JP2609586B2 - Liquid crystal display - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a smectic A phase.

[Conventional technology]

In the conventional display device driving method, the SII
Digest (1985), pp. 124-127 (SID
85 DIGEST (1985) pp124-127)
Once the entire display screen is erased, the display data is written using a drive waveform by a voltage averaging method or the like.

[Problems to be solved by the invention]

In the above-mentioned conventional driving method, when the screen is rewritten, the screen cannot be displayed unless the entire screen is always erased, so that it is difficult for the user to see. Also, as a driving method,
Since a driving method based on a conventional voltage averaging method or the like is used, since there are three or more levels of voltage sources, there is a disadvantage that this circuit type becomes complicated and circuit cost increases.

An object of the present invention is to provide a display device that is easy for a user to see and to provide a driving method that can reduce the cost of the driving circuit.

[Means for solving the problem]

The above object is achieved by selecting an effective value and / or an effective frequency of an applied voltage to be applied to a liquid crystal display, and setting a light transmission state, a light selection state, and a state in which these are held. Achieved.

Further, in the line-sequential scanning drive of the matrix display device, one scanning period of the driving voltage waveform is divided into a high-frequency voltage and a low-frequency voltage application time zone having the same voltage level, and the row electrode and column electrode driving waveforms are respectively different. This is achieved by having a selection and non-selection voltage waveforms having different phases from each other, and driving using a combination of these voltages and a memory property of the liquid crystal element.

[Action]

The present invention is based on the following facts newly discovered by the present inventors.

The liquid crystal exhibiting the smectic A phase changes its optical characteristics depending on the effective frequency and the effective value of the applied voltage.
There is a so-called electric field optical effect. This effect is shown in FIG. FIG. 2 shows an alignment state of liquid crystal molecules,
(A) is a light transparent state, (b) is a light scattering (white turbidity) state. In FIG. 2, the effective value V _S and the frequency
_When the voltage of _S is applied, the light scattering state, effective value V _W , frequency
_When a voltage of _W is applied, a transparent state of light is exhibited, and display becomes possible by this binary state. Note that this binary state
It is maintained unless the voltage application state is changed.

By the way, if this effect is represented by the frequency on the horizontal axis and the reflected light intensity B on the vertical axis, the result is as shown in FIG. In FIG. 3, (I) shows the -B characteristic when the liquid crystal element is changed from the transparent state to the scattering state, and (II) shows the -B characteristic when the liquid crystal element is changed from the scattering state to the transparent state. In this example, representative of the voltage and frequency reflected light intensity B is saturated scattering state and V _S and _S, the voltage and frequency to the transparent state as V _W and _W. Here f _s and f _w and f shown in FIG. 3, respectively
-The frequency at the intersection of the extension line of the slope line of the -B characteristic and the state line reaching saturation. These characteristics change in both (I) and (II) depending on the effective values V _S ′ and V _W ′ of the applied voltage as shown in (I) ′ and (II) ′, respectively.

From the characteristics of FIG. 3, when the frequency of the applied voltage and the application condition of the effective value for scattering and clearing the liquid crystal element are obtained,
As shown in FIG. The first area (S) in FIG. 4 is a driving area in which the applied voltage for setting the light scattering state is an effective value and a frequency, and the area (W) in FIG. 2 is a light transmitting state. Region for driving the effective value and frequency of the applied voltage. The third region (N) deviating from this region does not change the alignment state of the liquid crystal even when a voltage is applied, and maintains the previous scattering or transparent state. For example, when the effective value of the applied voltage is set to V ₀ and the frequency is changed, when the value is ₁ , the light is scattered, and when the value is ₂ , the light is in a transparent state. When the effective value of the applied voltage is V 'and the frequency is', the alignment state of the liquid crystal does not change.

FIG. 10 shows the relationship among the frequency-luminance characteristic, frequency-comparative electric power characteristic, and frequency-effective value characteristic of the liquid crystal.

The characteristics shown in FIG. 4 vary depending on the liquid crystal material, the orientation of the device, and the like.

