JPH1152917A - Liquid crystal driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance display quality by preventing the occurrence of cross talk even when the gradation data is fluctuated. SOLUTION: In this method, when driving a liquid crystal panel on which a matrix of scanning electrodes and signal electrodes is arranged, a liquid crystal driving which makes gradation display by controlling the period of a maximum voltage impressed on the crystal is conducted by modulating the pulse width of data pulse D to be impressed on the signal electrode in accordance with the gradation data and further by switching the rear increment based on the front side of the selected pulse S and the front increment based on the rear side of the selected pulse S each for a specified period of time in this pulse width modulation. In this case, the non-selection voltage to be impressed on the non-selected scanning electrode is amplitude-modulated and switched to +Vmo and -Vmo in accordance with the kind of gradation data. The non-selection voltage can be varied also by pulse-width modulation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal driving method capable of displaying an image having an intermediate gradation on a matrix type liquid crystal panel.

[0002]

2. Description of the Related Art Conventionally, a display device having a simple matrix type liquid crystal panel in which scanning electrodes and signal electrodes are arranged in a matrix with a liquid crystal layer interposed therebetween as shown in FIG. An image having a gradation is displayed. In the case of displaying an intermediate gradation, a PW that performs pulse width modulation on a data pulse applied to a signal electrode according to gradation data
An M drive system is known. However, if the pulse width modulation for the data pulse is only the post-step method (a method in which the pulse width modulation reference is set to the front side and the rear side is changed) or only the front-step method, crosstalk occurs on the display screen. There was a problem.

The main cause of this crosstalk is that the effective voltage between pixels varies from the ideal effective voltage due to the influence of noise induced by capacitive coupling between the scanning electrode and the signal electrode with a liquid crystal interposed. It has become.

In order to solve such a problem, as shown in FIG. 4, a method in which a pre-step method and a post-step method are mixed in pulse width modulation, and the pre-step method and the post-step method are switched at a predetermined cycle. It is known, and the occurrence of crosstalk is prevented by a novel driving method using the same.

[0005] However, the new driving method is effective in suppressing crosstalk when the number of pixels at the high gradation level and the number of pixels at the low gradation level are balanced. At the time of falling, there is a problem that imbalance occurs in the effective voltage due to noise induced by the unselected scan electrodes, and as a result, crosstalk occurs.

This point will be described with reference to FIG. FIG. 5 shows a high gradation data pulse represented by a waveform a (a mixture of a post-step pulse a1 and a pre-step pulse a2) and a waveform b.
Represents a low gradation data pulse (mixed pulse b1 and pulse b2) and a waveform c of an unselected scan electrode in which noise is induced by these data pulses. FIG. 1A shows the case where the ratio of the data pulse a to the low gradation data pulse b is 2: 2 and 3:
1 is shown in FIG. 2B and 1: 3 is shown in FIG. The pulse a is applied to the non-selected scanning electrodes.
Downward noise at time t2 and t3 due to the fall of 1 and b1, and t1 due to the rise of pulses b2 and a2
At 2, t13, upward noise is induced at a ratio of 2: 2. In (B) and (C) of the figure, the hatched portion indicates the difference between the voltage c of the unselected scan electrode and the voltages a and b of the data pulse, and the hatched portion is the basis of the effective voltage. . Further, the number with + indicates the degree to which the induced noise contributes to the increase in the effective voltage, and the number with-indicates the degree to which the induced noise contributes to the decrease in the effective voltage.

As shown in FIG. 1A, when the ratio between the high gradation data pulse a and the low gradation data pulse b is balanced, between the pixels shown in FIGS. Since the degree of decrease in the effective voltage due to noise is the same as -4, there is no difference in the effective voltage between the pixel to which the high gradation data pulse a is applied and the pixel to which the low gradation data pulse b is applied when not selected. , Crosstalk is prevented.

