JPH09230302A - Phase transition type liquid crystal panel driving method and phase transition type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a response time required for resetting and to perform a real time display. SOLUTION: A rectangular wave with a maximum value Va and a minimum value Vc' is outputted from a common driver as a common waveform 201 in a resetting period. Its amplitude based on a voltage Vb is a drive voltage Vd in its upper side, and becomes larger than the Vd in its lower side. A transmission waveform 202 or a scattered waveform 203 is outputted from another segment driver. These waveforms 202, 203 are equal to the waveform shifting the phase of the common waveform 201 by 180 deg.. Potential difference between the common waveform 201 and the transmission waveform 202 or the scattered waveform 203 is applied to a liquid crystal as the voltage, and the top and bottom amplitudes of a composite waveform 204 exhibiting it become the magnitude exceeding the double of the drive voltage Vd also.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for driving a phase transition type liquid crystal panel in which information is displayed by utilizing a nematic-cholesteric phase transition.

[0002]

2. Description of the Related Art In recent years, liquid crystal displays (LCD) are
Compared with other displays, it has advantages such as light weight and can be driven at a low voltage, and is therefore widely used in information processing equipment.

An LCD is a display device which utilizes the characteristic that the orientation (molecular orientation) of liquid crystal molecules is changed by an applied electric field. There are various kinds of liquid crystal materials used for them, which are classified according to their properties. Cholesteric phase liquid crystal is one of them.

This cholesteric phase liquid crystal is characterized in that each liquid crystal molecule continuously changes its direction to form a so-called spiral staircase structure. Its helical structure gradually extends its helical pitch when an electric field is applied to the liquid crystal,
Eventually, the pitch extends to infinity and the phase transitions to a nematic phase liquid crystal. Thus, the cholesteric phase liquid crystal is called a phase transition type liquid crystal because it causes a nematic-cholesteric phase transition due to electric field induction, and a display device using the phase transition type liquid crystal is a phase transition type liquid crystal display device (phase transition type liquid crystal display device). Transfer type LCD).

FIG. 3 is a diagram showing the VT (electro-optical) characteristics of the phase transition type liquid crystal. In FIG. 3, the horizontal axis represents the applied voltage and the vertical axis represents the light transmittance. The display principle of the phase transition type liquid crystal will be described with reference to FIG.

As shown in FIG. 3, in the phase transition type liquid crystal, when no low voltage is applied (low voltage or 0 V is applied), the liquid crystal molecules form a cholesteric phase and scatter light. However, when a high voltage is applied, the liquid crystal molecules change their state to a nematic phase and transmit light.

Hysteresis appears in the nematic-cholesteric phase transition induced by an electric field. Therefore, for example, at the voltage of V _{d in} the figure, either state can be a metastable state (memory effect). From this, the phase transition type liquid crystal display device displays information by utilizing these three states that appear when a low voltage is not applied, when a high voltage is applied, and when an intermediate voltage is applied, that is, by utilizing the memory effect. .

In the phase transition type liquid crystal display device, the applied voltage is determined in consideration of the three states of the liquid crystal molecules. In FIG. 3, V _d is a drive voltage (holding voltage), and Δ is a hysteresis width. Usually, this hysteresis width Δ is a voltage at which a transmittance of 20% is obtained in the phase transition curve from the cholesteric phase to the nematic phase and a voltage at which a transmittance of 90% is obtained in the phase transition curve from the nematic phase to the cholesteric phase. Is defined as the difference between The drive voltage V _d is an intermediate voltage between the two voltages that define the hysteresis width Δ. The drive voltage V thus obtained
_d is applied to hold the liquid crystal molecules in the metastable state of each phase.

As is well known, an AC voltage is used to drive the liquid crystal. Conventionally, a driving voltage V is used to drive a phase transition type liquid crystal.
_{Based on d} , an alternating voltage having the same magnitude is applied to the two electrodes facing each other, and the phase of the alternating voltage is controlled. Since the voltage applied to the phase transition type liquid crystal is the potential difference between the two AC voltages, when the phases of the two AC voltages are shifted by 180 degrees, an AC voltage having an amplitude twice that is applied and the liquid crystal molecules are The state of the nematic phase is entered. On the other hand, when the phases are aligned, the voltages are equal, so a voltage of 0 V is applied, and the liquid crystal molecules are in the cholesteric phase state.

