JP2006091708A - Active matrix liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a further miniaturization of application equipment by adding a function as an input device in addition to the function as an output device to an active matrix liquid crystal display device. <P>SOLUTION: The active matrix liquid crystal display device comprises: columns of scanning lines 2F, 2G, 2 H; columns of signal lines 2D, 2E; and pixels 1B which are arranged in the form of matrix at the portion where each scanning line intersect with each signal line. Each pixel 1B includes a liquid crystal cell, display circuit 2A consisting of a thin film transistor, and light receiving circuit consisting of the thin film transistor similarly. A display circuit 2A drives liquid crystal cells in response to video signals that are input from the signal line 2D when selected by the scanning line 2F, thereby displaying videos in the matrix of pixels 1B. The light receiving circuit including a photodetector 3D is selected when the display circuit 2A is not operated, and outputs the light receiving signals based on the light quantity incident on the pixels 1B to another signal line 2E. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an active matrix liquid crystal display device. More specifically, the present invention relates to a pixel circuit configuration of an active matrix liquid crystal display device in which each pixel includes a light receiving circuit for inputting information in addition to a display circuit arranged for each pixel.

  An active matrix liquid crystal display device has low power consumption and can be miniaturized. Because of these features, active matrix liquid crystal display devices (LCDs) are surpassing conventional CRTs, which are typical displays, and are used for various displays. Particularly in recent years, LCDs have been widely used as mobile terminal displays by taking advantage of low power consumption and small size due to the development of communication environments.

  A mobile device requires an input device in addition to an output device device such as a display. Conventionally, a resistive thin film type touch panel has been used as an input device. However, since the touch panel detects a potential change at a contact point, it is impossible in principle to simultaneously detect two or more contact points. For this reason, the touch panel may not be compatible with game applications. Further, since the touch panel is installed on the display surface of the display device, there is a problem that the thickness of the device is inevitably increased and the luminance of the display is lowered.

  In recent years, mobile phones with a CCD camera or a CMOS camera as an input device are widely used. In addition, mobile phones with a built-in fingerprint sensor for personal authentication have also appeared. However, since these sensors as input devices are not integrated with the image display unit, there is a problem in that the mounting density of devices is increased.

  In view of the above-described problems of the prior art, the present invention achieves further downsizing of applied devices by adding a function as an input device to an active matrix liquid crystal display device in addition to a function as an output device. With the goal. In order to achieve this purpose, the following measures were taken. That is, an active matrix type liquid crystal display device according to the present invention includes a column of scanning lines, a column of signal lines, and pixels arranged in a matrix at a portion where each scanning line and each signal line intersect. Includes a liquid crystal element, a display circuit composed of a thin film transistor, and a light receiving circuit also composed of a thin film transistor, and the display circuit converts a video signal input from the signal line when selected by the scanning line. In response, the liquid crystal element is driven to display an image on a matrix pixel, and the light receiving circuit is selected when the display circuit is not operating, and a light receiving signal corresponding to the amount of light incident on the pixel Is output to another signal line.

  Preferably, the light receiving circuit detects the amount of light incident on the light receiving element formed in the pixel and outputs a corresponding light receiving signal. The light receiving circuit uses a thin film transistor as a light receiving element, a set portion for setting the thin film transistor in a reverse bias state, and amplifies a light leak current flowing through the light receiving element in accordance with the amount of light incident in the reverse bias state. And an amplification unit that generates a light reception signal. In addition, the light receiving circuit includes an input switch for taking a light leakage current flowing through the light receiving element in accordance with the amount of incident light into the amplifying unit, and a light receiving signal obtained by amplifying the taken light leakage current from the amplifying unit. And an output switch for reading out to the signal line, and the input switch and the output switch are on / off controlled at timings independent of each other. In this case, the light receiving circuit turns off both the input switch and the output switch while the display circuit is in operation, and first turns on the input switch when the display circuit is not in operation. Supply of the leak current is started, and then the output switch is turned on when the supply of the optical leak current is stabilized. In one aspect, the liquid crystal element is a light reflection type. In another aspect, the liquid crystal element is a light transmission type. Preferably, the thin film transistor has a polycrystalline silicon thin film as an active layer. Alternatively, the thin film transistor may be an amorphous silicon thin film as an active layer.

