JP2014006456A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the effect of noise at the time of touch detection, without being affected by noise due to lighting control of a back light, and to enable touch detection with high accuracy of detection.SOLUTION: A touch detection unit uses a touch panel 17 for the touch detection of a proximity object. The touch detection unit performs touch detection after a scanning period when a screen is scanned in one frame period when video is displayed on a liquid crystal panel 14. A back light 16 lights up the back light after a touch detection period, and after the response of liquid crystals of pixels of the liquid crystal panel 14 illuminated by the back light has completed.

Description

  The present invention includes a display device, and more specifically, a display that includes a display unit, a backlight that illuminates the display unit, and a touch detection unit that detects an external proximity object, and suppresses the generation of noise during touch detection. Relates to the device.

  By mounting a touch detection device that detects an external proximity object on a display device such as a liquid crystal display device, or by integrating the touch detection device with the display device and displaying various button images and the like on the display device, Display devices capable of inputting information in place of ordinary mechanical buttons are rapidly spreading and expanding. Such a display device is widely used not only for portable terminals and tablet terminals but also for automatic ticket machines and electronic white boards. In the future, the application to PCs (Personal Computers), televisions, etc. is expected to expand.

  Regarding the technology of a display device having a touch detection function, for example, Patent Document 1 discloses a display device for performing touch detection while suppressing the influence of noise. The display device includes a plurality of display elements that perform a display operation based on a pixel signal and a display drive signal, a touch detection element that detects an external proximity object based on a touch detection drive signal, and a pixel signal that is output to the plurality of display elements. The display scanning is performed by sequentially supplying time-divisionally, the scanning drive unit supplying the touch detection drive signal to the touch detection element, and the detection result from the touch detection element are sampled at a cycle shorter than the cycle of the display scan. A touch detection unit that detects the touch. The scan driving unit supplies a touch detection drive signal to the touch detection element in a touch detection operation period different from a display operation period in which display scanning is performed.

JP 2012-48295 A

  As touch detection devices, resistive type, ultrasonic type, capacitive type, optical type touch panel and proximity sensor type detection such as capacitive type, inductive type, ultrasonic type, electromagnetic wave type, infrared type etc. The device is known. In particular, since it has a relatively simple structure and can realize low power consumption, it is expected that capacitance type touch detection devices will be expanded in the future.

  However, in the capacitive touch detection device, the stability of the detection operation is impaired by noise generated inside the display device in addition to external noise caused by, for example, an inverter fluorescent lamp, an AM wave, or an AC power source. There is a problem of reducing detection sensitivity. In particular, in a display device using a liquid crystal panel, noise due to a liquid crystal drive signal becomes a problem. Further, in a display device including a backlight for illuminating a liquid crystal panel, noise when the backlight is turned on becomes a significant noise source. For example, when a backlight that controls a large current is turned on / off during touch detection, noise is mixed in the detection result of the touch detection device. Moreover, the noise source inside the display device is not limited to the capacitance type, and affects the touch detection accuracy of the touch detection device.

  FIG. 7 is a diagram for explaining an example of a backlight lighting period and touch detection timing. FIG. 7A shows a scanning period based on a video signal, FIG. 7B shows a backlight lighting period, FIG. 7C shows the timing of touch detection. Here, an example is shown in which normal display is performed in which one frame period is about 16.7 msec (60 Hz).

  As shown in FIG. 7A, one frame period of video display is composed of a scanning period S and a blanking period B in which scanning is paused. In the scanning period S, a voltage corresponding to each of the selection period and the non-selection period is output and scanned to the scanning signal line of the liquid crystal panel of the display unit, and the data signal of the video signal is output to the data signal line and selected. Image data is supplied and written to each of the pixels on the scanning signal line, and display according to the video signal is performed. The luminance of the pixel corresponding to the written image data is held for one frame period. The total period of the scanning period S and the blanking period B is one frame period. In normal display at 60 Hz, one frame period is about 16.7 msec.

  In FIG. 7B, the backlight lighting period L is set intermittently. Further, the backlights of a plurality of regions (four regions in FIG. 7B) are sequentially turned on while shifting the lighting period L. The backlight here performs pseudo impulse driving in which lighting periods and extinguishing periods are alternately provided in order to reduce motion blur. By performing pseudo impulse drive, for example, when there is a moving object in the screen, the area where the time integral value of the brightness becomes an intermediate value is narrowed, and the motion blur caused by the intermediate value is reduced. Can be made. At this time, not only simply blinking the backlight, but also dividing the backlight into a plurality of areas, and lighting the divided area backlights sequentially in synchronization with the video write end timing, etc. Control is performed.

