JPS60120391A - Double layer liquid crystal display element for bar graph indication - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a two-layer liquid crystal display element for bar graph display.

(Prior Art) 1. A bar graph display method using a liquid crystal is well known in the past in connection with Shiraishi 1, car tachometers, thermometers, and the like. For example, Figure 1 shows one of the bar graph display type thermometers.
An example is illustrated diagrammatically.

The bar graph display section includes N strip-shaped segments Bl,
B2. ...13L, ..., 13N are arranged linearly and have a long life.

Generally, in a bar graph display, for example, in the case of a thermometer as shown in Fig. 1, although the temperature is displayed as 120°C,
All segments in region A to the left of segment B7 corresponding to the temperature of 120°C, that is,
All segments from segment B1 to BJ are lit and displayed.

However, some people may prefer a display format in which only segments B and 2 corresponding to 120° C. are lit instead of the above display even though the same temperature of 120° C. is displayed.

In the bar graph display, a display form in which only the segment corresponding to the value to be displayed is lit is hereinafter referred to as a dot display for convenience. On the other hand, as in the case of FIG. 1 above, segments B and 2 corresponding to the values to be displayed
A display form in which all segments in area A, including , are lit will be referred to as a line display.

Using a bar graph display as a point display can be easily achieved by using a static drive method. However, in the case of the static drive method, driving elements corresponding to the number of segments constituting the display section are required, the input voltage is varied from A to D, and the decoder circuit also determines the lighting position and drives the display. It is necessary to give a signal to the element, and the circuit configuration becomes complicated.

Furthermore, when displaying dots using the Guinamisoku driving method, the wiring becomes extremely complicated.

(Purpose) Therefore, the present invention has simple circuit configuration and wiring, and
A new bar graph display 2 that can display points and easily switch between point display and line display.
The purpose of the present invention is to provide a layered liquid crystal display element.

(composition) The present invention will be explained below.

The two-layer liquid crystal display element for bar graph display of the present invention has a structure in which two liquid crystal cells are stacked on top of each other and sandwiched between two polarizing plates.

The two liquid crystal cells each have a display pattern, but
The display patterns of each cell are congruent with each other, and the liquid crystal cells are stacked so that the congruent display patterns overlap with each other.

The display pattern of each liquid crystal cell is formed by an arrangement of transparent segment electrodes, and the same segment electrode signal can be applied to the segment electrodes of each cell at the same location. Lively.

Each of the liquid crystals in the two liquid crystal cells is a TN field effect liquid crystal, that is, a liquid crystal whose polarization plane is rotated by 90 degrees due to the action of an electric field.

Further, in the two liquid crystal cells, the liquid crystals are selected and combined so that the color sum voltage vsl of one liquid crystal is smaller than the threshold voltage Vth2 of the other liquid crystal.

Before going into specific explanations, I would like to add some supplementary explanations regarding some terms.

First, the term "bar graph display" originates from the fact that each segment constituting the display pattern has a rectangular shape, that is, a bar shape. However, when referring to a bar graph display in this specification, the shape of a segment is not limited to a rectangular shape, but also includes other shapes such as a circular shape and an elliptical shape. Furthermore, the display pattern is determined by the shape of each segment and the arrangement of the segments, but in the present invention, the arrangement of the segments can be arranged in various ways, such as an arcuate arrangement or a circular arrangement, in addition to a linear arrangement. Arrays are possible.

Next, the color sum voltage Vs and threshold voltage Vth of the liquid crystal will be explained.

Consider an optical system as shown in Figure 2. In FIG. 2, numeral 1 indicates a liquid crystal cell, and numerals Pi and P2 each indicate a polarizing plate. The optical system in Figure 2 consists of a liquid crystal cell 1 and two polarizing plates P.
It is sandwiched between I and P2.

5 One liquid crystal cell 1 has a transparent electrode 1 on one side, as shown in FIG.
A transparent substrate 10 made of glass or the like provided with 0A and a transparent substrate 11 similarly provided with a transparent electrode 11A on one side are placed in parallel and close to each other with the transparent electrodes 10A and IIA facing each other, and the gap between them is It has a structure in which a TN field effect type liquid crystal 12 is filled and sealed. This liquid crystal cell 1,
When a voltage V is applied between the transparent electrodes 10A and IIA, an electric field is generated that runs through the liquid crystal 12 in the thickness direction, and the plane of polarization rotates due to the effect of this electric field. The turning angle is 0 at v-0
, ■ becomes 90° when it becomes sufficiently large.

Now, returning to FIG. 2, try irradiating light from the polarizing plate P1 side. Note that arrows α and β shown in the polarizing plates Pi and P2 indicate the polarization directions of the polarizing plates Pi and P2. The polarization directions α and β of the polarizing plates Pi and P2 are parallel to each other.

