JP2008203561A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which attains both an input function and an output function for image information. <P>SOLUTION: The liquid crystal display device includes a display panel DP having a plurality of scan lines with arrayed liquid crystal display elements PX each including an optical input element and a display pixel, a back light BL which is disposed opposite to the display panel to illuminate the display panel, and a control means CTL of controlling writing to display pixels and reading of detection signals from the optical input elements, wherein the control means is configured to control the display pixels to display an external light detection image substantially shielding the light from the back light for a first period of a one-frame period and a display image for a second period of the one-frame period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

In general, a display device using liquid crystal or the like is a device that outputs image information. However, by adding a light input function, information such as an image can be input. With this technology, it is possible to realize information input / output and bidirectional information exchange with a single device.
By using a liquid crystal display element to which an optical input function is added, a finger can be pressed against the liquid crystal display panel to read a fingerprint, and a document can be pressed against the liquid crystal display panel to read characters written there. Further, since the position when the display panel is touched with a finger or a pen can be optically read, a function equivalent to that of a touch panel can be added to the liquid crystal display device (see, for example, Patent Document 1).
JP 2001-292276 A

FIG. 16 is a diagram illustrating a conventional reading method.
In order to realize the touch panel function, at the start of reading, the display image displayed until then is switched to the reading image for reading the image. Since the read video needs to be a video that does not affect the reading, for example, a single color such as blue is uniformly displayed. The light source light from the backlight BL is once irradiated onto a document or the like on the liquid crystal display panel through the displayed read video. An image is read by detecting and processing the light reflected from the document or the like in the liquid crystal panel.

In this way, information is read in a state where the read video is displayed, and then the display of the display video is resumed as necessary.
Therefore, in the conventional method, in order to perform reading, it is necessary to temporarily stop displaying image information and switch to a reading screen. For this reason, when reading takes several seconds, the display of the image information is stopped during that time, and it has been pointed out that the display is uncomfortable.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a liquid crystal display device capable of achieving both an input function and an output function of image information.

  In order to solve the above problems, a liquid crystal display device according to the present invention includes a display panel provided with a plurality of scanning lines in which liquid crystal display elements including light input elements and display pixels are arranged, and a display panel disposed opposite to the display panel. And a backlight for illuminating the display panel, and a control means for controlling writing to the display pixel and reading of the detection signal of the light input element, the control means for a first period of one frame period. An external light detection image that substantially shields light from the backlight is displayed on the display pixel, and a display image is displayed on the display pixel over a second period of the one frame period.

  In addition, the liquid crystal display device according to the present invention includes a display panel including a plurality of scanning lines in which liquid crystal display elements including optical input elements and display pixels are arranged, and the display panel arranged to face the display panel. A backlight blinking means for blinking the backlight, and a control means for controlling writing to the display pixel and reading of the detection signal of the light input element, the backlight comprising: The control unit is configured to be able to blink, and changes the reference potential in synchronization with the blinking of the backlight.

  According to the present invention, it is possible to obtain a liquid crystal display device capable of achieving both an image information input function and an output function.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same referential mark is attached | subjected to the component which exhibits the same or similar function, and the overlapping description is abbreviate | omitted.

[First Embodiment]
FIG. 1 is a diagram showing a schematic configuration of a liquid crystal display device according to a first embodiment of the present invention.
The liquid crystal display device 100 includes a liquid crystal display panel DP having a plurality of liquid crystal display elements with a light input function, a control circuit CTL that controls the liquid crystal display panel DP, and a backlight BL that illuminates the liquid crystal display panel DP.
The liquid crystal display panel DP is provided with a display area 110, a gate line driving circuit 112, a data line driving circuit 114, and a data read processing circuit 116.

