JPH10143113A - Active matrix display device and driving method thereof - Google Patents

Abstract

(57) [Problem] To provide an active matrix display device capable of simultaneously removing vertical stripes and vertical crosstalk by a point-sequential precharge method and a driving method thereof. SOLUTION: P1 scanner 14, P2 scanner 15
Respectively, sequentially opens and closes the precharge switching elements P1SW and P2SW connected to the end of each signal line Y, and supplies the precharge signals Psig1 and Psig2 to each signal line Y.
Supply. Each signal line Y is first precharged with a black level constant voltage, subsequently with a gray level constant voltage, and then sampled and held the video signal Vsig. When this operation is repeated for the second and subsequent signal lines Y over the 1H period, each signal line Y is charged and discharged to the gray level at the time of sampling the video signal Vsig. Muscles can be removed. At the same time, the thin film transistor Tr
When the signal line Y is turned off, the signal lines Y are set to the black level to make the leak current uniform in all pixel regions, so that vertical crosstalk can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix display device and a driving method thereof.

[0002]

2. Description of the Related Art Conventionally, in an active matrix display device, a precharge signal is supplied to a signal line for sampling a video signal to prevent a potential fluctuation of a video line at the time of sampling the video signal. The battery was charged and discharged. As described above, as an active matrix display device that supplies a precharge signal to a signal line, a batch precharge method that collectively supplies a precharge signal to all signal lines during a horizontal blanking period (Japanese Patent Application Laid-Open No. 7-295521). ), Or a dot-sequential precharge system in which a precharge signal is supplied to each signal line in a dot-sequential manner prior to sampling of a video signal (JP-A-7-295520).

As the number of display pixels increases and the sampling rate increases as in recent years, the horizontal blanking period becomes extremely short. Therefore, a sufficient precharge signal can be supplied by the batch precharge method. In this case, a dot-sequential precharge method is used.

FIG. 3 is a circuit diagram showing a configuration of a conventional dot-sequential precharge type active matrix display device. The active matrix display device has a matrix circuit composed of row-like gate lines X, column-like signal lines Y, and matrix-like liquid crystal pixels LC arranged at intersections of the two, and each liquid crystal pixel LC is a thin film transistor Tr. Driven by Vertical scanning circuits (V scanners) 101 and 102 are provided on the left and right of the matrix circuit.
01 and 102 sequentially scan each gate line X and select one row of liquid crystal pixels LC every one horizontal period (1H).

A horizontal scanning circuit (H scanner) 103 is provided above the matrix circuit. The H scanner 103 sequentially samples the video signal Vsig to each signal line Y over one horizontal period, and 101, 10
The video signal Vsig is written into the liquid crystal pixels LC for one row selected in Step 2 in a dot-sequential manner. Further, a precharge circuit (P scanner) 104 is provided below the matrix circuit, and applies a gray level precharge signal Psig to each signal line Y prior to sampling of the video signal Vsig.
To charge and discharge each signal line Y to a constant voltage of gray level.

FIG. 4 is a timing chart showing signal waveforms at various parts in the active matrix display device of FIG. The P scanner 104 outputs a horizontal clock signal HCK1,
Horizontal clock signal PC one clock ahead of HCK2
The horizontal start signal PST is sequentially transferred in synchronization with K1 and PCK2, and sampling pulses # P1, # P2, # P3,.
..., ¢ Pn is output. The horizontal switching elements PSW are sequentially opened and closed by this sampling pulse, and the signal line Y is at the gray level voltage (the center voltage Vsi of the video signal Vsig).
gc ± 2.0 to 3.0 V) (period d in the figure).

The H scanner 103 outputs a horizontal start signal HS in synchronization with the horizontal clock signals HCK1 and HCK2.
T is sequentially transferred and sampling pulses ¢ H1, ¢ H2, ¢ H
3, ……, ¢ Hn are output. The horizontal switching elements HSW are sequentially opened and closed by this sampling pulse, and the video signal Vsig is sampled on the signal line Y (period e in the figure).

