Patent Application
20130147780
The present application claims priority from Japanese application JP2011-271137 filed on Dec. 12, 2011, the content of which is hereby incorporated by reference into this application.
1. Field of the Invention
The present invention relates to a display device.
2. Description of the Related Art
Conventionally, there is known a display device in which display is controlled by changing a voltage to be applied to each pixel in a display panel. Known examples include a liquid crystal display device for changing a voltage to be applied to a liquid crystal composition sealed in a liquid crystal display panel, and an organic EL display device. In such a display device, a pixel electrode is disposed in a region surrounded by data signal lines (image signal lines) and scanning signal lines that intersect with each other, and each pixel electrode is applied with a grayscale voltage from a data signal supplied via the data signal line.
For example, Japanese Patent Application Laid-open No. 2001-109435 and Japanese Patent No. 4027691 describe a display device in which a plurality of data signal lines are defined as a set and a plurality of sets of data signal lines are arranged in a display panel and which includes a selector circuit for switching a data signal line to be connected to an output terminal for outputting a data signal.
In Japanese Patent Application Laid-open No. 2001-109435 and Japanese Patent No. 4027691, however, when a transistor included in the selector circuit changes from the ON state to the OFF state, a feedthrough voltage is generated due to the parasitic capacitance of the transistor (such as the gate-drain parasitic capacitance). As a result, a voltage fluctuation occurs in the data signal, and hence a correct grayscale voltage cannot be applied to a pixel electrode.
To deal with this problem, it is conceivable to connect a transistor between the selector circuit and the data signal line and drive the transistor with the use of a gate signal in anti-phase to a gate signal input to the selector circuit, to thereby cancel out the voltage fluctuation caused by the feedthrough voltage. In this case, however, it is necessary to provide an additional gate signal line for operating the above-mentioned transistor, resulting in a problem in that the display device is increased in size and power consumption.
The present invention has been made in view of the above-mentioned problem, and it is an object thereof to provide a display device capable of reducing the influence of a feedthrough voltage while achieving downsizing and power saving.
According to an exemplary embodiment of the present invention, there is provided a display device, including: a data signal generation unit for generating a data signal for controlling a pixel; a plurality of transistors for supplying the data signal output from the data signal generation unit to a plurality of data signal lines of a display panel in a time sharing manner; a gate signal line for controlling each of the plurality of transistors; and a fluctuation suppression unit connected to the gate signal line that controls any one of the plurality of transistors, for suppressing, in accordance with a gate signal of the connected gate signal line, a voltage fluctuation in the data signal which occurs when another one of the plurality of transistors changes from an ON state to an OFF state. According to this exemplary embodiment of the present invention, the influence of the feedthrough voltage can be reduced while achieving downsizing and power saving of the display device.
Further, according to another exemplary embodiment of the present invention, the fluctuation suppression unit suppresses the voltage fluctuation in the data signal in accordance with a change in the gate signal of the connected gate signal line in a period from when the another one of the plurality of transistors has changed from the ON state to the OFF state until write timing of the data signal. According to this exemplary embodiment, the potential of the data signal can be maintained until the write timing, and hence an accurate grayscale voltage can be applied to a pixel electrode.
Further, according to still another exemplary embodiment of the present invention, the one of the plurality of transistors, which is controlled by the gate signal line connected to the fluctuation suppression unit, changes from the OFF state to the ON state in a case where the another one of the plurality of transistors changes from the ON state to the OFF state, and the fluctuation suppression unit suppresses the voltage fluctuation in the data signal in accordance with the gate signal that controls the one of the plurality of transistors, which is controlled by the connected gate signal line, so as to change from the OFF state to the ON state. According to this exemplary embodiment, at the timing at which a potential drop occurs due to the feedthrough voltage, a potential increase for cancelling out the potential drop can be applied to the data signal.
In the accompanying drawings:
Referring to the accompanying drawings, a display device according to an embodiment of the present invention is described in detail below. The following exemplifies the application of the display device according to the present invention to a liquid crystal display device.
Scanning signal lines GN controlled by a scanning signal drive circuit 130 and data signal lines DM controlled by a data signal drive circuit 140 are wired throughout the TFT substrate 120. The scanning signal lines GN and the data signal lines DM form pixel portions 150 of the liquid crystal display device 1. Note that, M of the data signal lines DM and N of the scanning signal lines GN are natural numbers corresponding to the number of columns and the number of lines of the pixel portions 150, respectively.
