WO2013024776A1 - Display device and drive method for same - Google Patents

Abstract

Provided is a display device in which a reduction in display quality is suppressed while power consumption is reduced more than conventional configurations. A liquid crystal display device performs so-called low-frequency refresh driving for providing an idle period after a scan period, and drives a gate line in two types of drive modes, a video display mode and a still image display mode. The liquid crystal display device performs two operations in still image display mode, a rewrite operation and a normal operation. The rewrite operation is performed during a still image rewrite period including two video scan periods (T11). Normal operation is performed by alternately repeating the video scan period (T11) and the still image rest period (T12) using a single still image frame period as a unit.

Description

Display device and driving method thereof

The present invention relates to a display device and a driving method thereof, and more particularly to a display device suitable for displaying a still image and a driving method thereof.

Conventionally, reduction of power consumption has been demanded in display devices such as liquid crystal display devices. Therefore, Patent Document 1 discloses a display device driving method in which a pause period T2 in which all the gate lines are in a non-scanning state is provided after a scanning period T1 in which the gate lines of the liquid crystal display device are scanned. In this idle period T2, no clock signal or the like is given to the gate driver. For this reason, since the driving frequency of the gate line as a whole is reduced, low power consumption can be achieved. Hereinafter, driving performed by providing the pause period T2 after the scanning period T1 as in the driving method described in Patent Document 1 is referred to as “low frequency refresh driving”. This low frequency refresh drive is mainly used for still image display.

In the low frequency refresh driving, the scanning period T1 is made shorter than the conventional one and a long pause period T2 is provided. For this reason, when low-frequency refresh driving is performed, the time for writing the video signal to each pixel formation portion is shortened, so that an image (afterimage) of the preceding frame period may be displayed.

Therefore, Patent Document 2 discloses a driving method of a display device shown in FIG. 11 in which the scanning period T1 is provided twice (the gate line is scanned twice) and then the pause period T2 is provided. According to the low-frequency refresh drive disclosed in Patent Document 2, the time for writing a video signal to each pixel forming unit is approximately twice as long as the low-frequency refresh drive described in Patent Document 1. For this reason, the display of an afterimage can be eliminated.

Japanese Unexamined Patent Publication No. 2001-31253 Japanese Unexamined Patent Publication No. 2002-278523

In the low-frequency refresh drive described in Patent Document 2, even when the same image is displayed in successive frame periods, the gate line is scanned twice in each frame period. However, in this case, it is not necessary to scan the gate line twice. Therefore, when the same image is displayed in successive frame periods, power consumption is increased by performing scanning that does not require a gate line.

Therefore, an object of the present invention is to provide a display device and a driving method thereof, in which power consumption is reduced as compared with the conventional one while suppressing deterioration in display quality.

A first aspect of the present invention is a display device,
A plurality of scanning signal lines, a plurality of video signal lines intersecting with the plurality of scanning signal lines, and switching elements arranged in a matrix corresponding to the plurality of scanning signal lines and the plurality of video signal lines, respectively. A display unit including a plurality of pixel forming units, and
A scanning signal line driving circuit capable of driving the plurality of scanning signal lines in two types of driving modes, a first driving mode and a second driving mode;
A video signal line driving circuit for driving the plurality of video signal lines;
A display control circuit for controlling the scanning signal line driving circuit and the video signal line driving circuit,
The scanning signal line driving circuit includes:
In the first driving mode, the plurality of scanning signal lines are driven with a period of a first frame period including a scanning period in which the plurality of scanning signal lines are sequentially selected,
In the second drive mode, the scan period and the scan period other than the predetermined period immediately after the change of the image to be displayed, including the scan period and a pause period in which all of the plurality of scan signal lines are in a non-selected state. The plurality of scanning signal lines are driven so that a pause period alternately appears with a second frame period composed of the scan period and the pause period as a cycle, and the length of the scan period in the second frame period Is the same as the length of the scanning period in the first frame period, and the ratio of the scanning period in the predetermined period is larger than the ratio of the scanning period in the second frame period.

According to a second aspect of the present invention, in the first aspect of the present invention,
The first frame period further includes the pause period;
The scanning signal line driving circuit drives the plurality of scanning signal lines so that the scanning period and the pause period appear alternately with the first frame period as a cycle.

According to a third aspect of the present invention, in the second aspect of the present invention,
The scanning signal line driving circuit is characterized in that the pause period in the second frame period is longer than the pause period in the first frame period.

According to a fourth aspect of the present invention, in the third aspect of the present invention,
Each pixel forming portion includes a liquid crystal layer,
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The video signal line driving circuit performs polarity inversion driving and makes signals given to the video signal lines have the same polarity in the two scanning periods in the predetermined period.

According to a fifth aspect of the present invention, in the third aspect of the present invention,
Each pixel forming portion includes a liquid crystal layer,
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The video signal line driving circuit performs polarity inversion driving and makes signals given to the video signal lines have different polarities in the two scanning periods in the predetermined period.

According to a sixth aspect of the present invention, in the fourth aspect or the fifth aspect of the present invention,
The predetermined period is the same as the scanning period in the first frame period, the same period as the pause period in the first frame period, and the same as the scanning period in the first frame period. It includes a scanning period having a length and a pause period having the same length as the pause period in the second frame period.

According to a seventh aspect of the present invention, in the fourth aspect or the fifth aspect of the present invention,
The predetermined period includes two scanning periods having the same length as the scanning period in the first frame period and a pause period having the same length as the pause period in the second frame period.

According to an eighth aspect of the present invention, in the third aspect of the present invention,
The scanning period included in the predetermined period includes the scanning period having the same length as the first frame period,
The predetermined period includes the scan period having the same length as the first frame period and the pause period having the same length as the pause period in the second frame period.

A ninth aspect of the present invention is the eighth aspect of the present invention,
Each pixel forming portion includes a liquid crystal layer,
The video signal line driving circuit is characterized by performing polarity inversion driving.

