JP2002140043A - Display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such problem that the degradation in image quality caused by a cross talk that is generated by the leak between sources and drains of transistor switches when the supply of video signals to signal electrodes is controlled with the switches in a time division manner. SOLUTION: In the active matrix driving type display device, supply of video signals Vsig being inputted from the external through a video signal input terminal 17 to signal electrodes..., 12m-1, 12m, 12m+1,... is controlled in a time division manner by transistor switches..., 16m-1, 16m, 16m+1,.... Transistor switches..., 20m-1, 20m, 20m+1,..., which are normally in an OFF state, are connected between the other ends of the electrodes..., 12m-1, 12m, 12m+1,... and an inverted video signal supply line 19. Inverted video signals VsigX having an opposite polarity with respect to the signals Vsig are provided to the line 19 in synchronism with the signals Vsig.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device and a method of driving the same, and more particularly, to a display device of an active matrix driving system in which supply of a video signal to a signal electrode is controlled by a transistor switch and a method of driving the same.

[0002]

2. Description of the Related Art In a display device of the active matrix drive system, a plurality of scanning electrodes and a plurality of signal electrodes are arranged in a matrix, pixels including switching elements are arranged at intersections thereof, and scanning is performed by vertical scanning. While the electrodes are sequentially selected, a video signal is written to the pixels of one row (one line) connected to the selected scanning electrode through the signal electrodes.

Further, there is a display device of the active matrix drive system in which supply of a video signal to a signal electrode is controlled in a time-division manner by a transistor switch. FIG. 6 shows an example of the configuration of this display device. Here, for simplification of the drawing, two rows (n rows, n + 1 rows) 3
The case of a pixel array of columns (m-1 column, m column, m + 1 column) is shown as an example.

In FIG. 6, scanning electrodes..., 101n, 1
01n + 1, ... and signal electrodes ..., 102m-1, 102
, m, 102m + 1,... are arranged in a matrix, and pixels 103 are arranged at intersections. Scan electrode ...,
One end of each of 101n, 101n + 1,... Is connected to each output end of the corresponding row of the scan electrode driving circuit 104.

Signal electrodes ..., 102m-1, 102m, 1
, 106m-1, 106m, 106m + are connected between one end of each of O.2m + 1,... And the video signal supply line 105.
Are connected to each other. A video signal Vsig is externally input to the video signal supply line 105 through a video signal input terminal 107. , 106m-1, 106m, 106m + 1,... Are sequentially turned ON / OFF by the signal electrode driving circuit 108.
Controlled.

By the way, the supply of the video signal Vsig to the display device having the above structure, ie, the signal electrodes..., 102m-1, 102m, 102m + 1,.
In the case of an active matrix drive type display device controlled by 106m-1, 106m, 106m + 1,..., A video signal input terminal 107 and a plurality of signal electrodes.
, 102m + 1, 102m + 1,... At the same time, a crosstalk occurs, which is a phenomenon in which an unintended video signal Vsig leaks to a signal electrode that should be in a non-conductive state. Will result in a decline.

In view of the above, naturally, in the display device of the active matrix driving system having the above configuration, the signal electrodes connected to the video signal input terminal 107 are time-divided under the driving control by the signal electrode driving circuit 108. This is a configuration in which the selection is performed one by one. Therefore,
At a certain moment, the transistor switches other than the selected signal electrode are turned off, and the connection between the selected signal electrode and the video signal input terminal 107 is turned off. As a result, the plurality of signal electrodes do not become completely conductive.

[0008]

SUMMARY OF THE INVENTION However, MOS
Transistor switch composed of transistors ..., 106
There are leaks between the source and the drain at m-1, 106m, 106m + 1,... So, in practice,
Transistor switch ..., 106m-1, 106m, 1
., 06m + 1,..., Only one of them is in the ON state, and the others are all in the OFF state.
The sig is mixed into signal electrodes other than the selected signal electrode through the transistor switch in the OFF state.

