JP3407327B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quality improvement of MIM liquid crystal display panels, and more particularly to improvement of contrast and measures for preventing afterimage and image sticking.

[0002]

2. Description of the Related Art In recent years, various video-related devices, measuring instruments, information devices, personal computer displays, etc.
Large-capacity matrix liquid crystal panels are beginning to be used. When these liquid crystal panels are classified by the address system, they can be classified into a simple matrix system, an active matrix system, an optical address system, a thermal address system and the like. In view of the above, the active matrix method has come into the market as a display with high image quality and large capacity. A typical active matrix liquid crystal panel is a TFT liquid crystal panel using amorphous silicon or polysilicon. In addition, MIM liquid crystal panels, which are easier to manufacture than TFT liquid crystal panels, have been manufactured. On the other hand, in the simple matrix system, the display capacity can be expanded by increasing the twist like STN and FTN, and a large amount has been sent to the market. Although the display quality of the MIM liquid crystal panel related to this patent has been remarkably improved as compared with the past, further improvement in contrast and a phenomenon called afterimage or burn-in that remains when a fixed pattern is displayed are still problems. It is left as.

FIG. 2 is a diagram showing an example of drive waveforms of a conventional MIM liquid crystal panel.

The signal applied to the Yj line (horizontal line) is 21, the signal applied to the Xi line (vertical line) is 22, and the signal Yj applied to the intersection of the Yj line and the Xi line.
The -Xi composite waveform is shown in 23. The composite waveform 23 can be divided into a selection period 24 and a non-selection period (holding period) 25. A pulse set to write a signal in a pixel during the selection period is referred to as a writing pulse 26. By changing the pulse width of the upper part, the on / off of the pixel and the gradation are determined. The holding period is a period for holding the signal written in the selection period. The signal voltage written in the liquid crystal layer in the pixel is shown by the broken line 27. The alternate long and short dash line 28 is called a bias voltage and represents the time average of the pulse voltage in one holding period. As shown in this example, the bias voltage 28 is not set to 0 volt but is set to several volts having the same polarity as the write pulse so that the signal voltage 27 written in the liquid crystal leaks less current through the MIM element and the contrast is secured. Easy to do. 29 is the period of the crosstalk compensation pulse, which is the pulse width 2 of the write pulse 26.
As 10 is larger, the pulse width of the crosstalk compensation pulse is 2
11 has a relationship of decreasing, and the total pulse width (sum of 210 and 211) is always almost constant in one selection period. By doing so, the high voltage period and the low voltage period of the pulse in the holding period are substantially equal to each other, and the appearance of crosstalk can be suppressed. FIG. 3 is an equivalent circuit diagram showing the configuration of the pixel portion of the MIM liquid crystal panel. An MIM element is formed on the Xi line 31, and its resistance component is 32 and its capacitance component is 33. M
Since the resistance component 32 of the IM element changes depending on the applied voltage, it is drawn as a variable resistance. 34 is a pixel electrode.
Reference numerals 35 and 36 respectively represent a resistance component and a capacitance component of the liquid crystal layer. 38 is a line-to-line capacitance between the Xi line 31 and the Yj line 37.

[0005]

However, the conventional driving method has the following problems.

In a MIM element, that is, in an element using an insulator as an electric current control layer, generally, once a large electric field is applied, the effect remains even after the electric field is removed, and the current-voltage characteristic of the element is a voltage. It had a phenomenon that it changed compared to before the application of. This phenomenon remarkably occurs as the applied voltage becomes higher, and it also occurs as the voltage is applied for a longer time. Then, when the voltage is cut off and left for a while, the characteristics return to their original values. This was strongly associated with the phenomenon of image quality defects such as afterimage and image sticking of the MIM panel. Furthermore, when displaying the same image on the MIM panel for a long time,
A large change in the element characteristics occurs in the high voltage application portion, and a small change in the element characteristic occurs in the low voltage application portion, and the difference appears in the display, resulting in an afterimage or burn-in.

