KR20140099198A - Liquid crystal display and the method of driving the same - Google Patents

Abstract

The present invention relates to a liquid crystal display which comprises: a plurality of pixels having at least one pair of a memory-type thin film transistor having a ferroelectric material in an insulating section of a gate and a general-type thin film transistor in which drains are connected to the gate of the memory-type thin film transistor; and a driving circuit which supplies data signals to a source of the general-type thin film transistor, scan signals to a gate of the general-type thin film transistor, and pixel signals to a source of the memory-type thin film transistor.

Description

[0001] The present invention relates to a liquid crystal display device and a method of driving the same,

The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a thin film transistor (TFT) having a memory type thin film transistor (TFT), that is, a ferroelectric material, And more particularly, to a low power liquid crystal display device and a driving method thereof that can maintain pixel information for a long time even without refreshing using hysteresis of a liquid crystal display device.

A liquid crystal display device used as a display of various electronic products including a TV and a computer monitor is driven mainly in accordance with an active matrix type in which a thin film transistor (TFT) functions as a switching element for each pixel. Each pixel of such an active matrix type liquid crystal display device includes a thin film transistor in which a gate electrode is connected to a scanning line, one of a source electrode and a drain electrode is connected to a signal line, and the other of the source electrode and the drain electrode is connected to the pixel electrode, A capacitor formed between the pixel electrode and the capacitor electrode, and (3) a liquid crystal interposed between the pixel electrode and the counter electrode. In the active matrix liquid crystal display device configured as described above, individual pixel electrodes must be driven independently, and the same image is also required to be recharged for each frame, so that a large amount of driving power is consumed.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art by providing a memory type thin film transistor (TFT) a liquid crystal display device and a method of driving the same which can maintain information of a pixel for a long time even without refreshing using a hysteresis technique.

In order to achieve the above object, a first embodiment of a liquid crystal display device according to the present invention includes: (1) a memory-type thin film transistor having a ferroelectric material in an insulation portion of a gate and a drain connected to a gate of the memory- A plurality of pixels provided with at least one pair of general thin film transistors, (2) a data signal to the source of the general thin film transistor, a scan signal to the gate of the general thin film transistor, and a pixel signal to the source of the memory thin film transistor Respectively.

In this case, each pixel includes first and second thin film transistors as the general thin film transistor, and third and fourth thin film transistors as the memory thin film transistor, wherein the drain of the first thin film transistor is connected to the gate of the third thin film transistor The drain of the second thin film transistor is connected to the gate of the fourth thin film transistor, the drain of the third thin film transistor and the drain of the fourth thin film transistor are connected to the pixel electrode, and (2) A first scan line for supplying a scan signal, a second scan line for supplying a second scan signal, a data line for supplying a data signal, a first pixel line for supplying a first pixel signal, Wherein the first scan line is connected to the gate of the first thin film transistor of each pixel and the second scan line is connected to the gate of the second thin film transistor of each pixel, The data line is connected to the sources of the first and second thin film transistors, the first pixel line is connected to the source of the third thin film transistor, and the second pixel line is connected to the source of the fourth thin film transistor .

In addition, a first capacitor connected between the drain of the first thin film transistor and the capacitor electrode, and a second capacitor connected between the drain of the second thin film transistor and the capacitor electrode may be further included.

The first capacitor may be connected between the drain of the first thin film transistor and the pixel electrode, and the second capacitor may be connected between the drain of the second thin film transistor and the pixel electrode.

Each of the pixels includes a first thin film transistor as the general thin film transistor, a second thin film transistor as the memory thin film transistor, and a resistor R connected to one side of the drain of the second thin film transistor, The drain of the transistor and the gate of the second thin film transistor are connected, the drain of the second thin film transistor is connected to the pixel electrode, and the size of the resistor R is equal to the resistance (R _{T2 , on} and the resistance R _{T2 , off} when the second thin film transistor is turned _off , and (2) the driving circuit supplies a scan signal to the pixels, A first pixel line for supplying a first pixel signal, and a second pixel line for supplying a second pixel signal, wherein the scan line is connected to the gate of the first thin film transistor The data line is connected to the source of the first thin film transistor, the first pixel line is connected to the source of the second thin film transistor, and the second pixel line is connected to the other side of the resistor R .

The organic light emitting display further includes a capacitor connected between the drain of the first thin film transistor and the capacitor electrode.

In addition, the capacitor may be connected between the drain of the first thin film transistor and the pixel electrode.

Particularly, in the first and second embodiments, either the first pixel line or the second pixel line supplies a white signal and the other supplies a black signal.

On the other hand, a relation of 100 x R _{T2, on} <R <100 x R _{T2, off} is satisfied between R, R _{T2, on} and R _{T2, off} .

A plurality of pixels and a driving circuit including a memory type thin film transistor having a ferroelectric material in an insulating portion of a gate and a general thin film transistor having a drain connected to a gate of the memory type thin film transistor, Type liquid crystal display device that supplies a data signal to the source of the general thin film transistor, a scan signal to the gate of the general thin film transistor, and a pixel signal to the source of the memory thin film transistor, A programming step of supplying a data signal and a scan signal to induce hysteresis in a memory-type thin film transistor of each pixel, and (2) a display step of supplying pixel signals and a scan signal to display pixel information in each pixel.

Specifically, the programming step moves the threshold voltage of the memory-type thin film transistor in the negative or positive direction according to the pixel information to be displayed in the display step.

Each pixel includes two pairs of the memory thin film transistor and the general thin film transistor. Accordingly, the programming step includes (1) a first step of moving a threshold voltage of a memory thin film transistor in a negative direction, 2) a second step of shifting the threshold voltage of the other memory-type thin film transistor in the positive direction.

