JPH0682760A - Driving method for ferroelectric liquid crystal display device - Google Patents

Abstract

PURPOSE:To improve the display quality at a generally used low temperature by varying the application frequency of both polarity pulses in conformation to the temperature of a FLC panel. CONSTITUTION:A ferroelectric liquid crystal(FLC) display has a scanning side driving circuit 2 connected to the scanning electrode L of a FLC panel 1 and a signal side driving circuit 3 connected to a signal electrode S. The change of transmitted light quantity in a first picture element formed of the scanning electrode to which a non- selective voltage and the signal electrode to which a rewrite voltage is applied is made nearly equal to that of a second picture element formed of the scanning electrode to which the non-selective voltage is applied and the signal electrode to which a holding voltage is applied, and the change of transmitted light quantity in a third picture element formed of the scanning electrode to which a selective voltage is applied and the signal electrode to which the holding voltage is applied is made nearly equal to or smaller than those in the first and second picture elements. According to the temperature of a ferroelectric liquid crystal molecule forming the liquid crystal panel, the application frequency of both polarity pulses to be applied to the first, second and third picture elements is changed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of driving a liquid crystal display device, and more particularly to a method of driving a display device of a ferroelectric liquid crystal (hereinafter abbreviated as FLC) panel.

[0002]

2. Description of the Related Art The structure of an FLC panel is shown in a schematic sectional view in FIG. That is, two glass substrates 5
a and 5b are arranged to face each other, and a plurality of transparent signal electrodes S made of indium tin oxide (hereinafter abbreviated as ITO) or the like are arranged in parallel on the surface of one glass substrate 5a, It is covered with a transparent insulating film 6a made of SiO ₂ or the like. On the surface of the other glass substrate 5b facing the signal electrode S, a plurality of transparent scanning electrodes L made of ITO or the like are arranged in parallel to each other in a direction orthogonal to the signal electrode S, and SiO ₂ is formed on the transparent scanning electrodes L. Is covered with a transparent insulating film 6b.

A transparent alignment film 7 made of polyvinyl alcohol or the like, which has been subjected to a rubbing treatment, is formed on each of the insulating films 6a and 6b.
a and 7b are formed respectively. These two glass substrates 5
a and 5b are bonded together with a sealant 8 leaving an injection port in part, and after the FLC 9 is introduced by vacuum injection into the space sandwiched between the alignment films 7a and 7b from the injection port, the injection port is sealed. It is sealed with a stopper 8. The two glass substrates 5a and 5b thus bonded together are sandwiched by two polarizing plates 10a and 10b arranged such that their polarization axes are orthogonal to each other.

FIG. 4 shows the scanning electrodes L of the FLC panel 1.
FIG. 3 is a plan view showing a schematic configuration of an FLC display (hereinafter abbreviated as FLCD) 4 in which the scanning side drive circuit 2 is connected to and the signal side drive circuit 3 is connected to the signal electrode S. Here, for simplification of description, the case where the number of scan electrodes L is 16 and the number of signal electrodes S is 16, that is, the case of the FLCD 4 configured by 16 × 16 pixels is shown, and each of the scan electrodes L is shown. The subscript i (i = 0 to F) is added to the reference symbol L for distinction, and each signal electrode S has a subscript j (j = 0 to 0) added to the reference symbol S.
F) is added for distinction. Also, in the following explanation,
A pixel at a portion where an arbitrary scan electrode Li and an arbitrary signal electrode Sj intersect is represented by a symbol Aij.

The scanning side driving circuit 2 is a circuit for applying a voltage to the scanning electrode L, and is composed of an address decoder, a latch and an analog switch (not shown).
The selection voltage VC1 is applied to the scan electrodes Li corresponding to the designated address Ax, and the other scan electrodes Lk (k ≠ i)
The non-selection voltage VC0 is applied to. The signal side drive circuit 3 is a circuit for applying a voltage to the signal electrode S, and is composed of a shift register (not shown), a latch and an analog switch, and the active voltage VS1 is applied to the signal electrode S corresponding to the data DATA of "1". Is applied, and the non-active voltage VS0 is applied to the signal electrode S corresponding to the data DATA of "0".