In addition, the touch detection device appropriately sets a touch detection period for performing a touch detection operation. For example, in Cited Document 1, as shown in FIG. 7C, a touch detection period D for performing touch detection is provided in the blanking period B in the video display control. By performing touch detection in the blanking period B, the influence of noise due to the display operation is avoided. Also, cited document 1 describes that touch detection is performed at a timing at which scanning is interrupted during the scanning period in addition to the blanking period.
However, as shown in FIG. 7B, usually, the backlight lighting control is also executed during the blanking period B and the scanning period S. If touch detection is performed at this time, noise caused by the on / off of the backlight is mixed, and the detection accuracy of the contact detection device deteriorates.

FIG. 8 is a diagram for explaining another example of the backlight lighting period and the touch detection timing, in which one frame period is so-called double speed display of about 8.3 msec (120 Hz). In double-speed display, frame interpolation of an input video signal is performed to generate an interpolation frame, and display is performed at a frame rate of 120 Hz.
In the double speed display, the same problem as the normal display in FIG. 7 occurs. Here, as shown in FIG. 8A, one frame period of video display is composed of a scanning period S and a blanking period B in which scanning is paused. In this case, the period becomes 1/2.

Then, as shown in FIG. 8B, the backlight lighting period L is intermittently set, and the backlights in a plurality of regions are sequentially lighted while the lighting period L is shifted.
In addition, as shown in FIG. 8C, the touch detection device provides a touch detection period D for performing touch detection in a blanking period B in video display control. Alternatively, touch detection can be performed at a timing at which scanning is interrupted during the scanning period other than the blanking period.
However, as shown in FIG. 8B, the backlight lighting control is also executed during these blanking periods and display scanning periods even during double-speed display. If touch detection is performed at this time, noise caused by turning on / off the backlight is mixed, and the detection accuracy of the touch detection device deteriorates.

Some display devices perform so-called quadruple speed display in which display is performed at a frame rate of 240 Hz. At a frame rate of 240 Hz, for example, as a 3D display image, a right-eye image is alternately displayed every two frames, and the same image is continuously displayed for two frames.
Even in this case, if the backlight lighting control is performed during the touch detection period in the same manner as described above, the detection accuracy of the touch detection device deteriorates due to noise caused by the backlight on / off. Occurs.

In the display device disclosed in Patent Document 1, touch detection is performed in a touch detection operation period different from the display operation period in which display scanning is performed. Specifically, touch detection is performed during the blanking period when the display operation period ends. In addition, an example in which touch detection is performed during a period when the display operation is interrupted, or even during the display operation period, the detection signal is sampled at a slight timing until the pixel position signal of each pixel is applied to the data signal line. An example of touch detection is also described.
However, in the display device of Patent Document 1, it is necessary to perform touch detection in an area corresponding to the entire screen in a very short time such as a blanking period, and it is difficult to stably perform high-precision touch detection. there were.

  The present invention has been made in view of the above circumstances, and reduces the influence of noise at the time of touch detection without receiving noise due to backlight lighting control, and provides a sufficient touch detection period. It is an object of the present invention to provide a display device that can stably perform highly accurate touch detection.

  In order to solve the above-described problem, a first technical means of the present invention is a display unit in which pixels made of liquid crystal modulation elements are arranged in a matrix, and a line of each pixel of the display unit is divided into a plurality of scanning signal lines. And a display control unit that displays the video on the display unit by driving the liquid crystal by supplying the data signal from the data signal line to the pixels of the selected line and scanning the line sequentially by the line, and the display unit A display device comprising: a touch detection unit that is provided near or close to the touch detection unit and detects a touch by an external proximity object; and a backlight including a light source that illuminates the display unit. In one frame period of video to be displayed, the touch detection unit detects the touch after a scanning period in which the display control unit scans one screen with a plurality of scanning signal lines of the display unit ends. The backlight turns on the light source after a period for performing the operation for detecting the touch, and the period for turning on the light source is a response of the liquid crystal modulation element of the display unit driven in the scanning period. After completion of the above, the light source corresponding to the liquid crystal modulation element for which the response has been completed is turned on.

