Optical shuttered touchscreen and method therefor

A touchscreen display system (418) is provided which includes a touchscreen (420), a touchscreen input detector (422), a capacitive sensor driver (423), and a display driver (424). The touchscreen input detector (422) is coupled to a first layer (504) of the touchscreen (420) and determines a touchscreen (420) input in response to sensing tactile inputs during a sensing time interval (610). The display driver (424) is coupled to a second layer (506) of the touchscreen (420) and provides a drive voltage (606, 608) at a first voltage level to the plurality of optical shutter segments (508) during a first portion (620) of the sensing time interval (610) and maintains the drive voltage (606, 608) at substantially zero volts during a second portion (622) of the sensing time interval (610), the second portion (622) being greater than half of the sensing time interval (610).

FIELD OF THE DISCLOSURE

The present invention generally relates to touchscreens and display drivers, and more particularly relates to optical shuttered touchscreens and their operation.

BACKGROUND OF THE DISCLOSURE

In many portable electronic devices, such as mobile communication devices, displays present information to a user. For example, polymer-dispersed liquid crystal (PDLC) display technology can display video and text information and, utilizing twisted nematic (TN) polymer segments, can also provide an optical shutter operation. Optical shuttering is sometimes used to present information to a user and is particularly adapted to touchscreen operation where the information represents control icons (e.g., forward, reverse, pause, and play control symbols for video operation). TN/PDLC displays typically include an electroluminescent (EL) backlight for operation in both high and low ambient light conditions.

While providing modular optical shuttering operation by selectively driving the TN segment electrodes, operation of the EL backlight and selective driving of the TN segment electrodes disadvantageously creates an electrically noisy environment for sensing touchscreen inputs, thereby hampering touchscreen operation. Conventionally, an indium-tin oxide (ITO) ground plane is provided below the TN segment electrodes and above the EL backlight to control the electrical noise and improve the touchscreen operation. However, addition of the ITO ground plane increases the thickness of the display and the cost and complexity of the display manufacture. In addition, the ITO ground plane connection is susceptible to failure, thereby reducing display yield and/or increasing field failure defects. Also, the ITO ground plane is not fully transmissive, thereby reducing the brightness and effectiveness of the EL backlight.

Thus, there is an opportunity to eliminate an ITO ground plane from a TN/PDLC touchscreen. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

DETAILED DESCRIPTION

A method determines touchscreen inputs in response to sensing tactile inputs on a face of the touchscreen while optically shuttering the touchscreen. The method includes the steps of charging a capacitive sensor layer of the touchscreen while providing a drive voltage at a first voltage level to a plurality of optical shutter segments in the display during a first time interval and sensing a charge fluctuation on the capacitive sensor layer while maintaining the drive voltage at substantially zero volts during a second time interval. The first and second time intervals combine to form a sensing time interval for sensing touchscreen inputs, and the second time interval is greater than half of the complete sensing time interval.

A touchscreen system includes a display, a touchscreen input detector, and a display driver. The display includes a first layer for sensing tactile inputs on a face of the display and a second layer having a plurality of optical shutter segments. The touchscreen input detector is coupled to the first layer of the display and determines a touchscreen input in response to capacitively sensing the tactile inputs for a sensing time interval. And the display driver is coupled to the second layer of the display and provides a drive voltage at a first voltage level to the plurality of optical shutter segments during a first portion of the sensing time interval and maintains the drive voltage at a second voltage level during a second portion of the sensing time interval. The second voltage level is substantially zero volts, and the first portion appended by the second portion is substantially the sensing time interval. In addition, the second portion is greater than half of the sensing time interval.

FIG. 1shows a mobile communication device100implementing a touchscreen with aligned optical shutter and backlight cells in accordance with an embodiment of the present invention. While the electronic device shown is a mobile communication device100, such as a flip-style cellular telephone, the touchscreen with aligned optical shutter and backlight cells can also be implemented in cellular telephones with other housing styles, personal digital assistants, television remote controls, video cassette players, household appliances, automobile dashboards, billboards, point-of-sale displays, landline telephones, and other electronic devices.

The mobile communication device100has a first housing102and a second housing104movably connected by a hinge106. The first housing102and the second housing104pivot between an open position and a closed position. An antenna108transmits and receives radio frequency (RF) signals for communicating with a complementary communication device such as a cellular base station. A display110positioned on the first housing102can be used for functions such as displaying names, telephone numbers, transmitted and received information, user interface commands, scrolled menus, and other information. A microphone112receives sound for transmission, and an audio speaker114transmits audio signals to a user.