As described above, the signal electrodes...
The supply of the video signal to 102m, 102m + 1,...
In a conventional display device controlled in a time-division manner by m + 1,.
, 106m + 1,..., the unintended video signal Vsig leaks into the signal electrode which should be in a non-conductive state, and crosstalk occurs.
At present, the image quality is degraded.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce crosstalk caused by source-drain leakage of a transistor switch, thereby improving image quality. A display device and a driving method thereof are provided.

[0011]

In order to achieve the above object, the present invention provides a display device comprising a plurality of scanning electrodes and a plurality of signal electrodes arranged in a matrix. The supply of the video signal to the plurality of signal electrodes is controlled in a time-sharing manner by a first transistor switch group connected between the first signal line to which the video signal is supplied and the plurality of signal electrodes. On the other hand, while the second transistor switch group connected between the second signal line and the plurality of signal electrodes is always turned off,
An inverted video signal having a polarity opposite to that of the video signal input to the second signal line is supplied.

In a display device in which the supply of a video signal to a signal electrode is controlled in a time-division manner by a first transistor switch group, when a video signal is supplied to a certain signal electrode, the supply of the video signal is caused by leakage of the transistor switch. Unintended video signals leak into other signal electrodes, and the potential of the signal electrode fluctuates. At this time, by supplying an inverted video signal to the second signal line, the second signal line which is always in the OFF state is supplied.
The inverted video signal leaks into the signal electrode also in the transistor switch group. Since the leaked signal component has a polarity opposite to that of the previous leaked component, the potential fluctuation of the signal electrode due to the leak of the transistor switch is canceled.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of an active matrix drive type display device according to one embodiment of the present invention. Here, for simplification of the drawing, two rows (n rows, n + 1 rows) and three columns (m-1 columns,
The case of a pixel array of (m columns, m + 1 columns) is shown as an example.

In FIG. 1, scanning electrodes 11n, 11
n + 1, ... and signal electrodes ..., 12m-1, 12m, 12m
+1 are wired in a matrix, and pixels 13 are arranged at the intersections. Scan electrode ..., 11n, 11n
One end of each of +1,... Is connected to each output end of the corresponding row of the scan electrode drive circuit 14. The scan electrode drive circuit 14 is formed of, for example, a shift register, and applies vertical scan pulses..., ΦVn, φVn−1,... Sequentially to the scan electrodes. ) Select by unit.

Signal electrodes ..., 12m-1, 12m, 12m
+1... And the video signal supply line 15, a transistor switch composed of, for example, an Nch MOS transistor,..., 16m-1, 16m, 16m + 1,.
(First transistor switch group) are connected to each other. The video signal supply line 15 receives a video signal Vsig from the outside through a video signal input terminal 17.

Transistor switch ..., 16m-1, 1
Each of the gate electrodes 6m, 16m + 1,... Is connected to each output terminal of the corresponding column of the signal electrode drive circuit 18. The signal electrode drive circuit 18 is constituted by a shift register, for example, and includes transistor switches.
Horizontal scanning pulses..., ΦHm−1, φHm, φHm + are sequentially applied to gate electrodes −1, 16m, 16m + 1,.
By giving 1, ... the transistor switch ...,
16m-1, 16m, 16m + 1, ... ON in time division
/ OFF drive.

Signal electrodes ..., 12m-1, 12m, 12m
+1... And the inverted video signal supply line 19, for example, transistor switches..., 20m−1, 20m, 20m + 1,.
(The second transistor switch group) are connected to each other. The inverted video signal supply line 19 has a video signal Vs input from outside through the video signal input terminal 17.
An inverted video signal VsigX having a polarity opposite to that of the video signal ig is given in synchronization with the video signal Vsig.

Transistor switches, 20m-1, 2
The MOS transistors of 0m, 20m + 1,... Are preferably transistor switches.
The MOS transistors having substantially the same characteristics as those of the MOS transistors 1, 16m, 16m + 1,... Are used. The gate electrodes of the transistor switches..., 20m-1, 20m, 20m + 1,.

