JPH10143118A - Active matrix display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix display device capable of division precharge with hourly margin, a difference between luminance in divided parts by a simple method and with excellent uniformity of a display. SOLUTION: Respective gate lines X are divided to left/right on a central part, and vertical scanning circuits 1 are provided respectively on the divided left/right gate lines, and respective signal lines Y are divided to left/right groups on the division part of the gate lines X, and a precharge means 4 supplies a prescribed precharge signal at different timing for respective left/right groups of the divided signal lines Y, and supplies it simultaneously for respective signal lines Y in the group. A horizontal scanning circuit 2 samples respective signal lines Y from a left end part successively toward the division part for the left group of the divided signal lines for pixels by one row selected by the vertical scanning circuit 1, and samples respective signal lines Y from a right end successively toward the division part for the right group of the divided signal lines Y to perform the write-in of the video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active matrix display device, and more particularly to an improvement in uniformity of an active matrix display device driven in a point sequence.

[0002]

2. Description of the Related Art A configuration of a conventional active matrix display device will be briefly described with reference to FIG. As shown
The active matrix display device includes a row-shaped gate line X and a column-shaped signal line Y, and matrix-shaped pixels are arranged at the intersection of the two. Each pixel is, for example, a liquid crystal cell LC
And a thin film transistor Tr for driving the same and a capacitor C for holding signal charges.

The gate line X is a V scanner (vertical scanning circuit)
The V scanner sequentially scans each gate line X and selects one row of liquid crystal pixels every horizontal period.
The signal line Y is driven by a horizontal scanning circuit, and the horizontal scanning circuit H scanner sequentially applies a video signal VSIG to each signal line Y.
Is sampled, and the video signal VSIG is written to each pixel of one row selected within one horizontal period.

The horizontal scanning circuit comprises a horizontal switch HSW provided at an end of the signal line Y and an H scanner for sequentially controlling the opening and closing of these switches. Each signal line Y is connected to a video line by the horizontal switch HSW, and a video signal VSIG is supplied to the video line from a signal driver. The H scanner has sampling pulse signals φH1, φH2, φ for sequentially controlling the opening and closing of each horizontal switch HSW.
H3 is output.

By the way, as the miniaturization of the active matrix display device progresses and the number of pixels increases remarkably, the sampling rate of the video signal is correspondingly increased. Miniaturization of this active matrix display device,
The increased sampling rate causes variations in the width of the sampling pulse signal.

When a sampling pulse signal is applied to the corresponding horizontal switch HSW, the video signal VSIG supplied from the video line is sampled on each signal line Y via the conductive horizontal switch HSW. By the way, since each signal line Y has a predetermined capacitance component, charging and discharging of the signal line Y occurs in accordance with the sampling pulse signal, thereby causing fluctuation in the potential of the video line. This fluctuation is further increased due to the non-uniform charge / discharge amount due to the above-mentioned variation in the width of the sampling pulse signal. There was such a problem.

[0007] Normal NTSC (National Television Sy)
stem Committee) In the case of video signals that comply with the standard, the sampling rate is relatively low, and the timing of the next sampling pulse signal falls after the fluctuation of the potential of the video line has subsided, so the effect of the fluctuation of the potential Is relatively small. However, HDTV (High Definit
In the case of ion TV) drive or double-speed NTSC drive, the sampling rate rises extremely, and it is difficult to effectively suppress fluctuations in the potential of the video line.

The sampling pulse signal supplied to the horizontal switch HSW is generated by an H scanner including a shift register composed of a thin film transistor (TFT).
Thin film transistors (TFTs) have lower mobility than conventional transistors made of single-crystal silicon and have large variations in physical constants. Therefore, it is not possible to precisely control the width of a sampling pulse signal created by this circuit. Have difficulty. Further, in addition to the variation in the width of the sampling pulse signal, there is also a certain variation in the on-resistance of the horizontal switch HSW, so that the cause of variation in the charge / discharge characteristics of the signal is further increased.

In order to solve such a problem, the inventors of the present invention pre-charge means (point-sequential) for sequentially supplying a predetermined pre-charge signal to each signal line Y prior to sequential sampling of a video signal for each signal line Y. Active matrix display device provided with precharge means (Japanese Patent Laid-Open No. 7-295)
520) and an active matrix display device including a precharge means (batch precharge means) for simultaneously supplying a predetermined precharge signal to each signal line Y immediately before writing a video signal to pixels of one row (Japanese Patent Application Laid-Open No. 7-29
5521).