According to a tenth aspect of the present invention, in the first aspect of the present invention,
Each pixel forming portion includes a liquid crystal layer,
The one frame period is composed of the scanning period.
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The predetermined period includes a scanning period having the same length as the scanning period in two of the first frame periods and the pause period in the second frame period in order,
The video signal line driving circuit performs polarity inversion driving and makes signals given to the video signal lines have the same polarity in the two scanning periods in the predetermined period.

According to an eleventh aspect of the present invention, in the first aspect of the present invention,
Each pixel forming portion includes a liquid crystal layer,
The one frame period is composed of the scanning period.
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The predetermined period includes a scanning period having the same length as the scanning period in two of the first frame periods and the pause period in the second frame period in order,
The video signal line driving circuit performs polarity inversion driving and makes signals given to the video signal lines have different polarities in the two scanning periods in the predetermined period.

A twelfth aspect of the present invention is any one of the first to eleventh aspects of the present invention,
The display control circuit includes:
When displaying a moving image in the display unit, the scanning signal line driving circuit is controlled so that the scanning signal line driving circuit drives the plurality of scanning signal line driving circuits in a first driving mode;
When performing still image display in the display unit, the scanning signal line driving circuit is controlled so that the scanning signal line driving circuit drives the plurality of scanning signal line driving circuits in a second driving mode. And

According to a thirteenth aspect of the present invention, in any one of the first to twelfth aspects of the present invention,
The switching element is a thin film transistor in which a semiconductor layer is formed of an oxide semiconductor.

According to a fourteenth aspect of the present invention, there is provided a display unit including a plurality of scanning signal lines, and a scanning signal line capable of driving the plurality of scanning signal lines in two types of driving modes, a first driving mode and a second driving mode. A driving method of a display device comprising a driving circuit,
Driving the plurality of scanning signal lines in a cycle of a first frame period including a scanning period in which the plurality of scanning signal lines are sequentially selected in the first drive mode;
In the second drive mode, the scan period and the scan period other than a predetermined period immediately after a change of an image to be displayed, including the scan period and a pause period in which all of the plurality of scan signal lines are in a non-selected state. The plurality of scanning signal lines are driven so that a pause period alternately appears with a second frame period composed of the scan period and the pause period as a cycle, and the length of the scan period in the second frame period And the length of the scanning period in the first frame period, and the ratio of the scanning period in the predetermined period is larger than the ratio of the scanning period in the second frame period. .

According to the first aspect of the present invention, images are displayed in two types of drive modes, the first drive mode and the second drive mode. In this second drive mode, so-called low frequency refresh drive is performed in which a pause period is provided after the scan period, so that power consumption can be reduced. Further, in the predetermined period in the second drive mode, a scanning period longer than the scanning period in the second frame period is provided. For this reason, the potential corresponding to the image to be displayed is sufficiently written to each pixel formation portion, so that the display of the afterimage is eliminated. Thereby, the fall of display quality can be suppressed. On the other hand, in the period other than the predetermined period in the second drive mode, the scanning period similar to the scanning period in the first frame period is provided only once for each second frame period. The power consumption required for driving can be further reduced.

According to the second aspect of the present invention, in the first driving mode, so-called low-frequency refresh driving is performed in which a pause period is provided after the scanning period, so that further reduction in power consumption can be achieved.

According to the third aspect of the present invention, since the pause period in the second frame period is longer than the pause period in the pause period in the first frame period, further reduction in power consumption can be achieved in the second drive mode. .

According to the fourth aspect or the fifth aspect of the present invention, in the liquid crystal display device that performs polarity inversion driving, the predetermined period in the second driving mode includes two scanning periods in the first frame period. . For this reason, the potential corresponding to the image to be displayed is sufficiently written to each pixel formation portion, so that the display of the afterimage is eliminated. Thereby, it is possible to sufficiently suppress the deterioration of display quality.

According to the sixth aspect or the seventh aspect of the present invention, the same effects as the fourth aspect or the fifth aspect of the present invention can be achieved while performing the low-frequency refresh drive even in the predetermined period. it can. Further, according to the seventh aspect of the present invention, since the number of times of switching between the operation in the scanning period and the operation in the pause period is reduced as compared with the sixth aspect of the present invention, it is possible to further reduce power consumption. it can.

According to the eighth aspect of the present invention, the predetermined period in the second drive mode includes one scanning period having the same length as the first frame period. For this reason, the potential corresponding to the image to be displayed is sufficiently written to each pixel formation portion, so that the display of the afterimage is eliminated. Thereby, it is possible to sufficiently suppress the deterioration of display quality. Further, since the drive frequency of the scanning signal line during the operation for changing the image to be displayed is reduced, further reduction in power consumption can be achieved.

According to the ninth aspect of the present invention, in the liquid crystal display device in which polarity inversion driving is performed, the same effect as in the eighth aspect of the present invention can be achieved.

According to the tenth aspect or the eleventh aspect of the present invention, in the liquid crystal display device that performs polarity inversion driving, the predetermined period in the second driving mode includes scanning periods in two first frame periods. For this reason, the potential corresponding to the image to be displayed is sufficiently written to each pixel formation portion, so that the display of the afterimage is eliminated. Thereby, it is possible to sufficiently suppress the deterioration of display quality.

According to the twelfth aspect of the present invention, the first drive mode can be used for moving image display, and the second drive mode can be used for still image display.

According to the thirteenth aspect of the present invention, a thin film transistor in which a semiconductor layer is formed of an oxide semiconductor is used as a switching element in a pixel formation portion. Therefore, the potential written in the pixel formation portion can be held for a long time, so that a sufficient rest period can be provided. Therefore, since the driving frequency of the gate line is further reduced as compared with the conventional low frequency refresh driving, it is possible to further reduce power consumption. Further, the writing of the potential corresponding to the image to be displayed to the pixel formation portion can be speeded up, that is, the scanning period can be shortened, so that the amplitude of the luminance waveform of the display portion is reduced. As a result, flicker becomes difficult to be recognized.

