JPH06123870A - Method for driving matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To decrease the number of potentials of data signal and to suppress deterioration in image quality according thereto by providing a compensation term in each field term and impressing the data signal and a scanning signal so as to compensate the ununiformity in the screen with effective voltage for the same gradation to be applied to a liquid crystal pixel in a driving method using a multiline scanning method. CONSTITUTION:The figure shows an example of four rows simultaneous selection by eight pieces of scanning lines for explaining simply. Eight pieces of selection terms t1-t8 are provided in the field term and the scanning signal in the field term is similar to a conventional example. The scanning signal takes compensation potential in the compensation term t'provided in the field term. Though the signal takes +a in the example, may take 0 or -a. The potential of the data signal in the compensation term t' is not controlled by the output of an adder circuit but controlled by the output of a compensation signal circuit, and the potential takes -b of opposite phase to the scanning signal potential in the compensation term of the field interval when the data signal comes off from an ideal value of 0 and + or -b once or above and takes +b of the same phase when no signal comes off once.

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. Among them, the simple matrix system such as STN (Super Twisted Nematic) is cheaper than the active matrix system, but it is possible to have a large capacity and 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, the data signal is applied to the data line.
STN and E are typical liquid crystal display modes capable of high multiplex used in such a simple matrix.
There is CB (electric field control birefringence mode). However, both of them have a weak point that the contrast and the response speed decrease when the number of divisions of the multiplex is increased. In particular, the contrast and the response speed are in a trade-off relationship, and improving one of them reduces the other. It has been clarified by the inventors that the cause is a "frame response".
[Reference 1: Kaneko et al .. Proc. EuroDisplay'90,
p.100, 1990].

The conventional simple matrix method uses a single line scanning method, and its drawback is that the electric energy applied to the liquid crystal pixels is concentrated in the selection period as the resolution becomes higher. Further, in the STN mode or the like, the liquid crystal that basically responds with an effective voltage has a property of responding to a pulse. This property becomes stronger as the liquid crystal material having a quick response and the cell forming conditions are used. The "frame response" is a phenomenon based on the energy concentration due to this single line scanning and the property of STN, and when aiming for a high-speed response with a high resolution, the liquid crystal responds to a selection pulse for each frame, resulting in a significant loss of contrast. .

In recent years, as a method for reducing the "frame response", "active driving method" [Reference 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 before,
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 having a non-selection potential 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 is simultaneous selection of all lines, while the latter is simultaneous selection of partial lines. However, since the principles are the same, in the description of the present invention, M
It will be called the LS (multi-line scanning) method.

FIG. 3 is an example of a waveform diagram of the MLS method. For simplification of description, the number of scanning lines is reduced, and an example of simultaneous selection of 4 rows with 8 scanning lines is shown. Eight selection periods t1 to t8 are provided in the field period. Odd-numbered selection period t
At 1, t3, t5, and t7, odd-numbered scan signals φ1 and φ
3, φ5, φ7 have selection potentials ± a, and even-numbered scan signals φ2, φ4, φ6, φ8 have 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 of 0. Subscript 0 of data signal ψ
Indicates that all pixels are not lit, and subscripts 1 and 2 indicate that the liquid crystal pixels of the first and second scanning lines are lit. The data signal ψ is obtained by multiplying each scanning signal potential by −1 if it is lit and by +1 if it is not lit 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 set to b in the figure. The signal applied to the liquid crystal pixel is obtained as shown in the figure by the difference between the scanning signal φ and the data signal ψ. In the figure, it is shown as a = b = 1. Unlike conventional single-line scanning, ML has the point that electric energy is dispersed because the selection period is dispersed.
This is a characteristic 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. By the MLS type drive, even in the simple matrix system, the contrast and response speed comparable to those in the active matrix system are possible.

