JP2892951B2 - Display device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an AV (Audio V)
isal) equipment, Office Automation (OA)
The present invention relates to a display device such as a simple matrix type liquid crystal display device having a high-speed and large-capacity display surface, and a method of driving the display device.

[0002]

2. Description of the Related Art In recent years, with the progress of the advanced information society,
There is an increasing demand for a liquid crystal display device capable of displaying moving images while achieving both high contrast and high-speed response. The liquid crystal display panel provided in the liquid crystal display device is roughly classified into a simple matrix type and an active matrix type. Comparing the simple matrix type and the active matrix type, the simple matrix type liquid crystal display panel has a panel structure that is more simple. Because of the simplification, the manufacturing process is easy and the cost is advantageous.

[0003] By the way, a simple matrix type liquid crystal display panel capable of large-capacity display is provided between a pair of substrates.
TN (Super Twisted Nematic)
An STN liquid crystal display panel having a configuration in which liquid crystal is provided and a polarizing plate is provided outside both substrates is used. This structure will be described in more detail. A plurality of data electrodes (signal electrodes) parallel to each other are formed on one substrate, and an alignment film is coated thereon. On the other substrate, a plurality of scanning electrodes extending in a direction parallel to each other and perpendicular to the direction in which the data electrodes extend are formed, and an alignment film is coated thereon. In order to realize high contrast, a so-called STN liquid crystal in which liquid crystal molecules are twisted from about 180 degrees to about 270 degrees and a polarizing plate is combined is provided between these substrates.

Further, a STN liquid crystal display panel in which a phase compensator made of a liquid crystal or a polymer film is incorporated into the STN liquid crystal display panel has been commercialized. Such a structure is currently the mainstream of a simple matrix type liquid crystal display panel. It has become.

On the other hand, in order to improve the response characteristics of the liquid crystal display panel, a thinner liquid crystal layer and a lower viscosity of the liquid crystal material have been studied.
A liquid crystal display panel having a sub-ms period is being developed.

Normally, in a simple matrix type liquid crystal display panel, a line sequential scanning driving method is used in which each scanning electrode is sequentially selected one by one and a data signal is applied to a data electrode in synchronization with the selection. In this case, the repetition cycle (frame cycle) in which all data electrodes are selected is usually 20 ms or less.

However, the time τ of the sum of the rise time and the fall time of the liquid crystal is 15
When a high-speed response liquid crystal display panel smaller than 0 ms is driven, the liquid crystal deviates from the response to the original effective value, and the transmittance changes in response to the applied voltage waveform of the display pixel and the non-display pixel. This causes a so-called frame response phenomenon. In other words, the transmittance of the non-display pixel portion increases and the transmittance of the display pixel portion decreases, so that the contrast of the displayed image decreases and good display characteristics cannot be obtained.

Therefore, in recent years, the following two methods have been proposed as driving methods for suppressing the frame response phenomenon. One of them is an active addressing method (AAM method). This method uses WALS for the orthogonal function.
Using an H function or the like, a positive or negative voltage (1 or −1) derived from the H function is applied to all the scanning electrodes ( _F1 to F16) at a time as shown in FIG.
Are driven so that orthogonality is established (the inner product of the row vectors becomes 0) (TJ. Scheff).
er, et al. , SID'92, Digest,
p. 228, JP-A-5-100642 and others).

Another driving method is a sequence addressing method (SAT method). In this method, as shown in FIG. 23, one frame period is equally divided into a plurality of periods, a plurality of, in this example, four scanning electrodes are simultaneously selected in each period, and orthogonality is reduced in one frame period _TF . This is a method of driving so as to be established (TN Ruckmongat)
han et al. , Japan Display
92, Digest, p. 65, JP-A-5-46127
other).

[0010]

However, although the conventional AAM method and SAT method described above have the effect of improving the frame response phenomenon, they both have a large capacity buffer memory for storing a data signal for one screen. Is required. In the AAM method, since the scanning electrodes are simultaneously selected for all lines, the scale of the arithmetic circuit is increased.
There is a problem that the circuit configuration becomes large and the cost and power consumption increase.

Further, when the AAM method and the SAT method were applied to the driving of the above-mentioned high-speed response type liquid crystal display panel, and a display experiment was actually performed, the display information of one scanning electrode affected the display state of another scanning electrode. And it was found that the display became uneven. This poses a serious problem in terms of uniformity of image quality and gradation display.

By the way, the IHAT method (Improved) for simultaneously selecting a plurality of scanning electrodes to lower the voltage peak value.
Hybrid Addressing Techniq
ue) has been proposed by Ruckmongathan (1988, International Di).
spray Research Conference
e, p. 80-85). In this IHAT method, as shown in FIG. 24, one frame period T _F is equally divided into a plurality of periods, and L scanning electrodes in each period T, in this example, four scanning electrodes are simultaneously selected. This is a driving method in which orthogonality is established in a portion surrounded by a line in the figure.

By the IHAT method, two types of STN liquid crystal display panels whose response time τ of the liquid crystal display panel is 100 msec and 140 msec are driven.
An experiment was performed to evaluate display unevenness using ten types of display patterns as shown in J. As a result, although the contrast is reduced as a whole due to the frame response phenomenon, the degree of variation in the transmittance depending on the display pattern changes depending on the size of one block, that is, the number L of the simultaneously selected scanning electrodes. all right. This
26, in which the response time τ is 100 msec, and FIG. 27, in which the response time τ is 140 msec.

