JPH10153984A - Active matrix display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an active matrix display device and its driving method in which voltage of pre-charge signals charged and discharged to/from each signal line can be uniformalized even if phases of pre-charge signals are deviated. SOLUTION: In an active matrix display device, pre-charge pulses PCG, PCG' are outputted from a pre-charge circuit 14, when a pre-charge signal Psig is supplied to a corresponding signal line Y, such so-called 'fluctuation' phenomenon is caused that voltage Gate of a gate line X and voltage Cs of an opposed electrode line 25 are once boosted, after that, voltage is attenuated gradually. As pulse width of pre-charge pulses PCG, PCG' are set fully longer than an attenuation time of the 'fluctuation' phenomenon, even if deviation of phases of pre-charge pulses PCG, PCG' occurs, as the voltage Gate and voltage Cs the opposed electrode line 25 are fully attenuated at the last, voltage Vsig, Vsig' of each signal line Y pre-charged are equalized to voltage of the pre-charge signal Psig.

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 the potential fluctuation of a video line at the time of sampling the video signal, and the signal line is set in advance. The battery was charged and discharged. As described above, as an active matrix display device that supplies a precharge signal to a signal line,
For example, a batch precharge system in which a precharge signal is collectively supplied to all signal lines during a horizontal blanking period is known (Japanese Patent Application Laid-Open No. 7-295521).

In this active matrix display device, a gate and a source are connected to a video line to which a video signal is input, a row-shaped gate line, a column-shaped signal line, and an intersection of the gate line and the signal line. A matrix circuit including a thin film transistor, a pixel in which one terminal is connected to the drain of the thin film transistor, and a counter electrode line in which the other terminal of the pixel is connected in common for one row; each liquid crystal pixel is driven by the thin film transistor Is done.

A vertical scanning circuit (V scanner) is provided on the left and right sides of the matrix circuit. The V scanner sequentially scans each gate line and selects one row of liquid crystal pixels every one horizontal period (1H). . A horizontal scanning circuit (H scanner) is provided above the matrix circuit. The H scanner sequentially samples the video signal to each signal line over one horizontal period, and scans the image signal for one row selected by the V scanner. A video signal is written to the liquid crystal pixels in dot sequence. Further, a precharge circuit (P scanner) is provided below the matrix circuit, and supplies a gray level precharge signal to each signal line via a precharge switching element prior to sampling of a video signal. Each signal line Y is charged and discharged to a constant gray level voltage.

On the other hand, a so-called wide screen (aspect ratio of 1) is used.
6: 9), a screen aspect function of displaying both sides of the screen in black to project a normal screen (aspect ratio 4: 3) is generally known. In the charge circuit, separate the precharge signal for the signal lines in the boundary part on both sides displayed in black and the signal lines in other areas, and switch the supply or stop of the precharge signal to the signal line in the boundary part Have been able to. Therefore, precharge pulses for driving the precharge switching elements are separately output from the precharge circuit (see FIG. 1).

[0006]

However, in an active matrix display device that separately outputs precharge pulses, when the phase of the precharge signal is shifted, the voltage charged and discharged to the signal line becomes non-uniform. There is. FIG. 4 is a timing chart showing a precharge signal and a voltage waveform of a signal line in a conventional active matrix display device.

That is, the precharge pulses PCG, P
When the precharge switching element is opened and closed by CG 'to supply the precharge signal Psig to each signal line, when the precharge switching element is turned on, the voltage C of the common electrode line is simultaneously set with the voltage Vsig, Vsig' of the signal line.
s, the voltage Gate of the gate line once rises and then gradually attenuates. This is because the AC component of the precharge signal Psig is supplied to the counter electrode line and the gate line due to the cross capacitance between the signal line and the counter electrode line and the cross capacitance between the signal line and the gate line.

