GB2067813A

GB2067813A - Liquid Crystal Display Device

Info

Publication number: GB2067813A
Application number: GB8040218A
Authority: GB
Original assignee: Hosiden Electronics Co Ltd
Current assignee: Hosiden Electronics Co Ltd
Priority date: 1979-12-24
Filing date: 1980-12-16
Publication date: 1981-07-30
Also published as: FR2472794A1; FR2472794B1; GB2067813B; IT8026912A0; DE3047146A1; IT1134883B; DE3047146C2

Abstract

First and second colour liquid crystal display elements 12, 13 of the negative guest-host type are superposed and provide a display in different colours, at least one of electrodes 18, 19, 25, 26 of each colour liquid crystal display element having formed therein a display pattern 27, 28. By the control of a changeover switch 52 an alternating drive voltage is applied from a drive circuit 29 to one of the first and second colour liquid crystal display elements to change the colour of the background (36) of the display in accordance with the control of the changeover switch. A set of such paired elements may be used in a T.V. channel selector, the liquid crystal elements 12, 13 being red and blue respectively so as to produce either a purple pattern 27 on a blue background or a purple pattern 28 on a red background. <IMAGE>

Description

SPECIFICATION Liquid Crystal Display Device The present invention relates to a liquid crystal display device which selectively provides a plurality of displays, using colour liquid crystal display elements.

For selectively providing a plurality of displays, there has been proposed a display device, for example, of the type in which display elements arranged in a plane are selectively irradiated by light from behind to provide desired displays.

Such a display device, however, has the defects that the overall display area is large and that the display position varies with the display element being selected. Further, there has been proposed a display device in which two colour liquid display elements are assembled together in opposing relation and their patterns are selectively displayed.

In this display device, the patterns are displayed in different colours but with a background of the same colour. Accordingly, the display position remains unchanged. However, when the display pattern is relatively small, it is difficult for the user instantaneously to judge which one of the two display patterns is being displayed.

When it is necessary to provide a plurality of display patterns and indicate that one of them is being selected, as in the case of a channel display device of TV receiver sets, it is preferred that the selected and unselected display patterns can readily be discerned from each other. In view of this, no satisfactory channel display devices employing liquid crystals are available at present.

It is an object of the present invention to provide a liquid crystal display device which is small in its display area and is capable of selectively providing a plurality of displays in colour at the same position.

Another object of the present invention is to provide a liquid crystal display device which permits an easy interpretation of a display pattern even if viewed from a distance or for a very short time.

Yet another object of the present invention is to provide a liquid crystal display device which is able to provide a selected one or more of a plurality of displays, making a clear distinction between the selected and the unselected displays.

According to the present invention there is provided a liquid crystal display device in which first and second liquid crystal display elements are disposed in adjacent and opposing relation and, in use, an alternating drive voltage from a drive circuit is applied by the control of a changeover switch to one of the first and second liquid crystal display elements selectively to drive them for displaying their patterns, characterised in that the first and second liquid crystal display elements are colour liquid display elements of different colours, and the colour of the background of the display is changed by the control of the changeover switch.

Preferably a plurality of channel display sections, each composed of such two colour liquid crystal display elements, are arranged in line. On the electrode of at least one of the colour liquid crystal display elements of each channel display is formed a character, figure or symbol indicating the channel and by selectively controlling one or more of the changeover switches of a desired one of the channel display sections, the channel display section is displayed with a background of a colour different from those of the other unselected channel display sections.

