JP3666147B2 - Active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix display device, and more particularly to improvement in uniformity of an active matrix display device driven in a point sequence.
[0002]
[Prior art]
The configuration of a conventional active matrix display device will be briefly described with reference to FIG. As shown in the figure, the active matrix display device includes row-like gate lines X and column-like signal lines Y, and matrix-like pixels are arranged at the intersections between the two. Each pixel includes, for example, a liquid crystal cell LC, a thin film transistor Tr that drives the liquid crystal cell LC, and a capacitor C that holds signal charges.
[0003]
The gate line X is driven by a V scanner (vertical scanning circuit), and the V scanner sequentially scans each gate line X to select one row of liquid crystal pixels every horizontal period.
The signal line Y is driven by the horizontal scanning circuit, and the horizontal scanning circuit H scanner sequentially samples the video signal VSIG for each signal line Y, and the video is respectively output to the pixels for one row selected within one horizontal period. Write signal VSIG.
[0004]
The horizontal scanning circuit is composed of a horizontal switch HSW provided at the end of the signal line Y and an H scanner for sequentially opening and closing these switches. Each signal line Y is connected to a video line by the horizontal switch HSW, and a video signal VSIG is supplied from the signal driver to the video line. The H scanner outputs sampling pulse signals φH1, φH2, φH3,... For sequentially opening and closing the horizontal switches HSW.
[0005]
By the way, if the active matrix display device is further miniaturized and the number of pixels is remarkably increased, the sampling rate of the video signal is increased accordingly. Due to the miniaturization of the active matrix display device and the increase in the sampling rate, the width of the sampling pulse signal varies.
[0006]
When the 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 horizontal switch HSW which is turned on.
By the way, since each signal line Y has a predetermined capacitance component, charging / discharging of the signal line Y is generated according to the sampling pulse signal, thereby causing fluctuation in the potential of the video line. This fluctuation is further increased when the charge / discharge amount is not constant due to the variation in the width of the sampling pulse signal described above, so-called uniformity is deteriorated and vertical stripes appear in the displayed image, thereby degrading the image quality. There were problems such as.
[0007]
In the case of a video signal in accordance with the normal National Television System Committee (NTSC) standard, the sampling rate is relatively low, and the timing of the next sampling pulse signal rises after the fluctuation of the video line potential has subsided. The influence of potential fluctuation is relatively small. However, when HDTV (High Definition TV) driving or double-speed NTSC driving is used, the sampling rate is extremely increased, and it is difficult to effectively suppress fluctuations in the potential of the video line.
[0008]
The sampling pulse signal supplied to the horizontal switch HSW is created by an H scanner composed of a shift register composed of a thin film transistor (TFT). Thin film transistors (TFTs) have lower mobility than normal transistors made of single-crystal silicon and have large variations in physical constants, so it is not possible to precisely control the width of the sampling pulse signal created by this circuit. Have difficulty. Furthermore, in addition to the variation in the width of the sampling pulse signal, the on-resistance of the horizontal switch HSW also varies to some extent, so that the cause of fluctuation in the charge / discharge characteristics of the signal is further increased.
[0009]
In order to solve such a problem, the inventors have precharge means (dot sequential precharge means) that sequentially supplies a predetermined precharge signal to each signal line Y prior to sequential sampling of the video signal for each signal line Y. ) And an active matrix display device (Japanese Patent Laid-Open No. 7-295520) and precharge means (collective precharge) for supplying a predetermined precharge signal simultaneously to each signal line Y immediately before writing a video signal to pixels for one row. An active matrix display device (Japanese Patent Laid-Open No. 7-295521) having a charging means is proposed.
[0010]
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. When the signal line Y is precharged to a potential close to the video signal at a timing that does not affect the display operation in this way, the charge / discharge amount when the actual video signal is sampled on each signal line Y, Since the difference between the video signal level and the precharge can be reduced, the potential fluctuation of the video line can be suppressed, the fixed pattern of the vertical stripe can be removed, and the image quality can be improved.