FIG. 4 is a graph showing how the conductivity-voltage characteristic of the device changes by applying a voltage.
Since the conduction of the MIM element is considered to be centered on the conduction mechanism called pool Frenkel conduction, the horizontal axis represents the square root of voltage and the vertical axis represents the ratio of current to voltage, that is, the logarithm of conductivity. When the same element is repeatedly measured, a voltage is applied to the element due to the measurement, so its characteristic is 4
It drifts to the lower right gradually as 1, 42 and 43. This drift eventually saturates and does not change even when a voltage is applied to the device.

The afterimage of the MIM liquid crystal panel is caused by such characteristic drift of the element, and impurity ions or molecules with strong polarity are adsorbed at the interface between the liquid crystal layer and the alignment film due to the direct current component applied to the panel. There are things that arise. The afterimage cannot be erased unless both are removed. Since the former afterimage is due to the property of the insulating film of the element as described above, it is necessary to change the conductive property of the element itself or compensate for it during driving.

In view of the above points, an object of the present invention is to provide a method of eliminating the afterimage of the MIM panel (the former afterimage) in driving and simultaneously improve the contrast.

[0010]

The liquid crystal display device of the present invention has the following features.

The drive waveform of a liquid crystal panel using a substrate on which MIM elements are formed (horizontal line applied signal-vertical line applied signal composite waveform) has a pulse for writing a signal to a pixel (hereinafter referred to as a write pulse). However, the drive waveform is such that the time average of the potential of the pulse during the period in which the signal written in the pixel by the write pulse is held until the next write pulse comes (hereinafter referred to as the holding period) has the same polarity as the write pulse. , And a correction pulse having a polarity opposite to that of the write pulse.

The liquid crystal display device according to the present invention is characterized in that the shape of the correction pulse does not correspond to the waveform of the write pulse that changes due to gradation or the like and is always constant.

The waveform of the write pulse changes when the gradation is modulated by the pulse width, but the waveform of the correction waveform pulse also changes in response to the change in the shape of the write pulse. The relationship between the steps is 2 / of the total number of steps
The liquid crystal display device according to the present invention is characterized in that the pulse width of the correction waveform pulse decreases as the pulse width of the write pulse increases with respect to 3 or more steps.

The waveform of the write pulse changes when the gradation is modulated by the amplitude, and the waveform of the correction waveform pulse also changes in response to the change in the shape of the write pulse.
The relationship between the amplitude changes of these two waveforms is 2 / of the change width of all gradations.
The liquid crystal display device according to the present invention is characterized in that the amplitude of the correction waveform pulse decreases as the amplitude of the write pulse increases with respect to a change width of 3 or more.

The liquid crystal display device according to the present invention is characterized in that the period of the write pulse and the period of the correction pulse are different.

In the selection period for selecting each horizontal line of the liquid crystal panel, a crosstalk compensation pulse is included in addition to the write pulse and the correction pulse, and the crosstalk compensation pulse has the same polarity as the write pulse. It is characterized in that the pulse width (or amplitude) of the crosstalk compensating pulse decreases as the pulse width (or amplitude) of the write pulse increases with respect to 2/3 or more gradation steps. The liquid crystal display device according to the present invention.

The selection period for selecting each horizontal line of the liquid crystal panel includes a crosstalk compensation pulse in addition to the write pulse and the correction pulse, and the crosstalk compensation pulse has a polarity different from that of the write pulse. It is characterized in that there is a relation that the pulse width (or amplitude) of the crosstalk compensation pulse increases as the pulse width (or amplitude) of the write pulse increases with respect to the step of 2/3 or more of the gradation step. The liquid crystal display device according to the present invention.