Although simplified in
The scanning signal line GN is supplied with a scanning signal from the scanning signal drive circuit 130. A thin film transistor included in the pixel portion 150 is turned ON/OFF based on the scanning signal. The data signal line DM, on the other hand, is supplied with a data signal from the data signal drive circuit 140. When the thin film transistor in the pixel portion 150 is turned ON (when write timing has come), the data signal is supplied from the data signal line DM so that a grayscale voltage is applied to a pixel electrode, thereby changing the orientation direction of liquid crystal molecules of the liquid crystal composition. As a result, light transmissivity changes, thereby performing display control of the liquid crystal display device 1.
Note that, the liquid crystal display panel 100 may employ an in-plane switching (IPS) mode in which two electrodes are provided on the TFT substrate 120 or alternatively a twisted nematic (TN) or vertical alignment (VA) mode in which an electrode is provided on each of the color filter substrate 110 and the TFT substrate 120.
As illustrated in
The controller 180 acquires at least display information and a control signal from an external device (such as a flexible board (not shown)). The control signal output from the controller 180 includes timing signals such as a clock signal for the source IC unit 160 to fetch the display information, a time sharing control signal for switching the output of the distribution control unit 170 to the data signal line DM, a frame start instruction signal for driving the scanning signal drive circuit 130, and a gate clock signal for sequentially outputting the scanning signals.
The display information output from the controller 180 is input to the source IC unit 160 via the data bus line 161. Pieces of the display information are output through the data bus line 161 in a predetermined order. The source IC unit 160 fetches data to be displayed from among the pieces of display information output in order. Timing at which the source IC unit 160 fetches the display information is based on the clock signal output from the controller 180. Note that, a signal line for the source IC unit 160 to acquire the clock signal from the controller 180 is omitted in
The source IC unit 160 is disposed in, for example, the lateral direction (X axis direction) along the periphery of the TFT substrate 120. In this embodiment, the source IC unit 160 functions as a data signal generation unit for generating a data signal for controlling the pixel portion 150 (that is, the orientation of liquid crystal).
For example, the source IC unit 160 acquires display information from the controller 180 via the data bus line 161, thereby generating and outputting a data signal. For example, the source IC unit 160 converts the display information input from the controller 180 into a data signal indicating a grayscale voltage corresponding to the display information, and outputs the data signal to the distribution control unit 170 via an output signal line 162.
Note that, in this embodiment, the number of the output signal lines 162 corresponds to the number “M” of the data signal lines DM. The output signal line 162 corresponding to the data signal line DM is hereinafter referred to as “output signal line 162M”.
The distribution control unit 170 is connected to the output signal line 162M. The output of the distribution control unit 170 is connected to the data signal line DM. The distribution control unit 170 supplies the data signal output from the source IC unit 160 to the plurality of data signal lines DM in a time sharing manner. In other words, the distribution control unit 170 switches the connections between the output signal line 162 of the source IC unit 160 and the plurality of data signal lines Dm. More specifically, the distribution control unit 170 switches the connections between the output signal line 162M and the plurality of data signal lines DM in accordance with a distribution control signal supplied from the controller 180 via the distribution control signal line 171, and outputs the data signal to the data signal line DM for a predetermined period.
In this embodiment, the distribution control unit 170 includes a distribution unit 172M and a fluctuation suppression unit 173M. Note that, “M” of the distribution unit 172M and the fluctuation suppression unit 173M corresponds to “M” of the data signal line DM.
The distribution unit 172M is connected to the output signal line 162M. The connection destination of the output signal line 162M is switched for every predetermined period by the distribution unit 172M. Thus, the output of the source IC unit 160 can be input to any one of data signal lines DRM, DGM and DBM corresponding to red (R), green (G), and blue (B) pixels, respectively.
For example, in a period during which the source IC unit 160 and the data signal line DM are connected to each other by the distribution unit 172M, a data signal is output from the source IC unit 160 to the data signal line D. Similarly, in a period during which the source IC unit 160 and the data signal line DGM are connected to each other, a data signal is output from the source IC unit 160 to the data signal line DGM. In a period during which the source IC unit 160 and the data signal line DBM are connected to each other, a data signal is output from the source IC unit 160 to the data signal line DBM.
The fluctuation suppression unit 173M is disposed between the distribution unit 172M and the data signal line DM, and suppresses a voltage fluctuation in the data signal caused by a feedthrough voltage. The feedthrough voltage is generated when the distribution unit 172M switches the connections. The fluctuation suppression unit 173M is driven by the distribution control signal supplied from the controller 180 via the distribution control signal line 171.