  According to a second technical means, in the first technical means, the backlight performs lighting control of the light source for each of a plurality of areas corresponding to a region obtained by dividing the pixel region of the display unit into a plurality of regions. It is a feature.

  According to a third technical means, in the first or second technical means, the liquid crystal modulation element of each pixel of the display unit includes a transistor for controlling writing of an image signal to each pixel, and the semiconductor layer of the transistor Is characterized by containing an oxide semiconductor.

  According to the present invention, it is possible to reduce the influence of noise at the time of touch detection without receiving noise due to backlight lighting control, and to provide a sufficient touch detection period, thereby enabling high-precision touch detection. It is possible to provide a display device capable of stably performing the above.

It is a block diagram which shows the principal part of the structural example of the display apparatus which concerns on this invention. 4 is a timing chart showing an example of video display control and backlight control in the display device according to the present invention. It is a timing chart which shows the other example of the video display control in the display apparatus by this invention, and backlight control. It is a figure which shows an example of the characteristic of TFT using the TFT using a-Si, and the oxide semiconductor comprised from In-Ga-Zn. It is a figure explaining the other example of the lighting period of a backlight, and a touch detection timing. It is a figure explaining the further another example of the lighting period of a backlight, and a touch detection timing. It is a figure explaining the example of the lighting period of the conventional backlight, and a touch detection timing. It is a figure explaining the other example of the lighting period of the conventional backlight, and a touch detection timing.

FIG. 1 is a block diagram showing a main part of a configuration example of a display device according to the present invention.
The video signal to be displayed on the display device is input to the timing control unit 11. The timing control unit 11 supplies control signals to the data driver 12, the gate driver 13, the backlight control unit 15, the touch detection driver 18, the touch position detection unit 19, and the shutter glasses control unit 20, respectively. It is a circuit part which controls so that it may operate | move synchronously.

  The video signal input to the timing controller 11 is subjected to double speed interpolation processing as necessary. The double speed interpolation process is an interpolation process for performing a double speed display by performing a conversion process of the frame rate of the input video signal. Here, interpolation processing for interpolating between frames is performed on the video data of the input video signal, whereby the frame frequency is multiplied by n (n is a natural number of 2 or more) before interpolation. For example, in the double-speed interpolation processing, an interpolated frame between frames is generated by motion compensation using a motion vector of an input video signal, and the generated interpolated frame signal is sequentially output together with the input frame signal, so that the input image signal The frame rate is converted from 60 frames per second (60 Hz) to 120 frames per second (120 Hz) at double speed. Alternatively, a 60 Hz input video signal can be converted to 240 Hz at a quadruple speed and output.

  In addition, when the display device corresponds to the 3D display mode and performs display in the 3D display mode, a quadruple speed interpolation process is performed, and at this time, the same frame image for the right eye is displayed twice in succession, The same frame image is displayed twice in succession, and so-called double writing can be performed in which this is repeated alternately. Double writing is performed in order to avoid a deterioration in display quality due to a delay in the response of the liquid crystal when video data is written and a lack of transmittance due to a change in the capacitance of the liquid crystal modulation element.

  The liquid crystal panel 14 corresponds to the display unit of the present invention, and includes a screen on which pixels made up of liquid crystal modulation elements are arranged in a matrix, a plurality of scanning signal lines that select and scan the screen in line sequence, And a plurality of data signal lines for supplying data signals to the pixels of the selected line. The scanning signal line and the data signal line are orthogonal to each other.

  The gate driver 13 is a scanning signal line driver, and outputs a voltage corresponding to each of the selection period and the non-selection period to each scanning signal line of the liquid crystal panel 14 under the control of the timing control unit 11. The data driver 12 is a data signal line driver, outputs a data signal to each data signal line of the liquid crystal panel 14, and supplies image data to each pixel on the selected scanning signal line.

The timing controller 11 provides a gate start pulse signal and a gate clock signal to the gate driver 13, and provides RGB data, a source start pulse signal, a source latch strobe signal, and a source clock signal to the data driver 12. All these signals are synchronized.
The gate driver 13 starts scanning the liquid crystal panel 14 in response to the gate start pulse signal, and sequentially applies a selection voltage to each scanning signal line in accordance with the gate clock signal. Based on the source start pulse signal, the data driver 12 stores the received gradation data of each pixel in a register in accordance with the source clock signal, and applies gradation to each data signal line of the liquid crystal panel 14 in accordance with the next source latch strobe signal. Write data.

