JPH11174415A - Electro-optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain fine display under a temperature condition over a wide range by changing a scanning selection signal supply period and an erasing signal supply period in accordance with temperature information. SOLUTION: An erasing signal Se is a voltage pulse to be supplied to each scanning electrode and a voltage wave height value Ve is a negative pulse with a variable pulse width. A scanning selection signal Ss is supplied to a scanning electrode selected after the supply of the signal Se and a scanning non-selection signal Sn is supplied to an unselected scanning electrode and becomes reference voltage in one horizontal scanning period 1H. A writing information signal Iw generates a combined waveform Vw to be impressed to a selected pixel and a non-writing information signal In generates a non- writing synthetic waveform Vn to be impressed to a pixel. These information signals Iw, In are exclusively selected in accordance with picture information to be displayed and supplied to respective information electrodes. When one horizontal scanning period is fixed and the length of the scanning selection signal supply period is changed in accordance with the temperature, fine display can be obtained even over a wide temperature range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electro-optical device used for a display device or the like, and more particularly to an electro-optical device using a chiral smectic liquid crystal exhibiting a phase transition series exhibiting a chiral smectic phase.

[0002]

2. Description of the Related Art For example, TN type and STN type liquid crystal display devices using a nematic liquid crystal have been known as electro-optical devices. However, these liquid crystal display elements
Since the response speed of the electro-optical effect is as slow as the order of ms, there is a drawback that the screen is disturbed or the contrast is reduced when high-speed driving is attempted, and the displayable capacity is limited. Therefore, in recent years, practical use of a liquid crystal display device using a ferroelectric or antiferroelectric liquid crystal has been studied as a next-generation liquid crystal display device.

[0003] In 1975, R. B. From the discussion of molecular symmetry, Meyer et al. Show that chiral smectic C phase (SmC ^* phase) exhibits ferroelectricity if an optically active molecule has a dipole moment in a direction perpendicular to the long axis of the molecule. Is expected, DOBAMBC (2-methylbu
tyl p- [p- (decyloxybenzyli
denene-amino] -cinnamate) and succeeded in confirming the ferroelectricity of a liquid crystal for the first time (RB Meyer, L. Lierbert,
L. Strzelecki and P.S. Kelle
r: J. Phys. (Paris) 36 (1975) L
69. reference).

Here, the structure of the SmC ^* phase exhibiting ferroelectricity will be described. In the SmC ^* phase, the position of the center of gravity of the liquid crystal molecules in the layer is disordered. However, as schematically shown as a cone 101 in FIG. 27A, the major axis of the liquid crystal molecules (director 102) is different from that of the smectic layer. It is inclined by a fixed angle θ with respect to a layer normal z which is a normal of the layer surface 103 to be separated. The direction in which the director 102 tilts slightly shifts from layer to layer. As a result, the orientation of the liquid crystal molecules has a helical structure. Spiral pitch (helical pitch)
Is on the order of 1 μm, which is much larger than the layer spacing of about 1 nm.

A phase having such a molecular arrangement has been confirmed not only in a ferroelectric chiral smectic liquid crystal but also in an antiferroelectric chiral smectic liquid crystal (ADL Chandiani, T. Hagiwari).
a, Y. Suzuki, Y .; Ouchi, H .; Take
Zooe and A. Fukuda: Jpn. J. Ap
pl. Phys. 27 (1988) L729. reference).
In antiferroelectric liquid crystals, when the optical purity is changed, Sm
A C ^* phase appears, or MHPOBC (4- (1-
methylheptyloxycarbonyl) p
henyl 4'-octyloxybiphenyl
−4-carboxylate), optical purity 1
Clark and Lagerwall, in which a SmC ^* phase also appears even in the case of 00% R-form or S-form, have a spiral structure that disappears when the cell thickness becomes less than about 1 μm (about the same as the pitch of the spiral). As shown in FIG. 27B, it has been found that the molecules 104 of each layer take one of the bistable states in accordance with the applied electric field, and the surface-stabilized ferroelectric liquid crystal display device (SSFLC: surface first) has been discovered.
available ferroelectric li
liquid crystal). This is disclosed in JP-A-56-107216 and U.S. Pat.
No. 7924 and the like. FIG. 27
In (b), the direction of the electric field applied to the molecule 104 is a direction perpendicular to the plane of the paper and from the back side of the paper to the front side. The electric dipole moments of the molecules 104 are all aligned in the direction of the applied electric field as shown in each molecule in FIG.

The principle of operation will be described with reference to FIG. As described above, the SSFLC molecule 104 formed as a thin cell assumes one of two stable states A and B depending on the direction of the applied electric field, as shown in FIG. In the state A shown in FIG.
The direction of the electric field applied to the molecule 104 is perpendicular to the plane of the drawing and goes from the front side to the back side of the drawing. In the state B, the direction is perpendicular to the plane of the drawing and goes from the back side to the front side of the drawing.

Therefore, between two orthogonal polarizers,
For example, by arranging the SSFLC cells such that the long axis of the molecule in the state B is parallel to one direction of the polarizer (the direction 111 indicated by the arrow in the figure), the light in the state A The light is transmitted and becomes a bright state, and in the case of state B, the light is shut off and becomes a dark state. In other words, by switching the direction of the applied electric field, black and white display can be performed.