In the display area 110, a plurality of liquid crystal display elements 130 with a light input function are arranged in a matrix. A plurality of gate lines (not shown) are arranged along a row of the plurality of liquid crystal display elements 130 with a light input function. A plurality of data lines (not shown) are arranged along a row of the plurality of liquid crystal display elements 130 with a light input function.
The gate line driving circuit 112 sequentially drives a plurality of gate lines. The data line driving circuit 114 outputs data to the data line in accordance with the driving of each gate line. The data read processing circuit 116 takes out the data read from each liquid crystal display element 130 with an optical input function and processes it.

  The control circuit CTL controls operations of the gate line driving circuit 112, the data line driving circuit 114, and the data read processing circuit 116.

FIG. 2 is an equivalent circuit showing the configuration of the liquid crystal display element with a light input function according to the first embodiment of the present invention.
Note that the display gate line, the precharge gate line, and the signal readout gate line shown in the figure are gate lines arranged along a row of a plurality of liquid crystal display elements. A line is a data line arranged along a row of a plurality of liquid crystal display elements.

  Each of the liquid crystal display elements with a light input function includes a display unit and a reading unit as shown in FIG. Note that this reading unit is not required to have a high resolution as long as it realizes a touch panel function, so it is not necessary to provide it for all liquid crystal display elements, and it may be provided for any one of a plurality of liquid crystal display element groups. .

The display unit includes a liquid crystal pixel PX, and a pixel TFT is connected to each liquid crystal pixel PX. The pixel electrode PE, the common electrode CE, and the liquid crystal layer sandwiched between them constitute the liquid crystal pixel PX. The pixel TFT is a thin film transistor as a switching element.
The pixel electrode PE is connected to the drain of the pixel TFT, and a common voltage Vcom is applied to the common electrode CE. The gate of the pixel TFT is connected to the display gate line, and the source-drain path is connected between the signal line and the pixel electrode PE. The pixel TFT becomes conductive when driven through the display gate line, and applies the potential of the signal line to the pixel electrode PE.

The readout unit is provided with a photodiode, a sensor capacitor, an amplifier, a precharge TFT, and a readout TFT. The precharge TFT and the readout TFT are thin film transistors as switching elements.
The photodiode and the sensor capacitor are connected in parallel, and one end thereof is connected to the drain of the precharge TFT and the input end of the amplifier. The gate of the precharge TFT is connected to the precharge gate line, and the source-drain path is connected between the precharge line and the input terminal of the amplifier. The gate of the readout TFT is connected to the signal readout gate line, and the source-drain path is formed between the signal readout line and the output terminal of the amplifier.

  With such a configuration, for example, a predetermined charge is precharged in the sensor capacitor, and the charge is leaked according to the amount of light incident on the photodiode. Then, the light intensity at each position can be measured by reading the charge remaining in the sensor capacitor.

Next, the operation of the liquid crystal display device will be described. The control circuit CTL controls the operation of the liquid crystal display device described below.
In the present embodiment, the external light detection method shown in FIG. 3 and the reflected light detection method shown in FIG. 4 are used in combination.
As shown in FIG. 3, in the light detection method using external light, external light applied to a region other than the shadowed region is detected according to the finger tip position, and an image image is a shadowed region depending on the finger tip position. That is, only the touch part is recognized as black, and the others are recognized as white. On the contrary, as shown in FIG. 4, in the light detection method using reflected light, the reflected light of the backlight BL reflected at the tip position of the finger is detected, and as an image image, only the touch part is recognized as white contrary to the above. .

In the present embodiment, display scanning is performed twice within one frame, and by performing two light detection scannings of light detection by reflected light and light detection by external light, information is displayed simultaneously with image display. Realize input.
FIG. 5 is a diagram for explaining an image reading method according to the first embodiment of the present invention.
(1) in FIG. 5 shows a display image displayed on the liquid crystal display panel DP at a certain point in time. A band-shaped black image is displayed on a part of the display image, and the band-shaped black image moves from the top to the bottom of the screen within one frame.