In addition, the liquid crystal display device may be configured according to the first embodiment, and the programming step may include: (1) supplying a high level voltage to the first scan signal in the first step, The first thin film transistor is turned on and the second thin film transistor is turned on by supplying a high level voltage to the second scan signal in the second step, A positive voltage V ₊ and a negative voltage V _- (the absolute magnitudes of V ₊ and V _- being the same) are supplied to the data signal simultaneously with the scan signal, and (2) to the V ₊ supply by moving the threshold voltage of the third thin film transistor to negative the voltage V to the data signal in the second step _- and by supplying the movement in the threshold voltage of the fourth thin film transistor in an amount, said first a data signal in phase the voltage V _- Supply to and moving the threshold voltage of the third thin film transistor in an amount further comprises the step of moving the threshold voltage of the fourth thin film transistor by supplying the voltage ₊ V to the data signal in the second step to the sound.

When the first pixel line supplies a white signal and the second pixel line supplies a black signal, the programming step includes the steps of: (1) when a white signal is displayed on the pixel in the displaying step, further comprising the step of supplying a _- supplying the voltage ₊ V to the data signal from, (2) the voltage V to the data signal at the first stage when the pixel to be displayed the black signal in the display step.

In particular, when one of the first pixel line and the second pixel line supplies a white signal and the other supplies a black signal, the displaying step may include: (1) applying the first scan signal and the second scan signal, A third step of supplying a voltage of a high level, respectively; (2) the first scan signal and a second, but by supplying a voltage to the respective (low) level at the same time supplying the black signal and white signal to the scan signals, the black signal to a positive voltage V ₊₂ and the V a fourth step of supplying a negative voltage of _-2 V to ₊₂ reverse voltage, and then, supplies the signals to the white is a positive voltage V ₊₃ and _-3 V voltage of a negative voltage and then inverting the V ₊₃ .

The liquid crystal display device is configured according to the second embodiment, and thus the programming step includes: (1) supplying a high level voltage to the scan signal to turn on the first thin film transistor; (2) supplying a positive voltage V ₊ as a data signal simultaneously with the scan signal to move a threshold voltage of the second thin film transistor in a negative direction, or supplying a negative voltage V _- And moving the threshold voltage of the thin film transistor in the positive direction.

The liquid crystal display device and the driving method according to the present invention configured as described above can implement the low power liquid crystal display device and the driving method thereof by allowing information of pixels to be retained for a long time without refreshing.

1 shows hysteresis of a thin film transistor having a memory function.
2 is a view showing one pixel of a liquid crystal display device according to the first embodiment of the present invention.
3 is a view showing one pixel of a liquid crystal display device according to a second embodiment of the present invention.
4 is a view showing one pixel of a liquid crystal display device according to a third embodiment of the present invention.
5 is a view showing one pixel of a liquid crystal display device according to a fourth embodiment of the present invention.
6 is a view illustrating a driving principle in which a white signal is displayed in one pixel of a liquid crystal display device according to the first embodiment of the present invention.
7 is a view showing a driving principle in which a black signal is displayed in one pixel of a liquid crystal display device according to the first embodiment of the present invention.
8 is a diagram showing a driving signal for displaying a white signal or a black signal in 2x2 pixels of a liquid crystal display device according to the first embodiment of the present invention.
9 is a view illustrating a driving principle in which a white signal is displayed in one pixel of a liquid crystal display device according to a second embodiment of the present invention.
10 is a view showing a driving principle in which a black signal is displayed in one pixel of a liquid crystal display device according to a second embodiment of the present invention.
11 is a diagram showing a drive signal for displaying a white signal or a black signal in 2 占 pixels of a liquid crystal display device according to a second embodiment of the present invention;
FIGS. 12 to 15 are diagrams illustrating a driving principle of one pixel of a liquid crystal display device according to a third embodiment of the present invention. FIG.
16 to 18 are diagrams illustrating a driving principle of one pixel of a liquid crystal display device according to a fourth embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, . In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

Furthermore, terms used herein are for the purpose of illustrating embodiments and are not intended to limit the present invention. In this specification, the singular forms include plural forms as the case may be, unless the context clearly indicates otherwise. &Quot; comprises "and / or" comprising "used in the specification do not exclude the presence or addition of one or more other elements other than the stated element. Unless defined otherwise, all terms used herein may be used in a sense commonly understood by one of ordinary skill in the art to which this invention belongs. In addition, commonly used predefined terms are not ideally or excessively interpreted unless explicitly defined otherwise.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a hysteresis of a thin film transistor (hereinafter referred to as a "memory thin film transistor") having a memory function and having a ferroelectric material in an insulator of a gate. That is, as shown in FIG. 1, when a positive voltage is applied to the gate of the memory thin film transistor for a predetermined time, the threshold voltage of the memory thin film transistor moves in the negative direction, When 0 V (volt) is applied to the gate of the thin film transistor, the memory thin film transistor maintains the on state for a predetermined time. On the contrary, when a negative voltage is applied to the gate of the memory thin film transistor for a predetermined time, the threshold voltage of the memory thin film transistor moves in the positive direction. At this time, 0 V is applied to the gate of the memory thin film transistor The memory-type thin film transistor is kept off for a predetermined time. When the threshold voltage of the memory thin film transistor is shifted to a positive or negative voltage and then 0 V is applied, the on or off state of the thin film transistor can be maintained for a predetermined time without additional recharging. Hereinafter, a liquid crystal display device including such a memory-type thin film transistor will be described.

