JPS60188928A - Thermal write type liquid crystal display device - Google Patents

Abstract

PURPOSE:To make it always possible to heat up to an optional set temperature even if a temperature of a liquid crystal display panel is varied, and to keep a display quality constant by detecting a temperature of a heating electrode, and controlling a heating time. CONSTITUTION:A resistor 20 being an element for converting a current of a heating electrode 11 to a voltage, an amplifier 21 for amplifying a voltage generated by the resistor 20 to a desired level, a reference power source 22, and a voltage comparator 23 for comparing a voltage of this reference power source 22 and a voltage from the amplifier 21 are added to a usual circuit. In accordance with it, a heating electrode driving circuit 16 is constituted of an address decoder 24, an AND gate 25 and a switch element 26, and also a signal electrode driving circuit 18 is constituted of a shift register 27 and a switch element 28. In this way, by detecting a temperature of the heating electrode and controlling a heating time, it is always possible to heat up to an optional set temperature even if a temperature of a liquid crystal display panel is varied, and a display quality is kept constant.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a thermal writing liquid crystal display device, and more particularly to a thermal writing liquid crystal display device having a function of memorizing and retaining display contents using smectic liquid crystal. It is something.

[Technical background of the invention and its problems]

An example of a thermal writing type liquid crystal display device using a conventional smectic liquid crystal is explained with reference to Fig. 1.

In other words, the base is composed of two transparent substrates (2+) facing each other through the conductor (1), of which the inner surface of the transparent substrate (3) is provided with a plurality of parallel wires for generating heat. Heating W and poles (4) are arranged in an array to form a first electrode substrate, and a plurality of signal electrodes (5) parallel to each other for applying display signals are formed on the inner surface of the transparent substrate (2). The heating electrode (4) and the signal electrode (5) are arranged in an array to form a second electrode substrate, and the heating electrode (4) and the signal electrode (5) are arranged perpendicular to each other. The smectic liquid crystal is injected and sealed to form 14 liquid crystal panels.

The heating electrode (4) of this liquid crystal panel is connected to a power source (8) via a heating electrode drive circuit (6) consisting of a switching element, and the signal electrode (5) is connected to a signal electrode drive circuit consisting of a switching element. m (71) is connected to the power supply (9).

The smectic liquid crystal used in a thermal writing type liquid crystal display device having such a structure changes into a sysmectic state, a nematic state, and a liquid state depending on the temperature.

The temperature at which the smectic state changes to the nematic state (
For example, the temperature at which the nematic state changes to the liquid state (hereinafter referred to as TNI) is around 53°C (hereinafter referred to as TSN).
is adjusted to be around 56°C, and is in a smectic state at normal operating temperature.

Next, the operating principle of a thermal writing type liquid crystal display device using smectic liquid crystal will be explained with reference to FIG.

That is, the smectic liquid crystal is in a smectic state at room temperature, but from this state a heating electrode drive circuit (6) is connected to a heating electrode (4) corresponding to a display pixel that performs display motion.
When a voltage vH as shown in FIG. 2(a) is applied, the temperature of the smectic liquid crystal rises from, for example, room temperature T, as shown in FIG. 2(b), and reaches a temperature TNI or higher at which it no longer exhibits liquid crystal properties. At the point when the voltage VH is applied, the application of the voltage vH is stopped, and at the same time, as shown in FIG. Apply at a certain angle. In this case, as shown in FIG. 2(b), the liquid crystal is naturally cooled from the time when the application of voltage TH to the heating electrode (4) is stopped,
When the temperature is below, it becomes a nematic state. At this time, the molecular arrangement of the liquid crystal in the display pixel part where a potential difference occurs between the heating electrode (4) and the signal electrode (5) is such that the long axis direction of the molecules is the substrate (2+, (
31, the molecular arrangement of the liquid crystal in the display pixel portion where there is no potential difference becomes irregular. Furthermore, the liquid crystal temperature is T8N
Below this, the liquid crystal becomes a smectic state, and the molecular arrangement of the liquid crystal at this time is similar to the molecular arrangement of the liquid crystal in the nematic state. In other words, in the nematic state, the parts where the liquid crystal molecules are perpendicular to the substrates (2), (3) K become perpendicular to that point and become transparent, while in other parts the liquid crystal molecules are arranged irregularly. ), it appears as a cloudy state.