  (2) in FIG. 5 shows the timing of the read operation. When the black display is started, the readout portion of the line is precharged almost at the same time, and the light input information is read immediately before the black display is finished. During the black display period, even if the backlight BL is lit, the light source light is blocked by the liquid crystal, so that a shadow caused by external light from the touch unit is input to the reading unit. After the black display is finished, image information is displayed. During this display period, precharging is performed, and the information optically input just before the display is finished is read out. In the video display period, since the light of the backlight BL is irradiated, reflected light from the touch unit is input to the reading unit.

FIG. 6 is a time chart for explaining the read operation of the first embodiment.
The horizontal axis in the figure represents time, and the time changes from left to right. The vertical axis represents the scanning position of the screen, the upper end portion indicates the upper end position of the screen, and the lower end portion indicates the lower end position of the screen.

  Each frame period is divided into a first period and a second period, and a first period corresponding to a quarter frame period is assigned to black display for detecting external light and preventing reverse transition of OCB liquid crystal described later, A second period corresponding to a 3/4 frame period is assigned to reflected light detection and image display. The backlight BL is turned on at the time when the external light detection period ends for all scanning lines, and the backlight BL is turned off when the next external light detection period is started.

  First, over the 1/4 frame period of one frame period, the display gate line is set in the active state, and the external light detection black image is written to the pixel PX from the signal line, and the precharge gate line is set in the active state. The external light detection precharge is executed via This operation is realized by sequentially scanning the display gate line and the precharge gate line from the upper end of the screen toward the lower end of the screen. Therefore, on the display screen, black images are sequentially displayed from the upper end of the screen toward the lower end of the screen.

  For each scanning line, the external light detection period ends after elapse of a predetermined time, for example, 1/4 frame period from scanning of the display gate line and the precharge gate line.

  The external light detection period for each scanning line is set to be equal, and the charge held in the sensor capacitor of the reading unit is determined based on the external light amount in the external light detection period. In the external light detection period, the light of the backlight BL is blocked by the liquid crystal on which the black image is written, but it is desirable to turn off the backlight BL in order to improve detection accuracy.

  At the end of the external light detection period, the signal read gate line is activated and the external light detection signals are sequentially read over the 1/4 frame period via the signal read line.

  In synchronization with this reading, the display gate line is set in an active state over a ¼ frame period, and display image information is written from the signal line to the pixel PX. This operation is realized by sequentially scanning the display gate lines from the upper end of the screen toward the lower end of the screen. That is, the display image is displayed sequentially from the upper end of the screen toward the lower end of the screen.

  Then, when display image information is displayed for each scanning line on the screen, the backlight BL is turned on to realize image display. Further, in synchronization with the lighting of the backlight BL, the precharge gate line is activated and the reflected light detection precharge is sequentially scanned from the scan line at the upper end position of the screen over a quarter frame period. And execute.

  The reflected light detection period for each scanning line is set to be substantially equal, and the voltage held in the sensor capacitor of the reading unit is determined based on the amount of reflected light in this reflected light detection period.

Then, after the end of the predetermined reflected light detection period, the reflected light detection signal is read through the signal read line with the signal read gate line in an active state. This operation is sequentially scanned over a ¼ frame period from the upper end of the screen toward the lower end of the screen, and is completed by the end of the frame period.
The backlight BL continues to be turned on until the writing of the external light detection black image of the next frame is started. Then, the external light detection operation for the next frame period is started in synchronization with the backlight BL being turned off.

  In addition, during the backlight BL lighting period, the black image writing for the external light detection period of the next frame is started from the time when the writing of the image information is completed so that the display of good image information can be realized without in-plane luminance gradient. It is set before it starts.