A liquid crystal display device according to the present invention is an active matrix type liquid crystal display device and includes a plurality of pixels and a driving circuit.

First, FIG. 2 shows a structure of a liquid crystal display device according to a first embodiment of the present invention, which is included in one pixel.

2, each pixel of the liquid crystal display according to the first embodiment of the present invention includes first, second, third, and fourth thin film transistors 10, 20, 30, and 40, A first capacitor 50 connected between the drain of the thin film transistor 10 and the capacitor electrode and a second capacitor 60 connected between the drain of the second thin film transistor 20 and the capacitor electrode . The first and second thin film transistors 10 and 20 are commonly used thin film transistors, and the first and second thin film transistors 10 and 20 are commonly used. And the third and fourth thin film transistors 30 and 40 are the memory thin film transistors.

Specifically, the drain of the first thin film transistor 10 is connected to the gate of the third thin film transistor 30, the drain of the second thin film transistor 20 is connected to the gate of the fourth thin film transistor 30, And the drains of the third and fourth thin film transistors 30 and 40 are connected to the pixel electrodes.

The driving circuit includes a first scan line 110 for supplying a first scan signal to each pixel, a second scan line 120 for supplying a second scan signal, a data line 130 for supplying a data signal, A first pixel line 140 for supplying a pixel signal, and a second pixel line 150 for supplying a second pixel signal.

Specifically, the first scan signal and the second scan signal are signals for turning on and off the first thin film transistor 10 and the second thin film transistor 20 of each pixel, and in a commonly used liquid crystal display device, a "gate signal" It is also called. Accordingly, the first scan line 110 is connected to the gate of the first thin film transistor 10 of each pixel and the second scan line 120 is connected to the gate of the second thin film transistor 20 of each pixel respectively.

In addition, the data signal passes through the first thin film transistor 10 and the second thin film transistor 20 which are turned on by the first scan signal and the second scan signal, and the memory thin film transistor, that is, the third thin film transistor 30 And the fourth thin film transistor 40 are turned on or off. Accordingly, the data line 130 is connected to the sources of the first and second thin film transistors 10 and 20. Thus, the first capacitor (50) is connected to the third thin film transistor (30). The second capacitor 60 holds the data signal supplied to the fourth thin film transistor 40 through the data line 130 for a predetermined time.

On the other hand, the first pixel signal and the second pixel signal are signals containing information desired to be displayed on each pixel, and are also referred to as "pixel information signal" in a commonly used liquid crystal display device. Specifically, the first pixel signal is supplied to the third thin film transistor 30 which is turned on by the data signal, the second pixel signal is supplied to the fourth thin film transistor 40 which is turned on by the data signal, The first pixel signal or the second pixel signal is supplied to the pixel electrode in accordance with the thin film transistor 30 or the fourth thin film transistor 40. [ The first pixel line 140 is connected to the source of the third thin film transistor 30 and the second pixel line 150 is connected to the source of the fourth thin film transistor 40. [ Respectively.

The liquid crystal display according to the first embodiment of the present invention includes a counter electrode facing the pixel electrode, a liquid crystal interposed between the pixel electrode and the counter electrode, And a common voltage line 160 for supplying a common voltage V _COM to the electrodes. The liquid crystal display device according to the present invention makes it possible to change the transmissivity of the liquid crystal to a voltage between the pixel electrode and the counter electrode in the same manner as in a conventional liquid crystal display device.

FIG. 3 shows a configuration of a liquid crystal display device according to a second embodiment of the present invention.

3, each pixel of the liquid crystal display according to the second exemplary embodiment of the present invention includes a first thin film transistor 210, a second thin film transistor 220 as the memory thin film transistor, A capacitor 230 connected between the drain of the transistor 210 and the capacitor electrode and a resistor R 240 connected to one end of the drain of the second thin film transistor 220. The capacitor electrode is grounded from the outside and functions to improve the charging characteristic of the pixel electrode to reduce the voltage loss.

The drain of the first thin film transistor 210 and the gate of the second thin film transistor 220 are connected to each other and the drain of the second thin film transistor 220 is connected to the pixel electrode 220. [ Lt; / RTI &gt;

In particular, the resistance R is larger than the resistance R _{T2, on of} the second thin film transistor 220 when the second thin film transistor 220 is turned _on , It should be bigger than double. The size of the resistor R is smaller than the resistance value R _{T2, off of} the second thin film transistor 220 when the second thin film transistor 220 is turned _off , do. Accordingly, if R is different from R _{T2, on} or R _{T2, off} by 100 times or more, V _W or V _B can be applied to the pixel electrode within an error of 1%.

The driving circuit includes a scan line 310 for supplying a scan signal to each pixel, a data line 320 for supplying a data signal, a first pixel line 330 for supplying a first pixel signal, And a second pixel line 340 for supplying the second pixel line.

The scan signal is a signal for turning on or off the first thin film transistor 210 of each pixel, and is also referred to as a "gate signal " in a commonly used liquid crystal display device. Accordingly, the scan line 310 is connected to the gate of the first thin film transistor 210.

The data signal passes through the first thin film transistor 210 turned on by the scan signal to turn on or off the memory thin film transistor, that is, the second thin film transistor 220. Accordingly, the data line 320 is connected to a source of the first thin film transistor 210.

The first pixel line 330 is connected to the source of the second thin film transistor 220 and the second pixel line 340 is connected to the other side of the resistor R. Since the first pixel signal and the second pixel signal are the same as those described in the first embodiment, the description thereof will be omitted.

