JP3258092B2 - Driving method of matrix liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION Liquid crystal display devices are widely applied as low power consumption flat panel displays. Above all, a simple matrix system such as STN (super twisted nematic) is cheaper than an active matrix system, is capable of high-capacity, high-quality, and is widely used for information terminals such as personal computers and word processors. The present invention relates to a driving method of a simple matrix type liquid crystal display device capable of high contrast and high speed response.

[0002]

2. Description of the Related Art A simple matrix liquid crystal display device has a plurality of data lines and scanning lines and liquid crystal pixels provided at intersections of the data lines and scanning lines, and a scanning signal is applied to the scanning lines. Then, a data signal is applied to the data line.
Typical liquid crystal display modes capable of high multiplexing used in such a simple matrix include STN and E.
There is CB (electric field control birefringence mode). However, any of them has a drawback that increasing the number of divisions of the multiplex reduces the contrast and the response speed. In particular, the contrast and the response speed are in a trade-off relationship, and when one of them is improved, the other decreases. It has been clarified by the inventors that this cause is due to a “frame response”.
[Reference 1: Kaneko et al .. Proc. EuroDisplay'90,
p.100, 1990].

The conventional simple matrix system uses a single-line scanning method, and its disadvantage is that the higher the division, the more the electric energy applied to the liquid crystal pixels is concentrated in the selection period. In modes such as STN, the liquid crystal that basically responds with an effective voltage has the property of responding to a pulse. This property becomes stronger as the liquid crystal material having a faster response and the cell forming conditions are used. The "frame response" is a phenomenon based on the concentration of energy due to the single-line scanning and the nature of STN. If a high-speed response is aimed at with high division, the liquid crystal responds to a selection pulse for each frame, resulting in a significant loss of contrast. .

In recent years, as a method of reducing this “frame response”, an “active driving method” [Ref. 2: TJSheffe
r et al. SID 92 Digest, 228, 1992] and "MLS (multi-line scanning) method" [Reference 3: S. Ihara et al. S]
ID 92 Digest, 232, 1992] has been proposed. These are based on similar principles that have been proposed previously,
Each field period has a selection period in which a plurality of scanning lines are simultaneously selected, the scanning signal applied to the selected scanning line has a selection potential, and the scanning signals applied to the other scanning lines are The data signal applied to the data line has a non-selection potential, and has a potential based on the display content of the liquid crystal pixel at the intersection with the scanning line selected in each selection period. The difference between References 2 and 3 is that the former selects all lines simultaneously, while the latter selects partial lines simultaneously. However, since the concept is the same in principle, in the description of the present invention, M
This is referred to as an LS (multi-line scanning) method.

FIG. 3 is an example of a waveform diagram of the MLS method. For the sake of simplicity, an example in which the number of scanning lines is reduced and eight rows are selected simultaneously with four rows is shown. In the field period, eight selection periods t1 to t8 are provided. Odd number selection period t
At 1, t3, t5, and t7, the odd-numbered scanning signals φ1, φ
3, φ5 and φ7 have a selection potential ± a, and even-numbered scanning signals φ2, φ4, φ6 and φ8 have a non-selection potential 0. Similarly, in the even-numbered selection periods t2, t4, t6, and t8, the even-numbered scanning signals φ2, φ4, φ6, and φ8 have the selection potential ± a, and the odd-numbered scanning signals φ1, φ3, φ5, and φ7.
Has a non-selection potential 0. Subscript 0 of data signal 0
Indicates that all pixels are not lit, and the subscripts 1, 2 and the like indicate that the liquid crystal pixels of the first and second scanning lines are lit, respectively. The data signal ψ is obtained by multiplying the respective scanning signal potentials by -1 for lighting and +1 for non-lighting and taking the sum. Although there is an optimum value for the relative voltage ratio between the scanning signal and the data signal, the coefficient of the data signal is b in the figure. The signal applied to the liquid crystal pixel is obtained from the difference between the scanning signal φ and the data signal ψ as shown in the figure. In the figure, a = b = 1 is shown. Unlike the conventional single line scanning, the electric energy is dispersed because the selection period is dispersed.
This is a feature of the S method. Therefore, even if a liquid crystal material or a cell gap for high-speed response is used, "frame response" does not occur and the contrast does not decrease. The MLS type driving enables a contrast and a response speed equivalent to those of the active matrix system even in the simple matrix system.

Although the MLS method is very effective as described above, it has a disadvantage that the number of data signal potentials increases. For example, to select m scanning lines simultaneously, the number of potentials needs to be m + 1. In the example of FIG.
The data signal needs five potentials of 0, ± b, ± 2b.
In Reference 2, since all of the 240 scanning lines are simultaneously selected, 241 potentials are ideally required. However, there are too many, so only 64 potentials are used. Reference 2 describes that 64 lines are sufficient and have no effect on image quality. Certainly, image quality degradation is not so large stochastically. However, once the worst pattern or a pattern close to the worst pattern is displayed, very large crosstalk occurs.