By the way, as described above, one frame is divided into a first period and a second period, and in order to display two images in each period, a high-speed liquid crystal is required. This is because even if the signal is rewritten, there is no effect if the display image cannot follow. Therefore, for example, an OCB type liquid crystal capable of realizing a high-speed response can be used.
By the way, in the OCB liquid crystal, even when transitioning to bend alignment, when the voltage application state below the level at which spray alignment energy and bend alignment energy antagonize or when no voltage application state continues for a long time, it reversely transitions back to spray alignment. It has the property of end up.
Conventionally, in order to prevent a reverse transition from bend alignment to spray alignment, for example, a driving method has been adopted in which a large voltage is applied to the liquid crystal for each field displaying an image of one frame. In a normally white liquid crystal display panel, improvement of moving image visibility and prevention of reverse transition can be realized simultaneously by using a pixel voltage for black display as this voltage, which is called black insertion driving.

  Therefore, in this embodiment, the black image inserted to maintain the bend orientation for the reverse transition prevention period is used as the external light detection black image in the first period. According to such driving, OCB type liquid crystal can realize image display with excellent moving image visibility as well as information reading without requiring application of a separate reverse transition prevention voltage.

Next, a method for processing the read detection signal will be described.
When inputting a document to be read with the panel surface in close contact like a scanner, it is not necessary to consider the influence of external light. However, when used as a touch panel as in the present embodiment, it is necessary to consider the influence of external light.
FIG. 7 is a diagram for explaining the influence of external light and the backlight BL. For example, assume that a finger touches the liquid crystal panel.

  (1) of FIG. 7 shows a case where the backlight BL is on.

When the external light is strong, the external light is blocked by the finger in the shadow portion of the finger, so that the external light input to the readout unit is small and dark, and the portion other than the finger is bright and strong external light enters. When the backlight BL is turned on in this state, the light source light from the backlight BL is reflected by the finger portion, and this reflected light is input to the readout unit, so that a bright image with low contrast as a whole is obtained. .
Conversely, when the outside light is weak, there is almost no influence of the outside light, and the light source light from the backlight BL is reflected by the finger, and this light is detected. Therefore, an image with high contrast in which the finger portion is selectively a bright signal can be obtained.

(2) of FIG. 7 shows a case where the backlight BL is off. When the external light is strong, since the external light is blocked by the finger in the shadow portion of the finger, an image with high contrast is obtained in which the finger portion is a dark shadow signal.
Conversely, when the outside light is weak, the shadow portion of the finger becomes black, but the outside light is also weak in the other portions, so that a dark image with a low contrast is obtained as a whole.

As described above, the obtained image changes depending on the intensity of the external light. Therefore, when only one of the image in the external light detection period or the image in the reflected light detection period is used, accurate position detection may be difficult.
In order to prevent this, for example, an illuminance sensor can be provided and an image to be used can be selected according to the intensity of external light. However, when the intensity of external light is not known, it is determined which image should be used. It is difficult. Of course, one of the first and second periods may be selected and operated based on the detection result of the illuminance sensor.

  In the present embodiment, an accurate finger input pattern is obtained by calculating two types of detection images obtained in the first period (reflected light detection) and the second period (external light detection). To win.

  Here, in these detected images, (i) the external light pattern and the reflected light pattern are in a negative image relationship with each other, and (ii) one of the images obtained by the intensity of the external light is clear on one side. There is a fact that a finger input pattern is obtained. Therefore, a desired pattern can be obtained by performing a logical operation so as to further clarify a black and white (binary) image of both images.

For example, after binarizing each image, the image when the backlight BL is on is inverted. Then, an AND operation is performed on the inverted image and the image when the backlight BL is off. By this calculation process, an image in which the finger is black is obtained.
Alternatively, each image is binarized and the image when the backlight BL is off is inverted. Then, an OR operation between the inverted image and the image when the backlight BL is on is executed. By this calculation process, an image with a finger whitened is obtained.
Each image is binarized and an EOR (exclusive OR) operation is performed. By this calculation process, an image in which the finger is black is obtained.

Further, in addition to the above-described logical operation, the luminance difference between both images may be calculated and binarized according to the result, or the quotient of both images may be calculated and binarized according to the result. This is because both have the function of emphasizing light and shadow.
Further, the above-described processes may be performed in combination.

