JPH0438331B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a matrix type liquid crystal optical device.

[Prior Art] Ferroelectric liquid crystals have recently been attracting attention in place of TN liquid crystals, and optical devices using them are being developed.

The optical modes of ferroelectric liquid crystals include birefringent optical mode and guest-host optical mode. When driving these, unlike conventional TN-type liquid crystals, the optical response state (brightness and darkness) is controlled by the direction of electric field application, so the driving method used for TN-type liquid crystals cannot be used, and special driving methods are required. We need a method.

Among them, JP-A No. 60-176097 is outstanding in that it can realize bistability of the optical response state during multi-digit driving using a driving electric signal, making it easy to manufacture ferroelectric liquid crystal cells, and has received particular attention. There is.

[Problems to be Solved by the Invention] However, in this driving method, a high DC voltage is applied to the pixels on the selected line, and a high frequency AC voltage biased with the high DC voltage is applied to the pixels on the non-selected line. applied. For this reason, a DC component is applied to each pixel, so when driven for a long time, the transparent electrode may be reduced and become dark.
There was a problem that caused the deterioration of the liquid crystal.

In addition, since the DC bias voltage on the non-selected line is the same high voltage as the write voltage, a high-voltage, high-frequency AC voltage is required to maintain bistability and prevent crosstalk, which increases the overall drive voltage. There was a problem that the price was high.

The present invention is designed to prevent blackening of transparent electrodes and deterioration of liquid crystals even when driven for a long time, and to obtain high contrast without crosstalk, as well as to obtain intermediate tones.

[Means for Solving the Problems] The present invention forms a matrix type optical device using a liquid crystal that has an alternating current stabilizing effect by changing the orientation of molecules depending on the direction of application of an electric field, and sequentially connects scanning electrodes. A data signal is supplied to the control electrode in synchronization with the selection to bring the pixel into a desired optical response state, and after that, the optical response state is maintained by an AC stabilizing effect, and the pulse applied to the image base is achieves the above objective by ensuring that there is a pulse of negative polarity with a symmetrical waveform for every pulse of positive polarity, and also by adjusting the voltage of the write pulse according to the gradation. Further, by sequentially supplying an initialization signal and a subsequent selection signal to the scan electrodes, writing pixels in one scan electrode and simultaneously initializing pixels in the next scan electrode. This allows the time division cycle to be shortened.

[Example] In FIG. 1, a ferroelectric liquid crystal having an AC stabilizing effect is interposed between scanning electrodes _L1 to _L7 and control electrodes _R1 to _R5 facing each other, and a plurality of pixels are formed at the intersections of each electrode. The selection circuit SE generates a selection signal S ₁ (Fig. 2) that sequentially and time-divisionally selects the scanning electrodes L ₁ to L ₇ , and when this selection signal is not supplied, a non-selection signal NS ₁ is generated. Occur. Selection signal S ₁
is the voltage -(V-2v), (V-v), -V (preferably,
V/2≧v), and the non-selection signal NS ₁ consists of a voltage of 0 and ±H.

On the other hand, the drive control circuit DR outputs the response signal D ₁ or reverse response signal RD ₁ shown in FIG. 2 as a data signal.
is generated and supplied to control electrodes _R1 to _R5 . In other words, when the pixel is placed in a responsive state (for example, a light transmitting state), a response signal D ₁ is supplied to the control electrode, and when the pixel is placed in a reverse responsive state (for example, a light blocking state), a reverse signal is supplied to the control electrode. It supplies the response signal _RD1 .

By supplying the following signals, the first pulse group P1 is applied to the pixel for which a response state is desired, and the first pulse group _P1 is applied to the pixel for which a reverse response state is desired.
P ₂ is applied. In the pulse group P ₁ , a voltage (V-2v) pulse is first applied, but the liquid crystal does not respond to this, and the next pulse ₁₁ causes it to temporarily go into a reverse response state, but then a write pulse P ₁₂ is applied. ignites, which causes the pixel to become saturated. After this, a pulse of voltage -(V-2v) is applied, but the liquid crystal does not respond to this pulse,
There will be no reverse response state. In this pulse group P ₁ ,
For every positive pulse, there is a negative pulse with a symmetrical waveform, making it a complete alternating current pulse.