FLC molecule 11 constituting this pixel Aij
Has a spontaneous polarization Ps perpendicular to the long axis direction of the molecule as shown in FIG. 5B, and is proportional to the vector product of the electric field E generated from the voltage of the scan electrode L and the voltage of the signal electrode S and the spontaneous polarization Ps. It receives the force and moves on the surface of the cone 12 having the apex angle of twice the tilt angle 2θ. The FLC molecule 11 has two stable states, and the electric field E causes the FLC molecule 11 to move as shown in FIG.
When the FLC molecule 11 is moved to the axis 16 by the electric field E, the stable state 15 is obtained. FLC molecule 1
When 1 is moved from the given stable state by the electric field E, a restoring force for returning to the original stable state acts on the FLC molecule 11 unless the stable state is changed.

In general, the spontaneous polarization P at a certain temperature T °
s, electric field E, rotational viscosity η of FLC molecule 11 and response speed τ
It is said that there is a relation of τ = k2 (T) × η / (Ps × E) (1) between and. Also, due to the electric field E, FL
C molecule 11 from axis 16 to axis 17 or axis 17 to axis 16
Between the memory pulse width τm and the response speed τ required to change the FLC molecule 11 from one stable state to the other stable state by τm = k3 (T, E) × τ (2 ) Is said to have a relationship.

In fact, for a liquid crystal composition A K Sc Sa N I liquid crystal composition A. <-20 ° .55 ° .67 ° .73 °. FIG. 6 shows the response speed τ and the memory pulse width τm measured in the range of 40 °.

As can be seen from FIG. 6, the FLC response speed τ
And the temperature dependence of memory pulse width τm is very large. Therefore, there is a patent application in which a temperature sensor or the like is attached to the FLC panel 1 and the applied voltage V and the memory pulse width τm are changed according to the temperature of the panel, for example, JP-A-62-118.
It is made in 326 mag.

However, in addition to the force proportional to the spontaneous polarization Ps and the electric field E, the FLC molecule has a force proportional to the square of the electric field E and the difference Δε in the dielectric constant between the major axis direction and the minor axis direction of the FLC molecule. work. That force F acting on FLC molecules becomes F = k0 × Ps × E + k1 × Δε × E 2 (3). Therefore, if an FLC material with a negative dielectric anisotropy Δε is sealed in the panel, the force acting on the FLC molecules will be a certain electric field Ee.
Has the maximum value Fe.

According to the driving method of Japanese Patent Application No. 3-293179, in an FLCD having a negative dielectric anisotropy Δε, a voltage V0 / Ve <4 (4) with respect to a voltage Ve which gives an electric field Ee to FLC molecules, The force acting on the FLC molecule when 2 is F0 F0 = k0 x Ps x (E0 / 2) + k1 x Δε x (E0 / 2) ² (5) and when the voltage V0 + V1> Ve (6) V0 + V1 FLC molecule The forces V1 F1 = k0 × Ps × (E0 + E1) + k1 × Δε × (E0 + E1) ² (7) and the voltage V0 / 2, V0 + V1 that satisfies the relationship F0 = F1 (8) Utilizing the existence, by using the combination of voltage waveforms of (A) and (B) of FIG. 1, the following three cases 1) FLC molecules constituting a pixel are changed from one stable state to the other stable state. When rewriting, 2) change the FLC molecule forming the pixel from the other stable state When rewriting to one stable state, 3) when the stable state of the FLC molecule forming the pixel is not rewritten is distinguished, and 1) when rewriting the pixel to the other stable state,
When the voltage of 5) in FIG. 1A and the voltage of 6) in FIG. 1B are applied to the pixel and 2) the pixel is rewritten to one stable state,
When the voltage of 6) in (A) and the voltage of 5) in FIG. 1 (B) are applied to the pixel and 3) the stable state of the pixel is not rewritten,
This is a driving method in which the voltage 6) in (A) and the voltage 6) in FIG. 1B are applied to the pixel.

The waveform shown in 1) of FIG. 1A is the scanning electrode L.
is a selection voltage VCA applied to i to rewrite the FLC molecule forming the pixel Aij on the scan electrode Li to the other stable state, and the waveform shown in 2) of FIG. Applied to the scan electrode Lk (i ≠ k),
The non-selection voltage VCB that prevents the stable state of the FLC molecules constituting the pixel Akj on the scan electrode Lk from being rewritten. The waveform shown in 3) of FIG. 1A is applied to the signal electrode Sj and the selection voltage This is the active voltage VSC for rewriting the FLC molecules constituting the pixel Aij on the scan electrode Li to which VCA is applied to the other stable state, which is 4) in FIG. 1A.
The waveform shown in FIG. 4 is applied to the signal electrode Sl and F constituting the pixel Ail on the scan electrode Li to which the selection voltage VCA is applied.
Non-active voltage V that does not rewrite the stable state of LC molecules
It is SD.