  In the first embodiment, three types of gate lines (display gate line, precharge gate line, and signal readout gate line) are provided. Therefore, in a liquid crystal device using amorphous silicon, it is necessary to prepare three types of gate drivers, and the number of pads to be mounted outside increases, resulting in an increase in external dimensions. Therefore, in the first embodiment, low-temperature polysilicon is used and a gate driver is built on the glass. Similarly, the source side that supplies the image also needs to form a detection circuit or the like, which is also formed of a low-temperature polysilicon circuit. The low temperature polysilicon type active matrix system is suitable for configuring the first embodiment.

  In the above-described embodiment, scanning is performed in a quarter frame period. However, by increasing the scanning speed, the time aperture ratio can be improved, and in particular, by using the OCB type liquid crystal, the time aperture ratio is improved. Can be expected.

[Second Embodiment]
In the second embodiment, a reflected light detection period different from that in the first embodiment is provided. Accordingly, the same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 8 is a time chart for explaining a read operation according to the second embodiment.
The horizontal axis in the figure represents time, and the time changes from left to right. The vertical axis represents the scanning position of the screen, the upper end portion indicates the upper end position of the screen, and the lower end portion indicates the lower end position of the screen.

  As in the first embodiment, each frame period is divided into a first period and a second period, and the first period corresponding to a ¼ frame period is used to detect outside light and prevent reverse transition of the OCB liquid crystal described later. A second period corresponding to a 3/4 frame period is allocated to reflected light detection and image display. In this embodiment, since the entire second period is assigned to the reflected light detection period, a high S / N ratio can be obtained and detection accuracy can be improved.

  Similar to the first embodiment, the display gate line is set in an active state over a quarter frame period, and a black image for detecting external light is written from the signal line to the pixel PX, and the precharge gate line is set in the active state. A precharge for detecting external light is executed through the charge line. This operation is realized by sequentially scanning the display gate line and the precharge gate line from the upper end of the screen toward the lower end of the screen. Therefore, on the display screen, black images are sequentially displayed from the upper end of the screen toward the lower end of the screen.

  The external light detection period for each scanning line is set to a ¼ frame period, and the voltage held in the sensor capacitor of the reading unit is determined based on the external light amount in the external light detection period. The backlight BL is turned off until the external light detection period for all the scanning lines ends.

  Then, in synchronization with the end of each external light detection period, the signal read gate line is set in an active state to read the external light detection signal to the signal read line.

Simultaneously with the above readout, the display gate line is activated for a quarter frame period, and display image information is written from the signal line to the pixel PX, and the precharge gate line is activated and the precharge line is activated. Then, the reflected light detection precharge is executed.
This operation is scanned from the upper end of the screen toward the lower end of the screen. The backlight BL is turned on when the writing of display image information to each scanning line is completed.

  Then, after the reflected light detection precharge is completed and the 3/4 frame period elapses, the reflected light detection signal is sequentially read out to the signal readout line by setting the signal readout gate line to an active state over a 1/4 frame period. This operation is also executed by sequentially scanning from the upper end of the screen toward the lower end of the screen. When the backlight BL is turned on, the black image writing for the external light detection period of the next frame is started from the time when the writing of the image information is completed so that a good image information display can be realized without in-plane luminance gradient. It is set in between.

Next, a method for processing the read detection signal will be described.
In the second embodiment, each reading unit includes a period in which the backlight BL is off and a period in which the backlight BL is on in the reflected light detection period.
Therefore, the signal detected in the reflected light detection period is a signal in which the backlight BL signal shown in (1) and (2) of FIG. 7 is combined with the ON signal.

  By the way, the liquid crystal panel is in a transmissive state only in the reflected light detection period and when the backlight BL is lit. For this reason, it is considered that the same light input as that in the external light detection period is performed in the reflected light detection period in which the backlight BL is turned off. The proportion of the reflected light detection period during which the backlight BL is extinguished is constant in any reading unit. Therefore, a predetermined relationship is established between the amount of charge discharged from the sensor capacitor during the reflected light detection period when the backlight BL is turned off and the amount of charge discharged from the sensor capacitor during the external light detection period. Therefore, by correcting the signal detected during the reflected light detection period with the signal detected during the external light detection period, the detection signal during the period when the backlight BL is lit can be calculated.

