JPH11271716A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve display characteristics such as contrast and display uniformity of an active matrix type liquid crystal display device. SOLUTION: This device has a liquid crystal display element 24 comprising liquid crystal with self-polarization which is either characteristic or induced by being applied with an electric field, of pixel electrodes which are arrayed in matrix, of a counter electrode which faces the pixel electrodes across the liquid crystal, and of a switching element which periodically supplies a display signal to the pixel electrodes and with a polarity inverting circuit 20 which inverts the polarity of a voltage applied to the liquid crystal in a period longer than that of periodic supply of display signals to the pixel electrodes. Signals applied to the pixel electrodes or the counter electrode are corrected with a signal attenuating with time throughout the period from the inversion of the polarity of the voltage applied to the liquid crystal by the polarity inverting circuit 20 to the next inversion of the polarity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art As a liquid crystal material used in a liquid crystal display device,
Ferroelectric liquid crystal: FLC (Ferroelectric Liquid Crysta)
l) Antiferroelectric liquid crystal: AFLC (Anti Ferroelectric
LiquidCrystal), DHF (Distorted Helical Ferroe)
lectric Liquid Crystal), twisted liquid crystal: TFLC (Twis
In recent years, attention has been paid to those having spontaneous polarization induced by application of an intrinsic or electric field, such as ted Ferroelectric Liquid Crystal).

The relationship between the electric field and the orientation of a thresholdless antiferroelectric liquid crystal, which is an example of a liquid crystal material having spontaneous polarization induced by application of an intrinsic or electric field (hereinafter, abbreviated as liquid crystal having spontaneous polarization), is described. As shown in FIG. In the state A when no voltage is applied, the molecules 1 of the antiferroelectric liquid crystal are arranged alternately to cancel spontaneous polarization. In this case, the optical axis 2 of the average molecule 1 is in the vertical direction. Therefore, as shown by arrows 3 and 4, when two polarizing plates are arranged in crossed Nicols so as to be in the same direction and the orthogonal direction to the optical axis 2, a dark state (normally black) is obtained. However, in a B state or a C state in which a positive voltage or a negative voltage is applied, the molecules 1 of the antiferroelectric liquid crystal are arranged in one direction according to the direction of the electric field 5, and
The optical axis 2 is deviated from the polarization direction of the polarizing plate, resulting in a bright state. That is, in the antiferroelectric liquid crystal, the arrangement of liquid crystal molecules differs between the application of a positive voltage and the application of a negative voltage.

Further, the thresholdless antiferroelectric liquid crystal has no voltage applied state (A state), positive voltage applied state (B state), and negative voltage applied state (C state) depending on the magnitude of the voltage applied between the electrodes. It is possible to take not only the three orientations of (state), but also any orientation in the middle of these states. Therefore, although the memory property is poor or not, the T
The present invention is applied to an active matrix type display device in which a switching element made of an active element such as FT is formed, and by maintaining a voltage that takes the arbitrary alignment state even during a non-selection period, it is possible to perform gradation display. Become.

FIG. 2 shows an example in which a liquid crystal display device in which a nematic liquid crystal and a liquid crystal having spontaneous polarization are sandwiched between a pixel electrode arranged in a matrix and a counter electrode is driven by an active matrix type frame inversion. 5 shows a voltage and light transmittance applied to one pixel. In this case, the polarizing plate is arranged so as to be normally black.

It is assumed that a gate signal 6 is periodically input to the liquid crystal from a gate line as shown in FIG. In this case, the cycle of the gate signal 6 is the frame frequency f _F
Corresponding to As shown in FIG. 2B, a voltage 7 whose polarity is inverted at a period equal to the frame frequency is applied to the signal line (the potential of the counter electrode is displayed as 0 V).

When the gate signal is input and applied to the gate as described above, the switching element is turned on during t 1, as shown in FIG. It is supplied to the pixel electrode. Since the liquid crystal layer and the auxiliary capacitance function as a capacitor, the holding voltage 9a of the nematic liquid crystal cell is, as shown in FIG.
The retention is almost constant and almost constant. That is, when impurities are mixed in the liquid crystal, the holding voltage is reduced, but when a fluorine-based liquid crystal containing almost no ionic impurities is used, the holding voltage is kept almost constant as in this example. It is. The light transmittance of the liquid crystal cell in this case is shown in FIG. The nematic liquid crystal has a low response speed, so that the light transmittance 10a rises slowly. However, since the voltage held at the pixel electrode does not affect the orientation of the liquid crystal regardless of whether the voltage is positive or negative, the light transmittance 10a thereafter becomes It is almost constant.