This creates a clear distinction between the selected channel display section and the unselected ones, permitting an instantaneous interpretation of the selected display. Especially when that of the colour liquid display elements of each channel display section which has formed therein the display pattern is disposed on the front side, the selected channel display stands out in relief relative to the other channel displays.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a front view illustrating an embodiment of a liquid crystal display device of the present invention; Fig. 2 is a sectional view of two liquid crystal display element of a single channel display section for use in the present invention; Fjg. 3 is a sectional view explanatory of the liquid crystal display operation of a liquid crystal display element; Fig. 4 is a schematic diagram showing examples of liquid crystal display elements and a drive circuit of a channel display section; Figs. 5A to 5D are waveform diagrams showing drive voltages which are applied to respective electrodes of an unselected channel display section;; Figs. 6A to 6C are diagrams respectively showing displays of liquid crystal display elements of the unselected channel display section and their combined display; Figs. 7A to 7D are waveform diagrams showing drive voltages which are applied to respective electrodes of a selected channel display section; Figs. 8A to 8C are diagrams respectively showing displays of the liquid crystal display elements of the selected channel display section and their combined display; Fig. 9 is a diagram, corresponding to Fig. 4, illustrating another embodiment of the liquid crystal display device of the present invention; and Figs. 1 OA and 1 OB are diagrams respectively showing examples of displays which are provided by the embodiment of Fig. 9.

Referring first to Fig. 1, channel display sections D1, ..... . are arranged on a display panel 11, for example, in a lateral direction.

Adjacent the channel display sections D1,D2,...

are provided knobs S,, S2, . . . of changeover switches for controlling their channels. The channel display sections Dr, D2,... are each formed by two color liquid crystal display elements 12 and 13 which are assembled together in opposing relation. In the color liquid crystal display element 12, a liquid crystal 1 6 is interposed between a pair of opposing glass plates 14 and 15, their marginal portions are sealed by sealing members 17 and transparent electrodes 18 and 19 are respectively deposited on the interior surfaces of the glass plates 14 and 15. Also the color liquid crystal display element 13 similarly comprises of a pair of glass plates 21 and 22, a liquid crystal 23, sealing members 24 and electrodes 25 and 26.The color liquid crystal display elements 12 and 13 are assembled together, with their glass plates 15 and 21 held in close contact with each other. In this case, it is also possible to form the display elements 12 and 13 as a unitary structure, using a common glass plate as a partition wall.

The liquid crystal display elements 12 and 13 provide different color displays, displaying characters, symbols, figures or like patterns indicating the channel. For example, the liquid crystal display elements 12 and 13 of the channel display sections D,, D,,.. . are of the guest-host negative type and designed so that when supplied with no drive voltage, the liquid crystal display element 12 looks red over its entire area and the liquid crystal display element 13 looks blue. At least one of the electrodes 18 and 19 of the liquid crystal display element 12 of each channel display section is formed in such a manner that a channel number of a display pattern 27 indicating each channel is provided in the form of a negative pattern. Also in the liquid crystal display elements 13 of the channel display sections D,, D2, . .. are respectively formed display patterns.28 indicating the channels. In this example, the display patterns 28 are shown to indicate the channels in patterns different from the display patterns 27 of the liquid crystal display elements 12. The display pattern 27 is formed as the channel number and the display pattern 28 is formed as the channel designation; namely. at least one of the electrodes 25 and 26 of each channel display section is formed so that a channel designation, for example, TBS, NTV, NET, NHK or the like is provided in the form of a negative pattern as the display pattern 28. Fig. 1 shows the case where the knob S4 of the changeover switch is selectively controlled.In this case, "4" of the display pattern 27 of the liquid crystal display element 12 of the channel display section D4 is not dispiayed and "T8S", "NTV", "NET", etc.

except "NHK" of +he display patterns 28 of the liquid crystal display elements 1 3 of the channel display sections D, D, Da, D5, etc., a, e not displayed, either.

The liquid crystal display elements 12 and 13 are color liquid crystal display elements and can be formed by various types of liquid crystals. For example, in the case of using the negative guesthost type as mentioned previously, dichroic dye molecules 1 6d are dissolved in a liquid crystal of nematic liquid crystal molecules 1 61 with a positive dielectric anisotropy AE, as shown in Fig.

