JPH11153984A - Liquid crystal display device drive method and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of a vertical crosstalk like display fault by transmitting a specified image signal to an image signal line at the same polarity as the image signal applied to a pixel electrode just after a blanking period during the blanking period. SOLUTION: An image signal 21 contains a liquid crystal drive voltage Vsig in which the polarity is inverted for a counter electrode potential 12 at every period T and is added with a liquid crystal drive voltage Vpc of a maximum voltage VLmax or above applied to a pixel electrode in the just before a blanking period T1. Further, gate signal pulses β and α whose timings are deviated by one pixel component are applied from a circuit block for the blanking period T1 to the signal write-in transistors connected to the image signal lines adjacent to pulse signals 23 (n) and 23 (n+1)for gate electrodes of signal write-in transistors connected to n-th and (n+1)-th image signal lines. At this time, a signal 24n containing the liquid crystal drive voltage Vpc of the VLmax or above is transmitted to the n-th image signal line.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving method of a liquid crystal display device having a built-in peripheral driving circuit using a polysilicon thin film transistor and a liquid crystal display device.

[0002]

2. Description of the Related Art FIG. 4 shows a part of a configuration diagram of a conventional liquid crystal display device having a built-in peripheral driving circuit using a polysilicon thin film transistor. In FIG. 4, reference numeral 1 denotes a scanning line, 2 denotes an image signal line, and a pixel transistor 3 and a pixel electrode 4 are arranged in a matrix. The scanning line 1 is a scanning signal circuit 8
And the image signal line 2 is connected to a signal writing transistor 5 (one of the signal writing transistors 5 is connected to one of the image signal lines 2 in the drawing, but two of a p-type transistor and an n-type transistor are connected). Signal writing transistor, which is connected to a circuit block (not shown as a circuit diagram, but usually includes a shift register and its output buffer) 10 which includes a shift register. 5 operates as a transfer gate transistor, and an image signal from the signal line 6 is written to the image signal line 2.

FIG. 4 shows one signal wiring 6 for a monochrome display panel. However, in the case of color display, three signal wirings 6 are used in parallel corresponding to three colors of RGB. Although not shown, a liquid crystal (a TN liquid crystal having a dielectric anisotropy in a currently marketed liquid crystal, the larger the voltage applied to the liquid crystal, the larger the capacity), a counter electrode, a backlight and a polarizing plate A liquid crystal display device is constituted by such peripheral members and an external circuit section for shaping an input signal.

FIG. 5 is a schematic diagram for explaining a mechanism for transmitting a liquid crystal drive voltage to the pixel electrode 4 in the conventional dot sequential driving in the conventional liquid crystal display device shown in FIG. In FIG. 5, a signal applied to a signal writing transistor 5 related to a certain image signal line 2,
Further, a state of a signal transmitted to a certain pixel electrode 4 connected to the image signal line 2 is shown. Reference numeral 11 denotes an image signal applied to the signal wiring 6, and a signal corresponding to an image of one scanning line of the image signal 11 is input for each period T. In the period T, T1 is actually an image. Is a blanking period in which no signal is input, and T2 is an actual display period in which an actual image signal (liquid crystal drive signal transmitted to the pixel) is input.

[0005] Depending on the system, when displaying from an NTSC signal used in a normal TV, T is 63.
Microseconds and T1 is around 10 microseconds.
The image signal 11 includes a liquid crystal drive voltage Vsig whose polarity is inverted with respect to the counter electrode potential 12 every period T. The liquid crystal drive voltage Vsig is changed according to the strength of an image for one scanning line.

Reference numeral 13 (n) denotes a pulse signal applied from the circuit block 10 including the shift register to the gate electrode of the signal writing transistor 5 connected to the n-th image signal line 2; The signal writing transistor 5 is turned on (in this case, the signal writing transistor 5 is an n-type transistor), and the signal writing transistor 5 connected to the adjacent image signal line 2
The gate signal pulse 1 whose timing is shifted by one pixel
3 (n + 1) is applied.