  Since the subsequent processing is the same as that of the first embodiment, detailed description thereof is omitted.

[Third Embodiment]
In the third embodiment, the on / off period of the backlight BL is different from that of the second embodiment. Accordingly, the same parts as those of the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 9 is a time chart for explaining the read operation of the third embodiment.
In the third embodiment, the backlight BL is turned on when the signal reading for the external light detection period is executed at the upper end of the screen, and is turned off when the signal reading for the reflected light detection period is executed at the lower end of the screen. To do.
Accordingly, the backlight BL is lit even during the outside light detection period, but since the black display is performed during this period, the illumination of the finger by the backlight BL can be ignored and the influence on the detection signal is not considered. Also good.

  In the present embodiment, two types of detection images of the reflected light detection period and the external light detection period are obtained, and the finger input pattern is calculated by calculating these two types of images. Since this calculation method has been described in the first embodiment, a duplicate description is omitted.

[Fourth Embodiment]
In the fourth embodiment, the configuration of the liquid crystal display element is different from that of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 10 is a diagram showing an equivalent circuit configuration of the liquid crystal display element of the fourth embodiment.
In the fourth embodiment, the precharge line and the signal readout line are shared to form a shared line, and the precharge gate line and the signal readout gate line are shared to form a shared gate line. With this configuration, two wires can be reduced, and a significant improvement in aperture ratio can be realized.

  In order to realize this operation, the precharge gate pulse and the signal readout gate pulse are switched and output from the common gate line, and the precharge and the signal readout common line that are vertical wirings are pre-charged accordingly. Supply and signal readout were switched alternately every horizontal scanning period. For this reason, although the scanning period is twice that of the above embodiment, the time aperture ratio can be prevented from decreasing by increasing the scanning speed at this time.

[Fifth Embodiment]
In the fifth embodiment, the configuration of the liquid crystal display element is different from that of the first embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 11 is a diagram showing an equivalent circuit configuration of the liquid crystal display element of the fifth embodiment.
In the fifth embodiment, the precharge gate line and the signal readout gate line are shared to form a shared gate line, and the Cst line used for liquid crystal display is diverted as the precharge line. With this configuration, it is possible to reduce the number of wirings and realize a significant improvement in aperture ratio.

Since the precharge line functions to charge the sensor capacitor with a constant value of charge, a fixed precharge power source may be used. In the fifth embodiment, the Cst line and the precharge line used for the liquid crystal display can be switched and used.
A charge corresponding to the pixel voltage is stored in the auxiliary capacitor Cst. By applying the compensation voltage Ve to the Cst line connected to the auxiliary capacitor Cst at a predetermined timing, the fluctuation of the pixel voltage due to the influence of the parasitic capacitance when the pixel TFT becomes non-conductive can be substantially canceled. .

In the fifth embodiment, scanning is performed by switching the precharge gate pulse and the signal readout gate pulse from the shared gate line, and in accordance with this, the precharge potential is supplied to the fixed potential line, and the signal is read from the readout unit to the signal readout line. Read the signal.
When supplying the precharge voltage to the fixed potential line (Cst line), a switch (not shown) switches the fixed potential line (Cst line) to a precharge power source (not shown) and connects them. After the charging is completed, a switch (not shown) switches the connection of the fixed potential line (Cst line) to the reading IC that is in the original state.

[Sixth Embodiment]
In the sixth embodiment, the configuration of the liquid crystal display element is different from that of the first embodiment. The same parts as those in the sixth embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 12 is a diagram showing an equivalent circuit configuration of the liquid crystal display element of the sixth embodiment.
In the sixth embodiment, the signal line and the signal readout line of the fifth embodiment are further shared. With this configuration, it is possible to reduce the number of wirings and realize a significant improvement in aperture ratio.