While the voltages of the counter electrode line and the gate line are attenuating, the precharge pulses PCG, PCG
When the timing of closing the precharge switching element is shifted due to the phase shift of G ′, the voltage Vs of each signal line
ig, Vsig ′ are different voltages ({V, △
(V 'reduced). Therefore, an object of the present invention is to provide an active matrix display device and a driving method thereof that can make the voltage of the precharge signal charged and discharged to each signal line uniform even when the phase of the precharge signal is shifted. I do.

[0009]

According to a first aspect of the present invention, there is provided an active matrix display device comprising: a video line to which a video signal is input; a row-shaped gate line; A pixel transistor in which a gate electrode and a source electrode are respectively connected to intersections of the gate line and the signal line; a pixel in which one terminal is connected to a drain electrode of the pixel transistor; A counter electrode line to which the other terminal is commonly connected for one row, a vertical scanning circuit that sequentially scans each gate line, and selects one row of the pixel transistors every one horizontal period; A horizontal scanning circuit for sequentially selecting a signal line and supplying the video signal to the selected signal line, wherein a pixel driven by the selected pixel transistor is supplied to the signal line. In an active matrix display device for writing a video signal, when a precharge signal is separately supplied between the signal lines prior to the supply of the video signal, a precharge that sets a supply time of the precharge signal to a predetermined time or more. A circuit is provided.

It is preferable that the precharge circuit includes a switching circuit that switches supply or stop of the precharge signal to some of the signal lines. Further, it is preferable that the predetermined time is a time required until voltage fluctuation of the counter electrode line or the gate line caused by a precharge signal supplied to the signal line is attenuated. Preferably, the precharge circuit includes a switching element provided at an end of each of the signal lines, and supplies the precharge signal to the signal line by opening and closing the switching element.

According to a fifth aspect of the present invention, there is provided a driving method of an active matrix display device, wherein a video line to which a video signal is input, a row-shaped gate line, a column-shaped signal line, an intersection of the gate line and the signal line. A pixel transistor in which a gate electrode and a source electrode are respectively connected to a portion, a pixel in which one terminal is connected to a drain electrode of the pixel transistor, and a counter electrode line in which the other terminal of the pixel is commonly connected for one row A vertical scanning circuit that sequentially scans each gate line and selects one row of the pixel transistors every one horizontal period, and sequentially selects the signal lines within the one horizontal period, and An active matrix, comprising: a horizontal scanning circuit that supplies the video signal; and writing a video signal supplied to the signal line to a pixel driven by the selected pixel transistor. In the method of driving shown device,
When a precharge signal is separately supplied between the signal lines prior to the supply of the video signal, a supply time of the precharge signal is set to a predetermined time or more.

In the present invention, when a precharge signal is separately supplied between the signal lines prior to the supply of the video signal, a supply time of the precharge signal is set to a predetermined time or more.

[0013]

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 the active matrix display device according to the embodiment. The active matrix display device 1 includes a video line 23 to which a video signal Video is input, a gate line X in a row, a signal line Y in a column, a thin film transistor Tr arranged at an intersection of the gate line X and the signal line Y, Of the liquid crystal pixels LC. Each liquid crystal pixel LC is a thin film transistor T
Driven by r. 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 one terminal of the corresponding liquid crystal pixel LC. The other terminal of the liquid crystal pixel LC is connected to the counter electrode line 25, and one row of the liquid crystal pixels LC is commonly connected to each counter electrode line 25.

Vertical scanning circuits (V scanners) 11 and 12 are provided on the left and right sides of the matrix circuit 5. The V scanners 11 and 12 sequentially scan each gate line X and scan one horizontal line (1
H) One row of liquid crystal pixels LC is selected every period. 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 can be halved. The V scanners 11 and 12 output the vertical clock signal VCK.
, And outputs a selection pulse ¢ V1, 各 V2, に し た が っ て V3,..., ¢ Vm to each gate line X in accordance with the vertical start signal VST synchronized with. Thereby, the thin film transistor Tr connected to the corresponding gate line X 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 is connected to the video line 23,
The video signal Video is supplied. The H scanner 13 outputs sampling pulses # H1, # H2, # H3, ..., #Hn in accordance with a horizontal start signal HST synchronized with predetermined horizontal clock signals HCK1 and HCK2. The horizontal switching elements are opened and closed by sampling pulses ¢ H1, ¢ H2, ¢ H3,..., ¢ Hn, and each signal line Y
Sample and hold the video signal Video. The sampled and held video signal Video 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 Video on each signal line Y within the 1H period, and dot-sequentially transfers the video signal Video to one row of liquid crystal pixels LC selected by the V scanners 11 and 12.
Write.