FIG. 4 shows an example in which ± 2b of the potential of the data signal in the example of FIG. Of the data signals, # 1,2 are the same as the ideal values, but # 0 and # 1-8 have different shaded portions from the ideal values. The voltage applied to the liquid crystal pixels is ideal for the liquid crystal pixels on the data lines to which the data signals ψ1, 2 are applied, but deviates from the ideal value for the liquid crystal pixels on the data lines to which the data signals ψ0 and ψ1 to 8 are applied. . Assuming that a = b = 1 in the example of FIG. 4, the ideal effective voltages for one field are 1.414 and 1.0 for the lit pixel and the non-lit pixel, respectively.
00. However, these correspond to the worst patterns of 1.000 when φ1−ψ1 to 8 are applied to the illuminated pixels, and 0.707 when φ1−ψ0 is applied to the non-illuminated pixels. As described above, by omitting the number of potentials adopted in Reference Material 2, even if the pixel is a lit pixel or a non-lit pixel that should have the same gradation, it is 1.414 to 1.000 or 1.
Depending on the pattern, such as 000 to 0.707, a large voltage difference may occur, causing image quality degradation.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an MLS.
It is an object of the present invention to provide a method for driving a matrix display device using a method, which can reduce the number of potentials of a data signal and also suppress a problematic image quality deterioration.

[0009]

In order to achieve the above object, in the method of driving a matrix liquid crystal display device of the present invention, each field period has at least a compensation period, and a data line and a data line are connected during the compensation period. A data signal and a scanning signal are applied to the scanning lines so as to compensate for non-uniformity in the screen of the effective voltage for the same gradation applied to the liquid crystal pixels in each field period. That is, in a matrix liquid crystal display device including a plurality of data lines and scanning lines and liquid crystal pixels provided corresponding to intersections of the data lines and scanning lines, a scanning signal is applied to the scanning lines, and the data lines are applied to the data lines. A data signal is applied, and each field period has a selection period in which a plurality of scanning lines are simultaneously selected. When the potentials of the scanning signal and the data signal are defined based on a reference potential defined in the entire system, the selection is performed. The scanning signals applied to the scanning lines have a selection potential, the scanning signals applied to the other scanning lines have a non-selection potential, and the data signals applied to the data lines are in each selection period. driving how the matrix liquid crystal display device using the multi-line scanning method with a potential based on the display contents of the liquid crystal pixel at the intersection of the scanning lines selected
In the above, the number of potentials and the number of potentials less than the ideal potential number
And, and wherein in each field period includes a compensation period at least, the scanning lines and the data lines at the said compensation period screen of the effective voltage for the same gray level to be applied to the liquid crystal pixels in each field period A data signal and a scanning signal that compensate for the non-uniformity of the data are applied . Also,
When the number of scanning lines selected at the same time is m, the number of potentials based on the reference potential of the data signal is smaller than the ideal value m + 1, and when a potential different from the ideal value within one field period is selected, presence, number, and measuring at least one relationship between the selected potential and the ideal value, the data signal potential of the compensation period is characterized in that are compensated on the basis of the measurement results. Further, when the the number of the scanning lines m simultaneously selected, the potential number based on the said reference potential of the data signal is less than m + 1 of the ideal value, and an ideal value in a selected period of time within one field period If different potentials are selected to record the scanning signal potential and the data signal potential at the said selection period, the scanning signal potential and the data signal potential of the compensation period is characterized that it is set on the basis of the measurement result .

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 shows a block diagram of a matrix liquid crystal display device using the present invention. The matrix panel 4 is provided with a plurality of data lines 1 and a plurality of scanning lines 2 in a matrix, and liquid crystal pixels 3 are formed corresponding to the intersections. The data line 1 is connected to a data line driver 5 for supplying a data signal, and the scanning line 2 is connected to a scanning line driver 6 for supplying a scanning signal. A timing signal is supplied from the timing circuit 11 to each driver.
The feature of the MLS method lies in how to create a data signal. The data signal is obtained by multiplying the scanning signal potential by -1 if it is turned on and +1 if it is not turned on in each selection period to obtain the sum. This is nothing more than taking the exclusive OR of the potential pattern of the scanning signal and the display pattern and taking the sum as described in Reference 2. Therefore, the display pattern after the scan signal pattern supplied from the timing circuit and the data input 7 are once developed in the buffer memory 8 are exclusive ORed.
The calculation is performed by an (XOR) circuit 9, and the sum thereof is calculated by an addition circuit 10. A feature of the present invention resides in the compensation signal circuit 12. Prior to the description, a driving waveform will be described with reference to FIG.