From FIG. 4, the condition of the frequency and the effective voltage at which the liquid crystal exhibiting the smectic A phase exhibits the electro-optic effect can be modeled as shown in FIG.

The horizontal axis in FIG. 5 is the frequency of the applied voltage, and the vertical axis is the effective value V of the applied voltage. In Figure 5, the first region (S) is a condition of the frequency _S and Denko value V _S to the liquid crystal layer in scattering state and the second region (W), a transparent liquid crystal layer state _Is the condition of the frequency _W and the effective value VW to make The region of FIG. 3 (N) is a condition of a frequency _N and the effective value V _N that does not contribute to any state of the scattering and transparent.

Since the liquid crystal exhibiting the smectic A phase has a memory property, once a voltage that satisfies the driving conditions of the first region (S) and the second region (W) is applied, the liquid crystal is scattered and becomes transparent. Except for the driving condition, the vehicle is kept in the previously forward-facing state for a long time. That is, when a display device is driven by using this liquid crystal, a selected pixel is scattered by applying a voltage and / or an effective value that satisfies the region (S) or the region (W) during the selection period. Alternatively, if the device can be driven to be transparent so that a voltage having a frequency and / or an effective value in the third region (N) is applied outside the selection period, display is possible.

〔Example〕

FIG. 6 is a configuration example of a matrix display device using the present invention.

In FIG. 6, 1 is a liquid crystal matrix panel,
As in the conventional liquid crystal matrix display device, a known liquid crystal exhibiting a smectic A phase is sealed between two glass substrates coated with a plurality of row electrodes 2 and a plurality of column electrodes 3. The pixel at the intersection of the row electrode 2 and the column electrode 3
The display is made by scattering (S) or transmitting (T) light of P _ij . In this embodiment, for the sake of simplicity, the description will be made using an example of a 2 × 3 matrix, and the display will be as shown in the figure.

The row electrode 2 and the column electrode 3 are connected to a row electrode drive circuit 4 and a column electrode drive circuit 5, respectively. They are,
The multiplexer group 6 selects one of the two channels.

The selection voltage signal V _XS is input to one end of the multiplexer of the row electrode drive circuit 4, and the non-selection voltage signal V _XNS is input to the other end of the multiplexer. V _YS and the non-selection voltage signal V _YNS are input.

FIG. 1 shows a state diagram of these voltage signals. V _X is the row electrode signal and V _Y is the column electrode signal. In the pixel unit _Pij , one scanning cycle is set to _TL , and V
The voltage of _Pij is applied. Next, the voltage waveform will be described.

Row electrode signal V _X and the column electrode signal V _Y, as described above, each selection voltage signal V _XS, V _YS and non-selection voltage signal V _XNS, V _YNS
In both cases, the peak value of the voltage is V ₀ . Further, one scanning period _TL is divided into a high frequency signal and a low frequency signal in the first half and the second half. Here, for convenience of explanation, the high frequency component is represented as two cycles, and the low frequency component is represented as one cycle.
These may both be voltage signals of a plurality of cycles in accordance with the characteristics of the liquid crystal element.

In this embodiment, the selection voltage signal V _XS row electrode signal V _X, the first half of the high frequency, and the second half to the low frequency. Conversely, the non-selection voltage signal _VNS has a low frequency in the first half and a high frequency in the second half. On the other hand, the column electrode signal V _Y
Selection voltage signal V _YS and non-selection voltage signal V _YNS, the row electrode signal V _X, before, while the second half of the frequency Conversely, are different from those in phase.

Was but connexion, the V _X, by a combination of V _Y signal, the pixel application voltage V _Pij, so in Figure 1. That is, the pixel
For P _ij , the voltage during the first half and the second half during which V _XS is applied to the row electrode (that is, when the row electrode is selected) has an effective value V ₀ , and the frequencies are ₁ and ₂ . When V _XNS is applied to the row electrode (that is, when the row electrode is not selected), the effective value is A voltage of ₁ <'< ₂ is applied as an equivalent effective frequency'. The control of these applied voltages is performed by controlling the multiplexer group shown in FIG.