FIG. 26A shows a response time τ = 100 ms.
ec, the number of row scanning electrodes N = 200, the number of simultaneously selected scanning electrodes L = 100, and the transmittance characteristics when driven at a frame frequency F = 60 Hz. Transmissivity is plotted on the vertical axis and voltage is plotted on the horizontal axis. Is shown. As can be understood from this figure, there is a very large variation in transmittance depending on the display pattern.

FIG. 26B shows the number L of simultaneously selected scanning electrodes.
Is set to 50 lines, and the transmittance characteristics when driven as before are shown. As understood from this figure, the aforementioned L = 100
Compared with the case where the setting is made to the book, the variation in the transmittance due to the display pattern is greatly reduced.

FIG. 27A shows a response time τ = 140 ms.
ec, transmittance characteristics when the number of row scanning electrodes N = 200, the number of simultaneously selected scanning electrodes L = 100, and the frame frequency F = 60 Hz. As can be understood from this figure, the variation in the transmittance due to the display pattern is as shown in FIG.
It is smaller than the panel of FIG.

FIG. 27 (b) shows transmittance characteristics obtained by driving the scanning electrodes in the same manner as in FIG. 27 (a) by setting the number of simultaneously selected scanning electrodes L to 50. As can be understood from this figure, the variation in the transmittance due to the display pattern is smaller than that in FIG. 26B as in the case of L = 100 lines.

By the way, when the number L of simultaneously selected scanning electrodes is changed or when the response speed of the liquid crystal display panel is changed, the variation in transmittance due to the display pattern is improved as follows. Can be considered.

In general, the effective voltage value <Uij> of the dot (pixel) on the i-th row and the j-th column of the display pixel in the liquid crystal display panel.
Is given by the following equations (1) and (2).

[0020]

(Equation 2)

Here, <Uij> is the effective voltage value of the i-th row and the j-th column, Iij is the display data (ON is -1 and OFF is +1), _TF is one frame period. Is established, that is, when the dot product of the row vector becomes 0,
In the above two equations

[0022]

(Equation 3)

Becomes zero. Therefore, the display pattern Iij
Display unevenness due to the variation of the effective value due to the above. For example, in the display experiment described above, L = 50 lines, 1
In the case of 00 lines, the orthogonality between the scanning electrodes is established, and considering the time when the correlation term portion in the above two equations becomes zero, the scanning electrodes are connected at １ ／ and ２ of one frame, respectively. Is established, the portion of the correlation term shown in the second term becomes zero, and the variation of the effective value due to the display pattern is eliminated.

However, in the case of the high-speed response type liquid crystal display panel, the period in which the liquid crystal follows the cumulative response is much shorter than one frame period ( _TF ).
In the case of L = 100 lines having a long time until the orthogonality between the scanning electrodes is established, it is considered that large display unevenness occurs due to the display pattern.

The above result indicates that, from the driving principle, it takes one frame period for the orthogonality of the scanning electrodes to be established.
This indicates that this is an unavoidable problem in the AM method and the SAT method.

On the other hand, the IHAT method is based on the AAM method and the SA method.
This is advantageous in terms of display unevenness as compared with the T method. Also, AAM
Method and the SAT method, it is necessary to hold the display data for one frame period because the selection is repeated over one frame period. However, in the case of IHAT, the selection repetition range may be の or less of one frame. This is advantageous in terms of the buffer memory circuit scale. However, since the number of arithmetic circuits required is equal to the number of simultaneously selected scanning electrodes, the SAT
The arithmetic circuit scale tends to increase with respect to the method. Furthermore,
As with the AAM method, it is necessary to use an expensive analog driver for the data-side driver, and there is a problem in terms of cost and power consumption.

The present invention has been made to solve such problems of the prior art, and a display device capable of realizing high contrast and uniform display characteristics while suppressing a frame response phenomenon and display unevenness, and driving thereof. The aim is to provide a method.

[0028]

According to a method of driving a display device of the present invention, a plurality of mutually intersecting scan electrodes and data electrodes are provided, and a pixel is formed at each intersection of the scan electrode and the data electrode. Wherein the plurality of scan electrodes are divided into a plurality of blocks each having a smaller number of scan electrodes, and each block further includes a plurality of scan electrodes each having a smaller number. The scan electrodes of each block are sequentially supplied with a selection pulse train according to the orthogonal function for each group during a divided period obtained by dividing one frame period which is a period for displaying one screen. During the period, the voltage is applied at predetermined time intervals, and during the other periods, a voltage at a constant level is applied, and a voltage corresponding to the product sum of the orthogonal function and the display data is applied to the data electrode. To pressure, is performed for all blocks at different timings in one frame period, the object is achieved.

In the method of driving a display device according to the present invention, the number of the scan electrodes is N and the number of the data electrodes is M, and a voltage waveform applied to the i (1 to N) th row of the scan electrodes Is given by Fi (t), and j (1 to 1) of the data electrode
M) The voltage waveform applied to the column is

[0030]

(Equation 4)

When the proportional constant A is 1 / √
(N) <A ≦ {1 / {(N)} · 4.

In the display device driving method of the present invention, gradation display may be performed by frame modulation that changes the ratio of ON data to OFF data applied to the data electrode in a plurality of frames in accordance with display data.

In the display device driving method of the present invention, gradation display may be performed by pulse modulation for modulating the pulse width of a data signal according to display data.

In the method of driving a display device according to the present invention, gradation display may be performed by a combination of the frame modulation according to the third aspect and the pulse modulation according to the fourth aspect.

