JP3633152B2 - Active matrix display device and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device having a plurality of video lines and a driving method thereof.
[0002]
[Prior art]
Conventionally, this type of active matrix display device is driven by a plurality of video lines to which video signals are input, row-like gate lines X, column-like signal lines Y, thin film transistors connected to the intersections thereof, and thin film transistors. A matrix circuit including liquid crystal pixels LC. Each signal line Y is provided with a horizontal switching element HSW, and the signal line Y is connected to a corresponding video line by turning on the horizontal switching element HSW.
[0003]
A vertical scanning circuit (V scanner) is provided on the side of the matrix circuit, and the V scanner sequentially scans the gate lines X to turn on the thin film transistors Tr for one row every horizontal period.
A horizontal scanning circuit (H scanner) is provided above the matrix circuit, and the H scanner sequentially outputs a sampling pulse φH over one horizontal period, and a video line provided on the signal line Y by this sampling pulse φH. The number of horizontal switching elements HSW corresponding to the number of (for example, three) is simultaneously turned on. As a result, the video signal of each video line is simultaneously sampled on the corresponding signal line Y, and the video signal is written to the liquid crystal pixels LC driven by the thin film transistors for one row turned on by the selection pulse φV output from the V scanner. It is.
[0004]
In such an active matrix display device, there is a cross capacitance between each video line and each signal line. When the cross capacitance increases, the current consumption of a signal driver that supplies a video signal to the video line increases.
[0005]
[Problems to be solved by the invention]
The present applicant has found an active matrix display device that copes with this problem. In this active matrix display device, a horizontal switching element HSW is provided in a signal line portion before a signal line connected to a video line straddles another video line. This reduces the cross capacitance between the video line and the signal line (see FIG. 1).
[0006]
However, the active matrix display device having the plurality of video lines has a problem that, for example, horizontal crosstalk occurs when black is displayed in a predetermined area. FIG. 5 is a diagram showing a liquid crystal display screen in which horizontal crosstalk has occurred. That is, when displaying gray in the areas A and B of the display screen and black in the area C, first, the switching element HSW located in the area A is turned on, and the gray level signal (video signal) supplied to the signal line Y is turned on. The center value Vsigc + 2 [V]) is written in the liquid crystal pixel LC to turn off the switching element HSW.
Thereafter, the switching element HSW located in the region C is turned on, and the black level video signal (the center value Vsigc + 4.5 [V] of the video signal) supplied to the signal line Y is written in the liquid crystal pixel LC, and the switching element HSW is turned on. Turn off.
When this black level video signal is input to the video line, the black signal is applied to the signal line Y in the region A due to the cross capacitance between the signal line Y and the video line, even though the horizontal switching element HSW in the region A is off. The AC component (ΔV) of the level video signal is supplied.
[0007]
FIG. 6 is a timing chart showing the video signal Vsig input to the video line, the sampling pulse φH for driving the horizontal switching element HSW, the selection pulse φV for driving the thin film transistor Tr for one row, and the sampling signal of the signal line Y. The signal line Y in the area A is sampled at a potential (Vsigc + 2 [V] + ΔV) obtained by adding an AC component ΔV to the gray level (Vsigc + 2 [V]) video signal as indicated by a solid line d, and the thin film transistor Tr is turned off. When it becomes, the potential is held.
On the other hand, in the region B, since the black level video signal is not supplied to the video line while the thin film transistor Tr is on, the gray level video signal (Vsigc + 2 [V]) is held. As a result, a potential difference ΔV is generated between the region A and the region B, and lateral crosstalk occurs.