In the SSFLC, spontaneous polarization and an electric field directly interact with each other, so that, unlike ordinary switching using dielectric anisotropy in a nematic liquid crystal, a high-speed response on the order of ms or more to an electric field is possible. is there. Also,
Once the SSFLC switches to one of the bistable states, the SSFLC has a so-called memory property that maintains the state even when the electric field disappears. Therefore, it is not necessary to always apply a voltage.

As described above, the SSFLC-type liquid crystal display element can write display contents at high speed for each scanning line by utilizing the characteristics of high-speed response and memory characteristics, and can perform simple matrix driving. It has become possible to realize a large-capacity display, and is expected to be applied to a wall-mounted television.

[0010] Such a driving method of the liquid crystal display element is disclosed in US Patent No. 4,655,561 and US Patent No. 4,836,656.
The details are disclosed in the issue.

[0011] Such a method of manufacturing a liquid crystal display element or a technique of aligning liquid crystal is disclosed in detail in US Patent Nos. 4,639,089, 4,778,259 and 5,189,536.

A liquid crystal material suitable for the display device is disclosed in US Pat. No. 4,681,404 and US Pat.
No. 323, U.S. Pat. No. 5,120,466.

The FLC can be classified into two types, that is, positive and negative in dielectric anisotropy, and switching (change of alignment state) is performed depending on whether the dielectric anisotropy is positive or negative.
Are different in the relationship between the pulse width (τ) of the driving voltage and the pulse peak value (V), that is, the τ-V characteristic.

Taking an example of an ideal driving characteristic when a monopulse is applied, the combination of the pulse width and the pulse peak value of the driving pulse applied to the FLC is shown in FIGS. 29 (a) and 29 (b).
In the region above the threshold characteristic curve ([tau] -V curve), switching occurs. On the other hand, in the region below the characteristic curve, switching does not occur. For example, assuming that a drive pulse having a constant pulse width τ1 shown in FIG. 2A is applied to an FLC having a positive dielectric anisotropy, the pulse crest value of the drive pulse becomes as shown in FIG. In the case of V _off (V _off = V _th −V _d ), no switching occurs and V _on (V _on = V _th + V)
Switching occurs in case _d ).

As is apparent from a comparison of FIGS. 1A and 1B, in the FLC having a positive dielectric anisotropy, the pulse width required for switching becomes higher as the pulse height of the driving pulse becomes higher. It gets smaller monotonically. On the other hand, FLC having a negative dielectric anisotropy has a so-called τ-V _min characteristic in which a pulse peak value (V _min ) at which a pulse width required for switching has a minimum value exists, and than the low voltage side gradient of the graph in the high-voltage side becomes Kyu崚the V _min as a boundary.

Accordingly, FL having a negative dielectric anisotropy has
In C, _assuming that a drive pulse having a constant pulse width τ ₂ shown in FIG. 4B is applied, the pulse _peak value of this drive pulse becomes V _off1 (V _off1 = V
_th1 -V _d) or _{V on2 (V on2 = V th2} + V d)
In the case of, no switching occurs and V _on1 (V _on1 = V
_th1 + V _d) or _{V off2 (V off2 = V th2} + V d)
Switching occurs in the case of

That is, FLC having negative dielectric anisotropy
, Like the relationship between the above V _off1 and V _on1, non-writing voltage (FLC does not cause the switching pulse height) is the write voltage applied to the pixel in the selection period (F
A low-voltage drive method using a drive pulse that is lower than the pulse peak value at which LC causes switching, and conversely, the non-write voltage is higher than the write voltage, as in the relationship between V _off2 and V _on2 described above. It can be driven by such a high voltage driving method.

[0018] Incidentally, as described above, since than V _min gradient of the graph of the high-voltage side is steep, high voltage driving method, the difference between the response speed to the response speed and the writing voltage for the non-writing voltage Since it is large, there is an advantage that the allowable range of the unit pulse width (slot time) can be widened.

A display device using a liquid crystal material exhibiting such V _min and τ _min is disclosed in JP-A-1-214824, JP-A-1-214825, and JP-A-122228.
This is disclosed in detail in the official gazette.

Japanese Patent Application Laid-Open No. 9-127483 discloses that
A driving method of a display element using the above liquid crystal material is described. This driving method shows good display characteristics under a relatively wide range of temperature conditions, but is still insufficient.

On the other hand, Japanese Patent Application Laid-Open No. 8-101372 discloses that a voltage applied to a pixel and a pulse book according to a temperature condition increase a rate of change of the voltage with a rise in temperature.
In addition, there is described a temperature compensation method of a drive signal in which the voltage peak value is controlled to be low, and the rate of change of the pulse width is reduced as the temperature rises, and the pulse width is controlled to be reduced.

[0022]

As described above, in the conventional electro-optical device using the chiral smectic liquid crystal, the pulse width of the applied voltage must change the voltage peak value finely every time the temperature changes by several degrees Celsius. And the variable range must be two or three digits. Therefore, the design of the drive circuit for driving the electro-optical element and the design of the control circuit for controlling the drive circuit are complicated, which has caused a cost increase. In particular, under a low temperature condition, one horizontal scanning period becomes too long, which causes a problem that flicker occurs due to a low frame frequency. Further, a change in one horizontal scanning period depending on the temperature lowers the display characteristics of a moving image.