In the display device driving method according to the present invention, at least one of the scanning signal voltage applied to the scanning electrode and the data signal voltage applied to the data electrode is monotonically increased every time the application period of the selection pulse is started. The voltage waveforms may be monotonically decreased after the reduction, or may be monotonically decreased and then monotonically increased to obtain the voltage waveforms of the respective predetermined effective values.

In the method of driving a display device according to the present invention, a detection electrode is provided in parallel with the scanning electrode, and a scanning signal voltage applied to each scanning electrode is changed from an original scanning signal voltage to that of the detection electrode. A voltage waveform having a difference from the potential can be used.

The display device of the present invention is a simple matrix type display panel in which a plurality of mutually intersecting scan electrodes and data electrodes are arranged, and pixels are formed at the intersections of the scan electrodes and the data electrodes. And, the plurality of scan electrodes are divided into a plurality of blocks of a smaller number of scan electrodes, and each block is further divided into groups of a smaller number of a plurality of scan electrodes. In a divided period obtained by dividing one frame period which is a period for displaying one screen, a selection pulse train according to an orthogonal function is sequentially applied to each group, and applied at predetermined time intervals within the divided period. During a period of one frame, it is required to apply a voltage corresponding to a sum of the orthogonal function and the display data to the data electrodes while applying a voltage which is at a constant level during the period. ; And a driving means for performing for all blocks by shifting the timing, the object can be achieved.

[0038]

According to the driving method of the present invention, for example, as shown in FIG. 1, 16 scan electrodes (F1 to F16) are divided into smaller four blocks indicated by L, and each block is further divided. The group is divided into a group of a smaller number of a plurality of scan electrodes (upper two lines and lower two lines of L), and the following processing is performed.

During a divided period (T) obtained by dividing one frame period ( _TF ), which is a period for displaying one screen, a selection pulse (1 or -1) according to an orthogonal function is applied to the scanning electrodes of each block. Columns are sequentially applied to each group, and are applied at predetermined time intervals (の of T) within a divided period (T), and a voltage of a constant level (0) is applied during other periods. Applying a voltage corresponding to the product sum of the orthogonal function and the display data to the data electrodes is performed on all the blocks at a shifted timing in one frame period (T _F ). FIG. 1 shows only one example of the driving method of the present invention.

By the above processing, the above-mentioned signal waveform is applied to each pixel for one frame period (T _F ), and one screen is displayed.

Accordingly, in the case of the driving method of the present invention, the time required for the orthogonality to be established is the divided period (T), and the AAM method in which one frame period is required and the orthogonality between the scanning electrodes is established. And the time until the orthogonality is established is shorter than in the SAT method. For this reason, even in a display panel having a high response speed, uniform and high-contrast display characteristics in which display unevenness due to the above-described causes is suppressed can be realized. Further, since the above-mentioned display unevenness can be suppressed, it is very advantageous in performing gradation display.

Although the SAT method and the AAM method require a buffer memory for one frame in terms of the driving principle, according to the driving method of the present invention, the capacity of the SAT method and the AAM method is less than 1/2 of the capacity used in the SAT method and the AAM method. Since it can be realized with a buffer memory, it is very advantageous in terms of circuit size and cost. Further, while the operation scale of the AAM method is equal to the number of all the scanning electrodes, the circuit scale of the present invention can be realized by the number of the simultaneously selected scanning electrodes, which is very advantageous.

In the driving method according to the present invention, FIG.
As shown in (1), the selection pulse applied to the scan electrode is applied in a plurality of times in the T period, so that the circuit configuration (arithmetic circuit, orthogonal function generation circuit, etc.) is greatly simplified as compared with the IHAT method. And power consumption can be reduced.

Further, since the number of voltage levels of the data side driver increases in proportion to the number of simultaneously selected scanning electrodes, an expensive analog driver is required to realize the IHAT method and the AAM method. In the case of the driving method described above, only a few scanning electrodes can be selected at the same time.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.

FIG. 2A is a block diagram showing a liquid crystal display device according to one embodiment of the present invention. This liquid crystal display device 10
Includes a liquid crystal display panel 1. The liquid crystal display panel 1
It has N scanning electrodes 9 and M data electrodes 8, and each of the electrodes 9 and 8 has a scanning driver 2
And the data side driver 3 are connected. The scanning driver 2 outputs a signal potential of + Vr or -Vr when selected, and outputs a constant potential, for example, a signal potential of 0 volts when not selected, based on the orthogonal function data from the orthogonal function generation circuit 4. This potential output is performed in a state shown in FIG. 1 described above or FIG. 28 described later.

On the other hand, display data from the outside is once L
The data is stored in the buffer memory 5 having a capacity corresponding to the selected one of the scanning electrodes 9. The EX-OR circuit 6 selects the selected K in one block including L scan electrodes.
The K-bit output data corresponding to the scan electrode 9 and the K-bit function data from the orthogonal function generation circuit 4 are input, and the two data are compared. The adder circuit 7 calculates the total number of bits where both data do not match. The result is sent to the data side driver 3 and k + 1 voltages (VC1 to VC1) generated by the proportionality constant setting circuit 15 based on the data.
Ck + 1) is selected and simultaneously output to each data electrode 8 as a data signal voltage at predetermined time intervals.