The transistor TM supplies the data signal, which is input from the source IC unit 160 via the output signal line 162M, to the plurality of data signal lines DM of the liquid crystal display panel 100 in a time sharing manner. The distribution control signal line 171 connected to a gate terminal of the transistor TM functions as a gate signal line for controlling each of the plurality of transistors TM. In other words, based on the distribution control signal of the distribution control signal line 171, the transistor TM connected to the distribution control signal line 171 is controlled to be turned ON/OFF, thereby switching the connection destination of the output signal line 162M.
In this embodiment, the distribution control signal lines 171 connected to the gate terminals of the transistors TRM, TGM, and TBM are referred to as “distribution control signal lines 171R, 171G, and 171B”, respectively. When the transistors TRM, TGM, and TBM become electrically conductive, the output signal line 162M and the data signal line DM are connected to each other.
The transistor TRM connects the data signal line DRM for red (R) pixel and the output signal line 162M of the source IC unit 160 to each other for a period during which a data signal for red (R) is output. Similarly, the transistor TGM connects the data signal line DGM for green (G) pixel and the output signal line 162M of the source IC unit 160 to each other for a period during which a data signal for green (G) is output. The transistor TEN connects the data signal line DBM for blue (B) pixel and the output signal line 162M of the source IC unit 160 to each other for a period during which a data signal for blue (B) is output.
Note that, in this embodiment, description is given of an example where one horizontal scanning period is divided into three in a time sharing manner so that the data signals are repeatedly output from the source IC unit 160 in order of blue (B), green (G), and red (R). In other words, description is given of an example where the output signal line 162M is repeatedly connected to the data signal lines DBM, DGM, and DRM in the stated order.
As illustrated in
The canceller CM is formed of a capacitive element having a given electrostatic capacitance. In this embodiment, description is given of an example where the canceller CM is formed of a transistor whose source and drain are electrically connected to each other and whose gate electrode is connected to the distribution control signal line 171. The source or drain of the canceller CM is connected to the source or drain of another transistor TM. The canceller CM outputs a signal in anti-phase to the distribution control signal input to the another transistor TM, to thereby suppress the voltage fluctuation in the data signal caused by the feedthrough voltage. In other words, the canceller CM can be regarded as an element for providing the data signal with a potential increase corresponding to a potential drop caused by the feedthrough voltage generated in the another transistor TM.
Note that, the feedthrough voltage in this embodiment refers to a potential drop of the data signal which occurs when the transistor TM changes from the ON state to the OFF state. For example, the potential drop occurs due to the parasitic capacitance formed between the gate electrode of the transistor TM and the drain electrode and/or the source electrode thereof. In other words, when the data signal is affected by the feedthrough voltage, the potential of the data signal line DRM decreases by the feedthrough voltage. As a result, an accurate grayscale voltage may not be applied to the pixel electrode of the pixel portion 150.
To deal with this problem, in this embodiment, the canceller CM is used to suppress the voltage fluctuation in the data signal caused by the feedthrough voltage of the transistor TM. In this case, the cancellers CB1M and CB2M suppress a voltage fluctuation caused by a feedthrough voltage of the transistor TBM, and the canceller CGM suppresses a voltage fluctuation caused by a feedthrough voltage of the transistor T.
Further, in this embodiment, the canceller CM suppresses the voltage fluctuation in the data signal in accordance with a change in the distribution control signal (gate signal) of the connected distribution control signal line 171 in a period from when another transistor TM has changed from the ON state to the OFF state until the write timing of the data signal.
The write timing of the data signal is timing at which a grayscale voltage indicated by the data signal is applied to the pixel electrode, and is controlled by the scanning signal of the scanning signal line GN. For example, the write timing of the data signal is set to be timing at which a data signal line DM to be connected to the output signal line 162M last from among the plurality of data signal lines DM (such as the data signal line DRM) is disconnected. In this embodiment, timing at which the output signal line 162M and the data signal line DRM are disconnected from each other, that is, timing at which the transistor TRM changes from the ON state to the OFF state is set as the write timing of the data signal.
Further, in this embodiment, the transistor TM controlled by the distribution control signal line 171 connected to the canceller CM changes from the OFF state to the ON state when another transistor TM changes from the ON state to the OFF state. The canceller CM suppresses a voltage fluctuation in the data signal in accordance with the distribution control signal (gate signal) for controlling the transistor TM controlled by the connected distribution control signal line 171 so as to change from the OFF state to the ON state. In other words, when another transistor TM changes from the ON state to the OFF state, a distribution control signal in anti-phase to that of the another transistor TM is input to the canceller CM, with the result that the canceller CM outputs a voltage fluctuation in anti-phase to the voltage fluctuation occurring in the another transistor TM.
