JPH01154127A - Driving method for matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To suppress lowering of a dark level and to obtain a display of a high contrast without flickering by prohibiting inclusion of display control pulses for putting the title display device into a response state in pulse groups for putting the device into a reverse response state. CONSTITUTION:While the pulse groups P1 to be impressed to the liquid crystal for putting the device into the bright state contain the display control pulses for putting the device into the response state but do not contain the display control pulses for putting the same into the reverse response state; moreover, the pulses of the different polarities are made equal in both the voltage value and pulse width. While the pulse groups P2 to be impressed to the liquid crystal in order to put the device into the dark state contain the display control pulses for putting the device into the reverse response state but do not contain the display control pulses for putting the same into the response state and the pulses of the different polarities are made equal in both the voltage value and pulse width. The long-life display device is thereby obtd.; in addition, the lowering of the dark level is suppressed and the flicker-free display of the high contrast is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for driving a matrix liquid crystal display device using ferroelectric liquid crystal.

(Prior Art) Recently, ferroelectric liquid crystals have been attracting attention in place of TN type liquid crystals, and development of display devices using them is progressing.

The display modes of ferroelectric liquid crystals include a birefringent display mode and a guest-host display mode.

When driving these, unlike conventional TN-type liquid crystals, the display state g (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.
This requires a special driving method.

Furthermore, considering the lifespan of the display device, it is not preferable that a direct current component be applied to the display element for a long period of time, and a driving method that takes this point into consideration is required.

As a driving method that does not apply this DC component for a long time, it includes a display control pulse that brings the ferroelectric liquid crystal into a desired response state, and after the application of this display control pulse, there is a pulse that changes the response state of the ferroelectric liquid crystal. A group of pulses in which the waveform and number of pulses having different polarities are equal are applied to the display element in a time-sharing manner, and the ferroelectric liquid crystal is maintained in the responsive state when the pulse group is not applied. A device that applies alternating current pulses (Japanese Patent Application Laid-open No. 1983-
No. 230197), and the AC pulse to maintain the above response state is an AC pulse obtained by superimposing a high-frequency AC pulse on an AC pulse with a pulse height lower than the display control pulse (Japanese Unexamined Patent Publication No. 116925/1982). There are several driving methods such as

(Problems to be Solved by the Invention) -1 In the two driving methods, as a method of AC driving, display control is performed to make the response (bright) state before the display control pulse to make the reverse response (dark) state. Since a pulse is applied, there is a problem in that the dark level is lowered, the contrast is lowered, and moreover, flicker occurs when the frame frequency is low.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a long-life display device, to suppress a decrease in dark level, and to provide a high-contrast, flicker-free display.

(Means for Solving the Problems) A feature of the present invention is that a group of pulses applied to a display element can satisfy the condition that the voltage values and pulse widths of pulses with different polarities are equal, and at least reverse response ( The display control pulse with the voltage and width required to create a responsive (bright) state is not present in the pulse group for creating a dark (dark) state.

(Example) In FIGS. 1 and 2, the selection circuit SE generates a selection signal St (FIG. 2) for sequentially and time-divisionally selecting one of the scanning electrode groups Ll-Ln. When is not supplied, a non-selection signal NSI is generated.

Further, the drive control circuit DR generates a response signal DI or a reverse response signal RDI shown in FIG. 2, and the other control electrode group R1
~Supplied to RX. That is, the response signal DI is supplied to the other electrode of the response display element, and the reverse response signal RDI is supplied to the other electrode of the appropriate response display element.

Now, assuming that the pulse width of the response control pulse or reverse response control pulse for bringing the ferroelectric liquid crystal into the saturated response state or the reverse response state is 1, the selection signal Sl has a pulse width of 1/2 and the voltage - (V-v). , Voltage (V-v) when pulse width is 1, Voltage - and + (V-v) when pulse width is 1/2, Voltage - (V-v) when pulse width is 1, Voltage when pulse width is 1/2 (
V-v). The non-selection signal NSI has a voltage of 0.

The response signal DI has a pulse width of 1/2 and a voltage of -■, a pulse width of 1 and voltages of V, -V and V, respectively.

The pulse width is 1/2 and the voltage is ~V. The reverse response signal RDI has a pulse width of 1/2, a W voltage of V, a width of 7° of 1, a voltage of -v, v and -V, and a pulse width of 1/1.
2 and consists of voltage ■.

By supplying the above signals, the pulse group P1 is applied to the response display element due to the potential difference between the response signal D1 and the selection signal S1, and the pulse group P2 is applied to the inverse response element due to the potential difference between the reverse response signal RDI and the selection signal S1. is applied.

In the pulse group P1, the voltage (V-2
V), voltage -(V-2v) with pulse width 1.

A voltage (V-2v) is applied with a pulse width of 1/2, and a voltage -■ is applied with a pulse width of 1/2, but the liquid crystal does not respond to any of these pulses, and then the voltage V is displayed with a pulse width of 1. The liquid crystal enters a saturated response state (bright state) only after the control pulse a is applied. Even with a voltage of -V with a pulse width of 1/2, the liquid crystal does not respond and maintains a bright state. In other words, in the pulse group Pl applied to the liquid crystal to bring it into a bright state,
It includes a display control pulse for creating a response state, but does not include a display control pulse for creating a reverse response state, and the voltage values and pulse widths of the pulses with different polarities are both equal.

In addition, in the pulse group P2, the liquid crystal does not respond to a pulse with a pulse width of 1/2 and a voltage of V, and then with a pulse width of 1, the voltage becomes -
The liquid crystal enters a reverse response state (dark state) by the display control pulse b in (2), and the liquid crystal remains in a dark state without being sensitive to any pulse from the voltage V or voltage element (V-2v) with a subsequent pulse width of 1/2. hold. That is, the pulse group P2 applied to the liquid crystal to make it into a dark state includes a display control pulse to make it into a reverse response state, but it does not include a display control pulse to make it into a response state, and moreover, the polarity The voltage values and pulse widths of the different pulses are the same.