[0011]
By the way, the dot sequential precharge method disclosed in Japanese Patent Laid-Open No. 7-295520 has the advantage that the potential fluctuation of the gate line and the power supply line can be reduced, the operation margin is widened, and the driving ability of the precharge means is small and the power consumption can be saved. The batch precharge method disclosed in Japanese Patent Laid-Open No. 7-295521 has an advantage that precharge can be performed in a short time with a relatively simple circuit configuration.
[0012]
However, the precharge must be completed within the horizontal blanking period, but due to the distributed capacity of the signal line Y, the precharge does not always rise sufficiently early in the horizontal blanking period. Especially in XGA (Extended Graphics Array), S-XGA (Super Extended Graphics Array) or HDTV, which are high resolution graphics display standards,
1) Since the number of vertical pixels increases, the cross capacitance of the wiring increases.
2) The horizontal blanking period is very short, about 3-4 μsec.
Therefore, it is difficult to cope with this with the conventional method, and there are cases where the precharge must be completed without reaching the level to which the original write is desired.
[0013]
As one method corresponding to this, the inventors have further proposed divided precharge as a precharge method.
FIG. 3 shows a circuit diagram of a conventional active matrix display device that performs divided precharge.
In this method, the gate lines of the pixel transistors, the line of the CS line, etc. are separated in the vicinity of the center of the matrix, and the input clock of the V scanner is divided between the left V scanner (VCKL) and the right V scanner (VCKR). Separately, the precharge signal (PSIGL, PSIGR) and the precharge pulse (PCGL, PCGR) are also separated on the left and right sides. In addition, VCKL and VCKR, PSIGL and PSIGR, and PCGL and PCGR are approximately half the phase of one horizontal period. I shifted it.
[0014]
In this way, the distribution capacity of the signal line viewed from the precharge signal is halved, and when the left half of the screen of the active matrix display device is writing the video signal, the right half of the screen writes the precharge signal (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 it is possible to devote nearly half of the horizontal period to the precharge signal and the precharge level is sufficient. It can be raised to the level you want to write.
[0015]
FIG. 4 shows a timing chart of each part of this apparatus.
As an example, a waveform diagram of sampling pulse signals φH1, φH2, φH3... ΦH14 for controlling the opening / closing of each horizontal switch HSW in the order of 14 horizontal switches HSW is shown in FIG. 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 charge as an example of a row line.
[0016]
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, when the horizontal switches HSW1, HSW2, HSW3,... Are sequentially opened and closed by the sampling pulse signals .phi.H1, .phi.H2, .phi.H3, and the video level Vv signals are sequentially stored in the capacitors, the voltages VL and VR of the CS line are also changed. It increases slightly due to the distributed impedance in the CS line. The influence of the voltage increase on the CS line affects the charge level of each capacitor C. Even if the printer is charged, the charge level fluctuates, that is, appears as a difference in display level of the liquid crystal cell LC.
[0017]
The same phenomenon can be applied to the gate line X of the pixel transistor.
In particular, when the divided printer charge is performed, the CS line and the gate line X are separated at the center, and this fluctuation is shown in FIGS. 4B and 4C at the left and right of the separated part. So different. In other words, 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 and VPR> VPL in the portion to the right of the separation. The difference in brightness will be noticeable.
[0018]
[Problems to be solved by the invention]
As described above, in the active matrix display device using the divided precharge method in which the precharge method is performed by dividing the display method with a high resolution and a short horizontal blanking period, there is a problem that a difference in luminance is observed in the divided portions. there were.
