KR101712198B1 - Display device having touch sensor - Google Patents

Abstract

The present invention relates to a touch sensor built-in display device, wherein the touch sensor of the touch sensor built-in display device includes a switch TFT. The switch TFT includes a gate connected to a node between the liquid crystal cell and the capacitor, a drain supplied with an AC drive voltage swinging between a high potential voltage and a low potential voltage, and a source connected to an input terminal of the touch sensor output processing circuit . The touch recognition unit detects the touch input in each of the high-potential voltage section and the low-potential voltage section of the AC drive voltage.

Description

{DISPLAY DEVICE HAVING TOUCH SENSOR}

The present invention relates to a touch sensor built-in display device.

BACKGROUND ART [0002] Liquid crystal display devices are becoming increasingly widespread due to features such as light weight, thinness, and low power consumption driving. This liquid crystal display device is used as a portable computer such as a notebook PC, an office automation device, an audio / video device, and an indoor / outdoor advertisement display device. The transmissive liquid crystal display device which occupies most of the liquid crystal display device controls an electric field applied to the liquid crystal layer to adjust the light incident from the backlight unit according to the data voltage to display an image.

In order to improve the convenience of the user interface, a technique of integrating a touch panel on a liquid crystal display panel has attracted attention. Recently, a technology (touch sensor with a built-in pixel array) in which a touch sensor is incorporated in a pixel array of a liquid crystal display panel without bonding a separate touch panel on a liquid crystal display panel has been developed. The pixel array built-in touch sensor includes a capacitor for sampling a voltage that changes depending on whether the touch screen is touched, and a switch element for supplying a touch voltage charged in the capacitor to an external touch sensor output processing circuit. The switch element may be implemented as a thin film transistor (hereinafter referred to as "TFT"). The switch TFT receives a touch voltage that changes depending on whether it is touched, as a gate voltage, and adjusts the current supplied to the touch sensor output processing circuit.

A DC driving voltage is supplied to a drain terminal or a source terminal of the switch TFT. This direct current driving voltage causes a change in the threshold voltage of the switch TFT. Therefore, in order to secure the long-term reliability of the touch sensor, it is required to prevent a change in the threshold voltage of the switch TFT.

The present invention provides a touch sensor built-in display device capable of preventing a change in threshold voltage of a switch TFT.

A display device with a built-in touch sensor of the present invention includes: a display panel including a first liquid crystal cell for displaying video data and a touch sensor for sensing a touch input using a second liquid crystal cell; A data driving circuit for supplying a data voltage of the video data to the data lines of the display panel; A gate driving circuit for sequentially supplying gate pulses to the gate lines of the display panel; A touch sensor output processing circuit for sampling the touch voltage from the output of the touch sensor; And a touch recognition unit that receives an output signal of the touch sensor output processing circuit and detects a touch input. The touch sensor includes a capacitor connected to the second liquid crystal cell, and a switch TFT. The switch TFT has a gate connected to a node between the second liquid crystal cell and the capacitor, a drain supplied with an AC drive voltage swinging between a high potential voltage and a low potential voltage, and a drain connected to an input terminal of the touch sensor output processing circuit Lt; / RTI > source. The touch recognition unit detects the touch input in each of a high potential voltage interval and a low potential voltage interval of the AC driving voltage.

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The present invention drives a switch TFT of a touch sensor built in a pixel array of a display device with an AC drive voltage. As a result, the present invention can prevent the threshold voltage change of the switch TFT.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

The names of components used in the following description are selected in consideration of ease of specification, and may be different from actual product names.

1 to 3, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 100, a timing controller 101, a data driver 102, a gate driver 103, a touch sensor output processor 108, and a touch recognition unit 109. [

In the liquid crystal display panel 100, a liquid crystal layer is formed between two substrates. A TFT array including touch sensors and pixels is formed on the lower substrate GLS2. And the lower polarizer POL2 is bonded to the lower surface of the lower substrate GLS2. A color filter array including a color filter CF and a black matrix is formed on the upper substrate GLS1, and an upper plate common electrode is formed on the color filter array. The upper polarizer POL is bonded to the upper surface of the upper substrate GLS1.