3. Upon turning ON the switch S to apply the voltage of an AC power supply 10 across the electrodes 18 and 19, the liquid crystal molecules 16/ and the dichroic dye molecules 1 6d lying between the electrodes 18 and 19 are oriented with their longer axes substantially perpendicular to the electrodes 18 and 19. In the part which does not confront the electrode 19 and is not applied the voltage, however, the liquid crystal molecules 161 and the dichroic dye molecules 1 6d lie with their longer axes substantially parallel with the electrode 18. Light 21 from one side of the liquid crystal display element 12 is incident thereto passing through a polarizer 30.The polarizer 30 is disposed so that the direction of polarization of the light having passed through the polarizer 30 may coincide with the longer axes of the liquid crystal molecules 161 when no voltage is applied. On the other side of the liquid crystal element 12 the part of the electrode 19 looks colorless to the human eye 41 but the part which is not covered with the electrode 19 is of a color which is determined by the dichroic dye molecules 1 6d. Accordingly, in the case where the display pattern 27 is formed as a negative pattern in the electrode 19 as described previously, the display pattern 27 becomes colorless against a colored background. In the liquid crystal display elements 12 and 13, different dichroic dye molecules of the liquid crystals 1 6 and 23 are employed to provide displays, for example, in red and blue.The polarizer 30 on the liquid crystal display element 13 on the front side may be omitted.

The drive circuits of the channel display sections D1, ..... . are arranged so that when one of the changeover switch knobs S1, S2, . . is selectively actuated, the selected channel display section produces a display with a background color different from those of the unselected channel display sections. A description will be given, with reference to Fig. 4, of the driving of the channel display section D4. A drive circuit 29 is controlled by the changeover switch knob S4.

The drive circuit 29 has four output terminals 31 to 34. The terminals 31 and 32 are respectively connected to the electrodes 18 and 19 of the liquid crystal display elements 12 of the channel display section D4 and the output terminals 33 and 34 are respectively connected to the electrodes 25 and 26 of the liquid crystal display element 13. For example, as shown in Fig. 4, the drive circuit 29 includes a square wave voltage generator 42, which derives at its output terminals 43 and 44 such square wave voltages as shown in Figs. ISA and 5B which have a duty cycle of 509t0 and are 1800 out of phase relative to each other. The square wave voltage at the output terminal 43 is applied directly to output terminals 31 and 33 and AND gates 45 and 46.

The square wave voltage at the output terminal 44 is provided to AND gates 47 and 48. The outputs from the AND gates 45 and 47 are supplied via an OR gate 49 to an output terminal 32 and the outputs from the AND gates 46 and 48 are applied via an OR gate 51 to an output terminal 34. One end of a changeover switch 52 which is controlled by the knob S4 is connected to a DC power source 53 and the other end is connected directly to the AND gates 45 and 48 and to the AND gates 46 and 47 via an inverter 54.

In general, for simplicity of the drive circuit design, a unipolarity drive voltage is used to energize the liquid crystal. However, in order to allow a long life of the liquid crystal, unipolarity voltages of the same level are alternately applied to the electrodes on both sides of the liquid crystal so as to avoid application of a DC current to the liquid crystal, on average. In the present embodiment, the drive circuit 29 operates in the manner described hereinbelow. When the changeover switch knob S4 is not actuated, namely, the changeover switch 52 is in the OFF state, 1800 out-of-phase square wave voltages, such as shown in Figs.ISA and 5B, are respectively provided at the output terminals 31 and 32 and square wave voltages of the same waveform as the voltage of Fig. 5A, such as shown in Figs. 5C and 5D, are respectively provided at the output terminals 33 and 34. As a consequence, a potential difference occurs between the electrodes 18 and 19 of the liquid crystal display element 12, that is, a drive voltage is applied across them, and, as shown in Fig. 6A, the electrode area 35 of the electrode 19 having formed therein the display pattern 27 becomes colorless and the part of the display pattern 27 to which is not applied the drive voltage is displayed in red.In the liquid crystal display element 13, the same voltage is applied to the electrodes 33 and 34; namely, this means that no drive voltage is applied over the liquid crystal. As a result of this, the liquid crystal display element 13 assumes blue color over the entire area of its display surface. Accordingly, a display by the combination of the liquid crystal display elements becomes such as depicted in Fig. 6C in which the display pattern 27 is displayed in purple color which is a mixture of red and blue colors and the background 36 of the display pattern 27 is blue.

