Patent Application
20150302809
The present invention relates to a liquid crystal display device, and specifically relates to a liquid crystal display device which performs pause driving (low-frequency driving), and a method for driving same.
There has hitherto been known an active matrix-type liquid crystal display device provided with a TFT (thin film transistor) as a switching element. This liquid crystal display device is provided with a liquid crystal panel configured of two insulating substrates opposed to each other. The one substrate of the liquid crystal panel is provided with gate bus lines (scanning signal lines) and source bus lines (video signal lines) in a matrix form, and is provided with TFTs in the vicinity of intersections between the gate bus lines and the source bus lines. Each TFT is configured of a gate electrode connected to the gate bus line, a source electrode connected to the source bus line, and a drain electrode. The drain electrode of each TFT is connected to one of a plurality of pixel electrodes that are arranged in a matrix form on the substrate so as to form an image. The other substrate of the liquid crystal panel is provided with a common electrode for applying a voltage between the common electrode and the pixel electrodes through a liquid crystal layer. In such a configuration, based on a video signal that the source electrode of each TFT receives from the source bus line when the gate electrode of this TFT receives an active scanning signal from the gate bus line, a voltage is applied between the pixel electrode and the common electrode. This drives the liquid crystal, and a desired image is displayed on a display portion of the liquid crystal panel.
Incidentally, the liquid crystal has a property that it deteriorates when a DC voltage continues to be applied.
Accordingly, in the liquid crystal display device, AC driving to reverse polarities of pixel voltages (voltages between the pixel electrodes and the common electrode) has been performed in order to suppress deterioration in liquid crystal. As an AC driving technique, a driving technique called frame-reversal driving is known in which the polarities of the pixel voltages are reversed with respect to each frame in a state where the polarities of the pixel voltages in all the pixels are made the same. It is to be noted that the driving technique of reversing the polarities of the pixel voltages with respect to each predetermined period will be hereinafter referred to as a “reversal driving technique”. However, by the frame-reversal driving, flicker is relatively apt to occur at the time of image display. Hence there have hitherto been employed reversal driving techniques of a variety of polarity reversal patterns in order to suppress occurrence of flicker. As the reversal driving technique, column-reversal driving and dot-reversal driving are typically known.
The column-reversal driving is a driving technique of reversing the polarities of the pixel voltages with respect to each frame and each predetermined number of source bus lines. According to the column-reversal driving, the polarities of pixel voltages are reversed with respect to each predetermined number of source bus lines, and hence the frequency of spatial polarity reversal of a liquid crystal applied voltage becomes high as compared to the frame-reversal driving. For example, when the polarities of the pixel voltages are reversed with respect to each one frame and each one source bus line, polarities of pixel voltages in pixels on four rows and four columns in a certain frame become those as shown in
The dot-reversal driving is a driving technique of reversing the polarities of the pixel voltages with respect to each one frame and also reversing the polarities in the pixels adjacent in a vertical or horizontal direction. In this driving technique, polarities of pixel voltages in pixels on four rows and four columns in a certain frame become those as shown in
In general, when a polarity reversal pattern in an employed reversal driving technique is complex, flicker hardly occurs, but power consumption becomes large. On the other hand, when a polarity reversal pattern in an employed reversal driving technique is simple, power consumption becomes small, but flicker is apt to occur. There has thus been required a technique for reducing power consumption while suppressing occurrence of flicker. For example, according to a liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2005-215591, the dot-reversal driving and the column-reversal driving are switched in accordance with a frequency of an input video signal. Further, according to a liquid crystal display device disclosed in Japanese Patent Application Laid-Open No. 2003-337577, two-dot-reversal driving and one-dot-reversal driving are switched in accordance with a vertical frequency.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2005-215591
[Patent Document 2] Japanese Patent Application Laid-Open No. 2003-337577
In recent years, concerning the liquid crystal display device, there has been progress in the development of a driving method where “a pause frame (pause period) for suspending a writing operation by bringing all gate bus lines into a non-scanning state is provided between a refresh frame (writing period) and a refresh frame (writing period)”. Here, the refresh frame means a frame for charging a pixel capacitance in the display portion based on an image signal for one frame (for one screen). The driving method where the pause frame for suspending a writing operation is provided in this manner is called “pause driving”, “low-frequency driving”, and the like. In a liquid crystal display device to which the pause driving is employed, there is no need for giving a controlling signal or the like to a liquid crystal driving circuit (gate driver and source driver) in the pause frame. This leads to reduction in driving frequency of the liquid crystal driving circuit as a whole, thus allowing low power consumption.