According to the fourteenth aspect of the present invention, the same effect as that of the first aspect of the present invention can be achieved in the display device driving method.

1 is a block diagram illustrating an overall configuration of a liquid crystal display device according to a first embodiment of the present invention. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the said 1st Embodiment. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a wave form chart of panel brightness to three kinds of length scanning periods. (A) is a waveform diagram of panel luminance when the scanning period is Amsec. (B) is a waveform diagram of panel luminance when the scanning period is 2 A / 3 msec. (C) is a waveform diagram of panel luminance when the scanning period is A / 2 msec. It is a figure which shows the drain current-gate voltage characteristic of a-SiTFT and IGZOTFT. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the modification of the said 1st Embodiment. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the 2nd Embodiment of this invention. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the 1st modification of the said 2nd Embodiment. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the 2nd modification of the said 2nd Embodiment. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the 3rd modification of the said 2nd Embodiment. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. It is a signal waveform diagram for demonstrating operation | movement of the liquid crystal display device which concerns on the 3rd Embodiment of this invention. (A) is a signal waveform diagram in the moving image display mode. (B) is a signal waveform diagram in the still image display mode. FIG. 10 is a signal waveform diagram for explaining a method of driving the display device described in Patent Document 2.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, “substantially the same length” is included in the “same length” in this specification.
<1. First Embodiment>
<1.1 Overall configuration and operation>
FIG. 1 is a block diagram showing the overall configuration of an active matrix liquid crystal display device according to a first embodiment of the present invention. As shown in FIG. 1, this liquid crystal display device is common to a power supply 100, a DC / DC converter 110, a display control circuit 200, a source driver (video signal line driving circuit) 300, and a gate driver (scanning signal line driving circuit) 400. An electrode driving circuit 500 and a display unit 600 are provided. The source driver 300 and / or the gate driver 400 may be realized as an IC (Integrated Circuit), and is formed on a liquid crystal display panel including the display unit 600 using an oxide semiconductor (IGZO) or the like. May be.

The display unit 600 includes n source lines (video signal lines) SL1 to SLn, m gate lines (scanning signal lines) GL1 to GLm, source lines SL1 to SLn, and gate lines GL1 to GLm. M × n pixel forming portions provided corresponding to the respective intersections are formed. The m × n pixel forming portions are arranged in a matrix to constitute a pixel array. Each pixel forming portion includes a thin film transistor 80 which is a switching element having a gate terminal connected to a gate line passing through a corresponding intersection and a source terminal connected to a source line passing through the intersection, and a drain terminal of the thin film transistor 80 A common electrode Ec that is a common electrode provided in common to the plurality of pixel formation portions, and a common electrode Ec provided in common to the plurality of pixel formation portions. And a liquid crystal layer sandwiched therebetween. A pixel capacitor Cp is constituted by a liquid crystal capacitor formed by the pixel electrode and the common electrode Ec. Normally, an auxiliary capacitor is provided in parallel with the liquid crystal capacitor in order to reliably hold the voltage in the pixel capacitor Cp. However, since the auxiliary capacitor is not directly related to the present invention, its description and illustration are omitted.

The semiconductor layer of the thin film transistor 80 is formed of, for example, an oxide semiconductor (for example, IGZO). A specific implementation example using the IGZO will be described later.

The power supply 100 supplies a predetermined power supply voltage to the DC / DC converter 110, the display control circuit 200, and the common electrode drive circuit 500. The DC / DC converter 110 generates a predetermined DC voltage for operating the source driver 300 and the gate driver 400 from the power supply voltage and supplies it to the source driver 300 and the gate driver 400. The common electrode drive circuit 500 gives a predetermined potential Vcom to the common electrode Ec.

The display control circuit 200 receives an image signal DAT and a timing signal group TG such as a horizontal synchronization signal and a vertical synchronization signal sent from the outside, and receives a digital video signal DV and a source start pulse for controlling image display on the display unit 600. A signal SSP, a source clock signal SCK, a latch strobe signal LS, a gate start pulse signal GSP, and a gate clock signal GCK are output. The display control circuit 200 performs control for switching between a moving image display mode and a still image display mode, which will be described later.

The source driver 300 receives the digital video signal DV, the source start pulse signal SSP, the source clock signal SCK, and the latch strobe signal LS output from the display control circuit 200, and receives the video signal SS (1) on the source lines SL1 to SLn, respectively. Apply ~ SS (n).

Based on the gate start pulse signal GSP and the gate clock signal GCK output from the display control circuit 200, the gate driver 400 applies the on-level scanning signals GS (1) to GS (m) to the gate lines GL1 to GLm, respectively. The application is repeated with one frame period as a cycle. The gate driver 400 can drive the gate lines GL1 to GLm in two types of drive modes, a moving image display mode (first drive mode) and a still image display mode (second drive mode). The moving image display mode is a mode for displaying a moving image on the display unit 600. The still image display mode is a mode for displaying a still image on the display unit 600. Hereinafter, the moving image display mode and the still image display mode may be described not only as the modes of the gate driver 400 but also as the modes of the display control circuit 200 and the liquid crystal display device.

<1.2 Movie display mode and still image display mode>
A frame memory (not shown) is provided in the display control circuit 200. The display control circuit 200 stores the image signal DAT for one frame before one frame in this frame memory, and compares it with the image signal DAT for one frame of the current frame. The display control circuit 200 basically switches the gate driver 400 to the moving image display mode if the image signal DAT for one frame one frame before and the image signal DAT for one frame of the current frame do not match. The gate start pulse signal GSP and the gate clock signal GCK are output so that the source driver 300 operates with the source start pulse so that the source driver 300 outputs the desired video signals SS (1) to SS (n) in the moving image display mode. The signal SSP, the source clock signal SCK, and the latch strobe signal LS are output. Further, the display control circuit 200, when the image signal DAT of the previous frame and the image signal DAT of the current frame match, the gate start pulse signal GSP and the gate so as to operate the gate driver 400 in the still image display mode. The clock signal GCK is output, and the source start pulse signal SSP, the source clock signal SCK, and the latch strobe signal LS are output so that the source driver 300 outputs desired video signals SS (1) to SS (n) in the moving image display mode. Output.