On the other hand, in the liquid crystal having spontaneous polarization, the input of the gate signal 6 from the gate line shown in FIG. 2A and the voltage 7 applied to the signal line shown in FIG.
As a result, the write voltage 8 shown in FIG. 2C is supplied to the pixel. In this case, as shown in FIG. 2 (f), the holding voltage 9b of the liquid crystal cell decreases after writing and exhibits extremely poor holding characteristics. The light transmittance 10b of the liquid crystal cell shown in FIG. 2 (g) is as shown by a solid line. When the voltage 11 shown in FIG. 2 (h) is supplied to the signal line of this liquid crystal cell to perform static driving, a light transmittance 10c shown by a broken line in FIG. 2 (g) is obtained. When the active matrix driving (holding driving) is performed, the light transmittance at the time of ON is significantly reduced as compared with the static driving. As a result, the liquid crystal display device using the liquid crystal having spontaneous polarization has a problem that the contrast is lowered and the display quality is deteriorated.

As a result of a detailed examination of the above problem by the present inventors, it has been found that the following causes cause a decrease in contrast. That is, in the case of active matrix driving (holding driving), as shown in FIG.
The supply of the voltage for writing in one frame is performed only for a part of the period. Usually, the liquid crystal has a response time (80 μs) compared to the writing time (typically 64 μs or less).
s or more), the change in the arrangement of the liquid crystal molecules does not end within the writing time t1. Therefore, even in the remaining time t2 after the end of the writing, the change in the arrangement of the liquid crystal molecules continues due to the charges held in the storage capacitor, and the holding voltage decreases as shown in FIG. That is, the liquid crystal molecules cannot change to an arrangement obtained by static driving, and therefore the transmittance is lower than that in static driving.

In a nematic liquid crystal having no spontaneous polarization, liquid crystal molecules respond to an absolute value of an applied voltage. That is, the arrangement is the same when +5 V is applied and when -5 V is applied. Therefore, even if the alignment change of the liquid crystal is insufficient in the first frame from the off state to the on state, the alignment change of the liquid crystal molecules gradually occurs in the second and third frames, and the same voltage is applied statically after several to several tens of frames. The same arrangement as when applied by driving is reached. That is, after several to several tens of frames, the same transmittance as that of the static drive is shown.

On the other hand, liquid crystals having spontaneous polarization have different arrangements of liquid crystal molecules depending on the polarity of the applied voltage. That is,
The arrangement differs between when +5 V is applied and when -5 V is applied. The liquid crystal molecules are arranged in a positive polarity in the first frame from the off state to the on state, but the polarity is inverted in the second frame. Therefore, since the liquid crystal molecules pass through the alignment when no voltage is applied from the positive polarity alignment of the first frame, the alignment does not reach the alignment obtained by static driving as in the first frame which is turned on from off. Since the polarity of the subsequent frames is inverted for each frame, the arrangement does not reach the arrangement when the same voltage is applied by static driving. As a result, the transmittance is greatly reduced as compared with the static drive, and a display with low contrast is obtained.

The present inventors have proposed a driving method for changing the polarity of the applied voltage for each of a plurality of frames (Japanese Patent Application No. 8-235571). According to this driving method, by applying a voltage of the same polarity a plurality of times, the alignment state of the liquid crystal can be set to a desired state, thereby preventing a decrease in transmittance.

However, as a result of further study of the application of the above-mentioned driving method by the present inventors, as shown in FIG. 3, a phenomenon in which the transmittance increases in the order of several seconds was observed. In FIG. 3, (a) shows the case where the gate-on time is increased by 12 times only when the polarity is inverted, and (b) shows the case where the signal voltage during the gate-on time is further increased in addition to (a). In addition,
Regarding (b), the case where the holding voltages of the first frame and the second frame are adjusted to be equal after the polarity inversion, and
The measurement was performed on the case where the light transmittance of the first frame and the light transmittance of the second frame were adjusted to be equal after the polarity inversion, and the same result was obtained in both cases. In any of the driving methods, it was found that the display state immediately after rewriting the pixel, that is, the polarity inversion of the pixel, and the display state after a lapse of a certain time, that is, the display state before the polarity inversion, were different. When this result is replaced with the display of the entire screen, the display state immediately after the polarity reversal and the display state before the polarity reversal are distributed over the entire screen, which is a serious problem that display uniformity cannot be maintained. I found that there was.

[0014]

As described above, a liquid crystal having intrinsic or spontaneous polarization induced by applying an electric field has a different arrangement of liquid crystal molecules depending on the polarity of a voltage applied to the liquid crystal. When the active matrix type frame inversion driving is performed, there is a problem that the liquid crystal molecules cannot reach a desired alignment state and the contrast is reduced. To solve such a problem, a driving method of changing the polarity for each of a plurality of frames has been proposed. In this case, the display state immediately after the polarity inversion is different from the display state after a lapse of time, and the entire screen is different. There is a problem that uniformity of display cannot be maintained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. An active matrix type liquid crystal display device using a liquid crystal having a spontaneous polarization induced by applying an electric field is provided. It is an object of the present invention to improve display characteristics such as display uniformity.