In the case of a liquid crystal having a τ- _Vmin characteristic in which the influence of temperature on driving is relatively small, US Pat.
As described in Japanese Patent No. 02107, there is known a method of applying an AC voltage while changing its frequency in accordance with the temperature. However, this method is also a method capable of solving the above-mentioned complicated design and high cost. It is hard to say.

An object of the present invention is to provide an electro-optical device in which a drive circuit and a control circuit can be easily designed.

Another object of the present invention is to provide an electro-optical device which can be manufactured at low cost.

Another object of the present invention is to provide an electro-optical device capable of performing a good display under a wide range of temperature conditions.

[0027]

According to the present invention, there is provided an electro-optical element having a pair of substrates having a scanning electrode group and an information electrode group, and a chiral smectic liquid crystal disposed between the substrates.
In an electro-optical device having a scan electrode drive circuit for supplying a scan selection signal to the scan electrode group and an information electrode drive circuit for supplying an information signal to the information electrode group, one horizontal scanning period defined by the information signal Means for operating the scan electrode drive circuit so as to change the supply period of the scan selection signal according to the temperature information, and applying an erase signal to the scan electrode prior to the supply of the scan selection signal, Means for operating the scan electrode drive circuit so as to change the supply period of the erase signal according to the temperature information.

[0028]

FIG. 1 shows various signal waveforms used in the present invention. The erasing signal Se is a voltage pulse supplied to each scanning electrode, and is a negative pulse with a variable voltage peak value Ve pulse width. The scanning selection signal Ss indicates a waveform supplied to the selected scanning electrode after the erasing signal Se is supplied, and includes a first half composed of a reference voltage, a voltage peak value Vs, and a positive pulse having a pulse width τ. Consists of the second half.

The scan non-selection signal Sn indicates a waveform supplied to a non-selected scan electrode, and is a reference voltage during one horizontal scanning period (1H).

The write information signal Iw is a composite waveform V applied to the selected pixel in cooperation with the scan selection signal Ss.
This is a signal for generating w and supplied to the information electrode.

The non-writing information signal In is a signal for generating a non-writing composite waveform Vn applied to the pixel in cooperation with the scanning selection signal Ss, and is supplied to the information signal.

The two information signals Iw and In are mutually exclusive selected according to the image information to be displayed and supplied to the information electrodes.

Here, each voltage level is shown with reference to the voltage level Vc of the scanning non-selection signal Sn.

One of the features of the present invention resides in that one horizontal scanning period defined by the information signal is kept constant and the supply period of the scanning selection signal is changed. That is, in the example of FIG. 1, the pulse fall timing can be delayed until the end of the next horizontal scanning period (1H ₂ ) by changing the pulse width of the positive pulse.

By changing the length of the supply period according to the temperature, good display can be performed even under a wide range of temperature conditions.

[0036] More specifically, as described below, at relatively high under temperature, by shortening the pulse width, the fall of the pulse is synchronized with the end of the horizontal scanning period IH _1.

On the other hand, under conditions where the temperature is relatively low, the pulse width is increased, and the falling of the pulse is synchronized with the end of the next horizontal scanning period (1H ₂ ).

In addition, another feature of the present invention is that the supply period (pulse width) of the erase signal Se is changed according to the temperature while one horizontal scanning period is fixed. Further, it is preferable to change it in accordance with the supply period (pulse width) of the scanning selection signal.

The supply period of the erasing signal should be one horizontal scanning period or more, and more preferably, it can be selected from the range of two horizontal scanning periods to four horizontal scanning periods in accordance with the temperature.

[0040] The positive pulse width of FIG. 1, the scanning selection signal Ss is set to 1.5 times the tau, and the waveform of the case where the information signal in the next horizontal scanning period IH ₂ is the same as the horizontal scanning period IH ₁ before In addition, it is indicated by a broken line. In the present invention,
Inversion (switching) and non-inversion (non-switching) of the liquid crystal can be selected by a combination of whether the pulse in the first half of the horizontal scanning period is positive or negative and the peak value of the pulse in the latter half is small or large. This is because the liquid crystal used has τ-V _min characteristics.

FIG. 2 is an example of a threshold characteristic curve of a liquid crystal material exhibiting negative dielectric anisotropy. CH0 arranges liquid crystal exhibiting negative dielectric anisotropy between a pair of electrodes, and sets a threshold value when a simple rectangular voltage pulse same as the scan selection signal Ss of FIG. 1 is applied between the electrodes. FIG.
1 is a characteristic curve showing a threshold value when the same signal as the write composite signal Vw in FIG. 1 is applied, and CH2 is a characteristic curve showing a threshold value when the same signal as the non-write composite signal Vn in FIG. 1 is applied. It is a curve. In any case, since the pulse width τ has a minimum value (minimum value) at a voltage peak value Vs, such a characteristic is called a τ- _Vmin characteristic. Each characteristic curve C
When a signal of a pulse width and a voltage corresponding to an area above H0, CH1, and CH2 is applied, the liquid crystal performs switching, and when a signal of a pulse width and a voltage corresponding to an area below it is applied, the liquid crystal does not switch.

That is, it is shown that changing the waveform of the applied signal changes the pulse width and the voltage value satisfying the threshold value.