An object of the present invention is to solve this point and to realize an active matrix display device excellent in display uniformity by eliminating a luminance difference in divided portions by a simple method.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a plurality of matrix-like pixels arranged at each intersection of a plurality of row-shaped gate lines, a plurality of column-shaped signal lines, and the gate lines and the signal lines. A vertical scanning circuit that sequentially scans each of the gate lines and selects the image elements for one row every horizontal period, and selects each of the signal lines in one horizontal period and selects them by the vertical scanning circuit A horizontal scanning circuit for writing video signals dot-sequentially to the image elements for one row, and a pre-charge signal supplied to each signal line prior to sequential sampling of the video signals for each signal line. In the active matrix display device comprising a charging means, each gate line is divided into left and right at the center, and the vertical scanning circuit is provided for each of the left and right divided gate lines. Were divided into groups of left and right split portions of the gate lines, the precharging means supplies out of phase with respect to each group of the left and right predetermined precharge signal the divided signal lines, I hereinafter The distribution capacity of the signal lines as viewed from the precharge means is halved, and the horizontal scanning circuit is different from the left group of the divided signal lines with respect to the image elements for one row selected by the vertical scanning circuit. The signal lines are sampled sequentially from the left end toward the dividing unit, and for the right group of the divided signal lines, each signal line is sampled sequentially from the right end toward the dividing unit, and the luminance difference in the dividing unit Video signals are written so as to prevent the occurrence of the signal lines, or for the left group of the divided signal lines, each signal line is sequentially sampled from the dividing section toward the left end portion, and the divided signal lines are For each group on the right, Sequentially toward the right end from the split unit and performs writing of a video signal such that the luminance difference in the divided portion by sampling does not occur.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
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 an embodiment of an 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, and C is Capacitor, CS1 is the left CS line, CS2 is the right CS line, HSW1 to HSW14 are horizontal switches, LC is a liquid crystal picture element, PSW1 to PSW14 are precharge switches, Tr is a transistor, Vcom is the applied voltage of the CS line, and X is a gate Line Y is a signal line.
[0021]
As can be seen from this figure, the gate line X is divided into left and right at the center, and the signal line Y is divided into left and right groups accordingly, and the pixel composed of the capacitor C, the transistor Tr, and the liquid crystal image element LC is also left and right. It is divided into groups.
[0022]
The divided printer charging means 4 supplies predetermined precharge signals (PSIGL, PSIGR) immediately before writing the video signal VSIG to each pixel, and reduces the charge / discharge amount of each signal line Y when sampling the video signal VSIG. . At this time, the precharge signal (PSIGL, PSIGR) and the precharge pulse (PCGL, PCGR) are also separated on the left and right sides, and the input clock of the V scanner is set to the left V scanner (VCKL) and the right V scanner (VCKR), The precharge signals (PSIGL, PSIGR) and precharge pulses (PCGL, PCGR) are shifted in phase by about half of one horizontal period on the left and right.
[0023]
In this way, the distribution capacity of the signal line viewed from the precharge signal is halved, and when the left half of the screen of the active matrix display device is writing the video signal, the precharge signal (PSIGR) is simultaneously transmitted on the right half of the screen. When writing, when the right half of the screen is writing the video signal, the precharge signal (PSIGL) is written all at once in the left half of the screen, so it is possible to devote almost half of the horizontal period to writing the precharge signal. It is possible to raise the charge level to a level where it is desired to write.
[0024]
The precharge level of the precharge signals (PSIGL, PSIGR) has an ash level with respect to a video signal that changes between a white level and a black level.
In the case of AC driving in which the polarity of the video signal VSIG supplied to the video line 3 is inverted every horizontal period, the precharge level of the precharge signal (PSIGL, PSIGR) is also inverted every horizontal period. The polarity of the video signal VSIG is matched. As an example, a waveform diagram of sampling pulse signals φH1, φH2, φH3... ΦH14 for controlling the opening / closing of each horizontal switch HSW in the order of 14 horizontal switches HSW is shown in FIG. FIGS. 2B and 2C show changes in the voltage of the electrode line (CS line) on the opposite side of the pixel transistor of the capacitor that holds the signal charge.