[0016]

According to the present invention, there is provided a liquid crystal display device comprising: a liquid crystal having a spontaneous polarization induced by applying a unique or electric field; a pixel electrode arranged in a matrix; A counter electrode opposed to the pixel electrode with a switching element for periodically supplying a display signal to the pixel electrode; and a switching element for applying a display signal to the pixel electrode at a longer cycle than a cycle for periodically supplying a display signal to the pixel electrode. Polarity inverting means for inverting the polarity of the voltage to be applied, and a signal that attenuates with time between the inversion of the polarity of the voltage applied to the liquid crystal by the polarity inversion means and the subsequent inversion of the polarity. Means for correcting a signal applied to the counter electrode.

In the case where an auxiliary capacitance element having the pixel electrode as one electrode and the other electrode as an auxiliary capacitance electrode is provided, the pixel electrode, the counter electrode, or the auxiliary capacitance electrode is provided by the signal attenuating with time. A means for correcting the signal applied to is provided.

As an example of the signal attenuating with time, the transmitted light intensity and T0 when the time t has elapsed since the polarity of the voltage applied to the liquid crystal is inverted by the polarity inverting means, and T0 is the liquid crystal. T (t) / T0 = 1-exp [-(t / t0) ⁿ ] is generated based on the above equation, where t0 and n are the predetermined constants just before inverting the polarity of the voltage to be applied to. You can give something.

According to the present invention, in an active matrix type liquid crystal display device using a liquid crystal having a spontaneous polarization induced by applying a unique or electric field, a driving method of inverting the polarity every plural frames is adopted. If
Since the signal applied to the pixel electrode and the like is corrected by the correction signal that attenuates with time, the display state immediately after the polarity inversion and the display state after the lapse of time can be kept uniform, and the display characteristics can be improved. Can be.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 shows a configuration of a liquid crystal display device according to one embodiment of the present invention. That is, in this liquid crystal display device, a signal line driver 25 for driving a liquid crystal display element 24 and a scanning line driver 26 are connected to a display timing controller 23 to which a display signal 21 and a synchronization signal 22 are input. A polarity inversion control circuit 20 for appropriately inverting the polarity of the display signal is connected to the timing controller 23.

The liquid crystal display element 24 includes a switching element made of a TFT or the like in a matrix and an ITO on the inner surface of one of a pair of glass substrates facing each other.
A pixel electrode made of a transparent conductive film such as (Indium Thin Oxide) is provided, and an alignment film made of a polyimide resin or the like is provided on these switching elements and the pixel electrode. On the inner surface of the other second substrate, a color filter, a counter electrode made of a transparent conductive film such as ITO are provided on the color filter, and an alignment film made of a polyimide resin is provided on the counter electrode. ing. Then, between the switching element and the pixel electrode provided on the first substrate and the counter electrode provided on the second substrate,
Ferroelectric liquid crystal FLC, antiferroelectric liquid crystal AFLC, DH
A liquid crystal having a spontaneous polarization induced by application of an intrinsic or electric field, such as F or TFLC, is sandwiched. Further, the first and second substrates have a structure in which a polarizing plate is disposed on the outer surface.

The polarity inversion control circuit 20 inverts the polarities of all the pixel electrodes located on one scanning line when rewriting the screen of one frame. As shown in FIG. 5, the polarity inversion control circuit 20 has a line counter 31 for counting the number of scanning lines in the screen, a frame counter 32 for counting the number of times of rewriting of the screen, and an inversion determination circuit 34 including a comparator 33. , The timing signal 2 supplied from the display timing controller 23 shown in FIG.
8 controls the inversion of the polarity of the display signal.

Each time the screen is rewritten, the line counter 31 is cleared (reset) by the synchronizing signal of the negative polarity shown in FIG. 6C. As shown in FIGS. Count the number of. On the other hand, as shown in FIG. 6B, the frame counter 32 counts the number of times of rewriting of the screen, but does not particularly perform a reset or the like, and repeats counting from 1 again when the counting of one screen is completed. The comparator 33 has a numerical value updated each time the screen is rewritten from the frame counter 32,
Two kinds of numerical values are supplied from the line counter 31 and a numerical value updated for each scanning line. When the numerical values from the frame counter 32 and the line counter 31 match with a certain numerical value n, the matching output is output to the exclusive OR circuit 35 as shown in FIG. In addition,
FIG. 6A shows the display timing controller 2 of FIG.
3 shows a vertical synchronizing signal among the synchronizing signals 28 supplied to the control signal 3.