[0043] When fed a waveform V _w with the pulse width and voltage in charge, for example, a point PA, since there is a point PA to the upper region of the characteristic curve CH1, the liquid crystal is switched.

However, in the case of the waveform Vn, the point P
The liquid crystal does not switch even when a signal having a pulse width and voltage satisfying A is given. This is because the point PA is located below the characteristic curve CH2.

Therefore, when the liquid crystal of a certain pixel is switched, a signal indicating the characteristic curve CH1 is used. When the liquid crystal is not switched, a signal indicating the characteristic curve CH2 is used. Further, each signal is selected from the hatched area in FIG. The switching of the liquid crystal can be controlled by increasing the pulse width and voltage.

FIG. 3 shows an example of a driving characteristic curve of a liquid crystal material having a positive dielectric anisotropy.

CH0 'is obtained by disposing a liquid crystal exhibiting positive dielectric anisotropy between a pair of electrodes, and applying a simple rectangular voltage pulse same as the scan selection signal Ss of FIG. 1 between the electrodes. A characteristic curve showing the threshold value, CH1 'is a characteristic curve showing the threshold value when the composite signal for writing Vw of FIG. 1 is applied, and CH2' is a characteristic curve showing the characteristic when the non-write composite signal Vn of FIG. 1 is applied. 6 is a characteristic curve showing a threshold. When a signal of a pulse width and a voltage corresponding to an area on the upper right side of each of the characteristic curves CH0 ', CH1' and CH2 'is applied, the liquid crystal causes switching, and a signal of a pulse width and a voltage corresponding to an area on the lower left side is applied. The liquid crystal does not switch.

That is, it is shown that changing the waveform of the applied signal changes the pulse width and the voltage value satisfying the threshold value.

For example, when a waveform Vw having a pulse width and a voltage corresponding to the point PB is given, the characteristic curve CH1 '
, The liquid crystal does not switch.

However, in the case of the waveform Vn, the point P
When a pulse width and voltage signal satisfying B are applied, the liquid crystal causes switching. Because the point PB has the characteristic curve CH
This is because it is in the upper right area of 2 '.

Therefore, if the signal indicating the characteristic curve CH2 'is used when switching the liquid crystal of a certain pixel and the signal indicating the characteristic curve CH1' is used when the liquid crystal is not switched, the region shown by hatching in FIG. The pulse width and voltage of each signal can be selected.

When the pulse widths and voltages of the signal waveforms Vw and Vn are determined, the pulse width can be selected from a wide range of τ ₁₁ to τ ₁₂ when the voltage V ₁₁ is selected according to the characteristics shown in FIG.

Meanwhile, in the case of characteristics of Figure 3, the selectable range of the pulse width when you select voltage V ₁₁ becomes narrow range of τ ₁₃ ~τ _14.

In other words, the selection range (margin) of the driving condition in which the pixel can be switched or non-switched according to the image information is larger in the liquid crystal having the characteristics shown in FIG. Further, as described above, the characteristic of FIG. 2 shows the dependence on the applied voltage waveform, and thus is suitably used in the present invention.

(Temperature Compensation by Pulse Width Modulation of Scan Selection Signal) Since the above-mentioned margin changes with temperature,
First, the pulse width of the positive pulse of the scan selection signal must be modulated according to the temperature.

FIG. 4 is an enlarged view of one pixel portion of a liquid crystal element as an electro-optical element used in the present invention.

Reference numerals 1a and 1b denote transparent substrates such as glass.
2b is a transparent conductive film of ITO or the like, 3a and 3b are insulating films provided as needed to widen margins, 4a and 4b
Is an alignment film, which is preferably rubbed so as to obtain a chevron layer structure in which a chiral smectic liquid crystal is U2 uniform aligned.

Reference numeral 5 denotes a chiral smectic liquid crystal exhibiting ferroelectricity. Although not shown, light can be transmitted or blocked according to the alignment state (stable state) of the liquid crystal molecules by combining the element in FIG. 4 with a polarizing element.

Here, the molecular orientation of a chiral smectic liquid crystal having a chevron layer structure will be described.

FIG. 5A is a schematic view showing the arrangement of directors at various positions between substrates in each state of C1 orientation. In the figure, 51 to 54 show the state where the director is projected on the bottom surface of the cone in each state and this is viewed from the bottom direction. 51 and 52 are the spray state, and 53 and 54 are the uniform state considered to be the uniform state. Arrangement. As can be seen from the figure, in the two states 53 and 54 of the uniform, the position of the liquid crystal molecules at the upper or lower substrate interface is replaced with the position in the spray state.
FIG. 5B shows the C2 orientation. The C2 orientation includes a C2 spray state (55, 56) and a C2 uniform state (57, 58) in which there is no interface switching and there are two states of internal switching.

In the present invention, it is preferable to use such a C2 uniform orientation. For C2 uniform orientation, see U.S. Patent Nos. 4,932,758 and 5,200,848 and IDW97, PP. 269-
272 is detailed.

FIG. 6 shows an electro-optical device according to the present invention, which has a simple matrix type liquid crystal element 10 having pixels having a sectional structure as shown in FIG.

The liquid crystal element 10 has a scanning electrode driving circuit 13 connected to the scanning electrode group 11 and an information electrode group 12
Is driven by the information electrode drive circuit 14 connected to the power supply.

