This application claims the benefit of Korean Patent Application No. 10-2010-0031561 filed on Apr. 6, 2010, the subject matter of which is hereby incorporated by reference.
The inventive concept relates to display systems incorporating a touch panel, and more particularly, to methods of compensating for and/or removing various parasitic capacitances associated with a touch panel so as to maximize sensing sensitivity.
Portable electronic devices have become smaller and thinner to meet user demand. Touch screens that do not include mechanical buttons and switches, and that provide improved performance and appealing designs are widely used, for example, in general asynchronous transfer mode (ATM) devices, televisions (TVs), and general home appliances as well as small-sized devices. In particular, cell phones, portable multimedia players (PMPs), personal digital assistants (PDAs), e-books, and the like, have been greatly reduced in overall size for easy carrying. In order to further reduce the size of portable devices, methods of unifying (or incorporating) user input buttons with a screen has been the subject of intense research and development. Within certain methods of unifying input buttons with a screen, touch perception technology for a touch screen capable of detecting a touch input to a touch panel has become increasingly important.
Generally, a touch screen is an input device operates as an interface between an information communication device having various displays and a user. The user directly contacts the touch screen using an input tool, such as a finger, a pen, or the like. Examples of flat panel display devices including a touch screen include liquid crystal display (LCD) devices, field emission display (FED) devices, organic light-emitting diode (OLED) devices, plasma display (PDP) devices, and the like.
The flat panel display devices generally include a plurality of pixels arranged in a matrix so as to display images. For example, LCD devices may include a plurality of scan lines transmitting gate signals and a plurality of data lines transmitting gray scale data. The plurality of pixels are formed at a point in which the plurality of scan lines and the plurality of data lines intersect. Each of the pixels may include a transistor and a capacitor, or only a capacitor.
A touch screen may use one of several different methods of operation, such as a resistive overlay method, a capacitive overlay method, a surface acoustic wave method, an infrared ray method, a surface elastic wave method, an inductive method, and the like.
In the touch screen using the resistive overlay method, a resistive material is coated on a glass or transparent plastic plate, and a polyester film is covered thereon, and insulating rods are installed at regular intervals so that two sides of the polyester film do not contact each other. In this case, resistance and voltage are varied. The position (e.g., a touch point) of a touch input device (e.g., a user's finger) contacting the touch screen is perceived in relation to a degree of voltage variation. The touch screen using the resistive overlay method has superior characteristics, such as the input of cursive script, but has drawbacks such as low transmittance, low durability, and non-detection of multi-contact points.
In the touch screen using the surface acoustic wave method, a transmitter emitting sound waves and a reflector reflecting the sound waves are attached to a glass surface at regular opposing intervals. When a touch input device interrupts a transmission path for sound waves between the transmitter and reflector, a time value is calculated to detect a corresponding touch point.
In the touch screen using the infrared ray method, directivity of infrared rays are used in a manner similar to the sound waves of a surface acoustic wave method. A matrix is formed by disposing in an opposing manner an infrared light-emitting diode (LED) as a spontaneous emission device and a phototransistor. The interruption of light transmitted between the LED and phototransistor by a touch input device is detected within the matrix, thereby allowing the detection of a corresponding touch point.
Contemporary portable electronic devices mainly use the resistive overlay method which is low cost and capable of operating in response to a range of touch devices. However, as research into user interfaces using a multi-touch have been actively pursued, touch screens using the capacitive overlay method by which multi-touch perception may be performed, has come into the spotlight.
Embodiments of the inventive concept provide a touch controller that compensates for and/or removes the effects of certain parasitic capacitances associated with a touch sensing unit. Embodiments of the inventive concept also provide a touch system including this type of touch controller, as well as methods of compensating for parasitic capacitances in touch systems.
In one aspect, the inventive concept provides a touch controller comprising a parasitic capacitance compensation unit. The parasitic capacitance compensation unit receives a common electrode voltage to generate a quantity of charge capable of compensating for a quantity of charge associated with a parasitic capacitance between a sensing channel and a common electrode in a touch panel capable of capacitive sensing of a touch input.
In another aspect, the inventive concept provides a touch display device compensating for parasitic capacitance, the touch display device comprising; a touch panel comprising a plurality of sensing channels that perform a touch screen operation sensing variation in a sensing unit disposed in the plurality of sensing channels, and outputting a variation signal of the sensing unit, and a touch controller comprising a signal conversion unit that receives the variation signal, converts the variation signal into a voltage, and outputs the voltage, wherein the touch controller comprises a parasitic capacitance compensation unit that receives a common electrode voltage to generate a quantity of charge capable of compensating for a quantity of charge associated with a parasitic capacitance between a sensing channel and a common electrode in the touch panel.