The liquid crystal display according to the second embodiment has a counter electrode, a liquid crystal interposed between the pixel electrode and the counter electrode, and a common electrode (V _COM ) And a common voltage line (350).

In the meantime, each pixel of the liquid crystal display according to the first and second embodiments of the present invention receives a white signal V _W as a first pixel signal through the first pixel lines 140 and 330, And a black signal V _B (a signal for displaying black on the pixel) is supplied to the second pixel signal through the second pixel lines 150 and 340. Conversely, a black signal V _B may be supplied as a first pixel signal, a white signal V _W may be supplied as a second pixel signal, and a black signal V _B And a white signal V _W may be alternately supplied. In addition, when inversion driving is required to prevent a residual image due to residual ions in the liquid crystal, the white signal (V _W ) and the black signal (V _B ) may be supplied in an alternating voltage of a form larger than the common voltage. At this time, it is preferable that the white signal (V _W ) and the black signal (V _B ) have the same polarity, and that the two voltages are changed to positive and negative for each frame. Accordingly, the period of the AC voltage corresponds to 2f (f is one frame time) and is higher than the common voltage (V _COM ) supplied through the common voltage lines 160 and 350 every frame. Or a low voltage is applied. As in a conventional liquid crystal display device, a voltage of a suitable magnitude may be applied according to a normally white mode or a normally black mode to control the degree of movement of the liquid crystal.

In addition, the capacitor electrodes of the first and second embodiments are grounded to become reference voltage points, as shown in Figs. 2 and 3.

On the other hand, FIG. 4 shows a configuration of a liquid crystal display device according to a third embodiment of the present invention.

4, each pixel of the liquid crystal display device according to the third embodiment of the present invention includes first and second thin film transistors 410 and 420 which are general thin film transistors, third and fourth thin film transistors A first capacitor 450 connected between the drain of the first TFT 410 and the pixel electrode, a drain connected to the drain of the second TFT 420, And a second capacitor 460 connected between the electrodes. The driving circuit includes a first scan line 510 for supplying a first scan signal to each pixel, a second scan line 520 for supplying a second scan signal, a data line 530 for supplying a data signal, A first pixel line 540 for supplying a first pixel signal, a second pixel line 550 for supplying a second pixel signal, and a common voltage line 560 for supplying a common voltage V _COM to the counter electrode . The liquid crystal display according to the third embodiment of the present invention is the same as the liquid crystal display according to the first embodiment of the present invention described with reference to FIG. 2 except for the position where the first and second capacitors 50 and 60 are connected The description of each constitution will be omitted.

On the other hand, FIG. 5 shows a configuration of a liquid crystal display device according to a fourth embodiment of the present invention included in one pixel.

5, each pixel of the liquid crystal display according to the fourth exemplary embodiment of the present invention includes a first thin film transistor 610 as a general thin film transistor, a second thin film transistor 620 as a memory thin film transistor, A capacitor 630 connected between the drain of the first thin film transistor 610 and the pixel electrode and a resistor R 640 having one side connected to the drain of the second thin film transistor 620, do. The driving circuit includes a scan line 710 for supplying a scan signal to each pixel, a data line 720 for supplying a data signal, a first pixel line 730 for supplying a first pixel signal, And a common voltage line 750 for supplying a common voltage V _COM to the opposite electrode. The liquid crystal display device according to the fourth embodiment of the present invention is the same as the liquid crystal display device according to the second embodiment of the present invention described above with reference to FIG. 3 except for the position where the capacitors 230 are connected. The description of which will be omitted.

Hereinafter, a method for driving each pixel of a liquid crystal display device constructed in accordance with the first to fourth embodiments of the present invention will be described in detail.

A driving method of a liquid crystal display according to the present invention includes a memory type thin film transistor and a plurality of pixels and a driving circuit having a pair of common thin film transistors each having a drain connected to the gate of the memory type thin film transistor, Relates to a method of driving an active matrix liquid crystal display device that supplies a data signal to the source of the general thin film transistor, a scan signal to the gate of the general thin film transistor, and a pixel signal to the source of the memory thin film transistor .

More specifically, a method for driving each pixel of a liquid crystal display according to the present invention includes a programming step S100 for supplying a data signal and a scan signal to induce a hysteresis phenomenon in a memory-type thin film transistor of each pixel, And a display step (S200) of supplying scan signals and displaying pixel information in each pixel.

That is, the programming step S100 is a step of moving the threshold voltage of the memory-type thin film transistor in the negative or positive direction according to the pixel information to be displayed in the display step S200. Accordingly, in FIGS. 6 to 18, the signals supplied to the respective pixels of the liquid crystal display according to the present invention are divided according to the programming step S100 and the display step S200.

In particular, in the case where each pixel of the liquid crystal display device according to the present invention has two pairs of the memory thin film transistor and the general thin film transistor, that is, configured according to the first and third embodiments, S100 includes a first step S110 of moving a threshold voltage of a memory thin film transistor in a negative direction and a second step S120 of shifting a threshold voltage of the other memory thin film transistor in a positive direction do.

Specifically, as shown in FIGS. 6, 7, and 12 to 15, in the liquid crystal display apparatus constructed in accordance with the first and third embodiments, the programming step S100 includes the steps of: In step S110, a high level voltage is supplied to the first scan signal to turn on the first thin film transistor 10, and in the second step S120, The second thin film transistor 20 is turned on by supplying a high level voltage to the first thin film transistor 20 and simultaneously outputs the positive voltage V ₊ V _- (however, the absolute magnitudes of V ₊ and V _- are the same). At this time, the first data signal in step 1 (S110) and supplies the voltage V ₊ by moving the threshold voltage of the third thin film transistor 30 in the negative the voltage as a data signal in the second stage 2 (S120) V _- To move the threshold voltage of the fourth thin film transistor in the positive direction. In contrast the second data signal in step 1 (S110), the voltage V _- the voltage on the data signal from the first stage 2 (S120), by moving the threshold voltage of the third thin film transistor 30 to supply an amount of V ₊ To move the threshold voltage of the fourth thin film transistor 40 to the negative side.