Data lines 105, gate lines 106, lead-out lines 107, RL, pixels 10, and touch sensors 20 are provided on the lower substrate of the liquid crystal display panel 100 .

Each of the pixels 10 includes a pixel TFT Tpx, a first liquid crystal cell Clc1, and a first storage capacitor Cst1. The pixel TFT Tpx is turned on in accordance with the gate pulse from the gate line 106 to supply the video data voltage from the data line 105 to the pixel electrode of the first liquid crystal cell Clc1. The gate electrode of the pixel TFT (Tpx) is connected to the n-th (n is a positive integer) gate line 106. The drain electrode of the pixel TFT Tpx is connected to the data line 105, and the source electrode thereof is connected to the pixel electrode of the first liquid crystal cell Clc1. The first storage capacitor Cst1 keeps the voltage of the first liquid crystal cell Clc1 constant during one frame period. One electrode of the first storage capacitor Cst1 is connected to the source electrode of the pixel TFT Tpx and the pixel electrode of the first liquid crystal cell Clc1 and the other electrode thereof is connected to the common electrode formed on the lower substrate.

Each of the touch sensors 20 includes a second liquid crystal cell Clc2, a second storage capacitor Cst2, a pull-down TFT Tpd, and a switch TFT Tsw.

The second liquid crystal cell Clc2 is formed between the source / drain metal pattern SDM and the top plate common electrode formed on the upper substrate and has a cell gap lower than the cell gap of the first liquid crystal cell Clc. The common electrode (Vcom) is supplied to the top plate common electrode. The source / drain metal pattern SDM includes the same metal as the source / drain electrodes of the TFTs Tpx, Tpd, and Tsw. As shown in FIG. 2, when the upper substrate of the liquid crystal display panel 100 is pressed by the touch object, the cell gap of the second liquid crystal cell Clc2 is lowered. The second storage capacitor Cst2 stores the voltage of the A node which changes in the cell gap change of the second liquid crystal cell Clc2.

The pull-down TFT (Tpd) serves as a diode connected between the A node and the (n-1) th gate line 106 so that the A node voltage does not fluctuate due to the voltage of the (n-1) th gate line 106. The gate and source electrodes of the pull-down TFT (Tpd) are connected to the node A, and the drain electrode thereof is connected to the (n-1) th gate line 106.

The switch TFT (Tsw) is turned on according to the gate pulse from the (n-1) th gate line 106. The switch TFT Tsw adjusts the current flowing to the touch sensor output processing unit 108 through the lead-out line 107 to the voltage (gate voltage) of the node A which changes depending on whether or not the touch is made. And the gate electrode of the switch TFT (Tsw) is connected to the node A. A driving voltage (Vdrv) is supplied to the drain electrode of the switch TFT (Tsw). The source electrode of the switch TFT (Tsw) is connected to the input terminal of the touch sensor output processing section 108 through the lead-out line 107.

The liquid crystal display of the present invention can be implemented in any liquid crystal mode as well as a TN mode, a VA mode, an IPS mode, and an FFS mode. Further, the liquid crystal display device of the present invention can be implemented in any form such as a transmissive liquid crystal display device, a transflective liquid crystal display device, a reflective liquid crystal display device, and the like. In a transmissive liquid crystal display device and a transflective liquid crystal display device, a backlight unit is required. The backlight unit may be implemented as a direct type backlight unit or an edge type backlight unit.

The touch sensor built-in display device of the present invention is not limited to a liquid crystal display (LCD). For example, the touch sensor 20 can be embedded in a pixel array of a liquid crystal display device, and can be applied to an organic light emitting diode (OLED), a field emission display (FED) And may be embedded in a pixel array such as electrophoresis (EPD).

The data driver 102 samples and latches digital video data (RGB) under the control of the timing controller 101. The data driver 102 converts the digital video data RGB to an analog positive gamma compensation voltage and a negative gamma compensation voltage to invert the polarity of the data voltage. The gate driver 103 sequentially supplies gate pulses to the gate lines 106 under the control of the timing controller 101.