As illustrated in
Next, when the potential of the distribution control signal line 171B becomes Low (OFF voltage) at time t2, the transistor TBM becomes the OFF state (non-conductive state), and hence a feedthrough voltage is generated due to the parasitic capacitance of the transistor TBM. In other words, the potential of the data signal line DBM which has been originally connected to the transistor TBM, becomes a potential obtained by subtracting a drop caused by the feedthrough voltage from the potential V3.
At time t2, however, the potential of the distribution control signal line 171G becomes High, and hence a voltage increase occurs due to the parasitic capacitance of the canceller CB1M connected to the distribution control signal line 171G, and the voltage increase cancels out the feedthrough voltage drop corresponding to the transistor TBM. In other words, the potential of the data signal line DBM is maintained to be the potential V3.
Next, when the potential of the distribution control signal line 171G becomes Low at time t3, a feedthrough voltage is generated due to the parasitic capacitance of the canceller CB1M connected to the distribution control signal line 171G. At time t3, however, the potential of the distribution control signal line 171R becomes High, and hence a voltage increase occurs due to the parasitic capacitance of the canceller CB2M connected to the distribution control signal line 171R, and the voltage increase cancels out the feedthrough voltage drop generated in the canceller CB1M. In other words, the potential of the data signal line DBM is maintained to be the potential V3.
Then, when the write timing to the pixel portion 150 has come at time t4, the voltage V3 is applied to the pixel electrode of the pixel portion 150 corresponding to blue (B).
Next, description is given of writing to a green (G) pixel.
As illustrated in
At time t3, however, the potential of the distribution control signal line 171R becomes High, and hence a voltage increase occurs due to the parasitic capacitance of the canceller CGM connected to the distribution control signal line 171R, and the voltage increase cancels out the feedthrough voltage drop corresponding to the transistor TGM. In other words, the potential of the data signal line DGM is maintained to be the potential V1.
Then, when the write timing to the pixel portion 150 has come at time t4, writing to the pixel portion 150 corresponding to green (G) is performed, and the voltage V1 is applied to the pixel electrode.
Note that, at time t4, when the potential of the distribution control signal line 171R becomes Low, a voltage drop occurs due to the parasitic capacitance of the canceller CGM connected to the distribution control signal line 171R, with the result that the potential of the data signal line DGM becomes a potential obtained by subtracting the voltage drop (the amount of potential drop is represented by α) from the voltage V1 (times t4 and t5). However, before the voltage drop occurs, writing to the pixel portion 150 corresponding to green (G) has already been performed based on the voltage V1. Thus, the voltage fluctuation in the data signal does not affect the display control.
Finally, description is given of writing to a red (R) pixel.
As illustrated in
Then, when the write timing to the pixel portion 150 has come at time t4, writing to the pixel portion 150 corresponding to red (R) is performed, and the voltage V2 is applied to the pixel electrode.
Note that, at time t4, when the potential of the distribution control signal line 171R becomes Low, a voltage drop (the amount of potential drop is represented by β) occurs due to the parasitic capacitance of the transistor TRM connected to the distribution control signal line 171R, with the result that the potential of the data signal line DRM becomes a potential obtained by subtracting the voltage drop from the voltage V2 (times t4 to t6). However, before the voltage drop occurs, writing to the pixel portion 150 has already been performed based on the voltage V2. Thus, the fluctuation of the grayscale voltage does not affect the display control.
In the above description, the voltage fluctuation in the data signal is suppressed during times t1 to t4. However, the voltage fluctuation caused by the feedthrough voltage is also suppressed at subsequent times similarly.
As described above, in the liquid crystal display device 1 according to this embodiment, the canceller CM driven by the distribution control signal of the distribution control signal line 171 suppresses the voltage fluctuation caused by the feedthrough voltage of the transistor TM in accordance with the distribution control signal. Any additional signal line or the like is not required to suppress the voltage fluctuation caused by the feedthrough voltage. Thus, the influence of the feedthrough voltage can be reduced while achieving downsizing and power saving of the liquid crystal display device 1.
Further, the canceller CM suppresses the voltage fluctuation in the data signal in the period until the write timing to the pixel portion 150. Thus, the potential of the data signal can be maintained until the write timing, and hence an accurate grayscale voltage can be applied to the pixel electrode.
