JPH08241060A - Liquid crystal display device and its drive method - Google Patents

Abstract

PURPOSE: To reduce a spike-like distortion voltage of a scan waveform and to reduce the cross talk by reducing the switching of an ON voltage and an OFF voltage of a signal waveform in a gradation display by a pulse width modulation system. CONSTITUTION: A waveform 101 displaying 14-th gradation (white) is applied to a signal line 801, and the waveform 102 displaying first gradation (black) is applied to the signal line 802 so that the whole display picture is a white display of the 14-th gradation, and a black thin block of the first gradation is displayed in it. As the waveform 101 applied to the signal line 801, the OFF voltage (V2 ) is applied from T11 to T12 , and the ON voltage (V0 ) is applied from T12 to T14 in 1H from T11 to T14 . Then, the ON voltage is applied from T14 to T16 for displaying the same 14-th gradation (white), and the OFF voltage is applied from T16 to T17 in 1H from T14 to T17 . In such a case, the switch from the ON voltage to the OFF voltage of a signal voltage, or the switch from the OFF voltage to the ON voltage is made twice or fewer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gray scale display of a liquid crystal display device, and more particularly to crosstalk.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have come to be widely used as displays for word processors, personal computers, or televisions by taking advantage of their features such as thinness, light weight, and low power consumption. The demand for multi-gradation display, which is essential for display, has also increased. Among them, the pulse width modulation method, which is one of several gradation methods, can perform gradation display without flicker and is being developed because it is suitable for high quality display.

Here, the pulse width modulation method will be briefly described. First, the scanning line is line-sequentially scanned and the selective scanning voltage is applied for a certain period (selective scanning period). This selective scanning period is defined as one horizontal scanning period (1H). In the case of binary display, either ON voltage or OFF voltage is applied to the signal line for all 1H, but the gradation display method by the pulse width modulation method The gradation is displayed by dividing into several minutes and changing the period for applying the ON voltage.

However, in the pulse width modulation method, as can be seen from the above description, the signal waveform switches from the ON voltage to the OFF voltage or from the OFF voltage to the ON voltage during 1H, so that the scanning waveform is induced into the signal waveform at the switching portion. A spike-shaped distortion voltage is generated. Due to the influence of this distortion voltage, there is a problem that a partial difference occurs in the effective voltage between the pixels that must display the same gray scale, resulting in uneven display, or so-called crosstalk.

A conventional display by pulse width modulation will be described with reference to FIGS. 6 and 8. FIG. 8 is a diagram when the entire display screen is a white display of 14th gradation and a black thin block of the 1st gradation is displayed in it. FIG. 6 shows the drive waveform and the effective voltage at that time. T61 to T
64 and T64 to T67 are 1H, respectively, and FIG. 6 shows a waveform of 2H from T61 to T67.

At this time, the signal waveform 80 is applied to the signal line 601.
As shown in 1, the OFF voltage is applied from T61 to T62, the ON voltage is applied from T62 to T64, the OFF voltage is applied from T64 to T65 at the beginning of the next horizontal scanning period, and the ON voltage is applied again from T65. It
The drive waveform as described above has a problem that crosstalk occurs.

[0007]

In the conventional example described above, the ON voltage and the OFF voltage are frequently switched, and a spike-like distortion voltage is generated in the scanning voltage at the switching portion. As a result, the effective voltage 604 applied to the liquid crystal pixel 804 is equal to the effective voltage 605 applied to the liquid crystal pixel 805.
There is a problem that a so-called crosstalk phenomenon occurs in which the liquid crystal pixels 805 look white when viewed relatively, because the number of pixels is considerably reduced. The present invention provides a liquid crystal display device and a driving method thereof in which crosstalk, which is the above problem, is reduced.

[0008]

According to the present invention, there are provided liquid crystal pixels arranged in a matrix on an insulating substrate, a scanning electrode to which a plurality of liquid crystal pixels arranged in one direction of the matrix belong in common, and the scanning electrode. On the other hand, a plurality of liquid crystal pixels aligned in the vertical direction are commonly provided with a signal electrode, and the signal electrode is set to an ON voltage for each horizontal scanning period for an arbitrary period during the one horizontal scanning period and an OFF voltage for the remaining period. Is input to the liquid crystal pixel, and a voltage substantially corresponding to a difference between the scan voltage input to the scan electrode and the signal voltage is applied to the liquid crystal pixel, so that the light transmittance of the liquid crystal layer is increased. In the liquid crystal display device, the voltages applied to the liquid crystal pixels belonging to the same signal electrode are alternated every predetermined period, and adjacent to each other within the predetermined period and applied with ON voltage. 2 having between the OFF voltage application period
Within one horizontal scanning period, from the ON voltage of the signal voltage to O
The liquid crystal display device is characterized in that switching to the FF voltage or switching from the OFF voltage to the ON voltage is performed twice or less.

The present invention also provides a control circuit for controlling the start and end of reading of a data signal, a shift register for sequentially transferring the data signal, a latch for holding the data signal and sending it in synchronization, and a gradation generating clock. And a signal electrode driving IC having a GCP counter for converting the data signal into a pulse width modulation gradation data signal, and dividing one horizontal scanning period in which a selective scanning potential is applied to the scanning electrodes. In a liquid crystal display device that displays a gray scale by determining an ON potential application period by a GCP counter, the signal electrode driving IC includes two GCP counters A and B, and from one GCP counter A, each gray scale starts from an OFF potential. A gradation data signal for switching to the ON potential is applied, and from the other GCP counter B, each gradation changes from the ON potential to the ON potential. Gradation data signal switches to FF potential is applied, and the and the GCP counter A GCP
The counter B is a liquid crystal display device and a driving method thereof, which is provided with a unit that is alternately selected for each horizontal scanning period.

[0010]

The liquid crystal display device according to the present invention prepares two kinds of signal waveforms, one for which the ON voltage is applied in one horizontal scanning period for one gray scale and one for which the ON voltage is applied first. By alternately selecting every horizontal scanning period, ON voltage and OFF are compared to the case of one type of signal waveform.
By reducing the number of times of switching with the voltage, the spike-like distortion voltage generated in the scan waveform can be reduced, and crosstalk can be reduced.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The structure of the liquid crystal display device of this embodiment is shown in FIG. The X electrode group (scanning line) 901 which is a band-shaped transparent electrode is formed on the glass substrate 903, the Y electrode group (signal line) 902 is formed on the glass substrate 904, and the glass substrate 903 is arranged so as to be orthogonal to each other. 904 are arranged vertically. At this time, a large number of square portions appearing at the intersections of the X electrodes and the Y electrodes arranged in a matrix are called liquid crystal pixels. The number of pixels in this embodiment is 640 * 480 dots (VG
A). Then, the liquid crystal material 907 is sealed in the space sandwiched between the glass substrates 903 and 904, and the polarizing plates 905 and 906 are provided outside the upper and lower glass substrates 903 and 904.
Is the structure in which is arranged.

Here, the operation principle of display in the liquid crystal display device will be briefly described. Xs above and below each liquid crystal pixel
Between the electrode 901 and the Y electrode 902, a voltage higher than a threshold value (voltage generated by liquid crystal molecules, which varies depending on the liquid crystal material) is applied to cause liquid crystal molecules, or a voltage higher than the threshold value is not applied. The light transmittance of each liquid crystal pixel can be controlled depending on whether or not the liquid crystal molecules are laid down. The liquid crystal display device of this embodiment is in a normally black mode in which black is displayed when a voltage above the threshold is not applied and white is displayed when a voltage above the threshold is applied.

Further, the liquid crystal display device performs polarity inversion in which the polarity of the drive voltage is alternated every predetermined period in order to prevent deterioration of the liquid crystal material. The predetermined period is generally a plurality of horizontal scanning periods. Next, a pulse width modulation method, which is one of the gradation display methods, will be described with reference to FIGS. First, in the scanning waveform 1001 of the scanning line 1006, from T1 to T
It can be seen that the selective scanning voltage V0 is applied in the period up to 3, and then the selective scanning voltage V0 is applied in the period from T3 to T5 in the scanning waveform 1002 of the scanning line 1007. Such scanning is called line-sequential scanning, and a period in which a selective scanning voltage is applied to one scanning line such as T1 to T3 or T3 to T5 is referred to as one horizontal scanning period (1H).

At this time, the signal waveform 10 is applied to the signal line 1008.
Consider applying a voltage of 03. 1H from T1 to T3 relates to the display of the liquid crystal pixel 1009, and
1H up to 5 is related to the display of the liquid crystal pixel 1010. The signal waveform 1003 is the ON voltage V5 from T2 to T3 and from T4 to T5, respectively. At this time, the liquid crystal pixel 1009
To the pixel 1010, and an effective voltage 1005 is applied to the pixel 1010. Due to the difference in the effective voltage, the liquid crystal pixel 1010 displays whiter than the liquid crystal pixel 1009. As described above, the pulse width modulation method is a method of changing the effective voltage substantially corresponding to the difference between the scanning voltage and the signal voltage for each liquid crystal pixel to display a gray scale depending on the difference in the ON voltage application period of the signal waveform. is there.

The liquid crystal display device according to the present embodiment is a monochrome 16 gradation display by the pulse width modulation method, the gradation without ON voltage application at 1H is gradation 0, and the gradation where ON voltage is continuously applied at 1H is gradation. Set to 15. The potential in this embodiment is V0.
= 25 volts, V1 = 23.4 volts, V2 = 21.9
Volt, V3 = 3.1 Volt, V4 = 1.6 Volt, V
5 = 0 volt.

