JPH0689078A - Method to reset phase transfer-type liquid crystal display panel - Google Patents

Abstract

PURPOSE:To enable accurate data writing after reset to be conducted even at low temp. by applying voltage once on the whole liquid crystal cells of a phase transfer-type liquid crystal display panel and then applying voltage twice as high as the voltage for hold. CONSTITUTION:When voltage is applied to drive the liquid crystal display panel, first, OV voltage is applied on the whole liquid crystal cells in a hold state with voltage Vd applied so that writing is done for the all cells (to change into a scattering state). Then 2Vd which is twice as the hold voltage Vd is applied for reset. In this process, the liquid crystal element is changed into a nematic phase to give a transparent state. To write data after that, 2Vd voltage is applied on the liquid crystal element to be maintained as transparent, while voltage OV is added to the liquid crystal element for writing. Then, the hold voltage Vd is applied on all liquid crystal elements to hold the written state by using the hysterisis characteristics of the element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving method, and more particularly to a reset method for a phase transition type liquid crystal display panel using a cholesteric-nematic phase transition type liquid crystal.

[0002]

2. Description of the Related Art A liquid crystal display device is a display device which is different from a display device which displays an intended image by light emission such as a plasma display or a CRT, and displays by reflecting or not reflecting incident light. Compared with the above-mentioned plasma display, CRT, or the like that displays by light emission, such display uses reflected light, and therefore has the feature that the operator's eyes are not tired. Therefore, liquid crystal display devices are now widely used, and among them, display devices using phase transition type liquid crystal are also known. The phase transition type liquid crystal display device is characterized in that a display is made by utilizing transmission / scattering of light, so that a polarizing plate is unnecessary, bright and easy-to-see display is possible, and a memory function is provided.

FIG. 7 shows the light transmittance-applied voltage characteristics of a phase transition type liquid crystal, wherein (a) shows the case of room temperature, (b) shows the case of low temperature, and (c) shows the case of high temperature. As shown in the light transmittance-applied voltage characteristic curve in the figure, the liquid crystal undergoes a phase transition through different paths when the applied voltage rises (arrow X) and when the applied voltage falls (arrow Y). Draw a hysteresis curve.

In this case, when the applied voltage is low, the liquid crystal has a cholesteric phase (Ch
Phase), and light is scattered. When the applied voltage is high,
The liquid crystal has a nematic phase (N
Phase) and is in a transparent state that allows light to pass therethrough. A liquid crystal composition in which a cholesteric liquid crystal is mixed with a nematic liquid crystal (or vice versa) shows a cholesteric phase when a voltage is not applied, but changes to a nematic phase by applying an electric field, while reducing the electric field. Then, a phase transition occurs from the nematic phase to the cholesteric phase.

The transmission state and the scattering state of the light can be stably maintained at the same voltage by using the hysteresis effect, that is, the optically different bistable states can be obtained at the same voltage. Large-capacity display is possible by utilizing the memory effect.

Usually, in order to perform display on a phase transition type liquid crystal display device, the holding voltage Vd is set to 2 when the display panel is reset.
After applying the doubled voltage 2Vd to the liquid crystal element on the entire surface of the panel in the transmissive state, the voltage 2 is applied to the liquid crystal cell for displaying the transmissive state.
Writing is performed by applying Vd and a voltage OV to the liquid crystal cell to be written. After that, the holding voltage Vd is simultaneously applied to the liquid crystal cells on the entire surface of the display panel to hold the written state by utilizing the hysteresis characteristic. FIG. 8 shows the conventional drive waveform diagram.

[0007]

As described above, in the above phase transition type liquid crystal display device, as a reset after writing, a voltage 2Vd, which is twice the holding voltage Vd, is applied to the liquid crystal element on the entire surface of the panel to cause the transmissive state. Then, the voltage OV was applied and writing was performed.

By the way, as shown in FIGS. 7 (a), 7 (b) and 7 (c), the light transmittance-applied voltage characteristic curve of the phase transition type liquid crystal changes with a change in temperature, and its holding voltage Vd. Will also shift. That is, the holding voltage Vd ′ at low temperature, the holding voltage Vd at room temperature, and the holding voltage Vd ″ at high temperature have a relationship of Vd ′ <Vd <Vd ″. For this reason, a temperature correction circuit is provided in the drive circuit of the display device, and the holding voltage is shifted so that the holding voltage is Vd 'when the temperature is low and the holding voltage is Vd "when the temperature is high.