By performing data processing and voltage application for one frame as described above, the input display image pattern is reproduced on the screen of the liquid crystal display panel 1. Further, the liquid crystal display device 1 to which the driving method of the present invention is applied
For 0, the proportional constant setting circuit 15 for increasing the contrast is used as described above. The proportional constant setting circuit 15 can be configured to include amplifier circuits 15a and 15b such as an operation amplifier (operational amplifier) as shown in FIG. 2B, and the variable resistor 1 shown in FIG.
By changing 5c, the amplification factor can be arbitrarily set. FIG. 2D shows an example of a driving waveform of the scanning driver, and FIG. 2E shows an example of a driving waveform of the data driver. In FIG. 2, VDD
Is a power supply voltage, VH and VL are selection voltage levels of the scanning side driver, VM is a non-selection voltage level, and VC1 to VCk + 1 are output voltage levels of the data side driver.

The driving pattern that can be used in the present invention is not limited to the above-described FIG. 1, but includes the number of scanning electrodes L in one block and the number of scanning electrodes K to be simultaneously selected from the L scanning electrodes. Alternatively, it is possible to use a pattern in which the number of blocks for all the scanning electrodes or the number of divisions of one frame period _TF into a plurality is changed. An example will be described below.

FIG. 28 shows that the number of scanning electrodes N = 240,
An example of a function used for orthogonal transformation of a display pattern when the block size L is 120 and the number of simultaneously selected scanning electrodes K is 7 is shown. In this case, the number of groups per block is 18, and the division period T corresponding thereto is 14
It is divided into four selection pulse application periods. FIG. 29
Is used to generate a selection pulse train to be added to a period obtained by dividing one frame period in the driving example shown in FIG.
8 shows an eighth-order WALSH function.

Further, in consideration of the image quality, the components of the WALSH function can be replaced for each row and each column, and the sign of + or-can be replaced for each row.

(Embodiment 1) In this embodiment, an STN in which the response time τ is 100 msec and the number N of row scanning electrodes is 240
The number of scanning electrodes L included in one block of the liquid crystal display element is L =
Under the conditions of 120 lines, frame frequency F = 60 Hz, and 1/8 bias, driving was performed with different numbers of simultaneously selected scanning electrodes K.

FIG. 3 shows the relationship between the number K of simultaneously selected scanning electrodes and the contrast when the display state of the upper one line of the liquid crystal display panel is white or black display and the remaining pixels are all white display. . As can be understood from this figure, a characteristic in which the contrast is almost saturated is obtained when the number of simultaneously selected scanning electrodes is K = 4 or more.

By the way, the magnitude of K should be made as small as possible because it greatly affects the circuit scale and cost. However, as L becomes smaller, the scanning side drive amplitude voltage tends to increase. It is necessary to determine the number K of simultaneously selected scanning electrodes in consideration of the withstand voltage of the driver and the like.

(Embodiment 2) In this embodiment, an STN in which the response time τ is 100 msec and the number N of row scanning electrodes is 240
The liquid crystal display element is divided into a case where the number L of scanning electrodes included in one block is 120 and 60, and the number of simultaneously selected scanning electrodes K = 7, the frame frequency F = 60 Hz, and the proportional constant A is changed. Driven.

FIG. 4 shows the proportional constant A in that case.
The relationship between (horizontal axis) and contrast (vertical axis) is shown. As can be understood from this figure, according to the optimum bias method, the maximum contrast should be obtained around A = 1/16, but the peak value of the contrast is optimum bias at both L = 60 lines and 120 lines. It is around 1/8 which is larger than the value. Even when the proportionality constant A is 1/4, the contrast is higher than when A = 1/16.

Therefore, in the present invention, the number of scan electrodes is N, the number of data electrodes is M, and i (1
To (N) th row is given by Fi (t), and the voltage waveform applied to the j (1 to M) th column of the data electrode is

[0058]

(Equation 5)

When given by:
1 / {(N) <A ≦ {1 / {(N)}}.

(Embodiments 3 to 5) Next, the response time τ
= 100 msec, number of row scanning electrodes N = 240 ST
An example of a measurement result of optical characteristics in a case where the number of scanning electrodes L included in one block is 60 and 120 and the driving is performed according to the embodiment of the present invention and a case where the scanning electrode is driven by the SAT method using an N liquid crystal display element. And Examples 3 to 5 below. The display state was changed in seven lines at the upper part of the liquid crystal display panel as shown in FIG. 5, and the remaining pixel portions were displayed in all white. In addition, the orthogonal functions were exchanged in the column direction and the row direction, and three kinds of distribution states of bias voltages were virtually created. In this case, the number of simultaneously selected scanning electrodes K is 7
Book, frame frequency F is 60 Hz, proportional constant A is 1/8
And

(Embodiment 3) The present embodiment relates to the case of a drive waveform for ON display in a state where the bias voltage is concentrated.
6 and 7 show the case where the driving method according to the present invention is used. FIG. 6 shows the case where the number L of scanning electrodes included in one block is 60, and FIG. 7 shows the case where the number L of scanning electrodes is 120. .
FIG. 8 shows a case where a driving method based on the SAT method is used. The patterns A to H shown in FIGS. 6A, 7A, and 8A are the cases of the display patterns of the columns A to H in FIG. 5 described above.

In the SAT method, as shown in the drive voltage waveform of FIG. 8A, depending on the display data, the bias voltage concentrates on one portion of one frame depending on the drive principle. This causes a decrease in the overall contrast due to the frame response phenomenon. Further, it can be seen that the transmittance varies due to the display pattern due to the orthogonality of the function.