Next, the operation of the active matrix drive type display device having the above configuration will be described.

First, the scan electrode driving circuit 14 sequentially generates vertical scan pulses..., ΦVn, φVn−1,. Select an electrode. As a result, the switching elements (pixel transistors) in the pixels 13 connected to the scanning electrodes..., 11n, 11n + 1,. As a result, each of the pixels 13 is selected on a row (line) basis.

In a state where a certain line is selected, the signal electrode driving circuit 18 outputs the horizontal scanning pulses φHm−1,
Hm and φHm + 1 are sequentially generated and applied to the gate electrodes of the transistor switches..., 16m-1, 16m, 16m + 1,. Thereby, the transistor switches..., 16m-1, 16m, 16m +
Are turned on one by one in order.

That is, the signal electrode driving circuit 18 includes transistor switches..., 16m-1, 16m, 16m +
, 12m-1, 12m, 12m by sequentially controlling ON / OFF of 1, 2,.
+1... Are sequentially selected one by one, and conduction with the video signal input terminal 17 through the video signal supply line 15 is performed in a time-division manner.

As a result, the video signals Vsig input from the outside through the video signal input terminal 17 are sequentially turned on.
, 12m-1,..., m, 16m + 1,.
12m, 12m + 1,... Then, the video signal Vsi is applied to each of the pixels 13 for one line selected by the vertical scanning of the scan electrode driving circuit 14.
g will be written in order.

Now, consider the moment when only the m-th row of transistor switches 16m are in the ON state. At this time, the transistor switches 16m-1 and 16m + 1 are both OF
Although it is in the F state, the source of the MOS transistor
The transistor switch 16
The video signal Vsig to be transmitted only to the signal electrode 12m connected to the signal switch 12m is connected to the transistor switch 16m-
The signal also leaks to the signal electrodes 12m-1 and 12m + 1 connected to these transistor switches 16m-1 and 16m + 1 through the source-drain of 1,16m + 1.

Thus, for example, at the moment when only the transistor switch 16m is in the ON state, the MO
The video signal Vs to be transmitted only to the signal electrode 12m due to the leak between the source and the drain of the S transistor
ig is the transistor switch 16m-1, 16m + 1
Leaking into the signal electrodes 12m-1 and 12m + 1 through the gate electrode, the potentials of the signal electrodes 12m-1 and 12m + 1 fluctuate. This results in the above-mentioned crosstalk, which causes a reduction in image quality.

On the other hand, signal electrodes ..., 12m-1, 12m,
, 20m-1, 20m, 20m + 1,... Connected to the other ends of 12m + 1,... Are all OFF since their gate electrodes are grounded.
In state. The inverted video signal supply line 19 is supplied with an inverted video signal VsigX having a polarity opposite to that of the video signal Vsig in synchronization with the video signal Vsig input from the outside via the video signal input terminal 17.

Here, transistor switches..., 20 m
-1, 20m, 20m + 1,... Are also constituted by MOS transistors, and therefore, like the transistor switches..., 16m-1, 16m, 16m + 1,.
Source-drain leaks also exist in 1,. Therefore, the transistor switches 20m-1, 20m + 1
Video signal VsigX leaks into the signal electrodes 12m-1 and 12m + 1 through the source-drain of.

At this time, the transistor switches..., 16
.., 20 m−1, 20 m, 2
Assuming that the MOS transistors 0m + 1,... Have almost the same characteristics, the transistor switches 20m-1,.
The amount of signal components leaking into the signal electrodes 12m-1 and 12m + 1 through 20m + 1 (the amount of leakage) is determined by the signal electrodes 12m through the transistor switches 16m-1 and 16m + 1.
It can be considered that the amount of the signal component leaking into m−1, 12m + 1 is almost the same.