The magnitude of the AC voltage is set to the above-mentioned drive voltage Vd so that the liquid crystal molecules can be maintained in a metastable state by only applying one of the two. Therefore, when the phases of the two AC voltages are aligned, a voltage of 2V _d is applied as shown in FIG. 3, and the liquid crystal molecules change to a nematic phase state. This voltage 2V _d is a reset voltage for changing the liquid crystal molecules to the nematic phase state, that is, for resetting.

[0011]

As described above, conventionally, the phase transition type liquid crystal has been applied with a voltage twice the driving voltage V _d as the reset voltage. However, this reset voltage 2 V _d is applied. There is a problem in that the response time from the start of liquid crystal molecule change to the nematic phase state is long, and the display contents cannot be changed quickly.

To give a concrete numerical value, it took several tens of ms to reset the liquid crystal molecules. For this reason,
It took a long time to partially rewrite one screen, and real-time display was not possible.

In the phase transition type liquid crystal, the response time required for changing the liquid crystal molecules to the cholesteric phase state, that is, the set time is much shorter than that required for the reset. Therefore, it has been desired to shorten the response time required for resetting the phase transition type liquid crystal.

The present invention has been made in view of the above problems, and it is an object of the present invention to shorten the response time required for resetting and enable real-time display.

[0015]

A method of driving a phase transition type liquid crystal panel according to the present invention is a liquid crystal material which changes into a nematic phase, a cholesteric phase and a metastable state of each phase in response to an applied voltage. For a phase transition type liquid crystal panel encapsulating a liquid crystal material, it is premised that information is displayed by utilizing the nematic-cholesteric phase transition of the liquid crystal material, and the reset voltage applied to change the phase of the liquid crystal material to the nematic phase is set in advance. It is set to be larger than twice the drive voltage applied to maintain the liquid crystal material determined by the defined definition in the metastable state.

The phase transition type liquid crystal display device of the present invention is applied with an applied voltage.
Depending on the pressure, nematic phase, cholesteric phase, and
Liquid crystal materials that change into three states of metastable state of each phase
It is equipped with a phase transition type liquid crystal panel enclosing
Information transfer using the tick-cholesteric phase transition
It is displayed on the transferable liquid crystal panel and is set in advance.
The liquid crystal material, which is determined by the definition
Drive voltage V _dBased on multiple
The voltage supply means that supplies the voltage at each pressure value and the voltage supply means.
The voltage supplied from the power supply means is applied to the phase transition type liquid crystal panel.
Voltage applying means for controlling the liquid crystal material.
Voltage to change the phase from the clock phase to the nematic phase.
Reset voltage V applied by the adding means_rAnd drive voltage V_dNoseki
The clerk is V_r= Α ・ V_d However, α satisfies a coefficient having a value larger than 2.

In the above structure, the voltage supply means selects from among the voltages generated at the plurality of voltage values,
It is desirable to select a voltage to be applied to the phase transition type liquid crystal panel and supply it to the voltage applying means. Also, by making the cell thickness of the phase transition type liquid crystal panel thinner than 5 μm,
It is desirable to reduce the driving voltage V _d and improve the value of α, and it is desirable that the lower limit of the cell thickness of the phase transition type liquid crystal panel is 3.0 μm.

In a phase transition type liquid crystal, its VT
The driving voltage V _d for holding the liquid crystal molecules in the metastable state is determined in consideration of the (electro-optical) characteristics. This drive voltage V
Based on _d , a reset voltage V _r , which is separately set within a range of more than twice the driving voltage V _d and is applied to change the liquid crystal molecules into a nematic phase, is applied to the liquid crystal. As a result, a larger electric field acts on the liquid crystal molecules and the response speed thereof is improved.