The waveform shown at 5) in FIG. 1A is the scanning electrode L.
The FLC forming the pixel Aij when the selection voltage VCA is applied to i and the active voltage VSC is applied to the signal electrode Sj.
A voltage AC for rewriting the numerator to the other stable state. The waveform shown in 6) of FIG. 1 (A) has the selection voltage VCA applied to the scanning electrode Li and the non-active voltage VSD applied to the signal electrode Sl. At this time, the voltage A-D that does not rewrite the stable state of the FLC molecule forming the pixel Ail is shown in FIG.
The waveform shown in 7) of (A) is applied to the non-selection voltage V to the scan electrode Lk.
When CB is applied and the active voltage VSC is applied to the signal electrode Sj, it is the voltage B-C applied to the FLC molecules forming the pixel Akj. The waveform shown in 8) of FIG. The non-selection voltage VCB is applied to Lk, and the signal electrode Sl
When the non-active voltage VSD is applied to the FLC molecules, the voltage BD is applied to the FLC molecules constituting the pixel Akl.

The waveform shown in 1) of FIG. 1B is the scanning electrode L.
is a selection voltage VCA applied to i to rewrite the FLC molecules constituting the pixel Aij on the scan electrode Li to one stable state, and the waveform shown in 2) of FIG. The non-selection voltage VCB applied to the electrode Lk (i ≠ k) so as not to rewrite the stable state of the FLC molecule forming the pixel Akj on the scan electrode Lk, which is shown in 3) of FIG. 1B. The waveform is applied to the signal electrode Sj,
The pixel A on the scan electrode Li to which the selection voltage VCA is applied
The active voltage VSC that rewrites the FLC molecules forming ij to one stable state. The waveform shown in 4) of FIG. 1B is applied to the signal electrode Sl and the selection voltage VCA is applied to the scanning electrode Li. Is the non-active voltage VSD that does not rewrite the stable state of the FLC molecule that constitutes the pixel Ail.

The waveform shown in 5) of FIG. 1 (B) is the scanning electrode L.
The FLC forming the pixel Aij when the selection voltage VCA is applied to i and the active voltage VSC is applied to the signal electrode Sj.
The voltage A-C that rewrites the molecule to one stable state,
In the waveform shown in 6) of FIG. 1B, the selection voltage VCA is applied to the scan electrode Li and the non-active voltage VSD is applied to the signal electrode Sl.
Is a voltage A-D that does not rewrite the stable state of the FLC molecules forming the pixel Ail, and the waveform shown in 7) of FIG. 1B has a non-selection voltage VCB applied to the scan electrode Lk. When the active voltage VSC is applied to the signal electrode Sj, the voltage B applied to the FLC molecules forming the pixel Akj
-C, and the waveform shown in 8) of FIG.
The voltages BD are applied to the FLC molecules constituting the pixel Akl when the non-selection voltage VCB is applied to k and the non-active voltage VSD is applied to the signal electrode Sl.

By thus determining the voltage waveform to be applied to the pixel, in the driving method of Japanese Patent Application No. 3-293179, the voltage of 6) in FIG. 1A or 1B is applied to the pixel unless the pixel is rewritten. The waveform or the voltage waveform of 7) or 8) of FIG. 1A or 7) or 8) of FIG. 1B is applied.

The force F0 acting on the FLC molecule when the voltage V0 / 2 and the force F acting on the FLC molecule when the voltage V0 + V1 are applied in advance.
Since the voltages V0 / 2 and V0 + V1 are determined so that 1 becomes almost equal, the amount of light transmitted through the pixel when the voltage waveform of 6) in FIG. 1A or 1B is applied to the FLC molecule forming the pixel. Changes and 7) or 8) of FIG. 1 (A) or FIG.
FLC that configures the pixel with the voltage waveform of 7) or 8) of (B)
The change in the amount of transmitted light of the pixel when applied to the molecule should be almost equal, and flicker-free image display can be obtained regardless of the rewriting frequency unless the pixel is rewritten.