The precharge signal supplied by the precharge means has a gray level intermediate between the white level and the black level with respect to the video signal whose level changes between the white level and the black level. By pre-charging the signal line Y to a potential close to the video signal at a timing that does not affect the display operation as described above, the charge / discharge amount when the actual video signal is sampled on each signal line Y can be reduced. Since the difference can be reduced by stopping at the difference between the video signal level and the precharge, the fluctuation of the potential of the video line can be suppressed, and the fixed pattern of the vertical stripe can be removed, thereby improving the image quality.

The dot-sequential precharging method disclosed in Japanese Patent Application Laid-Open No. 7-295520 can reduce the fluctuation of the potential of the gate line and the power supply line, expand the operation margin, and reduce the driving capability of the precharging means, thereby saving power consumption. There is an advantage that the method of batch precharge described in JP-A-7-295521 has an advantage that precharge can be performed in a short time with a relatively simple circuit configuration.

However, the precharge must be completed within the horizontal blanking period. However, the precharge does not always start sufficiently early during the horizontal blanking period due to the distribution capacitance of the signal line Y. In particular, XGA (Extended Graphics Array), which is a high-resolution graphics display standard, S-
XGA (Super Extended Graphics Array) or H
In a DTV or the like, 1) Since the number of vertical pixels increases, the cross capacitance of the wiring increases. 2) The horizontal blanking period is very short, about 3 to 4 μsec. Therefore, it is difficult to cope with this with the conventional method. In some cases, the precharge has to be completed before the precharge level reaches the level to be originally written.

As a method corresponding to this, the inventors have further proposed a divided precharge as a precharge method. FIG. 3 shows a circuit diagram of a conventional active matrix display device that performs split precharge. In this method, a row line such as a gate line and a CS line of a pixel transistor is cut off near the center of the matrix, and the input clock of the V scanner is divided into a left V scanner (VCKL) and a right V scanner (VCKR). Separately, precharge signals (PSIGL, PSIGR) and precharge pulses (PCGL, PCGR) are also separated for left and right,
In addition, VCKL and VCKR, PSIGL and PSIGR, PCGL and P
The CGR is shifted in phase by about half of one horizontal period.

With this arrangement, the distribution capacitance of the signal line viewed from the precharge signal is reduced by half, and when the left half of the screen of the active matrix display device is writing a video signal, the right half of the screen is precharged (PSIGR). When the right half of the screen is writing the video signal, the left half of the screen writes the precharge signal (PSIGL), so nearly half of one horizontal period can be used for writing the precharge signal. The level can be raised sufficiently to the level originally intended for writing.

FIG. 4 shows a timing chart of each part of the apparatus. As an example, FIG. 4A shows a waveform diagram of the sampling pulse signals φH1, φH2, φH3,... ΦH14 for controlling the opening and closing of each horizontal switch HSW sequentially with the number of horizontal switches HSW being 14. FIGS. 4B and 4C show changes in the voltages of the left and right electrode lines (CS lines) on the opposite side of the pixel transistor of the capacitor holding the signal charges, as examples of the row-like lines.

Referring to FIGS. 4B and 4C, the voltages VL and VR of the left and right CS lines are initially at the level of the voltage Vcom. However, the sampling pulse signal φH1,
The horizontal switches HSW1, HSW2,.
When HSW3 is sequentially opened and closed and a signal of video level Vv is sequentially stored in each capacitor, the voltages VL and VR of the CS line also slightly increase due to the distributed impedance on the CS line. The effect of the rise in the voltage of the CS line affects the charge level of each capacitor C. Even if the printer is charged, it appears as fluctuation of the charge level, that is, a difference in the display level of the liquid crystal cell LC.

The same phenomenon can be applied to the gate line X of the pixel transistor. Especially when a split printer charge is performed, the CS line and the gate line X
Are separated from each other, so that the sway right and left of the separated portion is different as shown in FIGS. 4B and 4C. That is, the pixel write potential for charging the capacitor C is VPL in the portion immediately to the left of the separation, whereas the pixel write potential is VPR in the portion to the right of the separation in the relationship of VPR> VPL. The difference in luminance at the time is noticeable.