In particular, if a white signal is supplied to the first pixel line and a black signal is supplied to the second pixel line, the programming step (S100), when displaying a white signal on the pixel in the displaying step (S200) a _- the said voltage V in step 1 (S110) a data signal to the data signal from the first stage 1 (S110), if to be displayed in the pixel for the black signal in the display step (S200) and supplies the voltage V ₊ Supply.

6 and FIG. 7, in the case of the liquid crystal display device according to the first embodiment, the display step S200 outputs a high (high) signal as the first scan signal and a high ) Level, and supplies OV (volt) as a data signal.

12 to 15, in the case of the liquid crystal display device constructed in accordance with the third embodiment, the display step S200 is performed by applying a high (high) A third step S210 of supplying a voltage of a low level to the first scan signal and a second scan signal after the third step S210, and supply, but the white signal and the black signal is a positive voltage V _{+2 +2} V and the voltage and the supply voltage V of the notes _-2 inverted in turn, is a positive voltage to the white signal V and ₊₃ And a fourth step (S220) of sequentially supplying the negative voltage V _-3 inverted from the V ₊₃ voltage.

Hereinafter, the case of displaying a black signal and the case of displaying a white signal in one pixel of a liquid crystal display device constructed in accordance with the first embodiment of the present invention will be described separately.

When a white signal is displayed on one pixel, as shown in FIG. 6, a voltage of a high level as a first scan signal during a first step S110 of a programming step S100 is converted into a data signal The positive voltage V ₊ is supplied to turn on the first thin film transistor 10, thereby moving the threshold voltage of the third thin film transistor 30 in the negative direction. At this time, since the voltage of low level is supplied to the second scan signal, the second thin film transistor 20 is kept off. During the second step S110 of the programming step S100, a low level voltage is supplied to the first scan signal so that the first thin film transistor 10 is turned off and the second scan signal is turned high, the voltage level, the data signal of a negative voltage V _- is supplied to, and thus while the second TFT 20 turns on in accordance with the threshold voltage will move to the positive side of the fourth thin film transistor (40).

The threshold voltage of the third thin film transistor 30 is shifted in the negative direction through the programming step S100 and the threshold voltage of the fourth thin film transistor 40 is shifted in the positive direction. S200) to display the white signal on the pixel. 6, during the display step S200, a high-level voltage is supplied to the first scan signal and the second scan signal so that the first thin film transistor 10 and the second thin film transistor 20 ), And simultaneously supplies 0 V to the data signal. At this time, since the threshold voltage of the fourth thin film transistor 40 is shifted in the positive direction, the fourth thin film transistor 40 is not turned on. The third thin film transistor 30 is turned on because the threshold voltage of the third thin film transistor 30 is shifted in the negative direction and accordingly the first thin film transistor 30 connected to the source of the third thin film transistor 30 is turned on, The white signal V _W is supplied to the pixel electrode through the pixel line 140 and displayed on the liquid crystal.

Next, when a black signal is displayed on one pixel, the programming step (S100) supplies a data signal opposite to the case of FIG. 6 (in the case of displaying a white signal). That is, as shown in FIG. 7, and the voltage of the high (high) level to the first scan signal during a stage 1 (S110), a negative voltage V to the data _signal is supplied, whereby the first thin film transistor in accordance with ( 10 are turned on and the threshold voltage of the third thin film transistor 30 moves in the positive direction. At this time, since the voltage of low level is supplied to the second scan signal, the second thin film transistor 20 is kept off. During the second step S110, a low level voltage is supplied to the first scan signal so that the first thin film transistor 10 is turned off and a high level voltage is applied to the second scan signal, and a positive supply voltage V ₊ is, and thus while the second TFT 20 turns on in accordance with the threshold voltage of the fourth thin film transistor (40) moves in the negative direction.

6, a voltage of a high level is supplied to the first scan signal and the second scan signal during the display step S200 so that the first thin film transistor 10 and the second thin film transistor 20 are turned on And supplies 0 V to the data signal at the same time. At this time, the third thin film transistor 30 is not turned on, but the fourth thin film transistor 40 is turned on according to the threshold voltage, and accordingly, the second pixel line (not shown) connected to the source of the fourth thin film transistor 40, The black signal V _B is supplied to the pixel electrode through the signal line 150 and displayed on the liquid crystal.

Meanwhile, FIG. 8 shows pixels and driving signals of a liquid crystal display device composed of 2X2 pixels according to the first embodiment of the present invention. Two scan signals are required for each pixel so that the threshold voltages of the memory thin film transistors included in each pixel can be shifted in the positive or negative direction. Each pixel may represent only one bit of white and black, and in the programming step S100, depending on whether the threshold voltage of the memory-type thin film transistor has been moved to positive or negative, ) Or black (black). In order to display a screen as shown in FIG. 8A, the same scan signal is supplied to each pixel during a programming step S100, and a threshold voltage of the memory-type thin film transistor is shifted by supplying an appropriate data signal together with a scan signal. The corresponding data signal and scan signal are shown in Fig. 8 (b).