[0025]
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 .phi.H1, .phi.H2, .phi.H3, and the video level Vv signals are sequentially stored in the capacitors, the voltages VL and VR of the CS line are stored. Also increases slightly due to the distributed impedance of M on the CS line. The influence of the voltage increase on the CS line affects the charge level of each capacitor C. Even if the printer is charged, the charge level fluctuates, that is, appears as a difference in display level of the liquid crystal cell LC.
Such a similar phenomenon can be applied to the gate line X of the pixel transistor.
[0026]
By the way, 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 the conventional one, and as shown in FIG. The horizontal switch HSW is opened and closed from the left side to write a video signal from the video line 3, but the right half is opposite to the conventional method, and the horizontal switch HSW is opened and closed from the right side to write the video signal from the video line 3. It is.
As a result, the pixel write potential for charging the capacitor C is almost equal to VPL in the portion immediately to the left of the separation, and the pixel write potential VPR is almost equal to VPR in the portion immediately to the right of the separation. Disappear.
The left half opens and closes the horizontal switch HSW from the right side to write a video signal from the video line 3, and the right half opens and closes the horizontal switch HSW from the left side to write the video signal from the video line 3. Is obtained.
[0027]
【The invention's effect】
As described above, the invention according to claim 1 of the present invention has a plurality of matrix-like gates arranged at each intersection of a plurality of row-shaped gate lines, a plurality of column-shaped signal lines, and gate lines and signal lines. Selected by the vertical scanning circuit that sequentially scans each gate line and selects one row of image elements every horizontal period, and sequentially samples each signal line within one horizontal period. A horizontal scanning circuit for writing video signals dot-sequentially to one row of image elements, and precharge means for supplying a predetermined precharge signal to each signal line prior to sequential sampling of the video signals for each signal line In the active matrix display device provided, each gate line is divided into left and right at the central portion, and a vertical scanning circuit is provided for each of the left and right divided gate lines, and each signal line is divided into left and right at the gate line dividing portion. Minutes into groups The precharge means supplies a predetermined precharge signal simultaneously to each of the signal lines in the group at different timings for each of the left and right groups of the divided signal lines, and the horizontal scanning circuit For the left group of signal lines divided for the image elements for one row selected by the vertical scanning circuit, each signal line is sequentially sampled from the left end toward the division unit, and the right side of the divided signal line For the group, each signal line is sequentially sampled from the right end toward the dividing unit, and video signals are written.
According to the second aspect of the present invention, in contrast to the first aspect of the invention, the horizontal scanning circuit is for the image element for one row selected by the vertical scanning circuit, and for the left group of divided signal lines. For each group of signal lines, the signal lines are sampled sequentially from the dividing unit toward the left end, and the signal lines are sampled sequentially from the dividing unit toward the right end to write video signals. It is characterized by performing.
This makes it possible to precharge the display system with high resolution and a short horizontal blanking period using the divided precharge method with sufficient time, greatly reducing video line noise. In addition, it is possible to eliminate the difference in luminance at the divided portions by a simple method, eliminate the vertical streak fixed pattern, and realize an active matrix display device excellent in display uniformity.
[0028]
According to a third aspect of the present invention, the precharge means precharges the left group of the divided signal lines when the video signal is written to the right group of the divided signal lines. A charge signal is supplied, and a precharge signal is supplied to the right group of divided signal lines when a video signal is written to the left group of divided signal lines. And
As a result, it is possible to perform precharge with a margin in time using the divided precharge method for a display method having a high resolution and a short horizontal blanking period.
[0029]
The invention according to claim 4 of the present invention is characterized in that the precharge means supplies a precharge signal having an ash level to a video signal that changes between a white level and a black level.
Thereby, the noise of the video line can be greatly reduced and the vertical stripe fixing pattern can be eliminated.