When the irradiated light passes through the polarizing plate P1, it becomes light polarized in the α direction, passes through the liquid crystal cell 1, and passes through the polarizing plate P1.
and reaches the polarizing plate P2. At this time, if the value of the voltage applied between the transparent electrodes of the liquid crystal cell 1 is 0, the liquid crystal 1
2, since rotation of the plane of polarization does not occur, liquid crystal cell 1
The light that has passed through maintains the polarization direction α, and as it is,
It passes through the polarizing plate P2. However, when the applied voltage increases significantly, the plane of polarization of the light transmitted through the liquid crystal cell 1 rotates and is tilted with respect to the polarization direction β of the polarizing plate P2, so that the transmittance of the polarizing plate P2 decreases. do.

Therefore, we investigated how the transmittance of the optical system in Fig. 2 changes with respect to the applied voltage V mentioned above.
A curve such as that shown in FIG. 4 is generally obtained. This curve is a characteristic curve and is determined depending on the type of liquid crystal. Generally, when the applied voltage V is small, the transmittance decreases slowly, but when the applied voltage V exceeds a certain level, it decreases rapidly, and when the applied voltage is further increased, the transmittance almost becomes O
It becomes a value close to , and slowly approaches 0.

The threshold voltage vth is a concept that specifies the voltage region where the transmittance curve starts to decrease rapidly, and various definitions are possible, but in the following explanation, the transmittance is defined as
The value of the applied voltage that gives 90% of the transmittance at -0 is defined as the threshold voltage vth.

In addition, the color sum voltage Vs is a concept that characterizes a voltage region in which the transmittance decreases rapidly and then slowly approaches O again, and this can also be defined in various ways. In the following description, the color sum voltage Vs is defined as a voltage value such that the transmittance is 10% of the transmittance when -○.

Next, the present invention will be explained in detail.

Consider the optical system shown in FIG. In the figure, symbols PI,
P2. As in FIG. 2, L indicates a polarizing plate and light. Reference numerals 2 and 3 indicate liquid crystal cells. These liquid crystal cells 2 and 3 have the same structure as the liquid crystal cell 1 shown in FIG. However, the liquid crystal cells 2 and 3 use different liquid crystals.

That is, when the liquid crystal cell 2 is used in the manner shown in FIG. 2, it exhibits characteristics as shown by curve 2A in FIG. 5, and the threshold voltage and color sum of the TN field effect liquid crystal used are The voltages are vth and Vs, respectively.

On the other hand, when the liquid crystal cell 3 is used in the manner shown in FIG. 2, it has a characteristic curve as shown in curve 3A in FIG. The voltages are vth' and Vs', respectively.

These two liquid crystal cells 2 and 3 are placed one on top of the other as shown in FIG. 5 and arranged between polarizing plates Pi and P2, and light is incident from the polarizing plate P1 side. In this state, as shown in FIG.
Apply.

If this voltage V is gradually increased from 0, how will the intensity of the light transmitted through the polarizing plate P2, in other words, the transmittance of the optical system shown in FIG. 5 change?

Referring to FIG. 6, it is clear that the threshold voltage v
Below th and vth', the liquid crystal cells 2 and 3 are the same as ordinary transparent plates.

When Vth, Vth', Vs, and Vs' are compared, Vth < Vs <Vth'(Vs'). Therefore, for an applied voltage V that is smaller than vth', the behavior of the liquid crystal cell 3 is is the same as that of an ordinary transparent plate, so the transmittance in the optical system of FIG. 5 changes approximately in the same way as the characteristic curve 2A (FIG. 6).

In particular, in the region where the applied voltage V is Vs≦V≦vth', the transmittance becomes extremely small. This is because it is orthogonal to the direction β.

However, when the applied voltage (2) exceeds Vs', not only the liquid crystal cell 2 but also the liquid crystal cell 3 has the function of rotating the plane of polarization by 90 degrees. Therefore, the light that successively passes through the liquid crystal cells 2 and 3 is first rotated by 90 degrees by the liquid crystal cell 2, then rotated by 90 degrees by the liquid crystal cell 3, which is a total of 180 degrees, and finally passes through the liquid crystal cell 3. Then, the direction of the polarization plane is parallel to the polarization direction β of the polarizing plate P2, and the polarizing plate P2
Transparent. Therefore, when the applied voltage V exceeds Vs',
The transmittance of the optical system shown in FIG. 5 increases again.

In the end, the transmittance of the optical system shown in FIG. 5 changes as shown in FIG. 8 depending on the change in the applied voltage (2). The two-layer liquid crystal display element for bar graph display of the present invention utilizes the above phenomenon as its principle.