The timing controller 11 can control the driving frequency of the liquid crystal by setting the pulse interval of the gate start pulse signal. The pulse interval of the gate start pulse signal is about 16.7 msec when the display frame frequency is a normal 60 Hz. This value is called a data refresh cycle. When the liquid crystal is driven at double speed for display, the data refresh cycle is about 8.3 msec. In addition, when the liquid crystal is driven at a quadruple speed and displayed, the data refresh cycle is about 4.2 msec. The timing control unit 11 controls the length of one scanning period by setting the driving frequency of the gate clock signal.
The display control unit of the present invention corresponds to the timing control unit 11, the gate driver 13, and the data driver 12.

  When scanning one vertical period of the liquid crystal panel, the scanning period is the scanning period from the uppermost scanning signal line to the last scanning signal line in one vertical period, and the remaining period is the blanking period during which the liquid crystal driving is suspended. It is.

The backlight control unit 15 controls light emission of the backlight 16 that illuminates the liquid crystal panel 14 according to the control by the timing control unit 11. By modulating the light emission of the backlight 16 by the liquid crystal panel 14, an image corresponding to the image data can be displayed on the liquid crystal panel 14.
The backlight 16 can be comprised from the light source by several LED (Light Emitting Diode), for example. Further, the backlight 16 can perform light emission control for each of a plurality of areas (for example, areas 1 to 4), and an area obtained by dividing the pixel area of the liquid crystal panel is associated with each area. For example, each LED of the backlight is caused to emit light at a predetermined timing for each area of the backlight 16 corresponding to the divided area of the liquid crystal panel 14 in synchronization with the writing scanning of the video gradation data to the divided area of the liquid crystal panel 14. be able to.

The touch panel 17 is a capacitance type device that detects a touch position by a user or the like, and is configured as an in-cell type touch panel integrated with the liquid crystal panel 14 or a touch panel mounted close to the liquid crystal panel 14. Can do.
The touch panel 17 includes a plurality of stripe-shaped drive electrodes and a plurality of stripe-shaped touch detection electrodes extending in a direction orthogonal to the direction in which each drive electrode extends. In the electrode pattern in which the drive electrode and the touch electrode intersect, capacitance is formed at the intersecting portion. As a result, electrostatic capacity is formed in a matrix on the entire screen of the liquid crystal panel 14.

  The touch detection driver 18 sequentially supplies drive signals to the plurality of stripe-shaped drive electrodes of the touch panel 17 and performs line-sequential scanning drive in a time division manner. Then, according to this line sequential scanning drive, the touch electrode that intersects the drive electrode outputs a touch detection signal. The touch position detection unit 19 detects the touch position of a proximity object such as a user based on the touch detection signal output from the touch electrode of the touch panel 17. The touch detection result detected by the touch position detection unit 19 is output to a control unit (not shown), and control according to the touch position is performed. The touch detection unit of the present invention corresponds to the touch panel 17, the touch detection driver 18, and the touch position detection unit 19.

  The shutter glasses controller 20 is used to display an image in an active shutter 3D display mode. The shutter glasses control unit 20 generates a drive signal for driving active shutter glasses (not shown) based on the synchronization signal from the timing control unit 11, and transmits the drive signal to the active shutter glasses wirelessly (infrared communication). To do.

  Specifically, when displaying the 3D video, the shutter glasses control unit 20 drives the left shutter of the active shutter glasses on and the right shutter off based on the synchronization signal of the left eye video. Is output. On the other hand, the shutter glasses controller 20 outputs a drive signal for turning on the right shutter of the active shutter glasses and turning off the left shutter based on the synchronization signal of the right-eye video. The shutter glasses control unit 20 controls the driving of the active shutter glasses by alternately outputting the above drive signals. In addition, when double-speed interpolation processing is performed to display the same video frame for the same eye twice in succession, and so-called double writing that repeats this alternately, 3D display is performed, according to the display video Perform shutter control.