[0018]

As described above, in an active matrix display device using a divided precharge method for dividing and precharging a display system having a high resolution and a short horizontal blanking period, a divided portion is used. There was a problem that a difference in luminance was observed. It is an object of the present invention to solve this problem and to realize an active matrix display device excellent in display uniformity by eliminating a luminance difference in a divided portion by a simple method.

[0019]

In order to achieve the above object, the present invention provides a plurality of gate lines in a row, a plurality of signal lines in a column, and each intersection of the gate line and the signal line. A plurality of arranged picture elements in a matrix, a vertical scanning circuit that sequentially scans the gate lines and selects the picture elements for one row every one horizontal period, and sequentially connects the signal lines within one horizontal period A horizontal scanning circuit that performs sampling and writes a video signal in a dot sequence to one row of picture elements selected by the vertical scanning circuit, and a predetermined precharge signal prior to the sequential sampling of the video signal for each of the signal lines And a precharge means for supplying the signal lines to the respective signal lines, wherein the gate lines are divided into right and left at a central portion, and the vertical scanning circuit is divided into left and right divided gate lines. The signal lines are divided into left and right groups at a gate line dividing portion, and the precharge means separates a predetermined precharge signal from each of the left and right groups of the divided signal lines. At the same time, the signal lines in the group are supplied simultaneously, and the horizontal scanning circuit supplies the image elements for one row selected by the vertical scanning circuit to the left group of the divided signal lines. Each signal line is sequentially sampled from the left end toward the division unit, and for the right group of the divided signal lines, each signal line is sequentially sampled from the right end toward the division unit to obtain a video signal. For writing, or for the left group of the divided signal lines, each signal line is sampled sequentially from the division part toward the left end, and for the right group of the divided signal lines, Route signal lines sequentially from the division to the right end And performing writing of a video signal by sampling Te.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an active matrix display device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing one embodiment of the active matrix display device of the present invention. FIG. 2 is a timing chart of each part for explaining the operation of the embodiment shown in FIG. In FIG. 1, 1-1 is a left V scanner, 1-2 is a right V scanner, 2-1 is a left H scanner,
2-2 is a right H scanner, 3 is a video line, 4 is divided precharge means, C is a capacitor, CS1 is a left CS line, CS2 is a right CS line, HSW1 to HSW14 are horizontal switches, LC is a liquid crystal element, PSW1 PSW14 is a precharge switch, Tr is a transistor, Vcom is a voltage applied to a CS line, X is a gate line, and Y is a signal line.

As can be seen from this figure, the gate line X is divided right and left at the center, and accordingly the signal line Y is also divided into left and right groups, and comprises a capacitor C, a transistor Tr and a liquid crystal element LC. Pixels are also divided into left and right groups.

The divided printer charging means 4 supplies predetermined precharge signals (PSIGL, PSIGR) immediately before writing the video signal VSIG to each pixel, and charges and discharges each signal line Y when the video signal VSIG is sampled. To reduce. At this time, the precharge signals (PSIGL, PSIGR) and the precharge pulses (PCGL, PCGR) are also separated on the left and right, and the input clock of the V scanner is changed to the left V scanner (VCK
L) and the right V scanner (VCKR), precharge signals (PSIGL, PSIGR), precharge pulses (PCGL, PCC)
GR) is shifted from the left and right by about half of one horizontal period.

With this arrangement, the distribution capacity of the signal line viewed from the precharge signal is reduced by half, and when the left half of the screen of the active matrix display device is writing a video signal, the precharge signal (PSIGR) is displayed on the right half of the screen. Is written all at once, and when the right half of the screen is writing the video signal, the precharge signal (PSIGL) is written all at once on the left half of the screen, so nearly half of one horizontal period can be used for writing the precharge signal. As a result, the precharge level can be sufficiently raised to the level at which writing is originally desired.

The precharge level of the precharge signal (PSIGL, PSIGR) has a gray level with respect to a video signal which changes between a white level and a black level. When the video signal VSIG supplied to the video line 3 is AC driven in which the polarity is inverted every horizontal period, the precharge levels of the precharge signals (PSIGL, PSIGR) are also inverted every horizontal period. , And the polarity of the video signal VSIG. As an example, FIG. 2 (a) shows a waveform diagram of sampling pulse signals φH1, φH2, φH3... ΦH14 for controlling the opening and closing of each horizontal switch HSW sequentially with the number of horizontal switches HSW being 14. 2 (b) and 2 (c) show how the voltage of the electrode line (CS line) on the opposite side of the pixel transistor of the capacitor holding the signal charge changes.