However, as shown in FIGS. 2 and 3, when the ratio of the high gradation data pulse a and the low gradation data pulse b is largely different, the pixels of (B) and (C) are different. Since the effective voltage decreases due to noise, the difference in the effective voltage between the pixel to which the high gradation data pulse a is applied and the pixel to which the low gradation data pulse b is applied occurs when the pixel is not selected. Become.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to prevent crosstalk from occurring and to improve display quality even when there is variation in gradation data.

[0010]

According to the liquid crystal driving method of the present invention, when driving a liquid crystal panel in which scanning electrodes and signal electrodes are arranged in a matrix, a data pulse applied to the signal electrodes is converted into gradation data. In a liquid crystal driving method for performing gray scale display by pulse width modulation in response, a non-selection voltage applied to a non-selected scan electrode is varied according to a type of gray scale data.

According to the liquid crystal driving method of the present invention, when driving a liquid crystal panel in which scanning electrodes and signal electrodes are arranged in a matrix, a data pulse applied to the signal electrodes is pulse width modulated in accordance with gradation data. At the same time, the pulse width modulation is performed by switching the post-step based on the front side of the selection pulse and the pre-step based on the rear side of the selection pulse every predetermined period, thereby reducing the period of the maximum voltage applied to the liquid crystal. In a liquid crystal driving method for performing gradation display by controlling, a non-selection voltage applied to a non-selection scan electrode is changed according to a type of gradation data.

Further, a positive / negative non-selection voltage sandwiching a reference potential is used as the non-selection voltage, and a ratio of the positive / negative non-selection voltage in one scanning period is determined according to the type of the gradation data in one scanning period. You can switch.

Further, a positive / negative non-selection voltage sandwiching a reference potential is used as the non-selection voltage, and the positive / negative non-selection voltage is applied for one or more scanning periods according to the type of the gradation data in one scanning period. You can switch with.

[0014] Further, it is possible to obtain the total gradation of the gradation data in one scanning period, and to vary the non-selection voltage based on the result.

Further, each of the gradation data in one scanning period may be compared with reference gradation data, and the non-selection voltage may be varied according to the number of gradation data which is higher or lower than the reference gradation data. it can.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a waveform diagram showing an embodiment when a simple matrix type liquid crystal panel as shown in FIG. 2 is driven by using the driving method of the present invention, and is applied to an arbitrary pixel in the first to fourth fields. 3 shows the vicinity of the selection period, which is a portion having a large amplitude, in the voltage waveform. FIG. 2A shows a voltage waveform (solid line) applied to a scanning electrode forming the pixel and a voltage waveform (dashed line) applied to a signal electrode forming the pixel. FIG. The difference voltage between them is shown. Similar to the case of FIG. 4, the maximum voltage applied to the liquid crystal is changed by switching the pulse width modulation between the last step and the previous step every predetermined period in addition to the AC drive. Is a driving method of performing gradation display by controlling the period.
That is, pulse width modulation of the last step is performed in the first and second fields, pulse width modulation of the last step is performed in the third and fourth fields, and driving is performed with four fields as one cycle. The AC driving is performed with two fields as one cycle.

In FIG. 1, the selection pulse S has a voltage amplitude of ± V1 with respect to the reference voltage Vm, and the data pulse D has a voltage amplitude of ± V2 with respect to the reference voltage Vm. As the non-selection voltage applied to the scan electrode at the time of non-selection, two voltages having a potential of ± Vmo with respect to the reference voltage Vm are selectively used instead of the conventional reference voltage Vm.

Next, with reference to FIG. 3, a description will be given of a driving method for changing the non-selection voltage in the non-selection period shown in FIG. FIG. 3 illustrates an improvement made using the present invention to the conventional example shown in FIG. Here, for the various data pulses D output according to the gradation data in one scanning period, similarly to the description of FIG. 5, the high gradation data pulse represented by the waveform a (the post-step pulse a1 and the pre-step pulse a
2 and two types of low-gradation data pulses represented by the waveform b (the post-step pulse b1 and the post-step pulse b2 are mixed).