However, when the driving method according to the present invention is used, the driving waveform becomes 1 as shown in FIGS.
Since the light is dispersed in the frame, a decrease in contrast due to a frame response phenomenon can be suppressed as compared with the SAT method.
Furthermore, when the driving method according to the present invention is used, the period until the orthogonality of the function is established is shorter than that of the SAT method.
It can be seen that variations in transmittance due to the display pattern can be suppressed {see FIGS. 6 (b), 7 (b) and 8 (b)}.

(Embodiment 4) In this embodiment, a drive waveform for ON display in a state where the bias voltage is dispersed is described.
9 and 10 show the case where the driving method according to the present invention is used. FIG. 9 shows the case where the number L of scanning electrodes is 60, and FIG. 10 shows the case where the number L of scanning electrodes is 120. FIG. 11 shows SA
This is a case where a driving method based on the T method is used. Note that FIG.
Patterns A to H shown in FIGS. 10A, 10A, and 11A are the display patterns of the columns A to H in FIG. 5 described above.

In this embodiment, FIGS. 9 (a) to 11 (a)
As shown in the driving waveform of FIG. 7, the bias voltage is dispersed as compared with the third embodiment.

In this case, the contrast tends to increase as a whole no matter which driving method is used.
(A), when the driving method according to the present invention shown in FIG. 10 (a) is used, the reduction in contrast and display unevenness are smaller than in the case of the SAT method shown in FIG. 11 (a). b), FIG. 10 (b) and FIG. 11 (b)}.

(Embodiment 5) The present embodiment relates to a drive waveform for ON display in a state where the bias voltages are evenly distributed within one frame. 12 and 13 show the case where the driving method according to the present invention is used. FIG. 12 shows the case where the number L of scanning electrodes is 60, and FIG. 13 shows the case where the number L of scanning electrodes is 120. FIG. 14 shows a case where the driving method based on the SAT method is used. 12 (a), FIG. 13 (a), FIG.
4A are patterns A to H shown in FIG.
This is the case of the display patterns of the columns H to H.

In this embodiment, FIGS. 12 (a) to 14 (a)
As shown in the driving waveforms of the above, the bias voltage is almost uniformly distributed over one frame.

In this embodiment, in the case of the SAT method shown in FIG. However, since the bias state actually changes from the bias state shown in the third embodiment to the bias state shown in the present embodiment depending on the display data, the dispersion of the transmittance due to the display pattern due to the orthogonal function and the frame response Intense display unevenness occurs due to a synergistic effect of a change in transmittance due to the phenomenon (see FIG. 14B).

However, when the driving method of the present invention shown in FIGS. 12 (a) and 13 (a) is used, even when the bias voltage is concentrated as shown in the third embodiment, the bias is applied to one frame. Since the voltage is dispersed, variation in transmittance due to the frame response phenomenon can be suppressed {see FIGS. 12 (b) and 13 (b)}. In addition, since the period until the orthogonal function is established is shorter than the SAT method on the driving principle, it is possible to suppress display unevenness depending on the display pattern due to the orthogonality of the function.

(Embodiment 6) In this embodiment, a response time τ of 100 msec and the number of row scanning electrodes N = 380 STNs
The number of scanning electrodes L included in one block of the liquid crystal display element is L =
Driving was performed in the bias distribution state of Example 5 with 60 scanning electrodes, the number of simultaneously selected scanning electrodes K = 7, frame frequency F = 60 Hz, and 1/8 bias.

As a result, as in the case of N = 240 lines, almost no variation in transmittance due to the display pattern was observed.

(Comparative Example) When the STN liquid crystal display element of Example 6 was driven by the SAT method with the number of simultaneously selected scanning electrodes K = 7, the ON display transmittance was about 10% and the OFF display transmittance was depending on the display pattern. The variation was about 3%.

(Embodiment 7) The case of binary display has been described above. In this embodiment, a case of performing gradation display by changing the pulse width of a data signal will be described.

FIG. 15 shows a function used for orthogonal transformation of display data when four gradation display is performed according to this embodiment, and FIG. 16 shows an example of display data at that time.

In this embodiment, one of the divided periods (T) is used.
The pulse width for a fixed period (1H) of / 4 is divided into three,
As shown in FIG. 15B, the display data of the gradation level is 1,-.
The combination with the orthogonal function shown in FIG. 15A is performed at the timing of 1/3 of one horizontal period, the result is sent to the data side driver, and the data input to the driver is
The data signal is sent to the data driver every ３ scanning period, and the data signal voltage is output all at once.

FIG. 16B shows an example of a driving waveform when a gray scale level as shown in FIG. 16A is displayed. G1 (t) in FIG. 16 indicates a data signal voltage.

As can be understood from this figure, by performing data processing and voltage application for one frame,
Good display corresponding to the inputted gradation display pattern can be reproduced on the liquid crystal display panel.

(Eighth Embodiment) In this embodiment, several frames are
And the number of frames for ON display and OF
By changing the ratio to the number of frames for displaying F,
This is a case where an intermediate level between ON and OFF is displayed.

FIGS. 17A and 17B show functions used for orthogonal transformation of a data pattern in 4-gradation display.
FIG. 18B shows an example of a driving waveform when a gradation level as shown in FIG. 18A is displayed. G1 (t) in FIG. 18 indicates a data signal voltage.

In this embodiment, three frames are considered as one group, and the display data of four gradation levels is shown in FIG.
By displaying the combination of 1 and -1 as shown in (b) and changing the ratio between ON and OFF in three frames, it is possible to realize good display characteristics of four gradations.

(Embodiment 9) This embodiment is a case where gradation display is performed by combining the pulse width gradation described in Embodiment 7 and the frame gradation described in Embodiment 8.