An example of the operation of the liquid crystal display device of the present invention will be described here. In the above-described liquid crystal display device, the entire display screen is a white display with 14 gradations, and 14 gradations are provided on the signal line 801 shown in FIG. Waveform 1 displaying the eyes (white)
01 is applied, and the waveform 102 for displaying the first gradation (black) is applied to the signal line 802. FIG. 1 shows the driving waveform and the effective voltage at that time. T11 to T14
And T14 to T17 are 1H respectively, and FIG. 1 shows a waveform of 2H from T11 to T17.

In the case of the present embodiment, only the signal line 802 has a signal waveform showing black display, and all the other signal lines have the same signal waveform (white display) as 801. The waveform 102 is the scan waveform 10 of the scan line 803.
The effect on 3 is much smaller than the effect on the other signal lines including the signal line 108, and the spike caused by the signal waveform 102 on the signal line 802 is neglected. The selective scanning voltage is V5.

As the waveform 101 applied to the signal line 801, first, in 1H from T11 to T14, T1
OFF potential (V2) is applied from 1 to T12,
The ON voltage (V0) is applied from T14 to T14. Then T
At 1H from 14 to T17, the same 14th gradation (white)
To display the ON voltage (V
0) is applied, and the OFF voltage (V
2) is applied.

As described above, by alternately applying the signal waveform to which the ON voltage is applied first and the signal waveform to which the ON voltage is applied every 1H to the signal line, the switching of the signal waveform at the time of T14 is eliminated. The spike at T14 can be eliminated.

As a result, the difference between the effective voltage 104 applied to the pixel 804 and the effective voltage 105 applied to the pixel 805 can be made much smaller than in the conventional case, and crosstalk can be reduced. .

The above embodiment will be described from the viewpoint of a driving circuit with reference to FIG. FIG. 5 shows the signal line drive I in this embodiment.
It is the figure which showed the outline of C typically. Data acquisition is started by the enable input signal (EIO), and the data signals acquired by the clock signal (XSCL) are sequentially transferred to the latch A. The transferred data is taken into the latch B at the falling edge of the latch pulse (LP). From the outside, the basic clock GCP (A) for gradation generation,
GCP (B) is input. Those clocks,
Input into two GCP counter A and GCP counter B respectively, count according to the data signal in the latch B,
A gradation data signal for pulse width modulation is obtained. These two G
Switching of the CP counter is performed by a gradation generation basic clock selection signal (EN).

According to the gradation data signal, if the data is the selection data (ON), the ON voltage V5 (the voltage V5 when the polarity is inverted)
0) is OFF voltage V3 for non-selected data (OFF)
(Voltage V2 when polarity is inverted) is selected and output to each signal line.

In this embodiment, 4-bit data is input, 16 gradations are output based on this digital data, and the 4-bit input data signal corresponding to each gradation is' 0.
000 'is black display with gradation 0, and' 1111 'is white display with gradation 15.

FIG. 2 shows GCP (A), and FIG. 3 shows GCP (B).
And the signal waveform of each gradation.
Both GCP (A) and GCP (B) have 14 pulses in the 1H period. The 14 pulse timings are
GCP (A) and GCP are applied during the ON voltage application period of the same gradation.
It is the same as in (B), and the order of gradation 0 to gradation 15 in 1H is set to be reversed.

Here, the gradation 1 will be described as an example. The gradation 1 corresponds to the data signal '0001'. This signal is latch B
Is input to the GCP counter A and the GCP counter B in synchronization with the latch pulse (LP). In response to this, the GCP counter A and the GCP counter B count GCP (A) and GCP (B), respectively, and output the signal waveform of gradation 1 in FIGS. 2 and 3. Then, as shown in the timing chart of FIG. 4, these two types of signal waveforms are alternately selected by the EN signal every 1H. By doing this, as shown in FIG. 1, if the end of 1H is the ON voltage, the next 1H starts from the ON voltage, and if the end of 1H is the OFF voltage, the next 1H starts from the OFF voltage. To the 1H break T
It is possible to eliminate unnecessary switching of ON voltage and OFF voltage in 14 and reduce crosstalk.

According to the present embodiment, in the gradation display by pulse width modulation, the switching of ON voltage and OFF voltage of the signal waveform is reduced, the spike-like distortion voltage generated in the scanning waveform due to the switching is minimized, and the crossing is performed. It is possible to reduce talk.

The present invention is not limited to the above embodiment, and it goes without saying that many modifications or changes can be made to this embodiment within the scope of the present invention. For example, for a liquid crystal display device that performs polarity inversion, frame inversion, 13
The present invention is effective not only for line inversion but also for other liquid crystal display devices which perform line inversion. Further, it can be applied to a color display and a liquid crystal display device having other gradations.