Incidentally, it is necessary to distinguish between a case where an image (still image) to be displayed changes in the still image display mode and a case where the still image display mode shifts to the moving image display mode. Therefore, in more detail, the display control circuit 200 determines that the image signal DAT for one frame before one frame and the image signal DAT for one frame of the current frame in the still image display mode do not match the predetermined frame. In the case of continuing, the driving mode of the gate driver 400 is shifted to the moving image display mode. On the other hand, in the still image display mode, the image signal DAT for one frame one frame before and the image signal DAT for one frame of the current frame do not coincide with each other, and this may continue for less than the predetermined number of times. For example, the gate driver 400 performs an operation for rewriting a still image in the still image display mode.

In the moving image display mode, the display control circuit 200 determines that the image signal DAT for one frame one frame before and the image signal DAT for one frame of the current frame match for a predetermined number of times. To the still image display mode.

In the above description, by comparing the image signal DAT for one frame one frame before stored in the frame memory with the image signal DAT for one frame of the current frame, the image is either a moving image or a still image. Although it is determined whether or not there is, the present invention is not limited to this. For example, by adding control data indicating that the image signal DAT is moving image data or still image data to the image signal DAT itself, it is determined whether the image to be displayed is a moving image or a still image It is also good.

<1.3 Operation of liquid crystal display device>
FIG. 2 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the present embodiment. More specifically, FIG. 2A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 2B is a signal waveform diagram for explaining the operation in the still image display mode. 2A and 2B, the scanning signal GS (1) applied to the gate line GL (1) in the first row and the video signal applied to any source line among the source lines SL1 to SLn. , And the average luminance of the entire liquid crystal display panel including the display unit 600 (hereinafter referred to as “panel luminance”). Here, it is assumed that the liquid crystal display panel is a normally black mode panel. In the following description, it is assumed that so-called polarity inversion driving is performed in the present embodiment. Further, in the still image display mode for simplifying the description of the operation of the liquid crystal display device, video signals having the same polarity are written in the m × n pixel forming portions in the display portion 600 in one frame period. In addition, video signals having different polarities in any two consecutive frame periods are written in each pixel formation unit.

<1.3.1 Operation in video display mode>
In the present embodiment, so-called low frequency refresh driving is performed. That is, as shown in FIG. 2A, a moving image frame period that is a frame period (first frame period) in the moving image display mode in the present embodiment includes a scanning period, and a pause period provided after the scanning period. It is made up of. In this scanning period, the scanning signals GS (1) to GS (m) are sequentially set to the high level potential based on the gate clock signal GCK. On the other hand, in the idle period, all of the m gate lines GL1 to GLm (scanning signals GS (1) to GS (m)) are at the low level potential. Hereinafter, the scanning period in the moving image display mode is referred to as a “moving image scanning period”, and is denoted by reference numeral T11. In addition, the pause period in the movie display mode is referred to as a “movie pause period” and is denoted by reference numeral T12. In the moving image scanning period, the gate lines GL1 to GLm are driven at a speed higher than 60 Hz (16.7 msec), for example.

In the moving image scanning period T11, each video signal is positive. As the gate lines GL1 to GLm are sequentially selected based on the scanning signals GS (1) to GS (m), a positive video signal is written to each pixel formation portion. For this reason, the panel luminance increases as shown in FIG.

In the video pause period T12, each video signal is fixed to the Vcom potential. Thereby, fluctuations in the pixel potential (referred to as the potential of the pixel electrode) due to the off-leak current of the thin film transistor 80 in each pixel formation portion can be reduced. Each video signal may be fixed to a potential other than the Vcom potential (for example, an average luminance value of each video signal in one frame period). In addition, after applying a Vcom potential or the like to each video signal line, the video signal line may be in a high impedance state. However, the off-leakage current is not completely eliminated, and as described above, the pixel potential in each pixel formation portion approaches the Vcom potential by fixing each video signal to the Vcom potential. For this reason, as shown in FIG. 2A, the panel brightness decreases during the moving image suspension period T12.

The liquid crystal display device according to this embodiment operates in the moving image display mode by alternately repeating the moving image scanning period T11 and the moving image pause period T12 described above in units of one moving image frame period.

In the above-described example, one moving image frame period is described as one moving image scanning period T11 and moving image pause period T12. However, the configuration of this one moving image frame period (operation in one moving image frame period) is as follows. Various changes can be made according to the required display quality. For example, each moving image frame period may include two moving image scanning periods T11 and a moving image pause period T12 provided after them. Further, for example, a moving image frame period composed of one moving image scanning period T11 and a moving image suspension period T12 and a moving image frame period composed of two moving image scanning periods T11 and a moving image suspension period T12 may be alternately repeated.

<1.3.2 Operation in still image display mode>
As shown in FIG. 2B, in the still image display mode, the operation for rewriting the above-described still image (hereinafter referred to as “rewriting operation”) and the operation for displaying the same still image (hereinafter referred to as “normal operation”). Two types of operations are performed. In the example shown in FIG. 2B, the rewriting operation from the display image A to the display image B is performed.

A still image frame period, which is a frame period (second frame period) in the still image display mode, is a scanning period having the same length as the moving image scanning period T11 (hereinafter simply referred to as “moving image scanning period T11”). It consists of a pause period (hereinafter referred to as “still picture pause period”) longer than the moving picture pause period T12 provided after the period T11. In the following, the still image pause period is represented by T2. Note that the operations in the scanning period and the rest period are the same in the moving image display mode and in the still image display mode except for the length of the period.