[0018]

The electric field Ee that maximizes the force exerted on FLC molecules having a negative dielectric anisotropy Δε is expressed by the relationship between the voltage V applied to the panel and the response speed τ of the FLC or the memory pulse width τm. This can be understood from the voltage Ve at which the response speed τ or the memory pulse width τm becomes the minimum and the cell thickness of the panel.

Therefore, the liquid crystal composition SCE-8 manufactured by BDH
Liquid crystal composition B having the following transition temperature in which compound B having a negative dielectric anisotropy is added to Applied voltage V in the range of temperature T = 25 ° to 50 °
FIG. 7 shows the relationship between the pulse width and the memory pulse width τ m.

It can be seen from FIG. 7 that the temperature dependence of the memory pulse width τm is very large, but the temperature dependence of the voltage Ve at which the memory pulse width τm is minimum is very small. From this result, in the driving method of Japanese Patent Application No. 3-293179,
It is understood that the voltages V0 / 2 and V0 + V1 do not need to change much even if the temperature of the panel changes, but the memory pulse width .tau.m needs to change greatly depending on the temperature. In such a driving method in which the dielectric anisotropy is negative, Japanese Patent Laid-Open No.
2-118326, etc., if the applied voltage V and the memory pulse width τm are changed according to the temperature of the panel, the memory pulse width τm must be reduced as the temperature rises (since the voltage V is almost constant). I won't.

However, since the liquid crystal panel can be electrically treated like a capacitor, the voltage v applied to the liquid crystal panel is
Where v = Va × sin (2πft) (9), the current i supplied to the liquid crystal panel of the capacitance C is i = C × dv / dt = 2πfCVa × cos (2πft) (10), and the frequency f is high. More current is needed.

That is, in the driving method in which the dielectric anisotropy is negative, in consideration of reducing the memory pulse width τm as the temperature rises as in the conventional case, the scanning side drive circuit 2 and the signal side drive circuit 3 increase as the temperature rises. It is necessary to supply a large current from.

However, the amount of heat generated in the semiconductor generally increases in proportion to the amount of current supplied, and the amount of heat released from the semiconductor decreases as the ambient temperature rises. As a result, the current supply capability of the semiconductor decreases as the ambient temperature increases. For example, the output current of the NEC operational amplifier μPC157D is shown in the catalog as shown in FIG.

Considering the output current characteristics of such a semiconductor, in the driving method in which the dielectric anisotropy is negative, in order to reduce the memory pulse width τm as the temperature increases, conversely, first, at the maximum operating temperature, The period 2t0 of the applied voltage of
From the memory pulse width τm at that temperature, the number of pulse application times N of FIG. 1 must be determined. However, compared with the temperature change of the current supply capacity of the semiconductor shown in FIG. 8, the FLC shown in FIG.
Since the temperature variation of the memory pulse width τm of the panel is very large, the ratio of the period 2t0 of the applied voltage at the maximum operating temperature to the memory pulse width τm is small, and the number of times N of application is small, so even if the operating temperature becomes low If the number of applications N is constant (even though the number of applications N can be increased), the contrast remains poor. The present invention has been made to solve such a problem.

[0025]

According to the present invention, a ferroelectric liquid crystal having a negative dielectric anisotropy is interposed between a plurality of scanning electrodes and a plurality of signal electrodes arranged in directions intersecting with each other, and To selectively apply the selection voltage or the non-selection voltage to the signal electrode and selectively apply the rewriting voltage or the holding voltage to the signal electrode to change the display of each pixel in the region where the scan electrode and the signal electrode intersect. In the driving method of the liquid crystal display device, a first pixel including a scan electrode to which a non-selection voltage is applied and a signal electrode to which a rewriting voltage is applied, a scan electrode to which a non-selection voltage is applied, and a holding voltage are applied. A bipolar pulse composed of a positive voltage and a negative voltage was applied to the second pixel composed of the signal electrode a plurality of times to make the changes in the transmitted light amount of the first and second pixels substantially equal, and a selection voltage was applied. Scan electrode and holding voltage The third consists of pressurizing the signal electrodes
To the pixel, from the positive or negative voltage in the region where the negative effect of the dielectric anisotropy acting on the ferroelectric liquid crystal molecule is large and the negative or positive voltage in the region where the negative effect of the negative dielectric anisotropy acting on the ferroelectric liquid crystal molecule is small. By applying the constituted bipolar pulse a plurality of times to make the change in the amount of transmitted light of the third pixel substantially equal to or smaller than the change in the amount of transmitted light of the first and second pixels, and to configure the liquid crystal panel. According to the temperature of the ferroelectric liquid crystal molecules,
The present invention provides a method for driving a liquid crystal display device, which solves the above-mentioned problems by changing the number of times of application of bipolar pulses applied to the first, second and third pixels.