However, especially at a low temperature, even if the voltage 2Vd 'is applied as the reset voltage, Vd'<Vd, so naturally 2Vd '<2Vd, and a voltage lower than the voltage required at room temperature is used as the reset voltage. Will be applied. Therefore, the liquid crystal cell does not completely enter the nematic phase (transmission state), and a phenomenon in which the pattern written immediately before is slightly left occurs, which is a problem.

Further, when the voltage OV is applied and writing is performed immediately after the reset, the liquid crystal molecules immediately after the writing are in an unstable state close to a nematic phase, and are in a completely transmissive state and are not stationary. Therefore, accurate writing is performed. There was a problem that could not be done, which was a problem.

An object of the present invention is to provide a liquid crystal display panel using a phase transition type liquid crystal element, so that the liquid crystal element after data writing is completely reset so that the next writing can be performed accurately. That is.

[0012]

In the reset method for a phase transition type liquid crystal display panel according to the first aspect of the present invention, a voltage OV is once applied to all liquid crystal cells of the phase transition type liquid crystal display panel, and then twice the holding voltage is applied. It is characterized in that a voltage is applied.

The resetting method of the phase transition type liquid crystal display panel of the second invention is characterized in that the maximum withstand voltage of the IC in the drive circuit is applied to all the liquid crystal cells of the phase transition type liquid crystal display panel.

In the resetting method for the phase transition type liquid crystal display panel according to the third aspect of the invention, after applying a voltage twice the holding voltage to all the liquid crystal cells of the phase transition type liquid crystal display panel, it is held before the next writing. A feature is that a wait period for applying a voltage is provided.

[0015]

In the first aspect of the invention, since the voltage OV is applied to all the liquid crystal cells first, the liquid crystal molecules are uniformly brought into the cholesteric phase, and if a voltage twice the holding voltage is applied after that, for example, at a low temperature, Therefore, even if a lower holding voltage is applied and a lower reset voltage than at room temperature is applied, the liquid crystal molecules become completely in the nematic phase, and the previously written pattern does not remain, that is, it is completely reset. Then, the data writing after the next reset can be accurately performed.

In the second aspect of the invention, since the IC maximum withstand voltage in the drive circuit is applied as the reset voltage, a sufficiently high voltage is applied as the reset voltage even at a low temperature. Therefore, the liquid crystal molecules are completely in the nematic phase and the previously written pattern does not remain, that is, the liquid crystal molecules are completely reset and the data writing after the reset can be performed accurately.

In the third aspect of the invention, first, a voltage that is twice the holding voltage is applied to all the liquid crystal cells, and then the holding voltage is applied before the next writing, so that the liquid crystal molecules continue to be in the nematic phase. Since the data is held and stabilized, that is, written in the stable state, the data writing after the reset can be accurately performed.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram of an example of a phase transition type liquid crystal display device.
(A) is a perspective view of the display device unit, and (b) is
It is a schematic diagram of the liquid crystal display panel and its drive circuit incorporated in (a).

In the figure, since the liquid crystal itself has a memory function in the phase transition type liquid crystal display device, the number of pixels can be up to tens of millions of pixels in principle. The structure of the liquid crystal display panel 10 is a matrix type of cholesteric-nematic phase transition type liquid crystal, and the electrodes also have a normal matrix configuration. The drive circuit 11 includes a segment driver 12 and a common driver 13.

FIG. 5 is a block diagram of an example of the drive circuit 11. The liquid crystal display panel 10 is configured to be dynamically driven, and is driven by the segment driver 12 and the common driver 13.

The common driver 13 and the segment driver 12 are drive-controlled by the controller 14. The controller 14 adds the data to be displayed to the segment driver 12 (DATA), and the segment driver 12 drives each liquid crystal cell corresponding to the data. At this time, the controller 14 applies the clocks CL1 and CL2 and the alternating signal M to the segment driver 12. Further, the frame synchronization signal FLM, the clock CL1, and the alternating signal M are added to the common driver 13.