The exclusive OR circuit 35 receives an output from the memory 36 holding the polarity reversal signal in addition to the coincidence output shown in FIG. 6 (f). The output is inverted. That is, when the output of the frame counter 32 is n, the polarity is inverted only for n lines. This inversion, that is, the updated exclusive OR circuit 3
5 is output to the display timing controller 23 shown in FIG. 4 via the switching circuit 37 and the latch circuit 38. The output of the exclusive OR circuit 35 is fed back to the memory 36 via the switching circuit 37 and held until the next update. Memory 36
Are controlled by a memory address counter 39, and the address of the memory address counter 39 is created at the same address as the line counter 31.

Here, the coincidence output from the comparator 33 (FIG. 6)
(F)) is applied to the exclusive OR circuit 35 to perform the polarity inversion control, and the coincidence signal is output to the analog signal generator 27 shown in FIG.

The coincidence signal via the latch circuit 41 is
Counter 5 in analog signal generator 27 shown in FIG.
By being input to 1, the counter 51 counts the number of scanning lines with the polarity inversion being zero. The correction amount (correction value) of the signal voltage is stored in advance in the correction memory 52 of FIG.
Is stored, and the correction amount is output to the D / A converter 53 based on the numerical value supplied from the counter 51.
Then, a corrected analog signal obtained by adding the output from the gamma correction voltage circuit used in the ordinary liquid crystal display device to the output converted into analog by the DA converter 53 is shown in FIG.
Is output to the signal line driver 25. The corrected analog signal sent from the analog signal generator 27 to the signal line driver 25 in this manner is supplied to the liquid crystal display element 24 based on the display signal 29 from the display timing controller 23.

In the example shown in FIG. 4, the corrected signal is supplied to the signal line driver 25, in other words, to the pixel electrode of the liquid crystal display element 24. However, as shown in FIG. In other words, the corrected signal may be supplied to the counter electrode of the liquid crystal display element 24 (that is, the common electrode and the counter electrode are preferably formed in a stripe shape along the scanning line).
In this case, the correction signal is added to the voltage applied to the counter electrode. Further, in a liquid crystal display element having an auxiliary capacitance element in which a pixel electrode is one electrode and the other electrode (auxiliary capacitance electrode) is formed of a transparent conductive film or the like, a corrected signal is supplied to the auxiliary capacitance electrode. Is also good.

Next, a specific example of the present invention will be described. [Embodiment 1] First, as a first embodiment, a case where the voltage applied to the pixel electrode is corrected will be described.

A soluble polyimide thin film is offset-printed on a first substrate on which TFTs and pixel electrodes are formed in a matrix and on a second substrate on which a color filter and a counter electrode are formed, respectively. ,
The resultant was baked at 180 ° C. for 30 minutes in an N ₂ oven for 30 minutes to form an alignment film made of a polyimide film having a thickness of 65 μm. Thereafter, a rubbing treatment was performed while heating the first and second substrates to 100 ° C. As a result, the orientation film was sufficiently stretched and oriented in the polyimide film even at the step portion due to TFT or the like, and uniform orientation of the smectic phase was obtained.

Next, spacer particles were sprayed on the first substrate. Further, a sealant made of an ultraviolet curable resin was printed on a peripheral portion of the second substrate. And these first and second
The substrates were combined face-to-face, irradiated with ultraviolet light under pressure to cure the sealant, and heated at 160 ° C. for 1 hour to form a cell. Thereafter, the cell was placed in a vacuum chamber, an antiferroelectric liquid crystal (response time: 80 μs) was injected from the injection port, and the injection port was sealed with epoxy resin. Thereafter, a polarizing plate was further adhered to the outer surfaces of the first and second substrates to form a 10-inch diagonal liquid crystal display device.

When a driving method of changing the polarity of the applied voltage for each of a plurality of frames with a frame frequency of 60 Hz, a frame time of 16.7 ms, and a writing time of 42 μs is applied to this liquid crystal display element, The optical response shows a response as shown in FIG. This optical response characteristic is taken into the correction memory 52 in the analog signal generator 27 shown in FIG. 7 as optical response correction data. That is, when the driving method of changing the polarity of the applied voltage for each of a plurality of frames is applied, the optical response characteristic changes from a dark state to a bright state every several seconds as shown in FIG. The optical response which repeats light and dark in a cycle of several seconds is corrected so as to have a constant optical response.

FIG. 8 shows an example of correction data taken into the correction memory 52. The horizontal axis is the address of the correction memory 52, and the vertical axis is the correction value stored at that address. The correction value is D which converts the value of the correction memory 52 into an analog signal.
Although it depends on the accuracy of the / A converter 53, in order to perform accurate correction, it is desirable to set the minimum value of the correction value to 0 and set the maximum value of the correction value to the maximum value converted by the D / A converter 53. .