For example, in the preferred embodiment, V ₀ = 100 [V], ₁
<200 Hz, ₂ > 300 Hz, 200 Hz ≦ ′ ≦ 300 Hz.

In FIG. 1, the effective value of the voltage applied to the liquid crystal when the row electrode is not selected is It is. On the other hand, when this voltage deformation V ( _t ) is Fourier-transformed, it is expressed by the following equation.

In the above formula, ₁ is a frequency at which the scattering liquid crystal, a ₁ the same value of the first view, also, 2 ₁ of the second harmonic is ₂ the same value of the first view.

Therefore, in the above equation, if the components after the third harmonic are ignored, V ( _t ) becomes the same maximum value. Has the frequency components of ₁ and ₂ .

In the present invention, the effective frequency of the voltage applied to the liquid crystal is' Is defined as the effective frequency when the row electrode is not selected.

FIG. 7 is a drive timing chart for achieving the display example of FIG. 6 using this voltage waveform.

In Figure 7, V _X1 ~V to the row electrodes as shown in _X3 sequential selection voltage V _XS is applied. On the other hand, V _Y1 , V _Y2
Applying a selection voltage signal V _YS or non-selection voltage signal V _YNS in accordance with the display as shown in.

It was but connexion, signals applied to each pixel is as V _P. For example, an effective value V ₀ and a frequency ₂ voltage are applied to the pixel P ₁₁ in the first half of TL ₁ , and the effective value is applied in the other scanning periods _{TL 2} and TL _3. A voltage having an effective frequency 'is applied. Further, the P _12, the second half of the scanning period T _L1, V _{0, 1} voltage is applied, the other It is. Furthermore, the P ₂₁ is only in the latter half of the scanning period T _L2
V _{0, 1} of the voltage is applied.

In FIGS. 1 and 7, the values of V ₀ , ₁ and ₂ are
It is easily possible to set the same value as the voltage value V ₀ , the frequency ₁ in the area (S) and the frequency _{2 in} the area (W). The effective value of V 'in FIG. Further, according to the driving method described above, the effective frequency ′ as viewed from the liquid crystal is Is almost equal to

As shown in FIG. 6, in each case, in each pixel, only when the row electrode is the selection voltage signal V _XS , the selection and non-selection voltage signals V _YS , V _YNS applied from the column electrode apply to each pixel. A voltage that makes the pixel transparent and scattered is applied, and the alignment state of the liquid crystal does not change during the non-selection period of the other row electrodes.

Therefore, if the effective value V ₀ and the frequency of the applied voltage are set so as to satisfy the driving conditions as shown in FIG. 3, display becomes possible. Note that the above operation may be performed only when the display screen is changed because the liquid crystal element has a memory property.

FIG. 10, in this embodiment, is a diagram showing the brightness, dielectric constant and the relationship of the liquid crystal state with respect to the frequency of the voltage when the peak value was V _0. In this embodiment, the multiplexer 6 is used as the configuration of the row electrode drive circuit 4 and the column electrode drive circuit 5 shown in FIG.
This can also be achieved with a circuit configuration as shown in the figure.

In FIG. 8, 11 is a load resistance, 12 is a driving transistor, and 13 is a buffer. The logic level is input from the input terminal D, and the transistor 12 is driven via the buffer 13. Accordingly, the output terminal X _n, the Y _n, and outputs the V ₀ or 0-level voltage. Since this output can be performed by controlling the input logic so as to have the waveform shown in FIG. 5, the same effect as in the above-described embodiment can be obtained, and the drive circuit can be further simplified.

FIG. 8 shows an example in which a transistor and a resistor are used as a driver stage. However, this can be achieved even when a field effect type active element such as a push-pull type or a thin film MOS transistor is used.

FIG. 9 shows an embodiment of the liquid crystal display device of the present invention having a function of reading image information.