The liquid crystal panel is usually driven by an LSI or the like, and the magnitude of the reset voltage V _{r that} can be applied is limited by the withstand voltage of the LSI. The driving voltage V _d will vary depending on the cell thickness of the liquid crystal panel, a tendency decreases known as driving voltage V _d the cell thickness decreases. Focusing on these points, by adopting a liquid crystal panel with a thin cell thickness, the value of α obtained within the limit range due to the withstand voltage of the LSI becomes large, and a larger electric field can be applied to liquid crystal molecules. It will be possible.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit configuration diagram of a phase transition type liquid crystal display device to which this embodiment is applied. The configuration and operation of the liquid crystal display device will be described with reference to FIG.
The liquid crystal panel 101 is a phase transition type liquid crystal panel in which cholesteric phase liquid crystal is sealed as a liquid crystal material. The liquid crystal panel 101 is driven in a simple matrix by the common driver 102 and the segment driver 103 to display information in a dot matrix.

The phase transition type liquid crystal display has an advantage that there is no limit to the display capacity because the display content can be retained only by applying the drive voltage V _d (see FIG. 3) due to the memory effect of the liquid crystal. . Therefore, it is often applied to a display device having a large-capacity, large-area display screen (liquid crystal panel).

When the liquid crystal panel has a large capacity, a partial rewriting function for partially rewriting the information to be displayed becomes necessary in order to quickly display the information to be displayed. The liquid crystal panel 101 used in this embodiment has a large capacity. Therefore, the liquid crystal panel 101 can be partially rewritten,
Common driver 102 and segment driver 103
Applies a voltage (AC voltage) to the liquid crystal panel 101 according to a control signal output from the controller 104 by a sequential writing drive method.

The controller 104 inputs the contents to be displayed from the host computer as an input signal,
By outputting the control signal generated based on this input signal to the common driver 102 and the segment driver 103, the content to be displayed on the liquid crystal panel 101 is displayed.

A voltage is externally supplied to the display device via terminals a and b. The voltage Va is applied to the terminal a, and the voltage -VLCD is applied to the other terminal b. The voltage Va applied to the terminal a is supplied to the common driver 102 and the segment driver 103, respectively.

Between terminals a and b, resistors R1, R2 and R are provided.
3, R4 are connected in series in that order from the terminal a side. These resistors R1 to R4 divide the potential difference (voltage) between the terminals a and b.

The voltage Va dropped by the resistor R1 is input to the non-inverting terminal of the operational amplifier OP1. Similarly, the operational amplifier OP2 has a voltage Va dropped by resistors R1 and R2, and the operational amplifier OP3 has resistors R1 and R2.
The voltage Va dropped by 2 and R3 is input to its non-inverting terminal, respectively. These operational amplifier OP
The output is fed back to the inverting terminals of 1 to OP3. Therefore, each of the operational amplifiers OP1 to OP3 has an imaginary short, and each of the operational amplifiers OP1 to OP1
The outputs Vb, Vc and Vc 'of OP3 are respectively equal to the input voltage of its inverting terminal.

The output voltage Vb of the operational amplifier OP1 is output to the common driver 102, and the output voltages Vc and Vc 'of the operational amplifiers OP2 and OP3 are both the selector 105.
Is output to

The selector 105 is the controller 10
According to the reset signal output by 6, the operational amplifier OP2,
, And OP3, one of the output voltages Vc and Vc ′ input respectively is selected, and the selected output voltage is selected by the common driver 10
2 and the segment driver 103, respectively. The selector 105 selects the output voltage Vc ′ of the operational amplifier OP3 when the reset signal is active, and the operational amplifier OP when the reset signal is inactive.
The output voltage Vc of 2 is selected.

The above voltages Va, Vb, Vc, and Vc 'are
Each of the drivers 102 and 103 has a voltage applied to the liquid crystal panel 101. Each driver 102 and 103 is
According to the control signal input from the controller 104, an AC voltage waveform is generated using these supplied voltages Va, Vb, Vc, and Vc ′, and the generated AC voltage waveform is applied to the liquid crystal panel 101.

The above is the configuration of the liquid crystal display device shown in FIG.
And the operation of each part. Next, with reference to FIG. 2, the voltage level applied to the liquid crystal panel 101 by the common driver 102 and the segment driver 103 and its waveform will be described in detail.