Note that the signal voltage VS is set to a voltage higher than the voltage (for example, 15 V) at which liquid crystal molecules begin to respond when the smectic liquid crystal is in the nematic state, but in the smectic state, it no longer responds to the signal voltage Vs and the transparent or cloudy state is maintained. Therefore, it is not necessary to apply voltage to the heating electrode (4) and the signal electrode (5) except when changing the displayed content.

The problem with a thermal writing type liquid crystal display device with such a configuration is that it uses means to heat the liquid crystal during display operation, so when the temperature of the liquid crystal panel changes, the heating requirements also change, and it is difficult to maintain constant heating conditions. This makes it difficult to always perform optimal display operations. Note that the main factors that cause the temperature of the liquid crystal panel to change are changes in the operating environment temperature and increases in temperature of the liquid crystal panel due to repeated display operations. .

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems.In particular, it is an object of the present invention to provide a thermal writing type liquid crystal display device that enables optimum heating operation. There is.

[Summary of the invention]

That is, the present invention includes a first electrode substrate on which signal electrodes extending from a plurality of parallel transparent conductive films are arranged and formed on a transparent insulating substrate, and a signal electrode facing the first electrode substrate. A liquid crystal panel consisting of a second electrode substrate on which a plurality of orthogonal heating electrodes are arranged, a smectic liquid crystal injected between the signal electrode and the heating electrode, and a liquid crystal panel for driving the signal electrode (
% In a thermal writing type liquid crystal display device consisting of an electrode drive circuit and a heating electrode drive circuit that drives a heating electrode, an element that converts a current value flowing through the heating electrode into a voltage, and an element that converts the voltage value to an arbitrary set value. A function is added to control the voltage output of the heating electrode drive circuit using the voltage comparator to be compared and the output signal of the voltage comparator, making it possible to always heat the smectic liquid crystal to the optimum heating temperature even if the temperature of the liquid crystal panel changes. This is a thermal writing type liquid crystal display device characterized by the following features.

[Embodiments of the invention]

Next, an embodiment of the thermal writing type liquid crystal display device of the present invention will be explained with reference to FIG.

That is, there is a first electrode substrate (141) on which signal electrodes QD made of a plurality of parallel transparent conductive films are arranged and formed on a transparent insulating substrate, and a strip (141) along the first electrode substrate α.
A plurality of heating electrodes (E
A liquid crystal panel consists of a second electrode base, a pole (+31), and a smectic liquid crystal injected and sealed between the signal electrode (2) and the heating electrode (Ll), and the heating electrode (1).
1), the heating electrode drive circuit αe and power supply (Iη), and the signal electrode drive circuit (18) that drives the signal electrode f121.
1 and a power source a (to) are similar to the conventional one, but in this embodiment, a resistor (2o) as an element that converts the current of the heating electrode 01) into voltage, An amplifier (2j) that amplifies the voltage generated by the resistor (21) to a desired level, and a reference power supply (23, a voltage comparator 023 that compares the voltage of the 12 reference power supplies with the voltage from the amplifier (21)) Correspondingly, the heating electrode drive circuit tl[il is an address decoder (24
), an AND gate (to), and a switch element (a), and the signal electrode drive circuit U is composed of a shift register (5) and a switch element (28).

Among these, the switch element (a) is composed of a bipolar transistor, and is connected to the output of the ant-game) (251).
It is turned on or off, and one switch element (28) is composed of a 0MO8) transistor,
Depending on the presence or absence of the output of the shift register (27), the power supply H side,
Alternatively, the level on the ground side can be switched and output.

Next, an example of the operation of the thermal writing type liquid crystal display device of this embodiment will be explained.