A keyless input device150is carried by the second housing104. The keyless input device150is implemented as a touchscreen with a display. A main image151represents a standard, twelve-key telephone keypad. Along the bottom of the keyless input device150, images152,153,154,156represent an on/off button, a function button, a handwriting recognition mode button, and a telephone mode button. Along the top of the keyless input device150, images157,158,159represent a “clear” button, a phonebook mode button, and an “OK” button. Additional or different images, buttons or icons representing modes, and command buttons can be implemented using the keyless input device. Each image151,152,153,154,156,157,158,159is a direct driven pixel, and this keyless input device uses a display with aligned optical shutter and backlight cells to selectively reveal one or more images and provide contrast for the revealed images in both low-light and bright-light conditions.

Referring toFIG. 2, a cross section of a conventional touchscreen200is depicted with aligned optical shutter and backlight cells and is usable for the keyless input device150with the cross-section being a portion of a view taken along line2-2ofFIG. 1. The conventional display200is a stack with a user-viewable and user-accessible face201and multiple layers below the face201, including a graphic coverlay layer202and a capacitive sensor layer204with an indium-tin oxide (ITO) electrode205. The graphic coverlay202provides an upper layer viewable to and touchable by a user and may provide some glare reduction. The capacitive sensor layer204senses touchscreen inputs on the graphic coverlay layer202of the display200. Beneath the capacitive sensor layer204is a twisted nematic (TN) stack layer206including a TN backplane electrode210and TN segment electrodes208between two substrates212,214for providing the optical shutter operation of the display200. The TN backplane electrode210and TN segment electrodes208are formed of indium-tin oxide (ITO) material to provide both transparency and electrical conductivity for operation of the TN stack. Also, while the TN backplane electrode210is depicted above the TN segment electrodes208, a TN stack layer206having the TN backplane electrode210below the TN segment electrodes208would function similarly.

The TN stack layer206utilizes, for example, twisted nematic (TN) liquid crystal (TNLC) display technology employing TN optical shutter material in an optical shutter layer213and the TN segment electrodes208to provide optical shutter operation. While TNLC technology is described herein for the optical shuttering operation, the optical shutter layer213, sandwiched between the TN backplane electrodes210and the TN polymer segment electrodes208, can alternatively be made using nematic liquid crystal technology (such as twisted nematic or super twisted nematic liquid crystals), polymer-dispersed liquid crystal technology (PDLC), ferro-electric liquid crystal technology, electrically-controlled birefringent technology, optically-compensated bend mode technology, guest-host technology, and other types of light modulating techniques which use optical shutter material213such as TN polymer material, PDLC material, cholesteric material, or electro-optical material. The electric field created by the electrodes208,210alter the light transmission properties of the TNLC optical shutter material213, and the pattern of the TN segment electrode layer208defines pixels of the display. These pixels lay over the images151,152,153,154,156,157,158,159shown inFIG. 1. In the absence of the electric field, the liquid crystal material and dichroic dye in the TNLC material213are randomly aligned and absorb most incident light. In the presence of the electric field, the liquid crystal material and dichroic dye align in the direction of the applied field and transmit substantial amounts of incident light. In this manner, a pixel of the TNLC cell can be switched from a relatively non-transparent state to a relatively transparent state. Each pixel can be independently controlled to be closed-shuttered or open-shuttered, depending on the application of an electric field, and the pixels act as “windows” with optical shutters that can be opened or closed, to reveal images underneath (e.g. images151,152,153,154,156,157,158,159).

Beneath the TN stack layer206is an electroluminescent (EL) stack layer216separated from the TN stack layer206by an ITO ground layer218. The EL stack layer216includes a backplane and electrodes which provide backlight for operation of the display200in both ambient light and low light conditions by alternately applying a high voltage level, such as one hundred volts, to the backplane and electrode. The ITO ground layer218is coupled to ground and provides an ITO ground plane218for reducing the effect on the capacitive sensor layer204of any electrical noise generated by the operation of the EL stack layer216or other lower layers within the display200. Beneath the EL stack layer216is a base layer220which may include one or more layers such as a force sensing switch layer and/or a flex base layer. The various layers202,204,206,218,216and220are adhered together by adhesive layers applied therebetween.

Conventional operation of the display200is illustrated inFIG. 3, wherein the charge302from the capacitive sensor layer204, the voltage304of the TN backplane210and the voltages306,308of first and second portions of the TN segment electrodes208are depicted. To perform capacitive sensing during a period310, a charging voltage is provided to the ITO electrode205of the capacitive sensor layer204for a first portion322of the period310. After the charging voltage is removed from the electrode205, the charge302has two different decay profiles312,314depending on whether a user's touch is detected on the display200. In an electrically noisy environment, the signal-to-noise ratio (SNR) of the capacitive sensing (i.e., of the voltage of the detectable charge), where the charge is the multiple of the capacitance (determined from a distance of user's finger from the face201) times the voltage thereof, is small, thereby complicating detection of touchscreen inputs. The ITO ground plane layer218provides some isolation between the high voltage EL backlight layer216and the low voltage TN stack layer206, thereby increasing the SNR of the capacitive sensing.