  According to the present invention, a display circuit and a light receiving circuit are integrated and formed by thin film transistors or the like in each pixel of an active matrix liquid crystal display device. The display circuit can output an image display by driving the liquid crystal element in accordance with the video signal. On the other hand, the light receiving circuit allows the input of image information by flowing a light leakage current corresponding to the amount of incident light in a state where a reverse bias voltage is applied to the thin film transistor and further amplifying it. The liquid crystal display device according to the present invention can optically detect a coordinate position without using a touch panel or the like, and can also detect two or more simultaneous coordinates in principle. In addition, since it is not necessary to separately install a position detection device on the display for coordinate detection, a high-luminance image display can be obtained. Further, as an application other than coordinate detection, a scanner based on light detection in pixel units can be realized. Thereby, a liquid crystal display device with high added value can be provided. In particular, in the present invention, the light receiving circuit improves the light receiving sensitivity by independently performing the light receiving current control and the amplification output control. Although the present invention uses a liquid crystal element for a pixel, it can be applied to an active matrix display device using a self-luminous element such as an organic EL element instead.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic plan view showing the configuration of an active matrix liquid crystal display device according to the present invention. As shown in the figure, this liquid crystal display device includes a panel 1A and peripheral circuits for driving the panel 1A. The panel 1A includes a pixel array 1K in which pixels 1B are integrated and formed in a matrix. A circuit group arranged so as to surround this from the periphery includes a video signal line driving integrated circuit 1C, a video signal control circuit 1D, a scanning line driving integrated circuit 1E, a scanning line control circuit 1F, a light receiving signal processing substrate 1G, and a light receiving signal. A transmission flexible cable 1H and the like are included. In the present embodiment, the video signal line driving integrated circuit 1C is mounted on a flexible cable. The video signal control circuit 1D is connected to the panel 1A via a flexible cable on which the video signal line driving integrated circuit 1C is mounted. Similarly, the scanning line control circuit 1F is connected to the panel 1A via a flexible cable on which the scanning line driving integrated circuit 1E is mounted.

  FIG. 2 is a schematic plan view showing the configuration of the pixel 1B shown in FIG. As shown in the figure, the pixel 1B is arranged at a portion where the scanning line column and the signal line column intersect. Two signal lines are arranged per pixel, and there are a display signal line 2D and an output signal line 2E. The display signal line 2D is connected to the video signal line driving integrated circuit 1C shown in FIG. On the other hand, the output signal line 2E is connected to the received light signal processing substrate 1G shown in FIG. Three scanning lines are arranged per pixel, and there are a display scanning line 2F, an input scanning line 2G, and an output scanning line 2H. These scanning lines 2F, 2G, and 2H are connected to the scanning line driving integrated circuit 1E shown in FIG.

  The pixel 1B includes a liquid crystal element, a display circuit 2A composed of a thin film transistor, and a light receiving circuit also composed of a thin film transistor. This embodiment is of a reflective type, and the liquid crystal element is composed of liquid crystal sandwiched between the reflective electrode 2R and a transparent electrode facing the reflective electrode 2R. When the display circuit 2A is selected by the display scanning line 2F, the display circuit 2A drives the liquid crystal element in accordance with the video signal input from the display signal line 2D, thereby displaying the video on the matrix pixels. On the other hand, the light receiving circuit is selected when the display circuit 2A is not operating, and outputs a light receiving signal corresponding to the amount of light incident on the pixel 1B to the output signal line 2E.

  In the present embodiment, the light receiving circuit detects the amount of light incident on the light receiving element 3D formed in the pixel 1B, and outputs a corresponding light receiving signal. In the present embodiment, a thin film transistor is used as the light receiving element 3D. Furthermore, a setting unit that sets the thin film transistor in a reverse bias state and an amplification unit that amplifies a light leakage current flowing through the light receiving element 3D according to the amount of light incident in the reverse bias state to generate a light reception signal. The light receiving circuit includes an input switch that takes in the light leakage current flowing through the light receiving element 3D in accordance with the amount of incident light, and an output signal line 2E that receives the light reception signal obtained by amplifying the taken light leakage current from the amplifier. Output switch. The input switch and the output switch are ON / OFF controlled by the input scanning line 2G and the output scanning line 2H, respectively, at timings independent of each other. When the display circuit 2A stops operating, the light receiving circuit first turns on the input switch to start supplying the light leakage current to the amplifier, and then turns on the output switch when the supply of the light leakage current is stabilized. The display circuit 2A is disposed below the reflective electrode 2R. On the other hand, the light receiving element 3D is arranged so as to be aligned with the opening formed in the reflective electrode 2R in order to take in light from the outside.

