JPH0442657B2 - - 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. It requires a method.

Furthermore, considering the lifespan of the optical device, it is undesirable for a DC component to be applied to the pixels for a long period of time, and a driving method that takes this point into account is required.

As a driving method that does not apply this DC component for a long time, it includes a write pulse that brings the pixel into a desired optical response state, and after application of this write pulse, there is no pulse that changes the optical response state of the pixel, and A pulse group in which there are pulses of negative polarity with a symmetrical waveform with respect to pulses of positive polarity is applied to the pixel in a time-sharing manner, and when the pulse group is not applied, an alternating current pulse is applied to maintain the pixel in the response state. (Japanese Unexamined Patent Publication No. 61-230197),
and an alternating current pulse that maintains the above response state,
There are driving methods such as an AC pulse in which a high frequency AC pulse is superimposed on an AC pulse having a pulse height lower than that of the write pulse (Japanese Patent Application Laid-open No. 116925/1983).

(Problems to be Solved by the Invention) In the above driving method, as a method of AC driving, a write pulse for creating a responsive (bright) state is applied before a writing pulse for creating a reverse responsive (dark) state. Therefore, there was a problem that the dark level was lowered, the contrast was lowered, and moreover, flickering occurred when the frame frequency was low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to extend the service life, suppress the decrease in dark level, and obtain high contrast.

(Means for solving the problem) The present invention is characterized in that the pulse group applied to the pixel is such that the average voltage value of positive polarity pulses is equal in absolute value to the average voltage value of negative polarity pulses, The above object is achieved by making sure that the second pulse group that is applied to bring the pixel into the dark state does not contain pulses that bring the pixel into the bright state.

In addition, the contrast can be further improved by eliminating the presence of pulses that cause the pixels to become dark in the first pulse group that is applied to bring the pixels into the bright state.

(Example) In FIG. 1, a ferroelectric liquid crystal is interposed between the control electrodes R1 to RX facing the scanning electrodes L1 to Ln, and a plurality of pixels are formed at the intersections of each electrode. From the selection circuit SE, one scan electrode L1~
Selection signal S1 for sequentially and time-divisionally selecting Ln
(Fig. 2) is generated, and when this selection signal is not supplied, a non-selection signal NS1 is generated.

Further, from the drive control circuit DR, the response signal D1 in FIG. 2 is generated as a first data signal, or the reverse response signal RD1 is generated as a second data signal, and is supplied to the control electrodes R1 to Rx. That is, the response signal D1 is supplied to the control electrode of a pixel for which a bright state is desired, and the reverse response signal RD1 is supplied to the control electrode of a pixel for which a dark state is desired.

Now, when the pulse width of the write pulse for bringing the pixel into the saturated response (bright) state or the pulse width for bringing the pixel into the reverse response (dark) state is 1, the selection signal S1
is the voltage - (V-v) when the pulse width is 1/2, the voltage (V-v) when the pulse width is 1, and the voltage - (V-v) when the pulse width is 1/2, respectively.
and +(V-v), voltage (V-v) with pulse width 1,
Consists of voltage (V-v) with pulse width 1/2. The non-selection signal NS1 is made up of a voltage O.

The response signal D1 has a pulse width of 1/2 and a voltage of -v, a pulse width of 1 and voltages of v, -v, and v, respectively, and a pulse width of 1/2 and a voltage of -v. The reverse response signal RD1 has a pulse width of 1/2 and a voltage v, a pulse width of 1 and voltages -v, v, and -v, and a pulse width of 1/2 and a voltage -v.

By supplying the above-mentioned signals, the first pulse group P1 is applied to the pixel for which a bright state is desired due to the potential difference between the response signal D1 and the selection signal S1, and the reverse response is applied to the pixel for which a dark state is desired. The second pulse group P2 is applied based on the potential difference between the signal RD1 and the selection signal S1.

In the first pulse group P1, first, the voltage (V-2v) with a pulse width of 1/2, the voltage - (V-2v) with a pulse width of 1,
A voltage (V-2v) is applied with a pulse width of 1/2, and a voltage -V with a pulse width of 1/2, but the liquid crystal does not respond to any of these pulses, and then a voltage of V with a pulse width of 1 is applied.
The first pixel enters a saturated response state (bright state) by application of the write pulse a. Next pulse width 1/
2, the liquid crystal is not sensitive to voltage -V and maintains a bright state. That is, the pulse group 1 applied to the pixel to bring it into a bright state includes a write pulse to bring it into a responsive (bright) state, but does not include a pulse to bring it into an inverse responsive (dark) state. Furthermore, the average voltage value of the pulses of positive polarity is equal in absolute value to the average voltage value of the pulses of negative polarity. In other words, the total area of the positive pulse waveform is equal to the total area of the negative pulse waveform, and a biased DC voltage is not applied.

In addition, in the second pulse group P2, first the pulse width is 1/
At 2, the liquid crystal does not respond to the pulse of voltage V, and with the next pulse width of 1, the pixel becomes an inverse response state (dark state) due to the write pulse b of voltage -V, and after that, the voltage changes at 1/2 of the pulse width. The liquid crystal remains in a dark state without being sensitive to any pulse of V or voltage ±(V-2v). That is, the pulse group P2 applied to the pixel to make it into a dark state includes a write pulse to make it into a reverse response (dark) state, but does not include a pulse to make it into a response (bright) state. Moreover, the average voltage value of the pulses of positive polarity is equal in absolute value to the average voltage value of the pulses of negative polarity.