When the switch element 81 is set to the W side, the operation becomes exactly the same as that in FIG. 6, and it is connected to the row and column electrode drive voltage sources 71, 72 and 73, 74 and can display. On the other hand, reference numeral 82 denotes a device for locally heating a built-in semiconductor laser or the like. When this is pressed onto the liquid crystal panel 1, the thermo-electro-optic effect of the liquid crystal showing the smectic A phase sealed in the liquid crystal panel causes
When the voltage is 0, the light is scattered, and when the voltage is higher than a certain voltage, the light is transparent. That is, in addition to the display by the electric field from the row and column electrode driving circuits 4 and 5, the display can be performed by the heating means 82.

Incidentally, the capacitance is different between the scattering (S) and the transparent (T) pixel portions of the liquid crystal. In the present embodiment, this change in capacitance can be regarded as a change in image information.

The reading of the image information is performed with the switch element 81 set to the R side. 75 is a detection voltage generation source, and 76 is a detection signal processing circuit. This detection method is described in, for example,
It is not described because it is described in detail in Japanese Patent No. 39619.

Therefore, if the configuration of the display device is as shown in FIG. 9, it is possible to display and read image information.

〔The invention's effect〕

According to the present invention, in a display device using the electric field optical effect of a liquid crystal exhibiting a smectic A phase, a screen can be displayed by one scan, so that a conventional display by a two-step operation of writing after erasing the screen is performed. There is an effect that the difficulty of seeing can be eliminated.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a driving waveform according to an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the electric field optical effect of the smectic A phase liquid crystal,
FIG. 3 is an explanatory diagram of the characteristics of the liquid crystal, FIG. 4 is a diagram showing a driving range of the liquid crystal, FIG. 5 is a diagram modeling FIG. 4, and FIG. 6 is a display device using the driving method of the present invention. FIG. 7 is a driving timing chart of FIG. 6, FIG. 8 is another embodiment of the driving circuit, and FIG. 9 is a liquid crystal display device having a reading function of the present invention. This is an embodiment of the present invention. Tenth
In the present invention, when the peak value of the voltage is V ₀ in the present invention,
FIG. 3 is a diagram illustrating a relationship between luminance, non-dielectric constant, and liquid crystal state with respect to a frequency of a voltage applied to a pixel. 1 ... liquid crystal panel, 2 ... row electrode, 3 ... column electrode, 4 ...
… Row electrode drive circuit, 5… column electrode drive circuit, V _XS …… row electrode selection voltage, V _XNS …… row electrode non-selection voltage, V _YS …… column electrode selection voltage, V _YNS …… column electrode non-selection Voltage.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-59-208531 (JP, A) JP-A-60-123825 (JP, A) JP-A-61-223897 (JP, A)

Claims (2)

(57) [Claims] 1. A state in which light is scattered depending on an effective value of an applied voltage and an effective frequency on a pair of substrate surfaces having a plurality of row electrodes on one of opposing surfaces and a plurality of column electrodes on the other. In a liquid crystal display device holding a liquid crystal capable of taking a state of transmitting light, and a state of maintaining a state of scattering or transmitting light, a peak value of a voltage applied to the row electrode and the column electrode The row electrodes are applied with a high-frequency voltage as a row selection signal in the first half of one scanning cycle and a low-frequency voltage in the second half as a row selection signal. The high-frequency voltage is applied to the column electrodes, the high-frequency voltage is applied to the column electrodes as a column selection signal in the first half of the one scanning cycle, and the low-frequency voltage is applied to the second half of the one scanning cycle, and the column selection signal is in phase with the column selection signal. By applying different voltage signals When a row selection signal is applied to the row electrode and a column selection signal is applied to the column electrode, the corresponding liquid crystal portion is set in a light transmitting state, a row selection signal is applied to the row electrode, and the column electrode is applied to the column electrode. When a column non-selection signal is applied, the corresponding liquid crystal portion is made to scatter light, and when a row non-selection signal is applied to the row electrode, the corresponding liquid crystal portion is applied regardless of the signal applied to the column electrode. Is maintained in the state before one scan. 2. The liquid crystal display device according to claim 1, wherein a smectic A phase is used as said liquid crystal.