As described above, by charging / discharging the signal line Y to a gray level voltage before sampling the video signal Vsig, the potential fluctuation of the video line 105 is greatly reduced, and the fixed pattern of the vertical streak is displayed from the displayed image. Can be excluded.

On the other hand, the applicant of the present application has proposed a technique of supplying a constant black level voltage to each signal line during a period in which image writing is not affected, in order to prevent the occurrence of vertical crosstalk. This will be described below. For example, when a black window pattern is input to a liquid crystal panel, vertical crosstalk usually occurs in an area A above and below the black window pattern C. FIG. 5 is a diagram showing a display state of the liquid crystal panel to which the black window pattern has been input. FIG. 6 is a timing chart showing pixel potentials in a region A where vertical crosstalk has occurred and a region B where vertical crosstalk has not occurred.

In the periods T2 and T4 of the period in which the thin film transistor is off, a black level voltage is supplied to the signal line in the area A, but a black level voltage is supplied to the signal line in the area B. Absent. Thereby, this section T2,
At T4, the leakage currents of the thin film transistors in the region A and the region B are different, and the pixel potential of the thin film transistor in the region A is smaller than that in the region B. In particular, due to the asymmetry of the leak current between the drain and the source of the thin film transistor, the difference is large on the low voltage side in the section T4, and the vertical crosstalk occurs significantly.

As a countermeasure, while the thin film transistors are turned off, a black level voltage (a voltage larger than the maximum amplitude of the video signal) is supplied to each signal line in all the pixel regions to reduce the leakage current of all the thin film transistors. T2, T
It has been studied to eliminate the difference in the leakage current of the thin film transistor between the regions and to eliminate the vertical crosstalk by aligning them with the case of 4.

[0012]

However, in the precharge circuit, since the fixed pattern of the vertical stripe is removed,
A gray level voltage is supplied to the signal line Y prior to the video signal Vsig, but the gray level voltage cannot eliminate the vertical crosstalk. That is, in order to eliminate the vertical stroke, a black level voltage must be supplied to the signal line Y, and since the voltage levels are different,
Vertical streaks and vertical crosstalk could not be removed at the same time.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an active matrix display device capable of simultaneously removing vertical stripes and vertical crosstalk by a dot-sequential precharge method and a driving method thereof.

[0014]

In order to achieve the above object, an active matrix display device according to a first aspect of the present invention comprises a row-shaped gate line, a column-shaped signal line, a gate line, and a gate line. A pixel arranged at the intersection of the signal lines and a vertical scanning circuit that sequentially scans each gate line and selects one row of pixels every one horizontal period, and sequentially selects each signal line within the one horizontal period A horizontal scanning circuit that supplies the video signal to the selected one row of pixels in a dot-sequential manner, and selects the signal line. A precharge circuit that supplies a first precharge signal of a black level and a second precharge signal of a gray level in time series prior to the supply of the video signal.

The precharge circuit has a first precharge circuit and a second precharge circuit. The first precharge circuit and the second precharge circuit each select the signal line to generate the first precharge signal. And the second
Preferably, a precharge signal is provided. further,
It is preferable that the first precharge signal is a signal having a black level larger than a maximum amplitude of the video signal. Also,
The first precharge circuit, the second precharge circuit, and the horizontal scanning circuit each have a switching element provided at an end of each signal line, and open and close the switching element to provide the first precharge signal to the signal line. It is preferable to supply the second precharge signal and the video signal in time series. Further, it is preferable that the first precharge signal, the second precharge signal, and the video signal are inverted every one horizontal period.