In another aspect, the inventive concept comprises a method compensating for parasitic capacitance in a touch system, the method comprising; sensing variation in capacitance for a plurality of sensing units disposed in a plurality of sensing channels in response to a touch input, and outputting a sensing signal corresponding to the variation, receiving, amplifying, and outputting the sensing signal, wherein the receiving, amplifying, and outputting of the sensing signal is performed by a touch controller, and receiving a common electrode voltage to generate a quantity of charge capable of compensating for a quantity of charge associated with a parasitic capacitance between the plurality of sensing channels and a common electrode, wherein the receiving of the common electrode voltage is performed by a parasitic capacitance compensation unit of the touch controller.
Embodiments of the inventive concept will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which:
Reference will now be made in some additional detail to certain embodiments of the inventive concept illustrated in the accompanying drawings. However, the inventive concept may be variously embodied and is not limited to only the illustrated embodiments. Throughout the drawings and written description, like reference numbers and labels are used to denote like or similar elements. In certain drawings, the thickness and relative thicknesses of layers and regions may be exaggerated for clarity.
It will be understood that when an element, such as a layer, a region, or a substrate, is referred to as being “on,” “connected to” or “coupled to” another element, it may be directly on, connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on,” “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present. Like reference numerals refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that, although the terms first, second, third, etc., may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of exemplary embodiments.
Spatially relative terms, such as “above,” “upper,” “beneath,” “below,” “lower,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “above” may encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of exemplary embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may be to include deviations in shapes that result, for example, from manufacturing.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which exemplary embodiments belong. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
(FIG.) 1 illustrates a touch screen panel and a signal processing unit for processing touch signals of a touch screen system 10. Referring to
The touch screen panel 11 includes a plurality of sensing units disposed in a row direction and a plurality of sensing units disposed in a column direction. As illustrated in
The signal processing unit 12 generates touch data by sensing variations in capacitance of the sensing units of the touch screen panel 11. For example, the touch screen system 10 may sense a variation in capacitance between rows and/or columns, thereby detecting a touch input position.
However, there are certain parasitic capacitances that are always present in the sensing units of the touch screen panel 11. The parasitic capacitances may include horizontal capacitance components generated between sensing units, and vertical capacitance components generated between a sensing unit and a display panel. When the cumulative parasitic capacitances are large, the ability of the touch system to faithfully detect a touch input is greatly reduced, since the actual capacitance variation associated with the touch input may be quite small. For example, as a touch input device approaches a predetermined sensing unit, the capacitance of the sensing unit will increase. If the sensing unit has a high parasitic capacitance, corresponding sensing sensitivity will decrease. Also, a variation in an electrode voltage (VCOM) supplied to the top glass of the display panel causes sensing noise during a touch detection operation due to a vertical parasitic capacitance.
Thus, in a touch screen system using a capacitive overlay method, the relative “sizes” (i.e., the associated capacitive variations) for the touch input and the cumulative parasitic capacitance is quite important, and may become a significant system operating characteristic.
Referring to
The touch screen panel 33 may also comprise a plurality of sensing units SU connected to a plurality of sensing lines disposed in a row direction (x-direction) and a plurality of sensing units SU connected to a plurality of sensing lines disposed in a column direction.
The sensing units SU respectively introduce certain parasitic capacitance components associated with their arrangement structure. For example, the sensing units SU introduce a horizontal parasitic capacitance component Cadj generated between the adjacent sensing units SU, and vertical parasitic capacitance components Cbx and Cby generated between the sensing units SU and the display panel 35. When the parasitic capacitances are relatively large, as compared with the capacitance components associated with a touch input close to (or contacting) the sensing units SU, even when capacitances of the sensing units SU vary due to the touch input, sensing sensitivity may be significantly decreased.
Period A shown in
However, when various noise is present, as illustrated in
Various types of noise may be generated in the LCD panel and the OLED panel. For example, when a touch panel is disposed on the OLED panel, a common electrode layer for generating a common voltage Vcom is formed under a touch sense channel. The common electrode layer is maintained at a predetermined constant voltage by using an external switching mode power supply (SMPS). Thus, in the case of the OLED panel, noise accumulated in the touch sense channel is very small.
On the other hand, the LCD panel is driven using two methods, i.e., a method of driving a common electrode with a constant voltage and a method of continuously inversing the common electrode. A voltage width of the common electrode is approximately 5V, and thus it is impossible to disregard accumulation of such voltage switching in a touch sense channel. In both the method of driving a common electrode with a constant voltage and the method of continuously inversing the common electrode, much noise is accumulated whenever data is written in a source channel. This is because a LCD panel is affected by slew as well as by the data written to the source channel.
