equal to the TFT turn-off voltage VGLsuperimposed with the integration voltage VY. In the touch sensing state, each of the second gate voltages generated by the respective gate voltage generator700,750,800,850,900or950tracks a change of the integration voltage VY, i.e., varies by the first variation at the predetermined slew rate.

Referring toFIG. 7A, in some implementations, the integration voltage VYhas a magnitude in a first range (e.g., 1.2V-3.2V), and is converted to the TFT turn-on voltage VGHhaving a magnitude in a second range (e.g., 8V-10V). In a display driving state enabled by a display enable signal DISP_EN, the output associated with the TFT turn-on voltage VGH(e.g., VGHO) is electrically coupled to a low-end high supply voltage VGHO1that has a voltage level of 8V via a first switch S1. In a touch sensing state enabled by a touch enable signal TOUCH_EN, the output associated with the TFT turn-on voltage VGH(e.g., VGHO) is decoupled from the low-end high supply signal VGHO1. While the integration voltage VYvaries in the first range of 1.2V-3.2V, the output VGHO is electrically coupled to an intermediate signal VGHOSR via a second switch S2, and therefore, configured to track a variation of the integration voltage VY. When the integration voltage VYreaches either rail of the first range (e.g., 1.2V or 3.2V), the second switch S2is turned off to decouple the output VGHO from the intermediate signal VGHOSR, and a third switch S3is turned on to couple the output VGHO to a high-end high supply voltage VGHO2that has an example voltage level of 10V. The low-end and high-end high supply voltages are defined according to the integration voltage VY, and has a difference that is substantially equal to the first voltage variation of the integration voltage VY.

Both operational amplifiers702and704are electrically coupled as unity buffers. In some implementations, while the integration voltage VYvaries in the first range, an output of the amplifier702creates a reference voltage VREFH for another amplifier706. The amplifier706generates an attenuated version of the integration voltage VYto the input to the amplifier706via one or more resistors (e.g., R1), and the attenuated version of the integration voltage VYis level shifted with reference to the high-end high supply voltage VGHO2. The amplifier706converts the attenuated version of the integration voltage VYbased on the reference voltage VREFH created by the amplifier702. As such, the TFT turn-on voltage VGH(i.e., VGHO) is generated to track the variation of the integration voltage VY. Resistors having resistances of R1and R2are used to provide feedback to the amplifier706and enable the first voltage variation of the integration voltage VYon the outputted TFT turn-on voltage VGHO.

Similarly, referring toFIG. 7B, the gate voltage generator750is configured generate the TFT turn-off voltage VGLto track the first voltage variation of the integration voltage VY. Specifically, the gate voltage generator750is configured to generate a reference voltage VREFL between a low-end low supply voltage VGLO1and a high-end low supply voltage VGLO2. The integration voltage VYis attenuated and level shifted into a desired range with the help of a resistor divider made of resistors R3and R4. An operational amplifier708is then used to process the attenuated and level shifted integration voltage VYto generate the TFT turn-off voltage VGLhaving a desired voltage level and variation (i.e., having the first voltage variation).

Referring toFIG. 8A, in some implementations, the integration voltage VYhas the magnitude in the first range (e.g., 1.2V-3.2V), and is converted to the TFT turn-on voltage VGHhaving the magnitude in a second range (e.g., 8V-10V). In a display driving state enabled by a display enable signal DISP_EN, the output associated with the TFT turn-on voltage VGH(e.g., VGHO) is electrically coupled to a low-end high supply voltage VGHO1that has an example voltage level of 8V via a switch S4. In a touch sensing state enabled by a touch enable signal TOUCH_EN, the output associated with the TFT turn-on voltage VGH(e.g., VGHO) is decoupled from the low-end supply signal VGHO1, and coupled to an output of an operational amplifier802via a switch S5. The amplifier802is electrically coupled as a unity gain buffer, and configured to couple to the low-end high supply voltage VGHO1via a switch RST. When the integration voltage VYvaries in the first range, the input to the amplifier802has an example dc voltage level of 8V, and tracks a variation of the integration voltage VYuntil the integration voltage VYslews down and the switch RST is asserted.

Similarly, referring toFIG. 8B, when the integration voltage VYis substantially low (e.g., at a voltage level of 1.2V) in a touch sensing state, the switch RST is turned on to connect an input of an operation amplifier804to the low-end low supply voltage VGLO1. When the integration voltage VYincreases, the switch RST is turned off allowing charge stored in a level-shifting capacitor CLS to couple a variation of the integration voltage VYto the input and output of the amplifier804. Alternatively, in some implementations, a coupling capacitor is applied to couple the TFT turn-on voltage VGH(e.g., VGHO) and the TFT turn-off voltage VGL(e.g., VGLO). In some circumstances, the coupling capacitor is configured to convert the TFT turn-off voltage VGLO generated by the gate voltage generator850to the TFT turn-on voltage VGHO. In some circumstances, the coupling capacitor is configured to convert the TFT turn-on voltage VGHO generated by the gate voltage generator800to the TFT turn-off voltage VGLO.