FIG. 2 is a timing chart of drive voltage waveforms applied to the liquid crystal panel 101 by the common driver 102 and the segment driver 103. As described above, in the present embodiment, the liquid crystal panel 101 is driven by the sequential writing type driving method. FIG. 2 shows a liquid crystal panel 10 designated by a control signal sent from the controller 104.
3 shows a drive voltage waveform applied to one pixel of 1 from the start of writing to the end thereof.

In FIG. 2, a common waveform 201 is a drive voltage waveform output by the common driver 102, and a transparent waveform 20.
2, and the scattered waveform 203 is the segment driver 103.
Is a drive voltage waveform output by. Also, the composite waveform 204
Is a voltage waveform that is actually applied to the liquid crystal by applying the common waveform 201, the transmission waveform 202, and the scattering waveform 203. The voltage actually applied to the liquid crystal, that is, the composite waveform 204, is the common waveform 201, the transmission waveform 202,
Alternatively, it is a potential difference with the scattered waveform 203.

As shown in FIG. 2, the period in which a voltage is applied to a pixel is classified into a reset period, a selection period, and a holding period depending on the voltage applied to the pixel, that is, the shape of the composite waveform 204. It The period including the reset period and the selection period is a period required for writing pixels.

The common waveform 201 output from the common driver 102 is a common waveform irrespective of the writing content of the pixel. The shape of the waveform is normally a DC voltage of Vb, and during the reset period in which pixel writing is performed and in the selection period, the voltage becomes a rectangular wave in which the voltage alternates between Va and Vc 'in a predetermined cycle.

The magnitude relationships among the voltages Va, Vb, Vc, and Vc 'are Va>Vb>Vc>Vc', and Va>Vb>Vc> Vc '.
And the potential difference between Vb and Vb and Vc are
The drive voltage is V _d (see FIG. 3). The voltage Vb is a voltage applied as a bias.

The controller 104 shown in FIG. 1 activates the reset signal during the reset period and the selection period. Therefore, the common waveform 201 during the reset period
Indicates that the upper side of the voltage Vb has a shape shown by a solid line, but the voltage Vb
The lower side of b has a shape shown by a solid line and a dotted line, and its amplitude is larger than the driving voltage V _d . Since the controller 104 outputs the active reset signal also in the selection period following the reset period, the common waveform 201 has the shapes shown by the solid line and the broken line, as in the reset period. When the selection period elapses, the common waveform 201 changes to the voltage Vb.
It becomes the direct current of.

In the phase transition type liquid crystal, as shown in FIG. 3, by applying a driving voltage V _d , liquid crystal molecules can be held in a metastable state. The drive voltage V _d for holding the metastable state may be applied using either the common driver 102, the segment driver 103, or both, but in the present embodiment, it is applied to the segment driver 103. Is being applied.

The segment driver 103 normally applies a rectangular wave whose voltage alternates between Va and Vc to all the signal lines connected to it, and changes its phase as necessary.

In this embodiment, when writing a pixel, irrespective of the content to be written, immediately before the reset period, all the pixels to be written are temporarily set, that is, the liquid crystal is changed to the cholesteric phase, and then the writing is performed. I'm trying to do. The setting is performed by matching the phase with the common waveform 201.

When the setting of the liquid crystal is completed, the reset period starts. In this reset period, the transmission waveform 20
2 and the scattered waveform 203 have the same shape, and when shifting to the reset period, the segment driver 103 shifts the phase of the AC voltage applied up to that point by 180 degrees, in other words, the phase with the common waveform 201 by 180 degrees. During this reset period, the voltage Vc ′ is supplied from the selector 105. Therefore, the transmission waveform 202 and the scattering waveform 203
Has a shape indicated by a solid line and a broken line.

The composite waveform 204 is the liquid crystal as described above.
Is the voltage that is actually applied to the
The driver 102 and the segment driver 103 are
It is the difference between the applied voltages. Actual during reset period
The waveform indicated by the line is the drive voltage V _dWith twice the reset voltage
Yes, this corresponds to a conventional reset voltage. Against this
However, in the present embodiment, the common waveform in the reset period
201, transmission waveform 202, and scattering waveform 203
Since the minimum voltage of is set to Vc ', it is shown by the solid line and the broken line.
Waveform and drive voltage V_dVoltage greater than twice
Applied to liquid crystal.