During the same time period310, the voltages304,306,308supplied to the TN backplane210and the TN segment electrodes208are switched between a positive voltage, typically about five volts, and zero volts. The voltage306of the portion of the TN segment electrodes208that are turned “on” to render corresponding portions of the display200over such portion of the TN segment electrodes208relatively transparent are switched opposite to the voltage304of the TN backplane210(i.e., when the voltage304of the TN backplane is high, the voltage306of the “on” portion of the TN segment electrodes208is low). Conversely, the voltage308of the portion of the TN segment electrodes208that are turned “off” optically shutter corresponding portions of the display200over such portion of the TN segment electrodes208because their voltage is switched in the same manner as the voltage304of the TN backplane210. It can be seen fromFIG. 3that during period310, the voltages306,308supplied to the TN segment electrodes208and the TN backplane210are high approximately fifty per cent of the time period310.

FIG. 4depicts a block diagram of an electronic device400, such as the mobile communication device100ofFIG. 1, in accordance with an embodiment of the present invention. Although the electronic device400is depicted as a cellular telephone, the electronic device can be implemented as any wired or wireless electronic device utilizing a touchscreen display user interface such as a pager, a computer, a personal digital assistant, an equipment control device, or the like.

In this embodiment, the electronic device400includes the antenna108for receiving and transmitting radio frequency (RF) signals. The antenna108is coupled to transceiver circuitry404in a manner familiar to those skilled in the art. The transceiver circuitry404includes receiver circuitry and transmitter circuitry. The receiver circuitry demodulates and decodes received RF signals to derive information therefrom and is coupled to a controller406and provides the decoded information to the controller406for utilization by the controller406in accordance with the function(s) of the electronic device400. The controller406also provides information to the transmitter circuitry of the transceiver circuitry404for encoding and modulating the information into RF signals for transmission from the antenna108.

As is well-known in the art, the controller406is coupled to a memory408which stores data and operational information for use by the controller406to perform the functions of the electronic device400. The controller406is also coupled to conventional user interface devices such as any or all of: a microphone112, a speaker114, a display110, and/or functional key inputs416.

In accordance with an embodiment of the present invention, the electronic device400also includes a touchscreen display system418including a touchscreen420, a touchscreen input detector422, a capacitive sensor driver423, a TN stack driver424, and a timing device426. The touchscreen420enables the keyless input device150(FIG. 1). The controller406provides control signals to the capacitive sensor driver423which, in response to the control signals, provides charging voltages to a capacitive sensor layer of the touchscreen420for operation. In addition, the controller406provides control signals to the TN stack driver424which, in response to the control signals, provides drive voltages to a TN stack layer of the touchscreen420for optical shuttering operation. The controller406provides additional signals to the touchscreen420for other functions such as controlling voltages for operation of a backlight layer of the touchscreen420. The touchscreen input detector422is coupled to the touchscreen420for detecting the charge from the capacitive sensing layer thereof and translating the detected charges into user input signals for providing to the controller406. The timing device426is coupled to the touchscreen input detector422, the capacitive sensor driver423, and the TN stack display driver424for control of their operation in accordance with an embodiment of the present invention.

The timing device426, the capacitive sensor driver423, and the TN stack driver424are typically implemented as separate elements. In accordance with one aspect of the present invention, however, the synergy of the three elements and the ability to coordinate the timing of control signals provided to the capacitive sensing layer504, the TN backplane510, and the TN segment electrodes508(as will be described in accordance withFIGS. 5 and 6) can be utilized to incorporate all three elements into a single semiconductor device for advantageously simplifying manufacture of the touchscreen display system418and/or of the electronic device400. Alternatively, as depicted inFIG. 4, the timing device426, the touchscreen input detector422, the capacitive sensor driver423, and the TN stack driver424can be implemented as a single semiconductor device428. The synergy of these four elements and the ability to coordinate the detection of charge within the capacitive sensing layer504with the timing of control signals provided to the capacitive sensing layer504, the TN backplane510, and the TN segment electrodes508and the detection of charge within the capacitive sensing layer504further simplifies manufacture of the touchscreen display system418and/or of the electronic device400.