In general, with the increase in the number of gradations, the frame gradation causes display flickering, and the pulse width gradation causes display unevenness due to an increase in high frequency components. When the multi-gradation display is performed by appropriately combining the frame gradations, the drawbacks of both methods can be complemented, so that good gradation display characteristics can be realized in which flicker and unevenness of display are suppressed.

When driving the STN liquid crystal display device according to the present embodiment, it is possible to suppress display unevenness caused by the orthogonal condition which is a problem in the above-described AAM method and SAT method. Better gradation display characteristics can be realized.

(Embodiment 10) This embodiment is intended to reduce display unevenness caused by superimposing a spike-like distortion voltage waveform induced on a scanning electrode via the capacitance of a liquid crystal layer on a scanning signal voltage. The method is described.

The liquid crystal display device is equivalently constituted by an RC series circuit comprising capacitance via a liquid crystal layer, wiring resistance of scanning electrodes and data electrodes, and output resistance of scanning drivers and data drivers. Thus, it can be considered as a differentiating circuit that passes only the voltage change.

When the data signal voltage applied to the data electrode changes, as shown in FIG. 19, a spike-shaped distortion voltage waveform (Sp) differentiated via the capacitance of the liquid crystal layer is applied to the scanning electrode. And is superimposed on the scanning signal voltage (Y1 in the illustrated example). Then, such a distorted voltage waveform (Sp) causes a difference in the effective voltage value applied to the pixel, resulting in display unevenness.

Therefore, as shown in FIG. 21, at least one of the scanning signal voltage applied to the scanning electrode by the scanning driver and the data signal voltage applied to each data electrode by the data driver is changed to the selection pulse of the selection pulse as shown in FIG. Each time the application period starts, the distortion voltage is suppressed by first monotonically increasing and then monotonically decreasing (convex), or first monotonically decreasing and then monotonically increasing (concave). Furthermore, display distortion can be eliminated by detecting only a distortion voltage with a detection electrode described later and performing distortion correction on the scanning signal voltage.

FIG. 20 shows a configuration example of a liquid crystal display device provided with the drive circuit of this embodiment. The liquid crystal display panel 1 includes a plurality of scanning electrodes 9 and a plurality of data electrodes 8 that intersect each other, and a strain detection electrode 10 is provided in parallel with the scanning electrodes 9. The scanning driver 9 is connected to the plurality of scanning electrodes 9, the data driver 3 is connected to the plurality of data electrodes 8, and the distortion correction circuit 11 is connected to the distortion detecting electrode 10.

The scanning driver 2 and the data driver 3 receive output signals from the display control circuit 12. The display control circuit 12 includes a buffer memory, an orthogonal function generation circuit, an EX-OR circuit, and various timing signal generators, and outputs a predetermined signal to each of the drivers 2, 3, and the like. This display control circuit 12
The sine wave generation circuit 13 receiving the output from the sine wave generates a voltage based on two kinds of sine wave signals.

The distortion correction circuit 11 provided on the output side of the sine wave generation circuit 13 includes a capacitor C, a resistor R4,
R5 and an amplifier 6a. Amplifier 6a
A signal passing through a circuit in which a capacitor C and a resistor R5 are connected in series and a signal passing the output of the amplifier 6a through a resistor R4 are input to the minus terminal. Further, the signal {spike-shaped distortion voltage waveform (Sp)} detected by the distortion detection electrode 10 is input to the capacitor C. On the other hand, the + terminal of the amplifier 6a is connected to the output terminal of the sine wave generation circuit 13 or the ground. Therefore, the distortion correction circuit 11 outputs the two types of voltages and 0
Based on the volt voltage (ground voltage) and the spike-shaped distortion voltage waveform (Sp) detected by the distortion detection electrode 10, a signal partially having a reverse potential signal for canceling the distortion voltage. And outputs the output signal to the scanning driver 2.

The scanning driver 2 outputs a voltage waveform to each scanning electrode 9 based on the signal from the distortion correction circuit 11 and the orthogonal function data from the display control circuit 12. On the other hand, the data side driver 3 includes a sine wave generation circuit 1
The multi-valued voltage obtained by further dividing the two types of voltage waveforms generated in step 3 by resistance division is supplied via a buffer circuit 14, and the data signal voltage is changed in the display control circuit 12 in accordance with the operation data orthogonally transformed. LCD panel 1
Is output to each data electrode 8. As a result, the difference voltage between the scanning voltage and the data voltage is applied to the liquid crystal display panel 1, and the data conversion process and the data voltage application for one frame period are completed, so that the display pattern is displayed on the liquid crystal display panel 1. Will be reproduced.

FIG. 21 is a waveform diagram of the scanning signal voltage and the data signal voltage in the liquid crystal display device having such a configuration.
FIG. 21 shows a case where the number N of scanning electrodes is 8, the size L of the block is 4, and the number of simultaneously selected lines is 2.

As can be understood from this figure, the waveform of each scanning signal voltage is modified so that the voltage waveform according to the orthogonal function changes irregularly every application period of the selection pulse. Also, since the distortion correction circuit 11 performs distortion correction so as to cancel the distortion voltage induced in the detection electrode 10, no distortion voltage waveform appears.

As described above, when the voltage waveform of the scanning signal voltage or the data signal voltage applied to the scanning electrode or the data electrode changes gradually in the form of irregularities, the pixel voltage becomes smaller than that in the case where the voltage changes sharply in the form of a square pulse. The change in the distortion voltage of the differential waveform generated at the electrode that opposes via the capacitance can be extremely small. Since such a sharp waveform distortion does not occur, distortion correction can be reliably performed even if a circuit element having a relatively slow response speed is used for the distortion correction circuit.