The drive voltage generation circuit 15 generates a voltage of a predetermined potential for generating a voltage applied to each electrode of the liquid crystal element 10 and supplies the generated voltage to the drive circuits 13 and 14.

Reference numeral 16 denotes a control circuit.
A signal for turning on / off the switching transistor provided inside 14 is supplied. The control circuit 16 supplies a signal for changing the voltage level generated by the drive voltage generation circuit 15 to the circuit 15.

Further, in accordance with temperature information from a temperature sensor integrated with the liquid crystal element 17 or a temperature sensor 17 disposed in contact with or near the liquid crystal element 10, the control circuit controls the circuit 15. On / off of the switching transistor in the drive circuit 15 is controlled.

FIG. 7 is a diagram showing an example of the operation of the scan electrode drive circuit according to the present invention, and only parts relating to two output terminals are shown for ease of explanation.

The logic circuits LG1 and LG2 are connected to the power supply voltage Vcc.
It operates with more power supplied, and is controlled by a clock CLK, a start pulse STP, and a temperature compensation control signal TCNT.

[0069] the start pulse STP When a high-level pulse is supplied as a temperature compensating control signal TCNT1 inputted circuit LG1 outputs a pulse of high level from the terminal phi _1. Switch SW ₁₁ is turned on to erase signal Ve is supplied to a single-th scanning electrode from the output terminal S1. At this time, the output of the NOR gate NOR1 is switch SW ₁ becomes low is turned off. Since the outputs of the terminals φ ₁₁ and φ ₁₂ of the logic circuit LG2 are both at the low level, the switch SW
₂₁ and SW ₂₂ are also off.

[0070] Then the output of the terminal phi ₂ control signal TCNT1 becomes high level again becomes high level, the switch SW ₁₂ is turned on, the erase signal Ve is supplied to two-th scanning electrode from the output terminal S2. When the output terminal phi ₂ becomes low level, the output of the NOR gate NOR1 is the switch SW ₁ to the high level is turned on, the output terminal S1
Is supplied with a voltage Vc.

[0071] Then the output of the terminal phi ₂ is the output of the NOR gate NOR2 becomes a low level to a high level, the switch SW ₂ is turned on, the voltage Vc supplied from the output terminal S2.

[0072] Thus, after a predetermined period of time from the supply erase voltage Ve, the voltage Vs switch SW ₂₁ is high-level pulse from the terminal phi ₁₁ of the logic circuit LG2 output is turned on
Is output from the output terminal S1 and supplied to the first scan electrode. At this time, the output of the NOR gate NOR1 is switch SW ₁ because of the low level is turned off.

[0073] Similarly from the terminal phi ₁₂ of the high level pulse is output, the voltage Vs is supplied to the two-th scanning electrode switch SW ₂₂ is turned on. The supply period of the voltage Vs is controlled by the pulse timing of the temperature compensation control signal TCNT2.

Since only the switches SW ₁ and SW ₂ are turned on during the non-selection period, the scanning electrode is maintained at the voltage Vc level.

FIG. 7B shows the clock CLK, the temperature compensation control signal TCNT terminals φ ₁ , φ ₂ , φ ₁₁ , φ ₁₂
And the timing of the output of the gates NOR1 and NOR2. The timing at which the terminals φ ₁ and φ ₂ rise and the timing at which the output pulses at the terminals φ ₁₁ and φ ₁₂ rise at the timing when the high-level pulse is supplied to TCNT are determined.

In this manner, the pulse width is modulated according to the temperature as indicated by the arrow in the figure, and the temperature can be compensated.

As described in detail above, according to the present invention, the switches SW ₁₁ , SW ₁₂ , SW ₁₂ according to the control signal TCNT input according to the information from the temperature sensor 17.
_The periods (on periods) in which the switches ₂₁ and ₂₂ are turned on are controlled.

FIG. 8 shows a drive waveform modulated by temperature used in the present invention. The potential relationship is V1> V
3>VC>V4> V2, | V1 |> | V2 |, |
V2 |> | V3 |, | V3 | = | V4 |. The driving waveform D is a waveform used when the temperature of the liquid crystal element is high (TH).

[0079] First, the voltage before the horizontal scanning period IH ₁ defining the display state of pixels on a certain scanning electrode V2, a pulse width Δ
A negative pulse Se for erasing Tr (1H × 2) is supplied to the scan electrodes. At this time, regardless of whether the information signal is Iw or In, the pixel has a composite waveform V having a pulse width and voltage sufficient to align the liquid crystal of the pixel in one alignment state.
E1 and VE1 'are applied. Thus, all the pixels on the scanning line to which the pulse Se is supplied are reset to a dark (or bright) state. Next, after a lapse of a predetermined period, the scanning selection signal S
s is supplied to the scanning electrode, and the information signal Iw
Alternatively, In is supplied to the information electrode. The composite signal Vw with the information signal Iw for switching the liquid crystal of the reset pixel is a voltage V3 in the _first half of the horizontal scanning signal 1H1.
And a large pulse of the latter half of the voltage (V1-V3).

The composite waveform Vn with the information signal In for preventing the liquid crystal of the pixel in the reset state from switching is represented by:
A small negative pulse of voltage V4 (<0) followed by a voltage (V
1-V4).

The driving waveform E is a waveform used at the time of medium temperature (TM). The difference from the drive waveform D is that the fall of the positive pulse of the scan selection signal Ss is delayed, the pulse width is twice as large as the signal Ss of the drive waveform A, and the pulse width of the erase signal Se is 1.5 times. That is the point. Accordingly, the synthetic waveform applied to the pixel in the next horizontal scanning period IH ₂ is different from the case of the driving waveform A. Whether the voltage of the first half of the pulse of the next horizontal scanning period IH ₂ is either V1-V3 becomes V1-V4, dependent on the information signal supplied to the next horizontal scanning period IH _2. Similarly dependent on the following information signal voltage in the second half of the pulse of the horizontal scanning period IH ₂ is supplied to the period of IH ₂ may be either V4 becomes V3.

The driving waveform F is a waveform used at a low temperature (TL). The difference from the drive waveform E is that the fall of the positive pulse of the scan selection signal Ss is further delayed and the pulse width is
This is a point that is three times the positive pulse of the scan selection signal Ss of the drive waveform B. The pulse width of the erase signal Se is twice as large as that of the waveform D.

FIG. 9 shows the temperature dependence of the τ-V characteristic in the case of the driving waveform D. The voltage V1 of the scan selection signal is set to the minimum value τ.
_When V ₂₁ is determined to be _min , the pulse width selection range (margin) when the temperature of the liquid crystal element is high is τ ₂₁ to τ ₂₂ , and the pulse width margin becomes wider as the temperature becomes lower to middle temperature. The width itself has also increased.

FIG. 10 is a graph similar to FIG.
5 shows the temperature dependence of the V characteristic.

FIG. 11 shows the temperature dependence of the τ-V characteristic in the case of the driving waveform F. FIG. 12 is a graph plotting selectable pulse widths when the scan selection signal V1 is fixed at V21 on the horizontal axis and temperature on the vertical axis based on the characteristics of FIGS.

The pulse width ΔTd is fixed to T ₃₀ , the driving waveform D is used under high temperature conditions, and the driving waveform E is used under medium temperature conditions.
By using the driving waveform F under the low temperature condition, the switching or non-switching of the pixel can be reliably determined within the temperature range from the highest temperature TMP1 to the lowest temperature TMP4.

For example, the driving waveform D is used in the high temperature region of the temperatures TMP1 to TMP2, and the driving waveform E is used in the middle temperature region of the temperatures TMP2 to TMP3.
In the low temperature region of No. 4, the driving waveform F may be used.

In the case of a liquid crystal element exhibiting this characteristic, since the margin of the drive waveform E and the margin of the drive waveform F overlap greatly, the switching between the drive waveforms E and F may use the temperature TMP5 as the threshold value. .

Making the pulse width ΔTd constant means that one horizontal scanning period, that is, a period in which one scanning electrode is selected, is constant, and the frame frequency is always constant. Therefore, large-screen display of a moving image becomes very easy.

A liquid crystal device having a structure as shown in FIG. 4 was manufactured. An indium tin oxide (ITO) film having a thickness of 70 nm is formed on each of two glass substrates by a sputtering method, and thereafter, a film having a thickness of 120 nm is formed by a sputtering method.
A tantalum oxide (Ta ₂ O ₃ ) film was formed.

On the tantalum oxide films of the two substrates, NMP (N-methylpyrrolidone) of polyamic acid LP-64 (manufactured by Toray Industries, Ltd.): n-BC
The (n-butyl cellosolve) mixed solution was spin-coated. The coating solution was prepared by adjusting LP-64 to 1% by weight in a mixed solvent of NMP: n-BC = 2: 1 and spinning at 45 rpm for 20 seconds.

The substrate was dried in an oven at 80 ° C. for 5 minutes, and then heated and baked in an oven at 200 ° C. for 1 hour to imidize the substrate. The obtained polyimide film was about 10 nm thick, and this film was rubbed to form an alignment film. Rubbing was performed twice in the same direction using a nylon cloth wound around a roller having a diameter of 10 cm, at 16.7 rotations / sec, 0.4 mm of cloth being pressed against the alignment film surface, and a substrate feed rate of 10 mm / sec. One-way rubbing was performed.

Then, an average particle size of 1.2 μm
m silica beads dispersed at 0.008% by weight
A (isopropyl alcohol) solution is spin-coated at 25 rpm for 10 seconds, and the distribution density is 300 / m
A bead spacer of about m ² was sprayed.

The two substrates obtained as described above are bonded together facing each other so that the rubbing directions are the same, and are thermally cured in an oven at 150 ° C. for 90 minutes.
Cell.

In this cell, a ferroelectric liquid crystal “FELIX” having a negative dielectric constant anisotropy τ-V _min characteristic manufactured by Hoechst Co., Ltd.
−016/030 ”was injected under reduced pressure (10 Pa) at an isotropic phase temperature (100 ° C.), and gradually cooled to an Sm ^* C phase to obtain a liquid crystal element. FIG. 13 shows τ-V characteristics when a simple driving pulse is applied to the liquid crystal.

FIG. 14 shows other data of the phase transition series of the liquid crystal.

The liquid crystal device thus obtained is driven by applying drive waveforms D to F as shown in FIG.

At this time, a temperature compensating circuit for voltage modulation as shown in FIG. 15 is added, and the scan selection signal Ss according to the temperature is added.
The positive pulse voltage V1 was changed so as to increase as the temperature rose.

FIG. 15 shows a temperature compensation circuit for voltage modulation used in the present invention.

The temperature information from the temperature sensor 17 such as a thermistor is converted into digital data by an analog / digital converter 17a and sent to the control circuit 17.

The control circuit 17 compares the digitized temperature information with the value of the temperature compensation table stored in the ROM, and outputs the corresponding voltage data as a digital value.

A digital-to-analog converter 15a in the drive voltage generation circuit 15 converts digital voltage data determined based on temperature information into voltage-modulated analog voltage data.

The comparator 15b in the drive voltage generation circuit 15
Receives analog voltage data and a reference voltage Vpw, amplifies the difference, and determines the voltage peak value of the scan selection signal.
The reference voltage for driving the liquid crystal element thus obtained is output to the scan electrode driving circuit via the buffer amplifier 15C.

FIG. 16 shows the peak values V1 and V1 of each pulse in FIG.
The relationship between the values of V2, V3, V4, and VC and the temperature is shown. V2, V3, V4, and VC are constant over the entire temperature range under use conditions. FIG. 17 shows each pulse width ΔT in FIG.
The relationship between the values of r, ΔTs, 1H, ΔTd and temperature is shown. ΔTr is the pulse width of the erase pulse, and is changed in 11 steps so that the pulse width becomes shorter as the temperature rises.

ΔTs is the pulse width of the positive pulse of the scanning selection signal Ss, and is changed in 11 steps so that the pulse width becomes shorter as the temperature rises.

The horizontal scanning period (1H) and the unit pulse width (ΔTd) of the information signal are constant within the entire temperature range.

FIG. 18 shows the temperature dependence of the τ-V characteristic of the liquid crystal element of this example. This characteristic is obtained when the driving waveform D in FIG. 8 is used as the driving waveform.

As the temperature rises, the pulse width ΔTd
The minimum value of the threshold value has decreased.

Therefore, this waveform is more suitable for driving under high temperature than driving under low temperature.

FIG. 19 shows the τ-V characteristics at 10 ° C. for each of the drive waveforms D to F.

It can be seen that the driving waveform F is optimal under a low temperature condition such as 10 ° C.

FIG. 20 shows a selection range of the pulse width at the drive voltage which can minimize the pulse width for each drive waveform while finely changing the temperature condition.

As shown in FIG. 20, the driving waveform D is used under a high temperature condition near 40 ° C., the driving waveform E is used under a medium temperature condition near 25 ° C., and the driving waveform F is used under a low temperature condition near 10 ° C. By using the above method, it is possible to perform a good display over the entire temperature range only by keeping one horizontal scanning period (1H) constant and changing the voltage within the range of 2 to 3 V according to the temperature.

In the example of FIG. 17, the number of variable steps of ΔTs is 11
Although the number of steps is three, the number of steps may be three, that is, drive waveforms D to F, or the number of steps may be two when the operating temperature range of the liquid crystal element is narrow.

As the temperature rises, as in the case of the ferroelectric liquid crystal “FELIX-016 / 100” manufactured by Hoechst, the minimum value of the pulse width τ decreases and the voltage wave corresponding to the temperature increases. Some materials exhibit characteristics where the high value is also reduced.

FIG. 21 shows an example of this.

When such a liquid crystal material is used, it is desirable to control the pulse peak value of the scanning selection signal so as to decrease as the temperature increases as shown in FIG. 22 instead of FIG.

FIGS. 23 to 25 show the waveforms of the scanning signal and the information signal used when the temperature of the liquid crystal element is high, medium, and low, and the display state of each pixel on the liquid crystal element at that time.

FIG. 26 shows another driving waveform used in the present invention. The drive waveform G is a waveform suitably used in the case of a high temperature, and is different from the drive waveform D shown in FIG. 8 in the information signal waveform. The information signal waveform in this example is the first ΔTd /
The period of 2 and the first period of ΔTd / 2 are DC compensation pulses of the same polarity, and the period of ΔTd between these periods is a pulse that determines the display state of the pixel.

Similarly, the driving waveform H is a suitable waveform at the time of medium temperature,
The driving waveform I is a suitable waveform at a low temperature, and each mechanically corresponds to the waveforms E and F in FIG.

As described above, by changing the pulse width ΔTs of the scanning selection signal and the pulse width ΔTr of the erasing signal in accordance with the temperature while keeping one horizontal scanning period constant, excellent display can be performed over a wide temperature range. Can be performed.

[0122]

According to the present invention, since temperature compensation can be performed while keeping one horizontal scanning selection period constant, the design of a drive circuit and a control circuit becomes easy.

Thus, the electro-optical device can be manufactured at low cost.

Further, since one horizontal scan can be performed in several tens of microseconds even under low temperature conditions, display characteristics of moving images and the like are improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a driving waveform of an electro-optical element used in an electro-optical device according to the present invention.

FIG. 2 is a diagram showing threshold characteristics of an electro-optical element used in the electro-optical device of the present invention.

FIG. 3 is a diagram showing another example of the threshold characteristics of the electro-optical element.

FIG. 4 is a schematic view showing the structure of an electro-optical element used in the present invention.

FIG. 5 is a schematic diagram for explaining the orientation of an electro-optical element used in the present invention.

FIG. 6 is a diagram illustrating an example of an electro-optical device according to the invention.

FIG. 7 is a circuit diagram showing an example of a scan electrode drive circuit used in the electro-optical device of the present invention.

FIG. 8 is a diagram showing another example of the driving waveform of the electro-optical element used in the electro-optical device of the present invention.

FIG. 9 is a diagram showing threshold characteristics of an electro-optical element used in the present invention.

FIG. 10 is a diagram showing threshold characteristics of an electro-optical element used in the present invention.

FIG. 11 is a diagram showing threshold characteristics of an electro-optical element used in the present invention.

FIG. 12 is a diagram illustrating an example of the temperature dependence of a driving margin of the electro-optical device according to the invention.

FIG. 13 is a diagram illustrating threshold characteristics of an electro-optical element used in the electro-optical device according to the invention.

FIG. 14 is a view showing a phase transition series of a liquid crystal used in the electro-optical device of the invention.

FIG. 15 is a diagram illustrating an example of a voltage modulation circuit used in the electro-optical device according to the invention.

FIG. 16 is a diagram illustrating an example of a driving voltage of an electro-optical element used in the electro-optical device according to the invention.

FIG. 17 is a diagram illustrating an example of a drive voltage pulse width of an electro-optical element used in the electro-optical device according to the invention.

FIG. 18 is a diagram showing threshold characteristics of another electro-optical element used in the present invention.

FIG. 19 is a diagram showing threshold characteristics of another electro-optical element used in the present invention.

FIG. 20 is a diagram illustrating an example of the temperature dependence of a drive margin of another electro-optical device according to the invention.

FIG. 21 is a diagram illustrating threshold characteristics of an electro-optical element used in the electro-optical device according to the invention.

FIG. 22 is a diagram showing an example of a drive voltage of another electro-optical element used in the present invention.

FIG. 23 is a diagram showing supply timings of driving waveforms used in the present invention.

FIG. 24 is a diagram showing supply timings of driving waveforms used in the present invention.

FIG. 25 is a diagram showing supply timings of driving waveforms used in the present invention.

FIG. 26 is a diagram showing another example of the driving waveform of the electro-optical element used in the electro-optical device according to the invention.

FIG. 27 is a schematic diagram for explaining the molecular orientation of a chiral smectic liquid crystal.

FIG. 28 is a schematic view for explaining the orientation of a ferroelectric chiral smectic liquid crystal.

FIG. 29 shows threshold characteristics of a liquid crystal element using two representative chiral smectic liquid crystals.

Claims (13)

[Claims] 1. An electro-optical element having a pair of substrates having a scanning electrode group and an information electrode group, and a chiral smectic liquid crystal disposed between the substrates, and a scanning electrode for supplying a scanning selection signal to the scanning electrode group. In an electro-optical device having a driving circuit and an information electrode driving circuit for supplying an information signal to the information electrode group, a horizontal scanning period defined by the information signal is fixed, and a supply period of the scanning selection signal is set to a temperature. Means for operating the scan electrode drive circuit so as to change according to the information; and applying an erase signal to the scan electrode prior to the supply of the scan selection signal, and setting a supply period of the erase signal according to the temperature information. Means for operating the scan electrode drive circuit so that the scan electrode drive circuit is changed. 2. The electro-optical device according to claim 1, further comprising means for operating the scan electrode drive circuit so as to change a voltage applied to a selected pixel in accordance with temperature information. 3. The electro-optical device according to claim 1, wherein the chiral smectic liquid crystal has a chevron layer structure. 4. The electro-optical device according to claim 1, wherein the chiral smectic liquid crystal exhibits a C2 orientation. 5. The electro-optical device according to claim 1, wherein the chiral smectic liquid crystal has a negative dielectric anisotropy. 6. The electro-optical device according to claim 1, wherein the chiral smectic liquid crystal has a minimum value of a threshold characteristic curve. 7. The electro-optical device according to claim 1, wherein an insulating film is provided between the conductive film and the alignment film on the inner surfaces of the pair of substrates. 8. The scan selection signal supplied to the n-th selected scan electrode and the scan selection signal supplied to the (n + 1) -th selected scan electrode are supplied in time overlap. 2. The electro-optical device according to 1. 9. The electro-optical device according to claim 8, wherein the overlapping period is changed according to the temperature information. 10. The electro-optical device according to claim 1, wherein an erasing signal is supplied for a period longer than one horizontal scanning period before supplying the scanning selection signal. 11. The electro-optical device according to claim 1, wherein the scan selection signal is supplied after a lapse of one horizontal scanning period after the supply of the erase signal. 12. An application signal for inverting an optical state of a pixel includes a first voltage pulse of one polarity followed by a second voltage pulse of one polarity within one horizontal scanning period. 2. The electro-optical device according to claim 1, wherein the peak value of the voltage pulse is larger than the peak value of the first voltage pulse. 13. The applied signal that does not invert the optical state of the pixel includes, within one horizontal period, a third voltage pulse of opposite polarity followed by a fourth voltage pulse of one polarity, and 13. The electro-optical device according to claim 1, wherein a peak value of the pulse is larger than a peak value of the third voltage pulse.