When each pixel of the liquid crystal display according to the present invention is configured according to the second and fourth embodiments, as shown in FIGS. 9, 10 and 16 to 18, the programming step S100 A high level voltage is supplied to the scan signal to turn on the first thin film transistor 210 and a positive voltage V ₊ is supplied to the second thin film transistor 220) to move in the threshold voltage in a negative direction or a negative voltage _V-is supplied thereby to move the threshold voltage of the second thin film transistor in the positive direction.

In particular, if a white signal is supplied to the first pixel line and a black signal is supplied to the second pixel line, the programming step S100 may display the white signal on the pixel in the display step S200, and by supplying the voltage V _+, the voltage V to the contrary, when the data signal to be displayed on a black pixel signal from said display step (S200) _- supplies.

9 and 10, in the case of the liquid crystal display device according to the second embodiment, the display step S200 supplies a positive voltage as a scan signal, volts.

16 to 18, in the case of the liquid crystal display device constructed in accordance with the fourth embodiment, the display step S200 includes a step of supplying a high level voltage to the scan signal, A black signal and a white signal are simultaneously supplied while supplying a low level voltage to the scan signal after the third step S210 and the third step S210, ₊₂ and a negative voltage V- ₂ obtained by inverting the voltage V _{+ 2} in this order, and the white signal is supplied with a positive voltage V ₊₃ and a negative voltage V _-3 obtained by inverting the voltage V ₊₃ (Step S220).

Hereinafter, the case of displaying a black signal and the case of displaying a white signal in one pixel of the liquid crystal display device constructed in accordance with the second embodiment of the present invention will be described separately.

First, as shown in FIG. 9, when a white signal is displayed on one pixel, a high level voltage is supplied to the scan signal and a positive voltage is supplied to the data signal, respectively, in the programming step S100, The threshold voltage of the second thin film transistor 220 is shifted in the negative direction while the thin film transistor 210 is being driven. Then, in the display step S200, the second thin film transistor 220 is kept turned on while 0 V is supplied as a data signal. At this time, since the resistance value R _{T2, on} of the second thin film transistor 220 is smaller than the resistance value of the resistor R 240, the white signal V _W supplied through the first pixel line 330 is supplied to the pixel And is displayed on the liquid crystal while being transferred to the electrode.

Next, as shown in FIG. 10, when a black signal is displayed on one pixel, a high level voltage is supplied to the scan signal and a negative voltage is supplied to the data signal in the programming step S100, 1 thin film transistor 210 while moving the threshold voltage of the second thin film transistor 220 in the positive direction. Then, in the display step S200, the second thin film transistor 220 maintains the off state while supplying 0 V to the data signal. At this time, since the resistance value R _{T2, off} of the turned off second thin film transistor 220 is greater than the resistance value of the resistor R 240, the black signal V _B supplied through the second pixel line 340 is supplied to the pixel And is displayed on the liquid crystal while being transferred to the electrode.

On the other hand, FIG. 11 shows pixels and driving signals of a liquid crystal display device composed of 2X2 pixels according to the second embodiment of the present invention. As shown in FIG. 11, one scan signal is required per pixel so that the threshold voltage of a memory thin film transistor including one pixel in each pixel can be shifted in the positive or negative direction. Each pixel may represent only one bit of white and black and may be either black or white depending on whether the threshold voltage of the memory thin film transistor is shifted to positive or negative black) is displayed. In order to display a screen as shown in FIG. 11A, the same scan signal is supplied to each pixel during a programming step S100, and a threshold voltage of the memory-type thin film transistor is shifted by supplying an appropriate data signal together with the scan signal. The corresponding data signal and scan signal are shown in Fig. 11 (b).

In the method of driving a liquid crystal display device constructed in accordance with the first and second embodiments, the display step S200 supplies an alternating voltage of a form that is larger than a common voltage by the white and black signals, It is preferable that the period of the alternating voltage is 2f (f is a time of one frame).

Hereinafter, a case where a black signal is displayed on one pixel of a liquid crystal display device constructed in accordance with a third embodiment of the present invention will be described. 12, a high level voltage is supplied to the first scan signal and a positive voltage V ₊ is supplied to the data signal during the first step S110 of the programming step S100, The first thin film transistor 410 is turned on and the threshold voltage of the third thin film transistor 430 moves in the negative direction. At this time, since the voltage of low level is supplied to the second scan signal, the second thin film transistor 420 is kept off.

Next, as shown in FIG. 13, a low level voltage is supplied to the first scan signal during the second step S110 of the programming step S100 so that the first thin film transistor 410 is turned off, the high-voltage (high) level to the second scan signal, a data signal of a negative voltage V _- is supplied, while the second thin film transistor 420 is turned on accordingly, the threshold voltage, the amount of the fourth thin film transistor 440 Direction.

The threshold voltage of the third thin film transistor 430 is shifted in the negative direction through the programming step S100 and the threshold voltage of the fourth thin film transistor 440 is shifted in the positive direction. S200 to display the black signal on the pixel. 14, during the third step S210 of the display step S200, a voltage of a high level is supplied to the first scan signal and the second scan signal so that the first thin film transistor 410 is turned on, And the second thin film transistor 420 are turned on, and at the same time, 0 V is supplied as a data signal. At this time, since the threshold voltage of the fourth thin film transistor 440 is shifted in the positive direction, the fourth thin film transistor 440 is not turned on. The third thin film transistor 430 is turned on because the threshold voltage of the third thin film transistor 430 is shifted in the negative direction and accordingly the first thin film transistor 430 is connected to the first pixel line The black signal V _B is supplied to the pixel electrode through the liquid crystal layer 540 and displayed on the liquid crystal.

15, during the fourth step S220 of the display step S200, the first scan signal and the second scan signal supply a low level voltage to the first thin film transistor 410 And the second thin film transistor 420 are turned off. When the third thin film transistor 430 is turned on and the fourth thin film transistor 440 is turned off by supplying V ₊₂ as a black signal and then supplying V _{+ 3} as a white signal in order, the first pixel line 540 The black signal V _{+ 2} supplied to the pixel electrode is displayed on the liquid crystal while being transferred to the pixel electrode. At this time, since the first thin film transistor 410 and the second thin film transistor 420 are turned off, the gates of the third thin film transistor 430 and the fourth thin film transistor 440 are both floating (floating) ) State. The charge amount and the value of the capacitor are constant and the voltage of the pixel electrode is increased by V ₊₂ according to the relation of [amount of charge = voltage of capacitor X] in the floating state, so that the charge of the first capacitor 450 and the boot of the second capacitor 460 A bootstrap operation occurs and the gate voltages of the third thin film transistor 430 and the fourth thin film transistor 440 rise by V _{+ 2} . Accordingly, the voltage difference between the gate and the source of the third thin film transistor 430 is kept the same as in the third step S210 of the display step S200.

Hereinafter, a case where a black signal is displayed on one pixel of the liquid crystal display device constructed in accordance with the fourth embodiment of the present invention will be described. As shown in FIG. 16, in the programming step S100, a high level voltage is supplied to the scan signal and a positive voltage is supplied to the data signal to turn on the first thin film transistor 610, 620 in the negative direction. Then, as shown in FIG. 17, in the display step S200, the second thin film transistor 620 is kept turned on while 0 V is supplied as a data signal. At this time, since the resistance value R _{T2, on} of the second thin film transistor 620 is smaller than the resistance value of the resistor R 640, the black signal V _B supplied through the first pixel line 730 is supplied to the pixel And is displayed on the liquid crystal while being transferred to the electrode. Next, as shown in FIG. 18, during a third step S220 of the display step S200, the first scan signal supplies a low level voltage to turn off the first thin film transistor 610. [ Also supplying a ₊₂ V as a black signal, and when the supply of ₊₃ V to turn white signal, it is turned on is smaller than the resistance value of the second thin film transistor 620, the resistance (R _{T2, on),} the resistance R (640) of Therefore, the black signal V _{+ 2} supplied through the first pixel line 730 is transferred to the pixel electrode and displayed on the liquid crystal. At this time, since the first thin film transistor 610 is turned off, the gate of the second thin film transistor 620 becomes a floating state in which there is no path through which charge can escape. Therefore, a bootstrap ) Operation and the gate voltage of the second thin film transistor 620 increases by V _{+ 2} . Accordingly, the voltage difference between the gate and the source of the second thin film transistor 620 remains the same as in the third step S220 of the display step S200.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be appreciated that one embodiment is possible. Accordingly, the true scope of the present invention should be determined by the technical idea of the claims.

10, 210, 410, 610: a first thin film transistor
20, 220, 420, 620: a second thin film transistor
30, 430: third thin film transistor 40, 440: fourth thin film transistor
50, 450: first capacitor 60, 460: second capacitor
110, 510, 710: first scan line 120, 520: second scan line
130, 320, 530, 720: data lines 140, 330, 540, 730:
150, 340, 550, 740: second pixel line 160, 350, 560, 750: common voltage line
230, 630: capacitors 240, 640: resistance (R)
R _{T2, on} : Resistance when the second thin film transistor is turned on
R _{T2, off} : Resistance when the second thin film transistor is turned off

Claims (19)