At this time, the signal 14 n is transmitted to the n-th image signal line 2. Strictly, there is a signal leakage, a coupling of a capacitance component, or a potential fluctuation accompanying writing to the pixel electrode 4. Since these are small fluctuation components not directly related to the purpose of the present invention, they are omitted from the figure.

When a signal 15m is applied to the gate electrode of the pixel transistor 3 connected to the m-th scanning line 1, the image signal 16 is applied to the pixel electrode 4 in the m-th row and the n-th column.
The liquid crystal is driven by transmitting (m, n) and generating a liquid crystal driving voltage Vsig between the pixel electrode and the counter electrode (the driving method for transmitting the liquid crystal driving voltage as described above is a dot sequential driving). Name). In addition, as a liquid crystal, usually,
A TN liquid crystal having dielectric anisotropy is used.

For example, as a liquid crystal display (LCD), the flat panel display 1994 magazine (published by Nikkei BP, 1993), pages 190 to 193, and the driving method is the flat panel display 1990 magazine. (Nikkei BP Publishing, 198
Related content is described on pages 110 to 133 etc. (issued in 9 years).

[0010]

However, in the conventional liquid crystal display driving method and liquid crystal display described above, display unevenness such as crosstalk in the vertical direction may be conspicuous, and in particular, applications in which a bright backlight is used. In this case, the display unevenness such as the vertical crosstalk shown in the image diagram in FIG. 6 is emphasized, so that the display unevenness becomes conspicuous. In an extreme case, the image display as shown in FIG. 6 has a problem that a display as shown in FIG. 6B results.

In FIG. 6, the shades of gray are represented by the number of diagonal lines. Actually, FIG. 6A shows a black background on a gray background, and FIG. 6B shows darker gray portions above and below the black square than FIG. 6A.

The present invention solves the above-mentioned conventional problems. In a display image, display defects such as vertical crosstalk are less likely to occur, and streak-like display unevenness is less likely to occur. Provided are a driving method of a liquid crystal display device and a liquid crystal display device which can improve some display unevenness and improve display quality.

[0013]

In order to solve the above-mentioned problems, a driving method of a liquid crystal display device and a liquid crystal display device according to the present invention use a maximum image signal voltage VLmax used for black display in a normally white display. In this case, the image signal Vpc including the liquid crystal drive voltage equal to or higher than VLmax is temporarily written to the image signal line during the blanking period. It is characterized in that a change due to display contents of a liquid crystal capacitance component of a line is reduced.

As described above, in the display image, display defects such as vertical crosstalk hardly occur, streak-like display unevenness hardly occurs, and some other display unevenness can be improved. The display quality can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The driving method of a liquid crystal display device according to the first aspect of the present invention is a peripheral driving circuit in which an image signal line is a dot sequential driving type having a capacitance component of a liquid crystal having a dielectric anisotropy. A method of driving a built-in liquid crystal display device,
When the maximum voltage of the image signal applied to the pixel electrode for driving the liquid crystal at the time of image display is VLmax, during the blanking period in which the image signal is not written on the screen, the pixel electrode immediately after the blanking period And transmitting an image signal having a liquid crystal drive voltage having the same polarity as that of the image signal to be applied to the pixel signal line and equal to or higher than the VLmax to the image signal line.

According to a second aspect of the present invention, there is provided a driving method of a liquid crystal display device, wherein the liquid crystal of the first aspect is driven by a thin film transistor formed by using a polysilicon thin film formed by using an excimer laser. It is driven by a circuit.

According to a third aspect of the present invention, there is provided a liquid crystal display device with a built-in peripheral driving circuit, wherein the image signal lines are of a point sequential drive type having a capacitance component of liquid crystal having dielectric anisotropy. When the maximum voltage of the image signal applied to the pixel electrode in order to drive the liquid crystal at the time of VLmax, the image signal is applied to the pixel electrode immediately after the blanking period during a blanking period in which the image signal is not written on the screen. An image signal having the same polarity as the image signal to be transmitted and including a liquid crystal drive voltage equal to or higher than VLmax is transmitted to the image signal line.

According to a fourth aspect of the present invention, the peripheral driving circuit for driving the liquid crystal according to the third aspect includes a thin film transistor formed using a polysilicon thin film formed by using an excimer laser.