Hereinafter, specific examples will be explained.

FIG. 8 shows a partial cross-sectional view of an example of a two-layer liquid crystal display element for bar graph display embodying the present invention.

This two-layer liquid crystal display element for bar graph display consists of liquid crystal cells 4 and 5 stacked in two layers, and two polarizing plates PIO and P2O.
It has a structure that is sandwiched between.

Liquid crystal cells 4 and 5 are structurally identical, but the liquid crystals (TN field effect type) used in them are different.

The liquid crystal cell 4 has a transparent common electrode 4 made of indium oxide or the like.
A transparent dielectric film 40 with a thickness of 150 μm or less and a transparent dielectric film 41 with a thickness of 150 μm or less and a transparent bar graph electrode 41A formed thereon.
The electrodes are placed close to each other so as to face each other, and the gap between them is filled and sealed with TN field effect liquid crystal.

Regarding this liquid crystal cell 4, the threshold voltage is Vthl.

Let the color sum voltage be vsl. Of course, vthl<vsl
It is.

The liquid crystal cell 5 has a thickness of 1 with a transparent common electrode 50C formed thereon.
A transparent dielectric film 50 with a thickness of 50 μm or less and a transparent dielectric film 51 with a thickness of 150 μm or less on which a transparent bar graph electrode 51A is formed are placed close to each other so that the electrodes face each other, and the gap between them is is filled with TN field effect type liquid crystal and sealed.

Regarding the liquid crystal cell 5, the threshold voltage is Vth 2 and the color sum voltage is VS2. Vth 2 (VS 2.

Vth+, Vs+, Vth2. In VS2, the liquid crystal of each cell is selected so that Vs 1 (Vthl).

For example, as a liquid crystal for liquid crystal cell 4, ROT manufactured by Lodge Co., Ltd.
N701: Vth+ = 1.10 V, Vs+
= 1.57V), the liquid crystal for the liquid crystal cell 5 is, for example, ZLI 2457; V manufactured by Merck & Co.
It is possible to select th2=1.76V and VS2=3°55V.

Incidentally, as the transparent dielectric films 40, 41, 50, 51, m fat films such as polyester and polysulfone are suitable.

Now, as shown in FIG. 10, the transparent bar graph electrode 41A formed on the transparent dielectric film 41 of the liquid crystal cell 4 consists of N rectangular segment electrodes Sl', 82. S
3. ...SL..., SN are arranged linearly. The transparent common electrode 40C to be paired with the bar graph electrode 41A is also strip-shaped, as shown in FIG. 10, and covers the entire array of segment electrodes S=.

The structure of the bar graph electrode 51A in the liquid crystal cell 5 is completely the same as the bar graph electrode 41, and the transparent common electrode 50
C is exactly the same as the transparent common electrode 40C.

Since the arrangement of the segment electrodes in the bar graph electrode' gives the display pattern, the fact that the arrangement of the segment electrodes in liquid crystal cells 4 and 5 is the same means that the display pattern of liquid crystal cell 4 and that of liquid crystal cell 5 are the same. This means that the display pattern is congruent.

The liquid crystal cells 4 and 5 are stacked on top of each other so that the display patterns overlap each other (see FIG. 9).

In addition, when overlapping the liquid crystal cells 4 and 5, instead of doing as shown in FIG. 9, the liquid crystal cells 4 or 5 may be placed upside down from the state shown in FIG. 9.

Now, how the point display is possible in the embodiment shown in FIG. 9 will be explained below.

As mentioned above, the dot display is a display form in which only the segment corresponding to the value to be displayed is displayed by lighting.

FIG. 11 shows the wiring state in the display element shown in FIG. 9.

Both transparent common electrodes 40C and 50C are grounded. On the other hand, the number of resistors R1 and R equal to the number of segment electrodes N
2, R3, . . . , RN are connected in series, one end of which is grounded, and a voltage V is applied to a terminal T. The resistors R1, R2, . . . , RN have the same resistance value and constitute a resistance divider circuit. The dividing points of the resistor divider circuit with yl,
y2. fl, 3. ..., pL, IL +1, ...
...yN-1°yN.

And the 9th (b=1~N) dividing point? L is connected to the ninth segment s=, s=' of each bar graph electrode 41A, 51A.

In this way, when the voltage ■ is applied to the terminal T, the voltage V at the l-th (L-1 to N) division point 1 becomes 1 digit, and this voltage Vi is applied to the segment hs=,s =', and a voltage of 7 is applied between these segments) SL, SQ' and the common electrodes 40C and 50C. That is, the same segment electrode signal Vi (j=1 to N) is applied to the segment electrodes S and SL' (L = l to N) at the same location and corresponding to each other in each of the liquid crystal cells 4 and 5. become.