  FIG. 2 is a timing chart showing an example of video display control and backlight control in the display device according to the present invention. In the liquid crystal panel of the display device, a video signal is written by vertical scanning from the uppermost pixel. That is, the video is updated in order from the first line (N = 1) of the scanning signal line, which is a horizontal line of the liquid crystal panel, and the video of the last scanning signal line at the bottom is updated while the writing timing is gradually delayed. The updated video is held for one frame period. There are various numbers of scanning signal lines. For example, in the case of a liquid crystal panel having 1080 pixels × 1920 pixels, N = 1080.

Here, in order to simplify the description, it is assumed that the number of scanning signal lines N of the liquid crystal panel 14 is N = 20. In the backlight, it is assumed that the lighting region is divided into four, and the divided region of the lighting region is set corresponding to each scanning signal line N = 5 rows. Here, the scanning electrodes SCL corresponding to the pixels of the scanning signal lines for 20 rows are represented by reference numerals SCL1 to SCL20 in the order of line-sequential scanning. The liquid crystal transmittance of the pixel scanned by the last scan electrode SCL20 that is scanned line-sequentially is indicated as the liquid crystal transmittance 20.
Further, the control lines BCL of the divided areas of the backlight are represented by BCL1 to BCL4 in order from the top. In this case, the pixels corresponding to the scan electrodes SCL1 to SCL5 are illuminated by the backlight controlled by BCL1. Hereinafter, the backlight control lines in the respective divided regions correspond to the five scan electrodes.

  The period T indicates a length obtained by dividing one frame period into 40 for the sake of explanation, and scanning of the scanning signal lines of N = 1 to 20 is completed within a period of 15T in one frame period. To do. One frame period is a period of 40T. Therefore, the blanking period after the scanning in one frame period is 25T after the 15T scanning period. This example shows an example at the time of normal display with a normal frame frequency of 60 Hz, and one frame period is about 16.7 msec.

  In the embodiment according to the present invention, the touch detection period by the touch panel is set after the scanning period ends. The backlight lighting period is set after the touch detection is completed and after the response of the liquid crystal elements of the liquid crystal panel 14 corresponding to each backlight is completed. As a result, the backlight is turned on after the response of the liquid crystal element is completed, and a touch detection period is provided between them, so that a sufficient touch detection period can be provided within one frame period, and high-accuracy touch detection is stable. And be able to do it.

  In order to turn on the backlight after the response of the liquid crystal element is completed within one frame period, it is necessary to end the scanning period in a short time and secure a blanking period. In order to realize this, in the embodiment according to the present invention, a semiconductor layer of a thin film transistor that constitutes a TFT (Thin Film Transistor) of the liquid crystal panel 14 may include an oxide semiconductor. As the oxide semiconductor, an oxide of In—Ga—Zn (indium-gallium-zinc) can be used. The function and characteristics of the oxide semiconductor will be described later.

  In FIG. 2, the touch detection period D is set after the scanning period. In this example, the touch detection period D is set to a length of 20T with respect to 15T of the scanning period. Here, the touch detection driver 18 sequentially supplies drive signals to the plurality of stripe-like drive electrodes of the touch panel 17 and performs line-sequential scanning drive in a time division manner. Then, according to this line sequential scanning drive, the touch electrode that intersects the drive electrode outputs a touch detection signal. The touch position detection unit 19 detects the touch position of the user or the like based on the touch detection signal output from the touch electrode of the touch panel 17. By performing touch detection after the display scan is completed, the influence of noise due to the display operation is avoided.

In order to prevent the backlight on / off control during the touch detection period and to turn on the backlight after the liquid crystal response is completed, the backlights of the four regions controlled by BCL1 to BCL4 are turned on. The period L is set after the touch detection period D and is controlled so that each backlight emits light after the response of the corresponding liquid crystal element is completed.
In this case, since the scanning with respect to the lowermost scanning electrode SCL20 is the last within one frame period, after the scanning electrode SCL20 is finished, the backlight lighting period is reached at the timing when the liquid crystal response is completed. L is provided. In this example, all the backlights are turned on at the same timing, and the touch detection period D is set between the backlight lighting period L and the scanning period.
Here, as shown by the liquid crystal transmittance 20, the backlight lighting period L is provided after the response of the liquid crystal driven by the lowermost scan electrode SCL20 is completed and the transmittance corresponds to the target gradation. The time for which the response of the liquid crystal is completed is the maximum value of the time required to reach the target gradation when the gradation of the liquid crystal is changed, and is uniquely determined according to the display device.

