Patent Application
20100289755
1. Field
This disclosure is related to a liquid crystal display with touch-sensing capability.
2. Information
Liquid-crystal displays (LCDs) have been implemented in a variety of display applications, such as computer displays, personal display assistants (PDAs), kiosks, cell phone displays, etc. Touch sensing displays may allow users to select particular regions on a screen using a variety of input devices, simply by touching that area of the display or placing and object such as a finger, stylus, or pen, etc. touching or in close proximity to that region.
One approach to integrate an LCD display with a touch-sensing function includes integrating photo sensor arrays into the thin film transistors (TFT) backplane of an LCD panel. Such photo sensor arrays may sense one or more objects such as a finger on or above the display screen by detecting a shadow of ambient light cast by an object or reflected light from an object, which is illuminated by a controlled light source. This kind of photo sensor array may have different structures and comprise different materials from an LCD TFT backplane. Then, integrating these sensor arrays into TFT backplane typically adds fabrication process steps. This may result in increased manufacturing expense and complexity of the display, as well as reduce the manufacturing yield of the display. Furthermore, such a photo sensor array may reduce an aperture ratio of pixels in an LCD panel, affecting the performance of the display. So far, such approaches are limited for small size LCD display because of fabrication difficulties.
Therefore, it is desired to achieve an LCD display with touch-sensing capability which does not significantly increase the cost and affect the performance of the display.
Non-limiting and non-exhaustive features will be described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures, in which:
In the following detailed description, numerous specific details are set forth to provide a thorough understanding of claimed subject matter. However, it will be understood by those skilled in the art that claimed subject matter may be practiced without these specific details. In other instances, methods, apparatuses or systems that would be known by one of ordinary skill have not been described in detail so as not to obscure claimed subject matter.
Reference throughout this specification to “one embodiment” or “an embodiment” may mean that a particular feature, structure, or characteristic described in connection with a particular embodiment may be included in at least one embodiment of claimed subject matter. Thus, appearances of the phrase “in one embodiment” or “an embodiment” in various places throughout this specification are not necessarily intended to refer to the same embodiment or to any one particular embodiment described. Furthermore, it is to be understood that particular features, structures, or characteristics described may be combined in various ways in one or more embodiments. In general, of course, these and other issues may vary with the particular context of usage. Therefore, the particular context of the description or the usage of these terms may provide helpful guidance regarding inferences to be drawn for that context.
To provide an LCD display with touch-sensing capabilities and with out significantly increasing the cost and complexity of the LCD display, according to particular embodiments, a backlight unit of an LCD display may include localized light detectors or sensors which are adapted to respond to changes in incident light caused by a physical touching. Signals received from the light detectors may be processed to estimate a location of the physical touching on a surface of an LCD panel. By disposing localized light detectors on a backlight unit, the complexity and expense associated with integrating photo sensor arrays into TFT's of a backplane of an LCD panel may be avoided.
Optical light-guide 101 may comprise a uniform transparent plate, such as acrylic plate or Plexiglas®, having a refractive index larger than 1.0. The thickness of optical light-guide 101 may be in the range of 4.0 mm to 20.0 mm for example. It should be understood, however, that different thicknesses and materials may be used. The touch-sensing light source 104 may emit non-visible light, such as near infrared light with a wavelength range of 750 nm to 1000 nm, into optical light-guide 101 through the edge surface of light-guide 101. It should be understood, however, that light of different wavelength may be used. It is well-known that, total internal reflection may occur in a medium with a refractive index n1 at a boundary with another medium of lower refractive index n2 if the incident angle at the boundary larger than a critical angle θc. Where the critical angle θc is calculated with Snell's law equation: n1*sin (θc)=n2. For example, in this case, if the light-guide 101 is acrylic plate, its refractive index may be about n1=1.5, and another material is air with a refractive index of about n2=1.0, then the critical angle may be determined to be about 41.8°. Then at the boundary of light-guide 101 and air, if the light incident angles are larger than 41.8° the light may be totally reflected and trapped within light-guide 101 bouncing between its upper and lower surface. Light trapped within light-guide 101 is shown as touch-sensing light 110. Upon a physical touch from an object such as a finger in contact with a surface of optical light-guide 101, internal refraction may be interrupted as light, otherwise trapped in optical light guide 101, escapes from the light-guide 101 in response to the physical touch. Such escaped light is denoted as 109 in