[0030]
According to a fifth aspect of the present invention, the precharge means supplies a precharge signal that is inverted every horizontal period in order to match the polarity of the video signal that is inverted every horizontal period. To do.
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 an embodiment of an active matrix display device of the present invention.
2 is a timing chart of each part for explaining the operation of the embodiment shown in FIG. 1; FIG.
FIG. 3 is a circuit diagram showing a conventional divided precharge type active matrix display device.
4 is a timing chart of each part 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 ... Division precharge means, C ... Capacitor, CS1 ... Left CS line, CS2 ... Right CS line, HSW1 to HSW14 ... Horizontal switch, LC ... Liquid crystal element, PSW1 to PSW14 ... Precharge switch, Tr ... Transistor, Vcom ... ... applied voltage of CS line, X ... gate line, Y ... signal line.

Claims (5)

A plurality of row-shaped gate lines, a plurality of column-shaped signal lines, a plurality of matrix-like image elements arranged at intersections of the gate lines and the signal lines, and the gate lines are sequentially scanned. A vertical scanning circuit that selects the image elements for one row for each horizontal period, and dot-sequentially applies the image elements for one row selected by the vertical scanning circuit by sequentially sampling the signal lines within one horizontal period. An active matrix display device comprising: a horizontal scanning circuit for writing a video signal; and precharge means for supplying a predetermined precharge signal to each signal line prior to sequential sampling of the video signal for each signal line ,
The gate lines are divided into left and right at the center, and the vertical scanning circuits are provided for the left and right divided gate lines, respectively.
Divide each signal line into left and right groups at the gate line dividing part,
The precharge means supplies a predetermined precharge signal to each of the left and right groups of the divided signal lines with a phase shift , thereby halving the distribution capacity of the signal line viewed from the precharge means. ,
The horizontal scanning circuit samples each signal line sequentially from the left end toward the dividing unit for the left group of the divided signal lines for the image elements for one row selected by the vertical scanning circuit, and For the right group of divided signal lines, each signal line is sampled sequentially from the right end toward the dividing unit, and video signals are written so as not to cause a luminance difference in the dividing unit. Active matrix display. A plurality of row-shaped gate lines, a plurality of column-shaped signal lines, a plurality of matrix-like image elements arranged at intersections of the gate lines and the signal lines, and the gate lines are sequentially scanned. A vertical scanning circuit that selects the image elements for one row for each horizontal period, and dot-sequentially applies the image elements for one row selected by the vertical scanning circuit by sequentially sampling the signal lines within one horizontal period. An active matrix display device comprising: a horizontal scanning circuit for writing a video signal; and precharge means for supplying a predetermined precharge signal to each signal line prior to sequential sampling of the video signal for each signal line ,
The gate lines are divided into left and right at the center, and the vertical scanning circuits are provided for the left and right divided gate lines, respectively.
Divide each signal line into left and right groups at the gate line dividing part,
The precharge means supplies a predetermined precharge signal to each of the left and right groups of the divided signal lines with a phase shift , thereby halving the distribution capacity of the signal line viewed from the precharge means. ,
The horizontal scanning circuit samples each signal line from the division unit sequentially toward the left end portion for the left group of the divided signal lines with respect to the image element for one row selected by the vertical scanning circuit. For the right group of divided signal lines, each signal line is sampled sequentially from the dividing unit toward the right end portion, and video signals are written so as not to cause a luminance difference in the dividing unit. Active matrix display.   The precharge means supplies a precharge signal to the left group of the divided signal lines when a video signal is written to the right group of the divided signal lines, and 2. The precharge signal is supplied 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. Alternatively, the active matrix display device according to claim 2.   3. The active matrix display device according to claim 1, wherein the precharge means supplies a precharge signal having an ash level with respect to a video signal that changes between a white level and a black level.   3. The precharge means supplies a precharge signal that is inverted every horizontal period in order to match the polarity of the video signal that is inverted every horizontal period. Active matrix display device.

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