FIG. 1 is an embodiment of a waveform diagram in the driving method of the present invention corresponding to FIGS. For simplicity of explanation, this is an example of simultaneous selection of four rows with eight scanning lines as in FIGS. In the field period, eight selection periods t1 to t8 are provided. The scanning signals in the selection period are the same as those in the examples of FIGS. 3 and 4. In the odd-numbered selection periods t1, t3, t5, and t7, the odd-numbered scanning signals φ1, φ3, φ5, and φ7 have the selection potential ± a. , Even-numbered scanning signals φ2, φ4, φ6, φ8
Has a non-selection potential 0. Similarly, in the even-numbered selection periods t2, t4, t6, and t8, the even-numbered scanning signals φ2, φ2
4, φ6 and φ8 have a selection potential ± a, and odd-numbered scanning signals φ1, φ3, φ5 and φ7 have a non-selection potential 0. The data signal during the selection period is the same as in the examples of FIGS. The feature of this embodiment lies in a compensation period t 'provided in the field period. In the main compensation period t ', the scanning signal takes a compensation potential. Although + a is taken in the embodiment of FIG. 1, it may be 0 or -a. Further, it may be changed, for example, to + a and -a within the compensation period. In the example of FIG. 1, the length of the compensation period is set to be the same as each of the selection periods t1 to t8, but may be different. Can be set. In the present embodiment, the number of potentials of the data signal is not the ideal value of 5 as in the example of FIG. The data signal potential in the compensation period t 'is set as follows in this embodiment. In FIG. 2, when the addition result of the addition circuit originally requires ± 2b in a certain selection period, the addition circuit 10 outputs 13 to select the data signal potential as ± b and sends a signal different from the ideal value. The compensation signal circuit 12
Send to This embodiment employs the simplest compensation. The compensation signal circuit has a 1-bit register,
It stores whether the value deviated from the ideal value at least once over the entire selection period. In the compensation period t ′, the data line driver does not use the output 13 of the adder circuit 10 but the compensation signal circuit 12.
In the compensation period of the field period which deviates from the ideal value one or more times, the potential of the data signal is -b which is opposite in phase to + a of the scanning signal potential, and is in phase if it has not been shifted once. Of + b.

In the embodiment of the present invention as described above, the voltage fluctuation in the same gradation state, which is a problem in FIG. 4, is considerably reduced. When a = b = 1, as shown in FIG. 4, the effective voltage of the lighting pixel fluctuates from 1.414 to 1.000 as described above.
The effective voltage of the non-lighted pixel also changed from 1.000 to 0.707. In this embodiment, the lighted pixel is 1.333 to 1.155, and the non-lighted pixel is 1.054 to 0.943.
And the difference is considerably reduced. This value can be further adjusted by the length of the compensation period and the potential to be taken as described above. Further, in the present embodiment, the measurement is performed only once or not to deviate from the ideal value one or more times. However, the number of times a potential different from the ideal value is selected may be measured to change the length of the compensation period or the potential. Further, the relationship such as the sign of the difference between the selected potential and the ideal potential may be measured and used as the data.

FIG. 5 is a waveform diagram of a driving method according to another embodiment of the present invention. In the embodiment of FIG. 1, the potentials of the scanning signals during the compensation period t 'were all common. However, different potentials are taken in the compensation periods t'1 and t'2 in this embodiment. The compensation signal circuit 12 in FIG. 2 has a plurality of registers differently from the embodiment of FIG. 1, and when the data signal potential deviates from an ideal value, the scanning signal potential and the data signal potential in the selected period. Measure and record The compensation period is set based on the recorded scanning signal potential and data signal potential. In the embodiment of FIG. 5, data signals # 0 and # 1 to # 8 deviated from the ideal values during the selection periods t1 and t2 were used. Therefore, the compensation signal circuit 12 records the scanning signal potential and the data signal potential in the selection periods t1 and t2, and uses the exact same potential as the scanning signal and the data signal in the compensation periods t'1 and t'2.

In the embodiment of the present invention as described above, the voltage fluctuation in the same gradation state, which is a problem in FIG. 4, is significantly reduced. When a = b = 1, 1.304 to 1.140 for a lit pixel and 1.000 to 0.70 for a non-lit pixel
The difference from 7 is considerably reduced. When the number of scanning lines is small as in FIG. 5, the effect is less than in the example of FIG. 1, but when the number of scanning lines is large, the effect is large. The method of this embodiment assumes that the probability of deviation from the ideal value within one field period is small and is within the number of small periods (2 in this embodiment) within the compensation period. If the frequency is higher, the effect is small. In the above embodiments, the potentials of the recorded scanning signal and data signal were used for the compensation period as they were, but some potentials were omitted,
A coefficient may be multiplied.