As described above, when the pause driving is employed, low power consumption can be realized. However, in the pause driving, flicker is apt to be visually recognized when the refresh rate is low. Therefore, the pause driving also requires a technique for reducing power consumption while suppressing occurrence of flicker. With regard to this, even when the technique disclosed in Japanese Patent Application Laid-Open No. 2005-215591 is employed, a more preferable reversal driving technique is not decided in accordance with a frequency of an input video signal in the pause driving, and hence a desired effect cannot be obtained. Further, even when the technique disclosed in Japanese Patent Application Laid-Open No. 2003-337577 is employed, the frequency of refreshes has a larger influence on occurrence of flicker than the vertical frequency in the pause driving, and hence a desired effect cannot be obtained.
Accordingly, an object of the present invention is to effectively suppress occurrence of flicker while suppressing an increase in power consumption in a liquid crystal display device for performing pause driving.
A first aspect of the present invention is directed to a liquid crystal display device, which employs pause driving to provide a pause frame for suspending a refresh of a screen between two refresh frames for performing a refresh of the screen, and performs image display by applying an AC voltage to liquid crystal based on an image signal irregularly inputted from an external portion, the liquid crystal display device comprising:
a liquid crystal panel that includes a plurality of pixel electrodes arranged in a matrix form and a common electrode provided for applying a voltage between the common electrode and the plurality of pixel electrodes through the liquid crystal, and displays an image based on the image signal;
a liquid crystal panel driving portion that drives the liquid crystal panel; and
a reversal driving control portion that receives the image signal, decides which of a refresh frame or a pause frame each frame is set to, and decides a reversal driving technique for applying an AC voltage to the liquid crystal to be either a first reversal driving technique where the frequency of the spatial polarity reversal of the voltage applied to liquid crystal is relatively low or a second reversal driving technique where the frequency of the spatial polarity reversal of the voltage applied to the liquid crystal is relatively high, to control an operation of the liquid crystal panel driving portion, wherein,
when a frame in which the image signal is inputted from the external portion without requesting the external portion to input the image signal is defined as a first input frame, the reversal driving control portion
sets the reversal driving technique in the first input frame to the first reversal driving technique while setting the first input frame to a refresh frame that is defined as a first refresh frame,
sets n (n is an integer not smaller than 1) frames subsequent to the first refresh frame to pause frames,
sets a frame subsequent to the final pause frame to a refresh frame that is defined as a second refresh frame, and
sets the reversal driving technique in the second refresh frame to the second reversal driving technique.
According to a second aspect of the present invention, in the first aspect of the present invention,
the reversal driving control portion requests the external portion to input the image signal when the image signal is not inputted over a period corresponding to a previously set number of frames.
According to a third aspect of the present invention, in the second aspect of the present invention,
when a frame in which the image signal is inputted from the external portion by requesting the external portion to input the image signal is defined as a second input frame, the reversal driving control portion sets the second input frame to a refresh frame that is defined as the first refresh frame in addition to the first input frame, and sets the reversal driving technique in the second input frame to the first reversal driving technique.
According to a fourth aspect of the present invention, in the second aspect of the present invention,
when a frame in which the image signal is inputted from the external portion by requesting the external portion to input the image signal is defined as a second input frame, the reversal driving control portion sets the second input frame to a refresh frame, and sets the reversal driving technique in the second input frame to the second reversal driving technique.
According to a fifth aspect of the present invention, in the fourth aspect of the present invention,
when an image based on the image signal changes in the second input frame as compared to the previous refresh frame, the reversal driving control portion sets the second input frame to a refresh frame that is defined as the first refresh frame in addition to the first input frame.
According to a sixth aspect of the present invention, in the first aspect of the present invention,
the second refresh frame is made up of a plurality of frames.
According to a seventh aspect of the present invention, in the first aspect of the present invention,
the first reversal driving technique is a column-reversal driving technique, and the second reversal driving technique is a dot-reversal driving technique.
According to an eighth aspect of the present invention, in the first aspect of the present invention,
a potential of the common electrode is set to a value that is different between at the time when the liquid crystal panel is driven by the first reversal driving technique and at the time when the liquid crystal panel is driven by the second reversal driving technique.