[0008]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an active matrix display device capable of preventing the occurrence of lateral crosstalk due to cross capacitance between video lines and signal lines, and a driving method thereof.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an active matrix display device according to claim 1 of the present invention includes a plurality of video lines to which video signals are input, row-shaped gate lines, column-shaped signal lines, and gates. Vertical scanning that sequentially scans the pixel transistors connected to the intersections of the lines and the signal lines, the pixels driven by the pixel transistors, and the gate lines, and selects one row of the pixel transistors every horizontal period A selected pixel transistor comprising: a circuit; and a horizontal scanning circuit that simultaneously selects a number of signal lines corresponding to the video lines within the one horizontal period and sequentially supplies the video signal to one line of signal lines. In the active matrix display device in which the video signal supplied to the signal line is written to the corresponding pixel, the video signal is supplied to the one line of signal lines after the video signal is supplied. On the one horizontal period to the end of the selection of the partial pixel transistors a black level signal, comprising the black level signal supply circuit for supplying to said video line.
[0010]
The black level signal is preferably a constant voltage signal having an amplitude equal to or greater than a maximum amplitude of the video signal.
Further, the black level signal supply circuit includes an analog switch that switches between the video signal and the black level signal supplied to the video line, and the one line after the video signal is supplied to the signal line for one line. And a driver circuit for outputting a drive signal for driving the analog switch in the one horizontal period until the selection of the pixel transistors for the second minute is completed.
[0011]
Also, a horizontal switching element is provided in the signal line portion before the signal line connected to the video line crosses another video line, and the horizontal scanning circuit turns the horizontal switching element on to turn the signal line on. It is preferable to select and supply a video signal from the video line.
[0012]
According to a fifth aspect of the present invention, there is provided a driving method for an active matrix display device, wherein a vertical scanning circuit sequentially scans each row of gate lines to select one row of pixel transistors every horizontal period, and a horizontal scanning circuit selects the one horizontal line. The number of signal lines corresponding to the video lines to which video signals are input within the period is simultaneously selected, and the video signals are sequentially supplied to the signal lines for one row, and are supplied to the signal lines by the selected pixel transistors. In the driving method of the active matrix display device for writing the video signal to the corresponding pixel, the one horizontal line from the end of supplying the video signal to the signal line for one row until the selection of the pixel transistor for the one row is finished. A black level signal is supplied to the video line during the period.
[0013]
In the active matrix display device of the present invention, the vertical scanning circuit sequentially scans each row of gate lines to select one row of pixel transistors for each horizontal period, and the horizontal scanning circuit outputs a video signal within the horizontal period. A number of signal lines corresponding to the input video lines are simultaneously selected, and the video signals are sequentially supplied to the signal lines for one row, and the video signals supplied to the signal lines by the selected pixel transistors are associated. When writing to the pixels, the black level signal is supplied during the one horizontal period after the video signal is supplied to the signal lines for one row by the black level signal supply circuit until the selection of the pixel transistors for the one row is completed. Supply to video line.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of an active matrix display device and a driving method thereof according to the present invention will be described. The active matrix display device in this embodiment is applied to a liquid crystal display panel.
FIG. 1 is a circuit diagram showing a configuration of a liquid crystal display panel. The liquid crystal display panel 1 includes three video lines Video1, Video2, Video3 to which a video signal is input, a row gate line X, a column signal line Y (Y1, Y2, Y3,... Yn), and an intersection of the two. A matrix circuit 5 including a thin film transistor Tr connected to the unit and a liquid crystal pixel LC driven by the thin film transistor Tr. The source electrode of the thin film transistor Tr is connected to the corresponding signal line Y, the gate electrode is connected to the corresponding gate line X, and the drain electrode is connected to the corresponding liquid crystal pixel LC.
[0015]
Further, signal lines Y (Y1, Y2, Y3,..., Yn) are sequentially connected to the video lines Video1, Video2, and Video3, and the signal lines Y connected to the video lines are connected to other video lines or opposite to each other. Horizontal switching elements HSW (HSW1, HSW2, HSW3,... HSWn) are provided in the signal line Y portion before the electrode line 25. That is, the switching element HSW3 provided in the signal line Y3 is located between the video line Video3 and the video line Video2. Similarly, the switching element HSW2 provided in the signal line Y2 is located between the video line Video2 and the video line Video1. The horizontal switching element HSW1 provided in the signal line Y1 is located between the video line Video1 and the counter electrode line 25. Thus, the cross capacitance Cr between the video line and the signal line Y can be reduced by arranging the horizontal switching element HSW.