  With the above timing control, it is possible to prevent deterioration of touch detection accuracy due to backlight on / off, and a touch detection period can be sufficiently long within one frame period. Touch detection can be performed stably.

  FIG. 3 is a timing chart showing another example of video display control and backlight control in the display device according to the present invention. Similar to FIG. 2, the timing chart of FIG. 3 shows an example of the control timing when the backlight is controlled to emit light in four divided areas with the number N of scanning signal lines (horizontal lines) N = 20. Here, one frame period of the display video is displayed by performing double speed interpolation processing at double speed. Therefore, one frame period of the display video is a ½ frame period of the input video signal. Here, one frame period of the display image is about 8.3 msec.

The period T indicates a length obtained by dividing one frame period into 40 equal parts for the sake of explanation, and therefore, the length of 1T in FIG. 3 is longer than the length of 1T in normal display shown in FIG. That is halved. Here, scanning of scanning signal lines with N = 1 to 20 is completed within a period of 20T in one frame period. One frame period is a period of 40T. Therefore, the blanking period after the scanning in one frame period is 20T after the 20T scanning period.
Further, among the scanning electrodes SCL1 to SCL5 corresponding to the uppermost divided area of the four divided areas of the backlight, the liquid crystal transmittance of the pixel scanned by the lowermost scanning electrode SCL5 in which the line sequential scanning is last. Is expressed as a liquid crystal transmittance of 5. Similarly, the liquid crystal transmittance of a pixel scanned by the lowermost scan electrode SCL20 in which line sequential scanning is last among the scan electrodes SCL16 to SCL20 corresponding to the lowermost divided region of the four divided regions of the backlight. Is expressed as a liquid crystal transmittance of 20.

  In FIG. 3, the touch detection period D is set after the scanning period. In this example, the touch detection period D is set to a length of 15T with respect to 20T of the scanning period. The touch detection driver 18 sequentially supplies drive signals to the plurality of stripe-shaped drive electrodes of the touch panel 17 and performs line-sequential scanning drive in a time division manner. Then, according to this line sequential scanning drive, the touch electrode that intersects the drive electrode outputs a touch detection signal. The touch position detection unit 19 detects the touch position of the user or the like based on the touch detection signal output from the touch electrode of the touch panel 17. By performing touch detection after the scanning period ends, the influence of noise due to the display operation is avoided.

In order to prevent the backlight on / off control during the touch detection period and to turn on the backlight after the liquid crystal response is completed, the backlights of the four regions controlled by BCL1 to BCL4 are turned on. The period L is set after the touch detection period D and is controlled so that each backlight emits light after the response of the corresponding liquid crystal element is completed.
In this example, each backlight controlled by each of the BCL1 to BCL4 provides a lighting period at the timing when the maximum value of the time for completing the corresponding liquid crystal response has elapsed. The light emission timing of the backlight in each region is gradually delayed from the top to the bottom in order to ensure the response time of the liquid crystal. Here, as shown in the liquid crystal transmittance 5 and the liquid crystal transmittance 20, the liquid crystal response of the liquid crystal element driven by the lowermost scanning electrode SCL among the liquid crystal elements corresponding to the backlights of the divided regions is completed. Each backlight lighting period L is provided after transition to the transmittance corresponding to the target gradation.

  With the above timing control, it is possible to prevent deterioration of touch detection accuracy due to backlight on / off, and a touch detection period can be sufficiently long within one frame period. Touch detection can be performed stably.

As described above, in the display device according to the present invention, in one frame period, touch detection is performed after the scanning period in which one screen is scanned by a plurality of scanning signal lines, and the response of the liquid crystal is completed after the touch detection. The backlight is turned on later.
In a normal liquid crystal panel, the gradation is determined for each frame period based on the video signal to be displayed. Therefore, if the gradation is changed, the liquid crystal moves in response to the changed gradation, and after the change The liquid crystal is stabilized in a state corresponding to the gradation of. When the backlight is turned on while the liquid crystal is moving, the average gray level visually recognized during the lighting period deviates from the target gray level, which may be a cause of deterioration in video quality such as generation of a pseudo contour. Therefore, after the response of the liquid crystal at the time of changing the gradation is completed, it is possible to display an image with high image quality by turning on the backlight.