Referring toFIGS. 9A and 9B, when used as power supplies of gate drivers404, the TFT turn-on voltage VGHO and the TFT turn-off voltage VGLO are controlled to act as a shield during the touch sensing state based on a ground-kicker scheme. In the display driving state, an isolation switch S6is coupled between the TFT turn-on voltage VGHO and the low-end high supply voltage VGHO1, and an isolation switch S7is coupled between the TFT turn-off voltage VGLO and the low-end low supply voltage VGLO1. In the display driving state, the isolation switches S6and S7are turned on, and voltage regulators (e.g., low drop-out circuits902and904) are configured to provide the TFT turn-on or turn-off voltage to power the gate drivers404. Under these circumstances, the integration voltage VYis static and a switch VISO is turned on to create a decoupling path from the TFT turn-on and turn-off voltages to ground.

In some implementations, in the touch sensing state, the isolation switches S6and S7are turned off. The TFT turn-on voltage VGHO, the TFT turn-off voltage VGLO and an intermediate reference voltage VGK are floated. In this situation, when the integration voltage VYvaries, it is level-shifted upwards onto the TFT turn-on voltage VGHO and downwards onto the TFT turn-off voltage VGLO. As such, the TFT turn-on voltage VGHO and the TFT turn-off voltage VGLO are configured to track the first voltage variation of the integration voltage VYwithout interfering with pixel voltages that enable current display operations of the display pixel array125. In some implementations, an amplifier906is configured to drive an output of the gate voltage generator900or950(i.e., a pin VCOM_OPT). The pin VCOM_OPT is coupled to drive an optional common mode shield layer to the same voltage as the integration voltage. Optionally, the optional common mode shield layer is configured to provide one or more alternative sense elements128B.

Further in some implementations, referring toFIG. 9B, the intermediate reference voltage VGK is completely discharged during the display driving state, and needs a duration of time to charge back up to the integration voltage VYwhen a touch sensing mode is enabled. In some implementations, the output of the gate voltage generator950(i.e., the pin VCOM_OPT) is controlled by a force sense enable signal FS_EN.

FIG. 10is a flowchart of a method1000of detecting touch events using a display pixel array125in accordance with some implementations. The method1000is implemented at a processing device110coupled to the display pixel array125. The display pixel array125includes a plurality of display pixels250, a plurality of display electrodes214and a plurality of common electrodes128. Each display pixel250is disposed between a display electrode214and a common electrode128. The processing device110electrically couples (1002) a first subset of the plurality of common electrodes128to a capacitance sense circuit101for touch detection, and drives (1004) the first subset of common electrodes128with an integration voltage VYthat varies by a first voltage variation at a predetermined slew rate. The processing device110also drives (1006) a first subset of display electrodes214corresponding to the first subset of common electrodes128in a synchronous manner with the first subset of common electrodes, thereby reducing an impact of parasitic capacitance associated with the first subset of common electrodes128. Each of the first subset of display electrodes214is driven with an adjusted display voltage VADPthat varies by the first voltage variation at the predetermined slew rate. While driving the first subset of common electrodes and the first subset of display electrodes214, the processing device110measures (1008) a capacitive sense signal associated with the first subset of common electrodes128at an output of the capacitance sense circuit101.

In some implementations, the processing device110drives a second subset of common electrodes in a synchronous manner with the first subset of common electrodes, wherein the second subset of common electrodes is distinct from the first subset of common electrodes. In some implementations, the second subset of common electrodes is located in the same row or column of the first subset of common electrodes. The second subset of common electrodes can be driven with a common electrode voltage that tracks and is substantially equal to the integration voltage driving the first subset of common electrodes. Additionally, in some implementations, while measuring the capacitive sense signal, the processing device110drives a second subset of display electrodes in a synchronous manner with the first subset of common electrodes. The second subset of display electrodes are distinct from the first subset of display electrodes, and correspond to a distinct subset of display pixels from those corresponding to the first subset of display electrodes and the first subset of common electrodes.

In some implementations, each of the first subset of display electrodes is driven by a thin film transistor (TFT) that is coupled to a gate electrode and a source electrode. For each of the first subset of display electrodes, both the gate electrode and the source electrode are driven in a synchronous manner with the first subset of common electrodes. The gate electrode and the source electrode are driven by a gate voltage and a source voltage, respectively, and both the gate and source voltages vary by the first voltage variation at the predetermined slew rate.