Based on these signals, the segment driver 12 and the common driver 13 drive the liquid crystal display panel 10. The liquid crystal display panel 10 cannot operate with a single power supply, and a plurality of voltages applied to each liquid crystal cell are generated by the liquid crystal drive power supply circuit 15. And controller 1
4, a control signal is applied to the liquid crystal drive power supply circuit 15, and a required power supply voltage is applied from the liquid crystal drive power supply circuit 15.

FIG. 6 is a block diagram of an example of the liquid crystal driving power supply circuit 15. Since the liquid crystal display panel 10 which requires a large number of power supply voltage as described above, the input power supply V _a (+ 5V),
And a plurality of voltages are generated from two power sources of V _LCD .
For simplification, only two voltages are shown and the others are omitted.

According to the figure, resistors R13 and R are connected to the power supply V _a.
One end of the series circuit of R12 and R11 is connected, and the other end is the power supply V
Connected to _LCD . Connection terminals of the respective resistors, for example, from the midpoint of the resistors R13 R12 through the buffer B2 and a power source V _b, also has an intermediate point of the resistor R12 resistor R11 via the buffer B1 to the power supply V _c.

Further, as the power supply V _d from the other end of the resistor R11, the buffers B2 and B1 are supplied with power from the power supply V _a and the power supply V _d . The buffers B2 and B1 are differential amplifiers and operate as so-called buffers in which the output is added to the negative input terminal.

In the configuration as described above, for example, the power source V
By changing a volume (not shown) provided on the _LCD side, the current flowing from the power supply V _a to the power supply V _LCD via the resistors R13, R12 and R11 changes, and the voltage between the resistors is determined in proportion to the current. .

The segment driver 12 has power supplies V _a and V
_b and V _d , and the common driver 13 has power supplies V _a and V
_c and V _d are added. The common driver 13 and the segment driver 12 control the display of the liquid crystal display panel 10 using such a power supply voltage. It has been described above that a plurality of power supplies V _b and V _c are provided.

FIG. 1 is an explanatory view of the operation of the first embodiment of the present invention, in which (a) is the light transmittance-applied voltage characteristic of the phase transition type liquid crystal, which is the same as that shown in FIG. , (B) are drive waveform diagrams.

As shown in FIGS. 1 (a) and 1 (b), the liquid crystal display
For application of voltage for driving the display panel 10 (see FIG. 4)
First of all, the voltage V_dFrom holding state to apply
A voltage OV is applied to the liquid crystal cell to perform full writing (scattering).
Disturbance state), then holding voltage V _dTwice the voltage of 2V_dMark
Add and reset. At this time, the liquid crystal element is nematic
It becomes a dark phase and becomes transparent.

Next, when writing is performed, a voltage of 2 V _d is applied to the liquid crystal element whose transmissive state is desired to be maintained, and a voltage OV is applied to the liquid crystal element which is desired to be written. Next, the holding voltage V _d is applied to all the liquid crystal elements at the same time to hold the written state by utilizing the hysteresis characteristic.

As described above, in the first embodiment, as the resetting method of the liquid crystal display panel, the voltage OV is once applied to all the liquid crystal elements to write the entire surface to make the entire surface scattering state, and then the voltage 2V _d is applied. To make the whole surface transparent. Conventionally, as shown in FIG. 8, resetting is performed by immediately applying a voltage 2V _d after holding the written state.

Therefore, even when the temperature is low, the holding voltage V _d
Even when the voltage is lower than that at room temperature and the reset voltage (double the holding voltage) is lower than that at room temperature, the (voltage) OV is first applied to all liquid crystal cells, so that the liquid crystal molecules are uniformly brought into the cholesteric phase. Then, when the voltage 2V _d is applied thereafter, the nematic phase is completely established, so that the previously written pattern does not remain, that is, the pattern is completely reset and the next data writing can be accurately performed.

FIG. 2 is a drive waveform diagram of the second embodiment of the present invention. The light transmittance-applied voltage characteristic of the phase transition type liquid crystal is the same as that of FIG. 1A shown in the first embodiment, and the description thereof is omitted.

As shown in FIG. 2, in the second embodiment, when the voltage is applied, the maximum withstand voltage V of the IC in the drive circuit (segment driver 12, common driver 13, etc.) is used as the reset voltage of the liquid crystal display panel. _m is being applied. Conventionally, as shown in FIG. 8, the reset voltage is a voltage 2V _d that is twice the holding voltage V _d . Here, writing and holding are the same as in the conventional case.

