JP2001042292A - Liquid crystal display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device arranged to efficiently fetch temperature information by reducing power consumption, and a driving method thereof. SOLUTION: A liquid crystal element comprising memory type liquid crystal is reset to a homeotropic state by applying a reset pulse of a voltage value V1 thereto during a rewrite period, and is also reset to a focal conic state by applying a reset pulse of a voltage value V2 thereto, and further desired pixels are set to a planar state by applying a selection pulse of a voltage value V3 thereto. Before re-writing such a display, environmental temperature information is taker in from a temperature sensor and fed back to driving voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a liquid crystal display device and a method of driving the same, and more particularly, to a liquid crystal display device having a liquid crystal display element constituted by using a memory liquid crystal and a method of driving the same.

[0002]

2. Description of the Related Art In a conventionally known liquid crystal exhibiting a cholesteric phase at room temperature, for example, a liquid crystal display element in which a cholesteric liquid crystal or a chiral nematic liquid crystal is sandwiched between two substrates, the state of the liquid crystal is changed between a planar state and a focal conic state. The state can be switched to display.

That is, when the liquid crystal is in a planar state, and the helical pitch of the liquid crystal is P and the average refractive index is n, λ = P · n
Is selectively reflected. In the focal conic state, the liquid crystal scatters when the selective reflection wavelength of the liquid crystal is in the infrared region, and transmits visible light when the selective reflection wavelength is shorter than that. Therefore, by setting the selective reflection wavelength in the visible region and providing the light absorbing layer on the side opposite to the observation side of the element, it is possible to display the selective reflection color in the planar state and black in the focal conic state.

Further, by setting the selective reflection wavelength in the infrared region and providing a light absorption layer on the side opposite to the observation side of the element, light in the infrared region is reflected in the planar state, but light in the visible region is reflected. Is transmitted, so that black and white can be displayed by scattering in the focal conic state. In addition, by stacking three layers of elements whose selective reflection colors are set to red, green, and blue, color display becomes possible.

In this type of liquid crystal display device, a planar state or a focal conic state can be selected by applying a voltage. Assuming that the threshold voltage for untwisting the liquid crystal is Vth1, if Vth1 is applied for a sufficient time and then lowered to Vth2 or less, a planar state is established. When a voltage of Vth2 or more and Vth1 or less is applied for a sufficient time, a focal conic state is established. These two states are stable even after the application of the voltage is stopped. It is also known that there is a state in which these two states are mixed, and halftone display is possible.

[0006]

Incidentally, the display state of the liquid crystal tends to depend on the ambient temperature. In a normal nematic liquid crystal, driving voltage must be continuously applied to maintain the display, and environmental temperature information is always taken from a temperature sensor and reflected in driving conditions. However, always taking in temperature information has a problem that a load on a control unit (CPU) is large and power consumption is also large.

On the other hand, in the case of a liquid crystal such as a cholesteric liquid crystal or a chiral nematic liquid crystal having a memory characteristic capable of maintaining a display state even when the application of a driving voltage is stopped, it has not been known at what timing the temperature information is taken in. It was a solution.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal display device capable of efficiently loading temperature information while reducing the load on the control means and suppressing power consumption, and a driving method thereof.

[0009]

In order to achieve the above objects, a liquid crystal display device according to the present invention comprises a liquid crystal display element formed by using a memory-type liquid crystal and a temperature sensor for detecting environmental temperature information. And control means for rewriting the display of the liquid crystal display element and maintaining the display without applying a driving voltage by utilizing the memory properties of the liquid crystal. Captures environmental temperature information from sensors.

Further, the liquid crystal display device according to the present invention has a normal display mode in which the display of the liquid crystal display element is maintained until a rewrite request is instructed, and a fast-forward display mode in which the next rewrite process is started immediately after the end of the rewrite. When the normal display mode is executed, when a rewrite request is instructed, the control means captures environmental temperature information from the temperature sensor prior to rewriting the display, and executes the fast forward mode once at the start of the fast forward mode during the fast forward mode. After fetching the environmental temperature information from the temperature sensor, after ending the fast forward mode, fetching the next environmental temperature information from the temperature sensor is performed.

In the present invention, when a rewrite request is instructed, environmental temperature information is fetched from a temperature sensor prior to rewriting and reflected in driving conditions. When the fast-forward mode is executed, the temperature information is fetched at the start of the mode, and the next temperature information is not fetched until the end of the mode.

That is, in the present invention, since it is not necessary to always take in temperature information, the CPU is put into a sleep state during a period other than a rewriting period, or a portion other than a minimum necessary for detecting a display rewriting instruction is put into a sleep state. In this state, power consumption can be reduced.

[0013]

Embodiments of a liquid crystal display device and a method of driving the same according to the present invention will be described below with reference to the accompanying drawings.