After the above-mentioned pulse group P ₁ is applied, an AC pulse A ₁ or A ₂ in which a high-frequency AC pulse exhibiting an AC stabilizing effect is superimposed on a voltage ±v lower than the voltage V by a non-selection signal NS ₁ is applied to a second pulse group. The optical response state of the pixel is maintained. That is, the AC pulses A ₁ and A ₂ are AC pulses with a frequency that exhibits an AC stabilizing effect, and since there are negative polarity pulses for all positive polarity pulses, the optical response state of the pixel is stable. It is maintained as follows. In particular, in forced liquid crystals with negative dielectric anisotropy, the high-frequency AC pulse exerts a force that orients the liquid crystal molecules parallel to the electrode substrate, so stable holding force is achieved as in JP-A-60-176097. can get.

On the other hand, in pulse group P ₂ , a pulse of ±(V-2v) is first applied so that the liquid crystal does not respond, and then, contrary to pulse group P ₁ , pulse P ₂₁ is applied, and then a reverse response is made. A write pulse P ₂₂ of is applied,
It becomes a reverse response state. Further, when the non-selection signal NS ₁ is supplied, the AC pulse A ₁ or A ₂ is applied, and the reverse response state is maintained.

In this way, the first pulse group P ₁ , P ₂ and the second pulse group AC pulses A ₁ , A ₂ are transparent because there are negative polarity pulses for all positive polarity pulses. This prevents blackening of the electrodes and deterioration of the liquid crystal.

Incidentally, in a 10 μm thick ferroelectric liquid crystal cell, V=
By setting the pulse width of the write pulse to 10 volts and 250 μS, a saturated response condition or a saturated inverse response condition is obtained.

The frequency of the high-frequency AC pulse is preferably twice or more (preferably four times or more, an integral multiple) of the write pulse frequency, and the pulse height H is determined by the optical Although it is determined as appropriate so that the response state is maintained stably, it is usually preferable to set it to about the write pulse height V or lower.

FIGS. 3, 4, and 5 show other examples of each signal waveform, and all can perform the same driving as in FIG. 2.

Next, an example will be described in which a pixel is once initialized at a timing before a selection signal is supplied, and then an optical response state is written. In FIG. 6, the selection signal _S2 consisting of voltages V-v and -(V-v) is sequentially supplied to the scanning electrodes _L1 to _L7 in FIG. 1, but at a timing before that,
It supplies an initialization signal RS consisting of voltages -(V+v) and V+v. At the time of non-selection, a non-selection signal NS ₂ consisting of voltage ±H is supplied.

On the other hand, control electrodes R ₁ to _{R 5} are supplied with voltages −v and response signals D ₂ of v or voltage v as data signals.
and _-v .

First, by supplying the initialization signal RS, an initialization pulse group P ₃ or P ₄ is applied, thereby once initializing it to a saturated reverse response state. And to enter the response state, select signal S ₂ and response signal D ₂
To apply the first pulse group P ₅ and bring about the reverse response state, the selection signal S ₂ and the reverse response signal RD ₂ are applied.
A first pulse group P ₆ is applied by. Pulse group P ₆ maintains the saturated reverse response state caused by pulse group P ₃ or P ₄ without changing.

When the non-selection signal NS ₂ is supplied, the second pulse group, AC pulse A ₃ or A ₄ is applied, and the response state or reverse response state is maintained.

According to this example, pixels in the next scan electrode can be initialized when writing pixels in one scan electrode, and the supply time of each signal is 1/2 or 2/3 of the above examples. , the number of digits that can be scanned within the same period can be doubled or 1.5 times,
Multi-digit drive is possible. In other words, for the same number of digits, one scan time can be reduced to 1/2 or 2/3, crosstalk can be reduced, and contrast can be improved.

Next, an example of obtaining halftones will be explained. 7th
8 and 8, the examples shown in FIGS. 5 and 6 are applied to produce halftones. 7th
In FIGS. 5 and 8, the initialization signal, selection signal and non-selection signal are the same as in FIGS. 5 and 6, and the control signals C ₁ and C which are data signals supplied to the control electrodes R ₁ to R ₅ The voltage a of _{No. 2} is controlled according to the gradation. In FIG. 7, pulses P ₃₁ and P ₃₂ are first applied by the first pulse group P ₇ based on the potential difference between the selection signal and the control signal C ₁ to initialize the state to a saturated reverse response state. Thereafter, the saturation inverse response state is maintained even with pulse P ₃₃ , and finally, write pulse P ₃₄ for producing halftones is applied to write halftones.

In FIG. 8, an initialization pulse group P ₈ is generated by an initialization signal RS and a control signal C ₂ which is a data signal.
After being initialized to the saturated reverse response state, the saturated reverse response state is maintained at pulse P ₃₅ by the first pulse group P ₉ based on the potential difference between the selection signal S ₂ and the control signal C ₂ . Halftones are written with write pulse _P36 . Thereafter, a high frequency alternating current pulse is applied according to the non-selection signal and the control signal, and the above-mentioned halftone optical response state is maintained.