Although the sine wave is used in the tenth embodiment, the shape of the unevenness of the voltage waveform that can be used in the present invention is not limited to this. For example, in the case of a convex shape, during the application period of the selection pulse, the voltage first monotonically increases with the passage of time without temporarily decreasing and reaches a maximum value, and thereafter the time without temporarily increasing. The shape may be any shape as long as it changes so as to monotonously decrease with the passage of time, such as a half cycle of a sine wave, a semicircle, a semipolygon, or a triangle. Further, this shape is preferably symmetrical with respect to a point in time at which the application period of the selection pulse is divided into two, but is not limited to this.

In the above description, a liquid crystal display panel in which liquid crystal is interposed as a display medium between a pair of substrates has been described as an example. However, the present invention is not limited to this. It can be applied to display panels in general.

[0098]

As described above, according to the present invention, in an STN liquid crystal display device having a high-speed response, the frame response phenomenon is suppressed even when an image is displayed at a normal frame frequency (about 60 Hz). It is possible to realize uniform and high-contrast display characteristics in which display unevenness caused by the AAM method, the SAT method, or the like is suppressed.

Also, the driving method according to the present invention requires only a small number of scan electrodes, and therefore requires only a small buffer memory (1/2 or less compared to the SAT method and the AAM method) and a small arithmetic circuit. The effect of being advantageous in cost and power consumption was obtained.

Although an expensive analog driver is required to realize the IHAT method and the AAM method, the driving method according to the present invention requires only a few scan electrodes to be simultaneously selected, so that an inexpensive multilevel There is an effect that it can be realized by the driver of (1).

[Brief description of the drawings]

FIG. 1 is a diagram showing an orthogonal function used in the present invention.

FIG. 2 is a diagram showing a configuration of a drive circuit and a proportional constant setting circuit according to an embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the number k of simultaneously selected scanning electrodes and contrast according to the present invention.

FIG. 4 is a diagram showing a relationship between a proportionality constant A and a contrast for each scanning electrode number L included in one block of the present invention.

FIG. 5 is a diagram showing display patterns used for optical measurements of Examples 3 to 5.

FIG. 6 (a) shows a state where bias voltages are concentrated when the size L of a block according to the present invention is set to 60;
FIG. 7B is a diagram illustrating a driving waveform of N display, and FIG. 7B is a diagram illustrating transmittance characteristics in the bias state of FIG.

FIG. 7 (a) shows a block size L of the present invention set to 120.
FIG. 7B is a diagram showing a drive waveform of ON display in a state where bias voltages are concentrated in a case where the bias voltage is concentrated, and FIG. 7B shows a transmission waveform in the bias state of FIG. It is a figure which shows a rate characteristic.

FIG. 8A is a diagram illustrating a drive waveform of ON display in a state where bias voltages are concentrated in the case of the SAT method;
(B) is a diagram showing the transmittance characteristics in the bias state of (a) in the case of the SAT method.

FIG. 9A shows O in a state where the bias voltage is dispersed when the size L of the block of the present invention is set to 60;
FIG. 7B is a diagram illustrating a driving waveform of N display, and FIG. 7B is a diagram illustrating transmittance characteristics in the bias state of FIG.

FIG. 10A shows a case where the size L of the block according to the present invention is 12;
FIG. 4B is a diagram showing a drive waveform of ON display in a state where bias voltages are dispersed when zero blocks are used.
FIG. 4 is a diagram showing transmittance characteristics in a bias state of FIG.

FIG. 11A is a diagram showing a drive waveform of ON display in a state where bias voltages are dispersed in the case of the SAT method;
(B) is a diagram showing the transmittance characteristics in the bias state of (a) in the case of the SAT method.

FIG. 12A shows a case where the size L of the block according to the present invention is 60;
FIG. 7 is a diagram showing ON display drive waveforms in a state where bias voltages are evenly distributed within one frame in the case of the present embodiment.
(B) is a diagram showing transmittance characteristics in the bias state of (a) when the size L of the block of the present invention is set to 60.

FIG. 13A shows a case where the block size L of the present invention is 12;
FIG. 9 is a diagram showing ON display drive waveforms in a state where bias voltages are evenly distributed within one frame when 0 lines are used;
(B) is a diagram showing transmittance characteristics in the bias state of (a) when the size L of the block of the present invention is 120.

14A is a diagram showing a driving waveform of ON display in a state where bias voltages are uniformly distributed within one frame in the case of the SAT method, and FIG. 14B is a diagram showing a driving waveform of the SAT method in the case of the SAT method;
FIG. 3A is a diagram illustrating transmittance characteristics in a bias state of FIG.

15A is a diagram showing an orthogonal function used in gradation display for modulating a pulse width in the present invention, and FIG. 15B is a diagram showing display data of four gradations used in gradation display for modulating a pulse width in the present invention; FIG.

FIG. 16 is a diagram showing a driving waveform of pulse width gradation display in the present invention.

17A is a diagram showing an orthogonal function used in gradation display by frame modulation according to the present invention, and FIG. 17B is a diagram showing display data of four gradations used in gradation display by frame modulation in the present invention. is there.

FIG. 18 is a diagram showing a driving waveform of gradation display by frame modulation in the present invention.

FIG. 19 is a diagram showing a spike-like distortion voltage or the like induced on a scanning electrode when a driving voltage waveform is a rectangular pulse.

FIG. 20 is a block diagram illustrating a configuration of a liquid crystal display according to a tenth embodiment of the present invention.

FIG. 21 is a diagram illustrating a liquid crystal display according to a tenth embodiment of the present invention, and is a diagram illustrating waveforms of a scanning signal voltage and a data signal voltage.

FIG. 22 is a diagram showing an example of an orthogonal function used in the AAM method.

FIG. 23 is a diagram showing an example of an orthogonal function used in the SAT method.

FIG. 24 is a diagram showing an example of an orthogonal function used in the IHAT method.

FIG. 25 is a diagram showing a display pattern used for the optical measurement in FIGS. 26 and 27.

26A is a diagram showing transmittance characteristics when a liquid crystal display panel having a response time τ of 100 msec is driven by the IHAT method with 100 simultaneously selected lines L, and FIG. In a 100 msec liquid crystal display panel, the number L of simultaneously selected lines is 5 by the IHAT method.
FIG. 9 is a diagram illustrating transmittance characteristics when the driving is performed with zero lines.

27A is a diagram showing transmittance characteristics when a liquid crystal display panel having a response time τ of 140 msec is driven by the IHAT method with the number of simultaneously selected lines L being 100, and FIG. In a 140 msec liquid crystal display panel, the number of simultaneously selected lines L is 5 by the IHAT method.
FIG. 9 is a diagram illustrating transmittance characteristics when the driving is performed with zero lines.

FIG. 28 is a diagram for explaining another driving example that can be used in the present invention.

FIG. 29 illustrates an eighth-order WALSH function used to generate a selection pulse train to be added to a period obtained by dividing one frame period in the driving example illustrated in FIG. 28;

[Explanation of symbols]

 Reference Signs List 1 liquid crystal display panel 2 scanning side driver 3 data side driver 4 orthogonal function generation circuit 5 buffer memory 6 EX-OR circuit 7 addition circuit 8 data electrode 9 scanning electrode 10 distortion detection electrode 11 distortion correction circuit 12 display control circuit 13 sine wave Generation circuit 14 Buffer circuit 15 Proportional constant setting circuit

──────────────────────────────────────────────────続 き Continuation of front page (72) Kunihiko Yamamoto 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) References JP-A-6-67628 (JP, A) JP-A-6-676 138853 (JP, A) JP-A-7-287552 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/133 545

Claims (8)

(57) [Claims] 1. A driving method of a simple matrix display device, wherein a plurality of mutually intersecting scan electrodes and data electrodes are respectively wired, and pixels are formed at respective intersections of the scan electrodes and the data electrodes. The plurality of scan electrodes are divided into a plurality of blocks of a smaller number of scan electrodes, and each block is further divided into groups of a smaller number of a plurality of scan electrodes. During a divided period obtained by dividing one frame period, which is a period for displaying one screen, a selection pulse train according to an orthogonal function is sequentially applied to each group, and is applied at predetermined time intervals within the divided period. It is necessary to apply a voltage corresponding to the sum of the orthogonal function and the display data to the data electrode at the same time as applying a voltage at a constant level to the data electrode during one frame period. The driving method of a display device that performs for all blocks by shifting the grayed. 2. The method according to claim 1, wherein the number of the scanning electrodes is N and the number of the data electrodes is M, and a voltage waveform applied to the i-th to (n) th rows of the scanning electrodes is given by Fi (t). , The voltage waveform applied to the j-th (1-M) th column of the data electrode is Where the proportionality constant A is 1 / √ (N) <A ≦
The method for driving a display device according to claim 1, wherein the method is selected from a range of {1 / {(N)} · 4 ”. 3. The driving method of a display device according to claim 1, wherein gradation display is performed by frame modulation that changes a ratio between ON data and OFF data applied to the data electrode in a plurality of frames in accordance with the display data. 4. The method for driving a display device according to claim 1, wherein gradation display is performed by pulse modulation for modulating a pulse width of a data signal according to display data. 5. The frame modulation according to claim 3 and claim 4.
The driving method of a display device according to claim 1, wherein gradation display is performed by a combination with the pulse modulation. 6. A scanning signal voltage applied to the scanning electrode,
And at least one of the data signal voltages applied to the data electrodes, each time the application period of the selection pulse starts,
The method according to any one of claims 1 to 5, wherein the voltage waveform is monotonically increased and then monotonically decreased, or monotonically decreased and then monotonically increased to obtain voltage waveforms having respective predetermined effective values. 7. A detection electrode is arranged in parallel with the scanning electrode, and a scanning signal voltage applied to each scanning electrode is set to a voltage waveform of a difference between an original scanning signal voltage and a potential of the detection electrode. The method for driving a display device according to claim 1. 8. A simple matrix type display panel in which a plurality of mutually intersecting scan electrodes and data electrodes are respectively wired, and pixels are formed at respective intersections of the scan electrodes and the data electrodes; The scan electrodes are divided into a plurality of blocks of a smaller number of scan electrodes, and each block is further divided into groups of a smaller number of a plurality of scan electrodes,
During a divided period obtained by dividing one frame period, which is a period for displaying one screen, a scanning pulse of each block is sequentially supplied with a selection pulse train in accordance with an orthogonal function for each group, and a predetermined time is set within the divided period. In each frame, a voltage corresponding to the sum of the orthogonal function and the display data is applied to the data electrodes while applying a voltage that is a constant level during the other periods. And a driving unit for shifting all the blocks.