When the number of scanning lines of the liquid crystal display element is M lines, the address 0 of the correction memory 52 to M-1
The correction data may be captured before. This correction memory 5
The correction data captured in 2 is read out by the address created by the counter 51. Since the counter 51 counts the scanning lines by setting the polarity inversion time to 0, the scanning is performed in the order of the scanning line numbers 1... L. M. If the polarity inversion is performed on the Lth line, the next L
Since the + 1st line is the scanning line immediately before the polarity inversion, L +
In one line, the correction is performed using the correction data at the address M-1 of the correction memory 52. Similarly, the correction is performed using the correction data at the address M-2 of the correction memory 52 for the L + 2 line and the correction data at the address M-3 of the correction memory 52 for the L + 3 line. Therefore, the address created by the counter 51 is set to 0 at the time of polarity inversion, and
The address must be such that the value decreases from 1. If the counter 51 is not a counter for decreasing the address value, as shown in FIG.
The correction memory 52 in which the relationship between the address and the correction value is replaced with the correction characteristic shown in FIG.

The correction value read from the correction memory 52 is converted into an analog signal by a D / A converter 53, the amplitude is adjusted by a correction value amplitude adjustment volume 54, and a DC offset adjustment volume 55 and a DC offset The DC offset adjustment signal created by the adjustment operation amplifier 58 and the operational amplifier 59 are added. After that, the voltage is subtracted by the operational amplifier 60 from a reference voltage for creating a display signal of the liquid crystal display element created by the volume 56, that is, a so-called gamma correction voltage, and output to the signal line driver 25 in FIG. Therefore, the gamma correction voltage output to the signal line driver 25 is a value obtained by subtracting the characteristic of FIG. 8 or 9 from the normal gamma correction voltage, that is, a voltage at which the gamma correction voltage value decreases with time. And the characteristic for correcting the optical response shown in FIG. The signal thus obtained is added to the display signal 29 of FIG.
Are supplied to the pixel electrodes. That is, a signal obtained by correcting a display signal with a time-attenuating correction signal is applied to each pixel of the liquid crystal display element.

According to the above-described driving method, as shown in FIG. 13, the luminance of the pixel before the polarity inversion (the amount of transmitted light) becomes equal to the luminance of the pixel after the polarity inversion, so that the display uniformity is maintained. Thus, a liquid crystal display device having good display characteristics was obtained.

Second Embodiment Next, as a second embodiment, another example in which the voltage applied to the pixel electrode is corrected will be described.

A cell was formed in the same manner as in Example 1 except that the rubbing treatment was carried out while heating the alignment film. A DHF liquid crystal (response time: 110 μs) was injected into the cell, and a diagonal 12 inch liquid crystal display element was formed. It was created.

When a driving method of changing the polarity of an applied voltage for each of a plurality of frames with a frame frequency of 60 Hz, a frame time of 16.7 ms, and a writing time of 38 μs is applied to the liquid crystal display element, The optical response showed a response as shown in FIG. This optical response characteristic is taken into the correction memory 52 in the analog signal generator 27 shown in FIG. 7 as optical response correction data. That is, when the driving method of changing the polarity of the applied voltage for each of a plurality of frames is applied, the optical response characteristic changes from a dark state to a bright state every several seconds as shown in FIG. The optical response which repeats light and dark in a cycle of several seconds is corrected so as to have a constant optical response. Hereinafter, similarly to the method of the first embodiment, driving for applying a signal corrected by a correction signal that attenuates the display signal over time is performed for each pixel of the liquid crystal display element.

With the above driving method, as shown in FIG. 13, the luminance of the pixel before the polarity inversion and the luminance of the pixel after the polarity inversion become the same, and the uniformity of the display can be maintained. A liquid crystal display device having good display characteristics was obtained.

Third Embodiment Next, as a third embodiment, a case where the voltage applied to the counter electrode is corrected will be described.

A first substrate on which TFTs and pixel electrodes are formed in a matrix, and a second substrate on which counter electrodes are formed in stripes in parallel with the scanning lines when combined with the color filter and the first substrate. in each thin film offset printing a soluble polyimide, 80 ° C. using a hot plate for 3 minutes, further with N ₂ in oven 220
The resultant was baked at 30 ° C. for 30 minutes to form an alignment film made of a polyimide film having a thickness of 40 μm. Thereafter, a rubbing treatment was performed while heating the first and second substrates to 80 ° C. As a result, the orientation film was sufficiently stretched and oriented in the polyimide film even at the step portion due to TFT or the like, and uniform orientation of the smectic phase was obtained.

Next, spacer particles were sprayed on the first substrate. Further, a sealant made of an ultraviolet curable resin was printed on a peripheral portion of the second substrate. And these first and second
The substrates were combined face-to-face, irradiated with ultraviolet light under pressure to cure the sealant, and heated at 160 ° C. for 1 hour to form a cell. Thereafter, the cell was placed in a vacuum chamber, an antiferroelectric liquid crystal (response time: 70 μs) was injected from the inlet, and the inlet was sealed with epoxy resin. Thereafter, a polarizing plate was further adhered to the outer surfaces of the first and second substrates to form a 12-inch diagonal liquid crystal display device.