When the knob S4 is actuated to turn ON the changeover switch 52, square wave voltages of the same waveform, such as shown in Figs. 7A and 78, are yielded at the output terminals 31 and 32, respectively, and a voltage of Fig. 7C which has the same waveform as the voltage of Fig. 7A and a voltage of Fig. 7D which is displaced 1800 apart in phase from the voltage of Fig. 7C are provided at the output terminals 33 and 34, respectively. Accordingly, the liquid crystal display element 12 is not driven and remains red over the entire area of its display surface, as shown in Fig.

8A, and the liquid crystal display element 13 is supplied with the drive voltage, by which an electrode area 37 having formed therein the display pattern 28 becomes colorless and the part of the display pattern 28 to which the drive voltage is not applied is displayed in blue color, as shown in Fig. 88. As a result of this, the combined display of the liquid crystal display elements 12 and 13 becomes such as depicted in Fig. SC in which the display pattern 28 is displayed in purple color and its background 36 is red. The square wave voltage generator 42 and the power supply 53 can be used in common to corresponding parts of the channel display sections D1,D2...

Thus, by the operation of the changeover switch 52, the displays on the liquid crystal display elements 12 and 13 are changed over to each other.

With such an arrangement as described above, when none of the changeover switch knobs Sr, S,,... is actuatqd in Fig. 1, "1", "2", "3", .

of the display patterns 27 of the channel display sections D1, ..... . are all displayed in purple against backgrounds of blue color. In this case, for instance, when the knob S4 alone is controlled to turn ON the corresponding changeover switch 52, the display pattern 28 of only the channel display section D4 is displayed in purple color against a background of red color, but the displays of the other channel display sections remain unchanged.

In this way, the background color of each channel display section indicates whether its channel is selected or not and, consequently, the user can intuitively learn the selected channel without reading its content from the display of the display pattern. In addition, also by changing the display format of the display pattern depending on whether its channel is selected or not, as in the above example, it is possible to provide an indication of whether the channel is selected or not. The display patterns 27 and 28 may also be of the same shape.

Since it can be displayed by the background color whether each channel is selected or not, it is possible to discern the selected channel from the unselected ones even from a distance where the displays of the display patterns cannot be read or in such a short time that the displays cannot be read. Further, it is also possible to make the selected channel display conspicuous by selecting the background color, for example, by using a brighter color than the unselected channels.

Moreover, in the case where the channel display when selected is produced by the liquid crystal display element 13 on the front and the channel display when not selected is provided by the liquid crystal display element 12 on the back, as in this embodiment, the display pattern of the selected channel display is displayed standing out against its background, whereas the display patterns of the unselected channel displays are displayed standing back from the display surface of the channel display. As a result of this, the display of the selected channel stands out from the displays of the other unselected channels and hence is easy to read. The liquid crystal display element 13 may also be disposed behind the liquid crystal display element 12 so that the display pattern of the selected channel is displayed standing back from the display surface of the channel display.

For producing such a conspicuous display of the selected channel; it is preferred to increase the thickness of each glass plate of the channel display. It has been found that where each glass plate is about 3 mm thick and the overall thickness of the assembly of the display elements 12 and 13 is approximately 12 mm, the display pattern 28 of the selected channel is displayed appreciably standing out from the display patterns of the unselected channels.