Now, the threshold voltage Vth+ of the liquid crystal cells 4 and 5.

Vth2. As mentioned above, there is a relationship between the color sum voltages VSI and VS2 in terms of the magnitude of Vth+ (Vs+ (Vth2(VS2). Therefore, referring to FIG. 8, Vth+,
Vs+, Vth2. VS2 corresponds to Vth, Vs, Vth', and Vs' in FIG. 8, respectively. Therefore, in the embodiment of FIG. 9, the polarizing plate PIO
Or, if the light is incident from the P2O side, the polarizing plate PL
When the polarization directions of O and P20 are parallel, V#) V
82 or V” < Vtht o, the light is
The light passes through the display element at the positions of segments SL and sL'. Furthermore, when sl≦V=≦Vthz, almost no light passes through the display element at the positions of the segments SA and SL''.

By selecting the resistance value of the resistor RL (L = l to N), and by applying the voltage V to the terminal T,
Only the 9th segment part in the display pattern,
It can be displayed in black on a white background by lighting up. In this case, the displayed ninth segment is displayed in black because the transmitted light is blocked, so the expression "lit" is not necessarily accurate, but in this specification Inside,
Such a case is also called a lighting display. Oh, polarizing plate P
If the polarization directions of the 10° P2O are made perpendicular to each other, by applying a voltage V to the terminal T, only the ninth segment in the display pattern can be illuminated in white on a black background.

Next, if you want to display a line, you can do as follows. That is, a bias voltage of -Vs+ is applied to the transparent common electrodes 40C and 50C. In this way, even when no voltage is applied to the terminal T, the liquid crystal 4 of each liquid crystal cell 4, 5
At 2.52, a voltage of VSI is applied, and the polarization plane of the liquid crystal 42 is turned by 900 degrees.

v Therefore, in this state, V#+l+V8t--=+ +V
By applying voltage V to terminal T so that 81+VS2N,
The first to ninth segments of the display pattern can be displayed by lighting, and line display is possible.

FIG. 12 shows how the liquid crystal cell 4.5 of the embodiment shown in FIG. 9 is connected to external electrodes.

−17= In liquid crystal cells 4 and 5, transparent dielectric film 40.5
0 has its end protruding, and the extraction electrode part is
It is formed on this protruding part.

Then, the conductor printed with the hot-melt conductive paste is adhesively fixed to the polyimide film 6 on these protruding portions to perform wiring connection.

Here, the effects of the embodiment shown in FIG. 9 will be explained.

In this embodiment, a transparent dielectric film having a thickness of 150 μm or less, for example, 100 μm, is used to form the liquid crystal cell, so that the entire display element can be made thinner. In addition, because the transparent dielectric film is thin, there is little misalignment between opposing segments, and even though two liquid crystal cells are stacked,
The viewing angle range does not become narrower. Furthermore, since the flexibility of the transparent dielectric film is used to connect the wiring as shown in FIG. 12, the connecting portions are on the same plane, allowing for a thinner device.

(effect) As described above, according to the present invention, the novel bar graph display 18- A two-layer liquid crystal display device can be provided.

This display element can perform both dot display and line display, and even if the number of segments is increased, the number of active elements for driving does not need to be increased.

Furthermore, an analog signal can be converted into a dot display on a liquid crystal using only a resistor without using an active element for AD conversion. Furthermore, there are three signal lines in total: one for the common electrode, one for the analog signal, and one for the ground, so even if the display section is cut off, it can be driven with fewer signal lines. be.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining bar graph display, Figures 2 to 4 are diagrams for explaining the action of a liquid crystal cell,
5 to 8 are diagrams for explaining the present invention in detail, FIG. 9 is a partial sectional view showing one embodiment of the present invention, and FIG. 10 is a display pattern in the above embodiment. FIG. 11 is a diagram for explaining the point display in the above embodiment, and FIG. 12 is a diagram for explaining the wiring connection in the above embodiment. 4.5...Liquid crystal cell, PLO, P2O...Polarizing plate,
41A. 51A... Bar graph electrode, S O S L/... Segment electrode

Claims (1)

[Scope of Claims] Two liquid crystal cells whose display patterns are congruent with each other are stacked so that the display patterns overlap each other, and these are sandwiched between two polarizing plates, and the liquid crystal cells are arranged at the same corresponding location on each liquid crystal cell. A two-layer liquid crystal display element capable of applying the same segment electrode signal to the segment electrodes, wherein each liquid crystal in the two liquid crystal cells is a TN field effect liquid crystal, and the color of one liquid crystal is A two-layer liquid crystal display element for bar graph display, characterized in that a sum voltage VSI is smaller than a threshold voltage Vthz of the other liquid crystal.