Moreover, these signal components have opposite polarities. Therefore, the video signal Vsig to be transmitted only to the signal electrode 12m is applied to the transistor switch 16m-
Signal electrodes 12m-1, 12m + through 1,16m + 1
1 and these signal electrodes 12m-1, 12m + 1
Is changed, the video signal VsigX having the opposite polarity to the video signal Vsig is supplied to the transistor switch 16m-
Signal electrodes 12m-1, 12m + through 1,16m + 1
1, the signal electrodes 12m-1, 12m + 1
Is canceled out. As a result, crosstalk due to source-drain leakage of the transistor switches 16m-1 and 16m + 1 can be reduced.

Here, the case where only the transistor switch 16m is in the ON state has been described as an example. However, even when only the transistor switch 16m-1 or 16m + 1 is in the ON state, The same is true for the above case.

In the above-described example, the leakage of the inverted video signal VsigX through the transistor switches 20m-1, 20m + 1 also occurs to the signal electrode 12m. However, since the amount of the leak is extremely small with respect to the signal component of the video signal Vsig transmitted to the signal electrode 12m through the transistor switch 16, it does not affect the original video display at all.

In the above embodiment, the NchMOS transistor is used as the switch element for controlling the supply of the video signal to the signal electrode in a time-division manner. However, the present invention is not limited to this. For example, as shown in FIG. 2, transmission gates..., 21m−1, 21m, 21m +
The same applies to the case where 1,... Are used as switch elements.

That is, transmission gates,
.. Are composed of an NchMOS transistor Qn1 and a PchMOS transistor Qp1 connected in parallel with each other, as shown in FIG. Therefore, there is a leak between the source and the drain also in these transmission gates..., 21m-1, 21m, 21m + 1,.

Therefore, the signal electrodes...
, and the inverted video signal supply line 19, as shown in FIG. 3B, the NchMOS transistors Qn2 and Pch connected in parallel with each other.
, 22m-1, 22m, 22m + 1,.
, And NchMOS transistor Qn
, 22m-1, 22 by connecting the gate electrode of the Pch 2 to the ground and connecting the gate electrode of the PchMOS transistor Qp2 to the power supply Vdd.
, 22m + 1,... are always in the OFF state.

Thus, for example, the video signal Vsig to be transmitted only to the signal electrode 12m is applied to the signal electrode 1 through the transmission gates 21m-1 and 21m + 1.
2m-1, 12m + 1 leaks into the signal electrode 12m-
Even when the potential of 1,12m + 1 fluctuates, the inverted video signal V of the opposite polarity is synchronized with the video signal Vsig.
sigv is the transmission gate 22m-1,
Leakage into the signal electrodes 12m-1 and 12m + 1 through 2m + 1 cancels potential fluctuations of the signal electrodes 12m-1 and 12m + 1, and as a result, crosstalk can be reduced.

FIG. 4 is a circuit diagram showing a configuration example of a pixel portion when the present invention is applied to, for example, a liquid crystal display device of an active matrix drive system. In the drawing, the same parts as those in FIG. Is shown. Here, for simplification of the drawing, a case of a pixel array of three rows (n-1 to n + 1 rows) and four columns (m-1 to m + 2 columns) is shown as an example.

In FIG. 4, the pixel 13 has a configuration including, for example, a thin film transistor TFT as a pixel transistor, a liquid crystal cell LC as a display element, and a storage capacitor Cs. Here, the liquid crystal cell LC means a capacitance generated between a pixel electrode formed by the thin film transistor TFT and a counter electrode formed to face the pixel electrode.

The thin-film transistor TFT has a gate electrode connected to the scanning electrodes..., 11n-1, 11n, 11n + 1,.
m, 12m + 1, 12m + 2,... In the liquid crystal cell LC, the pixel electrode is connected to the drain electrode of the thin film transistor TFT, and the counter electrode is connected to the common line 23. The storage capacitor Cs is a thin film transistor TFT
Is connected between the common electrode 23 and the common drain line 23. The common line 23 has a common voltage Vc as a reference voltage.
om is applied.

In a liquid crystal display device of the active matrix drive system, generally, a timing generator and an analog signal driver receive a video signal and a horizontal and vertical synchronizing signal (or a composite video signal including a horizontal and vertical synchronizing signal). Various timing signals are output from the generator, and an analog video signal that is AC-driven is output from the analog signal driver.
To drive the display.