According to a sixth aspect of the present invention, there is provided a driving method of an active matrix display device, comprising: a row-shaped gate line; a column-shaped signal line; a pixel disposed at an intersection of the gate line and the signal line; A vertical scanning circuit that sequentially scans the lines and selects one row of pixels every one horizontal period, and sequentially selects each signal line within the one horizontal period to sample a video signal, and A method for driving an active matrix display device including a horizontal scanning circuit that writes the video signal in a pixel in a dot-sequential manner, wherein the signal line is selected prior to the sampling of the video signal, and the selected signal line is set to black. A first precharge signal of a level is supplied, and after supplying the first precharge signal, a second precharge signal of a gray level is supplied to the signal line.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an active matrix display device and a method of driving the same according to the present invention will be described. FIG. 1 is a circuit diagram showing a configuration of a dot-sequential precharge type active matrix display device according to an embodiment. The active matrix display device 1 has a matrix circuit 5 including row-shaped gate lines X, column-shaped signal lines Y, and matrix-shaped liquid crystal pixels LC arranged at intersections of the two. Each liquid crystal pixel LC is driven by a 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 signal line X, and the drain electrode is connected to the corresponding liquid crystal pixel LC.

Vertical scanning circuits (V scanners) 11 and 12 are provided on the left and right sides of the matrix circuit 5, respectively. The V scanners 11 and 12 sequentially scan each gate line X, and scan one gate line X every one horizontal period (1H). The liquid crystal pixels LC for a row are selected. Since the vertical scanning circuits (V scanners) 11 and 12 are provided on the left and right, the end of the gate line X of the thin film transistor Tr is not opened, and the impedance thereof can be halved. The V scanners 11 and 12 output the vertical clock signal VCK.
, The vertical start signal VST is sequentially transferred, and selection pulses # V1, # V2, # V3,..., #Vm are output to each gate line X. Thereby, the thin film transistor Tr is opened and closed.

A horizontal scanning circuit (H scanner) 13 is provided above the matrix circuit 5. One end of each signal line Y has horizontal switching elements HSW1, HSW
, HSW3,..., HSWn, and each of the horizontal switching elements HSW1, HSW2, HSW3,.
, HSWn are connected to the video line 23 to receive the video signal Vsig. The H scanner 13 sequentially transfers the horizontal start signal HST in synchronization with predetermined horizontal clock signals HCK1 and HCK2, and outputs sampling pulses # H1, # H2, # H3, ..., #Hn. Sampling pulse ¢ H1, ¢ H2, ¢ H3, ……, ¢ Hn
Thereby, the horizontal switching elements are opened and closed to sample and hold the video signal Vsig on each signal line Y. The sampled and held video signal Vsig is supplied to the V scanner 1
The data is written to the liquid crystal pixel LC corresponding to the gate line X selected by 1 and 12. As described above, the H scanner 13 sequentially samples the video signal Vsig on each signal line Y within 1H, and writes the video signal Vsig in the dot sequence to the liquid crystal pixels LC of one row selected by the V scanners 11 and 12.

Further, two precharge circuits (P1 scanner, P2 scanner) 1 are provided below the matrix circuit 5.
4 and 15 are provided. The P1 scanner 14 includes precharge switching elements P1SW1, P1SW2, P1SW3,..., P1S connected to the end of each signal line Y.
Wn are sequentially opened and closed, and a precharge signal Ps is applied to each signal line Y.
ig1. In the present embodiment, the precharge signal Psig1 is the center voltage Vsigc of the video signal Vsig.
The voltage is set to a voltage of ± 4.5 V or more, that is, a black level voltage larger than the maximum amplitude of the video signal Vsig. When supplying the precharge signal Psig1, the P1 scanner 1
Numeral 4 sequentially transfers the horizontal start signal PST in synchronization with the horizontal clock signals PCK1 and PCK2 every 1H period, and outputs sampling pulses # P11, # P12, # P13, ..., # P1n.
Is output. The precharge switching elements are sequentially opened and closed by these sampling pulses.

As described above, the P1 scanner 14 supplies the precharge signal Psig1 to each signal line Y in a dot-sequential manner, thereby making the leak current of the thin film transistor Tr uniform in the pixel region.