As described above, all the data pulses D in one scanning period are divided into the high gradation data pulse a and the low gradation data pulse b, and the ratio is obtained. The imbalance of the effective voltage is obtained, and a correction process is performed to eliminate the imbalance.
The correction of the imbalance of the effective voltage is performed by changing the non-selection voltage applied to the non-selection scanning electrodes.

As shown in FIG. 3A, when the number of high gradation data pulses a and the number of low gradation data pulses b are considered to be balanced for all data pulses in one scanning period, It is determined that there is no effective voltage difference due to the induced noise between the pixel (B) driven by the high gradation data pulse a and the pixel (C) driven by the low gradation data pulse b, and the non-selected scanning electrode Non-selection voltage + V applied to
mo and -Vmo are switched at an intermediate point in the scanning period. The switching between the non-selection voltages + Vmo and -Vmo does not increase or decrease the effective voltage.

Next, as shown in FIGS. 3 (2) and (3), 1
When it is considered that there is an imbalance in the number of high gradation data pulses a and low gradation data pulses b with respect to the data pulses in the scanning period, the pixel (B) driven by the high gradation data pulse a Between the pixels (C) driven by the low gradation data pulse b, the effective voltage due to the noise induced on the non-selected scanning electrodes according to the difference between the number of high gradation data pulses and the number of low gradation data pulses. Judge that there is a difference,
In order to correct this, the ratio of the non-selection voltages + Vmo and -Vmo applied to the non-selection scanning electrodes in one scanning period is determined by the number of high gradation data pulses a and the number of low gradation data pulses b
Change according to the difference between

When it is considered that the number of high gradation data pulses a is greater than the number of low gradation data pulses b in one scanning period,
As shown in FIG. 3B, the effective voltage of the pixel (B) driven by the high gradation data pulse a is increased.
The ratio of the non-selection voltages + Vmo and -Vmo applied to the non-selection scanning electrodes in one scanning period is changed so as to decrease the effective voltage of the pixel (C) driven by the low gradation data pulse b. As a result, the difference between the effective voltage of the pixel (B) driven by the high gradation data pulse a and the effective voltage of the pixel (C) driven by the low gradation data pulse b can be made zero, and the effective voltage difference Can prevent the occurrence of crosstalk.

When it is considered that the number of high gradation data pulses a is smaller than the number of low gradation data pulses b during one scanning period, as shown in FIG. The non-selection voltage + Vmo applied to the non-selection scan electrodes so that the effective voltage of the pixel (B) driven is reduced, while the effective voltage of the pixel (C) driven by the low gradation data pulse b is increased. And -Vmo in one scanning period. As a result, the difference between the effective voltage of the pixel (B) driven by the high gradation data pulse a and the effective voltage of the pixel (C) driven by the low gradation data pulse b can be made zero, and the effective voltage difference Can prevent the occurrence of crosstalk.

The status of the data pulse D is determined for each scanning period, and the non-selection voltage applied to the non-selected scanning electrodes varies according to the status. The status of the data pulse D can be determined, for example, by calculating the total of the gradation data in one scanning period. Since the gradation data is expressed by expressing the gradation in a numerical value, the gradation state of the data in one scanning period can be roughly determined by calculating the total of the gradation data. For example, when the ratio of the high gradation data pulse a increases, the total value of the gradation increases, and when the ratio of the high gradation data pulse a decreases, the total value of the gradation decreases. Can be determined based on the total value of the gradation data.

The state of the data pulse D is determined by comparing each gradation data in one scanning period with reference gradation data and allocating the data, and determining the ratio of data larger and smaller than the reference gradation. Can also be determined.

In the above embodiment, in order to compensate for the fluctuation of the effective voltage due to the induced noise, the amplitude of the non-selection voltage, which has been fixed conventionally, is changed. Although the ratio between the selection voltages + Vmo and -Vmo was changed during one scanning period, the non-selection voltage + Vmo
By switching between -Vmo and -Vmo in a cycle of one scanning period or more, it is possible to correct the fluctuation of the effective voltage due to noise.