[0026]

[Function] Memory pulse width τ m and response speed τ of FLC molecule
It can be expected that the temperature dependence of is very large in general because of the very large temperature dependence of the spontaneous polarization Ps or the rotational viscosity η from the equation (1). However, while the temperature dependence of the memory pulse width τm and the response speed τ of the liquid crystal composition A of the conventional example changes in the order of several times or more as shown in FIG. 4, the temperature dependence of the spontaneous polarization Ps is examined. As shown in FIG. 9, it changes only on the order of several tenths.

From this, it can be concluded that the memory pulse width τ m and response speed τ of FLC molecules have a very large temperature dependence because the rotational viscosity η has a very large temperature dependence. Further, the temperature dependence of the voltage V-memory pulse width τm characteristic of the liquid crystal composition B of the conventional example is as shown in FIG.
The temperature dependence of the voltage Ve at which the force acting on the molecule is minimized is not seen so much. This and the force acting on the FLC molecule is (3)
Since the temperature dependence of the spontaneous polarization Ps of the FLC molecule is small as shown in FIG. 9, the temperature dependence of the dielectric anisotropy Δε should also be small, and the voltage V0 / 2 satisfying the formula (8)
It can be expected that the temperature dependence of the voltage V0 + V1 should be small.

Therefore, the operating temperature of the FLC panel 1 is set to T0.
The voltage V0 / 2 and the voltage V0 + V1 are kept constant regardless of the panel temperature. First, the pulse width t0 of the bipolar pulse is determined. At the ambient temperature T3 ° at which the maximum operating temperature T1 ° is given to the FLC, the current i0 that can be supplied from the scanning side driving circuit 2 and the signal side driving circuit 3 causes all the pixels on one scanning electrode of the FLC panel 1 to have the voltage V0 / Assuming that the time required for charging from 2 to the voltage-(V0 + V1) or from the voltage-(V0 + V1) to the voltage V0 / 2 is t1, the time t0 may be t0> t1 (11).

The time t0 is constant regardless of the panel temperature,
Assuming that the number of times the bipolar pulse is applied at a certain panel temperature Tp ° is P, the time product Wp of the absolute values of the voltage waveforms A-C applied to the pixel to be rewritten in FIG. 1A or 5B is Wp = (V1 + V0 / 2) .times.P.times.t0 (12).

The minimum number P of times the bipolar pulse is applied at the temperature Tp ° is Wp> Vm × τm> (V0 / 2) × t0 (13) from the relationship between the applied voltage Vm and the memory pulse width τm at the temperature Tp °. ) Is the minimum integer.

At the temperature Tp °, there is no problem if the number N of times of application of the bipolar pulse is P or more, and even at the temperature Tr where Tp <Tr (14), the bipolar property is decreased because the time product decreases with temperature. There is no problem if the pulse application count N is P or more.

Therefore, when the temperature of the panel is lowered, the number of times N of application of the bipolar pulse is set to P at the temperature T of Tp≤T (15), and the bipolar pulse is applied at the temperature T of T <Tp (16). The number of application times N is P + 1,
When the temperature of the panel is rising, the number of times N of application of the bipolar pulse is set to P + 1 at the temperature T of T <Tr (17), and the number of application N of the bipolar pulse is set to P + 1 at the temperature T of Tr ≤T (18). And

In this way, the FLC molecule has a temperature T0.
At ambient temperature T2 ° to T3 °, which gives ° to T1 °,
By the current i that can be supplied from the scanning side driving circuit 2 and the signal side driving circuit 3 at that temperature, the FLC panel 1 is supplied to the FLC panel 1 as shown in FIG.
And (B) voltage waveform combinations can be applied, and FLC
The panel 1 is guaranteed to operate normally. If the change in the selection period of the FLC panel is made smaller than the change in the application time of the bipolar pulse, the period of 0v application becomes longer as the temperature rises, and the heat generation amount of the scanning side drive circuit 2 and the signal side drive circuit 3 is suppressed. The current supply capacity from the drive circuit can be improved.