  FIG. 3 is a schematic diagram showing a cross-sectional structure of the liquid crystal display device for one pixel shown in FIG. As shown in the figure, the liquid crystal display device has a flat panel structure in which a liquid crystal 44 is sandwiched between a lower substrate 41 and an upper substrate 47. On the lower substrate 41, a display circuit 2A and a light receiving element 3D are formed. As shown in the drawing, the display circuit 2A is composed of a thin film transistor 3A and the like. Similarly, the light receiving element 3D is formed of a thin film transistor formed on the lower substrate 41. These thin film transistors have, for example, a polycrystalline silicon thin film as an active layer. In some cases, an amorphous silicon thin film may be used as the active layer instead of the polycrystalline silicon thin film. The display circuit 2A and the light receiving element 3D formed of thin film transistors are covered with a planarizing film 42, and a reflective electrode 2R is formed thereon. The reflective electrode 2R is connected to the display circuit 2A through a contact hole formed in the planarizing film 42. On the other hand, an opening 43 is formed above the light receiving element 3D by notching the reflective electrode 2R.

  On the other hand, a color filter 46 and a transparent electrode 45 are formed on the inner surface of the upper substrate 47, and a polarizing plate 48 is formed on the outer surface. A liquid crystal 44 is held between the transparent electrode 45 disposed on the upper substrate 47 and the reflective electrode 2R disposed on the lower substrate 41, and constitutes a light reflection type liquid crystal element in units of pixels. . This liquid crystal element modulates the transmittance of the liquid crystal 44 in accordance with the level of the video signal written from the display circuit 2A to the reflective electrode 2R. As a result, the amount of reflected light is modulated in units of pixels, thereby displaying an image.

  FIG. 4 is a graph showing current-voltage characteristics of a thin film transistor used as the light receiving element 3D. The horizontal axis represents the gate-source voltage, and the vertical axis represents the drain current logarithmically. In the forward bias state in which the gate-source voltage takes a positive value, the drain current Id flows according to the gate-source voltage after exceeding the threshold value of the thin film transistor. On the other hand, in the reverse bias state where the gate-source voltage takes a negative value, the drain current Id basically does not flow. However, at the time of reverse bias, a light leakage current flows due to photoexcitation of light incident from the outside. The light leakage current increases as the amount of light incident from the outside increases. In the present invention, light detection is performed by utilizing a change in drain current caused by photoexcitation of the thin film transistor. The absolute amount of the light leakage current in the reverse bias is smaller than the drain current in the forward bias. Therefore, the present invention performs light detection by amplifying the light leakage current.

  FIG. 5 is a circuit diagram showing a specific configuration of the pixel shown in FIG. As shown in the drawing, the pixel 1B includes a display circuit 2A and a light receiving circuit 2B. The display circuit 2A is arranged at a portion where the display signal line 2D and the display scanning line 2F intersect. The display circuit 2A is basically composed of a sampling transistor 3A. The sampling transistor 3A is an N-type thin film transistor. The gate of the sampling transistor 3A is connected to the display scanning line 2F, and the drain is connected to the display signal line 2D. One end of a liquid crystal element 3B and a storage capacitor 3C is connected to the source of the sampling transistor 3A. The other end of the liquid crystal element 3B is connected to a predetermined power supply voltage Vcom. The other end of the storage capacitor 3C is connected to a predetermined potential Vcs. As described with reference to FIG. 3, the liquid crystal element 3B includes a reflective electrode connected to the transistor 3A side, a transparent electrode facing the reflective electrode, and a liquid crystal layer held between them.

  On the other hand, the light receiving circuit 2B is arranged at a portion where the output signal line 2E and the scanning lines 2G and 2H intersect. One scanning line 2G is for input, and the other scanning line 2H is for output. The input scanning line 2G is connected to the gate of the input transistor 3E serving as an input switch. On the other hand, the output scanning line 2H is connected to the gate of the transistor 3H serving as an output switch. The drain of the light receiving transistor 3D serving as a light receiving element is connected to the drain of the input transistor 3E. A reverse bias gate voltage source Vb4 is connected to the gate of the light receiving transistor 3D to constitute a reverse bias set unit. A light receiving current generating voltage source Vb3 is connected to the source of the light receiving transistor 3D.