Further, it is essential to place a so-called “protection layer” under a touch sense channel of a general LCD touch panel in order to remove display noise. A main source of display noise is noise generated when data is written to a common electrode modulation voltage and a source channel as described above. However, the provision of a protection layer mandates the performance of related manufacturing processes and drives up the cost of fabrication. It also adversely increases the thickness of the panel.
Peripheral circuits and an effect caused by a parasitic resistance and capacitor components are not shown in
In Equation 1, the value of a resistor Rf 699 is several mega ohms (MΩ) and is very large. As a result, the ratio of an output voltage Vout 694 to the noise source Vc 691 is shown as the ratio of capacitances of a capacitor Cb 695 and a capacitor Cf 697, as shown in Equation 2:
Generally, in the case of the ON-cell type touch panel, the capacitance of the capacitor Cb 695 is several tens pF or more and thus, a gain caused by noise is 1 or more. In detail, the charge amp 69, which is a differential amplifier, increases noise accumulated in the VCOM panel 53 according to a gain caused by the capacitor Cb 695 and the capacitor Cf 697. This makes the output of the charge amp 69 be out of a dynamic region, and thus touch sensing cannot be substantially performed. In order to perform touch sensing without this problem, a method of reducing display noise is needed.
The term “touch controller” is generally used in relation to certain embodiments of the inventive concept to denote a circuit portion of a touch-DDI or a replacement thereof. The charge amplifier 750 is a signal conversion unit that converts an input touch signal into a voltage signal and amplifies the voltage signal, if necessary, and includes a differential op amplifier.
Referring to
The touch display device of the illustrated embodiment compensates for the parasitic capacitance Cb using the common electrode modulation voltage VCOMIN. That is, when a predetermined sense channel is selected by a touch input, the parasitic capacitance Cb is offset by generating a quantity of charge equal to the parasitic capacitance Cb. The common electrode modulation voltage VCOMIN generated by a common electrode voltage driver 710 is applied to the parasitic capacitance compensator 730 via the touch panel 71. The parasitic capacitance compensator 730 generates a capacitance that offsets the parasitic capacitance Cb, and applies the generated capacitance to the charge amplifier 750 in parallel with the parasitic capacitor Cb. A touch input signal compensated by the charge amplifier 750 may then be output as a display image signal via a filter 760, an analog-digital converter 770, and a digital filter 780.
The parasitic capacitance Cb may be directly sensed in a common electrode layer in
The common electrode voltage driver 710 outputs a common electrode modulation voltage VCOM and inputs the common electrode modulation voltage VCOM into the parasitic capacitance compensator 730 as the common electrode modulation voltage VCOMIN via the parasitic resistor Rs3. The common electrode modulation voltage VCOMIN is output via the parasitic resistor Rs3, and is differentiated from the common electrode modulation voltage VCOM.
Referring to
The parasitic capacitance compensator 730 includes a differential op amp, which has a non-inversion input terminal into which the common electrode modulation voltage VCOMIN and an excitation pulse VIN are input in parallel. An excitation pulse buffer 740 buffers the excitation pulse VIN and applies the excitation pulse VIN to an input terminal of the charge amplifier 750. A source driver 720 applies a source channel voltage in which the parasitic capacitance Cs of several tens nF is accumulated between a source channel and a common electrode panel. Resistors RX, RY, and RB connected to the non-inversion input terminal of the differential op amp may implement the same functions although the resistors RX, RY, and RB are replaced with capacitors C1, C2, and C3.
The parasitic capacitance compensator 730, which is an inversion amplifier, sums the common electrode modulation voltage VCOMIN and the excitation pulse VIN using the resistors RX, RY, and RB and inputs the summed value of the common electrode modulation voltage VCOMIN and the excitation pulse VIN into the non-inversion input terminal thereof. Thus, to sense a touch, the input signal Cx that is applied to the charge amplifier 750 must be input into the non-inversion input terminal of the parasitic capacitance compensator 730. In the same manner as shown in
Consideration into the above-mentioned parasitic resistors is omitted. The common electrode modulation voltage VCOMIN is replaced with a Vc voltage source 799. The total quantity of charge formed in the parasitic capacitance Cb is proportional to a difference between the excitation pulse VIN and a common electrode voltage Vc as shown in Equation 3 below.
ΔQb=Cb(−VIN−VC) (3)
The total quantity of charge formed in the negative capacitance Cq for compensating for parasitic capacitor charges may be expressed using Equation 4 below.
If it is assumed that Cq=2Cb, Equation 5 may be expressed below.