As can be seen from FIGS. 2B and 2C, the voltage VL of the left CS line CS1 and the voltage VR of the right CS line CS2 are initially at the level of the voltage Vcom. However, when the horizontal switches HSW1, HSW2, HSW3,... Are sequentially opened and closed by the sampling pulse signals φH1, φH2, φH3, and so on, and the video level Vv signals are sequentially stored in the respective capacitors, the voltages VL and VR of the CS line are obtained.
Also rises slightly due to the distributed impedance at the CS line. The effect of the rise in the voltage of the CS line affects the charge level of each capacitor C. Even if the printer is charged, it appears as fluctuation of the charge level, that is, a difference in the display level of the liquid crystal cell LC.
Such a similar event is caused by the gate line X of the pixel transistor.
The same is true for

The present invention is different from the conventional example of FIG. 3 in that the order of opening and closing the horizontal switches HSW1, HSW2, HSW3... Is changed from that of the prior art, and as shown in FIG. Writes the video signal from the video line 3 by opening and closing the horizontal switch HSW from the left side as before, and writes the video signal from the video line 3 by opening and closing the horizontal switch HSW from the right side contrary to the conventional case. That is the point As a result, in the portion immediately to the left of the separation, the pixel writing potential for charging the capacitor C becomes almost equal to VPL, and in the portion immediately to the right of the separation, the pixel writing potential becomes substantially equal to VPR. Disappears. The same result is obtained when the left half opens and closes the horizontal switch HSW from the right side and writes a video signal from the video line 3, and the right half opens and closes the horizontal switch HSW from the left side and writes a video signal from the video line 3. Is obtained.

[0027]

As described above, according to the first aspect of the present invention, a plurality of gate lines in a row, a plurality of signal lines in a column, and each intersection of a gate line and a signal line are arranged. A plurality of matrix-shaped picture elements, a vertical scanning circuit that sequentially scans each gate line and selects one row of picture elements every horizontal period, and a vertical scan by sequentially sampling each signal line within one horizontal period A horizontal scanning circuit for writing a video signal in a dot-sequential manner to one row of picture elements selected by the circuit, and supplying a predetermined precharge signal to each signal line prior to sequential sampling of the video signal for each signal line In an active matrix display device having a precharge means, each gate line is divided into right and left at a central portion, and a vertical scanning circuit is provided for each of the left and right divided gate lines, and each signal line is connected to the gate line. Division of The precharge means divides the signal lines into left and right groups, and supplies a predetermined precharge signal to each of the left and right groups of the divided signal lines at different timings simultaneously for each signal line in the group. In the horizontal scanning circuit, for the left group of signal lines divided for one row of picture elements selected by the vertical scanning circuit, each signal line was sampled and divided sequentially from the left end toward the division unit from the left end. For the right group of signal lines, each signal line is sequentially sampled from the right end toward the division unit to write a video signal. According to a second aspect of the present invention, in contrast to the first aspect of the present invention, the horizontal scanning circuit is applied to one row of picture elements selected by the vertical scanning circuit and to the left group of the divided signal lines. Sample each signal line sequentially from the division to the left end, and for the right group of divided signal lines, sample each signal line sequentially from the division to the right end to write the video signal. It is characterized by performing. As a result, it is possible to precharge the display method with a high resolution and a short horizontal blanking period with a margin in time by using the divided precharge method, thereby greatly reducing the noise of the video line. In addition, it is possible to eliminate the difference in luminance between the divided portions by a simple method, to eliminate the vertical streak fixing pattern, and to realize an active matrix display device excellent in display uniformity.

According to the invention of claim 3 of the present invention, the precharge means is provided for the left group of the divided signal lines when the video signal is being written to the right group of the divided signal lines. A precharge signal is supplied to the left group of the divided signal lines, and a precharge signal is supplied to the right group of the divided signal lines when the video signal is being written to the left group of the divided signal lines. It is characterized by the following. This makes it possible to precharge the display method with a high resolution and a short horizontal blanking period with a margin in time by using the divided precharge method.