On the other hand, the P2 scanner 15 has a precharge switching element P2SW connected to the end of each signal line Y.
1, P2SW2, P2SW3,..., P2SWn are sequentially opened and closed to supply a precharge signal Psig2 to each signal line Y. In the present embodiment, the precharge signal Psig2
Is the center voltage Vsigc ± 2.0 of the video signal Vsig.
The voltage is set to a gray level of 3.0 V. When supplying the precharge signal Psig2, the P2 scanner 15 outputs the horizontal clock signals PCK1 and PCK1 similarly to the P1 scanner 14.
Horizontal start signal PS every 1H period in synchronization with PCK2
T are sequentially transferred and the sampling pulses ¢ P21, ¢ P22,
¢ P23, ..., ¢ P2n are output. The precharge switching elements are sequentially opened and closed by these sampling pulses.

As described above, the P2 scanner 15 supplies the precharge signal Psig2 to each signal line Y in a dot-sequential manner prior to the sequential sampling of the video signal Vsig, thereby turning each signal line Y to a gray level voltage. The fluctuation of the potential of the video line 23 when the video signal Vsig is sampled by charging and discharging is greatly reduced.

FIG. 2 is a timing chart showing signal waveforms at various parts during 1H inversion driving in the active matrix display device. The P1 scanner 14 sequentially transfers the horizontal start signal P1ST every 1H period in synchronization with the horizontal clock signals PCK1 and PCK2 one clock ahead of the horizontal clock signals HCK1 and HCK2, and sampling pulses # P11, # P12, # P13,. …, Outputs P1n.
The precharge switching elements P1SW are sequentially opened and closed by this sampling pulse, and the corresponding signal line Y is precharged to a constant black level voltage by the precharge signal Psig1 (period a in the figure).

Further, the P2 scanner 15 sequentially transfers the horizontal start signal P2ST delayed by one clock from the P1 scanner 14 every 1H period in synchronization with the horizontal clock signals PCK1 and PCK2, and the sampling pulses # P21, # P22,.
¢ P23, ..., ¢ P2n are output. The horizontal switching elements P2SW are sequentially opened and closed by this sampling pulse, and the corresponding signal lines Y are precharged to a constant gray level voltage by the precharge signal Psig2 (period b in the figure).

Further, the H scanner 102 outputs a horizontal start signal H in synchronization with the horizontal clock signals HCK1 and HCK2.
ST is sequentially transferred every 1H period, and the sampling pulse
H1, ¢ H2, ¢ H3, ...,… Hn are output. The horizontal switching elements HSW are sequentially opened and closed by this sampling pulse, and the video signal Vsig is sampled and held on the corresponding signal line Y (period c in the figure). The video signal Vsig is a voltage waveform that changes between a white level and a black level. Therefore, each signal line Y is precharged first with a constant black level voltage, subsequently with a gray level constant voltage, and then sampled and held the video signal Vsig. When this operation is repeated for the second and subsequent signal lines Y over the 1H period, the inverted precharge signals Psig1, Psig2 and the video signal Vsig are precharged to each signal line Y over the next 1H period.

As described above, the precharge signal Psig2
When the video signal Vsig is sampled, each signal line Y
Is charged and discharged to the ash level.
Vertical streaks caused by the potential fluctuation of the electric potential can be removed. At the same time, the leakage current when the thin film transistor Tr is turned off by the precharge signal Psig1 is made uniform in all pixel regions, so that vertical crosstalk can be eliminated. In the above embodiment, the P1 scanner 1
4. Although the case where the P2 scanner 15 is provided at the end of the signal line Y opposite to the H scanner 13 is shown, it may be provided at the end of the signal line Y on the same side as the H scanner 13.

[0028]

According to the active matrix display device of the first aspect of the present invention, the signal line is selected by a precharge circuit, and black is supplied to the selected signal line prior to the supply of the video signal. Since the first precharge signal of the level and the second precharge signal of the gray level are supplied in time series, the vertical streak and the vertical crosstalk can be simultaneously removed by the dot sequential precharge method. As a result, high-quality image display can be performed.

According to the active matrix display device of the present invention, each of the first precharge circuit and the second precharge circuit selects the signal line and selects the first precharge circuit.
Since the precharge signal and the second precharge signal are supplied, the second precharge signal following the first precharge can be supplied to the signal line at an arbitrary timing prior to the video signal.