  In the sixth embodiment, since three types of signals including a display signal, a read display signal, and a read signal flow through the shared line, the three functions are switched in time series. As a result, one system is sufficient for the vertical wiring.

  Furthermore, sharing can be further promoted so that the display gate line, the precharge gate line, and the signal readout gate line can be shared. At this time, it is necessary to realize a gate line sharing four roles of display signal supply, read display signal supply, precharge, and signal read, and four types of high-speed switching and scanning are required. As a result, the horizontal wiring can be integrated into one system.

[Seventh Embodiment]
In the seventh embodiment, the configuration of the liquid crystal display element and the driving method thereof are different from those of the first embodiment. The same parts as those in the seventh embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

FIG. 13 is a diagram showing an equivalent circuit configuration of the liquid crystal display element of the seventh embodiment.
In the seventh embodiment, in the circuit configuration of the liquid crystal display element shown in FIG. 2, a potential addition circuit for controlling the potential direction in which charge leaks is connected to the end of the sensor capacitor. The operation of this potential addition circuit will be described later.

FIG. 14 is a time chart for explaining a read operation according to the seventh embodiment.
In this time chart, even when the external light detection period ends, signal readout and reflected light detection precharge are not executed. Then, when the backlight BL is turned on, a reflected light detection period is substantially started, and signal reading is performed at the timing when the backlight BL is turned off. That is, the signal readout is different from the above-described embodiments in that the signal is read once in, for example, one frame period including the external light detection period and the reflected light detection period. As will be described later, the reference potential at one terminal of the sensor capacitor is changed substantially in synchronization with the on / off of the backlight BL.

FIG. 15 is a diagram showing a change in potential of the terminal of the sensor capacitor.
The horizontal axis in the figure represents time, and the time changes from left to right. The vertical axis represents the potential of the sensor capacitance terminal.

When precharge for detecting external light is executed, the terminal of the sensor capacitor is set to the precharge potential. When the backlight BL is turned off, the potential adding circuit adds a high potential to the sensor capacitor terminal accordingly. As a result, the “leak waveform” rises stepwise in the figure.
By adding a high potential, if the light of the sensor capacitance leaks due to light, the potential increases toward the high potential, and as a result, the sensor capacitance increases with time according to the amount of light received. The terminal potential rises. At this time, the potential change amount of the portion that directly receives external light is larger than the potential change amount of the shaded portion.

Next, when the backlight BL is turned on, the potential adding circuit applies a low potential to the sensor capacitor terminal accordingly. As a result, in the figure, the “leak destination waveform” is stepped down.
Similarly, when the charge of the sensor capacitor leaks due to the addition of the low potential, the potential decreases toward the low potential, and as a result, the terminal potential of the sensor capacitor with time corresponds to the amount of received light. Descend. At this time, the potential change amount of the portion that receives the reflected light is larger than the potential change amount of the shaded portion.
As a result, when the signal is read at the timing when the backlight BL is turned off, the pattern when the backlight is on is opposite to the pattern when the backlight is turned off. By performing the correction, the finger image and the surrounding image can be easily separated.

  According to the present embodiment, for example, signals can be read out once in one frame period, and there is an advantage that only one set of memory for storing the read signals can be used or not. In the present embodiment, the processing performed by the calculation in each of the above-described embodiments is executed in an analog manner by switching the leak destination potential inside the panel.