According to a fourth aspect of the present invention, the precharge means supplies a precharge signal having a gray level to a video signal which changes between a white level and a black level. As a result, the noise of the video line can be significantly reduced, and the vertical stripe fixing pattern can be eliminated.

According to a fifth aspect of the present invention, the precharge means supplies a precharge signal which is also inverted every horizontal period so as to match the polarity with a video signal which is inverted every horizontal period. It is characterized by. Thereby, precharge can be performed effectively even when the video signal is AC-driven.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of an active matrix display device of the present invention.

FIG. 2 is a timing chart of each unit for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a circuit diagram showing a conventional divided precharge type active matrix display device.

4 is a timing chart of each section for explaining the operation of the conventional example of FIG. 3;

FIG. 5 is a circuit diagram showing a conventional active matrix display device.

[Explanation of symbols]

1-1 Left V Scanner 1-2 Right V Scanner 2
-1: Left H scanner, 2-2: Right H scanner, 3 ...
... video line, 4 ... divided precharge means, C ...
Capacitor, CS1 left CS line, CS2 right C
S line, HSW1 to HSW14 ... Horizontal switch, LC ...
Liquid crystal picture elements, PSW1 to PSW14... Precharge switches, Tr... Transistors, Vcom... CS line applied voltage, X... Gate lines, Y.

Claims (5)

[Claims] A plurality of row-shaped gate lines; a plurality of column-shaped signal lines; a plurality of matrix-shaped picture elements arranged at intersections of the gate lines and the signal lines; A vertical scanning circuit that sequentially scans lines to select the image elements for one row every one horizontal period, and a pixel for one row selected by the vertical scanning circuit by sequentially sampling each of the signal lines within one horizontal period A horizontal scanning circuit for writing a video signal in a dot-sequential manner to each pixel, and a precharge means for supplying a predetermined precharge signal to each signal line prior to the sequential sampling of the video signal for each signal line. In the active matrix display device, the gate lines are divided right and left at a central portion, and the vertical scanning circuit is provided for each of the left and right divided gate lines. The signal is divided into right and left groups, and the precharge means simultaneously applies predetermined precharge signals to the respective signal lines in the group at different timings for each of the left and right groups of the divided signal lines. The horizontal scanning circuit sequentially directs each signal line from the left end to the division unit for the left group of the divided signal lines for the image elements for one row selected by the vertical scanning circuit. An active matrix display device, wherein sampling is performed on a right group of the divided signal lines, and each signal line is sequentially sampled from a right end toward a division unit to write a video signal. 2. A plurality of row-shaped gate lines, a plurality of column-shaped signal lines, a plurality of matrix-shaped picture elements arranged at respective intersections of the gate lines and the signal lines, and the respective gates A vertical scanning circuit that sequentially scans lines to select the image elements for one row every one horizontal period, and a pixel for one row selected by the vertical scanning circuit by sequentially sampling each of the signal lines within one horizontal period A horizontal scanning circuit for writing a video signal in a dot-sequential manner to each pixel, and a precharge means for supplying a predetermined precharge signal to each signal line prior to the sequential sampling of the video signal for each signal line. In the active matrix display device, the gate lines are divided right and left at a central portion, and the vertical scanning circuit is provided for each of the left and right divided gate lines. The signal is divided into right and left groups, and the precharge means simultaneously applies predetermined precharge signals to the respective signal lines in the group at different timings for each of the left and right groups of the divided signal lines. The horizontal scanning circuit supplies the signal lines to the left group of the divided signal lines for the image elements for one row selected by the vertical scanning circuit in order from the divided portion toward the left end. An active matrix display device, characterized in that, for the right group of the sampled and divided signal lines, each signal line is sequentially sampled from a division portion toward a right end portion to write a video signal, and the video signal is written. 3. A precharge means for precharging a left group of the divided signal lines when a video signal is being written to the right group of the divided signal lines. And supplying a precharge signal to the right group of the divided signal lines when a video signal is being written to the left group of the divided signal lines. The active matrix display device according to claim 1 or 2, wherein 4. The precharge means according to claim 1, wherein said precharge means supplies a precharge signal having a gray level for a video signal which changes between a white level and a black level. Active matrix display device. 5. The precharge means according to claim 1, wherein the precharge means supplies a precharge signal which is also inverted every horizontal period so as to match the polarity with the video signal which is inverted every horizontal period. Alternatively, the active matrix display device according to claim 2.