A plurality of pixels each having at least one pair of a memory-type thin film transistor having a ferroelectric material in an insulation portion of a gate and a common thin film transistor having a drain connected to a gate of the memory-type thin film transistor; And
And a driving circuit for supplying a data signal to the source of the general thin film transistor, a scan signal to the gate of the general thin film transistor, and a pixel signal to the source of the memory thin film transistor, respectively. The method according to claim 1,
Each pixel includes first and second thin film transistors as the general thin film transistor and third and fourth thin film transistors as the memory thin film transistor,
The drain of the first thin film transistor is connected to the gate of the third thin film transistor, the drain of the second thin film transistor is connected to the gate of the fourth thin film transistor, and the drains of the third and fourth thin film transistors are connected to the pixel electrode Connected,
The driving circuit includes a first scan line supplying a first scan signal to each pixel, a second scan line supplying a second scan signal, a data line supplying a data signal, a first pixel line supplying a first pixel signal, And a second pixel line for supplying a second pixel signal,
Wherein the first scan line is connected to the gate of the first thin film transistor of each pixel and the second scan line is connected to the gate of the second thin film transistor of each pixel and the data line is connected to the source of the first and second thin film transistors Wherein the first pixel line is connected to the source of the third thin film transistor, and the second pixel line is connected to the source of the fourth thin film transistor, respectively. 3. The method of claim 2,
A first capacitor connected between the drain of the first TFT and the capacitor electrode, and a second capacitor connected between the drain of the second TFT and the capacitor electrode. 3. The method of claim 2,
A first capacitor connected between the drain of the first thin film transistor and the pixel electrode, and a second capacitor connected between the drain of the second thin film transistor and the pixel electrode. 3. The method of claim 2,
Wherein one of the first pixel line and the second pixel line supplies a white signal and the other supplies a black signal. The method according to claim 1,
Each pixel includes a first thin film transistor as the general thin film transistor, a second thin film transistor as the memory thin film transistor, and a resistor R connected to one side of the drain of the second thin film transistor,
The drain of the first thin film transistor and the gate of the second thin film transistor are connected, the drain of the second thin film transistor is connected to the pixel electrode,
The size of the resistor R is larger than the resistance R _{T2, on} when the second thin film transistor is turned _on and smaller than the resistance R _{T2, off} when the second thin film transistor is turned _off ,
The driving circuit includes a scan line for supplying a scan signal to each pixel, a data line for supplying a data signal, a first pixel line for supplying a first pixel signal, and a second pixel line for supplying a second pixel signal,
The scan line is connected to the gate of the first thin film transistor, the data line is connected to the source of the first thin film transistor,
Wherein the first pixel line is connected to the source of the second thin film transistor, and the second pixel line is connected to the other side of the resistor (R). The method according to claim 6,
And a capacitor connected between the drain of the first thin film transistor and the capacitor electrode. The method according to claim 6,
And a capacitor connected between the drain of the first thin film transistor and the pixel electrode. The method according to claim 6,
Wherein one of the first pixel line and the second pixel line supplies a white signal and the other supplies a black signal. 10. The method according to any one of claims 6 to 9,
_{Wherein a} relationship of 100 x R _{T2, on} <R <100 x R _{T2, off} is satisfied between R, R _{T2, on} and R _{T2, off} . A plurality of pixels and a driving circuit having a pair of a memory type thin film transistor having a ferroelectric material in an insulating portion of a gate and a common thin film transistor having a drain connected to a gate of the memory type thin film transistor, A method of driving an active matrix liquid crystal display device that supplies a data signal to a source of a general thin film transistor, a scan signal to a gate of the general thin film transistor, and a pixel signal to a source of the memory thin film transistor,
A programming step of supplying a data signal and a scan signal to induce hysteresis in a memory-type thin film transistor of each pixel;
A display step of supplying pixel signals and a scan signal and displaying pixel information in each pixel;
And a driving method of the liquid crystal display device. 12. The method of claim 11,
Wherein the programming comprises:
Wherein the threshold voltage of the memory thin film transistor is shifted in a negative or positive direction according to pixel information to be displayed in the display step. 12. The method of claim 11,
Each pixel has two pairs of the memory thin film transistor and the general thin film transistor,
Wherein the programming comprises:
A first step of moving a threshold voltage of a memory thin film transistor in a negative direction;
A second step of moving the threshold voltage of the other memory-type thin film transistor in the positive direction;
And a driving method of the liquid crystal display device 14. The method of claim 13,
The liquid crystal display device according to claim 2,
Wherein the programming comprises:
In the first step, a high level voltage is supplied to the first scan signal to turn on the first thin film transistor, and in the second step, a high level And supplies a positive voltage V ₊ and a negative voltage V _- as data signals simultaneously with the first scan signal and the second scan signal,
By supplying the voltage V ₊ in the first step into a data signal by moving the threshold voltage of the third thin film transistor to negative the voltage V to the data signal in the second step _- by supplying a threshold of the fourth thin film transistor Moving the voltage positive,
When the threshold voltage of the third thin film transistor is shifted in a positive direction by supplying the voltage V _- as a data signal in the first step, the voltage V ₊ is supplied as a data signal in the second step, Further comprising the step of moving the voltage to the negative side. 15. The method of claim 14,
The first pixel line supplies a white signal, the second pixel line supplies a black signal,
Wherein the programming comprises:
When the white signal is displayed on the pixel in the display step, the voltage V ₊ is supplied as a data signal in the first step,
When displayed on a black pixel signal from said display step, the voltage V to the data signal in the first _{stage-driving} method of the liquid crystal display device according to claim 1, further comprising the step of supplying. 15. The method of claim 14,
Wherein one of the first pixel line and the second pixel line supplies a white signal and the other supplies a black signal,
The display step may include:
A third step of supplying a high level voltage to the first scan signal and the second scan signal, respectively;
Wherein the first scan signal and a second, but by supplying a voltage to the respective (low) level at the same time supplying the black signal and white signal with the scanning signals, to the black signal is a positive voltage V _{+2 +2} V and the voltage and the supply voltage V to _-2 of negative reverse turn, the white signal is a positive voltage V ₊₃ and a fourth step of further supplying a voltage V _-3 turn of the negative turn the voltage V ₊₃ And a driving method of the liquid crystal display device. 12. The method of claim 11,
The liquid crystal display device is configured in accordance with claim 6,
Wherein the programming comprises:
A voltage of a high level is supplied to the scan signal to turn on the first thin film transistor,
The scanning signal and at the same time either to supply a positive voltage V ₊ to the data signal to move the threshold voltage of the second thin film transistor in the negative direction or the voltage V of the _negative by supplying a threshold voltage of the second thin film transistor And moving the liquid crystal display panel in a positive direction. 18. The method of claim 17,
The first pixel line supplies a white signal, the second pixel line supplies a black signal,
Wherein the programming comprises:
When the white signal is displayed on the pixel in the display step, the voltage V ₊ is supplied as a data signal,
A data signal to the pixel when displaying the black display signal in the phase the voltage V _- method of driving a liquid crystal display device according to claim 1, further comprising the step of supplying. 18. The method of claim 17,
Wherein one of the first pixel line and the second pixel line supplies a white signal and the other supplies a black signal,
The display step may include:
A third step of supplying a high level voltage to the scan signal;
While supplying the voltage of a scan signal to the (low) level, but at the same time supplying the black signal and a white signal and the black signal as the inversion of the positive voltage V _{+2 +2} V and the voltage negative voltage V _{- And a fourth step} of sequentially supplying a positive voltage V ₊₃ and a negative voltage V _-3 obtained by inverting the V ₊₃ voltage to the white signal in order, .

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