<1.3.2.1 Rewriting operation>
As shown in FIG. 2B, the rewriting operation is performed in a still image rewriting period as a predetermined period immediately after the change of the image to be displayed. The still image rewriting period in the present embodiment includes the one moving image frame period and the one still image frame period provided after the one moving image frame period. In other words, the still image rewriting period includes a moving image scanning period T11, a moving image pause period T12, a moving image scanning period T11, and a still image pause period T12. The ratio of the scanning period is larger than the period. In order to rewrite the display image A to the display image B, first, the gate lines GL1 to GLm are scanned once in the moving image scanning period T11 in the one moving image frame period, and the video signal (positive polarity) corresponding to the display image B is displayed. Is written in each pixel formation portion. However, as described above, in the moving image scanning period T11 in one moving image frame period, the gate lines GL1 to GLm are driven at high speed, so that the video signal corresponding to the display image B is sufficiently written to each pixel forming portion. Absent. Note that a moving image pause period T12 for low-frequency refresh driving is provided after the moving image scanning period T11.

Therefore, in the present embodiment, the gate lines GL1 to GLm are scanned again in the moving image scanning period T11 in one still image frame period provided after one moving image frame period, and the same as in the first moving image scanning period T11. The video signal corresponding to the polarity (positive polarity) display image B is written again in each pixel forming portion. For this reason, the video signal corresponding to the display image B is sufficiently written to each pixel forming portion. As a result, it is possible to eliminate afterimages resulting from insufficient video signal writing time. After the moving image scanning period T11, a still image pause period T2 for low frequency refresh driving is provided.

Note that, in the one moving image frame period at the time of the still image rewriting period in the present embodiment, similarly to the one moving image frame period in the moving image display mode, after the panel brightness increases in the moving image scanning period T11, Panel brightness decreases. Next, in one still image frame period during the still image rewriting period, the panel brightness increases during the still image pause period T12 after the panel brightness increases during the moving image scanning period T11.

<1.3.2.2 Normal operation>
The normal operation in the present embodiment is performed by alternately repeating the moving image scanning period T11 and the still image pause period T12 in units of one still image frame period. Here, one still image frame period after the still image rewriting period will be described as an example. As shown in FIG. 2B, in this one still image frame period, an operation for displaying the display image B is performed following the still image rewriting period. First, in the moving image scanning period T11 in one still image frame period, the gate lines GL1 to GLm are scanned once, and a video signal corresponding to the display image B is written in each pixel forming unit. The polarity of this video signal is negative, unlike during the still image rewriting period. After the moving image scanning period T11, the above-described operation in the still image pause period T12 is performed.

After the end of this one still image frame period, a positive video signal corresponding to the display image B is written in each pixel forming unit by the same operation in the subsequent one still image frame period. In this way, during normal operation, a video signal whose polarity changes every one still image frame period is written to each pixel forming unit once every one still image frame period. During this normal operation, the polarity of the video signal differs for each still image frame period, but the data (absolute value) itself always corresponds to the display image B. For this reason, during this normal operation, it is not necessary to secure the writing time of the video signal as in the above-described still image rewriting period. Therefore, it is not necessary to write video signals of the same polarity twice during normal operation. That is, it is only necessary to scan the gate lines GL1 to GLm once for each still image frame period.

<1.4 Change in panel brightness>
FIG. 3 is a waveform diagram of the panel luminance for three types of scanning periods (operation scanning period T11) when a flicker pattern is displayed in the still image display mode. More specifically, FIG. 3A is a waveform diagram of panel luminance when the scanning period is Amsec. FIG. 3B is a waveform diagram of the panel luminance when the scanning period is 2 A / 3 msec. FIG. 3C is a waveform diagram of panel luminance when the scanning period is A / 2 msec.

The shorter the scanning period, the shorter the video signal writing time to each pixel forming portion. For this reason, as shown in FIGS. 3A to 3C, the shorter the scanning period, the smaller the amplitude of the panel luminance waveform. Therefore, as the scanning period is shortened (the gate lines GL1 to GLm are driven at a higher speed), the flickering of the display image becomes less recognized.

<1.5 Implementation example>
Conventionally, a thin film transistor (hereinafter referred to as “a-Si TFT”) using amorphous silicon (a-Si) as a semiconductor layer has been used as a thin film transistor in each pixel formation portion of a liquid crystal display device. This a-Si TFT is particularly often used for a liquid crystal display device in which a gate driver or the like is monolithically formed. However, an oxide semiconductor is used for the semiconductor layer of the thin film transistor 80 in each pixel formation portion in this embodiment. Note that as the oxide semiconductor, typically, InGaZnO _x (hereinafter referred to as “IGZO”), which is an oxide semiconductor mainly containing indium, gallium, zinc, and oxygen, is used. It is not limited. For example, any oxide semiconductor containing at least one of indium, gallium, zinc, copper, silicon, tin, aluminum, calcium, germanium, and lead may be used.

FIG. 4 is a diagram showing drain current-gate voltage characteristics of a TFT using a-Si TFT and IGZO as a semiconductor layer (hereinafter referred to as “IGZOTFT”). In FIG. 4, the horizontal axis represents the gate voltage Vg, and the vertical axis represents the drain current Ids. As shown in FIG. 4, the off-leakage current of the IGZOTFT is 1/1000 or less of the off-leakage current of the a-Si TFT, and the on-current of the IGZOTFT is about 20 times the on-current of the a-Si TFT.

Since the IGZOTFT has a small off-leakage current as described above, when the IGZOTFT is used as the thin film transistor 80 in this embodiment, the pixel potential can be maintained for a longer time than when the a-Si TFT is used as the thin film transistor 80. For this reason, when IGZOTFT is used as the thin film transistor 80 in the present embodiment, a sufficient rest period can be provided.