[0016]
On the other hand, a vertical scanning circuit (V scanner) 11 is provided on the left side of the matrix circuit 5, and the V scanner 11 selects a selection pulse φV (φV1, φV2, φV3, according to a vertical start signal VST synchronized with the vertical clock signal VCK. ..., ΦVm) are sequentially output to each gate line X, and one row of thin film transistors Tr are turned on every horizontal (H) period.
[0017]
A horizontal scanning circuit (H scanner) 13 is provided on the upper side of the matrix circuit 5, and the H scanner 13 performs sampling pulses φH (φH 1, φH 2) according to a horizontal start signal HST synchronized with predetermined horizontal clock signals HCK 1 and HCK 2. φH3,..., φHk, k = n / 3) are output. The horizontal switching elements HSW (for example, HSW1, HSW2, HSW3) are each driven by the same sampling pulse φH, and the video signals Vsig supplied to the video lines Video1, Video2, Video3 are sampled on the corresponding signal lines Y, respectively. . The sampled video signal Vsig is written into the liquid crystal pixel LC corresponding to one row of thin film transistors Tr driven by the selection pulse φV output from the V scanner 11.
[0018]
FIG. 2 is a block diagram showing a configuration of an external driver that supplies a video signal and a black level signal to the video line. The external driver 31 is provided separately from the liquid crystal display panel 1 and mainly includes an analog switch 32 and a driver circuit (not shown). The video signal Vsig and the black level signal are input to the analog switch 32. The analog switch 32 receives the video signal Vsig and the black level supplied to the video lines Video1, Video2, and Video3 according to the drive signal X output from the driver circuit. Switch between signals. That is, when the drive signal X is at the L level, the video signal is output to each video line Video1, Video2, Video3, and when the drive signal X is at the H level, the black level signal is output to each video line Video1, Video2, Video3.
[0019]
Here, the drive signal X becomes H level in synchronization with the end of the sampling pulse φH for driving the horizontal switching elements HSW for one row from the H scanner 13, and at least one row of thin film transistors by the selection pulse φV output from the V scanner 11. The H level is held until Tr is turned off.
The black level signal is a constant voltage signal having an amplitude equal to or greater than the maximum amplitude of the video signal Vsig, and has a voltage of the center value Vsigc ± V1 (for example, V1 ≧ 4.5 [V]) of the video signal. The black level signal may be set to a predetermined voltage in advance, or may be set to a constant voltage with the maximum amplitude updated by monitoring the maximum amplitude of the video signal.
[0020]
FIG. 3 is a timing chart showing signal waveforms of respective parts of the liquid crystal display panel and the external driver. The signal waveform of each part in FIG. 3 is shown within 1H period, and the signal waveform of each part is inverted in the next 1H period.
The H scanner 13 sequentially outputs sampling pulses φH (φH1, φH2, φH3,..., ΦHk, k = n / 3) within 1H period in accordance with the horizontal start signal HST synchronized with the horizontal clock signals HCK1 and HCK2. The three horizontal switching elements HSW are simultaneously turned on by the sampling pulse φH, and the three video lines Video1, Video2, and Video3 are connected to the corresponding signal lines Y, respectively, and each video signal Vsig is sampled.
[0021]
FIG. 4 is a diagram showing a display screen of the liquid crystal display panel 1. When supplying the video signal Vsig of the black level (Vsigc + 4.5 [V]) to the video line in the region C and supplying the video signal Vsig of the gray level (Vsigc + 2 [V]) in the other regions A and B, In region A, the switching element HSW is turned on, the gray level video signal Vsig is sampled on the signal line Y, and then the switching element HSW is turned off (period a in the figure).