In the foregoing, the display pattern 28 indicating the channel is displayed in the channel display section when its channel is selected, but the display pattern 28 need not always be formed in the liquid crystal element 13. In such a case, the knobs S" S2, . . . are selectively operated to select a desired channel while observing the displays of the display patterns of the respective liquid crystal display elements 12 and the entire area of the channel display section of a selected channel is caused to assume a color different from the background color of unselected channels. Also it is possible to dispose the liquid crystal display element 13 behind the liquid crystal element 12 so that the display pattern 28 of the selected channel may be displayed standing back from the display patterns of the unselected channels.

By applying the present invention not only to the abovesaid channel display of the TV set but also to the case of selecting one or more of a plurality of ordinary channel displays or other displays, for example, for displaying a selected measurement point (channel) in the case of selecting data of a plurality of measurement points, it is possible to make a clear distinction between the display of the selected measurement point and the displays of the unselected ones.

The present invention is applicable as well to a selective display of two display patterns in a single display unit. That is, only one channel display unit shown in Fig. 4 may also be used as one display device. For example, as depicted in Fig. 9, the liquid crystal display elements 12 and 13 are disposed in adjacent and opposing relation. One of the electrodes of each of the liquid crystal display elements 12 and 13 has formed therein the display pattern 27 or 28, for example, in the form of a character "A" or "B".

The electrodes of the liquid crystal display elements 12 and 13 are respectively connected to the terminals 31 to 34 of such a drive circuit 29 as shown in Fig. 4. In the case where the liquid crystal display elements 12 and 13 respectively provide red and blue displays as is the case with Fig. 4, when the changeover switch 52 is in the OFF state, the character "A" of the display pattern 27 is displayed in purple color against a background of blue color, as shown in Fig. 1 OA.

When the changeover switch 52 is turned ON, the character "B" of the display pattern 28 is displayed in purple color against a background of red color, as shown in Fig. 1 or.

According to the embodiment of Fig. 9, by controlling the changeover switch 52, the display patterns 27 and 28 are selectively displayed against backgrounds of different colors.

Accordingly, the display content can be learned from the display pattern and even if the display pattern cannot be discerned from the other one when viewed from a distance, the display content can be understood from the color of its background. Further, the display content can be read out intuitively from the background color at a glance without reading the display pattern. By a suitable selection of the color of the display pattern and its background color, it is possible not only to permit an easy interpretation of the display pattern of the selected channel but also to attract particular attention to the display pattern.

Moreover, in the case where the liquid crystal display element 13 on the front side is energized, its display pattern is displayed standing out in relief and when the liquid crystal display element 12 on the back is energized, its display pattern is displayed standing back a little. Thus, a plurality of display patterns can selectively be displayed at the same position, as viewed from the front, and consequently the display area can be small.

In the embodiments of Figs. 1 and 9, the display colors of the liquid crystal display elements 12 and 13 are not limited specifically to red and blue colors but may also be selected as desired. It is also possible to effect the display of the liquid crystal display element 12 by using, as a shutter, the liquid crystal display element 13 in combination with polarization plates.

Alternatively, as a shutter, the liquid crystal display element 13 can be such one that is opaque and, by application of a voltage, becomes transparent. Also it is possible to diversify the color display functions by forming the liquid crystal display into a multi-layer structure with more than two layers.

For the liquid crystal display elements 12 and 13, use is made of the guest-host negative type display elements, but it is also possible to use not only the nematic type display elements as mentioned previously in respect of Fig. 3 but also, for example, phase-transition type display elements. In the phase-transition type display element, cholesteric liquid crystal and dyestuff are added to a positive nematic liquid crystal and, at the initial stage, the liquid crystal is made planar arrangement or focal-conic arrangement and then the cholesteric phase is altered to the nematic phase by the application of a voltage, performing a negative display.