Further, since the IGZOTFT has a large on-state current as described above, when the IGZOTFT is used as the thin film transistor 80 in this embodiment, the video signal is written to the pixel formation portion more than when the a-Si TFT is used as the thin film transistor 80. Can be speeded up. That is, the scanning period can be shortened.

<1.6 Effect>
According to this embodiment, in a liquid crystal display device that performs low-frequency refresh driving, an image is displayed in two types of driving modes: a moving image display mode and a still image display mode. The drive in the moving image display mode is the conventional low frequency refresh drive, while the drive in the still image display mode is realized by two types of operations, a rewrite operation and a normal operation. In the still image rewriting period in which the rewriting operation is performed, video signals having the same polarity are given to each pixel forming unit in two moving image scanning periods T11 when the display image changes in the still image display mode. For this reason, since the video signal is sufficiently written to each pixel forming portion, the display of the afterimage can be eliminated. On the other hand, in the normal operation, since the moving image scanning period T11 is provided only once for each still image frame period in the still image display mode, the power consumption required for driving the gate lines GL1 to GLm is reduced. Can do. In this normal operation, since the video signal data (absolute value) itself is constant, it is not necessary to secure the video signal writing time as in the still image rewriting period. Even if an afterimage occurs, it is not recognized as an afterimage because the display image is constant.

Further, according to the present embodiment, since the still image suspension period T2 is longer than the moving image suspension period T12, it is possible to further reduce power consumption in the still image display mode.

In addition, according to the present embodiment, an IGZO TFT is used for the thin film transistor 80 in each pixel formation portion. For this reason, since the pixel potential can be held for a long time, a sufficient rest period can be provided. Therefore, since the driving frequency of the gate line is further reduced as compared with the conventional low frequency refresh driving, it is possible to further reduce power consumption. In addition, the writing of the video signal to the pixel formation portion can be speeded up, that is, the scanning period can be shortened, so that the amplitude of the panel luminance waveform is reduced. As a result, flicker becomes difficult to be recognized.

<1.7 Modification>
FIG. 5 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the modification of the first embodiment. More specifically, FIG. 5A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 5B is a signal waveform diagram for explaining the operation in the still image display mode. The operation in the moving image display mode among the operations of the liquid crystal display device is the same as that in the first embodiment, and a description thereof will be omitted.

In the still image rewriting period in the first embodiment, as shown in FIG. 2B, the polarity of the video signal written to each pixel formation portion and the second moving image scanning period during the first moving image scanning period T11. The polarities of the video signals written in the pixel forming portions at T11 are the same (positive polarity). However, in this modified example, as shown in FIG. 5B, the polarity of the video signal written to each pixel forming portion during the first moving image scanning period T11 is positive, while the second moving image scanning period. The polarity of the video signal written to each pixel formation portion at T11 is negative. That is, in this modification, polarity inversion driving is performed even in the still image rewriting period. As described above, even when polarity inversion driving is performed in the still image rewriting period, a sufficient scanning period (two moving image scanning periods T11) is provided in the still image rewriting period, so that the video signal corresponding to the display image B is displayed. Writing to each pixel formation portion is sufficiently performed.

According to this modification, video signals having different polarities are given to each pixel forming unit in two moving image scanning periods T11 when the display image changes in the still image display mode. For this reason, since the video signal is sufficiently written to each pixel forming portion, the display of the afterimage can be eliminated as in the first embodiment.

<2. Second Embodiment>
<2.1 Operation of liquid crystal display device>
FIG. 6 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the second embodiment of the present invention. More specifically, FIG. 6A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 6B is a signal waveform diagram for explaining the operation in the still image display mode. Since this embodiment is the same as the first embodiment except for the operation of the liquid crystal display device, the description of the same portion is omitted. As shown in FIGS. 6A and 6B, the operation in the moving image display mode and the normal operation in the still image display mode among the operations of the liquid crystal display device are also the same as those in the first embodiment. Since it is the same, the description is abbreviate | omitted.

<2.1.1 Rewrite operation>
As shown in FIG. 6B, the still image rewriting period in this embodiment includes two moving image scanning periods T11 and a still image pause period T2 provided after these two moving image scanning periods T11. . In other words, the still image rewriting period in this embodiment includes one moving image scanning period T11 and one still image frame period provided after the moving image scanning period T11. That is, in the still image rewriting period, the ratio of the scanning period is larger than each still image frame period including the moving image scanning period T11 and the still image pause period T12. In order to rewrite the display image A to the display image B, first, the gate lines GL1 to GLm are scanned once in the moving image scanning period T11, and a video signal corresponding to the display image B (assuming positive polarity) is generated. It is written in each pixel formation portion. However, as described above, since the gate lines GL1 to GLm are driven at a high speed in the moving image scanning period T11, the video signal corresponding to the display image B is not sufficiently written to each pixel forming portion.

Therefore, in this embodiment, a moving image scanning period T11 (second time) is further provided after the moving image scanning period T11 (first time). For this reason, in the second moving image scanning period T11, the gate lines GL1 to GLm are scanned again, and video signals corresponding to the display image B having the same polarity (positive polarity) as in the first moving image scanning period T11 are displayed. It is written again in the pixel formation portion. For this reason, the video signal corresponding to the display image B is sufficiently written to each pixel forming portion. As a result, it is possible to eliminate afterimages resulting from insufficient video signal writing time. After these two moving image scanning periods T11, a still image pause period T2 for low frequency refresh driving is provided.

Note that, in the still image rewriting period in the present embodiment, the panel luminance increases slightly during the second moving image scanning period T11 after the panel luminance increases during the first moving image scanning period T11. Next, the panel brightness decreases during the still image pause period T2.

<2.2 Effect>
According to the present embodiment, the moving image pause period T12 in the still image rewriting period in the first embodiment is not provided. For this reason, since the frequency | count of switching between the operation | movement of a scanning period and the operation | movement of an idle period can be reduced, further reduction in power consumption can be achieved.

<2.3 First Modification>
FIG. 7 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the first modification of the second embodiment. More specifically, FIG. 7A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 7B is a signal waveform diagram for explaining the operation in the still image display mode. Note that the operation in the moving image display mode among the operations of the liquid crystal display device is the same as that in the second embodiment, and a description thereof will be omitted.

In the still image rewriting period in the second embodiment, as shown in FIG. 6B, the polarity of the video signal written to each pixel forming unit and the second moving image scanning period during the first moving image scanning period T11. The polarities of the video signals written in the pixel forming portions at T11 are the same (positive polarity). However, in this modified example, as shown in FIG. 7B, the polarity of the video signal written in each pixel formation portion during the first moving image scanning period T11 is positive, while the second moving image scanning period. The polarity of the video signal written to each pixel formation portion at T11 is negative. That is, in this modification, polarity inversion driving is performed even in the still image rewriting period. As described above, even when polarity inversion driving is performed in the still image rewriting period, a sufficient scanning period (two moving image scanning periods T11) is provided in the still image rewriting period, so that the video signal corresponding to the display image B is displayed. Writing to each pixel formation portion is sufficiently performed.

According to this modification, video signals having different polarities are given to each pixel forming unit in two moving image scanning periods T11 when the display image changes in the still image display mode. For this reason, since the video signal is sufficiently written to each pixel forming portion, display of an afterimage can be eliminated as in the second embodiment.

<2.4 Second Modification>
FIG. 8 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the second modification of the second embodiment. More specifically, FIG. 8A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 8B is a signal waveform diagram for explaining the operation in the still image display mode. Note that the operation in the still image display mode among the operations of the liquid crystal display device is the same as that in the second embodiment, and a description thereof will be omitted.

As shown in FIG. 8A, one moving image frame period in the present modification example is composed of one moving image scanning period T11. That is, in the present embodiment, the low frequency refresh drive is performed only in the still image display mode, and the low frequency refresh drive is not performed in the moving image display mode. For this reason, although the effect of reducing power consumption is inferior to that of the second embodiment, display of afterimages can be eliminated as in the second embodiment.

<2.5 Third Modification>
FIG. 9 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the third modification of the second embodiment. More specifically, FIG. 9A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 9B is a signal waveform diagram for explaining the operation in the still image display mode. In this modification, the operation in the moving image display mode is the same as in the second modification of the second embodiment, and the operation in the still image display mode is the same as in the first modification of the second embodiment. . Since these detailed descriptions are as shown in the second modification of the second embodiment and the first modification of the second embodiment, they are omitted.

According to this modification, the low frequency refresh drive is performed only in the still image display mode, and the low frequency refresh drive is not performed in the moving image display mode. For this reason, although the effect of reducing power consumption is inferior to that of the second embodiment, display of afterimages can be eliminated as in the second embodiment. Further, according to the present modification, video signals having different polarities are given to each pixel forming unit in two moving image scanning periods T11 when the display image changes in the still image display mode. As a result, the video signal is sufficiently written to each pixel forming portion, and thus the display of the afterimage can be eliminated as in the second embodiment.

<3. Third Embodiment>
<3.1 Operation of liquid crystal display device>
FIG. 10 is a signal waveform diagram for explaining the operation of the liquid crystal display device according to the third embodiment of the present invention. More specifically, FIG. 10A is a signal waveform diagram for explaining the operation in the moving image display mode. FIG. 10B is a signal waveform diagram for explaining the operation in the still image display mode. Since this embodiment is the same as the first embodiment except for the operation of the liquid crystal display device, the description of the same portion is omitted. As shown in FIGS. 10A and 10B, the operation in the moving image display mode and the normal operation in the still image display mode among the operations of the liquid crystal display device are also the same as those in the first embodiment. Since it is the same, the description is abbreviate | omitted.

<3.1.1 Rewrite operation>
As shown in FIG. 10B, the still image rewriting period in this embodiment is provided after the scanning period having the same length as the one moving image frame period (hereinafter referred to as “long-term scanning period”) and this long-term scanning period. The still image pause period T2 is set. In the following, the long-term scanning period is represented by reference numeral T10. In the still image rewriting period, the ratio of the scanning period is larger than each still image frame period including the moving image scanning period T11 and the still image pause period T12. Since the long-term scanning period T10 is longer than the moving image scanning period T11, the selection period of each gate line in the long-term scanning period T10 is longer than that in the moving image scanning period T11.

In order to rewrite the display image A to the display image B, first, the gate lines GL1 to GLm are scanned once in the long-term scanning period T10, and a video signal (assuming positive polarity) corresponding to the display image B is generated. It is written in each pixel formation portion. As described above, since the selection period of each gate line in the long-term scanning period T10 is longer than that in the moving image scanning period T12, the number of scans of the gate lines GL1 to GLm in the still image rewriting period in this embodiment is 1. However, the video signal corresponding to the display image B is sufficiently written to each pixel formation portion. After this long-term scanning period T10, a still image pause period T2 for low-frequency refresh driving is provided.

In the still image rewriting period in the present embodiment, after the panel brightness increases in the long-term scanning period T10, the panel brightness decreases in the subsequent still image pause period T2.

<3.2 Effects>
According to the present embodiment, since the long-term scanning period T10 is provided, the driving frequency of the gate lines GL1 to GLm during the rewriting operation is reduced, so that further reduction in power consumption can be achieved.

<4. Other>
Two moving image scanning periods T11 are provided in the still image rewriting period in the first and its modified examples and in the second embodiment and each modified example, but three or more moving image scanning periods T11 may be provided. good. Further, in the still image rewriting period in the third embodiment, only one long-term scanning period T10 is provided, but two or more long-term scanning periods T1 may be provided.

A relatively short period for performing various processes may be provided after each scanning period in each of the above embodiments.