  In order to turn on the backlight after waiting for the response of the liquid crystal as described above, it is effective to shorten the scanning period of one frame period. As a result, the time from the scanning to the scanning in the next frame becomes long, so the backlight is turned on after waiting for the response time of the liquid crystal according to the gradation change at the time of scanning. Becomes easier.

  In order to shorten the scanning period, it is necessary to increase the driving frequency of the liquid crystal to increase the data writing speed. In order to realize high-speed data writing, a semiconductor layer of a thin film transistor that constitutes a thin film transistor (TFT) of the liquid crystal panel 14 can include an oxide semiconductor. As the oxide semiconductor, an oxide of In—Ga—Zn (indium-gallium-zinc) can be used.

FIG. 4 is a diagram illustrating an example of characteristics of a TFT using a-Si and a TFT using an oxide semiconductor composed of In-Ga-Zn (indium-gallium-zinc).
In the TFT drain current-gate voltage switching characteristics using an oxide semiconductor composed of In-Ga-Zn, the leakage current (off current) that flows when the TFT is turned off is generally used in the past. The leakage current due to amorphous silicon (a-Si) is, for example, 1/1000 or less, and the on-current that flows when the TFT is switched on is, for example, 20 times or more that of the amorphous silicon.
That is, since the on-current is much larger than that of conventional amorphous silicon or the like, data writing to the pixel can be speeded up. Depending on the characteristics of the on-current at the time of switching of the TFT, it is possible to determine how much the drive frequency should be increased to shorten the scanning period.

  Further, in the case of a conventional TFT using, for example, amorphous silicon, since the leakage current is high, the pixel charge is discharged during the blanking period and the luminance changes. Therefore, if the blanking period is lengthened, flicker occurs on the display screen. . In contrast, in a TFT using an oxide semiconductor composed of In—Ga—Zn, leakage current is low, so that charge of a pixel is not lost even during a blanking period, and image quality is maintained without causing flicker. be able to. Therefore, for example, when a still image is displayed, the blanking period can be extended without degrading the image quality, and the backlight lighting period is set after the liquid crystal response at the time of gradation change is completed. Can be performed more easily.

  FIG. 5 is a diagram for explaining another example of the backlight lighting period and the touch detection timing. FIG. 5A is a scanning period based on a video signal in double-speed display (one frame period = about 8.3 msec). 5B is a backlight lighting period corresponding to the scanning period of FIG. 5A, FIG. 5C is a scanning period set shorter than that of FIG. 5A, and FIG. Is a backlight lighting period corresponding to the scanning period of FIG. 5C, and FIG. 5E shows a touch detection period corresponding to the scanning period of FIG.

  For example, when video display is performed in a double speed mode in which one frame period is about 8.3 msec, as shown in FIG. 5A, most of one frame period is set as a scanning period S, and the remaining period is blanked. Let it be period B. The image displayed in the scanning period S is, for example, a, a or a1, b, b or b1. When the same image is displayed continuously for two frames, it is a case where so-called double writing is performed by performing double speed interpolation processing in order to perform 3D display or the like.

Then, as shown in FIG. 5B, the backlight lighting period L is sequentially set corresponding to the scanning period S of FIG. Here, the backlight is divided into a plurality of areas, and the backlights of the divided areas are sequentially turned on in synchronization with the video writing end timing for each of the divided areas.
In this case, even if the touch detection period D is provided in the blanking period B in order to avoid the mixing of noise due to the video display control, the backlight is turned on / off in the blanking period B. The influence of noise due to on / off cannot be avoided.

  In order to accurately perform touch detection in the above-described double speed display, as shown in FIG. 5C, the scanning period S is further shortened, and scanning is terminated in a period of ¼ frame or less of the input video signal. . In other words, the scanning period is set substantially within the frame period during quadruple speed display. Then, as shown in FIG. 5D, a backlight lighting period L is set in correspondence with the shortened scanning period S. In order to shorten the scanning period, an oxide semiconductor of In—Ga—Zn (indium-gallium-zinc) can be used as the semiconductor layer of the thin film transistor included in the liquid crystal panel TFT as described above.

Since the scanning period S ends within a quarter frame period of the input video signal, the remaining blanking period B can be made longer. Since the backlight is sequentially turned on in synchronization with the video writing end timing in the scanning period S, the lighting control can be ended during the blanking period B.
As shown in FIG. 5E, if the touch detection period D is provided after the backlight lighting period L, the video display control in the scanning period S and the backlight on / off in the backlight lighting period L are provided. The touch detection can be performed stably without being influenced by the above.