[0022]
Thereafter, when a black level signal is input to the video line in the region C, an AC component (ΔV) is supplied to the signal line Y in the region A by the cross capacitance between the signal line Y and the video line in the region A, and the region A The potential of the signal line Y becomes Vsigc + 2 [V] + ΔV (period b in the figure).
[0023]
Then, in synchronization with the end of the sampling pulse φH for driving the horizontal switching elements HSW for one row, the drive signal X becomes H level, and the analog switch 32 converts the signal supplied to the video line from the video signal to the black level signal (Vsigc + V1). Switch to. The AC component ΔV1 of the black level signal is supplied to the signal line Y by the cross capacitance between the signal line Y and the video line, and the potential of the signal line Y rises to Vsigc + 2 [V] + ΔV1 as shown by the solid line (FIG. Medium period c). When the thin film transistor Tr connected to the gate line X is turned off by the selection pulse φV output from the V scanner 11, the gray level signal of the potential Vsigc + 2 [V] + ΔV1 is written in the liquid crystal pixel LC in the region A. .
[0024]
On the other hand, in the region B, since the black level video signal is not sampled on the signal line Y while the thin film transistor Tr connected to the gate line X is on, the signal line Y in the region B has the potential Vsigc + 2 [ Hold the gray level signal of [V].
[0025]
As in the case of the region A, the drive signal X becomes H level in synchronization with the end of the sampling pulse φH for driving the horizontal switching elements HSW for one row, and the analog switch 32 converts the signal supplied to the video line to the video When the signal Vsig is switched to the black level signal (Vsigc + V1), the potential of the signal line Y rises to Vsigc + 2 [V] + ΔV1, and the gray level signal having the same potential as that in the region A is written into the liquid crystal pixel LC.
[0026]
As described above, the maximum of the video signal Vsig is maintained in the period (period f in the figure) from the end of the supply of the sampling pulse φH for driving the horizontal switching elements HSW for one row until the thin film transistors Tr for one row are turned off by the selection pulse φV. By supplying a constant voltage black level signal having an amplitude greater than or equal to the amplitude to the video line, the liquid crystal pixel LC has the same potential in the region A and the region B, and therefore, occurrence of lateral crosstalk can be prevented. In the above embodiment, the case where there are three video lines has been described. However, the number of video lines is not particularly limited.
[0027]
【The invention's effect】
According to the active matrix display device of the first aspect of the present invention, the row-shaped gate lines are sequentially scanned by the vertical scanning circuit to select the pixel transistors for one row every horizontal period, and the horizontal scanning circuit is used to select the pixel transistors. A number of signal lines corresponding to video lines to which video signals are input within one horizontal period are simultaneously selected, and the video signals are sequentially supplied to the signal lines for one row, and the signal lines are supplied to the signal lines by the selected pixel transistors. When writing the supplied video signal to the corresponding pixel, the one from the end of supplying the video signal to the signal line for one row by the black level signal supply circuit until the selection of the pixel transistor for the one row is completed. Since a black level signal is supplied to the video line during a horizontal period, occurrence of lateral crosstalk due to cross capacitance between the video line and the signal line can be suppressed.
[0028]
According to the active matrix display device of the second aspect, since the black level signal is a constant voltage signal having an amplitude equal to or greater than the maximum amplitude of the video signal, the black level video signal is applied to a part of the display area. Even when displaying, it is possible to reliably prevent the occurrence of lateral crosstalk.
[0029]
4. The active matrix display device according to claim 3, wherein the black level signal supply circuit includes an analog switch that switches between the video signal and the black level signal supplied to the video line, and a signal line for one row. And a driver circuit for outputting a drive signal for driving the analog switch in the one horizontal period from the end of supplying the video signal to the end of selection of the pixel transistors for one row. Switching to a black level signal can be performed easily.
[0030]
According to the active matrix display device of claim 4, a horizontal switching element is provided in the signal line portion before the signal line connected to the video line straddles another video line, and the horizontal scanning circuit includes the horizontal scanning circuit. By turning on the horizontal switching element, the signal line is selected and the video signal is supplied from the video line, so that the cross capacitance can be reduced and the current consumption of the driver that supplies the video signal and the black level signal can be reduced. Less.