Further, at the timing at which a potential drop occurs due to the feedthrough voltage, a potential increase for cancelling out the potential drop can be applied to the data signal.
Note that, the present invention is not limited to the embodiment described above, and can be subjected to various modifications without departing from the gist of the present invention.
For example, in this embodiment, the data signals are input in order of blue (B), green (G), and red (R) between a write timing and the next write timing, but the data signals are only required to be input in a predetermined order. Alternatively, for example, the data signals may be input in order of red (R), green (G), and blue (B). In this case, two cancellers CM are disposed between the transistor TRM and the data signal line DRM, and are driven by the distribution control signal lines 171G and 171B, respectively. In addition, in this case, the cancellers CB1M and CB2M are unnecessary.
Further, for example, in this embodiment, the color filter of three colors is used. Alternatively, however, a color filter of four colors (such as red (R), green (G), blue (B), and yellow (Y)) maybe used. The cancellers CM are disposed in accordance with the number of colors of the color filter so as to suppress a voltage fluctuation caused by a feedthrough voltage.
Description is now given of an example where the liquid crystal display device 1 has a color filter of n colors. In this case, in the liquid crystal display device 1, n data signal lines DM corresponding to the n colors are connected as one set to the output signal line 162M in order in a time sharing manner. In the distribution unit 172M, n transistors TM are disposed, and the n transistors TM are driven by n distribution control signal lines 171.
In this case, between the source or drain of the transistor TM corresponding to an m-th (m is a natural number of 1 to n−1) data signal line DM to be connected to the output signal line 162M among the n data signal lines DM and the m-th data signal line DM, n-m cancellers CM are connected. Then, the respective n-m cancellers CM are connected to the distribution control signal lines 171 for controlling the transistors TM corresponding to the (m+1) th to n-th data signal lines DM to be connected to the output signal line 162M.
For example, the distribution control signal is supplied so that, when the distribution control signal line 171 for controlling the transistor TM corresponding to the m-th data signal line DM to be connected to the output signal line 162M changes from High to Low, the distribution control signal line 171 for controlling the transistor TM corresponding to the (m+1)th data signal line DM to be connected to the output signal line 162M may change from Low to High.
Note that, the scanning signal of the scanning signal line GN is controlled so that the write timing may come when the distribution control signal line 171 for controlling the transistor TM corresponding to the n-th data signal line DM to be connected to the output signal line 162M changes from High to Low.
Regardless of how many colors the color filter has, by supplying the distribution control signal to the cancellers CM arranged as described above, the voltage fluctuation in the data signal caused by the feedthrough voltage generated in the transistor TM can be suppressed similarly to the embodiment.
For example, the color filter arrangement may be the stripe arrangement described in the embodiment, or alternatively, for example, the mosaic arrangement where the same color is arranged diagonally or the delta arrangement where different colors are arranged like a triangle.
In this embodiment, the application of the display device according to the present invention to a liquid crystal display device has been exemplified. However, the display device according to the present invention is not limited to a liquid crystal display device, but is applicable to a display device in which a data signal from the data signal line is supplied to each pixel in a time sharing manner. Alternatively, for example, the display device according to the present invention may be applied to an organic EL display device.
Similarly to the liquid crystal display device 1 described in the embodiment, various signals for controlling the scanning signal drive circuit 230 and the data signal drive circuit 240 are supplied from a controller 280. Also similarly to the embodiment, the data signal drive circuit 240 includes a source IC unit 260 and a distribution control unit 270, which are supplied with signals from the controller 280 via a data bus line 261 and a distribution control signal line 271, respectively.
Also in the organic EL display device 2, the data signal output from the source IC unit 260 is supplied to data signal lines DM in a time sharing manner via an output signal line 262M under control of the distribution control unit 270. In the case where the distribution control unit 270 distributes the data signals, the influence of the feedthrough voltage cannot be ignored when the transistors for performing the distribution are switched from the ON state to the OFF state. However, the organic EL display device 2 includes a fluctuation suppression unit 273M, and hence a voltage drop caused by the feedthrough voltage can be suppressed. Note that, the distribution control unit 270 of the organic EL display device 2 has the same layout as the distribution control unit 170 of the liquid crystal display device 1.
As illustrated in
As illustrated in
While there have been described what are at present considered to be certain embodiments of the invention, it will be understood that various modifications may be made thereto, and it is intended that the appended claims cover all such modifications as fall within the true spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-271137 | Dec 2011 | JP | national |