[0018]

EXAMPLES Examples of the present invention will be described below. Figure 1
It is a graph which shows one Example of this invention. The signal applied to the Yj line (horizontal line) is shown in 12, the signal applied to the Xi line (vertical line) is shown in 13, and the Yj-Xi composite waveform applied to the intersection of the Yj line and the Xi line is shown in 11. .
The composite waveform 11 has a selection period 14 and a non-selection period (holding period).
The pulse that is set to write a signal in the pixel during the selection period is called a write pulse 16. By changing the pulse width of the upper part of this write pulse, the pixel is turned on / off and the gradation is changed. Has been decided. The holding period 15 is a period for holding the signal written in the selection period. The correction pulse 17 is provided between the write pulse 16 and the holding period 15, and its polarity is opposite to that of the write pulse. The pulse width 18 becomes smaller as the pulse width 19 of the write pulse 16 becomes larger and becomes smaller as it becomes smaller. Is set. This is done to provide sufficient contrast.
The broken line 110 indicates the signal voltage written in the liquid crystal layer in the pixel. By using the correction pulse 17, the peak value of the write pulse 16 cannot be supplied to the liquid crystal layer with the same voltage unless it is set higher than when the correction pulse 17 is not used. The high crest value of the write pulse 16 means that the voltage applied to the MIM element at that time also becomes larger than that in the prior art, so that the element characteristic drifts sufficiently and saturates. Therefore, it is possible to significantly reduce afterimages and burn-in, which are the drawbacks peculiar to the MIM panel.

FIG. 5 shows another embodiment of the present invention, and reference numeral 51 shows a Yj-Xi composite waveform applied to the intersection of the Yj line (horizontal line) and the Xi line (vertical line). Also in this embodiment, the composite waveform 51 can be divided into a selection period 14 and a non-selection period (holding period) 15, and a write pulse 16 provided for writing a signal to a pixel is included in the selection period. Therefore, the ON / OFF of the pixel and the gradation are determined by changing the pulse width of the upper part of the write pulse. The correction pulse 52 is provided between the write pulse 16 and the holding period 15, and the shape of the correction pulse 52 does not change even if the pulse width of the write pulse 16 changes, which is different from the example of FIG. different. Due to the presence of the correction pulse 52, the peak value of the write pulse 16 becomes high, the element drifts sufficiently and saturates, and the afterimage of the MIM panel is greatly reduced.

FIG. 6 shows another embodiment of the present invention, and 61 shows a Yj-Xi composite waveform applied to the intersection of the Yj line (horizontal line) and the Xi line (vertical line). 1 and 5 are examples in which gradation display is performed by pulse width modulation, this embodiment is one in which gradation is performed by amplitude modulation. The amplitude of the correction pulse 63 is set to be smaller as the amplitude of the write pulse 62 is larger, and is larger as the amplitude of the write pulse 62 is smaller. This is done so that sufficient contrast can be obtained.

As in the previous example, due to the presence of the correction pulse 63, the crest value of the write pulse 62 needs to be set higher than in the example without the correction pulse. By doing so, the drift characteristics of the device are sufficiently saturated and no afterimage is generated on the panel.

FIG. 7 shows another embodiment of the present invention. A Yj-Xi composite waveform applied at the intersection of the Yj line (horizontal line) and the Xi line (vertical line) is shown at 71. This is an example in which gradation display is performed by pulse width modulation as in FIG. However, the difference from the example of FIG. 1 is that the period 75 of the correction pulse 73 is
This is different from the period 74 of the write pulse 72.

FIG. 8 shows another embodiment of the present invention, and 81 shows a Yj-Xi composite waveform applied to the intersection of the Yj line (horizontal line) and the Xi line (vertical line). Also in this embodiment, the write pulse 82 and the correction pulse 83 are similar to the example of FIG.
However, a crosstalk compensation pulse 84 is provided in addition to the above. This crosstalk compensation pulse 84
Is set so that the ratio of the high voltage portion and the low voltage portion of the pulse in the holding period is as equal as possible. Therefore, the polarity of the crosstalk compensation pulse is equal to the polarity of the write pulse, and its pulse width has a relationship of decreasing as the pulse width of the write pulse increases.