The color combination of the liquid crystal display elements 12 and 13 is not limited specifically to red and blue colors but may also be in the form of various combinations, such as, for example, blue and yellow, red and yellow, green and red, purple and yellow, orange and blue, and so forth. In Fig. 1, the display elements have been explained as being prepared individually.

However, in a practical design, all the display elements can be formed as a unitary structure using continuous glass plates. Accordingly, those electrodes 18 of the liquid crystal display elements 12 of the channel display sections Ds, D2, ..... . which have no display patterns are formed as a continuous electrode face common to all of them, and those electrodes of the liquid crystal display elements 13 which have no display patterns are also formed as a continuous electrode face common to them. Further, such voltages as shown in Figs. 5C and 7A are respectively applied to the common electrodes of the liquid crystal display elements 12 and 13, so that voltages of the same phase as the abovesaid voltages are also provided to the liquid crystal display elements 1 3 of the unselected channel displays and the liquid crystal display element 12 of the selected channel display. In the case of using an independent electrode for each channel display, however, voltages are provided only to the liquid crystal display elements 1 2 in the unselected channel displays and only to the liquid crystal display element 13 in the selected channel display. Especially in the embodiment of Fig. 9, it is also possible to supply drive voltages only to a ,selected one of the liquid crystal display elements 12 and 13.

Claims

1. A liquid crystal display device in which first and second liquid crystal display elements are disposed in adjacent and opposing relation and, in use, an alternating drive voltage from a drive circuit is applied by the control of a changeover switch to one of the first and second liquid crystal display elements selectively to drive them for displaying their patterns, characterised in that the first and second liquid crystal display elements are colour liquid crystal display elements of different colours, and the colour of the background of the display is changed by the control of the changeover switch.

2. A liquid crystal display device as claimed in claim 1, wherein the first and second colour liquid crystal display elements are normally coloured uniformly over the entire areas thereof, and when the drive voltage is applied to the colour liquid crystal display elements, their display patterns are each displayed in the color before the application of the drive voltage and the background becomes colourless.

3. A liquid crystal display device as claimed in claim 2, wherein the first and second colour liquid crystal display elements respectively have negative patterns of their display patterns formed in their electrodes.

4. A liquid crystal display device as claimed in claim 1, wherein there are provided a plurality of channel display sections aligned on the same plane and each composed of the first and second colour liquid crystal display elements, an electrode of each first colour liquid crystal display element of each channel display section having formed therein a display pattern indicating the channel, such as a character, symbol or the like, channel selection means comprising a plurality of the changeover switches corresponding to the respective channel display sections, and a plurality of the drive circuits for applying the drive voltage to either the first or second colour display element of each channel display section such that when the corresponding changeover switch of the channel selection means is not actuated, the display pattern of the first colour liquid crystal display element is displayed, and otherwise the second colour liquid crystal display element is energised.

5. A liquid crystal display device as claimed in claim 4, wherein the electrode of each second colour liquid crystal display element has formed therein a display pattern, such as a character, symbol or the like, which is identical with or different from the display pattern of the corresponding first colour liquid crystal display element and indicates the channel.

6. A liquid crystal display device as claimed in claim 5, wherein the first colour liquid crystal display elements are disposed behind the second colour liquid crystal display elements.

7. A liquid crystal display device as claimed in any one of claims 4 to 6, wherein either of the first and second colour liquid crystal display elements are respectively formed as unitary structures using continuous glass plates common to all of the channel display sections, the electrodes on one side of the first colour liquid crystal display elements are formed as a continuous electrode face common to all of them, the electrodes on one side of the second colour liquid crystal display elements are formed as a continuous electrode face common to all of them, and the drive circuits apply voltages of the same phase to the common electrode and the electrode on the other side of the selected first colour liquid crystal display element and to the common electrode and the electrodes on the other side of the unselected second colour liquid crystal display elements.

8. A liquid crystal display device substantially as hereinbefore described with reference to and as shown in Figures 1 to 8, or Figures 9 and 10 of the accompanying drawings.