According to the active matrix display device of the third aspect, since the first precharge signal is a signal of a black level larger than the maximum amplitude of the video signal,
Vertical crosstalk can be reliably removed.

According to the active matrix display device of the present invention, the first precharge signal, the second precharge signal, and the video signal are supplied to the signal line in time series by opening and closing a switching element. , N
Switching elements can be easily formed by MOS, PMOS and CMOS.

According to the active matrix display device of the present invention, the first precharge signal, the second precharge signal and the video signal are inverted every one horizontal period, so that the inversion drive display is made every one horizontal period. Applicable to

According to the driving method of the active matrix display device of the present invention, the signal line is selected prior to the sampling of the video signal, and the selected signal line is subjected to the first precharge of the black level. After the signal is supplied and the first precharge signal is supplied, the gray level second precharge signal is supplied to the signal line, so that the vertical streak and the vertical crosstalk can be simultaneously removed by the dot sequential precharge method.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of an active matrix display device of a dot sequential precharge system according to an embodiment.

FIG. 2 is a timing chart showing signal waveforms of respective units at the time of 1H inversion driving in the active matrix display device.

FIG. 3 is a circuit diagram showing a configuration of a conventional dot-sequential precharge type active matrix display device.

FIG. 4 is a timing chart showing signal waveforms at various parts in the active matrix display device of FIG. 3;

FIG. 5 is a diagram showing a display state of a liquid crystal panel to which a black window pattern has been input.

FIG. 6 is a timing chart showing pixel potentials in a region A where vertical crosstalk has occurred and a region B where vertical crosstalk has not occurred.

[Explanation of symbols]

1 Active matrix display device, 5 Matrix circuit, 11, 12 V scanner, 13 H scanner, 14 P1 scanner, 15 P2 scanner.

Claims (6)

[Claims] 1. A gate line in a row, a signal line in a column, a pixel arranged at an intersection of the gate line and the signal line, and each gate line are sequentially scanned, and one row is scanned every one horizontal period. A vertical scanning circuit for selecting pixels, and a horizontal scanning circuit for sequentially selecting each signal line within the one horizontal period to supply a video signal, and writing the video signal to the selected one row of pixels in a dot-sequential manner An active matrix display device comprising: a first precharge signal of a black level and a second precharge signal of a gray level prior to the supply of the video signal to the selected signal line. An active matrix display device, comprising a precharge circuit for supplying chronologically. 2. The precharge circuit includes a first precharge circuit and a second precharge circuit, and each of the first precharge circuit and the second precharge circuit selects the signal line to perform the first precharge circuit. 2. The active matrix display device according to claim 1, wherein a charge signal and a second precharge signal are supplied. 3. The active matrix display device according to claim 1, wherein the first precharge signal is a signal having a black level larger than a maximum amplitude of the video signal. 4. The first precharge circuit, the second precharge circuit, and the horizontal scanning circuit each include a switching element provided at an end of each signal line, and the switching element is opened and closed. 2. The active matrix display device according to claim 1, wherein the first precharge signal, the second precharge signal, and the video signal are supplied in time series. 5. The active matrix display device according to claim 1, wherein the first precharge signal, the second precharge signal, and the video signal are inverted every one horizontal period. 6. A row-shaped gate line, a column-shaped signal line, a pixel disposed at an intersection of the gate line and the signal line, and each gate line are sequentially scanned, and one row is scanned every one horizontal period. A vertical scanning circuit for selecting pixels, and a horizontal scanning circuit for sequentially selecting each signal line within the one horizontal period, sampling a video signal, and writing the video signal dot-sequentially to the selected one row of pixels. A method for driving an active matrix display device, comprising: selecting the signal line prior to the sampling of the video signal; supplying a first precharge signal of a black level to the selected signal line; After supplying one precharge signal, the second
A method for driving an active matrix display device, wherein a precharge signal is supplied to the signal line.