After the selection signal S1 is applied, a non-selection signal NSI is applied to the same electrodes Ll to Ln, but a group of pulses P3, which is applied to the liquid crystal due to the potential difference between the non-selection signal and the response signal,
Since none of the pulse group P4 applied to the liquid crystal due to the potential difference between the non-selection signal and the reverse response signal includes a display control pulse for bringing the liquid crystal into a saturated response state or a reverse response state, the selection signal The response (bright) or reverse response (dark) state when is applied is maintained as is.

The third illustration shows another example of each signal waveform, in which the selection signal S1. Since both the response signal Dl and the reverse response signal RDL have the same waveform as shown in the second diagram, the pulse groups PL and P2 are also similar, and both can perform response and reverse response driving similar to those shown in the second diagram. However, in this example, the non-selection signal NSI
', a high frequency alternating current pulse is applied instead of voltage 0. For this reason, when not selected, a pulse group P3' or P4' in which a high-frequency AC pulse is superimposed on the non-selected pulse P3 or P4 shown in FIG. 2 is applied, thereby reducing fluctuations in contrast when not selected. Dielectric anisotropy is Δ
This is particularly effective for ferroelectric liquid crystals due to the AC stabilizing effect. The pulse width of the high frequency alternating current pulse is preferably 1/4 or less of the response control pulse, and both the pulse height and the pulse height are appropriately determined so that the response state can be stably maintained.

Illustration 4a shows still another example of the signal waveform,
Selection signal S2. Response signal D2. Since the width of each electrical signal of the reverse response signal RD2 is only 2.5 times the response control pulse width, the screen rewriting time can be shortened. A pulse group P5 is applied to the liquid crystal due to the potential difference between the selection signal S2 and the response signal D2. This pulse group P5 consists of a display control pulse C for setting the reverse response state and a display control pulse d for setting the response state. Therefore, once the body enters a dark state, it enters a light state and remains in this bright state from then on, but the existence of a momentary dark state before the light state can be seen from the relationship of dark adaptation. It is almost imperceptible to humans and does not cause flicker or contrast loss. The pulse group P6 is applied due to the potential difference between the selection signal S2 and the non-response signal RD2, but the pulse group P6 includes only the display control pulse C for setting the reverse response state, and the display for setting the response state. Since no control pulse is included, it is effective in preventing a decrease in the dark level and preventing flicker. Further, a pulse group P7 or P8 is applied to the liquid crystal by the non-selection signal NS2, but neither of them includes a display control pulse, and a response state or a reverse response state is maintained.

4b is an example in which a non-selection signal NS2' with a high frequency AC pulse similar to the non-selection signal shown in FIG. 3 is used instead of the non-selection signal NS2 of voltage 0 shown in FIG.
Similar to the illustration, this is intended to reduce fluctuations in contrast when not selected.

In the above explanation, we referred to a positive voltage as a response and a negative voltage as a reverse response, but the response and reverse response are two sides of the same coin. It may also be referred to as responding with the 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.

Further, in the above embodiment, a matrix display as shown in FIG. 1 was described, but the display is not limited to this. Needless to say, the present invention can also be applied to driving a liquid crystal shutter array for an optical printer, which is divided into several blocks and wired in a matrix.

(Effects of the Invention) According to the present invention, the voltage values and pulse widths of the pulses of different polarities in the pulse group applied to the display element are equal. )
Since the display control pulse for setting the response (bright) state is not included in the pulse group for setting the state, the reduction in the dark level can be suppressed and a high-contrast, flicker-free display can be achieved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of a display device, FIG. 2 is an explanatory diagram showing an example of a voltage waveform for realizing the present invention, and FIGS. 3, 4a, and 4b each illustrate the present invention. It is an explanatory diagram showing other waveform examples for realization. R1-Rx...Control electrode group, Ll-Ln...Scanning electrode group, Sl, S2...Selection signal, NSI, NSI', NS2. NS2'...non-selection signal, DI, D2...response signal, a-d...display control pulse RDI, RD2...reverse response signal, P1-P8...
- Pulse group. that's all

Claims (1)

[Claims] In a matrix liquid crystal display device in which a ferroelectric liquid crystal whose response state varies depending on the direction of electric field application is interposed between a scanning electrode group and a control electrode group, a selection signal is sequentially supplied to the scanning electrode group. However, when this selection signal is not supplied, a non-selection signal is supplied, a response signal or a reverse response signal is supplied to the control electrode group, and the potential difference between this response signal and the selection signal causes the ferroelectric liquid crystal to respond ( A group of pulses including a display control pulse having a voltage and width to create a state, and in which the voltage values and pulse widths of pulses with different polarities are both equal, are applied to the ferroelectric liquid crystal, and a reverse response signal is generated. includes a display control pulse having a voltage and width for causing the ferroelectric liquid crystal to be in a reverse response (dark) state due to a potential difference between the ferroelectric liquid crystal and the selection signal, and the voltage value and pulse width of the pulses having different polarities are both equal. applying a group of pulses to the ferroelectric liquid crystal, and applying an alternating current pulse to the ferroelectric liquid crystal to maintain the response state of the ferroelectric liquid crystal based on the potential difference between the response signal or inverse response signal and the non-selection signal; The display control pulse is characterized in that at least among the pulse group for creating the reverse response (dark) state, there is no display control pulse having the voltage and width for creating the responsive (bright) state. A method for driving a matrix liquid crystal display device.