Further, a precharge circuit (P scanner) 14 is provided below the matrix circuit 5. P
The scanner 14 includes precharge switching elements PSW1, PSW2, PSW connected to the end of each signal line Y.
3,..., PSWn are simultaneously opened and closed, and precharge pulses PCG, PCG ′ are output. While the H-level precharge pulses PCG, PCG ′ are being output, the precharge signal Psig is applied to each signal line Y for a predetermined period. Supply. In the present embodiment, the precharge signal Psig is the video signal V
The center voltage of the video is set to Vsigc ± 2 to 3 V, that is, a constant voltage at the gray level.

FIG. 2 shows the structure of the precharge circuit 14. The precharge circuit 14 includes three inverters and one NAND circuit, and receives a basic precharge pulse PCG. To generate two precharge pulses PCG and PCG ′. For example, when the aspect switching signal A is set to H level in the case of a so-called wide screen display, the precharge pulse PC
G and PCG ′ are both output from the precharge circuit 14, and all the precharge switching elements PSW are turned on to supply a precharge signal Psig to the signal line Y for a predetermined period. On the other hand, when displaying the normal screen on the wide screen, when the aspect switching signal is set to L level, the precharge pulse PCG ′ is not generated, and the precharge signal Ps is applied to the signal line Y corresponding to the precharge pulse PCG ′.
ig is not supplied.

The precharge pulses PCG and PCG 'are output together, and all the precharge switching elements PS
W is turned on and a precharge signal Psig is applied to each signal line Y.
Is started, the cross capacitance between the signal line Y and the gate line X or the signal line Y and the counter electrode line 25
Gate line X or counter electrode line 2 depending on the cross capacitance between
5 is also supplied with the AC component of the precharge signal Psig, so that a so-called "fluctuation" phenomenon occurs in which the voltage Gate on the gate line X and the voltage Cs on the counter electrode line 25 rise once and then gradually attenuate. This decay time is about 2-3
μsec.

FIG. 3 is a timing chart showing precharge signals and voltage waveforms of signal lines in the active matrix display device. In the present embodiment, the pulse widths of the precharge pulses PCG and PCG ′ are set to be sufficiently longer than the decay time of the “shake” phenomenon. Specifically, the pulse width is determined by looking at the waveform and image quality of “sway”. Therefore, as shown in FIG.
Even when a phase shift occurs in CG ', when the precharge pulses PCG and PCG' fall from the H level to the L level, the voltage Gate of the gate line X and the counter electrode line 25
Is sufficiently attenuated, the voltages Vsig and Vsig ′ of the precharged signal line Y become equal to the voltage of the precharge signal Psig, and the precharge voltage between the signal lines Y can be made uniform. it can. By precharging each signal line Y to a gray level voltage in this manner, the potential fluctuation of the video line 23 when the video signal Video is sampled on the signal line Y is reduced.

In the above embodiment, the supply time of each precharge signal, that is, the precharge pulses PCG, PG
Although the case where the pulse widths of the CG's are made the same is shown, different pulse widths may be used. Although the case where the P scanner 14 is provided at the end of the signal line Y opposite to the H scanner 13 is shown, the P scanner 14 may be provided at the end of the signal line Y on the same side as the H scanner 13. Furthermore, precharge pulses PCG, PCG '
Is shown, but the same effect can be obtained even if there are three or more.

[0021]

According to the active matrix display device of the first aspect of the present invention, when a precharge signal is separately supplied between the signal lines prior to the supply of the video signal, a precharge circuit is used. Since the supply time of the precharge signal is set to a predetermined time or longer, the voltage of the precharge signal charged and discharged to each signal line can be made uniform even when the phase of the precharge signal is shifted. Thereby, image quality can be improved.