In order to create a more uniform response to different material and size touch objects, a pressure transfer film can be placed above optical light-guide 101. As shown in
According to an embodiment, touch-sensing light sources 104 may comprise infrared light-emitting diodes (LEDs) with peak emission wavelength larger than 850 nm while less than 1000 nm. LEDs with high power emission at these wavelength ranges can be achieved without interference with an image displayed on LCD panel 102. Touch-sensing light sources 104 may be fixed to printed circuit board (PCB, not shown) by soldering and positioned at edges of the light-guide 101 as shown. A touch-sensing light source driving circuit 204 may control emission light intensity of light sources 104 in accordance with signals and/or instruction from touch-sensing LCD control unit 220. In order to efficiently couple emitted light into the light-guide 101, a touch-sensing light source 104 may have an angle of half intensity less than 40 degrees if the light-guide 101 is acrylic plate or Plexiglas, for example. In this context, an angle of half intensity is an angle at which light intensity from a light source decreases to half of its maximum emission intensity. Here, a touch-sensing light source 104 may be positioned at a certain angle relative to the edge of the light-guide plate 101.
In a particular implementation, LCD panel 102 may comprise a multilayer structure shown as
Although light transmission through a pixel can be changed by tuning a voltage applied to an associated pixel electrode 409, this tunable transmission through an LCD pixel may not be suitable for infrared light with wavelength larger than 850 mn, because a polarizer may not be able to polarize electromagnetic waves larger than 850 nm. Additionally, color filters may lose their function for infrared light (e.g., infrared light can pass the color filters). It has been determined that, about 70% of infrared light with peak emission at 880 nm may pass through an LCD panel while a dark image is displayed. Here, escaped light 109 may pass through LCD panel 102 to reach backlight unit 103.
Backlight unit 103 may include backlight light source 105 to transmit visible light to illuminate an image on LCD panel 102 so that the image displayed on LCD panel 102 can be seen by the user. Backlight light source 105 can be red, green and blue LEDs, white LEDs, or fluorescent lamps, just to name a few examples. Backlight unit 103 may comprise a backlight panel including a substrate having one or more light sources attached thereto. For example, such a backlight panel may include visible light sources soldered to a PCB (not shown), and the emission light intensity may be controlled by backlight light source driving circuit 205 in accordance with signals and/or instructions from touch-sensing LCD control unit 220.
Backlight unit 103 further includes photo detectors 106 for detecting light escaped from light-guide 101. Detectors 106 may include photodiodes, phototransistors, CCD or CMOS image sensors, just to name a few examples. Detectors 106 may be further capped with filter films matched to an output of touch-sensing light source 104. Detectors 106 may be soldered to a PCB (not shown) of backlight unit 103 and can be the same PCB to which visible light sources 105 are attached.
Output signals from light sensing detectors 106 may be in the form of analog signals, which may be converted to digital signals by an analog-to-digital conversion (ADC) device (not shown) which is integrated in sensing signal detecting circuit 206. These digital signals may be further analyzed by a digital signal processing circuit (not shown) which is also integrated in signal detecting circuit 206 to determine a touch object coordinate. However, other combinations of programmed processors, software and/or hardware may be used to process the digital signals. Flow chart shown in
Because the spectrum of ambient light may at least partially overlap with the spectrum of touch-sensing light, and since ambient light may vary in different environments and operating conditions, etc., ambient light may add background noise giving rise to false detections. In order to reduce such noise effects caused by ambient light, a detection frame may be divided into two periods. Here, touch-sensing light source 104 may be turned on throughout a first period and turned off throughout a second period. The digital signal processing circuit of signal sensing detecting circuit 206 may receive signals detected in the first period of the detection frame at block 601. Values associated with these signals may then be stored in a memory digital accessible by signal processing circuitry. Then, the signal processing circuitry may receive temporal subtraction signals detected in the second period of the detection frame at block 602. Block 603 may then subtract values of signals detected in the second period from values of signals detected in the second period. With the above processes, the background ambient light noise may be reduced or eliminated.