Here, the analog video signal driven by AC means an analog video signal whose polarity is inverted at a certain period around a reference voltage (signal center) Vcom. By driving the display of the liquid crystal using the analog video signal converted into an alternating current, it is possible to prevent the specific resistance (specific resistance value of the substance) of the liquid crystal from being degraded due to the continuous application of the same polarity DC voltage to the liquid crystal. Can be prevented.

This AC driven analog video signal V
sig and an inverted analog video signal Vs of the opposite polarity
Each waveform of igX is shown in FIG. In the figure, the video signal voltage center value Vsig center at the time of AC driving corresponds to the common voltage Vcom. With respect to the analog video signal Vsig, a waveform having a reverse polarity with respect to the video signal voltage center value Vsig center is the inverted analog video signal VsigX.

Here, the case where the present invention is applied to a liquid crystal display device has been described as an example. However, the present invention is not limited to this application example, and supply of a video signal to a signal electrode is performed by a transistor switch. The present invention can be applied to general display devices that perform time-division control.

[0043]

As described above, according to the present invention,
In a display device in which supply of an input video signal to a signal electrode is time-divisionally controlled by a transistor switch, an inverted video signal having a polarity opposite to that of the input video signal is supplied to the signal electrode via a transistor switch which is always OFF. With this configuration, crosstalk due to transistor switch leakage can be reduced, so that image quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an active matrix drive type display device according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration example of an active matrix drive type display device according to a modification of the present invention.

FIG. 3 is a circuit diagram showing a configuration of a transmission gate.

FIG. 4 is a circuit diagram showing a configuration example of a pixel portion when the present invention is applied to an active matrix driving type liquid crystal display device.

FIG. 5 is a waveform diagram showing waveforms of an analog video signal Vsig and an inverted analog video signal VsigX when applied to a liquid crystal display device.

FIG. 6 is a block diagram showing a configuration example of an active matrix drive type display device according to a conventional example.

[Description of Signs] 11n-1 to 11n + 1,..., Scanning electrode, 12m-1 to 1
2m + 2: signal electrode, 13: pixel, 14: scanning electrode drive circuit, 16m-1 to 16m + 1, 20m-1 to 20m +
1, transistor switch, 17 video signal input terminal, 18 signal electrode drive circuit, 21m-1 to 21m +
Transmission gate, LC: liquid crystal cell, TFT: thin film transistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA16 NA42 NA53 NC12 NC21 NC22 NC34 NC35 ND05 ND09 ND15 ND60 5C006 AA16 AC21 AF43 BB16 BC13 BF34 FA36 5C058 AA06 AB02 BA01 BA10 5C080 AA10 BB05 DD10 EE29 JJ03 JJ02

Claims (4)

[Claims] 1. A display device comprising pixels arranged at intersections of a plurality of scanning electrodes and a plurality of signal electrodes wired in a matrix, comprising: a first signal line to which a video signal is supplied; A first transistor switch group that is connected between the first and second signal electrodes and sequentially performs on / off operations;
A second transistor switch group which is connected between the signal line and the plurality of signal electrodes and is always in an OFF state. 2. The display device according to claim 1, wherein a display element of said pixel comprises a liquid crystal cell. 3. A method for driving a display device, wherein pixels are arranged at intersections of a plurality of scanning electrodes and a plurality of signal electrodes arranged in a matrix, wherein a video signal is supplied to the plurality of signal electrodes. Is controlled in a time-sharing manner by a first transistor switch group connected between the first signal line to which the video signal is supplied and the plurality of signal electrodes, and the second signal line and the A second transistor switch group connected between the plurality of signal electrodes is always turned off, and an inverted video signal having a polarity opposite to that of the video signal is supplied to the second signal line. Driving method for a display device. 4. The method according to claim 3, wherein the display element of the pixel is formed of a liquid crystal cell.