  In the present invention, the backlight may be modulated at a high frequency and a specific frequency component may be detected in synchronization therewith. In this case, the detection sensitivity can be greatly increased. At this time, it is not necessary to blink the backlight at the frame frequency, and it may be combined with high-frequency pulse width dimming (PWM dimming) for dimming the light intensity of the backlight. At this time, the frequency is usually a high frequency of 400 Hz or more.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

1 is a diagram showing a schematic configuration of a liquid crystal display device according to a first embodiment of the present invention. 2 is an equivalent circuit showing the configuration of the liquid crystal display element with an optical input function according to the first embodiment of the present invention. The figure explaining the light input system by external light. The figure explaining the light input system by reflected light. FIG. 3 is a diagram illustrating an image reading method according to the first embodiment of the present invention. 3 is a time chart for explaining a read operation according to the first embodiment. The figure explaining the influence of external light and the backlight BL. 6 is a time chart for explaining a read operation according to the second embodiment. 10 is a time chart for explaining a read operation according to the third embodiment. The figure which shows the equivalent circuit structure of the liquid crystal display element of 4th Embodiment. The figure which shows the equivalent circuit structure of the liquid crystal display element of 5th Embodiment. The figure which shows the equivalent circuit structure of the liquid crystal display element of 6th Embodiment. The figure which shows the equivalent circuit structure of the liquid crystal display element of 7th Embodiment. 10 is a time chart for explaining a read operation according to the seventh embodiment. The figure which shows the electric potential change of the terminal of a sensor capacity | capacitance. The figure which shows the conventional reading method.

Explanation of symbols

  DP ... Liquid crystal display panel, CTL ... Control circuit, PX ... Liquid crystal pixel, CLC ... Capacitor component, Cst ... Auxiliary capacitance, Ve ... Compensation voltage, 100 ... Liquid crystal display device, 110 ... Display area, 112 ... Gate line drive circuit, 114 Data line driving circuit 116 Data reading processing circuit 130 Liquid crystal display device with light input function

Claims (11)

A display panel having a plurality of scanning lines in which liquid crystal display elements including optical input elements and display pixels are arranged;
A backlight arranged to face the display panel and illuminate the display panel;
Control means for controlling writing to the display pixel and reading of the detection signal of the optical input element,
The control means includes
Displaying an external light detection image that substantially shields light from the backlight on the display pixels over a first period of one frame period;
A liquid crystal display device, wherein a display image is displayed on the display pixels over a second period of the one frame period.   The control means reads out the first detection signal of the optical input element at the start of the first period and reads out the second detection signal of the optical input element at the start of the second period. The liquid crystal display device according to claim 1.   The liquid crystal display device according to claim 2, wherein the control unit includes an arithmetic processing unit that performs arithmetic processing based on the result of reading the first detection signal and the result of reading the second detection signal.   2. The liquid crystal display device according to claim 1, wherein the control unit turns off the backlight from the start of the first period in the scanning line to the end of the first period in all the scanning lines. . 2. The liquid crystal display device according to claim 1, wherein the control means reads the detection signal of the optical input element at either the start of the first period or the start of the second period.   The liquid crystal display device according to claim 1, wherein the display pixel includes an OCB liquid crystal sandwiched between a pair of electrodes.   The liquid crystal display device according to claim 6, wherein the external light detection image is formed by applying a voltage of a level higher than a level at which the spray alignment energy and the bend alignment energy antagonize between the electrodes. A display panel having a plurality of scanning lines in which liquid crystal display elements including optical input elements and display pixels are arranged;
A backlight arranged to face the display panel and illuminate the display panel;
A backlight blinking means for blinking the backlight;
Control means for controlling writing to the display pixel and reading of the detection signal of the optical input element,
The liquid crystal display device, wherein the backlight is configured to be blinkable, and the control means changes a reference potential in synchronization with the blinking of the backlight. The control means includes
Displaying an external light detection image that substantially blocks light from the backlight on the display pixels over a first period of one frame period and turning off the backlight;
9. The liquid crystal display device according to claim 8, wherein a display image is displayed on the display pixels and the backlight is turned on over a second period of the one frame period.   The liquid crystal display device according to claim 9, wherein the control unit reads a detection signal from the optical input element at the end of the second period.   The liquid crystal display device according to claim 8, wherein the display pixel includes an OCB liquid crystal sandwiched between a pair of electrodes.

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