Referring toFIG. 5, a cross-sectional view of the touchscreen420in accordance with an embodiment of the present invention includes a graphic coverlay layer502, a capacitive sensor layer504with ITO electrode505, a TN stack layer506, an electroluminescent (EL) stack layer516and a base layer520(which may include one or more layers such as a force sensing switch layer and/or a flex base layer) adhered together by adhesive layers applied therebetween. The TN stack layer506includes two substrates512,514supporting a TN backplane electrode510and TN segment electrodes508with TN shutter material513sandwiched therebetween. In accordance with an embodiment of the present invention, the TN shutter material513is formulated to have a fast response (or rise) time and a slow decay time such that, in response to application of an electric field to the TN shutter material513, liquid crystal material and dichroic dye in the TN shutter material513quickly aligns in the direction of the applied field to transmit substantial amounts of incident light while, in response to removal of the electric field, the TN shutter material213slowly decays to its noncharged state where the liquid crystal material and the dichroic dye in the TN shutter material513randomly align, thereby absorbing most incident light.

Operation of the touchscreen420in accordance with an embodiment of the present invention allows removal of the ITO ground plane layer218shown inFIG. 2, thereby reducing both the thickness of the touchscreen420and the cost of its manufacture (e.g., one less process step as well as fewer layers of material and adhesive). In addition, since the ITO layer218is not fully light-transmissive (i.e., not fully transparent), removal of the ITO layer218allows more light from the electroluminescent layer516to pass through the optical shuttering TN stack layer506and thence to the user, providing sharper and better-defined images151,152,153,154,156,157,158,159(FIG. 1).

FIG. 6illustrates the enhanced operation of the touchscreen420in accordance with an embodiment of the present invention. The charge602from the ITO electrode505of the capacitive sensor layer504, the voltage604of the TN backplane510, and the voltages606,608of first and second portions of the TN segment electrodes508are depicted. Capacitive sensing during a sensing time interval610is performed similarly to conventional operation as described above in accordance withFIG. 3. Thus, a charging voltage is provided to the ITO electrode505of the capacitive sensor layer504for a charging portion612of the time interval610. After the charging voltage is removed from the electrode505, the charge602has two different decay profiles614,616during a decay period618of the time interval610depending on whether a user touches the touchscreen420.

During the sensing time interval610, the voltages604,606,608supplied to the TN backplane510and the TN segment electrodes508are switched between a positive voltage, typically about five volts, and zero volts. In accordance with an embodiment of the present invention, the drive voltages606,608are provided at a first voltage level of approximately five volts to a predetermined portion of the TN segment electrodes508and a remaining portion of the TN segment electrodes508, respectively, during a first portion620of the sensing time interval610and maintained at substantially zero volts during a second portion622of the sensing time interval. Provision of the TN shutter material513in accordance with an embodiment of the present invention, whereby the TN shutter material513has a quick response time and a slow decay time, advantageously allows for the second portion622to be greater than half of the sensing time interval610and can be about eighty per cent of the sensing time interval610.

To provide optical shuttering, the drive voltages604,608are provided at approximately five volts to the TN backplane510and the predetermined portion of the TN segment electrodes508for a first subportion624of the first portion620of the sensing time interval610while the voltage606of the remaining portion of the TN segment electrodes508is maintained at approximately zero volts. During a second subportion626, the drive voltage606of the remaining portion of the TN segment electrodes508is provided at approximately five volts, while the voltages604,608of the TN backplane510and the predetermined portion of the TN segment electrodes508is switched to approximately zero volts. In this manner, the predetermined portion of the TN segment electrodes508are “off”610and the remaining portion of the TN segment electrodes508are “on” during the sensing time interval610. A simple variation is to predetermine the “on” TN segment electrodes and reverse the timing of the applied voltages.

Operation in accordance with an embodiment allows optical shuttering operation with drive voltages604,606,608provided only during the first portion612of the sensing time interval610while a drive voltage602is also being provided to the capacitive sensor layer504simultaneously during a charging portion612of the sensing time interval610. Thus, the semiconductor device428can be utilized for providing the voltages to generate the charge602as well as the voltages604,606,608. In addition, the drive voltages604,606,608provided to the TN backplane510and the TN segment electrodes508are maintained near zero volts throughout the second portion622of the sensing time interval610which coincides with the decay period618thereby decreasing electrical noise during the decay period618and increasing the SNR of the measured charge602during the crucial time that the decay curve profiles614or616are being detected by the touchscreen input detector422. The timing device426is configured to provide timing for the TN stack driver424to provide the drive voltages604,606,608and for the capacitive sensor driver423to provide the charge to the ITO electrode505of the capacitive sensor layer504in accordance with an embodiment of the present invention as well as providing timing for the touchscreen input detector422to detect the decay curve profile614,616during the decay period618.