[0028]

According to the present invention, in gradation display by the pulse width modulation method, switching between ON voltage and OFF voltage of a signal waveform is reduced to reduce spike-like distortion voltage of a scanning waveform and to reduce crosstalk. Can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a drive waveform and an effective voltage of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a signal waveform of each gradation and a GCP timing in the GCP counter A in one embodiment of the present invention.

FIG. 3 is a diagram showing a signal waveform of each gradation and a GCP timing in the GCP counter B in one embodiment of the present invention.

FIG. 4 shows GCP (A) and G in one embodiment of the present invention.
It is a figure which shows the timing of selection of CP (B).

FIG. 5 is a diagram schematically showing an internal configuration of a drive IC of a liquid crystal display device according to an embodiment of the present invention.

FIG. 6 is a diagram showing a drive waveform and an effective voltage in a conventional liquid crystal display device.

FIG. 7 is a diagram schematically showing an internal configuration of a drive IC in a conventional liquid crystal display device.

FIG. 8 is a diagram showing electrodes and pixels of a simple matrix.

FIG. 9 is a diagram showing a structure of a simple matrix liquid crystal display device.

FIG. 10 is a diagram showing drive waveforms in pulse width modulation.

[Explanation of symbols]

 901 ... Scan electrode 902 ... Signal electrode 909 ... Liquid crystal display device 101 ... Signal waveform

Claims (4)

[Claims] 1. A liquid crystal pixel arranged in a matrix on an insulating substrate, a scanning electrode to which a plurality of liquid crystal pixels arranged in one direction of the matrix belong in common, and a plurality of scanning electrodes arranged in a direction perpendicular to the scanning electrode. A liquid crystal pixel commonly includes a signal electrode, and a signal voltage that is set to an ON voltage for any one horizontal scanning period and set to an OFF voltage for the remaining period is input to the signal electrode every horizontal scanning period. In the liquid crystal display device, the light transmittance of the liquid crystal layer is controlled by applying a voltage substantially corresponding to a difference between the scan voltage input to the scan electrode and the signal voltage to the liquid crystal pixel. The voltages applied to the liquid crystal pixels belonging to the same signal electrode are alternated every predetermined period, and are adjacent to each other in the predetermined period and each has an ON voltage application period and an OFF voltage application period. In two horizontal scanning periods having a liquid crystal display device, wherein the switching from ON voltage of the signal voltage to the OFF voltage or switching from OFF voltage to the ON voltage, is less than 2 times. 2. The liquid crystal display device according to claim 1,
Within the two horizontal scanning periods that are adjacent to each other within the predetermined period and each have an ON voltage application period and an OFF voltage application period, the signal voltage is switched from ON voltage to OFF voltage, or from OFF voltage to ON voltage. Switching is 2
A liquid crystal display device characterized in that it is a rotating device. 3. A control circuit for controlling the start and end of reading of a data signal, a shift register for sequentially transferring the data signal, a latch for holding the data signal and sending it in synchronization, and counting a gradation generation clock. A signal electrode driving IC having a GCP counter for converting the data signal into a pulse width modulation gradation data signal,
In a liquid crystal display device in which one horizontal scanning period in which a selective scanning potential is applied to the scanning electrodes is divided and an ON potential application period is determined by the GCP counter to display a gray scale, the signal electrode driving IC includes two GCP counters. Equipped with A and B, one GCP counter A turns off each gradation
A gradation data signal for switching from the potential to the ON potential is applied, a gradation data signal for switching from the ON potential to the OFF potential for each gradation is applied from the other GCP counter B, and the GCP counter A and the GCP counter are also applied. B
Is a liquid crystal display device comprising means for alternately selecting each horizontal scanning period. 4. A control circuit for controlling the start and end of reading of a data signal, a shift register for sequentially transferring the data signal, a latch for holding the data signal and sending it in synchronization, and counting a gradation generation clock. A method of driving a liquid crystal display device, comprising a signal electrode driving IC having a GCP counter for converting the data signal into a gradation data signal of pulse width modulation, wherein one horizontal scanning line in which a selective scanning potential is applied to the scanning electrodes. The scanning period is divided into
In a method of driving a liquid crystal display device in which an ON potential application period is determined by a CP counter to display a gray scale, the signal electrode driving IC includes two GCP counters A and B, and one gray scale counter is used for each gray scale. O from OFF potential
A gradation data signal for switching to N potential is applied, and from the other GCP counter B, each gradation is turned from ON potential to OFF.
A method of driving a liquid crystal display device, wherein a gradation data signal for switching to a potential is applied, and the GCP counter A and the GCP counter B are alternately selected every horizontal scanning period.