Although the MLS method is very effective as described above, it has a drawback that the number of data signal potentials increases. For example, if m scanning lines are selected at the same time, the number of potentials needs to be m + 1. In the example of FIG. 3 as well, the number of simultaneous selections is 4,
The data signal requires five potentials of 0, ± b, and ± 2b.
In Reference Document 2, ideally 241 potentials are required because all 240 scanning lines are simultaneously selected. However, since it is too much, only 64 potentials are used. In Reference Document 2, it is described that 64 lines are sufficient and the image quality is not affected. Certainly, the probability of image quality deterioration is not so great. However, once the worst pattern or a pattern close to it 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. 3 is omitted and three potentials are used. Of the data signals, ψ1, 2 are the same as the ideal values, but ψ0 and ψ1-8 are different from the ideal values in the shaded areas. The voltage applied to the liquid crystal pixels is ideal for the liquid crystal pixels of the data lines to which the data signals ψ1, 2 are applied, but deviates from the ideal value for the liquid crystal pixels of the data lines to which the data signals ψ0 and ψ1 to 8 are applied. . In the example of FIG. 4, assuming that a = b = 1, the ideal effective voltages in one field are 1.414 and 1.0 for the lit pixel and the unlit pixel, respectively.
00. However, even in the illuminated pixels, 1.000 when .phi.1-.psi.1 to 8 are applied, and 0.707 when .phi.1-.psi.0 is applied to the non-illuminated pixels, these correspond to the worst pattern. As described above, by omitting the number of potentials used in Reference Material 2, even if the pixel is a lit pixel or a non-lit pixel that should have the same gradation, 1.414 to 1.000 or 1.
Depending on the pattern, such as 000 to 0.707, a large voltage difference is generated and image quality is degraded.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is MLS.
In a method of driving a matrix display device using the method, it is possible to provide a method capable of reducing the number of potentials of a data signal and suppressing deterioration of image quality, which is a problem.

[0009]

In order to achieve the above object, in the driving method of the 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 provided in the compensation period. It is characterized in that a data signal and a scanning signal are applied to the scanning line so as to compensate the nonuniformity of the effective voltage applied to the liquid crystal pixels in each field period for the same gray level in the screen.

[0010]

Embodiments of the present invention will be described in detail below 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 at the intersections. A data line driver 5 for supplying a data signal is connected to the data line 1, and a scanning line driver 6 for supplying a scanning signal is connected to the scanning line 2. A timing signal is supplied from the timing circuit 11 to each driver.
A feature of the MLS method is how to create a data signal. The data signal is obtained by multiplying the scanning signal potential by -1 if the scanning signal potential is lit and by +1 if it is not lit in each selection period to obtain the sum. This is nothing but the exclusive OR of the potential pattern of the scanning signal and the display pattern and the sum of them, as described in Reference 2. Therefore, the scanning signal pattern supplied from the timing circuit and the display pattern after the data input 7 are once expanded in the buffer memory 8 are exclusively ORed.
The (XOR) circuit 9 operates and the sum is calculated by the adder circuit 10. The feature of the present invention lies in the compensation signal circuit 12, but the drive 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 simplification of description, an example of simultaneous selection of four rows with eight scanning lines is shown as in FIGS. Eight selection periods t1 to t8 are provided in the field period. The scanning signals in the selection period are similar to those in the examples of FIGS. 3 and 4, and in the odd-numbered selection periods t1, t3, t5, and t7, the odd-numbered scan signals φ1, φ3, φ5, and φ7 have the selection potential ± a. , Even-numbered scan signals φ2, φ4, φ6, φ8
Has a non-selection potential of 0. Similarly, in the even-numbered selection periods t2, t4, t6, and t8, the even-numbered scanning signals φ2, φ
4, φ6 and φ8 have the selection potential ± a, and odd-numbered scan signals φ1, φ3, φ5 and φ7 have the non-selection potential 0. The data signal in the selection period is also the same as in the example of FIGS. The feature of this embodiment resides in the compensation period t ′ provided in the field period. In the main compensation period t ′, the scanning signal has a compensation potential. Although + a is taken in the embodiment of FIG. 1, it may be 0 or -a. Further, it may be changed such as + 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 that of each selection period t1 to t8, but it may be different, and if necessary, from several times to several tens of times of each selection period t1 to t8. Can be set. In this embodiment, the number of potentials of the data signal is set to 3 by omitting ± 2b instead of 5 which is an ideal value as in the example of FIG. The data signal potential in the compensation period t'is set as follows in this embodiment. When the addition result of the adder circuit originally requires ± 2b in the selected period in FIG. 2, the adder circuit 10 outputs 13 to select the data signal potential as ± b and sends a signal different from the ideal value. Compensation signal circuit 12
Send to. This embodiment employs the simplest compensation. The compensation signal circuit has a 1-bit register,
It stores whether or not the deviation from the ideal value occurs once or more over the entire selection period. During the compensation period t ′, the data line driver is not the output 13 of the adder circuit 10 but the compensation signal circuit 12
Of the scanning signal potential, which is controlled by the output 14 of the output signal, deviates from -a, which is the opposite phase of + a of the scanning signal potential, in the compensation period of the field period, which is the same phase as the scanning signal potential. + B of