As described above, in the second embodiment, as the reset method for the liquid crystal display panel, the maximum withstand voltage V _m of the IC in the drive circuit is applied as the reset voltage. Therefore, even if the holding voltage V _d is low at low temperature, the reset voltage applied to the liquid crystal cell is sufficiently high. Therefore, the liquid crystal molecules are completely in the nematic phase and the previously written pattern does not remain, that is,
It will be completely reset and the next data writing will be performed correctly.

FIG. 3 is a drive waveform diagram of the third embodiment of the present invention. The light transmittance-applied voltage characteristic of the phase transition type liquid crystal is the same as that of FIG. 1A shown in the first embodiment, and the description thereof is omitted.

As shown in FIG. 3, in the third embodiment, as a reset method for a liquid crystal display panel, first after applying twice the voltage 2V _d hold voltage V _d, the next voltage OV
The voltage V _d is applied before writing by applying.
That is, a wait period is provided before writing. Here, writing and holding are the same as in the other embodiments.

As described above, in the third embodiment, as a method of resetting the liquid crystal display panel, after applying the voltage 2V _d to the transmissive state, the wait period for holding the state is provided. Therefore, by providing the wait period, the liquid crystal molecules are continuously placed in the transmissive state and stabilized, that is, the liquid crystal molecules are completely reset and the next data writing can be accurately performed.

In the above, the drive circuit and the power supply circuit are merely examples, and needless to say, are not limited to the above examples.

[0040]

As described above, according to the first aspect of the invention, even at a low temperature, the liquid crystal molecules are uniformly made into the cholesteric phase and then into the nematic phase, so that the previously written pattern does not remain. , Data can be written correctly after resetting.

Further, according to the second aspect of the invention, even at a low temperature, a sufficiently high voltage is applied as the reset voltage so that the liquid crystal molecules are completely in the nematic phase.
The previously written pattern does not remain, and the data can be written correctly after reset.

Further, according to the third aspect of the invention, since the wait period is provided before writing, the liquid crystal molecules are continuously held in the nematic phase and stabilized, so that the data writing after reset can be performed accurately. Become.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an operation of a first embodiment, (a) is a light transmittance-applied voltage characteristic of a phase transition type liquid crystal, and (b) is a drive waveform diagram.

FIG. 2 is a drive waveform diagram of the second embodiment.

FIG. 3 is a drive waveform diagram of a third embodiment.

FIG. 4 is a configuration diagram of an example of a phase transition type liquid crystal display device,
(A) is a perspective view of a display device unit, (b) is a schematic diagram of a liquid crystal display panel and its drive circuit.

FIG. 5 is a configuration diagram of an example of a drive circuit.

FIG. 6 is a configuration diagram of an example of a power supply circuit.

FIG. 7 shows light transmittance-applied voltage characteristics of a phase transition type liquid crystal, wherein (a) shows a room temperature, (b) shows a low temperature, and (c) shows a high temperature.

FIG. 8 is a conventional drive waveform diagram.

[Explanation of symbols]

10 Liquid crystal display panel V _d holding voltage V _m Maximum withstand voltage of IC

Claims (3)

[Claims] 1. A method of resetting a phase transition type liquid crystal display panel using a phase transition type liquid crystal, wherein a voltage O is applied to all liquid crystal cells of the phase transition type liquid crystal display panel.
A resetting method for a phase transition type liquid crystal display panel, which comprises applying V and then applying a voltage twice as high as a holding voltage for resetting. 2. A method of resetting a phase transition type liquid crystal display panel using a phase transition type liquid crystal, wherein the maximum withstand voltage of an IC in a drive circuit is applied to all liquid crystal cells of the phase transition type liquid crystal display panel. A method for resetting a phase transition type liquid crystal display panel, which is characterized by resetting by resetting. 3. A method of resetting a phase-transition type liquid crystal display panel using a phase-transition type liquid crystal, comprising applying a voltage that is twice a holding voltage to all liquid crystal cells of the phase-transition type liquid crystal display panel. A reset method for a phase transition type liquid crystal display panel, characterized in that a reset is performed by providing a wait period for applying a holding voltage before the next writing.