This device selects and heats an arbitrary heating electrode (11) in the same way as in the conventional case, and the selected heating electrode (11) is heated! ! The display operation is performed by applying a display signal corresponding to the display content of the display pixel on the L pole 01) to the signal electrode a2 at the same time as heating ends, but the heating temperature can also be controlled by detecting the temperature of the heating electrode αB. This is what I decided to do. That is, the heating electrode (Ll
) temperature is detected by using the fact that the resistance value of the heating electrode ( ) made of a thin aluminum film changes depending on the temperature.
If a constant voltage vH is applied to the heating electrode αυ, the value of the flowing current will correspond to the temperature of the heating electrode (11),
The current is converted into voltage by the resistor (2). In this case, the resistance value of the heating device made of aluminum thin film is at room temperature (e.g. 25°C) and at a temperature higher than TNI (e.g. 60°C).
) varies by about 12-. In addition, the resistance value of the resistor (A) is determined by the heating electrode (to prevent heat generation by the resistor
The resistance value of 11) is set to be sufficiently small, for example, 1/10 or less.

The voltage corresponding to the heating electrode temperature generated by this resistor (20) is amplified to a desired level by an amplifier (amplifier) and input to a voltage comparator (c). A reference power supply (22) is connected to the other input terminal of this voltage comparator (c), and the voltage value of this reference power supply (22) indicates that the temperature of the heating electrode (11) is TNI (for example, 60 In the above case, the amplifier (2
Set equal to the voltage value output from 11.

At this time, if the voltage output from the amplifier (213) is lower than the set voltage of the reference power supply (2), the voltage comparator (251)
When the voltage is turned on, the heating electrode drive circuit (
The AND gate (2) of 1e outputs a voltage that turns "OFF".

Through these operations, the voltage vH is applied to the heating electrode (1) via the switch (20) selected by the address decoder (24).
1), and the temperature of this heating electrode (]I) is TNI
(for example, 60'C) or more, it is possible to stop applying the voltage VH, and at the same time as heating is stopped, the signal electrode drive circuit sends a display signal to the signal ↑', 3. @x
(When applied to +21, display operation is performed.

In the actual Mii example described above, both substrates of the liquid crystal panel are transparent, but among these, the substrate on which the electrodes are arranged may be opaque.

〔Effect of the invention〕

As described above, according to the present invention, the temperature of the heating electrode is detected,
By controlling the heating time, even if the temperature of the liquid crystal display panel changes, it is possible to always heat the liquid crystal display panel at an arbitrary set temperature, and the display quality can also be kept constant.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a thermal writing type liquid crystal display device using conventional smectic sparse crystals, Figure 2 (a) (b) (C)
is an explanatory diagram showing the relationship between drive voltage waveform and liquid crystal temperature change,
FIG. 3 is a block diagram of an embodiment of the thermal writing type liquid crystal display device of the present invention. 2, 3.13.14... Transparent substrate 4.11... Heating electrode 5.12... Signal electrode 6.
16...Ka I4? ! Electrode drive circuit 7.18... Signal electrode drive circuit 20... Resistor 23... Voltage comparator 25... ANDGATE agent Patent attorney Inoue - Male Figure 1 Figure 2

Claims (1)

[Claims] a first electrode substrate on which signal electrodes made of a plurality of parallel transparent conductive films are arranged and formed on a transparent insulating substrate; and a plurality of heating electrodes facing the first electrode substrate and perpendicular to the signal electrodes. A liquid crystal panel includes a second electrode substrate on which electrodes are arranged, a smectic liquid crystal injected between the signal electrode and the heating electrode, and the signal 1! In a thermal writing type liquid crystal display device comprising a signal electrode drive circuit that drives a pole and a heating electrode drive circuit that drives a heating electrode, an element that converts a current value flowing through the heating electrode into a voltage value; A function is added to control the voltage output of the driving circuit of the heating electrode (by means of a voltage comparator that compares the voltage with an arbitrary set value and an output signal of the voltage comparator), so that even if the temperature of the liquid crystal panel changes, the A thermal writing type liquid crystal display device 0 characterized by a smectic liquid crystal that can be heated to the optimum heating temperature at all times.