(Configuration of Liquid Crystal Display Element) First, FIG. 1 shows an example of a reflection type liquid crystal display element constituting a liquid crystal display device according to the present invention. In the liquid crystal display element 10, a red display layer 11R for performing display by switching between red selective reflection and a transparent state is disposed on the light absorbing layer 19, and display is performed thereon by switching between green selective reflection and a transparent state. Green display layer 11 to be performed
G is laminated thereon, and further thereon, a blue display layer 11B for performing display by switching between blue selective reflection and a transparent state is laminated.

Each of the display layers 11R, 11G, and 11B includes a resin columnar structure 15, a cell thickness control spacer (not shown), and a liquid crystal exhibiting selective reflection of each color between transparent substrates 12 on which transparent electrodes 13 and 14 are formed, respectively. 16 are sandwiched. Further, an orientation control film or an insulating film (not shown) may be provided on the transparent electrodes 13 and 14, or spacer particles may be dispersed.

As the liquid crystal 16, a cholesteric liquid crystal exhibiting a cholesteric phase at room temperature or a chiral nematic liquid crystal can be used. A chiral nematic liquid crystal can be obtained by adding a chiral material to a nematic liquid crystal. The chiral material has a function of twisting the molecules of the nematic liquid crystal when added to the nematic liquid crystal, and the selective reflection wavelength of the liquid crystal is controlled by adjusting the amount of addition.

In this liquid crystal display element 10, the transparent electrodes 13 and 14 of each of the display layers 11R, 11G and 11B are connected to a drive circuit 20, respectively. A predetermined pulse voltage is applied. In response to this applied voltage, each liquid crystal 1
The display is switched between a transparent state where 6 transmits visible light (focal conic state) and a selective reflection state where the visible light is selectively reflected (planar state).

The transparent electrodes 13 and 14 are each composed of a plurality of strip-shaped electrodes arranged in parallel at a fine interval.
The belts are opposed to each other so that the directions arranged in a strip shape are perpendicular to each other. That is, a voltage is sequentially applied to each liquid crystal 16 in a matrix form, and display is performed. By performing such matrix driving sequentially or simultaneously for each of the color display layers 11R, 11G, and 11B, a full-color image is displayed on the liquid crystal display element 10.

By providing the light absorbing layer 19 on the lowermost layer with respect to the viewing direction (the direction of arrow A), each display layer 11
Light transmitted through R, 11G, and 11B is all absorbed by the light absorbing layer 19. That is, if all of the display layers are in a transparent state, black display is performed. As such a light absorption layer 19, for example, a black film can be used. Further, the light absorbing layer 19 may be formed by applying a black paint such as black ink on the lowermost surface of the display element 10.

In FIG. 1, the red display layer 11R shows a planar state, the green display layer 11G shows a focal conic state, and the blue display layer 11B shows a state where both the planar state and the focal conic state coexist. Liquid crystal display element 10
The order in which the display layers 11R, 11G, and 11B are stacked may be other than that shown in FIG.

(Driving Method, First Embodiment) There are many driving methods for a liquid crystal display device according to the present invention, such as a focal conic reset method, a phase transition driving method, and a dynamic drive driving method. Here, an example of a voltage waveform applied to the liquid crystal when driven by the focal conic reset method is shown in FIG. A time period in which a voltage is applied to any one of the scanning lines of the display layer is referred to as a rewriting period, and a time period between the rewriting period and the next rewriting period is referred to as a display period.

In the rewriting period, first, a first reset pulse having a voltage value of V1 is applied to
The liquid crystal loses its twisted structure and enters a homeotropic state. Next, by applying a second reset pulse having a voltage value of V2, the liquid crystal enters a focal conic state. Next, a selection pulse having a voltage value of V3 is applied to a pixel portion to be displayed. By the voltage value and width of this pulse,
The display state of the liquid crystal is determined.

FIG. 3 shows a control section relating to temperature compensation of the liquid crystal display device according to the present invention. The temperature detection unit 308 detects the environmental temperature. Prior to the rewriting period, when a data read signal is output from the data read control unit 307 to the temperature detection unit 308 at the timing of arrow B in FIG. 2, the temperature detection unit 308 outputs the temperature data to the data read control unit 307. I do. Data read control unit 307
Outputs a temperature correction data read control signal corresponding to the temperature data to the temperature correction data storage unit 306.

The temperature correction data storage unit 306 refers to the stored correction data according to the correction data read control signal output from the data read control unit 307,
The voltage value data is output to the voltage modulation control unit 304, and the pulse width data is output to the pulse width control unit 305. The voltage modulation control unit 304 controls the power supply 303 based on the received voltage value data.
Output a power control signal to The power supply 303 outputs a row voltage to the row driver 301 and a column voltage to the column driver 302 according to a power control signal. The pulse width control unit 305 controls the row driver 301 and the column driver 302 according to the received pulse width data. With such control, a pulse having a desired voltage value and pulse width can be applied to the liquid crystal display element 10.

As the temperature detecting section 308, for example, a temperature detecting circuit using a thermistor can be considered. FIG. 4 shows an example. A voltage is constantly applied to the thermistor 403, and temperature data is output via the A / D converter 402. When a temperature data read control signal is output from the data read control unit 307, the temperature data is latched by the latch circuit 401, and the latched temperature data is taken in by the data read control unit 307.