Signals extracted from subtraction at block 603 may be processed to estimate a location of a physical touching on LCD panel 102. Calibration values for light sensing detectors 106 may be based on a level of white noise and a non-uniform sensitivity for individual detectors 106, which were previously stored in a memory of digital signal processing circuitry, for example. These calibration values may be obtained by comparing signal values from detectors 106 measured in a totally dark ambient and in a uniform light illumination ambient. Values extracted from the subtraction may be mapped to and compared with calibration values to correct non-uniform response characteristics of detectors 106, such as sensitivity and white noise, at block 604. Values extracted at block 604 may be further compared with a threshold value stored previously in the digital signal processing circuit to extract the signals having values greater than the threshold value at block 605.
According to an embodiment, an intensity of a signal received at a light sensing detector 106 responsive to a physical touching on a surface of LCD panel 102 may vary as a function of a distance between the light sensing detector 106 and location of the physical touching on the surface of LCD panel 102. As such, touch sensing light detectors 106, which are laterally closer to physical touch object 107, may be expected to receive a stronger intensity light signal (e.g., light 109 escaping from optical light-guide 101) than those touch-sensing light detectors 106 at greater lateral distance away from the physical touch object 107. Accordingly, touch sensing light detectors 106 are used to detect a change in touch-sensing light (e.g., from escaping light 109) incident at a backlight panel in response to a physical touching on a surface of LCD panel 102. It should be understood, however, that this is merely one type of change in touch-sensing light (incident at a backlight panel) that may be detected according to particular embodiments, and that other types of changes such incident touch-sensing light may be detected without deviating from claimed subject matter. If light sensing detectors 106 have an arrangement as shown in
Unlike the photo detectors integrated in an LCD panel, where a pitch between two adjacent detectors may be only several hundred micrometers, a physical touching may be accurately located by signal values in a region. For the case of integrating detectors 106 in a backlight unit 103, as mentioned previously, in order to use fewer detectors (e.g., based on a cost consideration), a pitch between two detectors may be about ten millimeters, or even larger. In one particular implementation, to accurately estimate a location of a physical touching on LCD panel 102, an intensity of signals received by four surrounding detectors (e.g., bounding an area containing the location) may be applied to a light intensity distribution profile. Such a light intensity distribution profile may, for example, characterize a lateral distance between a location of physical touching and location of a detector 106 capturing a signal in question. In an alternative implementation, such an estimated location of a physical touching in an area bounded by detectors 106 may be selected from values in a look up table based, at least in part, on signal intensity values obtained from the detectors 106.
As an example, the look-up table can be configured by the following described method. Detectors in an array on the backlight plate can be divided into many blocks, each block consists of four detectors and the area surrounded by the four detectors (106.1, 106.2, 106.3 and 106.4), as shown in
By comparing the extracted signals in step 606 and map their compared result with the IDs of touch position stored in look-up table, the touch position then can be identified (step 607). An identified touch position may then be sent to touch-sensing LCD control unit 220 at block 608. Control unit 220 may give a response signal and/or instruction according to the estimated location of the physical touching to update an image displayed on the LCD panel, for example.
An implementation of the touch-sensing LCD 100 can be described referring to the flowchart of
The methodologies described herein may be implemented by various means depending upon applications according to particular features and/or examples. For example, such methodologies may be implemented in hardware, firmware, software, and/or combinations thereof. In a hardware implementation, for example, a processing unit may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, other devices units designed to perform the functions described herein, and/or combinations thereof.
Within this disclosure, the terms “one”, “one or more”, “at least one”, are considered to be substantially equivalent. If the disclosure describes one, for example, it would be considered inherent to apply similar teaching or concept to more than one.
While there has been illustrated and described what are presently considered to be example embodiments, it will be understood by those skilled in the art that various other modifications may be made, and equivalents may be substituted, without departing from claimed subject matter. Additionally, many modifications may be made to adapt a particular situation to the teachings of claimed subject matter without departing from the central concept described herein. Therefore, it is intended that claimed subject matter not be limited to the particular embodiments disclosed, but that such claimed subject matter may also include all embodiments falling within the scope of the appended claims, and equivalents thereof.