With respect to the liquid crystal display element prepared in this manner, the stripe-shaped counter electrode is set to the same potential, the frame frequency is set to 60 Hz, the frame time is set to 16.7 ms, and the writing time is set to 38 μs. When the driving method to be changed was applied, the optical response of each pixel of the liquid crystal display element showed a response as shown in FIG. 3, and unevenness in luminance was observed on the display screen.

FIG. 10 is a diagram in which the light transmittance and the time axis of the optical response waveform of FIG. 3 are replaced with the natural logarithmic axis. As shown in FIG. 10, the voltages (1, 3,.
Regardless of 5V), the optical response changes exponentially. Therefore, this characteristic can be approximated by a circuit characteristic having a certain time constant such as CR.

FIG. 11 shows a configuration example of the analog signal generation circuit 27 in the case where the optical response characteristics are approximated by the capacitor (C) 73 and the resistor (R) 72. In the example of FIG.
The coincidence signal via the latch circuit 41 is applied to the reset switch 71 in the analog signal generator 27, and resets the charge stored in the capacitor 73. Next, from the time when the coincidence signal from the latch circuit 41 is no longer applied, that is, the time after the polarity inversion is performed, the electric charge is accumulated in the capacitor 73 via the resistor 72, and the potential applied to the operational amplifier 74 becomes Going up exponentially. Therefore, by setting the time constant composed of the resistor 72 and the capacitor 73 in accordance with the characteristics of the liquid crystal display element, it is possible to obtain characteristics matching the optical response as shown in FIG.

The signal corresponding to the optical response generated here is subjected to amplitude adjustment by the correction value amplitude adjustment volume 54, and the DC offset adjustment volume 55 and the DC offset adjustment operational amplifier 58 generated by the DC offset adjustment operational amplifier 58. After being added by the operational amplifier 59 to the adjustment signal, the operational signal is subtracted by the operational amplifier 60 from a reference voltage for generating a display signal of the liquid crystal display element, which is generated by the volume 56, that is, a so-called gamma correction voltage. (Corresponding to the common driver 30).

Here, the opposing electrode driving circuit is a circuit for driving the opposing electrode of the liquid crystal display element. The opposing electrode is provided independently for each scanning line of the liquid crystal display element. It is assumed that the circuit is connected to each of the independent counter electrodes. The counter electrode driving circuit outputs a gamma correction voltage to which a correction signal is applied to the counter electrode. Therefore, the gamma correction voltage applied to the pixel of the liquid crystal display element is a voltage obtained by subtracting the correction characteristic created by CR from the normal gamma correction voltage, that is, a voltage at which the gamma correction voltage value decreases with time. And the characteristic for correcting the optical response shown in FIG. That is, a signal obtained by correcting a display signal with a time-attenuating correction signal is applied to each pixel of the liquid crystal display element.

With the above driving method, as shown in FIG. 13, the luminance of the pixel before the polarity inversion and the luminance of the pixel after the polarity inversion become the same, and the uniformity of the display can be maintained. A liquid crystal display device having excellent display characteristics can be obtained.

[Embodiment 4] Next, as a fourth embodiment, a liquid crystal display device having an auxiliary capacitance element in which a pixel electrode is one electrode and the other electrode (auxiliary capacitance electrode) is formed of a transparent conductive film will be described. The case where the voltage applied to the pixel electrode is corrected will be described.

A soluble polyimide thin film is offset-printed on a first substrate on which TFTs, pixel electrodes and auxiliary capacitance elements are formed in a matrix, and on a second substrate on which a color filter and a counter electrode are formed, respectively. At 85 ° C. for 3 minutes and then in an N ₂ oven at 180 ° C.
The resultant was baked at 1 ° C. for 1 hour to form an alignment film made of a polyimide film having a thickness of 45 μm. Thereafter, a rubbing treatment was performed while heating the first and second substrates to 90 ° C. Thus, the orientation film was sufficiently stretched and oriented in the polyimide film even at the stepped portion due to the TFT, the auxiliary capacitance element, and the like, and a uniform orientation of the smectic phase was obtained.

Next, spacer particles were sprayed on the first substrate. Further, a sealant made of an ultraviolet curable resin was printed on a peripheral portion of the second substrate. And these first and second
The substrates were combined face-to-face, irradiated with ultraviolet light under pressure to cure the sealant, and heated at 160 ° C. for 1 hour to form a cell. Thereafter, the cell was placed in a vacuum chamber, an antiferroelectric liquid crystal (response time: 95 μs) was injected from the injection port, and the injection port was sealed with epoxy resin. Thereafter, a polarizing plate was further adhered to the outer surfaces of the first and second substrates to form a 12-inch diagonal liquid crystal display device.