According to the above-described driving method and configuration, display unevenness such as vertical crosstalk hardly occurs, and display quality can be improved. This is considered as follows.

In the case of dot sequential driving using the capacitance component of the image signal line itself, the relationship between the liquid crystal driving voltage Vsig and the transmittance of the panel in FIG. 5 is as shown in FIG. 7 (showing the case of a normally used TN liquid crystal). This is a case of a normally white display in which white display is performed when Vsig = 0V.
The display becomes black when Vsig = VLmax). According to an experiment performed by the inventor of the present invention, when the capacity of the transistor is sufficient, the change from white to black becomes steeper (toward Vsig = 0 V) as the capacity of the image signal line increases.

By the way, unless the image signal line is shielded, the image signal line itself has a capacitance component due to the liquid crystal because the liquid crystal is sandwiched between the image signal line and the counter electrode. At this time, in a normal liquid crystal, the capacitance component increases as Vsig increases due to anisotropy of the dielectric constant. That is, as shown in FIG. 8, as the liquid crystal drive voltage Vsig is increased, the capacitance reaches a maximum just before black display.

Accordingly, the capacity of the image signal line performing a large amount of black display and the capacity of the image signal line performing a large amount of white display change (from the relationship of the response speed of the liquid crystal, the average value of several screens). Follow voltage). Therefore, a conventional liquid crystal display device with a built-in peripheral driving circuit and its driving method (dot sequential driving)
Then, as shown in FIG. 6B, it is considered that the transmission characteristics of the liquid crystal in a portion where black is displayed change, and the display is recognized as vertical crosstalk-like display unevenness.

On the other hand, in the driving method and configuration of the present invention, when the maximum image signal voltage used for black display in the case of the normally white display is VLmax, the liquid crystal driving voltage not lower than VLmax during the blanking period. This is because the change in the liquid crystal capacitance component of the image signal line due to the display content can be reduced by applying the black display voltage with a small capacitance change to write the image signal Vpc including the image signal once to the image signal line. it is conceivable that.

Hereinafter, a method of driving a liquid crystal display device and a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings. The liquid crystal display device of the present embodiment
The basic configuration is, as shown in FIG. 4, a liquid crystal display device with a built-in peripheral driving circuit, which is a dot-sequential driving type in which the image signal line 2 has a capacitance component of liquid crystal having dielectric anisotropy. Further, the image signal 21 including the liquid crystal driving voltage Vpc equal to or higher than VLmax is temporarily written to the image signal line 2 during the blanking period T1.

In FIG. 1, reference numeral 21 denotes an image signal applied to the signal wiring 6;
2 is a liquid crystal drive voltage Vs whose polarity is inverted every period T
ig and blanking period T1 immediately before
, A liquid crystal driving voltage Vpc equal to or higher than VLmax is added.

Also, 23 (n) and 23 (n + 1) are n
This is a pulse signal applied from the circuit block 10 including the shift register to the gate electrode of the signal writing transistor 5 (n-type transistor) connected to the first and (n + 1) th image signal lines 2. In addition to the conventional gate signal pulse β whose timing is shifted by one pixel, the gate signal pulse α is applied to the signal writing transistor 5 connected during the blanking period T1.

At this time, VLm is applied to the n-th image signal line 2.
The signal 24n including the liquid crystal drive voltage Vpc equal to or higher than ax is transmitted. With the above configuration of the liquid crystal display device, display defects such as vertical crosstalk hardly occur.

Specific examples of the driving method of the liquid crystal display device and the liquid crystal display device as described above will be described below. (Embodiment 1) As a basic configuration of a liquid crystal display device of Embodiment 1, as shown in FIG. 4, an image signal line has a dot sequence having a capacitance component of a TN liquid crystal having dielectric anisotropy. A description will be given using a liquid crystal display device with a built-in peripheral driving circuit, which is a driving type.

