JPS62161129A - Liquid crystal matrix driving method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a liquid crystal display device using smectic liquid crystal, and particularly relates to a liquid crystal display device suitable for large screen display. [Prior Art] Ferroelectric liquid crystal The molecules have a layered structure and a helical structure as shown in FIG. 1 is a liquid crystal molecule, and 2 is spontaneous polarization.

When an electric field E greater than a threshold voltage is applied perpendicular to the helical axis, the molecules move within the layer while maintaining the layered structure, unraveling the helix, and the permanent dipole moment perpendicular to the long axis of each molecule becomes parallel to the electric field. As shown in Part 2 (a), they are arranged parallel to each other not only within the layer but also between the layers.

Moreover, if the direction of the electric field is reversed, the result will be as shown in FIG. 2(c). In other words, by selecting the direction of the electric field, the liquid crystal molecules can be
Two states tilted at θ can be realized, and by utilizing birefringence or adding dichroic dyes, display elements and light shutter elements can be made.

In general, when the electric field is removed, ferroelectric liquid crystal molecules return to their original helical structure as shown in Figure 2(b) due to their oriented elastic restoring force, but for example, if the liquid crystal layer is thinned to about 1 μm, the electric field becomes zero. It is known that a bistable state in which the helix remains unwound as shown in Figures 2 (a') and (c) can be achieved even when .

A conventional example of a time-division driving method for a ferroelectric liquid crystal exhibiting this bistable state is shown in FIGS. 3 and 4.

FIG. 3 shows a schematic diagram of the liquid crystal element, with the X electrode 3
A liquid crystal exhibiting a chiral smectic phase is sealed between the Y electrode 4 and the Y electrode 4 as a ferroelectric liquid crystal.

FIG. 4 shows drive waveforms applied to the X electrode 3 and Y electrode 4 when pixel A is turned on and pixel B is turned off.

A voltage with a voltage value of ±2■ is sequentially applied to the X electrode, and Yf
A voltage having a voltage value of ±V or +V is applied to fitl. As a result, a voltage of +3V or ±■ is applied to the pixel A, and the pixel A is turned on. On the other hand, a voltage of -3V or ±V is applied to pixel B, and the pixel B is turned off.

By the way, in this driving method, the display state of the pixel is determined by ±3
The pulse time Δt of v is 1/of the selection time Ts of one line.
It is 4. Therefore, the optical response time of the liquid crystal is 1/4・J
It must be less than or equal to s.

On the other hand, the optical response time of the current smectic liquid crystal is
1 ms, and therefore, the rewriting time for one screen is the selection time for one line, Ts, assuming the number of scanning lines is N=500.
Since it is 4ms, it is very long, about 2 seconds.

Incidentally, related driving methods of this type include, for example,
JP-A-60-33535 is mentioned.

[Problem that the invention seeks to solve]

When the conventional driving method is applied to a large-screen, high-definition liquid crystal panel with a large number of scanning lines, it takes time to rewrite the entire screen, which poses a practical problem.

An object of the present invention is to provide a driving method that can shorten screen rewriting time in time-division driving of a ferroelectric liquid crystal exhibiting bistability.

[Means for solving problems]

The present invention utilizes the bistability of ferroelectric liquid crystal display to turn on or off the pixel whose display is to be rewritten in advance, and then, if the pixel is already in the on state by line sequential scanning driving, The feature is that a voltage that maintains that state or an off voltage is applied, and if the pixel is already in an off state, a voltage that maintains that state or an on voltage is applied.

[Effect]

Once all the desired pixels are set to the initial state, it is only necessary to select the other two types of voltage in line sequential driving.
The screen rewriting time is short and good.

〔Example〕

Examples of the present invention will be described in detail below. FIG. 5 schematically shows the structure of the liquid crystal display element 5. As shown in FIG. The device consists of a substrate 8 made of glass or the like on which electrodes 7 are formed and a substrate 11 made of glass or the like on which electrodes 6 are formed, facing each other at a constant interval, and a liquid crystal exhibiting a chiral smectic phase, which is a ferroelectric liquid crystal, is placed between the two plates. Contains 10.

The liquid crystal alignment film 9 is formed by applying the organic substance (polyimide) with a spinner and then subjecting it to a rubbing process, but it is possible to perform the above-mentioned alignment process only on one substrate, or even if both substrates are not subjected to any alignment process at all. This does not impair the optical memory operation described in .

Further, as the liquid crystal 10, a mixed liquid crystal shown in FIG. 6 and a liquid crystal shown in FIG. 7 are used. The display at this time may be either a birefringent display in which two polarizing plates are attached to the substrate of the liquid crystal display element 5, or a guest-host display in which a dichroic dye is sealed in the smectic liquid crystal 10. In particular, for the latter guest/host display, it is best to use the liquid crystal shown in FIG.

Next, an example of a method for aligning liquid crystal molecules will be described. First, after heating the liquid crystal to an isotropic liquid phase,
Allow to cool for about a minute. This results in a smectic C phase in which the long axis of the molecules is tilted from the layer normal.

The electro-optical characteristics of the liquid crystal display element obtained by the method described above are shown in FIGS. 8 and 9. FIG. 8 shows the optical response waveform B of the liquid crystal to the drive voltage Vd of the liquid crystal display element. . As shown in the figure, depending on the polarity of the drive voltage Vd, the display is turned off (negative polarity) or turned on (positive polarity). Furthermore, it exhibits a memory operation (bistability) in which the display remains in the off-state or on-state even after the voltage of negative or positive polarity is removed (OV). As a result of actual measurements, this memory time was several tens of seconds or more.

The liquid crystal drive voltage Vd shown in FIG. 8 has a waveform when the liquid crystal is statically driven. On the other hand, FIG. 9 shows an example of the drive voltage waveform when the liquid crystal matrix panel is time-divisionally driven and an example of the optical response waveform of the liquid crystal at that time.

The drive voltage Vd consists of a write voltage (voltage value ±Vw) and a bias voltage (voltage value ±Vb).
The write voltage described above is selected and applied only once in one frame period. Depending on the polarity of the last voltage applied during this selection period, the liquid crystal enters one display off or one display on state and continues to maintain this state until a new write voltage is applied.

On the other hand, during the non-selection period when no write voltage is applied, the aforementioned bias voltage is applied to the liquid crystal.

As a result, the brightness of the liquid crystal determined by the write voltage changes depending on the bias voltage. As a result of experiments, this amount of change is the voltage value ±vb of the bias voltage.

It has been confirmed that it depends on the pulse width Tb, pulse period Tcx, and application time TC2.

Next, FIG. 10 shows the relationship between the brightness of the liquid crystal and the write voltage and bias voltage. FIG. 10(a) shows the write voltage sealing characteristics.

The display turns on or off depending on the polarity of the write voltage, but the peak value of the write voltage at which the brightness B increases to 90% is set to the on-saturation value Vwsat (osL) The peak value at which the brightness B decreases to 10% is set to the off-saturation value Vwgat (orr ).

Further, FIG. 10(b) shows the bias voltage sealing characteristics during the bias voltage application period tcx shown in FIG. 9'.

The A characteristic is a characteristic when the initial state of brightness is turned off, and the B characteristic is a characteristic when the initial brightness state is turned on. In the illustrated characteristics, the peak value of the bias voltage when the brightness B decreases to 90% is the OFF threshold voltage Vbth (OFF), and the peak value when the brightness B increases to 10% is the ON threshold voltage V bth (ON). ).

In matrix driving, the write voltage and bias voltage must satisfy the following equation.

1vw1≧Vwsat (ON) + Vwsat (
OFF) −(1) lVbl≦Vbth (ON),
Vbth (OFF) .= (2) Next, an outline of the matrix drive described in the present invention is shown in FIG. FIG. 1(a) shows a schematic diagram of a matrix panel. The intersection of the signal electrode 12 and the scanning electrode 13 becomes a pixel 14.

Taking pixel Pxx as an example, the voltage waveforms applied to the liquid crystal pixel by the signal voltages V Y 1 , V v 2 , V v a and the scan voltages VXI, VX21 and Vxa applied to the signal electrodes 1 and 2.3 and the scanning electrodes 1 and 2.3 are as follows. explain.

FIG. 1(b) schematically shows the voltage waveform applied to the pixel Pzx. The voltage application timing consists of five periods: an initialization period Tts for all pixels, a non-selection period 'rssxtTNS2, a selection period TSL, and a rest period Tsy. Note that the pause period TsT may be omitted.

During the initialization period TIN, the display state of the liquid crystal is set to display on or
This is to set the display to off state. Waveform A is a waveform when the liquid crystal is turned off, and waveform B is turned on when the liquid crystal is displayed, during the initialization period.

The above-described operation is performed for all pixels, but may be performed for at least each pixel (line unit) whose display content is to be rewritten. In any case, the pixels targeted for initialization are
- Apply initialization voltage ±vKN simultaneously.

When the above-described initialization operation is completed, a voltage is applied to each pixel by line sequential scanning to turn the liquid crystal on or off within the selection period Tst.

For example, when the liquid crystal is turned off during the initialization period TIN as shown in waveform A, the selection period Tst.

In order to turn on the pixel, a write voltage higher than Vvsat (ON) must be applied to
Conversely, in order to maintain the off state, a voltage equal to or lower than Vbth (aN) is applied.

Furthermore, when the liquid crystal is turned on during the initialization period TrN as shown in waveform B, the voltage applied to the pixel during the selection period TSL must be Vvsa to turn the pixel off.
To apply a voltage equal to or lower than t(orr) and maintain the on state, a voltage equal to or lower than Vbth (OFF) is applied to the liquid crystal.

Furthermore, the voltage applied to the liquid crystal during the pause period Tst is Vbt
h (ON) or a state in which a voltage lower than Vbth (arp) or a voltage is not applied to the scanning electrode and the signal electrode. This state can be achieved by making the output of the drive circuit high impedance.

As described above, the feature of the present invention is that a voltage that determines the display state of the liquid crystal is applied during the initialization period T N I, while during the selection period TS
A voltage that maintains the display state described above or a voltage that inverts the display state is applied to L.

In the display characteristics of the liquid crystal described so far, it has been defined that the display is on when the applied voltage is positive, and the display is off when the applied voltage is negative, but this is only for convenience of explanation.

Below, a specific example of the voltage waveform applied to the liquid crystal panel is shown in the first section.
The explanation will be given with reference to the liquid crystal panel shown in FIG.

The voltage applied to the signal electrodes 15a to 15c is the signal voltage V Y
The voltages applied to the scanning electrodes 168 to 16c are defined as scanning voltages VX1 to Vxs. In addition, the scanning voltage V
x (V x 1 to V x a ) and signal voltage VY
The relationship between the polarity (Vyx to Vyx) and the brightness of the pixel 7 is shown in FIG.

When the polarity of the voltage applied to the pixel is positive, it is turned on, and when it is negative, it is turned off.

FIG. 13 shows an example of the states of the scanning voltage Vx, the signal voltage Vy, and the voltages applied to the pixels.

The scanning voltage Vrx and the signal voltage VIY are voltages for initializing the brightness of the pixel. Hereinafter, this will be referred to as the initialization voltage. Vs is a selection voltage and is applied to the selected scan electrode, while VMS is a non-selection voltage and is applied to the non-selected scan electrode.6Furthermore, VH is a holding voltage and is applied to the scan electrode after screen rewriting. Apply to the signal electrode.

On the other hand, VW is applied to the signal electrode when inverting the brightness of the pixel initialized with the write voltage, and VNW is applied to the signal electrode when the brightness of the pixel initialized with the non-write voltage is maintained. do.

In this drive waveform example, particularly in the scanning voltage Vx, the peak value of the non-selection voltage VNs is set to 1/2 of the selection voltage Vs. Note that the holding voltage VH may be omitted.

As a result, the voltage V x −V v applied to the pixel is the initialization period A, the write period B, and the holding period C, D, and E.

It consists of each part of F. During the initialization period A, the pixels are turned on, so during the write period B, the liquid crystal is turned on.

This is reversed and becomes the OFF state. Furthermore, C, D.

During the holding periods E and F, the pixel remains on.

In contrast to Fig. 13, when the initialization brightness is on,
On the other hand, FIG. 14 shows an example of the drive waveform when the brightness is turned off. For the waveform in FIG. 13, the initialization voltage V! of the scanning voltage Vx! x, Vs, the initialization voltage Vry of the signal voltage Vy, and the voltage including f, Vw.

The non-write voltages VNW each have a waveform whose phase is inverted.

As a result, during the initialization period A, the pixel is in the off state,
It is turned on during write period B. Furthermore, C, D, E, F
During the retention period, it remains off.

FIGS. 15 and 16 show other examples of drive waveforms. FIG. 15 shows an example of the waveform when the brightness is in the on state when the pixel is initialized, and FIG. 16 shows an example of the waveform when the brightness is in the off state.

FIGS. 17 and 18 show other examples of drive waveforms. FIG. 17 shows that the brightness during the initialization period is on,
FIG. 18 is an example of a drive waveform when the brightness during the initialization period is set to an OFF state.

FIG. 19, FIG. 20, and FIG. 21 are FIG.

This figure shows a modification of each of the drive waveforms in FIGS. 15 and 17.

A feature of the drive waveform shown in FIG. 19 is that a period ΔT of Ov is provided for the selection voltage Vs, the non-selection voltage VNS, the write voltage VW, and the non-write voltage VNIF.

As a result, the voltage Vx-VY applied to the pixel becomes Ov for a time period of ΔT in each of the writing period B, holding period C, D, and E.

This is especially true when the voltage waveform applied to the liquid crystal during the holding period (non-selection period) has a constant voltage amplitude value, and when the pulse width is narrowed, the optical threshold voltage of the liquid crystal Vbth (ON)
and vbth (o+=v) increases, the rise characteristics become steeper, and the characteristics can be improved (~c) This is based on experimental results.

FIGS. 20 and 21 show other drive waveform examples based on the same idea as the drive method explained in FIG. 19.

Although omitted for the modifications shown in FIGS. 14, 16, and 18, the same driving method as described above can be used.

Further, in FIGS. 19, 20, and 21, a period Ov may also be provided in the initialization period.

Next, in the liquid crystal panel of FIG. 11, the pixel P1t is turned on,
VX1? applied to the scanning electrode and signal electrode when turning off PI3 and PI3? Vxx+ Vxs and Vv
1 and the voltage waveform applied to the pixel are shown in FIGS. 22 and 23.

The waveforms shown in Figures 22 and 23 are similar to those shown in Figures 17 and 18.
This is based on the voltage waveform shown in the figure.

The t1 time is the time to initialize all pixels.

Therefore, V x 1 to V x s are initialized to the voltage V r
x, V y t - V y s is the initialization voltage VI
Make it Y. This results in +3V as shown in Figure 22.
A voltage of o is applied to the liquid crystal, and finally the liquid crystal turns on.

Next, select voltage Vs is applied to each scan electrode.

The voltages are sequentially applied during the period t4. At this time, a non-writing voltage VNII is applied to the signal electrode in order to turn the pixel into an on state like Pz. Thereby, the pixel retains its initial state before the start of scanning.

On the other hand, a write voltage Vw is applied to turn the pixel into an off state like PTT. As a result, the display state of the pixel is reversed and becomes an off state.

Through the operations described above, rewriting of one screen is completed. After finishing, apply VH lightning voltage to scanning electrode and signal electrode,
A voltage that does not reverse the initial state may be applied. for example,
Scan voltage is set to non-select voltage VNS.

Set the signal voltage to VNw.

FIG. 23 shows an example of a voltage waveform when the initial state is turned off.

FIG. 24 shows an embodiment of the drive circuit. 23a-23d
, 24a to 24d are analog switches, 25.26 are switches, 29 is a scanning circuit, 27 is a line memory, 28 is a shift register, 20 is a liquid crystal panel, 21 is a signal electrode,
22 is a scanning electrode.

Analog switches 23a to 23d output scanning signals C1 to C.
The a input is selected when N is l L + , and the b input is selected when d HF. Analog switch 24a-24
d selects the a input when the display signal r to Q is 1L'', and selects the b input when the display signal is ``H''.

Further, the switches 25 and 26 select the a input when the drive switching signal CP r is l Hl and select the b input when the drive switching signal CP r is l L +.
Select input.

The operation of this circuit is shown in FIG. The scanning circuit 29 and line memory are reset by the reset signal R8, and the scanning signal C! ~CN and display signal Qr~QL-1 as l L +
level. Furthermore, the drive switching signal CP r is changed to t
The period of E is set to 'H'. As a result, analog switch 2
The outputs of analog switches 3 to 23d are the initialization voltage Vzx, while the outputs of the analog switches 24a to 24d are the initialization voltage Vzx.
It becomes r+r. This brings all pixels into the initial state.

When this operation is completed, the output of the shift register 28 is taken into the line memory 27 at the timing of the synchronization signal SYH.

Then, during the period tl, the pixels of the first line are turned on or off, and this operation is repeated up to the Nth line. At this time, the switches 25 and 26 are set to V N S , respectively.
V + v w is selected.

When the rewriting of the entire screen is completed, the scanning circuit 29 and line memory 27 are reset by the reset signal R8, and the scanning signal Cr = CN and the display signal Q r -Q L are set to L'.
Make it. As a result, the non-selection voltage VNS is applied to all the scanning electrodes, and the non-writing voltage VNW is applied to all the signal electrodes, so that the display state is maintained.

An application example of the present invention will be explained using FIGS. 26 and 27. FIG. 26 schematically shows the liquid crystal panel 32 arranged in m rows and Q columns.

In this liquid crystal panel, m scanning electrodes are blocked,
A driving method when each block has n rows will be described.

Driving is performed by pairing initialization and write operations for each block. The outline of this driving method will be explained using FIG. 27.

The illustrated driving waveform has the number of rows in one block n = 10, and the second
It is based on the voltage state diagram shown in Figure 3. However, the initialization voltages Vxx and Vry have a period of Ov.

The t,ex period is a period for initializing all pixels included in block 1 (off state), and the subsequent twz
During the period, a write operation is performed on block 1 by line sequential scanning.

The operations described above are executed in blocks 2 and 3. ... to rewrite the entire screen.

Further, the screen rewriting operation may be performed at regular intervals, or may be performed only when changing the displayed content. In this case, only the blocks to be changed may be selected.

〔Effect of the invention〕

According to the present invention, the selection time for one line during matrix driving can be shortened, so that the screen rewriting time can be shortened. This allows a display with a large display capacity.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram of the present invention, Figure 2 is an arrangement diagram of liquid crystal molecules,
3 and 4 are diagrams showing the conventional example, FIGS. 5 to 7 are diagrams showing the structure and liquid crystal material of the liquid crystal panel of the present invention, and FIGS.
FIG. 10 is a characteristic diagram of the liquid crystal, FIGS. 11 to 23 are drive waveform diagrams according to the present invention, FIG. 24 is a specific example of the drive circuit, and FIG.
5 is a timing chart diagram of FIG. 24, and FIGS. 26 and 27 are diagrams showing application examples of the present invention. 6.13,16,22.30...scanning electrode, 7°12
．． 15,21.31...signal electrode, 14.17...
Pixel, 5, 20.32...Liquid crystal panel.

Claims (1)

[Claims] 1. In a matrix driving method for a liquid crystal display element in which a ferroelectric liquid crystal is sandwiched between X and Y electrodes, at least a pixel whose display content is to be rewritten is placed in one of a display on state or a display off state in advance. A method for driving a liquid crystal matrix, characterized in that the pixel is set to an initial state, and then selectively maintained in the initial state by time-division driving, or set to the other of a display-on state or a display-off state. . 2. In the liquid crystal matrix driving method according to claim 1, when the initial state is a display-on state, a write voltage of Vwsat (OFF) or lower that turns the liquid crystal into a display-off state or a first voltage of the liquid crystal is applied. Threshold voltage Vbth(OF
F) If the following voltage is applied and the initial state is changed to the display off state, Vwsa turns the liquid crystal into the display on state.
A method for driving a liquid crystal matrix, characterized in that a write voltage of t(ON) or higher or a voltage of lower than a second threshold voltage Vbth(ON) of a liquid crystal is applied.