According to a ninth aspect of the present invention, in the first aspect of the present invention,
the liquid crystal panel includes
a scanning signal line,
a video signal line which is applied with a video signal in accordance with the image signal, and
a thin film transistor where a control terminal is connected to the scanning signal line, a first conduction terminal is connected to the video signal line, a second conduction terminal is connected to the pixel electrode, and a channel layer is formed of an oxide semiconductor.
According to a tenth aspect of the present invention, in the ninth aspect of the present invention, the oxide semiconductor is indium gallium zinc oxide mainly composed of indium (In), gallium (Ga), zinc (Zn), and oxygen (O).
An eleventh aspect of the present invention is directed to a driving method of a liquid crystal display device, which employs pause driving to provide a pause frame for suspending a refresh of a screen between two refresh frames for performing a refresh of the screen and performs image display by applying an AC voltage to liquid crystal based on an image signal irregularly inputted from an external portion, the driving method comprising:
a liquid crystal panel driving step of driving a liquid crystal panel that includes a plurality of pixel electrodes arranged in a matrix form and a common electrode provided for applying a voltage between the common electrode and the plurality of pixel electrodes through the liquid crystal, and displays an image based on the image signal; and
a reversal driving control step of receiving the image signal, deciding which of a refresh frame or a pause frame each frame is set to, and deciding a reversal driving technique for applying an AC voltage to the liquid crystal to be either a first reversal driving technique where the frequency of the spatial polarity reversal of the voltage applied to the liquid crystal is relatively low or a second reversal driving technique where the frequency of the spatial polarity reversal of the voltage applied to the liquid crystal is relatively high, to control an operation of the liquid crystal panel driving portion, wherein,
when a frame in which the image signal is inputted from the external portion without requesting the external portion to input the image signal is defined as a first input frame, in the reversal driving control step,
the first input frame is set to a refresh frame that is defined as a first refresh frame, and the reversal driving technique in the first input frame is set to the first reversal driving technique,
n (n is an integer not smaller than 1) frames subsequent to the first refresh frame are set to pause frames,
a frame subsequent to the final pause frame is set to a refresh frame that is defined as a second refresh frame, and
the reversal driving technique in the second refresh frame is set to the second reversal driving technique.
According to the first aspect of the present invention, when an image signal is inputted from the external portion without requesting the external portion to input the image signal, there is performed a refresh by the first reversal driving technique with a relatively low frequency of spatial polarity reversal of the liquid crystal applied voltage. After a frame in which the refresh by the first reversal driving technique has been performed, a refresh frame (second refresh frame), in which the reversal driving technique is the second reversal driving technique with a relatively high frequency of spatial polarity reversal of the liquid crystal applied voltage, is provided with several pause frames put between the refresh frames. Here, when the image signal is frequently inputted (when the image signal is inputted again after input of the image signal and before appearance of the second refresh frame), a refresh by the second reversal driving technique is not performed, and only a refresh by the first reversal driving technique is performed. In contrast, when the frequency of input of the image signal is low, both the refresh by the first reversal driving technique and the refresh by the second reversal driving technique are performed. When a refresh is frequently performed, flicker is hardly visually recognized, and hence the display quality does not deteriorate even when the first reversal driving technique with a relatively low frequency of spatial polarity reversal of the liquid crystal applied voltage is employed. Instead there is obtained a power consumption reducing effect by employing such a reversal driving technique. Further, because a refresh by the second reversal driving technique with a relatively high frequency of the spatial polarity reversal of the liquid crystal applied voltage is inserted when the frequency of input of the image signal is low, deterioration in display quality due to flicker can be suppressed. From the above, according to the present embodiment, in the liquid crystal display device which performs the pause driving, it is possible to effectively suppress occurrence of flicker while suppressing an increase in power consumption.
According to the second aspect of the present invention, deterioration in pixel voltage due to performance of no refresh for a long period is prevented.
According to the third aspect of the present invention, even when the image signal is inputted by requesting the external portion to input the image signal, the refresh by the first reversal driving technique is performed. Then, the refresh by the second reversal driving technique is performed with several pause frames put between the refreshes. Therefore, even when the frequency of input of the image signal is extremely low, both the refresh by the first reversal driving technique and the refresh by the second reversal driving technique are performed. Thereby, similarly to the first aspect of the present invention, in the liquid crystal display device which performs the pause driving, it is possible to effectively suppress occurrence of flicker while suppressing an increase in power consumption.
According to the fourth aspect of the present invention, when the image signal is inputted by requesting the external portion to input the image signal, the refresh by the second reversal driving technique is performed. Therefore, when the image signal is not inputted for a long period, the refresh by the second reversal driving technique with a relatively high frequency of spatial polarity reversal of the liquid crystal applied voltage is performed. Accordingly, occurrence of flicker at the time of no image signal being inputted for a long period is effectively suppressed.
According to the fifth aspect of the present invention, at the time of the image signal being inputted by requesting the external portion to input the image signal, when the image changes, the refresh by the second reversal driving technique is performed with several pause frames put between the refreshes. Therefore, when the image changes after the state where the image signal is not inputted continues for a long time, a plurality of times of writing (charging) into the pixel capacitance are performed. Hence the pixel voltage reliably reaches a target voltage in each pixel, thereby preventing deterioration in display quality.
According to the sixth aspect of the present invention, the second refresh frame is made up of two frames. This suppresses occurrence of screen burn-in caused by deviation of the polarity of the pixel voltage in each pixel.
According to the seventh aspect of the present invention, the reversal driving technique is switched between the column-reversal driving technique where power consumption is low and the dot-reversal driving technique where flicker is hardly visually recognized, whereby it is possible to reliably achieve the effect of the first aspect of the present invention.
According to the eighth aspect of the present invention, even when the optimum common electrode potential is different between at the time when the liquid crystal panel is driven by the first reversal driving technique and at the time when the liquid crystal panel is driven by the second reversal driving technique, it is possible to suppress deterioration in liquid crystal.
According to the ninth aspect of the present invention, a thin film transistor where a channel layer is formed of an oxide semiconductor is used as the thin film transistor provided in the liquid crystal panel. Therefore, a voltage written into the capacitance (pixel capacitance) between the pixel electrode and the common electrode is held over a long time. Hence it is possible to lower the frequency of refreshes when the image signal is not inputted from the external portion, without causing deterioration in display quality. From the above, in the liquid crystal display device for performing the pause driving, it is possible to significantly reduce power consumption while suppressing occurrence of flicker.
According to the tenth aspect of the present invention, by using indium gallium zinc oxide as the oxide semiconductor that forms the channel layer, it is possible to reliably achieve the effect of the ninth aspect of the present invention.
According to the eleventh aspect of the present invention, a similar effect to that of the first aspect of the present invention can be obtained in the method for driving the liquid crystal display device.
Hereinafter, one embodiment of the present invention will be described with reference to attached drawings. It is to be noted that in the present specification, charging of a pixel capacitance in a display portion based on an image signal for one frame regardless of the presence or absence of an image change is referred to as “refresh”.
<1. Whole Configuration and Summary of Operation>
In the liquid crystal display device according to the present embodiment, pause driving (low-frequency driving) is performed (see
Concerning
As described above, in the liquid crystal display device according to the present embodiment, the pause driving is performed. In the present embodiment, an oxide TFT (thin film transistor using an oxide semiconductor for a channel layer) is typically used as the TFT 31 in the pixel formation portion. More specifically, the channel layer of the TFT 31 is formed of InGaZnOx: indium gallium zinc oxide, mainly composed of indium (In), gallium (Ga), zinc (Zn), and oxygen (O). Hereinafter, a TFT using InGaZnOx for the channel layer will be referred to as an “IGZO-TFT”. Incidentally, a thin film transistor using amorphous silicon or the like for the channel layer (hereinafter referred to as “silicon TFT”) has a relatively large off-leak current. For this reason, in the case of using the silicon TFT as the TFT 31 in the pixel formation portion, an electric charge held in the pixel capacitance Cp leaks through the TFT 31, resulting in fluctuation in voltage that is to be held at the time of an off-state. In contrast, the IGZO-TFT has a far smaller off-leak current as compared to the silicon TFT. Hence it is possible to hold a voltage written into the pixel capacitance Cp (liquid crystal applied voltage) for a longer period. The
IGZO-TFT is thus preferable for the case of performing the pause driving. It should be noted that a similar effect is obtained also in the case of using, for the channel layer, an oxide semiconductor containing at least one of indium, gallium, zinc, copper (Cu), silicon (Si), tin (Sn), aluminum (Al), calcium (Ca), germanium (Ge), and lead (Pb), for example. Further, using the oxide TFT as the TFT 31 in the pixel formation portion is a mere example, and in place of this, the silicon TFT or the like may be used.
Next, operations of the constitutional elements shown in
Accordingly, the plurality of gate bus lines GL are selectively driven one by one.
In such a manner as above, by the driving video signal being applied to each source bus line SL and the scanning signal being applied to each gate bus line GL, an image based on the image signal DAT is displayed on the display portion 30 of the liquid crystal panel 300.
As described above, the image signal DAT is irregularly transmitted from the external portion (host) to this liquid crystal display device. With regard to this, a frame in which the image signal DAT has been inputted from the external portion (host) without outputting a request signal RO to the external portion (host) will be hereinafter referred to as a “first input frame”. Further, a frame in which the image signal DAT has been inputted from the external portion by outputting the request signal RO to the external portion (host) will be hereinafter referred to as a “second input frame”. It is to be noted that the reason why the configuration has been formed so as to irregularly transmit the image signal DAT is because the image signal DAT is not necessarily required to be inputted in all frames in the liquid crystal display device that employs the pause driving.
<2. Configuration and Operation of Driver Control Portion>
Next, a description will be given of a configuration and an operation of the driver control portion 100 in the present embodiment.
The reversal driving control portion 10 receives the image signal DAT and decides which of a refresh frame or a pause frame each frame is set to, and also decides the reversal driving technique for applying an AC voltage to the liquid crystal. Then, in the frame that is set to the refresh frame, the reversal driving control portion 10 outputs the digital video signal DV based on the image signal DAT, and also outputs the source start pulse signal SSP, the source clock signal SCK, the latch strobe signal LS, the gate start pulse signal GSP, and the gate clock signal GCK such that the liquid crystal panel 300 is driven in accordance with the decided reversal driving technique. Further, the reversal driving control portion 10 outputs the request signal RO to the external portion (host) as required. A variety of set values concerning the decision of the refresh frame and the decision of the reversal driving technique are stored in the register group 12, and those set values are referred to by the reversal driving control portion 10.
In the present embodiment, it is assumed that the register group includes four registers having register names of “REF”, “NREF”, “REFINT”, and “REFDET”. What each register serves for will be described later. Further, it is assumed that values of the above four registers are set as follows.
It is to be noted that in the present embodiment, either column-reversal driving (see
Next, with reference to
In the present embodiment, the first input frame (frame in which the image signal DAT is inputted from the external portion without outputting the request signal RO) is set to a refresh frame. Further, regardless of the presence or absence of an image change and the number of times of pause frames after performance of the previous refresh, the reversal driving technique in the first input frame is set to the column-reversal driving. It is to be noted that, in the reversal driving control portion 10, for example, when a vertical synchronization signal is detected, it is determined that the image signal DAT has been inputted. For example, when an image signal DAT is inputted in the fifth frame on the assumption that a certain frame is taken as the zero-th frame, the fifth frame is set as a refresh frame, and the reversal driving technique in the fifth frame is set to the column-reversal driving, as shown in
Incidentally, when the number of times (nine times in the present embodiment) of pause frames set by the register NREF are generated after the previous refresh frame without input of the image signal DAT, the request signal RO is outputted to the external portion (host) such that the image signal DAT is inputted in the next frame after the final pause frame. In the present embodiment, when the previous refresh frame is taken as zero-th frame, the request signal RO is outputted in the ninth frame, as shown in
Further, in the present embodiment, a refresh is also performed after the first input frame as described later, and hence the first input frame is defined as the first refresh frame. The number of times (three times in the present embodiment) of frames set by the register REFINT, which follow the first refresh frame, are set as pause frames. Then, one or a plurality of frames subsequent to the final pause frame is set as a refresh frame (this refresh frame is defined as a second refresh frame). The number of second refresh frames is set such that a total of the number of first refresh frames (once in the present embodiment) and the number of second refresh frames becomes the number of times set by the register REFDET (three times in the present embodiment). The reversal driving technique in the second refresh frame is set to the dot-reversal driving. It is to be noted that in the second refresh frame, the image signal DAT is inputted from the external portion by the request signal RO being outputted in the previous frame. As grasped from the above, the register REFINT serves to hold the number of times of pause frames between the first refresh frame and the second refresh frame, and the register REFDET serves to hold a sum of the number of times of first refresh frames and second refresh frames.