The pulse for writing the halftone is not limited to modulation of the voltage a of the control signal, but may also be produced by pulse width modulation, but in either case, the pulse to write the halftone is once in a saturated reverse response state. It is important to initialize it to . If a pulse is simply applied to produce a halftone, the optical response state will change depending on the state of the pixel before the pulse is applied, making it impossible to obtain a stable halftone. For example, if we apply only a pulse that brings the pixel into an unsaturated inverse response state and a pulse that brings it into an unsaturated response state to produce a halftone to a pixel that is in a saturated response state, first, the unsaturated inverse response pulse A pixel that has entered an unsaturated inverse response state returns to a saturated response state by an unsaturated response pulse with a waveform that is opposite in polarity and symmetrical to the next unsaturated inverse response pulse, and an unsaturated response state (halftone) cannot be produced. Sometimes.

However, in the examples shown in Figures 7 and 8, since the optical response state is initialized to the saturated inverse response state before rewriting, stable halftones can be produced regardless of the previous optical response state. .

In the above explanation, the response depends on the voltage on the + side.
Although it has been referred to as a reverse response due to a voltage on the − side, since the response and reverse response are two sides of the same coin, it may also be referred to as a reverse response due to a voltage on the + side and a response due to a voltage on the − side.

By the way, the signals supplied to each electrode are not limited to the above, and various changes are possible.
A bias voltage may be applied as necessary.

Furthermore, it goes without saying that color display can be performed by driving a display device equipped with color filters for the three primary colors of R, G, and B using the present driving method.

[Effects of the Invention] According to the present invention, in the pulse group applied to the pixel, there is a negative polarity pulse with a symmetrical waveform to all the positive polarity pulses, so that the transparent electrode does not change even when driven for a long time. There is no darkening or deterioration of the liquid crystal. Moreover, when not selected, an AC pulse having a frequency that exhibits an AC stabilizing effect is applied to the pixel, so the optical response state is stably maintained and the contrast does not deteriorate even if the number of digits increases.

In addition, when using a ferroelectric liquid crystal with negative dielectric anisotropy, the high-frequency AC pulse component acts to orient the liquid crystal molecules parallel to the electrode substrate, resulting in more stable holding force and crosstalk. Achieves high contrast without any blemishes.

Furthermore, by introducing the initialization signal, it is possible to initialize the pixels in the next scan electrode when writing to pixels in one scan electrode, and it is possible to shorten the time for one cycle of the signal supplied to each electrode. Multiple digits can be scanned in a short time, and the number of drivable digits can be increased. In other words, if the number of digits is the same, the rewriting time of the optical response state can be shortened.
Eliminates crosstalk and improves contrast.

In addition, since halftones are generated by adjusting the voltage of the write pulse and pulses with symmetrical waveforms, halftones can be written without leaving any DC components.
It can produce stable halftones, and has great effects in many fields such as TV image display.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of a matrix type liquid crystal optical device, and FIGS. 2 to 8 are explanatory diagrams each showing voltage waveforms for realizing the present invention. _R1 to _R5 ...control electrode, _L1 to _L7 ...scanning electrode,
_S1 , _S2 ...Selection signal, _NS1 , _NS2 ...Non-selection signal, _D1 , _D2 ...Data signal, _RD1 , _RD2 ...Data signal, _A1 to _A4 ...Second A group of pulses, P ₁ ,
P ₂ , P ₅ ... first pulse group, P ₆ , P ₇ , P ₉ ... first pulse group, P ₃ , P ₄ , P ₈ ... initialization pulse group,
P ₁₂ , P ₂₂ , P ₃₄ , P ₃₆ ...Write pulse, RS...
Initialization signal.

Claims (1)