In some implementations, each display pixel is configured to enable display of a color when a display voltage is applied between the display electrode and the common electrode corresponding to the respective display pixel in a display driving state. In the display driving state, the processing device generates a touch detection enable signal for initiating a touch sensing state on the processing device, and disables the display driving state at a pixel drive circuit102. The pixel drive circuit102is configured to drive the display electrodes and the common electrodes of the display pixel array in the display driving state. Further, in some implementations, the processing device110alternates between the display driving state and the touch sensing state according to a predetermined duty cycle for the display driving state, thereby detecting a contact with or a proximity to a touch sensing surface associated with the display pixel array without interfering with current display operations of the display pixel array. An example predetermined duty cycle is 80%.

In some implementations, the display pixel array includes a first number of display pixels corresponding to the first number of display electrodes, and is divided into a second number of pixel sets, one of the second number of pixel sets including a first subset of display pixels corresponding to the first subset of display electrodes and the first subset of common electrodes. Further, the processing device110scans each of the second number of pixel sets in the touch sensing state, thereby detecting a contact with or a proximity to a touch sensing surface associated with the display pixel array without interfering with current display operations of the pixel display array. In a specific example, the display pixel array includes an array of 1920×1080 display pixels and is divided into 30×18 pixel sets, and each pixel set includes 64×60 display pixels. The first subset of display electrodes is driven by 64 gate lines and 60 source lines. The first subset of common electrodes includes a third number of common electrodes each of which corresponds to one of the first subset of display electrodes. The first subset of common electrodes includes a single common electrode corresponding to the first subset of display electrodes.

In some implementations, the predetermined slew rate is controlled to be less than a predetermined slew rate threshold such that the capacitive sense signal does not overshoot to cause current saturation in the capacitance sense circuit. For example, the predetermined slew rate of the integration voltage is not greater than 2 V/μsec. Further, in some implementations, in a display driving state, the plurality of common electrodes is electrically coupled to a ground. The first subset of common electrodes is driven between a first reference voltage level (e.g., 1.2V) and a second reference voltage level (e.g., 3.2V) that have a difference equal to the first voltage variation. The first voltage variation of the first subset of common electrodes is greater than 2V.

In some implementations, the first subset of display electrodes includes a first display electrode that is driven by a first TFT coupled to a first gate electrode and a first source electrode. In accordance with a display driving state, the first gate electrode is driven by a first gate voltage, and in accordance with the touch sensing state, the first gate electrode is driven in a synchronous manner with the first subset of common electrodes. The first gate electrode is driven by a second gate voltage that is substantially equal to the first gate voltage superimposed with the integration voltage, and varies by the first voltage variation at the predetermined slew rate. In some implementations, the processing device110generates the second gate voltage at a gate voltage generator. The gate voltage generator is selected from one of a resistive level shifter, a capacitive level shifter, and a ground kicker driver. The gate voltage generator is coupled to receive the integration voltage, biased under one of a TFT turn-on voltage and a TFT turn-off voltage, and configured to generate the second gate voltage that varies by the first variation at the predetermined slew rate.

In some situations, in accordance with the display driving state, the first gate voltage is substantially equal to a TFT turn-on voltage that turns on the first TFT for electrically coupling the first source electrode and the first display electrode. In the display driving state, both the first source electrode and the first display electrode are driven by a display voltage. In the touch sensing state that is subsequent to the display driving state, the display voltage is adjusted according to the integration voltage, and the adjusted display voltage is substantially equal to the display voltage superimposed with the integration voltage, and varies by the first voltage variation at the predetermined slew rate.

Alternatively, in some situations, in accordance with the display driving state, the first gate electrode was driven by a TFT turn-off voltage that turns off the first TFT for electrically decoupling the first source electrode and the first display electrode. Further, in some implementations, the first source electrode is maintained at the same voltage level of the first subset of common electrodes, and in the touch sensing state that is subsequent to the display driving state, the first source electrode is driven with a source voltage that tracks and is substantially equal to the integration voltage driving the first subset of common electrodes.

It should be understood that the particular order in which the operations inFIG. 10have been described is merely exemplary and are not intended to indicate that the described order is the only order in which the operations could be performed. One of ordinary skill in the art would recognize various ways to reorder the operations described herein. It is also noted that more details on the method of detecting touch events using the display pixel array125are explained above with reference toFIGS. 1-9. For brevity, these details are not repeated in the description herein.

It will be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first voltage could be termed a second voltage, and, similarly, a second voltage could be termed a first voltage, without departing from the scope of the various described implementations. The first voltage and the second voltage are both voltage levels, but they are not the same voltage level.

The above description, for purpose of explanation, has been described with reference to specific implementations. However, the illustrative discussions above are not intended to be exhaustive or to limit the scope of the claims to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The implementations were chosen in order to best explain the principles underlying the claims and their practical applications, to thereby enable others skilled in the art to best use the implementations with various modifications as are suited to the particular uses contemplated.