  A pair of transistors 3F and 3G constitute a current mirror circuit, which serves as an amplifying unit. The light leakage current Ip generated by the light receiving transistor 3D is input to the drain and gate of one transistor 3F through the input transistor 3E, and flows into the bias power supply Vb1 through the source. The other transistor 3G has a gate connected to the drain and gate of the transistor 3F, a source connected to the bias power supply Vb2, and a drain connected to the output signal line 2E via the output transistor 3H. The received light signal current Iread flowing through the output signal line 2E is a value obtained by amplifying the light leakage current Ip according to the size ratio of the transistors 3F and 3G constituting the current mirror circuit.

  FIG. 6 is a timing chart for explaining the operation of the pixel circuit shown in FIG. In the present embodiment, time-division control is performed with the first half of one frame as a display operation period (video period) and the second half as a light receiving operation period. The timing chart represents waveforms of a video signal, a display scanning signal, an output scanning signal, an input scanning signal, and the like. Correspondingly, changes in the light leakage current Ip and the light reception signal current Iread are also shown. The video signal is supplied from the external system to the input signal line 2D, the display scanning signal is supplied to the display scanning line 2F, the output scanning signal is supplied to the output scanning line 2H, and the input scanning signal is input. Is supplied to the scanning line 2G.

  First, in the display operation, the scanning signal for display is set to the high level, and the sampling transistor 3A is turned on. As a result, the video signal supplied from the display signal line 2D is taken in by the sampling transistor 3A and written to the corresponding liquid crystal element 3B. Thereby, the liquid crystal element 3B modulates the transmittance of the liquid crystal layer according to the level of the written video signal, and displays a desired image. The video signal captured by the sampling transistor 3A is also held in the holding capacitor 3C. Thus, an image can be stably displayed during a video display period corresponding to a half of one frame.

  In the latter light receiving operation period, first, the input scanning signal is set to the high level, and the optical leakage current Ip is caused to flow to one transistor 3F of the current mirror circuit via the input transistor 3E. At this time, the gate voltage Vg of the transistor 3F rises when the gate capacitance is charged by the light leakage current Ip. Then, when the charging of the gate is completed and Ip is saturated, the output scanning signal is set to the high level. As a result, the output transistor 3H is turned on, and the light reception signal Iread is supplied to the output signal line 2E. During this period, since both the input transistor 3E and the output transistor 3H are in the on state, the light reception signal Iread has a value obtained by amplifying the light leakage current Ip by the current mirror circuit configured by the transistors 3F and 3G.

  In the present invention, since the operating point of the current mirror circuit is determined during the light receiving period, the photocurrent is always supplied, and the light receiving sensitivity is increased. In addition, since the light leakage current is amplified in an analog manner by the current mirror circuit, gradation expression is also possible. Further, since the display circuit and the light receiving circuit are completely separated in the pixel, not only the method of equally separating one frame into the video display period and the light receiving detection period shown in the embodiment, but also, for example, the light receiving operation is performed vertically. A configuration performed during the ranking period is also possible, and there are few timing restrictions.

  As described above, in the present invention, the display circuit and the light receiving circuit are formed in the pixel of the active matrix type liquid crystal display device. A photoexcitation current can be generated by applying a reverse bias to the gate of the light receiving transistor during the light receiving period. Further, a display device capable of both video display and image detection can be formed by amplifying the photoexcitation current with a current mirror circuit. The display panel of the present invention can detect the coordinate position without separately using a touch panel or the like, and can detect a plurality of points simultaneously. In addition, since it is not necessary to install a position detection device on the display panel for coordinate detection, a high-luminance image can be obtained. In addition to coordinate position detection, a scanner that applies light detection can be integrally formed on the panel, so that a liquid crystal display device having high added value can be provided.

  FIG. 7 is a schematic view showing another embodiment of the liquid crystal display device according to the present invention, and is a plan view for one pixel. For easy understanding, the parts corresponding to those of the previous embodiment shown in FIG. The difference is that the previous embodiment shown in FIG. 2 incorporates a light-reflective liquid crystal element, whereas this embodiment uses a light-transmissive liquid crystal element. As shown in the figure, the pixel 1B is arranged at a portion where the signal lines 2D, 2E and the scanning lines 2F, 2G, 2H intersect, and is divided into a display circuit 2A and a light receiving circuit including a light receiving element 3D. A transparent electrode 2T of a liquid crystal element is formed so as to surround the display circuit 2A and the light receiving element 3D.