[0034]

EXAMPLE Since the structure of the FLC panel 1 used in this example is the same as that of the conventional example shown in FIG. 3, its explanation is omitted here. In the FLC panel 1 of this example, an alignment film PSI-X7355 manufactured by Chisso Co. was used as an alignment film, and a liquid crystal composition SCE-8 manufactured by BDH was used as a liquid crystal with a compound B having a negative dielectric anisotropy of 8: 2. The liquid crystal composition B mixed at a ratio is used.

One temperature detecting means used in this embodiment is
As shown in FIG. 10, it comprises a constant voltage source 18 of output voltage Vt, a thermistor 19, a constant resistance 22 of resistance value Rt, an operational amplifier 20 and an analog / digital converter 21. The thermistor 19 is brought into contact with the FLC panel 1. , The resistance value Rs of the thermistor 19 changes depending on the temperature like the diode type thermistor shown in FIG. 11, so that the output voltage V of the operational amplifier 20 becomes V = Vt × Rs / (Rs + Rt) (19) It is detected by changing.

Another temperature detecting means used in this embodiment is, as shown in FIG. 12, a light / voltage converter 23, an amplifier 24, a low pass filter 25, a digitizing circuit 26 and a detecting circuit 2.
7, a voltage control circuit 28, a voltage controlled oscillator 29, a counter 30, a voltage generator 31, and an attenuator 32.

This detector uses a voltage input from the voltage control circuit 28 to output a clock C from the voltage controlled oscillator 29.
P is generated, and the counter circuit 30 creates a time 2 × tk which is a constant multiple of the cycle of the clock CP, and this time 2 × tk
Is set to a field cycle Tf, and in the even-numbered field, the voltage Vth is output for tk time and then the voltage -Vth.
Is output for tk time, and then voltage 0 is output. In the odd-numbered field, the voltage -Vth is output for tk time, the voltage Vth is output for tk time, and then the voltage 0 is output.
This voltage waveform is attenuated by the attenuator 31 and applied to a dedicated electrode (not shown) of the FLC panel 1. The attenuation factor of the attenuator 31 is determined by actually rewriting the entire panel.

In this way, some pixels of the panel are periodically set to the "bright" and "dark" states, and the amount of transmitted light of the panel at this time is measured by the light / voltage converter 23 to obtain an analog voltage. Then, the voltage is amplified by the amplifier 24 and input to the digitizing circuit 26 through the low pass filter 25 for extracting the frequency close to the field period Tf. The digitizing circuit 26 converts the input voltage into a digital signal depending on whether the input voltage is higher or lower than the average value of the input voltage over several fields. This signal is input to the detection circuit 27, and the detection circuit 27 samples the input signal once per field, and if the values in the preceding and following fields are different, the output voltage of the voltage control circuit 28 is lowered a little and the voltage control oscillator is generated. The frequency of the output clock CP of 29 is increased, and if the values in the preceding and following fields are the same, the output voltage of the voltage control circuit 28 is increased a little and the voltage controlled oscillator 2
The frequency of the output clock CP of 9 is lowered.

The voltages applied to the panel at this time are shown in 1) and 3) of FIG. 13, and the expected amount of transmitted light corresponding to 1) and 3) of FIG. 13 is shown in the figure. 13-2),
4). In 1) of FIG. 13, the time when the voltage Vth is applied to the panel exceeds the threshold of the panel, and the transmitted light amount of the panel changes sufficiently as shown in 3) of FIG. 13, but in 3) of FIG. The time for which Vth is applied does not exceed the threshold value of the panel, and the amount of transmitted light of the panel does not change sufficiently as shown in 4) of FIG. The application time of the voltage Vth output from the attenuator 32 fluctuates between 1) and 3) in FIG. 13, but the central time is the memory pulse width τm itself of the panel at the voltage Vth. , Accurately indicate the temperature of the liquid crystal in the panel.