After the selection signal S1 is supplied, the same electrode L1
The non-selection signal NS1 is supplied to ~Ln, but the third pulse group P3 is applied to the pixel due to the potential difference between the non-selection signal and the response signal, and the potential difference between the non-selection signal and the reverse response signal. Since none of the third pulse group P4 applied to the pixel includes a write pulse for bringing the pixel into a saturated response state or an inverse response state, the response when the selection signal is supplied (bright) ) or the reverse response (dark) state is maintained.

The third diagram shows other examples of each signal waveform, including a selection signal S1, a response signal D1, and a reverse response signal.
Since both RD1 have the same waveform as shown in the second diagram, the pulse groups P1 and P2 are also similar, and both can perform driving with a response similar to that shown in the second diagram and a reverse response. However, in this example, instead of the voltage O, a high frequency alternating current pulse is applied as the non-selection signal NS1'.
For this reason, when not selected, a third pulse group P3' or P4', in which a high-frequency AC pulse is superimposed on pulse group P3 or P4 in FIG. 2, is applied, thereby reducing fluctuations in contrast when not selected. For ferroelectric liquid crystals with dielectric anisotropy of Δε<O, this is particularly effective due to the AC stabilizing effect. The pulse width of the high-frequency AC pulse is preferably 1/4 or less of the write pulse.
The pulse height is appropriately determined so that the optical response state can be stably maintained.

Fig. 4a shows still another example of the signal waveform, and the width of each electric signal of the selection signal S2, the response signal D2 which is the first data signal, and the reverse response signal RD2 which is the second data signal is , write pulse width
Since it only requires 2.5 times more, the time required to rewrite the screen can be reduced.
The first pulse group P5 is applied to the pixel due to the potential difference between the selection signal S2 and the response signal D2. This pulse group P5 consists of a write pulse c for creating a reverse response (dark) state and a write pulse d for creating a response (bright) state. Therefore, once it becomes a dark state, it becomes a light state, and from then on it will remain in this bright state, but the existence of a momentary dark state before the bright state is due to dark adaptation, and the viewer It is almost imperceptible and does not cause flicker or contrast loss. The second pulse group P6 is applied due to the potential difference between the selection signal S2 and the reverse response signal RD2.
During 6, a write pulse C is applied to create a reverse response state.
This is effective in preventing a decrease in the dark level and preventing flickering, since it does not include the write pulse that causes the response state. Further non-selection signal NS
2, the pixel receives the third pulse group P7 or P
8 is applied, but none of them includes a write pulse, and a response state or a reverse response state is maintained.

Figure 4b shows the non-selection signal of voltage O shown in figure 4a.
This is an example in which a non-selection signal NS2' using a high-frequency AC pulse similar to the non-selection signal shown in Figure 3 is used instead of NS2, and the aim is to reduce the fluctuation in contrast during non-selection in the same way as shown in Figure 3. It is ivy.

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 those described above, and various changes can be made, and a bias voltage may be applied as necessary.

Furthermore, in the above embodiment, the matrix optical device as shown in FIG. Needless to say, the present invention can also be applied to driving a liquid crystal shutter array.

(Effects of the Invention) According to the present invention, in the pulse group applied to a pixel, the average voltage value of positive polarity pulses is equal in absolute value to the average voltage value of negative polarity pulses, so that the lifespan of the liquid crystal can be extended. In addition, since the pulse group for creating a dark state does not include a pulse for creating a bright state, a decrease in the dark level can be suppressed, and an optical device with high contrast can be obtained.

In addition, contrast can be further improved by not including pulses for creating a dark state in the pulse group for creating a bright state.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing an example of a matrix type liquid crystal optical device, Fig. 2 is an explanatory diagram showing an example of voltage waveforms for realizing the present invention, and Figs. 3, 4a, and 4b are respectively FIG. 7 is an explanatory diagram showing another example of waveforms for realizing the present invention. R1-Rx...Control electrode, L1-Ln...Scanning electrode, S1, S2...Selection signal, NS1, NS2...
Non-selection signal, NS1', NS2'...Non-selection signal, D
1, D2...first data signal, a to d...write pulse, RD1, RD2...second data signal,
P1, P5...first pulse group, P2, P6...
Second pulse group, P3, P4...Third pulse group, P3', P4'...Third pulse group, P7, P
8...Third pulse group, P7', P8'...Third pulse group.

Claims (1)

[Scope of Claims] 1. A matrix in which a liquid crystal whose molecular orientation changes depending on the direction of application of an electric field 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 a type liquid crystal optical device, a selection signal is sequentially supplied to each scanning electrode, a non-selection signal is supplied when a selection signal is not supplied, and first data specifying a bright state is supplied to each control electrode. either the signal or a second data signal specifying a dark state is selectively supplied in synchronization with the supply of the selection signal, and the potential difference between the selection signal and the first data signal causes the pixel to have the first data signal. A group of pulses is applied to the pixel to create a bright state, and a second group of pulses is applied to the pixel to create a dark state depending on the potential difference between the selection signal and the second data signal. applying a third group of pulses that maintains the optical response state of the pixel by a potential difference with a data signal of the average voltage value of which is equal in absolute value to the average voltage value of the pulses of negative polarity, and the second pulse group includes a write pulse that puts the pixel in a dark state, but there is a pulse that brings the pixel into a bright state. and the average voltage value of the positive polarity pulse is equal to the average voltage value of the negative polarity pulse, and the third pulse group consists of pulses that maintain the optical response state of the pixel, and 1. A method for driving a matrix liquid crystal optical device, characterized in that the average voltage value of positive polarity pulses is equal in absolute value to the average voltage value of negative polarity pulses. 2. The method of driving a matrix type liquid crystal optical device according to claim 1, wherein the first pulse group does not include a pulse that causes a pixel to be in a dark state.