The non-selection voltages are + Vmo and -Vmo.
Although two types are used, the present invention is not limited to this, and two or more types of multi-stage voltages may be used so that amplitude modulation can be performed in multiple stages, or the voltage can be varied continuously. Voltage may be used.

In the above embodiment, when the number a of high gradation data pulses is large, small, or equivalent,
Although the example in which the non-selection voltage is changed in three patterns to correct the effective voltage has been described, the ratio of the data pulse regarded as the high gradation data pulse a or the low gradation data pulse b is set to 3
The voltage correction value can be divided into a plurality of stages or more, and the voltage correction value can be changed in multiple stages according to the division.

The present invention is most effective in preventing crosstalk when the pulse width modulation of the preceding step and the trailing step are mixed as in the above embodiment. Even when the pulse width modulation is not mixed, for example, in the case of performing either one of the pre-step and the post-step pulse width modulation, it is effective in preventing the crosstalk.

[0030]

As described above, according to the driving method of the present invention, even when there is a variation in the gradation data, the effective voltage fluctuation caused by the fluctuation can be corrected by the voltage fluctuation of the non-selected scanning electrodes. Therefore, it is possible to provide a liquid crystal panel with less crosstalk and good display quality by maintaining the difference in effective voltage between pixels uniformly.

[Brief description of the drawings]

FIG. 1 is a voltage waveform diagram showing one embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an electrode structure of a liquid crystal panel.

FIG. 3 is a detailed voltage waveform diagram showing one embodiment of the present invention.

FIG. 4 is a voltage waveform diagram showing a conventional example.

FIG. 5 is a detailed voltage waveform diagram of a conventional example.

[Explanation of symbols]

 S selection pulse D data pulse Vm reference voltage + Vmo non-selection voltage -Vmo non-selection voltage

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Seiji Yamane 3-201 Minamiyoshikata, Tottori City, Tottori Prefecture Tottori Sanyo Electric Co., Ltd.

Claims (6)

[Claims] When driving a liquid crystal panel in which scanning electrodes and signal electrodes are arranged in a matrix, gradation display is performed by pulse width modulation of data pulses applied to the signal electrodes in accordance with gradation data. In the liquid crystal driving method,
A liquid crystal driving method characterized in that a non-selection voltage applied to a non-selected scanning electrode is varied according to a type of gradation data. 2. When driving a liquid crystal panel in which scanning electrodes and signal electrodes are arranged in a matrix, a data pulse applied to the signal electrodes is subjected to pulse width modulation in accordance with gradation data, and the pulse width modulation is performed. Is switched by a predetermined interval between a subsequent step based on the front side of the selection pulse and a previous step based on the rear side of the selection pulse, thereby controlling the period of the maximum voltage to be applied to the liquid crystal, thereby performing gradation display. A non-selection voltage applied to a non-selection scanning electrode is varied according to a type of gradation data. 3. A positive / negative non-selection voltage sandwiching a reference potential is used as the non-selection voltage.
3. The liquid crystal driving method according to claim 1, wherein a ratio in a scanning period is switched according to a type of the gradation data in one scanning period. 4. A positive / negative non-selection voltage sandwiching a reference potential is used as the non-selection voltage, and the positive / negative non-selection voltage is set to 1
3. The liquid crystal driving method according to claim 1, wherein the switching is performed in one or more scanning periods according to the type of the gradation data in the scanning period. 5. The liquid crystal driving method according to claim 1, wherein a total of gradations of the gradation data in one scanning period is obtained, and the non-selection voltage is varied based on a result. 6. A method of comparing each of the grayscale data in one scanning period with reference grayscale data, and changing the non-selection voltage according to the number of grayscale data that is higher or lower than the reference grayscale data. 3. The liquid crystal driving method according to claim 1, wherein: