JPH06294951A - Driving method for liquid crystal element - Google Patents

Abstract

PURPOSE:To provide a driving method for the liquid crystal element which can make a gradation display with a high contrast ratio even in the case of temperature variation. CONSTITUTION:When half-tones are displayed by the driving method of the liquid crystal element which is equipped with plural information lines and plural scanning lines and has liquid crystal arranged between a couple of substrates, one half-tone signal selected from among plural half-tone signals determined by the 1st relation between the impressed signal and transmissivity of some pixel is impressed to an information line and when a display showing minimum or maximum transmissivity is made, a signal determined by the 2nd relation between the impressed signal and transmissivity of some pixel which is different from the 1st relation is impressed to the information line.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal element which can be used as a display element used in a television receiver, a viewfinder of a video camera, a monitor for a terminal of a computer and the like.

[0002]

2. Description of the Related Art A passive matrix drive type liquid crystal display device using TN liquid crystal is known as a device which can be manufactured at a relatively low cost. This element has a limit in terms of crosstalk and contrast, and a passive matrix drive type liquid crystal display element using TN liquid crystal is not suitable for a display element having a high density wiring, such as a liquid crystal television panel. Hard to say.

Clark and Lagerwall are Applied Physi
cs Le Midtone ers Vol. 36, No. 11 (198
Issued June 1, 2000) P. 899-901, JP-A-56-
107216, U.S. Pat. No. 4,367,924, U.S. Pat. No. 4,563,059, etc.,
Surface-stabilized ferroelectric liquid crystal (Surface-stabi)
lised ferroelectric liqui
The bistable ferroelectric liquid crystal device has been clarified by d crystal. This bistable ferroelectric liquid crystal device has a chiral smectic C phase (SmC *), H
A vertical molecular layer in which a liquid crystal is arranged between a pair of substrates set at a sufficiently small interval to control the formation of a helical alignment structure of liquid crystal molecules in the phase (SmH *), and which is organized by a plurality of liquid crystal molecules. It was realized by arranging in one direction.

Further, such a ferroelectric liquid crystal (FLC)
For a display element using, US Pat. No. 4,639,
089, 4,655, 561, 4,681, 4
As shown in the specification No. 04, etc., 1 to 3 μm
There is known a liquid crystal cell in which a ferroelectric liquid crystal is injected into a liquid crystal cell which is formed by facing two glass substrates having a transparent electrode formed on the inner surfaces of the two inner surfaces with a cell gap maintained between them and subjected to an alignment treatment.

The characteristics of the above-mentioned display device using the ferroelectric liquid crystal are that the ferroelectric liquid crystal has a spontaneous polarization, so that the coupling force between the external electric field and the spontaneous polarization can be used for switching, and that the length of the ferroelectric liquid crystal molecule is long. The axial direction has a one-to-one correspondence with the polarization direction of the spontaneous polarization, so that switching can be performed depending on the polarity of the external electric field. That is, in the state of the chiral smectic phase, one of the first optical stable state and the second optical stable state is taken in response to the applied electric field, and when the electric field is not applied, the state is changed. It has a property of maintaining, that is, bistability, and has a rapid response to a change in an electric field, and is expected to be widely used in the fields of high-speed and memory type display devices and the like.

As described above, the ferroelectric liquid crystal is generally a chiral smectic liquid crystal (SmC *, SmH *), so that the long axis of the liquid crystal molecules is twisted in the bulk state. Twisting of the long axis of the liquid crystal molecule can be eliminated by putting it in the cell having the cell gap of the second position (P213-P234 N.A. CLARK).
et al, MCLC, 1983, Vol 94).

A liquid crystal display device having a display panel formed of such a ferroelectric liquid crystal element is based on, for example, the multiplexing driving method described in the above-mentioned Kanabe et al. US Pat. No. 4,655,561. By using it, an image can be formed on the display screen of large-capacity pixels. The liquid crystal display device described above is a word processor, personal
It can be used for display screens of computers, micro printers, televisions and the like.

The ferroelectric liquid crystal element has two stable states as a light transmitting state and a light blocking state and is mainly used as a binary (white / black) display element, but it is also capable of multi-valued or halftone display. One of the halftone display methods is to create an intermediate light transmission state by controlling the area ratio of bistable states in a pixel. Hereinafter, this method (area modulation method) will be described in detail.

FIG. 1 is a diagram schematically showing the relationship between the switching pulse amplitude and the transmittance of a ferroelectric liquid crystal device. A cell (device) that was initially in a completely light-blocking (black) state had a one-shot single polarity. 6 is a graph in which the amount of transmitted light I after applying a pulse is plotted as a function of the amplitude V of a single shot pulse. When the pulse amplitude is less than or equal to the threshold value V _th (V <V _th ), the amount of transmitted light does not change, and the transmission state after the pulse application is the state before the application as shown in FIG. 2 (b). Does not change. When the pulse amplitude exceeds the threshold value (V _th <V <V _sat ), a part of the pixel transits to the other stable state, that is, the light transmission state shown in FIG. 2C, and shows an intermediate amount of transmitted light as a whole. When the pulse amplitude further increases and becomes equal to or higher than the saturation value V _sat (V _sat <V), all the pixels are in the light transmitting state as shown in FIG. 2D, so that the light amount reaches a constant value. That is, in the area modulation method, the voltage is pulse amplitude V is V _th <V <V
_The halftone is displayed by controlling to _sat .

However, according to such a simple driving method, since the relationship between the voltage and the amount of transmitted light in FIG. 1 also depends on the cell thickness and the temperature, if there is a cell thickness distribution or a temperature distribution in the display panel, There is a problem that different gradation levels are displayed for the applied pulse of the same voltage amplitude.

FIG. 3 is a diagram for explaining this.
2 is a graph showing the relationship between the voltage amplitude V and the transmitted light amount I as in FIG. 1, but shows two curves, a curve H and a curve L, which respectively represent the relationships at different temperatures, that is, at high temperature and low temperature. That is, it is not uncommon for the temperature distribution arises in large display (display device), the same pulse (display portion) of the display size, therefore, even if an attempt to display a halftone at a certain voltage V _ap, 3 As shown, the halftone level varies over the range from I ₁ to I ₂ , and a uniform display cannot be obtained.

Then, it was conceived that the inventor of the present invention was granted US Pat. It is a "4-pulse method" filed on Apr. 8, 1991 as No. 681,993. As shown in FIGS. 4 and 5, this driving method uses a plurality of pulses for the low threshold portion and the high threshold portion on the same scanning line in the pulse (in FIG. 5,
By applying (A, B, C, D), the same inversion area is finally obtained as shown in FIG. 4 ((D) in FIG. 5).

The inventor of the present invention has further filed US Pat. 9
The specification filed on Dec. 2, 1992 as No. 84,694 proposes the "pixel shift method" in which the writing time is shorter than the "4 pulse method".

The pixel shift method is a method of inputting different scanning signals to a plurality of scanning signal lines at the same time and selecting the scanning signal lines to form a distribution of electric field intensity across a plurality of scanning lines to display a gradation. .

The outline of the pixel shift method will be described below.

The liquid crystal cell that can be used is one in which the threshold value within one pixel has a distribution, as shown in an example in FIG. In the cell shown in FIG. 6, the FLC layer 55 between the electrodes is
Since the layer thickness of is changed, the switching threshold of FLC also has a distribution. When the voltage applied to such a pixel is increased, switching is performed in order from the portion having the smallest cell thickness.

This state is shown in FIG. 7 (a). Figure 7
In (a), T ₁ , T ₂ , and T ₃ indicate the temperatures of the observed portion in the panel. The switching threshold voltage of the FLC decreases as the temperature increases, and the relationship between the applied voltage and the light transmittance at the above three temperatures is shown by three curves.

Although there are other causes of the threshold value fluctuation than the temperature change, the mode of the present invention will be described mainly by using the temperature change for convenience of explanation.

As can be seen from FIG. 7A, when the entire pixel is first reset to the dark state and a voltage of V _i is applied to the pixel at the temperature T ₁ , the transmittance of X% can be obtained.
When the temperature rises to T ₂ or T ₃ , when the same voltage of V _i is applied to the pixel, the transmittance becomes 100%, and the gradation display cannot be performed properly. Figure 7 (c)
Shows the inversion state of the pixel after writing at each temperature. Under such a condition, the written gradation information is lost due to the temperature change, so that the application range as a display element is extremely limited.

Therefore, as shown in FIG. 7D, by displaying the information of one pixel over the two scanning signal lines S1 and S2, it is possible to perform stable gradation display against temperature fluctuation. Become.

The driving method will be described in detail below.

Prepare a ferroelectric liquid crystal cell having a continuous threshold distribution in a pixel: Use a liquid crystal cell having a continuous cell thickness distribution in the pixel as shown in FIG. You can In addition, the applicant of the present invention has disclosed that
A configuration having a potential gradient in the pixel or a configuration having a capacitance gradient as proposed in Japanese Patent No. 215 may be used.
In any case, by continuously distributing the threshold values in the pixel, the region (domain) corresponding to the bright state and the region (domain) corresponding to the dark state can be mixed in the pixel, and the domain of these domains can be mixed. The area ratio enables gradation display.

This method can be used even when the light quantity is modulated stepwise (for example, 16 gradations), but for analog gradation display, it is more preferable that the light quantity change as continuously as possible.

Selecting two scanning signal lines at the same time: This operation will be described with reference to FIG. FIG. 8A shows
7 shows the transmittance-applied voltage characteristics when the pixels on two scanning signal lines are grouped together. In FIG. 8A, the transmittance of 0% to 100% is set as the display area of the pixel B on the scanning line 2,
The transmittance of 100% to 200% is shown as the display area of the pixel A on the scanning signal line 1. That is, since one scanning signal line constitutes one pixel, when two lines are simultaneously scanned, the transmittance is 200% when both the pixel A and the pixel B are in the light transmitting state. Here, two scanning signal lines are simultaneously selected for one gradation information, but an area having an area of one pixel is allocated to display one gradation information. This will be described with reference to FIG.

At the temperature T ₁ , the inputted gradation information is written in a range corresponding to 0% when the applied voltage V ₀ and ₁₀₀ % when the applied voltage V 100. As can be seen from the figure, at temperature T ₁ , this range (pixel area) is entirely on the scanning signal line 2 (see FIG. 8).
(See the shaded area in (b)). However, the temperature changes from T ₁ to T ₂
If the same voltage is applied to the pixel, a region larger than that at the temperature T ₁ is inverted when the same voltage is applied to the pixel.

In order to correct this, the pixel area at the temperature T ₂ is set over the scanning signal line 1 and the scanning signal line 2 (the hatched portion showing the case of the temperature T _{2 in} FIG. 8B). ).

Next, when the temperature further rises to T ₃ , the applied voltage is changed from V _{0 to} V _100, and the pixel region to be drawn is set only on the scanning signal line 1 (FIG. 8).
The shaded portion showing the case of the temperature T _{3 in} (b)).

As described above, by setting the pixel regions for gradation display depending on the temperature so as to be shifted on the two scanning signal lines, it is possible to maintain correct gradation display in the temperature range of T ₁ to T _3. become.

It is assumed that the scanning signals applied to the two scanning signal lines selected at the same time are different from each other: As described above, the threshold variation of the liquid crystal inversion due to the temperature change is 2
In order to compensate by simultaneously selecting two scanning signal lines, the scanning signals applied to the two selected scanning signal lines must be different from each other. This point will be described with reference to FIG. 7.

The scanning signals applied to the scanning signal lines 1 and 2 are set so that the thresholds of the pixels B on the scanning signal line 2 and the pixels A on the scanning signal line 1 continuously change. In FIG. 7B, the transmittance-voltage curve when the temperature is T ₁ indicates that the transmittance is displayed up to 100% in the region on the scanning signal line 2, and then 200% is scanned signal line. 1 is displayed in the upper area. In this way, the transmittance-voltage curve needs to be set continuously from the pixel B to the pixel A and with an equal gradient.

Therefore, as shown in FIG. 9, the scanning signal line 1
The cell shapes of the upper pixel A and the pixel B on the scanning signal line 2 (see FIG.
Even if (b) is set to be equal, substantially the same display as in the case where continuous threshold characteristics are given to the pixels A and B (cell in FIG. 7B) is possible.

[0032]

When gradation display is to be performed by the above-mentioned pixel shift method, a "white" reset (reset to maximize transmittance) and a "black" reset (transmission) are performed for each scanning line. It is desirable that the resetting (minimizing the rate) is alternately performed because the time for selecting one line can be shortened.

Therefore, for black display, there are two methods, that is, "white" is reset and then "black" is written, and "black" is reset and "white" is not written.

However, since the FLC response is very fast following the input pulse, it is 1 in the "white" reset pulse direction.
If you want to write to black immediately after resetting,
Although the final display state is black in all cases, light leakage cannot be ignored, as compared with the case of erasing in the “black” direction and not writing “white”.

Considering changes in contrast and gradation level due to reset in the "white" direction,
The contrast ratio when only “black” is reset is R _B = I _W
/ And I _B. Here, I _W is the amount of transmitted light in the “white” state, and I _B is the amount of transmitted light in the “black” state.

Paying attention to the "white" reset line when "white" and "black" are alternately reset for each scanning line,
When the white erasing time T _W within 1 second is calculated, 1 scanning time is H
And the frame frequency is f,

[0037]

[Equation 1] Becomes Therefore, the contrast ratio R _W is

[0038]

[Equation 2] Becomes When H = 100 μs and f = 15 Hz, the following table is obtained.

[0039]

[Table 1]

The decrease in contrast due to the "white" reset is about 10 as compared with the case where only the "black" reset is performed.
%It can be seen that it is.

The variation of the gradation level is 1 when "white" is 1.
There is a white leakage of 1.5 ms per second (0.15%), but even when 256 steps are taken as the gradation level, the amount of change in the light amount in one step is 0.39%, so "white"
Even if a reset is applied, the amount of change in the gradation level is small.

However, if the frame frequency f increases or the one scanning time H increases, the gradation level itself is affected.

The following table shows changes in contrast (R _BW ) when the reset direction is changed for each scanning line and the reset direction is changed for each frame as a scanning method.

[0044]

[Table 2]

It can be seen that the amount of change in contrast becomes 10% or less.

However, if the temperature changes at the time of writing in the pixel shift method (or if temperature unevenness occurs on the same panel), the contrast variation when the "white" reset is turned on cannot be ignored. That is, FIG.
In (d), as the temperature of the pixel increases from T _{1 to} T ₃ , the pixel is reset to “black” and “white” is not written on the pixel which should not have “white”.

FIG. 10 is a schematic diagram showing how the display state of pixels having different thresholds changes to explain this situation.

There are two pixels whose previous display state showed half the maximum transmittance as shown by R, that is, 50% transmittance.

First, a line erasing signal is applied to the scanning lines to bring all the pixels on the selected scanning line into the "black" state, and the pixels are brought into the "black" state as indicated by a ₁ and a ₂ . In this case, the line erasing signal is set so as to be "black" regardless of the potential of the information line.

Assuming that the applied signal is set with reference to the high threshold value, a signal V _{i1 having} a voltage that does not invert the state reset in the previous step in order to write "black" next time.
Is applied. Here, FIG. 11 is a graph showing the relationship between the logarithm of the voltage V applied to the pixel and the transmittance. With this V _i1 , the reference high-threshold pixel becomes “black” like b ₁ , but the low-threshold pixel shows a transmittance of, for example, 70% like b ₂ . This is the case when the "white" reset described above is entered.

Since this method is, of course, for compensating for such fluctuations, by applying a compensation signal in the next step, the same "black" state as c ₁ is obtained as shown by c _2. By returning, the final display state can be obtained.

Assuming that the low threshold pixel in FIG. 10 has a lower threshold value due to temperature rise and the like, b ₂ is in the “white” state (maximum transmittance). In this case, the “white” state display of b ₂ can also be regarded as a reset for displaying the next c ₂ .

That is, a predetermined time interval (leaving time) must be provided between the step b ₁ (b ₂ ) and the step c ₁ (c ₂ ) in order to stabilize the alignment of liquid crystal molecules. . For example, the standing time is 500 μsec.

Comparing the contrasts when there is no temperature change when the frame frequency is f and there is no temperature change when only the "black" reset is performed and the rest time is u and the reset direction is set for each line at each high temperature. Let R _u be the contrast ratio when changing

[0055]

[Equation 3] Becomes When f = 15 Hz and u = 500 μs,

[0056]

[Table 3] It can be seen that the contrast ratio is greatly reduced.

Regarding the variation of the gradation level, "white" is set to 1
Occurs as 0.0075. Assuming that the display level is divided into 256 levels, one level is 0.0039, and it can be understood that a variation of about 2 levels occurs in the level.

An object of the present invention is to solve the above-mentioned technical problem, and to provide a driving method of a liquid crystal element capable of suppressing a change in contrast due to a pixel or a temperature change.

[0059]

The present invention provides a method of driving a liquid crystal element having a plurality of information lines and a plurality of scanning lines and having a liquid crystal disposed between a pair of substrates,

When performing halftone display, one halftone signal selected from a plurality of halftone signals determined from the first relationship between the applied signal of a pixel and the transmittance is applied to the information line. Then

In the case of displaying with the minimum transmittance or the maximum transmittance, there is a second relationship between the applied signal of a certain pixel and the transmittance, which is determined from a relationship different from the first relationship. Is applied to the information line, and relates to a method for driving a liquid crystal element.

Furthermore, the present invention is a method of driving a liquid crystal display device, which comprises a ferroelectric liquid crystal sandwiched between two electrode substrates arranged facing each other,

When gradation display is performed by forming a threshold value distribution in a pixel, writing to a state formed by an erase pulse and writing to a state formed in the polarity direction of a writing signal and an intermediate state are performed. The present invention relates to a method for driving a liquid crystal element, which is performed by discontinuous modulation of a signal.

An embodiment of the present invention will be described with reference to FIG. FIG. 12 is for explaining a case where gradation writing is performed by the voltage modulation method. In FIG. 12A, the vertical axis represents the transmittance and the horizontal axis represents the voltage. When the horizontal axis is a log scale, the transmittance-applied voltage signal characteristic moves in parallel on the horizontal axis depending on the temperature.

In the figure, (I) is the response in the low temperature state as the high threshold state, and (II) is the response characteristic in the high temperature state as the lower threshold state. The first relationship and the second relationship are shown. Corresponding to. At low temperature, gradation is displayed between V ₂ and V ₃ , and at high temperature, gradation is displayed in the voltage range of V ₁ and V ₂ .

FIG. 12B shows how to set the voltage of each signal when gradation display is performed by applying a scanning signal and an information signal corresponding thereto to a pixel having such characteristics. It was FIG. 12B shows a conventional modulation method, in which the information signal is continuously variable in voltage from I ₀ to I ₁₀₀ .

The voltage value V _S of the scanning signal S is (V ₂ + V ₃ ) /
2 and set, by applying a _{V I0 = (V 3 -V 2} ) / 2 as an information signal, the V ₂ is applied to transmission to the pixel is 0%.

On the other hand, as an information signal, V _I100 =-(V _3-
When V ₂ ) / 2 is applied, V ₃ is applied to the pixel and the transmittance becomes 100%. Therefore, the information signal has a voltage range of [V
_I0 , V _I100 ], it becomes a signal capable of continuous gradation display.

However, when the temperature fluctuates and is driven by the above-mentioned pixel shift method or the like, 500 to 600 μs until the second writing while the high temperature pixels are written in the “white” direction in the first writing. The light is leaked at this time and the contrast is significantly reduced.

Therefore, when displaying black (transmittance 0%), the voltage of V ₁ is applied to the pixel, not the voltage of V ₂ . That is, in the range of V ₂ or more and V ₃ or less, continuous signal modulation is performed, and other than that, V ₁ not depending on the modulation is used.

By doing so, the time of being left "white" is eliminated by the principle peculiar to the pixel shift method in "black" display regardless of the low temperature and high temperature portions, and the contrast can be improved.

An example of such a drive waveform is shown in FIG.

The scanning signal is V _S = (V ₁ + V ₃ ) / 2, and the information signal V _i is voltage-modulated within the range of [O, − (V ₃ −V ₁ ) / 2]. In addition, V is displayed when "black" is displayed.
A voltage of ₁₀₀ = (V ₃ −V ₁ ) / 2 is applied.

By doing so, the low threshold pixel in FIG. 10 described above, which has been in the display state as shown by b ₂ in the related art, is shown by b ₃ according to the preferred embodiment of the present invention. It is possible to obtain various display states.

As described above, in the present embodiment, the halftone modulation signal determined from the first relationship (VT characteristic) between the applied signal and the transmittance of the pixel in a certain reference state and the pixel in another state. And a "black" signal, which is determined from another second relationship when placed in odor.

Also, instead of the minimum transmittance, b in FIG.
_When the transmittance of about 10% appears as in 4 and there is no problem, the other VT characteristics (dashed line (III) in FIG. 12)
V ₀₀ may be used as the “black” signal determined from

In general, the contrast is defined by the ratio of the minimum transmitted light amount and the maximum transmitted light amount, and is "black" for human senses.
If is equal, then the mid-level fluctuations are less noticeable.

Further, if the method of changing the erasing direction on the same line for each frame is adopted, the state between the first and second writing occurs alternately in each frame even in the high temperature portion, because "black" and "white" alternate. After all, 3 points of 0%, 50%, 100% are
Since the same amount of light can be obtained regardless of temperature,
Display quality can be greatly improved by ensuring that the "black" level is achieved.

As the gradation modulation signal for performing gradation display in the present invention, pulse width modulation for modulating the pulse width with a constant voltage is used in addition to the voltage modulation as described above. Furthermore, these may be combined and phase modulation as one of pulse width modulation may be used.

[0080]

FIG. 13 is a block diagram of a display device according to the present invention. FIG. 14 is a timing chart for explaining the control system of FIG.

The operation will be described below with reference to the drawings.
The graphics controller 102 displays the scanning line address information designating the scanning electrodes and the image information (PD0 to PD3) on the scanning lines designated by the address information on the display drive circuit (the scanning line drive circuit 104 and the information line) of the liquid crystal display device 101. It is configured by the driving circuit 105) and transferred to 104/105. In this embodiment, since the image information having the scanning line address information and the display information is transferred through the same transmission line,
The two types of information must be distinguished. The signal for this identification is AH / DL, and when this AH / DL signal is at the Hi level, it indicates that it is scanning line address information, and when it is at the Lo level, it indicates that it is display information. .

The scanning line address information is used for the liquid crystal display device 10.
The image information PD0 to PD on the side of the drive control circuit 111 in 1
After being extracted from the image information transferred as 3,
It is output to the scanning line driving circuit 104 at the timing of driving the designated scanning line. This scanning line address information is input to the decoder 106 in the scanning line driving circuit 104, and the designated scanning electrode of the display panel 103 is driven by the scanning signal generating circuit 107 via the decoder 106. On the other hand, the display information is guided to the shift register 108 in the information line driving circuit 105 and is shifted in units of 4 pixels by the transfer clock. When the shift register 108 completes the shift of one scanning line in the horizontal direction, the display information for 1280 pixels is transferred to the line memory 109 provided side by side, and is stored for one horizontal scanning period. It is output from the generation circuit 110 to each information electrode as a display information signal.

In the information signal generating circuit 110, for example, based on display information including gradation display data, a first information signal modulated based on a certain VT characteristic and a "black" first information signal based on another VT characteristic. And a circuit for generating two information signals. As a concrete example of the simplest configuration, a plurality of reference voltage levels as the first information signal and one reference voltage level as the second information signal are generated by the reference voltage generating circuit, and these are generated in the transfer switch. Then, the data is transferred to the pixel. At this time, the reference voltage level is V of the liquid crystal panel used.
The T characteristic may be measured in advance and the reference voltage level may be determined based on this VT characteristic.

Further, in this embodiment, the driving of the display panel 103 in the liquid crystal display device 101 and the generation of the scanning line address information and the display information in the graphics controller 102 are performed asynchronously. It is necessary to synchronize (101/102).
The signal that controls this synchronization is SYNC, which is generated in the drive control circuit 111 in the liquid crystal display device 101 every horizontal scanning period. The graphics controller 102 side is always S
The YNC signal is monitored, and if the SYNC signal is at the Lo level, the image information is transferred. On the contrary, when it is at the Hi level, the transfer is not performed after the transfer of the image information for one horizontal scanning line is completed. That is, in FIG. 13, when the graphics controller 102 detects that the SYNC signal has become Lo level, it immediately sets the AH / DL signal to Hi level and starts transferring image information for one horizontal scanning line. The drive control circuit 111 in the liquid crystal display device 101 has a SYNC
The signal is set to Hi level during the image information transfer period. After the writing to the display panel 103 is completed after a predetermined one horizontal scanning period, the drive control circuit (FLCD controller) 1
11 can return the SYNC signal to the Lo level again and receive the pixel information of the next scanning line.

As another example, a liquid crystal cell having a cross-sectional shape as shown in FIG. 6 was produced. In the figure, the saw-tooth shape of the lower substrate was made by making a master on a mold and transferring it to a glass substrate with an acrylic UV curing resin 52.

On the saw-shaped UV curable resin 52,
An ITO film is formed by sputtering as the stripe electrode 51,
Further, an alignment film LQ-1802 manufactured by Hitachi Chemical Co., Ltd. was formed as an alignment film 54 on the upper layer thereof to a thickness of about 300 Å.

The cell substrate on the opposite side is a stripe electrode 51.
The same alignment film is formed on the upper surface, and no uneven shape is provided.

The rubbing directions of the upper and lower substrates were parallel to each other, and the rubbing direction of the lower substrate was shifted by about 6 ° with respect to the rubbing direction of the upper substrate to form a cell. The cell thickness was controlled so that the thin portion was about 1.0 μm and the thick portion was about 1.4 μm. In addition, the stripe electrode 51 of the lower substrate was patterned in a stripe shape along the ridges so that one side of the saw shape was one pixel.

The width of the stripe electrode 51 was set to 300 μm, and the pixel size was set to a rectangle of 300 μm × 200 μm.

Table 4 shows the liquid crystal materials used.

[0091]

[Table 4]

The drive signals used in this embodiment are shown in FIG. S1, S2, S3 scanning signal waveform, the information signal waveform I is applied to certain information line which is applied to three scan lines of adjacent liquid crystal panels, S2-I is scanned applied scan signal S ₂ The voltage applied to the pixel at the intersection of the line and the information line to which the information signal I is applied is shown.

In FIG. 15, | Ve | = 18.0V, | Vs
| = 17.0V, | Vi | = 5.0V, Δt = 40μ
s, δ = 26 μs, t ₁ = 7 μs, t ₂ = 7 μs.

The modulation method of the information signal is a phase modulation method, and FIG. 16 (b) shows the modulation method of the information signal.

The voltage waveform changes from I (0%) to I (100
%) (Each is an information signal for displaying information in parentheses), and the pulse width of the portion A in the figure is variably modulated. The voltage signal with a width of δ is set to have write information. In the modulation of the portion A, the ratio of (the pulse width on the δ side) and (the pulse width on the side opposite to δ) is 1 / γ: (1-1
/ Γ).

The reason for setting such a ratio is to make the inversion threshold value continuous in the pixel to which the scanning signal A at the first writing and the scanning signal B at the second writing in FIG. 15 are applied. Here, the width of δ is the selection time Δ of the scanning signal A.
It is 1 / γ of T. This constraint also exists to maintain the continuity of the threshold. Here, ∂ indicates the slope, ∂T / ∂λ, where the vertical axis represents the transmittance (T) and the horizontal axis represents the modulation parameter (λ).

Here, the modulation parameter will be described. A graph showing the relationship between the transmittance T “%” and the modulation parameter λ is shown in FIG. In the case of adopting the modulation method as shown in FIG. 16, the scale of the horizontal axis is set to 1n, but this is for causing the change in the threshold value of the liquid crystal due to the temperature change to appear as parallel movement on the graph. Figure 1
In FIG. 7, the change of the selection voltage composite waveform A is within a range of 14 V rectangle (b)-(b-1) to 20 V rectangle, (b)-(b-3) of FIG. is there.

Then, by taking the time weighted with the voltage as the modulation parameter, the transmittance-lnλ characteristic becomes a straight line as shown in FIG.

The following describes how to perform weighting. The pulse length of the portion of the peak value V ₁ is t ₁ (added when divided into two) The pulse length of the portion of the peak value V ₂ is t ₂

[0100]

[Equation 4] Here, t ₁ + t ₂ = 40 μs, V ₁ = 14 V, V ₂ = 20
V

When such a method of determining λ is performed under the conditions of FIGS. 15 and 16, the selection voltage waveform is 32 at the portion of 10V.
From the L-shaped waveform of 8μ at μs and 22V,
By increasing the pulse width of the part, 40μ
A rectangular waveform of s, 22V is modulated up to 100% writing.

In this range, gradation display is performed and 10 V, 4
Use a pulse of 0 μs when displaying 0%.
This is the waveform formed by the I (0%) information signal in FIG.

The essential point of the present invention is that I (-0%) exists in the information signal in FIG.

From I (0%) to I (100%), the width of A in the information signal continuously increases.
(−0%) has a discontinuous shape with respect to these. This effect will be described with reference to FIG. 16A. In the figure, # 1 is the transmittance (T) -parameter (λ) characteristic line of the low temperature portion, and # 2 is the T-λ characteristic line of the high temperature portion. According to the temperature, the T-λ characteristic line has ln (λ) without changing its slope γ.
Translate on the axis. At this time, from λ = t ₁ to λ = t ₂ , the information signals I (0%) to I (100%) are used for writing, and the above-mentioned pixel shift method is used to correct the variation due to temperature. The key is displayed.

However, the pixel is "black" (0%).
In the case of t ₀ , I (−0%) is used as the information signal. By doing this, when 0% is displayed, 0% can be displayed regardless of the temperature. At this time, the principle of the pixel shift method described above is not substantially used. Therefore,
I (0%) does not mean 0%, but a gradation level moved from 0% to the white side by the minimum gradation level.

In the above description regarding the line of "black" erasure "white" writing, when the scanning line is "white" erasure "black" writing, discontinuous information is displayed at 100% display. A signal will be applied.

As described above, by using the discontinuous information signal modulation method, it is possible to realize high-quality gradation display with high 100% / 0% contrast.

[0108]

As described above, by using the present invention, it is possible to realize a high-quality gradation display having a high contrast ratio even when the temperature changes.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the relationship between voltage and transmittance in a conventional area modulation method.

FIG. 2 is a diagram showing a voltage and a light transmission state of a pixel in a conventional area modulation method.

FIG. 3 is a diagram showing a relationship at different temperatures in the relationship diagram of FIG.

FIG. 4 is an explanatory diagram of a conventional four-pulse driving method.

FIG. 5 is an explanatory diagram of a conventional four-pulse driving method.

FIG. 6 is a schematic view of a liquid crystal cell applicable to the present invention.

FIG. 7 is an explanatory diagram of a pixel shift method.

FIG. 8 is an explanatory diagram of a pixel shift method.

FIG. 9 is an explanatory diagram of a pixel shift method.

FIG. 10 is a schematic diagram for explaining a method of driving a liquid crystal element.

FIG. 11 is a graph showing the relationship between the applied voltage and the transmittance of a certain liquid crystal element.

FIG. 12 is a diagram for explaining the relationship between the applied voltage and the transmittance of the liquid crystal element used in the present invention.

FIG. 13 is a drive circuit block diagram applicable to the present invention.

14 is a timing chart for explaining the drive circuit of FIG.

FIG. 15 is a diagram showing a waveform of a drive signal used in an embodiment of the present invention.

FIG. 16 is an explanatory diagram of an information signal waveform according to an embodiment of the present invention.

FIG. 17 is a graph showing the relationship between the transmittance and the modulation parameter according to the example of the present invention.

Claims (7)

[Claims] 1. A plurality of information lines and a plurality of scanning lines are provided,
In a method of driving a liquid crystal element having a liquid crystal disposed between a pair of substrates, when performing halftone display, a plurality of halftone signals determined from a first relationship between an applied signal and a transmittance of a pixel. When one halftone signal selected from the above is applied to the information line and a display exhibiting the minimum transmittance or the maximum transmittance is performed, there is a second relationship between the applied signal and the transmittance of a certain pixel. A method for driving a liquid crystal element, characterized in that a signal defined by a relationship different from the first relationship is applied to the information line. 2. A reset signal for resetting a pixel is applied to the scanning line, and then a selection signal for writing is applied, and the halftone signal or the signal is synchronized with the selection signal. The method for driving a liquid crystal element according to claim 1, wherein any one of them is applied to the information line. 3. The method of driving a liquid crystal element according to claim 2, wherein a signal for compensation is applied to the pixel thereafter. 4. The method for driving a liquid crystal element according to claim 1, wherein the first relationship has a higher threshold characteristic than the second relationship. 5. The first relationship is a relationship when the pixel is placed under a certain temperature condition, and the second relationship is that the pixel is placed under a temperature higher than the temperature condition. The method for driving a liquid crystal element according to claim 1, wherein the relationship is when the liquid crystal element is broken. 6. A method of driving a liquid crystal element, which comprises a ferroelectric liquid crystal sandwiched between two electrode substrates arranged to face each other, wherein a threshold value distribution is formed in a pixel and gradation display is performed. ,
A method for driving a liquid crystal element, characterized in that writing into a state formed by an erase pulse and writing into a state formed in a polarity direction of a write signal and an intermediate state are performed by discontinuous modulation of an information signal. 7. The liquid crystal device according to claim 6, wherein the driving method is a line-sequential scanning method of writing after line erasing, and there is a scanning line whose erasing direction is in a “white” state. Driving method.