[0031]
According to the driving method of the active matrix display device according to claim 5, the row-shaped gate lines are sequentially scanned by the vertical scanning circuit to select the pixel transistors for one row every horizontal period, and the horizontal scanning circuit performs the above-described operation. A number of signal lines corresponding to video lines to which video signals are input within one horizontal period are simultaneously selected, and the video signals are sequentially supplied to the signal lines for one row, and the signal lines are supplied to the signal lines by the selected pixel transistors. In the driving method of the active matrix display device that writes the supplied video signal to the corresponding pixel, the selection of the pixel transistor for one row after the video signal is supplied to the signal line for the one row is completed. Since the black level signal is supplied to the video line during one horizontal period, it is possible to suppress the occurrence of lateral crosstalk due to the cross capacitance between the video line and the signal line. .
[Brief description of the drawings]
FIG. 1 is a circuit diagram illustrating a configuration of a liquid crystal display panel.
FIG. 2 is a block diagram illustrating an external driver that supplies a video signal and a black level signal to a video line.
FIG. 3 is a timing chart showing signal waveforms of respective parts of a liquid crystal display panel and an external driver.
4 is a diagram showing a display screen of the liquid crystal display panel 1. FIG.
FIG. 5 is a diagram showing a liquid crystal display screen in which horizontal crosstalk has occurred.
6 is a timing chart showing a video signal Vsig input to a video line, a sampling pulse φH for driving a horizontal switching element HSW, a selection pulse φV for driving a thin film transistor Tr for one row, and a sampling signal for a signal line Y. FIG.
[Explanation of symbols]
1 ... Liquid crystal display panel, 5 ... Matrix circuit, 11 ... V scanner, 13 ... H scanner, 32 ... Analog switch.

Claims (5)

A plurality of video lines to which video signals are input, row-shaped gate lines, column-shaped signal lines, pixel transistors connected to intersections of the gate lines and the signal lines, and the pixel transistors are driven. A pixel and each gate line are sequentially scanned, and a vertical scanning circuit that selects one row of the pixel transistors every horizontal period, and a number of signal lines corresponding to the video lines within the horizontal period are simultaneously selected. A horizontal scanning circuit for sequentially supplying the video signal to the signal lines for one row,
In an active matrix display device that writes a video signal supplied to the signal line by the selected pixel transistor to a corresponding pixel,
A black level signal supply circuit for supplying a black level signal to the video line during the one horizontal period from the end of supplying the video signal to the signal line for one row until the selection of the pixel transistors for the one row is completed. An active matrix display device comprising: 2. The active matrix display device according to claim 1, wherein the black level signal is a constant voltage signal having an amplitude equal to or greater than a maximum amplitude of the video signal. The black level signal supply circuit includes:
An analog switch for switching between the video signal and the black level signal supplied to the video line;
A driver circuit that outputs a drive signal for driving the analog switch in the one horizontal period from the end of supplying the video signal to the signal line for one row until the selection of the pixel transistors for the one row is completed. The active matrix display device according to claim 1. A horizontal switching element is provided in the signal line portion before the signal line connected to the video line straddles another video line,
2. The active matrix display device according to claim 1, wherein the horizontal scanning circuit selects the signal line by turning on the horizontal switching element to supply a video signal from the video line. Each row of gate lines is sequentially scanned by a vertical scanning circuit to select one row of pixel transistors every horizontal period, and the number corresponding to video lines to which video signals are input within the horizontal period by the horizontal scanning circuit. Driving the active matrix display device that simultaneously selects the signal lines, sequentially supplies the video signals to the signal lines for one row, and writes the video signals supplied to the signal lines to the corresponding pixels by the selected pixel transistors. In the method
A black level signal is supplied to the video line during the one horizontal period from the end of supplying the video signal to the signal line for one row until the selection of the pixel transistors for the row is completed. A driving method of a matrix display device.

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