  FIG. 6 is a diagram for explaining still another example of a backlight lighting period and touch detection timing. FIG. 6A is based on a video signal in quadruple speed display (one frame period = about 4.2 msec). 6B is a backlight lighting period corresponding to the scanning period of FIG. 6A, FIG. 6C is a scanning period when scanning is stopped in a specific frame period, and FIG. 6D shows a backlight lighting period corresponding to the scanning period of FIG. 6C, and FIG. 6E shows a touch detection period corresponding to the scanning period of FIG.

  For example, when video display is performed in the quadruple speed mode in which one frame period is about 4.2 msec, as shown in FIG. 6A, the scanning period S and the blanking period B are set in one frame period of about 4.2 msec. Set. The video displayed in the scanning period S is, for example, a, a1, a2, a3, b, b1, b2,. In order to complete the scanning period within one frame period in the quadruple speed mode, an oxide semiconductor of In—Ga—Zn (indium-gallium-zinc) is used as the semiconductor layer of the thin film transistor that constitutes the liquid crystal panel TFT as described above. Can be applied.

Then, as shown in FIG. 6B, the backlight lighting period L is sequentially set corresponding to the scanning period S of FIG. Here, the backlight is divided into a plurality of areas, and the backlights of the divided areas are sequentially turned on in synchronization with the video writing end timing for each of the divided areas.
In this case, even if the touch detection period D is provided in the blanking period B in order to avoid the mixing of noise due to the video display control, the backlight is turned on / off in the blanking period B. The influence of noise due to on / off cannot be avoided.

In order to accurately perform touch detection in the quadruple speed display as described above, scanning is stopped in a part of the frame period, and touch detection is performed in that period.
For example, as shown in FIG. 6C, scanning in a part of the frame periods in the continuous frame period in quadruple speed display is stopped, and new scanning is not performed in the frame period. In this case, for example, in FIG. 6A, when one of the images a and a1 is the same image as in double writing, one scanning of the continuous frame period can be stopped.

Then, as shown in FIG. 6D, a backlight lighting period L is set in correspondence with each scanning period S. Each backlight performs control to turn on sequentially in synchronization with video writing end timing in the scanning period S.
In this case, the blanking period continues in the frame period in which scanning is not performed, and even if touch detection is performed, the display control is not affected. Then, as shown in FIG. 6E, if a touch detection period D is provided after the backlight lighting period L in this frame period, the video display control in the scanning period S and the backlight lighting period L Touch detection can be performed stably without being affected by whether the backlight is on or off.

DESCRIPTION OF SYMBOLS 11 ... Timing control part, 12 ... Data driver, 13 ... Gate driver, 14 ... Liquid crystal panel, 15 ... Backlight control part, 16 ... Backlight, 17 ... Touch panel, 18 ... Touch detection driver, 19 ... Touch position detection part, 20: Shutter glasses controller.

Claims (3)

A display unit in which pixels composed of liquid crystal modulation elements are arranged in a matrix;
A line of each pixel of the display unit is selected and scanned by a plurality of scanning signal lines sequentially, and a data signal is supplied from the data signal line to the pixels of the selected line to drive the liquid crystal. A display control unit for displaying an image;
A touch detection unit that is provided integrally with or in proximity to the display unit, and detects a touch by an external proximity object;
A backlight having a light source for illuminating the display unit, and a display device comprising:
In one frame period of an image to be displayed on the display unit, the touch detection unit detects the touch after a scanning period in which the display control unit scans one screen with a plurality of scanning signal lines of the display unit ends. Performing the operation, the backlight turns on the light source after a period of performing the operation of detecting the touch,
The period for turning on the light source is a period for turning on the light source corresponding to the liquid crystal modulation element for which the response has been completed after the response of the liquid crystal modulation element of the display unit driven in the scanning period is completed. Characteristic display device. The display device according to claim 1,
The display device performs lighting control of the light source for each of a plurality of areas corresponding to a region obtained by dividing the pixel region of the display unit into a plurality of regions. The display device according to claim 1 or 2,
The liquid crystal modulation element of each pixel of the display portion includes a transistor for controlling writing of an image signal to each pixel, and the semiconductor layer of the transistor includes an oxide semiconductor.

Images