The timing controller 101 rearranges the digital video data RGB input from the system board 104 and transmits the digital video data RGB to the data driver 102. [ The timing controller 101 uses a timing signal such as a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE and a dot clock CLK input from the system board 104 And generates control signals for controlling the operation timings of the data driver 102, the gate driver 103, and the touch sensor output processing circuit 108. The control signals include a gate timing control signal for controlling the operation timing of the gate drive circuit 103, a data timing control signal for controlling the operation timing of the data drive circuit 102 and the polarity of the data voltage, And a sensor timing control circuit for controlling the operation timing of the sensor 108.

The gate timing control signal includes a gate start pulse (GSP), a gate shift clock (GSC), a gate output enable signal (GOE), and the like. The gate start pulse GSP is applied to a gate drive IC (Integrated Circuit) which generates the first gate pulse to control the gate drive IC so that the first gate pulse is generated. The gate shift clock GSC is a clock signal commonly input to the gate drive ICs, and is a clock signal for shifting the gate start pulse GSP. The gate output enable signal GOE controls the output of the gate drive ICs.

The data timing control signal includes a source start pulse (SSP), a source sampling clock (SSC), a polarity control signal (POL), and a source output enable signal (SOE) . The source start pulse SSP controls the data sampling start timing of the data driving circuit. The source sampling clock SSC is a clock signal for controlling the sampling timing of data in the data driving circuit 102 on the basis of the rising or falling edge. The polarity control signal POL controls the polarity of the data voltage output from the data driving circuit 102. [ The source output enable signal SOE controls the output timing of the data driving circuit 102. The source start pulse SSP and the source sampling clock SSC may be omitted if the digital video data to be input to the data driving circuit 102 is transmitted in the mini LVDS (Low Voltage Differential Signaling) interface standard.

The sensor timing control signal includes a reset signal Reset, a reference voltage sampling switch control signal SHO, and a touch voltage sampling switching control signal SH1 as shown in Figs. 4 and 5. The gate high voltage of the gate pulse, the reference voltage sampling switch control signal SHO, and the touch voltage sampling switching control signal SH1 are generated in the low logic period of the reset signal as shown in FIG.

The touch sensor output processing unit 108 samples the touch voltage according to the current flowing through the switch TFT Tsw, amplifies the voltage, and converts the sampled touch voltage into digital data. The touch recognition unit 109 executes the touch recognition algorithm to analyze the digital data from the touch sensor output processing unit 108 and output touch coordinate data Txy indicating the position of the touch input.

FIG. 4 is a circuit diagram showing the details of the touch sensor 20 and the touch sensor output processing circuit 108 shown in FIG. 5 is a waveform diagram showing timing control signals (Reset, SHO, Vgate, SH1) of the touch sensor 20. In FIG.

4 and 5, the touch sensor output processing circuit 108 includes an operational amplifier, first and second switch elements SW (SH0) and SW (SH1), an amplifier 41, an analog-to-digital converter (Hereinafter referred to as "ADC") 42, and the like. A reset switch element {SW (Reset)} and a feedback capacitor (Cfb) are connected to the inverting input terminal and the output terminal of the operational amplifier. The inverting input terminal of the operational amplifier is connected to the source terminal of the switch TFT (Tsw). A reference voltage Vref of 2V is supplied to the non-inverting input terminal of the operational amplifier OPamp.

During the reset period, the reset switch element SW (Reset) is turned on in response to the reset signal Reset of the high logic voltage to initialize the voltage across the feedback capacitor Cfb. During this reset period, the switch TFT Tsw and the first and second switch elements SW (SH0) and SW (SH1) remain off.