In the above embodiment, only the potential control is performed for both the scanning signal and the data signal during the compensation period. However, the pulse width control is also effective. Further, the potential inversion for reducing the low-frequency component of the voltage applied to the liquid crystal pixels and reducing the frequency bandwidth may be performed within the compensation period, within the field, or for each field. In the above embodiment, the case of selecting the partial scanning line has been described. However, the same applies to the case of selecting all the scanning lines as in the second embodiment. In this embodiment, a period such as t1 and t2 in which the stripe pattern of each row has the worst pattern is used, but a period corresponding to such a pattern having a high probability of occurrence may be omitted. Further, the pattern recorded in the buffer memory 8 of FIG. 2 and the potential pattern of the scanning signal are compared in advance, and if the correlation is strong, the potential pattern of the scanning signal may be changed or skipped.
Similarly, when the output of the adding circuit 10 corresponds to the omitted potential, the potential pattern of the scanning signal may be changed or skipped. In the compensation period of the present invention, correction of crosstalk based on the number of inversions of the scanning signal and the data signal, the difference between the number of inversions of the positive polarity and the negative polarity, the number of illuminated pixels and non-illuminated pixels due to the liquid crystal capacitance, and the like are added. You may.

[0016]

According to the present invention, not only the effect of reducing the "frame response", which is the advantage of the MLS method, can be sufficiently exhibited, but also the disadvantages due to the large number of potentials, such as an increase in the cost of the driver circuit, the power supply circuit and the like. It is possible to improve the complexity of the control circuit and reduce image quality deterioration due to a change in the voltage applied to the liquid crystal pixels depending on the display pattern, which is a problem in such a case.

[Brief description of the drawings]

FIG. 1 is a waveform chart in an embodiment of a driving method according to the present invention.

FIG. 2 is a block diagram in an embodiment of a matrix liquid crystal display device using the driving method of the present invention.

FIG. 3 is a waveform chart in an example of a driving method using the MLS method.

FIG. 4 is a waveform diagram in an example of a driving method using the MLS method in which the number of data signal potentials is omitted.

FIG. 5 is a waveform chart in one embodiment of the driving method of the present invention.

[Explanation of symbols]

 Reference Signs List 1 data line 2 scanning line 3 liquid crystal pixel 12 compensation signal circuit φ1 to φ8 scanning signal 〜0, ψ1,2, ψ1 to 8 data signal t1 to t8 selection period t ', t'1, t'2 compensation period

Claims (3)

(57) [Claims] 1. A matrix liquid crystal display device having a plurality of data lines and scanning lines and liquid crystal pixels provided at intersections of the data lines and scanning lines, wherein a scanning signal is applied to the scanning lines, and A data signal is applied to the line, and each field period has a selection period in which a plurality of scanning lines are simultaneously selected, and the potentials of the scanning signal and the data signal are defined based on a reference potential defined in the entire system. Sometimes, a scanning signal applied to a selected scanning line has a selection potential, a scanning signal applied to other scanning lines has a non-selection potential, and a data signal applied to a data line is In a driving method of a matrix liquid crystal display device using a multiline scanning method having a potential based on the display content of a liquid crystal pixel at an intersection with a scanning line selected in a selection period, the number of potentials is set to a number smaller than the ideal potential number. Potential of And said
Each field period has at least a compensation period.
During the compensation period, the data line and the scanning line have each field period
Of the effective voltage for the same gradation applied to the liquid crystal pixels within
Data signal and scan to compensate for non-uniformity in the screen
The driving method of a matrix liquid crystal display device, characterized in that device signals is applied. 2. The number of the scanning lines selected at the same time is m
When the number of potentials with respect to the reference potential of the data signal is smaller than the ideal value m + 1 and a potential different from the ideal value within one field period is selected, the presence / absence, number of times, and the selected potential measuring at least one relationship between the ideal value, the data signal potential of the compensation period the driving method of a matrix liquid crystal display device according to claim 1, characterized in that are compensated on the basis of the measurement results. 3. The number of the scanning lines selected at the same time is m
When the number of potentials of the data signal with respect to the reference potential is smaller than the ideal value m + 1, and a potential different from the ideal value is selected in a certain selection period within one field period, the number of potentials in the selection period is reduced. the driving method of the scanning signal potential and the data signal potential to the recording, scanning signal potential and the data signal potential of the compensation period matrix liquid crystal display device according to claim 1, characterized in that set on the basis of the measurement result .