That is, this field period Tf is set to FLC.
If the system clock of D is counted, the temperature of the liquid crystal in the panel can be detected. Since the voltage V-memory pulse width .tau.m characteristic of the FLC panel 1 of this embodiment is as shown in FIG. 7, the voltages V0 / 2 and V0 + V1 were determined to be V0 / 2 = 12v V1 + V0 = 30v. The operating temperature of the FLC panel 1 is 25 ° to 50 °
When the panel temperature is 50 °, the rise of the voltage waveform supplied from the scanning side drive circuit 2 and the signal side drive circuit 3 to the FLC panel 1 is observed, and the time t0 is t0 = 30μ.
It was decided to be s. Further, the minimum number of times P of application of the bipolar pulse at each temperature in steps of 5 ° is as follows from the temperature Tp 25 ° 30 ° 35 ° 40 ° 45 ° 50 ° Minimum number of times of application P 12 8 5 4 3 2.

Therefore, when the temperature of the panel is lowered to the temperature Tp °, the number of times the bipolar pulse is applied is set to the temperature Tp-5 °.
Determine the minimum number of times P of application of bipolar pulse in
The number of times the bipolar pulse is applied when the temperature of the panel rises to p + 2 ° is determined as the minimum number of times P of application of the bipolar pulse at the temperature Tp °. That is, the allowable number of times Q of applying the bipolar pulse at each temperature is as follows: temperature Tp 25 ° 30 ° 32 ° 35 ° 37 ° 40 ° 42 ° allowable number of applications Q ・ 12 ・ 12〜8 ・ 8.8 ・ 8 ・ 5 ・ 5 ・5-4. 4 Temperature Tp 42 ° 45 ° 47 ° 50 ° Allowable number of times of application Q. 4 · 4 to 4 · 3 · 3.

Temperature data D detected by the temperature detecting means
T is the input control circuit 33 and the output control circuit 3 shown in FIG.
4, a display memory circuit 35, an identification memory circuit 36, a different memory circuit 37, and a drive control circuit 38, and a drive signal circuit 40 shown in FIG.
And a drive control circuit 38 including a ROM 41 and a drive voltage circuit 42. In the drive control circuit 38 of FIG. 15, if the current application number N of the bipolar pulse is different from the detected application number Q of the temperature data DT, the combination of a new voltage waveform from the drive signal circuit 40 to the ROM 41 by N and DT. Is output, and a new combination of voltage waveforms is output to the FLCD 4.

For example, an FLC panel 1 having the characteristics shown in FIG.
In the case of, when the temperature data DT detected by the temperature detecting means is 41 ° and the current number of times N of application of the bipolar pulse is 4,
Since the allowable number of times of application at 41 ° is 5 to 4, the address of the conventional combination of voltage waveforms of N = 4 is output from the drive signal circuit 40 to the ROM 41. Further, when the temperature data DT detected by the temperature detecting means is 43 ° and the current number of times N of application of the bipolar pulse is 4, the allowable number of times of application at 43 ° is 4, so the conventional N = from the drive signal circuit 40 to the ROM 41. The address of the combination of the four voltage waveforms is output.

However, the temperature data DT detected by the temperature detecting means is 39 °, and the present number of times N of application of the bipolar pulse is N.
Is 4, the allowable number of times of application at 39 ° is 5, so that an address of a combination of voltage waveforms of N = 5 is newly output from the drive signal circuit 40 to the ROM 41. Further, when the temperature data DT detected by the temperature detecting means is 41 ° and the current number of times N of application of the bipolar pulse is 5, the allowable number of times of application at 41 ° is 5 to 4, so the drive signal circuit 40 reads the ROM.
The address of the conventional combination of N = 5 voltage waveforms is output to 41.

In this case, the selection period t is fixed at 25t0. Changing the number of times the bipolar pulse is applied while fixing the selection period means, for example, that the number of times the bipolar pulse is applied N is 5 in the selection period t = 11t0 and one bipolar pulse of the combination of the voltage waveforms of FIG. 2 and the number of application times N of the bipolar pulse is 4, and the voltage waveforms in FIG. 2 are combined. Note that FIG. 2 is the same as FIG. 1 except for the number of times of pulse application, and therefore its explanation is omitted.

However, since the current supply capacity of the semiconductor does not cause any problem when the panel temperature is low, when the panel temperature is low, the selection period can be changed while changing the number of times the bipolar pulse is applied. That is, when the selection period is fixed to, for example, 17t0 at the lowest temperature (15 to 20 °) at which the FLCD 4 is normally used, and the number of times of applying the bipolar pulse must be 12 in order to use the FLCD 4 at low temperature,
The selection time may be changed to 25t0. At this time, the transfer time of the data DATA in one selection period is set to 17
If it is set earlier than t0, the selection period becomes 25t0 and there is no problem.

[0047]

According to the present invention, the display quality is not so good at a high temperature which is rarely used and corresponds to the temperature of the FLC panel, but it is possible to give a good display quality at a low temperature which is usually used.

[Brief description of drawings]

FIG. 1 is a waveform diagram showing each applied voltage used for driving an FLC panel in this embodiment.

FIG. 2 is a waveform diagram showing each applied voltage used for driving the FLC panel in the present embodiment.

FIG. 3 is a cross-sectional view showing a configuration of an FLC panel used in an FLCD.

FIG. 4 is a diagram showing a state in which characters “ABCD” are displayed on the FLCD.

FIG. 5 is an explanatory diagram showing FLC molecules, and (A) is a diagram showing a state of FLC molecules in a smectic C phase. (B) is a view of the state of FLC molecules in the smectic C phase viewed from the substrate side.

FIG. 6 is a graph showing characteristics of liquid crystal composition A with respect to temperature-response speed / memory pulse width.

FIG. 7 is a graph showing characteristics of voltage-memory pulse width when the temperature of liquid crystal composition B is changed.

FIG. 8 is a graph showing the output voltage-output current characteristics when the temperature of the operational amplifier is changed.

9 is a graph showing the tilt angle characteristics of liquid crystal composition B when the temperature is changed. FIG.

FIG. 10 is a block diagram showing a schematic configuration of a temperature detection circuit used in this embodiment.

FIG. 11 is an explanatory diagram showing temperature-resistance value characteristics of a diode type thermistor.

FIG. 12 is a block diagram showing a schematic configuration of a temperature detection circuit used in this embodiment.

13 is a waveform chart for explaining the operation of the temperature detector of FIG.

FIG. 14 is a block diagram showing a schematic configuration of a display control device used in this embodiment.

FIG. 15 is a block diagram showing a schematic configuration of a drive control circuit used in this embodiment.

[Explanation of symbols]

 1 FLC panel 2 Scanning side driving circuit 3 Signal side driving circuit 4 FLCD 5 Glass 6 Insulating film 7 Alignment film 8 Sealant 9 FLC 10 Polarizing plate 18 Constant voltage source 19 Thermistor 20 Operational amplifier 21, 26 Analog / digital converter 22 Resistance 23 Photodiode 24 Amplifier 25 Low-pass filter 27 Detector 28 Control voltage generator 29 Voltage controlled oscillator 30 Counter 31 Applied voltage generator 32 Attenuator 33 Input control circuit 34 Output control circuit 35 Display memory circuit 36 Group memory circuit 37 Same memory Circuit 38 Drive control circuit 39 Display control device circuit 40 Drive signal circuit 41 ROM 42 Drive voltage circuit L Scan electrode S Signal electrode

Claims (1)

[Claims] 1. A ferroelectric liquid crystal having a negative dielectric anisotropy is interposed between a plurality of scanning electrodes and a plurality of signal electrodes arranged in directions intersecting with each other, and a selection voltage or a non-selection voltage is applied to the scanning electrodes. A driving method of a liquid crystal display device, which selectively applies a rewriting voltage or a holding voltage to a signal electrode to change the display of each pixel in a region where a scanning electrode and a signal electrode intersect. The first pixel is composed of the scanning electrode to which the non-selection voltage is applied and the signal electrode to which the rewriting voltage is applied, and the second pixel composed of the scanning electrode to which the non-selection voltage is applied and the signal electrode to which the holding voltage is applied. A bipolar pulse composed of a positive voltage and a negative voltage is applied to the pixel a plurality of times to make the changes in the transmitted light amount of the first and second pixels substantially equal, and the scan electrode to which the selection voltage is applied and the holding voltage are applied. Consists of signal electrodes That the third pixel, and a positive or negative voltage dielectric anisotropy negative effects acting on the ferroelectric liquid crystal molecules is large area,
A bipolar pulse composed of a negative or positive voltage in a region where the negative effect of the dielectric anisotropy acting on the ferroelectric liquid crystal molecules is small is applied multiple times, and the change of the transmitted light amount of the third pixel is changed. Of the bipolar pulse applied to the first, second and third pixels according to the temperature of the ferroelectric liquid crystal molecules constituting the liquid crystal panel. A method for driving a liquid crystal display device, characterized in that the number of times of application is changed.