During the sensing period, the reset switch element SW (Reset) maintains the OFF state in response to the reset signal Reset of the low logic voltage. During the sensing period, the first switch element SW (SH0) is turned on in accordance with the first switch control signal SHO to sample the reference voltage Vref of approximately 2 V stored in the feedback capacitor Cfb, Tdata1 to the amplifier 41. Subsequently, when the first switch element {SW {SH0}} is turned off and the gate pulse Vgate is supplied to the (n-1) -th gate line 106, the switch TFT Tsw supplies the current amount (Ids) according to the voltage of the A node. When the touch object touches the upper substrate GLS1, the capacitance of the second storage capacitor Cst2 and the voltage of the A node change due to the cell gap change of the second liquid crystal cell Clc2. Subsequently, the second switch element SW (SH1) turns on according to the second switch control signal SH1 and outputs the touch voltage stored in the feedback capacitor Cfb to the amplifier 41 as the touch data Tdata2 .

The amplifier 41 differentially amplifies the voltage of the reference data Tdata1 and the voltage of the touch data Tdata2 and supplies the same to the ADC 42. [ The ADC 42 converts the voltage supplied from the amplifier 41 into digital data and supplies it to the touch recognition unit 109. [

The present invention applies the driving voltage of the switch TFT Tsw with the AC driving voltage Vdrv in order to reduce the threshold voltage variation of the switch TFT Tsw of the touch sensor 20. [ This will be described in detail with reference to FIGS. 6 to 8B.

Referring to FIG. 6, the AC drive voltage Vdrv swings between a predetermined high potential voltage and a predetermined low potential voltage. Here, the high-potential voltage may be set to 6 V and the low-potential voltage may be set to -2 V, but is not limited thereto. The high-potential voltage and the low-potential voltage of the AC drive voltage Vdrv may be switched in one frame period or N (N is a positive integer of 2 or more) frame period units (or in seconds).

When the voltage of the AC drive voltage Vdrv is a high potential voltage, a current (forward current) flows from the drain electrode of the switch TFT Tsw to the source electrode of the current flowing through the switch TFT Tsw as shown in Fig. 7A. When the voltage of the AC driving voltage Vdrv is fixed to the high potential voltage for a long time, the threshold voltage Vth of the switch TFT Tsw rises as shown in Fig. 8A. In order to recover such a threshold voltage shift, the voltage of the alternating-current driving voltage Vdrv changes to a low potential voltage after a predetermined time. When the voltage of the AC driving voltage Vdrv is a low potential voltage, a current flowing through the switch TFT Tsw flows from the source electrode of the switch TFT Tsw toward the drain electrode (reverse current) as shown in Fig. 7B. As a result, the threshold voltage (Vth) of the switch TFT (Tsw) shifts in the direction of decreasing and the threshold voltage (Vth) thereof is recovered.

The touch recognition unit 109 can detect touch or touch point position based on "Tdata1-Tdata2" when the AC drive voltage Vdrv is applied at a high potential, and the AC drive voltage Vdrv is low It is possible to detect the touch position and the touch point position based on the discharge voltage change "Tdata1 + Tdata2" of the second storage capacitor Cst2 when the voltage is applied.

FIG. 9 is a circuit diagram showing a second embodiment of the touch sensor 20 shown in FIG. 10 is a circuit diagram showing the touch sensor 20 and the touch sensor output processing circuit 108 shown in Fig. 11 is a waveform diagram showing the AC drive voltages Vdrv1 and Vdrv2 applied to the touch sensor 20 shown in Figs.

9 to 11, each of the touch sensors 20 includes a second liquid crystal cell Clc2, a second source capacitor Cst2, a pull-down TFT Tpd, a first switch TFT Tsw1, And a second switch TFT (Tsw1).

Each of the second liquid crystal cell Clc2, the second storage capacitor Cst2, the pull-down TFT Tpd, and the touch sensor output processing circuit 108 is substantially the same as the first embodiment described above, .