The response time at the time of resetting the phase transition type liquid crystal is
It is known that the larger the electric field applied to it, the shorter it becomes. In this embodiment, the voltage Vc ′ is adjusted and the reset voltage is set to 2.2 (= α) of the drive voltage V _d.
When the response time required for resetting was doubled and measured, the response time was 10 ms or less. The conventional response time is several tens of ms. As is clear from this,
The response time required for reset has been greatly reduced. As a result, the reset period can be set shorter, and real-time display can be performed.

When the reset period elapses and then proceeds to the subsequent selection period, the segment driver 103 changes the phase of the applied voltage according to the contents to be written in the pixel. Specifically, when the pixel is set to transmit light, as seen from the transmission waveform 202, when the pixel is set to scatter light without changing with respect to the phase during the reset period. As can be seen from the waveform 203, the phase is shifted by 180 degrees during the reset period. In other words, the phase of the scattered waveform 203 is matched with that of the common waveform 201. Thus, when the segment driver 103 applies the scattered waveform 203, the combined waveform 204 during the selection period
, The potential difference between the scattered waveform 203 and the common waveform 201 disappears and no voltage is applied, and the liquid crystal changes from the nematic phase to the cholesteric phase. On the other hand, when the segment driver 103 applies the transmission waveform 202, as shown by a broken line in the figure, an AC waveform having an amplitude larger than 2V _d is applied, and the liquid crystal remains in the nematic phase state.

In the holding period following the selection period, the maximum value is Va and the minimum value is V from the segment driver 103.
A rectangular wave of c is applied, and a DC voltage of voltage Vb is applied from the other common driver 102. Therefore, the composite waveform 204 is an AC waveform with an amplitude of V _d , the liquid crystal molecules are held in a metastable state, and the content written in the pixel is held.

In this embodiment, the controller 1
Reference numeral 04 keeps the reset signal active during the reset period and the selection period, but the reset signal may be activated only during the reset period.

By the way, in the phase transition type liquid crystal display, a super large capacity display which is not limited in principle can be realized, a display is bright because a polarizing plate is unnecessary, and a flicker-free display can be realized by a memory effect. There are advantages. However, on the other hand, since the threshold value (phase transition voltage) in the phase transition curve from the cholesteric phase to the nematic phase shown in FIG. 3 is high, there is a disadvantage that a high voltage must be applied.

In this embodiment, since the reset voltage exceeding twice the drive voltage V _d is applied, the applied voltage becomes higher. Usually, the common driver 102 and the segment driver 103 are mounted in the system in the form of LSI. It is not desirable to set the reset voltage too high in view of the withstand voltage of the LSI.

In this embodiment, the liquid crystal panel 101 having a small cell thickness (thickness of the liquid crystal layer) is adopted in order to suppress the magnitude of the reset voltage. When the cell thickness is reduced, the driving voltage V _d decreases accordingly. Therefore, a general-purpose LSI for driving a liquid crystal panel can be used, and the reset voltage and the driving voltage V _d that are obtained within the limit range due to the withstand voltage of the LSI can be used. The value of the ratio α (= reset voltage / driving voltage V _d ) becomes larger, and the effect that the response time required for reset can be further shortened can be obtained. Further, the present invention can be easily applied to a conventional phase transition type liquid crystal display device.

By making the reset voltage larger than twice the driving voltage V _d , each driver 102 and 103 is
On the other hand, it becomes necessary to supply a voltage having a different voltage value more than ever before. In the present embodiment, the selector 105 selects one of the voltages Vc and Vc 'and supplies it to each of the drivers 102 and 103, thereby canceling out the increase in the type of the supplied voltage. The increase in the number of terminals that each driver 102 and 103 should have is avoided. As a result, a general-purpose LSI is provided for each driver 1
02 and 103 are easy to use, and
The effect of facilitating the application of the present invention to a conventional phase transition type liquid crystal display device can be obtained.

Liquid crystal panel 101 adopted in this embodiment
Has a cell thickness of 4.5 μm. Usually, the cell thickness of a phase transition type liquid crystal panel is about 5 μm. In this way, by adopting the liquid crystal panel 101 having a small cell thickness and applying the reset voltage exceeding twice the drive voltage V _d , as described above, the reset voltage is suppressed to be equal to or lower than the withstand voltage of the LSI, and at the time of reset. The response time of was able to be shortened significantly. However, on the other hand, when the cell thickness is reduced, there is a problem that the contrast is lowered. Although depending on the operating environment, the liquid crystal material used, etc., it is desirable to set the cell thickness to about 3 μm as the limit of thinness in order to suppress the disadvantage that the contrast is lowered.

In this embodiment, a predetermined voltage is applied to the liquid crystal panel 101. However, in order to allow the user to arbitrarily set the response time according to the environment in which the display device is used, each driver 10
The voltage supplied to 2 and 103 may be adjustable. In addition, the voltage Vc ′ is set to the respective drivers 102 and 10.
However, the voltage Vc 'may be supplied to only one of them.

[0053]

The present invention described above, according to the present invention is based on the driving voltage V _d to be applied to hold the liquid crystal metastable were set separately in a range of more than twice the driving voltage V _d, the liquid crystal A reset voltage is applied to the liquid crystal panel to change the molecules into a nematic phase (reset). Therefore, the response time required for resetting becomes shorter,
Real-time display of information can be performed.

Further, in the present invention, since the liquid crystal panel having a thin cell thickness is adopted and the driving voltage V _d is made small, the value of α obtained within the limit range due to the withstand voltage of the LSI or the like becomes large, and the liquid crystal molecules are And a larger electric field can be applied. As a result, the response time of the liquid crystal can be further shortened.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a liquid crystal display device to which this embodiment is applied.

FIG. 2 is a timing chart of drive voltage waveforms.

FIG. 3 is a diagram showing VT (electro-optical) characteristics of a phase transition type liquid crystal.

[Explanation of symbols]

 101 liquid crystal panel 102 common driver 103 segment driver 104 controller 105 selectors OP1 to OP3 operational amplifiers R1 to R4 resistors

Claims (5)

[Claims] 1. A nematic liquid crystal material for a phase transition type liquid crystal panel in which a liquid crystal material that changes into three states of a nematic phase, a cholesteric phase, and a metastable state of each phase according to an applied voltage is enclosed. -A driving method for displaying information using a cholesteric phase transition, wherein a reset voltage applied for changing the phase of the liquid crystal material to a nematic phase is used for maintaining the liquid crystal material in the metastable state. A driving method for a phase-transition type liquid crystal panel, wherein the driving voltage applied to the liquid crystal display device is larger than twice the driving voltage applied to the liquid crystal display device. 2. A nematic liquid crystal material comprising a phase transition type liquid crystal panel enclosing a liquid crystal material that changes into three states of a nematic phase, a cholesteric phase, and a metastable state of each phase according to an applied voltage. A phase transition type liquid crystal display device for displaying information on the phase transition type liquid crystal panel by utilizing a cholesteric phase transition, the method being based on a driving voltage V _d for maintaining the liquid crystal material in the metastable state. Voltage supply means for supplying a voltage at each of a plurality of set voltage values, and voltage application means for applying the voltage supplied from the voltage supply means to the phase transition type liquid crystal panel, relationship of the reset voltage V _r and the driving voltage V _d of the voltage applying means in order to phase change to the nematic phase from the cholesteric phase is applied, however V _r = α · V _d , Alpha phase transition type liquid crystal display device characterized by satisfying the factor of 2 greater than. 3. The voltage supply means selects a voltage to be applied to the phase transition type liquid crystal panel from among voltages generated at the plurality of voltage values and supplies the selected voltage to the voltage application means. The phase transition type liquid crystal display device according to claim 2. 4. The cell thickness of the phase change type liquid crystal panel is 5 μm.
3. The phase transition type liquid crystal display device according to claim 2, wherein the drive voltage V _d is lowered and the value of α is improved by making the thickness thinner than m. 5. The cell thickness of the phase transition type liquid crystal panel is
5. The phase transition type liquid crystal display device according to claim 4, wherein the lower limit value is 3.0 μm.