[Claims] 1. A liquid crystal that changes the orientation of molecules depending on the direction of application of an electric field and has an AC stabilizing effect is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In the method for driving a matrix type liquid crystal optical device, each scanning electrode is sequentially supplied with a selection signal, a non-selection signal is supplied when the selection signal is not supplied, and each control electrode is supplied with a selection signal. synchronously supplying a data signal, applying a first pulse group to the pixel to achieve a desired optical response state based on the potential difference between the selection signal and the data signal; Then,
A second group of pulses is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, the first group of pulses including a write pulse that brings the pixel into a desired optical response state. , and there is a negative polarity pulse with a symmetrical waveform for all positive polarity pulses, and the second pulse group consists of AC pulses with a frequency that exhibits an AC stabilizing effect, and all positive polarity pulses are present. A method for driving a matrix type liquid crystal optical device, characterized in that a negative polarity pulse having a symmetrical waveform is present with respect to the pulse. 2. The method of driving a matrix type liquid crystal optical device according to claim 1, wherein the liquid crystal is a ferroelectric liquid crystal that exhibits negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 3. A matrix type liquid crystal in which a liquid crystal that has an alternating current stabilizing effect by varying the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, a selection signal is sequentially supplied to each scanning electrode, a non-selection signal is supplied when the selection signal is not supplied, and a data signal is supplied to each control electrode in synchronization with the supply of the selection signal. applying a first group of pulses to the pixel to bring it into a desired optical response state by applying a potential difference between the selection signal and the data signal;
A second group of pulses is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the first group of pulses includes a write pulse that brings the pixel into a desired optical response state. The second pulse group consists of AC pulses with a frequency that exhibits an AC stabilizing effect, and includes all positive polarity pulses, and has a negative polarity pulse with a symmetrical waveform to all positive polarity pulses. By changing the waveform of the data signal according to the gradation, the voltage of the write pulse is adjusted and the write pulse in the first pulse group is A method for driving a matrix type liquid crystal optical device, characterized in that the voltage of a pulse having a symmetrical waveform and a reverse polarity is adjusted to be equal to that of a write pulse after adjustment. 4. The method of driving a matrix-type liquid crystal optical device according to claim 3, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 5. A matrix type liquid crystal in which a liquid crystal that has an AC stabilizing effect by varying the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, an initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, a non-selection signal is supplied when the initialization signal and selection signal are not supplied, and each control electrode is supplied with: The data signal is supplied in synchronization with the supply of the selection signal, and the potential difference between the initialization signal and the data signal causes the
A group of initialization pulses is applied to the pixel to optically initialize it, and a first group of pulses is applied to the pixel to set it to a desired optical response state depending on the potential difference between the selection signal and the data signal, and a non-selection signal and Due to the potential difference with the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a negative polarity pulse with a symmetrical waveform for every positive polarity pulse, and the first pulse group is a write pulse or initialization pulse group that changes the pixel to a desired optical response state. Therefore, there is a negative polarity pulse that includes a pulse that maintains the initialized state and has a symmetrical waveform with respect to all positive polarity pulses, and the second pulse group exhibits an AC stabilizing effect. 1. A method for driving a matrix type liquid crystal optical device, comprising alternating current pulses having a high frequency, and a negative polarity pulse having a symmetrical waveform with respect to all positive polarity pulses. 6. The method of driving a matrix type liquid crystal optical device according to claim 5, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting negative dielectric anisotropy in the frequency range of AC pulses in the second pulse group. 7. A matrix type liquid crystal in which a liquid crystal that has an AC stabilizing effect by changing the orientation of molecules depending on the direction of electric field application is interposed between a plurality of scanning electrodes and a plurality of control electrodes, and pixels are formed at the intersections of each electrode. In a method for driving an optical device, an initialization signal and a subsequent selection signal are sequentially supplied to each scanning electrode, a non-selection signal is supplied when the initialization signal and selection signal are not supplied, and each control electrode is supplied with: The data signal is supplied in synchronization with the supply of the selection signal, and the potential difference between the initialization signal and the data signal causes the
A group of initialization pulses is applied to the pixel to optically initialize it, and a first group of pulses is applied to the pixel to set it to a desired optical response state depending on the potential difference between the selection signal and the data signal, and a non-selection signal and Due to the potential difference with the data signal,
A second pulse group is applied to the pixel to maintain the optical response state of the pixel by an AC stabilizing effect, and the initialization pulse group is to put the pixel into a light transmitting state or a light blocking state. , and there is a pulse of negative polarity with a symmetrical waveform for every pulse of positive polarity, and the first pulse group is a write pulse or initialization pulse group that changes the pixel to the desired optical response state. Therefore, there is a negative polarity pulse that includes a pulse that maintains the initialized state and has a symmetrical waveform with respect to all positive polarity pulses, and the second pulse group exhibits an AC stabilizing effect. It consists of alternating current pulses of high frequency, and there is a pulse of negative polarity with a symmetrical waveform for every pulse of positive polarity.By changing the waveform of the data signal according to the gradation, the voltage of the write pulse can be changed. A method for driving a matrix type liquid crystal optical device, comprising adjusting the voltage of a pulse having a symmetrical waveform and opposite polarity to the write pulse in the first pulse group so as to be equal to that of the adjusted write pulse. 8. The method of driving a matrix type liquid crystal optical device according to claim 7, wherein the liquid crystal is a ferroelectric liquid crystal exhibiting negative dielectric anisotropy in the frequency range of the AC pulses in the second pulse group.