Each of the first and second switch TFTs Tsw1 and Tsw2 receives the voltage of the node A, which varies depending on the presence or absence of the touch, as a gate voltage to control the current flowing to the touch sensor output processing unit 108. [ The gate electrode of the first switch TFT (Tsw1) is connected to node A. The first AC drive voltage Vdrv1 shown in Fig. 11 is supplied to the drain electrode of the switch TFT (Tsw1). The source electrode of the first switch TFT (Tsw1) is connected to the input terminal of the touch sensor output processing section (108). And the gate electrode of the second switch TFT (Tsw2) is connected to the node A. The second AC drive voltage Vdrv2 shown in Fig. 11 is supplied to the drain electrode of the second switch TFT (Tsw2). The source electrode of the second switch TFT (Tsw2) is connected to the input terminal of the touch sensor output processing section 108. [

Each of the first and second AC driving voltages Vdrv1 and Vdrv2 swings between a predetermined high potential voltage and a predetermined low potential voltage. Here, the high-potential voltage may be set to 6 V and the low-potential voltage may be set to -2 V, but is not limited thereto. The high-potential voltage and the low-potential voltage of the AC drive voltage Vdrv can be switched in one frame period or N frame period units (or every several seconds). The phases of the first and second AC driving voltages Vdrv1 and Vdrv2 are opposite to each other. For example, when the first AC drive voltage Vdrv1 is a high potential voltage, the second AC drive voltage Vdrv2 is a low potential voltage, and when the first AC drive voltage Vdrv1 is a low potential voltage, Vdrv2) is a high potential voltage. Accordingly, the first and second switch TFTs Tsw1 and Tsw2 are cross-driven in a predetermined time period.

When the voltages of the first and second AC drive voltages Vdrv1 and Vdrv2 are at a high potential, the current flowing through the first and second switch TFTs Tsw1 and Tsw2 flows through the switch TFTs Tsw1 and Tsw2, A current flows from the drain electrode to the source electrode. When the voltage of the AC driving voltage Vdrv is fixed to the high potential voltage for a long time, the threshold voltage Vth of the switch TFT Tsw rises as shown in Fig. 8A. When the voltages of the AC drive voltages Vdrv1 and Vdrv2 are low, the current flowing through the first and second switch TFTs Tsw1 and Tsw2 flows from the source electrodes of the switch TFTs Tsw1 and Tsw2, Current flows to the electrode. As a result, the threshold voltage Vth of the switch TFTs Tsw1 and Tsw2 is shifted in a direction in which the threshold voltage Vth is restored.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Therefore, the present invention should not be limited to the details described in the detailed description, but should be defined by the claims.

1 is a block diagram showing a liquid crystal display device and a touch sensor system according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the liquid crystal display panel shown in FIG. 1. FIG.

FIG. 3 is a circuit diagram showing a first embodiment of the touch sensor shown in FIG. 2. FIG.

4 is a circuit diagram showing the touch sensor and the touch sensor output processing circuit shown in FIG.

5 is a waveform diagram showing timing control signals of the touch sensor.

6 is a waveform diagram showing a first embodiment of the AC drive voltage applied to the touch sensor.

FIGS. 7A and 7B are diagrams showing changes in current flowing in the switch TFT by the AC drive voltage. FIG.

8A and 8B are graphs showing the threshold voltage recovery of the switch TFT by the AC drive voltage.

FIG. 9 is a circuit diagram showing a second embodiment of the touch sensor shown in FIG. 2. FIG.

10 is a circuit diagram showing the touch sensor and the touch sensor output processing circuit shown in FIG.

11 is a waveform diagram showing a second embodiment of the AC drive voltage applied to the touch sensor.

Description of the Related Art

100: liquid crystal display panel 101: timing controller

102: Data driver 103: Gate driver

108: Touch sensor output processing unit 109: Touch recognition unit

Claims (10)