According to the active matrix display device of the present invention, the precharge circuit includes a switching circuit for switching supply or stop of the precharge signal to some of the signal lines, so that a wide screen is provided. It can be applied to a screen aspect function that projects a normal screen on the screen.

According to the active matrix display device of the third aspect, the predetermined time is required until the voltage fluctuation of the counter electrode line or the gate line caused by the precharge signal supplied to the signal line is attenuated. Since it is a necessary time, the supply of the precharge signal can be released in a state where the so-called “sway” until the voltage of the counter electrode line or the gate line attenuates is surely reduced.

According to the active matrix display device of the fourth aspect, the precharge circuit includes a switching element provided at an end of each of the signal lines, and opens and closes the switching element to connect the precharge circuit to the signal line. Since the charge signal is supplied, the switching element can be easily formed by NMOS, PMOS, and CMOS.

According to the driving method of the active matrix display device described in claim 5, when a precharge signal is separately supplied between the signal lines prior to the supply of the video signal, the supply of the precharge signal is performed. Since the time is set to a predetermined time or more, even if the phase of the precharge signal is shifted, the voltage of the precharge signal charged and discharged to each signal line can be made uniform.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a configuration of a precharge circuit 14.

FIG. 3 is a timing chart showing a precharge signal and a voltage waveform of a signal line in the active matrix display device.

FIG. 4 is a timing chart showing a precharge signal and a voltage waveform of a signal line in a conventional active matrix display device.

[Explanation of symbols]

1 Active matrix display device, 14 Precharge circuit, 25 Counter electrode line, X Gate line, Y
……Signal line.

Claims (5)

[Claims] A video signal inputting a video signal, a row-shaped gate line, a column-shaped signal line, and a pixel having a gate electrode and a source electrode connected to an intersection of the gate line and the signal line, respectively. A transistor, a pixel in which one terminal is connected to a drain electrode of the pixel transistor, and a counter electrode line in which the other terminal of the pixel is commonly connected to one row,
A vertical scanning circuit that sequentially scans each gate line and selects one row of the pixel transistors every one horizontal period; and sequentially selects the signal lines within the one horizontal period, and displays the image on the selected signal line. A horizontal scanning circuit for supplying a signal, wherein the active matrix display device writes a video signal supplied to the signal line to a pixel driven by the selected pixel transistor. An active matrix display device comprising: a precharge circuit that sets a supply time of the precharge signal to a predetermined time or more when a charge signal is separately supplied between the signal lines. 2. The active matrix display device according to claim 1, wherein the precharge circuit includes a switching circuit for switching supply or stop of the precharge signal to some of the signal lines. 3. The method according to claim 1, wherein the predetermined time is a time required until a voltage fluctuation of the counter electrode line or the gate line caused by a precharge signal supplied to the signal line is attenuated. The active matrix display device according to the above. 4. The precharge circuit according to claim 1, wherein a switching element is provided at an end of each of the signal lines, and the precharge signal is supplied to the signal line by opening and closing the switching element. 2. The active matrix display device according to 1. 5. A pixel in which a video signal is input, a row-shaped gate line, a column-shaped signal line, and a gate electrode and a source electrode connected to an intersection of the gate line and the signal line, respectively. A transistor, a pixel in which one terminal is connected to a drain electrode of the pixel transistor, and a counter electrode line in which the other terminal of the pixel is commonly connected to one row,
A vertical scanning circuit that sequentially scans each gate line and selects one row of the pixel transistors every one horizontal period; and sequentially selects the signal lines within the one horizontal period, and displays the image on the selected signal line. A horizontal scanning circuit for supplying a signal, wherein a video signal supplied to the signal line is written to a pixel driven by the selected pixel transistor. And supplying a precharge signal to the signal lines separately, wherein the supply time of the precharge signal is set to a predetermined time or more.