To compensate for the parasitic capacitance Cb satisfying Equation 5, a value of the negative capacitance Cq must be set to be two times greater than that of the parasitic capacitance Cb. This is because an inner amp output of the parasitic capacitor compensator 730 may exceed a power voltage.
For reference, a touch sense operates at an analog power of 5V. A variation of the common electrode modulation voltage VCOMIN is approximately 5V. The resistors RX, RY, and RB determine whether or not the total quantity of charge for the negative capacitance Cq and the parasitic capacitance Cb are the same. In accordance with
A method and device compensating a parasitic capacitance by receiving a common electrode voltage are described above. A touch panel provided with a touch controller for compensating the parasitic capacitance may be an ON-cell type touch panel in which the touch panel and a display panel are unified within a common body. When the touch panel is an overlay type touch panel, the touch controller for compensating the parasitic capacitance according to an embodiment of the inventive concept may be applied. Even when a protection layer conventionally provided to prevent noise is removed, a circuit for compensating the parasitic capacitance according to an embodiment of the inventive concept may advantageously reduce the number of panel production processes and associated fabrication costs for the display device.
Referring to
The touch controller unit 810 may include various elements for performing operations of a touch screen. For example, the touch controller 810 may include a readout circuit 811 for generating touch data, a parasitic capacitance compensation unit 812 for reducing parasitic capacitance components of a sensing unit, an analog to digital converter (ADC) 813 for converting analog data into a digital signal, a power supply voltage generation unit 814 for generating a power supply voltage, a noise compensation block 815 for compensating for display noise, a micro control unit (MCU) 816, a digital finite impulse response (FIR) filter 817, an oscillator 818 for generating a low power oscillation signal, an interface unit 819 for transmitting and receiving signals to and from a host controller 850, a control logic unit 820, and a memory (not shown). Also, the display driver unit 830 may include a source driver 831 for generating gray scale data for display operations, a gray scale voltage generator 832, and a memory 833 for storing display data. The display driver unit 830 may include a timing control logic unit 834 and a power generation unit 835 for generating at least one power supply voltage, if necessary. Also, the display driver unit 830 may include a CPU for controlling the overall operation of the display driver unit 830 and an interface unit 836 for interfacing with the host controller 850.
The display driver unit 830 may receive at least one piece of information from the touch controller unit 810. For example, the display driver unit 830 may receive a status signal, e.g., a sleep status signal, from the touch controller unit 810, as illustrated in
Also, as illustrated in
Referring to
The window glass 910 is manufactured of material such as acryl, tempered glass, or the like, and protects a module from scratches caused by an external shock or a repetitive touch. The touch panel 920 is formed by patterning a transparent electrode, such as an indium tin oxide (ITO), on a glass substrate or a polyethylene terephthalate (PET) film. A touch screen controller 921 may be mounted on a flexible printed circuit board (FPCB) in the form of a chip on board (COB), senses a variation in capacitances from each electrode, extracts touch coordinates, and provides the touch coordinates to a host controller. The display panel 940 is generally formed by bonding two pieces of glass that constitute a top glass and a bottom glass of the display panel 940. Also, a display driver circuit 941 is attached to a display panel for a cell phone in the form of chip on glass (COG).
When the touch controller unit and the display driver unit are integrated in one semiconductor chip 1021, a voltage signal T_sig from the sensing unit SU and image data I_data from an external host are provided to the semiconductor chip 1021. Also, the semiconductor chip 1021 processes the image data I_data, generates gray scale data (not shown) for driving the display device 1000, and provides the gray scale data to the display panel 1020. To this end, the semiconductor chip 1021 may include a pad related to touch data T_data and a pad related to the image data I_data and the gray scale data (not shown). The semiconductor chip 1021 receives the voltage signal T_sig from the sensing unit SU via a conductive line connected to one side of the touch panel.
When the pads are disposed on the semiconductor chip 1021, the pad for receiving the voltage signal T_sig may be disposed adjacent to the conductive line for transferring the voltage signal T_sig (such that noise in the data can be reduced). Although not shown in
When the touch controller unit and the display driver circuit are disposed on separate chips, the touch controller unit may be usually disposed in the form of the COF, and the display driver circuit may be usually disposed in the form of the COG. However, the semiconductor chip in which the touch controller unit and the display driver circuit are installed, as illustrated in
The inventive concept may be implemented by a method, an apparatus, a system or the like. When the inventive concept is implemented by software, elements of the inventive concept are code segments for executing an essential work. Programs or code segments may be stored in a processor readable medium
While the inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the scope of the following claims.
Number | Date | Country | Kind |
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10-2010-0031561 | Apr 2010 | KR | national |