In the above embodiments, the liquid crystal display device has been described as an example, but the present invention is not limited to this. When the present invention is applied to a display device other than a liquid crystal display device, the above-described polarity inversion driving is not necessary. In addition, the above-described embodiments can be variously modified and implemented without departing from the spirit of the present invention.

As described above, according to the present invention, it is possible to provide a display device and a driving method thereof with reduced power consumption as compared with the related art while suppressing deterioration in display quality.

The present invention can be applied to a display device that performs low-frequency refresh driving.

80 ... Thin film transistor (switching element)
200: Display control circuit 300: Source driver (video signal line driving circuit)
400: Gate driver (scanning signal line driving circuit)
600 ... Display T2 ... Still image pause period T10 ... Long-term scanning period T11 ... Movie scanning period T12 ... Movie pause period

Claims (14)

A plurality of scanning signal lines, a plurality of video signal lines intersecting with the plurality of scanning signal lines, and switching elements arranged in a matrix corresponding to the plurality of scanning signal lines and the plurality of video signal lines, respectively. A display unit including a plurality of pixel forming units, and
A scanning signal line driving circuit capable of driving the plurality of scanning signal lines in two types of driving modes, a first driving mode and a second driving mode;
A video signal line driving circuit for driving the plurality of video signal lines;
A display control circuit for controlling the scanning signal line driving circuit and the video signal line driving circuit,
The scanning signal line driving circuit includes:
In the first driving mode, the plurality of scanning signal lines are driven with a period of a first frame period including a scanning period in which the plurality of scanning signal lines are sequentially selected,
In the second drive mode, the scan period and the scan period other than the predetermined period immediately after the change of the image to be displayed, including the scan period and a pause period in which all of the plurality of scan signal lines are in a non-selected state. The plurality of scanning signal lines are driven so that a pause period alternately appears with a second frame period composed of the scan period and the pause period as a cycle, and the length of the scan period in the second frame period The same as the length of the scanning period in the first frame period, and the ratio of the scanning period in the predetermined period is larger than the ratio of the scanning period in the second frame period. The first frame period further includes the pause period;
2. The scanning signal line driving circuit drives the plurality of scanning signal lines so that the scanning period and the pause period appear alternately with the first frame period as a cycle. Display device. 3. The display device according to claim 2, wherein the scanning signal line driving circuit makes the pause period in the second frame period longer than the pause period in the first frame period. Each pixel forming portion includes a liquid crystal layer,
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
4. The video signal line driving circuit performs polarity inversion driving and sets signals applied to the video signal lines to have the same polarity in the two scanning periods in the predetermined period. The display device described in 1. Each pixel forming portion includes a liquid crystal layer,
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
4. The video signal line driving circuit according to claim 3, wherein the video signal line driving circuit performs polarity inversion driving, and signals applied to the video signal lines have different polarities in the two scanning periods in the predetermined period. The display device described. The predetermined period is the same as the scanning period in the first frame period, the same period as the pause period in the first frame period, and the same as the scanning period in the first frame period. 6. The display device according to claim 4, wherein the display device includes a scanning period having a length and a pause period having the same length as the pause period in the second frame period. The predetermined period includes two scanning periods having the same length as the scanning period in the first frame period and a pause period having the same length as the pause period in the second frame period. The display device according to claim 4 or 5. The scanning period included in the predetermined period includes the scanning period having the same length as the first frame period,
The predetermined period includes the scan period having the same length as the first frame period and the pause period having the same length as the pause period in the second frame period in order. Display device. Each pixel forming portion includes a liquid crystal layer,
9. The display device according to claim 8, wherein the video signal line driving circuit performs polarity inversion driving. Each pixel forming portion includes a liquid crystal layer,
The one frame period is composed of the scanning period.
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The predetermined period includes a scanning period having the same length as the scanning period in two of the first frame periods and the pause period in the second frame period in order,
2. The video signal line driving circuit performs polarity inversion driving and sets a signal applied to each video signal line to have the same polarity in the two scanning periods in the predetermined period. The display device described in 1. Each pixel forming portion includes a liquid crystal layer,
The one frame period is composed of the scanning period.
The scanning period included in the predetermined period includes two scanning periods having the same length as the scanning period in the first frame period,
The predetermined period includes a scanning period having the same length as the scanning period in two of the first frame periods and the pause period in the second frame period in order,
2. The video signal line driving circuit according to claim 1, wherein the video signal line driving circuit performs polarity inversion driving, and signals applied to the video signal lines have different polarities in the two scanning periods in the predetermined period. The display device described. The display control circuit includes:
When displaying a moving image in the display unit, the scanning signal line driving circuit is controlled so that the scanning signal line driving circuit drives the plurality of scanning signal line driving circuits in a first driving mode;
When performing still image display in the display unit, the scanning signal line driving circuit is controlled so that the scanning signal line driving circuit drives the plurality of scanning signal line driving circuits in a second driving mode. The display device according to any one of claims 1 to 11. The display device according to any one of claims 1 to 12, wherein the switching element is a thin film transistor in which a semiconductor layer is formed of an oxide semiconductor. Driving a display device including a display unit including a plurality of scanning signal lines, and a scanning signal line driving circuit capable of driving the plurality of scanning signal lines in two types of driving modes, a first driving mode and a second driving mode. A method,
Driving the plurality of scanning signal lines in a cycle of a first frame period including a scanning period in which the plurality of scanning signal lines are sequentially selected in the first drive mode;
In the second drive mode, the scan period and the scan period other than a predetermined period immediately after a change of an image to be displayed, including the scan period and a pause period in which all of the plurality of scan signal lines are in a non-selected state. The plurality of scanning signal lines are driven so that a pause period alternately appears with a second frame period composed of the scan period and the pause period as a cycle, and the length of the scan period in the second frame period And the length of the scanning period in the first frame period, and the ratio of the scanning period in the predetermined period is larger than the ratio of the scanning period in the second frame period. Driving method.

Images