FIG. 1 is a schematic diagram for explaining a mechanism for transmitting a liquid crystal drive voltage to the pixel electrode 4. The signal applied to the writing transistor 5 related to a certain image signal line 2 and the image signal line 2 Pixel electrode 4 connected to
Shows the state of the signal transmitted to. In FIG. 1, reference numeral 21 denotes an image signal applied to the signal wiring 6. In a period T during which a signal corresponding to an image of one scanning line of the image signal 21 is input, T1 is actually an image signal. This is a blanking period in which no signal is input, and T2 is an actual display period in which an actual image signal (liquid crystal drive signal transmitted to the pixel) is input.

The image signal 21 includes a liquid crystal drive voltage Vsig whose polarity is inverted with respect to the counter electrode potential 12 every period T. At this time, unlike the case of FIG. 5 showing the conventional example,
V of the same polarity as Vsig following the blanking period T1
pc (when the maximum image signal voltage applied to the pixel electrode 4 for driving the liquid crystal during display is VLmax, the voltage is higher than VLmax) is applied.

23 (n) and 23 (n + 1) are applied from the circuit block 10 including the shift register to the gate electrodes of the signal writing transistors 5 connected to the nth and (n + 1) th image signal lines 2. This is a pulse signal, and when it is at the H level, the signal writing transistor 5 is turned on (in this case, the signal writing transistor 5
Is an n-type transistor). At this time, the pulse signal 23
In addition to the conventional pulse, a pulse (α) for writing Vpc to the image signal line 2 during the blanking time T1 is added to (n) and 23 (n + 1).

In this case, the signal 24n is transmitted to the n-th image signal line, and strictly speaking, there is a potential fluctuation due to signal leakage, coupling of a capacitance component, or writing to the pixel electrode 4. Are small fluctuation components not directly related to the purpose of the present invention, and are omitted from the figure.

When a signal 25m is further applied to the gate electrode of the pixel transistor 3 connected to the m-th scanning line, the image signal 26 (m, m,
n) is transmitted and the liquid crystal driving voltage Vsig is generated between the pixel electrode 4 and the counter electrode to drive the liquid crystal, and the signal 24n including the liquid crystal driving voltage Vpc is transmitted to the nth image signal line. become.

By driving with the above configuration, display defects such as vertical crosstalk hardly occur. (Embodiment 2) FIG. 2 is a configuration diagram of a liquid crystal display device according to Embodiment 2 of the present invention. In the liquid crystal display device of Embodiment 2, in order to facilitate the driving thereof, the conventional liquid crystal display device shown in FIG. This is a liquid crystal display device in which some circuits are added.

4 is different from the conventional liquid crystal display device shown in FIG. 4 in that a transistor 27 for writing Vpc, a gate signal line 28 to the transistor 27 and a signal line for writing Vpc are provided on the opposite side of the circuit block 10 including the shift register. This is the point that the signal line 29 of FIG.

In this case, a driving method as shown in FIG. 3 is employed. Reference numeral 11 denotes an image signal applied to the signal wiring 6, and a signal corresponding to an image of one scanning line of the image signal 11. T1 is a blanking period during which no image signal is actually input.
Reference numeral 2 denotes an actual display period during which an actual image signal (liquid crystal drive signal transmitted to the pixel) is input.

The image signal 11 includes a liquid crystal driving voltage Vsig whose polarity is inverted every period T with respect to the counter electrode potential 12. Vsig is changed according to the strength of an image for one scanning line. 39 is a Vpc write signal which is applied to the signal line 29. Reference numeral 38 denotes a gate signal for Vpc writing, which is applied to the gate signal line 28.

The gate electrode of the signal writing transistor 5 connected to the n-th image signal line 2 has a pulse signal 1 applied from a circuit block 10 including a shift register.
3 (n) is applied (not shown, but the same as FIG. 5). In this case, the signal 34n is transmitted to the n-th image signal line 2.

When a signal 35m is further applied to the gate electrode of the pixel transistor 3 connected to the m-th scanning line 1, the image signal 36 is applied to the pixel electrode 4 at the m-th row and the n-th column.
(M, n) is transmitted, and a liquid crystal driving voltage Vsig is generated between the pixel electrode 4 and the counter electrode to drive the liquid crystal.
The signal 34n including the liquid crystal drive voltage Vpc is transmitted to the n-th image signal line 2.