  FIG. 8 shows a cross-sectional structure along the line AA ′ of the liquid crystal display device for one pixel shown in FIG. As shown in the figure, the present liquid crystal display device is composed of a lower substrate 41, an upper substrate 47, and a liquid crystal 44 held between them. A polarizing plate 49 is disposed on the outer surface of the lower substrate 41, and a display circuit 2A and a light receiving element 3D are integrated on the inner surface. The display circuit 2A and the light receiving element 3D are covered with a planarizing film 42, and a transparent electrode 2T is formed thereon. The transparent electrode 2T is driven by the display circuit 2A.

  A polarizing plate 48 is disposed on the outer surface of the upper substrate 47, while a color filter 46 and a transparent electrode 45 are formed on the inner surface. A transmissive liquid crystal element is constituted by the liquid crystal 44 held between the transparent electrode 2T disposed on the lower substrate 41 and the transparent electrode 45 disposed on the upper substrate 47. The transmittance of the liquid crystal element changes according to the level of the video signal applied to the transparent electrode 2T via the display circuit 2A. In response to this, light incident from the lower substrate 41 is modulated and emitted from the upper substrate 47 as transmitted light. On the other hand, the transparent electrode 2T is removed from above the light receiving element 3D, and light incident from the outside can be detected.

1 is a block diagram showing an overall configuration of a liquid crystal display device according to the present invention. FIG. 2 is a plan view showing one pixel of the liquid crystal display device shown in FIG. 1. It is sectional drawing which similarly shows one pixel. It is a graph which shows the current-voltage characteristic of the light receiving element integrated in the liquid crystal display device concerning this invention. It is a circuit diagram which shows the specific structural example of the pixel circuit formed in the liquid crystal display device concerning this invention. 6 is a timing chart for explaining the operation of the pixel circuit shown in FIG. 5. It is a typical top view which shows other embodiment of the liquid crystal display device concerning this invention. Similarly it is sectional drawing of other embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A ... Panel, 1B ... Pixel, 2A ... Display circuit, 2B ... Light receiving circuit, 2D ... Display signal line, 2E ... Output signal line, 2F ... Display Scanning line, 2G ... input scanning line, 2H ... output scanning line, 3A ... sampling transistor, 3B ... liquid crystal element, 3D ... light receiving element, 3E ... input transistor, 3F ... Current mirror transistor, 3G ... Current mirror transistor, 3H ... Output transistor

Claims (9)

A column of scanning lines, a column of signal lines, and pixels arranged in a matrix at a portion where each scanning line and each signal line intersect,
Each pixel includes a liquid crystal element, a display circuit composed of a thin film transistor, and a light receiving circuit also composed of a thin film transistor,
The display circuit drives the liquid crystal element according to a video signal input from the signal line when selected by the scanning line, thereby displaying an image on a matrix of pixels,
An active matrix liquid crystal display device, wherein the light receiving circuit is selected when the display circuit is not operating, and outputs a light receiving signal corresponding to the amount of light incident on the pixel to another signal line.   2. The active matrix liquid crystal display device according to claim 1, wherein the light receiving circuit detects a light amount incident on a light receiving element formed in the pixel and outputs a corresponding light receiving signal.   The light receiving circuit uses a thin film transistor as a light receiving element, sets a thin film transistor in a reverse bias state, and amplifies a light leakage current flowing in the light receiving element in accordance with the amount of light incident in the reverse bias state to receive light. 3. The active matrix liquid crystal display device according to claim 2, further comprising an amplifying unit for generating a signal.   The light receiving circuit includes an input switch for taking a light leakage current flowing through the light receiving element in accordance with the amount of incident light into the amplification unit, and a light reception signal obtained by amplifying the taken light leakage current from the amplification unit to the signal line. 4. An active matrix type liquid crystal display device according to claim 3, further comprising an output switch for reading out the data, wherein the input switch and the output switch can be turned on and off at independent timings.   The light receiving circuit turns off both the input switch and the output switch while the display circuit is operating, and first turns on the input switch when the display circuit stops operating to reduce the light leakage current to the amplifying unit. 5. The active matrix liquid crystal display device according to claim 4, wherein the output switch is turned on when the supply is started and then the supply of the light leakage current is stabilized.   2. The active matrix liquid crystal display device according to claim 1, wherein the liquid crystal element is a light reflection type.   2. The active matrix liquid crystal display device according to claim 1, wherein the liquid crystal element is a light transmission type.   2. The active matrix liquid crystal display device according to claim 1, wherein the thin film transistor has a polycrystalline silicon thin film as an active layer.   2. The active matrix liquid crystal display device according to claim 1, wherein the thin film transistor includes an amorphous silicon thin film as an active layer.

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