For example, when an image signal DAT is inputted in the third frame on the assumption that a certain frame is taken as the zero-th frame, the fourth to sixth frames are set as pause frames, and the seventh and eighth frames are set as refresh frames (second refresh frames), as shown in
Further, in the present embodiment, a refresh is performed also after the second input frame. Therefore, the second input frame is also defined as the first refresh frame in addition to the first input frame. For example, when an image signal DAT is inputted from the external portion in the tenth frame by output of the request signal RO in the ninth frame on the assumption that the previous refresh frame is taken as the zero-th frame, the eleventh frame to the thirteenth frame are set as pause frames, and the fourteenth frame and the fifteenth frame are set as refresh frames (second refresh frames), as shown in
As described above, in the present embodiment, after the first refresh frame, three times of pause frames are generated, and then the second refresh frame is given. However, the image signal DAT may be inputted before generation of three times of pause frames. For example, it is assumed that a certain frame is taken as the zero-th frame, the image signal DAT is inputted in the first frame, and thereafter the image signal DAT is inputted also in the third frame. In this case, the third frame is set to a refresh frame, and the reversal driving technique in the third frame is set to the column-reversal driving (see
Further, when a refresh by the column-reversal driving is performed consecutively in two frames (the second and third frames in
<4. Concrete Example>
Next, with reference to
<4.1 First Concrete Example>
A first concrete example will be described with reference to
Thereafter, the image signal DAT is inputted in the ninth frame. Thereby, the ninth frame becomes a refresh frame in which the reversal driving technique is the column-reversal driving. Then, the tenth to twelfth frames become pause frames, and the thirteenth and fourteenth frames become refresh frames (second refresh frames) in which the reversal driving technique is the dot-reversal driving.
Thereafter, the image signal DAT is inputted in the twentieth frame, the thirty-second frame, the thirty-ninth frame, and the forty-sixth frame. Thereby, the refresh frame and the reversal driving technique are decided in a way similar to the time when the image signal DAT is inputted in the ninth frame. After performance of a refresh by the dot-reversal driving in the fifty-first frame, the number of times (nine times in the present embodiment) of pause frames (the fifty-second to sixtieth frames) set by the register NREF have been generated without input of the image signal DAT, and hence the request signal RO is outputted to the external portion (host) in the final pause frame (the sixtieth frame).
<4.2 Second concrete Example>
A second concrete example will be described with reference to
Thereafter, the twentieth frame and the twenty-first frame are made to be refresh frames as the second refresh frames. That is, the dot-reversal driving is performed in the twentieth frame and the twenty-first frame.
Thereafter, the number of times (nine times in the present embodiment) of pause frames (the twenty-second to thirtieth frames) set by the register NREF have been generated without input of the image signal DAT, and hence the request signal RO is outputted to the external portion (host) in the final pause frame (the thirtieth frame). Then, the image signal DAT is inputted from the external portion in the thirty-first frame. Thereby, the thirty-first frame becomes a refresh frame in which the reversal driving technique is the dot-reversal driving. Then, the thirty-second to thirty-fourth frames become pause frames, and the thirty-fifth and thirty-sixth frames become refresh frames (second refresh frames) where the reversal driving technique is the dot-reversal driving.
Thereafter, the number of times of pause frames (the thirty-seventh to forth-fifth frames) set by the register NREF have been generated without input of the image signal DAT, and hence the request signal RO is outputted to the external portion (host) in the final pause frame (the forty-fifth frame). Thereby, the forty-sixth frame becomes a refresh frame in which the reversal driving technique is the dot-reversal driving. Thereafter, the image signal DAT is inputted also in the forty-seventh frame, and the forty-seventh frame becomes a refresh frame in which the reversal driving technique is the dot-reversal driving. In such a manner, a refresh by the column-reversal driving is performed consecutively in two frames in the forty-sixth frame and the forty-seventh frame. Therefore, the second refresh frame is provided after the latter refresh frame (the forty-seventh frame) with three times of pause frames put between the refresh frames. That is, the fifty-first and fifty-second frames are refresh frames in which the reversal driving technique is the dot-reversal driving.