When a driving method in which the frame frequency is 60 Hz, the frame time is 16.7 ms, the writing time is 35 μs, and the polarity of the applied voltage is changed for each of a plurality of frames is applied to this liquid crystal display element, The optical response showed a response as shown in FIG. This optical response characteristic is taken into the correction memory 52 in the analog signal generator 27 shown in FIG. 7 as optical response correction data. That is, when the driving method of changing the polarity of the applied voltage for each of a plurality of frames is applied, the optical response characteristic changes from a dark state to a bright state every several seconds as shown in FIG. The optical response which repeats light and dark in a cycle of several seconds is corrected so as to have a constant optical response. Hereinafter, similarly to the method of the first embodiment, a signal voltage corrected by a correction signal that attenuates a display signal over time is applied to each pixel of the liquid crystal display element.

By the above driving method, as shown in FIG. 13, the luminance of the pixel before the polarity inversion and the luminance of the pixel after the polarity inversion become the same, and the uniformity of the display can be maintained. A liquid crystal display device having excellent display characteristics can be obtained.

[Embodiment 5] Next, as a fifth embodiment, a liquid crystal display element having an auxiliary capacitance element in which a pixel electrode is one electrode and the other electrode (auxiliary capacitance electrode) is formed of a transparent conductive film will be described. The case where the voltage applied to the auxiliary capacitance electrode is corrected will be described.

A first substrate on which TFTs, pixel electrodes and auxiliary capacitance elements are formed in a matrix, and a counter electrode on which a counter electrode is formed in a stripe parallel to the scanning lines when combined with a color filter and the first substrate. On each of the substrates 2, a soluble polyimide thin film was offset-printed, and baked at 80 ° C. for 3 minutes using a hot plate at 200 ° C. for 30 minutes in a N ₂ oven to obtain a film thickness of 35 μm.
An alignment film made of a polyimide film was formed. Thereafter, a rubbing treatment was performed while heating the first and second substrates to 80 ° C. Thus, the orientation film was sufficiently stretched and oriented in the polyimide film even at the stepped portion due to the TFT, the auxiliary capacitance element, and the like, and a uniform orientation of the smectic phase was obtained.

Next, spacer particles were sprayed on the first substrate. Further, a sealant made of an ultraviolet curable resin was printed on a peripheral portion of the second substrate. And these first and second
The substrates were combined face-to-face, irradiated with ultraviolet light under pressure to cure the sealant, and heated at 180 ° C. for 1 hour to form a cell. Thereafter, the cell was placed in a vacuum chamber, an antiferroelectric liquid crystal (response time: 75 μs) was injected from the injection port, and the injection port was sealed with epoxy resin. Thereafter, a polarizing plate was further adhered to the outer surfaces of the first and second substrates to form a 12-inch diagonal liquid crystal display device.

The stripe-shaped counter electrode is set to the same potential as that of the auxiliary capacitance electrode made of a transparent conductive film, and a frame frequency of 60 Hz and a frame time of 16.7 are applied to this liquid crystal display element.
ms, the writing time is 38 μs, and when the driving method of changing the polarity of the applied voltage for each of a plurality of frames is applied, the optical response of the liquid crystal display element shows a response as shown in FIG. 3, and the display screen has uneven brightness. Observed. Thereafter, similarly to the third embodiment, a correction signal is supplied to the counter electrode (that is, the counter electrode and the auxiliary capacitance electrode having the conductive potential), and the display signal is corrected for each pixel of the liquid crystal display element by a correction signal that attenuates the display signal over time. The applied voltage was applied.

According to the above driving method, as shown in FIG. 13, the luminance of the pixel before the polarity inversion and the luminance of the pixel after the polarity inversion become the same, and the uniformity of the display can be maintained. A liquid crystal display device having excellent display characteristics can be obtained.

As a result of further investigations by the present inventors, the phenomenon that the transmittance of the liquid crystal increases in the order of several seconds as shown in FIG. 3 is substantially caused by the following equation: T (t) / T0 = 1-exp [- (T / t0) ⁿ ]. Here, T (t) is the transmitted light intensity when the time t has elapsed since the polarity was inverted, T0 is the transmitted light intensity immediately before the polarity inversion, t0 is a constant depending on the liquid crystal material and the display voltage level, and n is the liquid crystal. This is a constant (approximately 0.1 to 4) depending on driving conditions such as a material and a frame time.

Therefore, from the relationship between the voltage applied to the liquid crystal and the transmitted light intensity, the correction value can be expressed as a function of time based on the above equation, and the correction value can be determined based on the above equation. is there.

Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0062]

According to the present invention, a signal applied to a pixel electrode or the like is corrected by a correction signal attenuating with time, so that uniformity of a display state can be maintained even after a lapse of time. In addition, it is possible to improve display characteristics.

[Brief description of the drawings]

FIG. 1 is a view for explaining an electric field response of a liquid crystal having a spontaneous polarization induced by applying an electric field inherently or by applying an electric field.