Even if the crosstalk compensation pulse is brought before the write pulse, the same effect as that shown in FIG. 8 can be obtained. In particular, when it is before the write pulse, it is preferable to reverse the polarity of the crosstalk compensation pulse so that the pulse width increases as the width of the write pulse increases.

[0025]

According to the present invention, M using the MIM element is used.
Afterimages and image sticking on the IM panel are eliminated and the contrast is improved.

In the present invention, any X-line signal and Y-line signal that can realize the Y-X composite waveform shown in the claims are included in the contents of this patent.

[Brief description of drawings]

FIG. 1 is a graph showing an example of the present invention.

FIG. 2 is a diagram showing an example of drive waveforms of a conventional MIM liquid crystal panel.

FIG. 3 is an equivalent circuit diagram showing a configuration of a pixel portion of an MIM liquid crystal panel.

FIG. 4 is a graph showing how the conductivity-voltage characteristic of the device changes by applying a voltage.

FIG. 5 is a diagram showing another embodiment of the present invention.

FIG. 6 is a diagram showing another embodiment of the present invention.

FIG. 7 is a diagram showing another embodiment of the present invention.

FIG. 8 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

17 ... Correction pulse 52 ... Correction pulse 63 ... Correction pulse 64 ... Write pulse at maximum amplitude 65 ... Write pulse at minimum amplitude 73 ... Correction pulse 83 ... Correction pulse 84 ... Crosstalk compensation pulse

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 550 G02F 1/133 575 G09G 3/36

Claims (7)

(57) [Claims] 1. A liquid crystal display device comprising an active matrix liquid crystal panel, wherein a drive waveform which is a composite waveform of a horizontal line application signal and a vertical line application signal of the active matrix liquid crystal panel writes a signal to a pixel. The write pulse has a write pulse, and the time average of the potentials of the pulses in the holding period for holding the signal written in the pixel by the write pulse until the next write pulse is applied has the same polarity as the write pulse. And a correction pulse having a polarity opposite to that of the writing pulse between the holding period and the holding period. 2. The liquid crystal display device according to claim 1, wherein the shape of the correction pulse is always constant regardless of the change in the waveform of the write pulse. 3. The waveform of the write pulse changes when the gradation is modulated by the pulse width, and the waveform of the correction waveform pulse also changes in response to the change of the waveform of the write pulse. The relationship between the gradation steps of the waveforms of the write pulse and the correction waveform pulse is that the pulse width of the correction waveform pulse increases as the pulse width of the write pulse increases with respect to the steps of ⅔ or more of the total number of gradation steps. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a relationship of decreasing. 4. The waveform of the write pulse changes when the gradation is modulated by the amplitude, and the waveform of the correction waveform pulse also changes in response to the change in the shape of the write pulse. The relationship between changes in the amplitude of the write pulse and the correction waveform pulse is that the amplitude of the correction waveform pulse decreases as the amplitude of the write pulse increases with respect to the change width of 2/3 or more of the change width of all gradations. The liquid crystal display device according to claim 1, wherein: 5. The liquid crystal display device according to claim 1, wherein a period of the write pulse and a period of the correction pulse are different from each other. 6. A selection period for selecting each horizontal line of the liquid crystal panel includes a crosstalk compensation pulse in addition to the write pulse and the correction pulse, the crosstalk compensation pulse being the same as the write pulse. It is characterized in that the pulse width or the amplitude of the crosstalk compensation pulse decreases as the pulse width or the amplitude of the write pulse increases with respect to the steps of ⅔ or more of all gradation steps having the same polarity. The liquid crystal display device according to claim 1. 7. A selection period for selecting each horizontal line of the liquid crystal panel includes a crosstalk compensation pulse in addition to the write pulse and the correction pulse, the crosstalk compensation pulse being the same as the write pulse. The polarities are different, and the pulse width or the amplitude of the crosstalk compensation pulse increases as the pulse width or the amplitude of the write pulse increases with respect to the step of ⅔ or more of all the gradation steps. The liquid crystal display device according to claim 1.