A display panel including a first liquid crystal cell for displaying video data and a touch sensor for sensing a touch input using a second liquid crystal cell; A data driving circuit for supplying a data voltage of the video data to the data lines of the display panel; A gate driving circuit for sequentially supplying gate pulses to the gate lines of the display panel; A touch sensor output processing circuit for sampling the touch voltage from the output of the touch sensor; And And a touch recognition unit which receives an output signal of the touch sensor output processing circuit and detects a touch input, Wherein the touch sensor includes a capacitor connected to the second liquid crystal cell, and a switch TFT, The switch TFT has a gate connected to a node between the second liquid crystal cell and the capacitor, a drain to which an AC drive voltage swinging between a high potential voltage and a low potential voltage is supplied, And a source connected to the input terminal of the transistor Wherein the touch recognition unit detects the touch input in each of a high potential voltage interval and a low potential voltage interval of the AC driving voltage. The method according to claim 1, Wherein the high-potential voltage and the low-potential voltage of the AC drive voltage are switched in a frame period unit. The method according to claim 1, Wherein the high-potential voltage and the low-potential voltage of the AC drive voltage are switched in units of seconds. delete A display panel including a first liquid crystal cell for displaying video data and a touch sensor for sensing a touch input using a second liquid crystal cell; A data driving circuit for supplying a data voltage of the video data to the data lines of the display panel; A gate driving circuit for sequentially supplying gate pulses to the gate lines of the display panel; A touch sensor output processing circuit for sampling the touch voltage from the output of the touch sensor; And And a touch recognition unit which receives an output signal of the touch sensor output processing circuit and detects a touch input, Wherein the touch sensor includes a capacitor connected to the second liquid crystal cell, a first switch TFT supplied with an AC drive voltage, and a second switch TFT supplied with the AC drive voltage, A gate of the first switch TFT and a gate of the second switch TFT are connected to a node between the second liquid crystal cell and the capacitor, Wherein the touch recognition unit detects the touch input in each of a high potential voltage interval and a low potential voltage interval of the AC driving voltage. 6. The method of claim 5, Wherein the AC drive voltage A first AC drive voltage supplied to the first switch TFT, And a second AC drive voltage supplied to the second switch TFT, Wherein the first and second AC driving voltages are opposite in phase to each other. The method according to claim 6, The first switch TFT is connected to the input terminal of the touch sensor output processing circuit through a gate connected to a node between the second liquid crystal cell and the capacitor, a drain supplied with the first AC drive voltage, and a lead- Gt; And the second switch TFT is connected to an input terminal of the touch sensor output processing unit through a gate connected to a node between the second liquid crystal cell and the capacitor, a drain to which the second AC drive voltage is supplied, and a lead- And a source connected to the touch sensor. The method according to any one of claims 1 to 3, 5 to 7, The touch sensor includes: Further comprising a pull-down TFT having a gate and a source connected to a node between the second liquid crystal cell and the capacitor, and a source connected to a gate line of the display panel. 8. The method of claim 1 or 7, The touch sensor output processing circuit includes: An operational amplifier having an inverting input terminal connected to the lead-out line, a non-inverting input terminal supplied with a reference voltage, and an output terminal connected to the first switch element and the second switch element; An amplifier connected to the first switch element and the second switch element; And And an analog-to-digital converter (ADC) converting the output voltage of the amplifier into digital data and supplying the digital data to the touch recognition unit, A reset switch element and a feedback capacitor are connected between the inverting input terminal and the output terminal of the operational amplifier, During the reset period, the reset switch element is turned on according to the high logic voltage of the reset signal to initialize the voltage across the feedback capacitor, During the sensing period, the reset switch element maintains an off state according to the low logic voltage of the reset signal, During the reset period, the switch TFT, the first switch element, and the second switch element maintain the off state, During the sensing period, the first switch element is turned on according to the first switch control signal to output reference data obtained by the voltage of the feedback capacitor to the amplifier, and then the second switch element outputs the second switch control signal And outputs the touch data obtained by the voltage of the feedback capacitor to the amplifier, And the gate pulse supplied to the n-1th (n is a positive integer) gate line is generated between the first switch control signal and the second switch control signal to operate the switch TFT. Device. 10. The method of claim 9, Wherein the touch recognition unit detects the touch input based on Tdata1 - Tdata2 in the high potential voltage interval of the AC drive voltage when the reference data is Tdata1 and the touch data is Tdata2, And the touch input is detected based on Tdata1 + Tdata2 in a voltage period.

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