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, in FIG. 4, the effective voltage of the lit pixel changes 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, 1.333 to 1.155 for the lit pixels and 1.054 to 0.943 for the unlit pixels.
And the difference is significantly 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, only the deviation from the ideal value is measured once or more, but the length of the compensation period and the potential may be changed by measuring the number of times the potential different from the ideal value is selected. Further, the relationship such as the magnitude 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 ′ are all common. However, different potentials are taken during the compensation periods t'1 and t'2 of this embodiment. The compensation signal circuit 12 in FIG. 2 has a plurality of registers unlike the embodiment of FIG. 1, and when the data signal potential deviates from the ideal value, the scanning signal potential and the data signal potential in the selected period. Measure and record. In the compensation period, it is set based on the recorded scanning signal potential and data signal potential. In the embodiment of FIG. 5, the data signals .psi.0 and .psi.1-8 deviating 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 exactly the 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 considerably reduced. When a = b = 1, 1.304 to 1.140 for lit pixels and 1.000 to 0.70 for non-lit pixels.
The difference from 7 is considerably reduced. When the number of scanning lines is small as shown in FIG. 5, the effect is less than that 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 within the compensation period (2 in this embodiment). If the frequency is higher than that, the effect becomes small. In the above embodiments, the potentials of the recorded scanning signal and data signal were used as they were in the compensation period, but some potentials were omitted,
You may multiply by a coefficient.

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

[0016]

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

[Brief description of drawings]

FIG. 1 is a waveform diagram in an embodiment of a driving method of the present invention.

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

FIG. 3 is a waveform diagram 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 diagram in one embodiment of the driving method of the present invention.

[Explanation of symbols]

 1 data line 2 scanning line 3 liquid crystal pixel 12 compensation signal circuit φ1 to φ8 scanning signal ψ0, ψ1, 2, ψ1 to 8 data signal t1 to t8 selection period t ', t'1, t'2 compensation period

Claims (3)

[Claims] 1. A matrix liquid crystal display device having a plurality of data lines and scanning lines and liquid crystal pixels provided corresponding to 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 by the entire system. Sometimes, the scanning signals applied to the selected scanning line 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 have their respective selection potentials. In the driving method of the matrix liquid crystal display device using the multi-line scanning method having the potential based on the display content of the liquid crystal pixel at the intersection with the scanning line selected in the selection period, the compensation period is reduced in each field period. In addition, in the compensation period, the data line and the scanning line have a data signal for compensating the non-uniformity in the screen of the effective voltage for the same gray level applied to the liquid crystal pixel in each field period. A method for driving a matrix liquid crystal display device, wherein a scanning signal is applied. 2. When the number of simultaneously selected scanning lines is m, the number of potentials based on the reference potential of the data signal is smaller than the ideal value m + 1, and a potential different from the ideal value is selected within one field period. If it is, the presence or absence, the number of times, at least one of the relationship between the selected potential and the ideal value is measured,
The method of driving a matrix liquid crystal display device according to claim 1, wherein the data signal potential in the compensation period is compensated based on the measurement result. 3. 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 less than the ideal value m + 1, and the ideal value is set in one selection period within one field period. 7. When different potentials are selected, the scanning signal potential and the data signal potential in the selection period are recorded, and the scanning signal potential and the data signal potential in the compensation period are set based on the measurement result. 2. The method for driving the matrix liquid crystal display device according to 1.