By driving with the above configuration, display defects such as vertical crosstalk hardly occur. As described above, when the maximum image signal voltage used for black display in the case of normally white display is VLmax, the image signal Vpc including the liquid crystal drive voltage equal to or higher than VLmax is temporarily written to the image signal line during the blanking period. Therefore, the change in the liquid crystal capacitance component of the image signal line due to the display content can be reduced by applying the black display voltage with a small capacitance change on average.

As a result, display defects such as vertical crosstalk are less likely to occur in a display image, and streak-like display unevenness is less likely to occur. Some display unevenness can also be improved, and display quality can be improved.

In each of the above embodiments, the peripheral drive circuit is formed by using a thin film transistor of a polysilicon thin film formed by using an excimer laser.
Good improvement results could be obtained.

[0043]

As described above, according to the present invention, when the maximum image signal voltage used for black display in normally white display is VLmax, a liquid crystal drive voltage not lower than VLmax is included during the blanking period. Since the image signal Vpc is once written to the image signal line, the change in the liquid crystal capacitance component of the image signal line due to the display content can be reduced by applying an average black display voltage with a small capacitance change.

Therefore, in a display image, display defects such as vertical crosstalk are unlikely to occur, and streak-like display unevenness is unlikely to occur. The display unevenness can also be improved, and the display quality can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic signal diagram of a driving method in a liquid crystal display device according to Embodiment 1 of the present invention.

FIG. 2 is a configuration diagram of a main part in a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is a signal schematic diagram according to a driving method in the liquid crystal display device of Embodiment 2.

FIG. 4 is a configuration diagram of a main part in a conventional liquid crystal display device with a built-in peripheral driving circuit.

FIG. 5 is a schematic diagram of a signal by a driving method in the liquid crystal display device of the conventional example.

FIG. 6 is an explanatory view of display unevenness like crosstalk in a vertical direction in the conventional example.

FIG. 7 is an explanatory diagram showing the relationship between the liquid crystal driving voltage and the transmittance of the panel when the image signal line is driven in a dot-sequential manner by a TN liquid crystal having dielectric anisotropy.

FIG. 8 is an explanatory diagram of a capacitance change due to anisotropy of a dielectric constant in a TN liquid crystal.

[Explanation of symbols]

Reference Signs List 1 scanning line 2 image signal line 3 pixel transistor 4 pixel electrode 5 signal writing transistor 6 signal wiring 8 scanning signal circuit 10 circuit block including shift register 27 Vpc writing transistor 28 gate signal line to Vpc writing transistor 29 Vpc writing Signal line for writing Vpc to transistor

Claims (4)

[Claims] 1. A method for driving a liquid crystal display device with a built-in peripheral driving circuit, which is a point-sequential driving type in which an image signal line has a capacitance component by a liquid crystal having a dielectric anisotropy. When the maximum voltage of the image signal applied to the pixel electrode to drive the pixel signal is VLmax, during a blanking period in which the image signal is not written on the screen, an image signal applied to the pixel electrode immediately after the blanking period. A method for driving a liquid crystal display device, comprising transmitting an image signal having the same polarity and including a liquid crystal drive voltage equal to or higher than VLmax to the image signal line. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal is driven by a peripheral driving circuit constituted by a thin film transistor formed using a polysilicon thin film formed using an excimer laser. Drive method. 3. In a liquid crystal display device with a built-in peripheral driving circuit, which is a point-sequential driving type in which an image signal line has a capacitance component of a liquid crystal having a dielectric anisotropy, in order to drive a liquid crystal during image display. When the maximum voltage of the image signal applied to the pixel electrode is VLmax, during a blanking period in which the image signal is not written on the screen, the image signal has the same polarity as the image signal applied to the pixel electrode immediately after the blanking period,
And an image signal including a liquid crystal drive voltage equal to or higher than VLmax,
A liquid crystal display device configured to transmit the signal to the image signal line. 4. The liquid crystal display device according to claim 3, wherein the peripheral driving circuit for driving the liquid crystal is constituted by a thin film transistor formed using a polysilicon thin film formed using an excimer laser.