<4.3 About Common Electrode Potential>
Incidentally, in the example shown in
<5. Effect>
According to the present embodiment, when the image signal DAT is inputted from the external portion without requesting the external portion to input the image signal DAT, a refresh by the column-reversal driving is performed. Further, when a previously set number of times of pause frames are generated after the previous refresh frame, the request signal RO for requesting the external portion to input the image signal DAT is outputted. Then, a refresh by the column-reversal driving is performed also when the image signal DAT is inputted in accordance with output of the request signal RO. After the refresh frame in which the column-reversal driving has been performed, a refresh frame (second refresh frame) in which the reversal driving technique is the dot-reversal driving is provided with several pause frames (three frames in the present embodiment) put between the refresh frames. From the above, when the image signal DAT is frequently inputted (see the first to sixteenth frames in
Moreover, as described above, after the refresh frame in which the column-reversal driving has been performed, a refresh frame (second refresh frame) in which the reversal driving technique is the dot-reversal driving is provided with a pause frame put between the refresh frames. This prevents deterioration in display quality due to continuing a state where writing into the pixel capacitance is performed by the column-reversal driving for a long time.
Further, the dot-reversal driving is performed in the second refresh frame. In the present embodiment, the second refresh frame is made up of two frames. This suppresses occurrence of screen burn-in caused by deviation of the polarity of the pixel voltage in each pixel.
Furthermore, according to the present embodiment, the potential of the common electrode 33 is set to a different value between at the time when the column-reversal driving is performed and at the time when the dot-reversal driving is performed. For this reason, even when the optimum common electrode potential is different between the column-reversal driving and the dot-reversal driving, it is possible to suppress deterioration in liquid crystal.
Further, when a TFT using an oxide semiconductor for a channel layer is employed as the TFT 31 that is provided in the display portion 30 of the liquid crystal panel 300, a voltage written in a capacitance (pixel capacitance Cp) between the pixel electrode 32 and the common electrode 33 is held over a long time. Hence it is possible to make a refresh rate still lower (make the set value of the foregoing register NREF larger) without causing deterioration in display quality. Accordingly, the frequency of refreshes when the image signal is not inputted from the external portion becomes low, thus allowing significant reduction in power consumption.
Especially by employing InGaZnOx as the oxide semiconductor, it is possible to reliably obtain a power consumption reducing effect.
<6 Modified Example>
<6.1 About Frame After Transmission of Request Signal>
In the above embodiment, the column-reversal driving is performed in the second input frame (a frame in which the image signal DAT has been inputted from the external portion by output of the request signal RO to the external portion), a refresh frame (second refresh frame) in which the reversal driving technique is the dot-reversal driving is provided after several frames since the second input frame. However, the present invention is not limited to this. The configuration may be such that “the dot-reversal driving is performed in the second input frame (see the tenth frame in
<6.2 About Reversal Driving Technique>
In the above embodiment, the reversal driving technique is switched between the column-reversal driving and the dot-reversal driving. However, the present invention is not limited to this. For example, assuming “p >q”, the configuration may be such that “a refresh by p-dot-reversal driving is performed in the first refresh frame, and a refresh by q-dot-reversal driving is performed in the second refresh frame”. In this case, the p-dot-reversal driving corresponds to the first reversal driving technique, and a q-dot-reversal driving corresponds to the second reversal driving technique. Further, the configuration may be such that “a refresh by the column-reversal driving is performed in the first refresh frame, and a refresh by multi-dot-reversal driving is performed in the second refresh frame”. In this case, the column-reversal driving corresponds to the first reversal driving technique, and the multi-dot-reversal driving corresponds to the second reversal driving technique. As described above, the two employed reversal driving techniques are not particularly limited.
10: REVERSAL DRIVING CONTROL PORTION
12: REGISTER GROUP
22: SOURCE DRIVER
24: GATE DRIVER
30: DISPLAY PORTION
31: TFT (THIN FILM TRANSISTOR)
32: PIXEL ELECTRODE
33: COMMON ELECTRODE
100: DRIVER CONTROL PORTION
200: PANEL DRIVING PORTION
300: LIQUID CRYSTAL PANEL
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-254457 | Nov 2012 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2013/080628 | 11/13/2013 | WO | 00 |