FIG. 5 shows another example of a temperature detection circuit using a thermistor. Normally, the power supply circuit is disconnected by the switch 504, and no voltage is applied to the thermistor 503. When the temperature data read control signal is output from the data read control unit 307, the switch 504 is turned on, a voltage is applied to the thermistor 503, and the thermistor 5
03 is output as temperature data via the A / D converter 502 and latched by the latch circuit 501.
The latched temperature data is read by the data read control unit 307.
Captures.

(Second Embodiment) Since the chiral nematic liquid crystal has a low response speed to the application of a voltage, the drawing speed is much lower than that of a normal nematic liquid crystal. For this reason, the liquid crystal display device is provided with a fast-forward mode in which the resolution and the contrast are adjusted to increase the drawing speed in order to execute a display in which the screen is rewritten one after another so as to flip the book.

In the second embodiment, the control section relating to the temperature compensation is the same as that shown in FIG. 3, and the voltage waveform for driving is shown in FIG.

In the case of drawing in the normal mode, as shown in the first embodiment, the temperature data is fetched at the timing shown by the arrow B in FIG. The timing is also indicated by arrow B in FIG.

On the other hand, when drawing in the fast-forward mode, 1
After the temperature data is fetched prior to the page rewriting period (see arrow C in FIG. 6), drawing is performed without fetching the temperature data until the fast-forward mode ends.

(Other Embodiments) The liquid crystal display device and the method of driving the same according to the present invention are not limited to the above embodiments, but can be variously modified within the scope of the invention.

In particular, the type of liquid crystal, the configuration of the liquid crystal display element, and the driving circuit thereof are arbitrary. Various waveforms other than the voltage waveforms shown in FIGS. 2 and 3 can be used for the reset pulse and the selection pulse.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a liquid crystal display element included in a liquid crystal display device according to the present invention.

FIG. 2 is a chart showing voltage waveforms in a first driving mode according to the present invention.

FIG. 3 is a block diagram showing a temperature compensation control unit of the liquid crystal display device according to the present invention.

FIG. 4 is a block diagram illustrating an example of a temperature detection circuit.

FIG. 5 is a block diagram showing another example of the temperature detection circuit.

FIG. 6 is a chart showing voltage waveforms in a second driving mode according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Liquid crystal display element 11R, 11G, 11B ... Display layer 13, 14 ... Electrode 16 ... Liquid crystal 306 ... Temperature correction data storage part 307 ... Data reading control part 308 ... Temperature detection part 403, 503 ... Thermistor

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H093 NA13 NA62 NB22 NC04 NC24 NC26 NC49 NC57 NC63 ND02 ND39 NF14 5C006 AA15 AA22 AF13 AF31 AF52 AF71 AF81 BA11 BB08 BB12 BF04 BF38 FA16 FA19 FA47 5C080 AA10 BB05 BB08 CB08 JJ02 JJ04 JJ06

Claims (4)

[Claims] 1. A liquid crystal display element formed by using a liquid crystal having a memory function, a temperature sensor for detecting environmental temperature information, a display of the liquid crystal display element is rewritten, and a drive is performed by utilizing a memory property of the liquid crystal. A liquid crystal display device, comprising: control means for maintaining display without applying a voltage, wherein the control means takes in environmental temperature information from the temperature sensor prior to rewriting display. 2. A normal display mode in which the display of the liquid crystal display element is maintained until a rewrite request is instructed, and a fast-forward display mode in which the next rewrite process is started immediately after the end of the rewrite. At the time of executing the normal display mode, when a rewrite request is instructed, environmental temperature information from the temperature sensor is fetched before the display is rewritten. At the time of executing the fast-forward mode, the environmental temperature information is fetched once at the start of the fast-forward mode. 2. The liquid crystal display device according to claim 1, wherein after the fast-forward mode is completed, environmental temperature information from the next temperature sensor is fetched. 3. A drive of a liquid crystal display device comprising: a liquid crystal display element constituted by using a memory liquid crystal; a temperature sensor for detecting an environmental temperature; and control means for controlling display of the liquid crystal display element. A method for rewriting a display of the liquid crystal display element,
A display period for maintaining display without applying a drive voltage by utilizing the memory property of the liquid crystal, and acquiring environmental temperature information from the temperature sensor prior to the rewriting period. . 4. A normal display mode comprising a normal display mode in which the display of the liquid crystal display element is maintained until a rewrite request is instructed, and a fast-forward display mode in which the next rewrite process is started immediately after the end of the rewrite. Sometimes when a rewrite request is instructed, environmental temperature information is fetched from the temperature sensor prior to the rewrite period, and when the fast-forward mode is executed, once the environmental temperature information is fetched from the temperature sensor at the start of the fast-forward mode, the fast-forward mode ends. 4. The driving method according to claim 3, wherein the environmental temperature information from the temperature sensor is fetched at the next time.