FIG. 2 is a diagram showing a voltage waveform and transmittance of each part of the liquid crystal display device.

FIG. 3 is a diagram illustrating a state in which the transmittance of a liquid crystal changes over time.

FIG. 4 is a diagram showing a configuration example of a liquid crystal display device according to an embodiment of the present invention.

5 is a diagram showing a part of the liquid crystal display device shown in FIG. 4 in detail.

FIG. 6 is a diagram showing signals of each part of the liquid crystal display device shown in FIG.

FIG. 7 is a diagram showing a part of the liquid crystal display device shown in FIG. 4 in detail.

FIG. 8 is a diagram illustrating an example of a correction characteristic according to the embodiment of the present invention.

FIG. 9 is a diagram showing another example of the correction characteristic according to the embodiment of the present invention.

FIG. 10 is a diagram showing a change in transmittance of liquid crystal over time.

FIG. 11 is a diagram showing a part of the liquid crystal display device shown in FIG. 4 in detail.

FIG. 12 is a diagram showing another configuration example of the liquid crystal display device according to the embodiment of the present invention.

FIG. 13 is a diagram showing transmittance characteristics of a liquid crystal display element obtained by the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Liquid crystal molecule 2 ... Optical axis 3, 4 ... Easy axis of a polarizing plate 5 ... Electric field application direction 6 ... Gate signal 7 ... Signal voltage 8 ... Writing voltage 9a, 9b ... Holding voltage 10a, 10b, 10c ... Light transmittance DESCRIPTION OF SYMBOLS 11 ... Applied voltage at the time of static drive 20 ... Polarity inversion control circuit 21 ... Display signal 22 ... Synchronous signal 23 ... Display timing controller 24 ... Liquid crystal display element 25 ... Signal line driver 26 ... Scan line driver 27 ... Analog signal generator 28 ... Timing signal 29 ... Display signal 30 ... Common driver 31 ... Line counter 32 ... Frame counter 33 ... Comparator 34 ... Inversion determination circuit 35 ... Exclusive OR circuit 36 ... Memory 37 ... Switching circuit 38 ... Latch circuit 39 ... Memory address counter 40: Initial pattern circuit 41: Latch circuit 51: Counter 2 ... Correction Memory 53 ... D / A converter 54 ... correction value amplitude adjustment knob 55 ... DC offset adjustment knob 56 ... gamma correction volume 57, 58, 59, 60 ... operational amplifier 71 ... Switch 72 ... resistor 73 ... Condenser

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomo Hasegawa 33, Shinisogo-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside Toshiba Production Technology Laboratory Co., Ltd. Address: Inside Toshiba Production Technology Laboratory (72) Inventor Hiroyuki Nagata 33, Shinisogo-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside Toshiba Production Technology Laboratory (72) Inventor: Takaki Takato Isogo-ku, Yokohama-shi, Kanagawa 33, Shinisogo-cho, Toshiba Production Technology Laboratory Co., Ltd.

Claims (3)

[Claims] A liquid crystal having a spontaneous polarization induced by applying a unique or electric field; a pixel electrode arranged in a matrix; a counter electrode facing the pixel electrode with the liquid crystal interposed therebetween; A switching element that periodically supplies a display signal to the pixel electrode, and a polarity inversion unit that inverts the polarity of a voltage applied to the liquid crystal at a cycle longer than a cycle of periodically supplying a display signal to the pixel electrode; Means for correcting the signal applied to the pixel electrode or the counter electrode with a signal that attenuates with time from the time when the polarity of the voltage applied to the liquid crystal is inverted by the polarity inversion means to the time when the polarity is subsequently inverted. A liquid crystal display device characterized by the above-mentioned. 2. A liquid crystal having a spontaneous polarization induced by applying a unique or electric field; pixel electrodes arranged in a matrix; a counter electrode facing the pixel electrode with the liquid crystal interposed therebetween; An auxiliary capacitance element having a pixel electrode as one electrode and the other electrode as an auxiliary capacitance electrode, a switching element for periodically supplying a display signal to the pixel electrode,
A polarity inversion means for inverting the polarity of the voltage applied to the liquid crystal at a cycle longer than a cycle of periodically supplying a display signal to the pixel electrode, and inverting the polarity of the voltage applied to the liquid crystal with the polarity inversion means; A liquid crystal display device comprising: means for correcting a signal applied to the pixel electrode, the counter electrode, or the auxiliary capacitance electrode with a signal that attenuates with time from the first to the next inversion of polarity. 3. The signal decaying with time is T
(T) is the transmitted light intensity when a time t has elapsed after inverting the polarity of the voltage applied to the liquid crystal by the polarity inversion means;
T (t) / T0 = 1-exp [-(t / t0) ⁿ ] ^where T0 is the transmitted light intensity immediately before inverting the polarity of the voltage applied to the liquid crystal, and t0 and n are predetermined constants. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is generated by: