FR2639754A1 - Improved liquid-crystal display device - Google Patents

Abstract

The present invention relates to a liquid-crystal display device comprising two parallel transparent plates fitted with respective electrodes on their facing surfaces and a liquid-crystal material placed between the two plates, characterised in that one of the plates comprises P groups 100 of Q electrodes 110, whereas the second plate comprises P electrodes 260 respectively superimposed on one of the P groups of Q electrodes of the first plate and the Q electrodes 110 of at least some of the P groups 100 of the first plate being respectively connected together.

Description

 The present invention relates to the field of liquid crystal display devices, in particular for motor vehicles.

 Numerous liquid crystal display devices have already been proposed comprising two parallel transparent plates provided with respective electrodes on their facing faces, and a liquid crystal material, most often a nematic liquid crystal, placed between the two plates.

 The operation of a liquid crystal display device is well known to those skilled in the art and will not be repeated later.

 The present invention now aims to refine the display pitch of a liquid crystal display without significantly increasing the number of electrical connections required with an external pilot circuit.

 This object is achieved according to the invention thanks to a liquid crystal display device of the aforementioned type, characterized in that one of the plates comprises P groups of Q electrodes, while the second plate comprises P electrodes respectively superimposed on one of the P groups of Q electrodes of the first plate, and the Q electrodes of at least some of the P groups of the first plate are respectively interconnected by a series or series of Q connection lines.

Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings given by way of nonlimiting examples and in which - Figures la and lb represent respectively electrodes provided
on first and second plates of a display conforming to a
first alternative embodiment of the present invention, - Figures 2a and 2b respectively represent the electrodes provided
on first and second plates of a display conforming to a
second alternative embodiment of the present invention, - Figures 3a and 3b respectively represent the electrodes provided
on first and second plates of a display conforming to a
third alternative embodiment of the present invention, - Figures 4, 5 and 6 show three variants of geometry
of electrodes, - Figure 7 shows another alternative embodiment of the electrodes
provided on the first plate of a display conforming to this
invention, - Figures 8a and 8b respectively represent the electrodes provided
on a first and a second plate of a display conforming to a
fourth alternative embodiment of the present invention, - Figures 9a and 9b respectively show the electrodes provided
on first and second plates of a display conforming to a
fifth embodiment of the present invention, and - Figure 10 shows a diagram of electrical signals intended for
be applied to a display device conforming to this
invention.

 We see in Figure la, P groups of Q electrodes provided on a first plate. More specifically, according to the particular, but nonlimiting, embodiment illustrated in FIG. 1a, 8 groups of 6 electrodes are provided.

 In this case, each of the Q electrodes of each of the P groups is formed by a crown sector centered on an axis O-O. More precisely still, according to FIG. La, the PQ electrodes are all of identical geometry and surface. The P groups are referenced 100i ... 100p clockwise.

 The Q electrodes of each of the P groups are referenced 110il 110ij 110iQ 'considered alternately clockwise, then anticlockwise, from one group to another.

 Thus, in FIG. 1a, for group 100j 1, the Q electrodes are referenced: 110. I ... 110j 10l-lr 110i-lQ counterclockwise; for group 100i, we referenced the Q electrodes: 100il ... lOOij ... 100iQ clockwise and for group 100i + l we referenced the Q electrodes: 110i + ll ...

ll0i + lj ... 110i + 1Q counterclockwise.

 According to FIG. 1a, the Q homologous electrodes 110 of the adjacent groups two by two are connected respectively by Q connection lines 120.

 The first plate therefore comprises a total of Q (P -I) connection lines 120.

Thus, the electrodes 110i-ll ... 110i-lj '110i-lQ of group 100i-l are connected respectively by Q connections 120i-l to electrodes 110. 110ij ... 110iQ of group 100 .. Likewise the electrodes
l .. II iQ i 110il ... 110ij ... ll0iQ of group 100i are connected via Q electrodes 120i to electrodes 110i + 11 .. 110i + lj ... 110i + lQ of group 100.

l + l
It will be noted that, to allow a simple production of the connection lines 120, these are provided alternately radially inside and radially outside the electrodes 110.

Thus, the connection lines 120i-l connecting the Q electrodes of group 100i-l to the Q homologous electrodes of group 100i are provided radially outside the electrodes 110, while the Q connection lines 120. connecting the Q electrodes of group 100. to Q
ii group 1001 + 1 electrodes are provided radially on the inside of these electrodes.

The electrodes 110 are supplied by Q lines referenced 130i ... 1301 ... 130 130Q connected respectively to the Q electrodes
1 Q from one of the groups.

 On the second plate there is provided, as illustrated in FIG. 1b, P electrodes 260l ... 260i ... 260p superimposed respectively on the aforementioned P groups of Q electrodes formed on the first plate.

Each of the P electrodes 260 is therefore formed
a crown sector centered on an axis OO, with the same radial extension as the above-mentioned electrodes 110, and having an angular opening equal to that of each of the P groups of Q electrodes 11 G.

 Each of the P electrodes 260 provided on the second plate is supplied via a respective line referenced 280î ... 280i ... 280p in Figure lb. The second plate therefore comprises P supply lines.

 Those skilled in the art will readily understand that the electrode structure illustrated in FIGS. 1a and 1b makes it possible to successively display PQ segments, ie PQ needle positions (by assimilating each of the PQ electrodes formed on the first plate to a needle) by applying appropriate electrical signals to supply lines 1301 to 130 and 2801 to 280p.

Q
By way of nonlimiting example, if it is assumed that the threshold voltage of the liquid crystal is 4 volts, to excite the liquid crystal placed opposite the 110in electrode, a voltage of +3 volts can be applied to ia supply line 130. and a voltage of -1 volt on the other supply lines 130, and apply a voltage of -3 volts on the supply line 280i and a voltage of +1 volt on the other lines d food 280.

This will give a potential difference of +6 volts between the electrodes 110 .. and 260i and a potential difference of t or
'J i 2 volts between the other pairs of electrodes considered respectively on the two plates.

 Of course, it is also possible to envisage viewing needles corresponding to several bonded electrodes 110 and not just a single electrode 110.

 If necessary to avoid any excitation of the liquid crystal material at crossings between the supply lines 130 and 280, or between the connection lines 120 and the supply lines 280, it is possible to provide opaque covers to cover the areas located radially outside the electrodes 110, 260 and to cover the central area located radially inside the same electrodes.

 The representation given in the appended figures is of course only schematic.

 In practice, in particular for an application to motor vehicles, it will be desirable to have electrodes having a significantly smaller angular opening, in order to obtain a very fine display. This leads by generalizing the arrangements illustrated in FIG. 1b to a large number of supply lines 280.

 In the context of an application to motor vehicles, the present invention can be used for example to display the speed of the vehicle, a number of rotational turns, or even the time.

 To limit the number of supply lines 280 required on the second plate, and therefore the number of connections with external electrical control means, provision may be made to connect some of the electrodes 260 of the second plate to each other.

It is thus possible to distribute the P electrodes 260 of the second plate in the form of X sets each comprising P / X electrodes 260 and to connect together respectively x by x the P / X homologous electrodes of each of the X sets, using d one or more series of
P / X connection lines 270. The second plate then comprises a total of P (XI) / X connection lines 270.

 However, to obtain a correct display, it is then necessary to divide the electrodes 110 of the first plate into X independent networks each comprising P / X groups of Q electrodes. At each of the X networks, the Q homologous electrodes of each of the P / X groups remain interconnected as described above with reference to FIG. However, there are no interconnections between the X networks. The first plate therefore therefore comprises Q (P-X) connection lines 120.

 The interconnections provided between the homologous electrodes of the X sets of P / X electrodes 260 on the second plate can be made, as indicated above with reference to FIG. 1a, using connection lines 270 provided alternately radially inside then outside the electrodes 260, from one pair of adjacent sets to the other.

 Of course each of the X independent networks comprising P / X groups of Q electrodes 110 must be respectively superimposed on one of the X sets of P / X electrodes 260.

 The distribution of the electrodes 260 of the second plate into X sets of P / X homologous electrodes respectively connected multiplies the number of supply lines 130 of the first plate by X, i.e. QX supply lines 130, but divides the number of lines supply 280 on the second plate by X, i.e. P / X supply lines 280.

The optimum number X of interconnected sets of P / X electrodes 260, and therefore the number X of independent networks of P / X groups of Q electrodes to be provided will be readily determined by those skilled in the art to obtain a total number supply lines
QX + P / X optimum.

 By way of nonlimiting example, FIG. 2b shows P = 8 electrodes 260 grouped together in the form of X = 2 sets of P / X = 4 homologous electrodes 260 respectively connected X = 2 to X = 2 by P (XI ) / X = 4 connections 270 and supplied by P / X = 4 supply lines 280.

 As illustrated in FIG. 2a, provision is therefore made for X = 2 independent networks of P / X = 4 groups of Q = 6 electrodes 110 superimposed respectively on the abovementioned assemblies. Each of the X = 2 networks of electrodes 110 is supplied by Q = 6 electrodes 130.

 Also shown in FIG. 3b, X = 4 sets of P / X = 2 electrodes 260 counterparts connected respectively X = 4 by X = 4 by P (XI) / X connection lines 270, and supplied by P / X = 2 supply lines 280. it is then provided as illustrated in FIG. 3a, X-4 independent networks of P / X = 2 groups of Q = 6 electrodes respectively superimposed on the aforementioned 4 sets. Each of the aforementioned 4 networks is supplied by Q respective supply lines 130.

 The electrodes 110 and 260 illustrated in the figures previously described are formed of crown sector having for a given plate the same radial extension and the same angular opening.

 Other devices can be used to refine the display pitch without reducing the width of each of the electrodes to a too large extent and therefore remaining in easily controllable lithography technology.

 To do this, as illustrated in FIG. 4, provision can be made to nest different electrodes corresponding to crown sectors of different radial extension. According to the embodiment of FIG. 4, three series of electrodes II 0A, 110B, II OC are thus provided corresponding to three types of crown sectors of different radial amplitude. The outer peripheral edge of the three sets of electrodes 110A, llOB, 110C rests on a common circle centered on the axis O-O.

According to FIG. 4, the electrodes 110B have a radial extension comprised between that of the electrodes 110A and 110C, the latter being the longest. One in two electrodes is of the 11 OA type. One in four electrodes is of the 100B or 110C type. This provision is of course not limiting. It will be noted that, according to FIG. 4, the lateral edges of the electrodes are defined by rectilinear generatrices corresponding respectively to rays drawn up from the axis O-O.

 The necessary interconnections between the homologous electrodes 110 of the type illustrated in FIG. 4, can be produced by coplanar interconnections 120 carried by the first plate, of the type illustrated in FIGS. 1, 2 and 3, when sufficient space is provided between the radially innermost portions of the longest liOC electrodes. As a variant, the interconnections required between the homologous electrodes can be obtained by means of links or straps leading to the second plate. Such connections between the two plates, that is to say depending on the thickness of the display, can be obtained according to any technique known to those skilled in the art, for example using beads. silver, conductive glues or any other electrically conductive trigger guard.

 To make the most of the space available, it is possible, as illustrated in FIG. 5, to delimit the lateral edges of the electrodes 110 in non-rectilinear form, for example in the form of a succession of rays drawn up from the axis 0-0.

 In FIG. 5, three series of electrodes Il 0a, 11 or, Il Oc are thus represented. The radially outer edge of the three series of electrodes IlOa, 11Gb and 110c is located on a common circle centered on the axis 0-0.

 The shortest IlGa electrodes correspond to crown sectors delimited only by two spokes 140a.

 The longest Il Oc electrodes are formed from three radially aligned sections. The radially outermost section is delimited by the above-mentioned spokes 140a. The radially innermost section of the 11Oc electrodes is delimited by two rays 140c. Finally, the median section of the electrodes 110c is delimited by spokes 140b.

The intermediate 11Gb electrodes are in turn formed from two radially aligned sections, including a radially external section delimited by the spokes 140a and a radially internal section delimited by the above-mentioned spokes 140b.

 Here again, the necessary interconnections 120 between the homologous electrodes 110 can be ensured by means of straps communicating with the second plate.

 Another embodiment of the electrodes 110 has been shown in FIG. 6.

According to the embodiment given in FIG. 6, each of the electrodes 110 is formed of two sections 111, 112, respectively radially external and radially internal. The radially external sections 111 correspond substantially to crown sectors centered on the axis 0-0. The radially internal sections 112 are generally rectilinear. Their function is to ensure interconnections between the
Q 110 electrodes per pair of P groups.

 For this, the internal sections 112 converge as illustrated in FIG. 6 with respect to the plane of symmetry (referenced S in FIG. 6) of the above-mentioned pairs of groups.

The liquid crystal display devices which have just been described can advantageously be used to visualize a needle whose width corresponds to the angular opening of each of the
P electrodes 260, ie the angular opening of each of the P groups of Q electrodes.

 The arrangements which have just been described indeed make it possible to visualize a displacement of the needle according to a step finer than its angular opening, more precisely according to a step corresponding to the angular opening of each of the PQ electrodes.

 However, in this hypothesis, it is necessary to avoid the unexpected excitation of the liquid crystal material located opposite two homologous electrodes 110 belonging to adjacent groups 100.

For example if we want to excite the liquid crystal material located opposite the electrodes 110i3 to 110il I referenced on the
i + lQ-l Figure 1, care must be taken not to excite the material located opposite the electrodes 100. à110.

i + 1Q-2 i + 13
Different variations of implementation can be envisaged for this.

 According to a first alternative embodiment, the process is carried out by time multiplexing, that is to say that when it is desired to excite part of the material located opposite two adjacent electrodes 260, these two electrodes are not simultaneously subjected to a excitation potential but are subjected to an excitation potential successively and cyclically.

 Simultaneously, the inactive electrodes 260 receive a voltage which does not risk exciting the facing liquid crystal material.

 Furthermore, the electrodes 110 placed on the first plate are controlled in synchronism with the electrodes 260.

The supply voltages to be applied to the supply lines 13gui at 130Q and 28gaz at 280p of the electrodes shown in FIGS. 1a and 1b are illustrated diagrammatically in FIG. 110i3 to 110il Ql
The applied excitation voltages can be broken down into cycles of period T, itself divided into two identical sub-periods T / 2.

During a first period T / 2 of each cycle, the supply lines receive for example the following excitation voltages: supply line 280.: +3 volts, supply line 280i 1 -1 volt, supply line 280 other than 280. and 280i + 1: - I volt, supply line 1303 to 130Q 2: ~ 3 volts, supply line 130Q I to 1304: - 3 volts and supply line 130 other than 1303 to 130Q: +1 During the next half-period T / 2 of the same cycle, the excitation voltages are as follows: supply line 280.: -Ivolt, supply line 280i + l: -3 volts and line d power supply 280 other than 280i and 280d + l: -1 volt, supply line 1303 to 130Q-2: + Ivolt, supply line 130 I to 130: -3volts and line 130 other
IQ Q.

than 1303 to 130Q: + volt.

 We can also consider to avoid a saccade movement of a needle corresponding to the angular opening of a 26G electrode, as illustrated in FIG. 7, not to connect the Q electrodes 110 of the ith group to the electrodes 110 homologous to the groups 100i-l and 100j + l but with homologous electrodes 110 of groups 100i-2 and 100i + 2.

 It is then necessary to provide, as illustrated in FIG. 7, two independent series of groups corresponding respectively to the groups of even order and to the groups of odd order.

 By analogy with FIGS. 1a and 1b, this leads to 2Q supply lines 130 on the first plate. The electrodes 110 shown in FIG. 7 can cooperate with electrodes 260 of the type shown in FIG. 1b. Provision may also be made to distribute each of the two series of groups of electrodes 110 shown in FIG. 7 into several networks which are themselves independent in order to cooperate respectively with interconnected sets of electrodes 260 of the type shown for example in FIGS. 2b or 3b .

 Another alternative embodiment for obtaining a jerky movement of a needle corresponding to the angular opening of an electrode 260 consists, as illustrated in FIGS. 8a and 8b, of mixing on each of the plates the groups of electrodes 110 shown. in FIG. 1a and the electrodes 260 shown in FIG. 1b, taking care to alternate these and to ensure correct superposition from one plate to another.

 FIG. 8a thus represents diagrammatically P groups of Q electrodes, the Q homologous electrodes of the P groups being interconnected by Q (P-1) links 120. The excitation of the Q electrodes of each group is effected by Q lines of food 130.

We also see in Figure 8a Electrodes 160 interposed between the P groups of Q electrodes. The R electrodes 160 are supplied by
R respective supply lines 180. Preferably, the angular opening of each of the R electrodes 160 corresponds to the angular opening of each of the P groups of Q electrodes. This provision is not, however, mandatory. Note that R is between Pl and P + l.

 Under these conditions, it is provided on the second plate, as illustrated in FIG. 8b, P electrodes 260 respectively superimposed on the P groups of Q electrodes 110. The P electrodes 100, 260 are supplied by P supply lines 280.

It is also provided on the second plate, inserted between the P electrodes 260, and superimposed on the R electrodes 160, R groups of T electrodes 210. Preferably, the number T equals the number
Q. The T homologous electrodes 210 of the R groups are connected to each other by T (RI) connection lines 220.

Finally, as shown in FIGS. 9a and 9b, it is possible to distribute the P groups of Q electrodes provided on the first plate by
X independent networks (two according to FIG. 9) superimposed on X interconnected sets of electrodes 260 provided on the second plate, while the R groups of T electrodes provided on the second plate are divided into Y independent networks superimposed on Y sets of interconnected electrodes 160 provided on the first plate.

 Of course the present invention is not limited to the particular embodiments which have just been described but extends to all variants in accordance with its spirit.

 In the appended figures, the electrodes cover an angular opening of less than 360. We can of course plan to cover 360 ".

 In addition, the electrodes can be formed of parallel rectilinear rods and not of crown sectors.

 Furthermore, to reduce the effect of "jerks", one can play on the display duty cycle of two adjacent needle positions. For example if you want to display an angular needle position α between two positions α 0 and α 1.

 We will alternately display the positions α 0 (with duty cycle of α 1 - α (with duty ratio of α - α 0).

 α 1 - α 0 α 1- α 0

Claims (10)

 1. Liquid crystal display device comprising two parallel transparent plates provided with respective electrodes on their facing faces and a liquid crystal material placed between the two plates, characterized in that one of the plates comprises P groups (100 ) of Q electrodes (110), while the second plate comprises P electrodes (260) respectively superimposed on one of the P groups of Q electrodes of the first plate and the Q electrodes (110) of at least some of the P groups ( 100) of the first plate are respectively interconnected by one or more series of Q connection lines (120).  2. Display device according to claim 1, characterized in that the electrodes (110, 260) have the shape of a crown sector.  3. Display device according to one of claims 1 and 2, characterized in that there are provided electrodes (110A, 11 OB, 110C) in the form of a crown sector having different radial amplitudes (Figure 4).  4. Display device according to one of claims 1 to 3, characterized in that at least some of the electrodes (llGa, 110b, floc) are delimited laterally by non-rectilinear edges (140a, 140b, 140c) corresponding to different radii erected from a common axis (OO) (Figure 5).  5. Display device according to one of claims 1 to 4, characterized in that the connection lines (120) between the groups of Q electrodes (110) are provided alternately radially outside and inside Q electrodes.  6. Display device according to one of claims I to 5, characterized in that each of the Q electrodes (110) is formed of a radially outer section (111) and a radially inner section (112), the radially outer sections (111) being formed of a crown sector, while the radially inner sections (112) converge with respect to a plane of symmetry S separating two adjacent groups of Q electrodes so that the Internal sections (112) provide the interconnection of homologous electrodes of said two adjacent groups.  7. Display device according to one of claims I to 6, characterized in that the P groups of Q electrodes (110) are distributed in X networks of P / X groups of Q electrodes supplied by QX supply lines (130), interconnected by Q (P - X) connection lines (120) and superimposed respectively on X sets of P / X electrodes (260) in which the P / X homologous electrodes of each of the X sets are interconnected by P ( X - I) / X connection lines (270) and supplied by P / X supply lines (280) (Figures 2 and 3).  8. Display device according to one of claims I to 7, characterized in that to excite the liquid crystal located opposite two adjacent electrodes (260) of the second plate, we proceed by time multiplexing, alternately exciting these two electrodes (figure 10).  9. Display device according to one of claims I to 8, characterized in that the P groups of Q electrodes are distributed in two independent series of groups of even and odd order respectively at which the Q homologous electrodes ( 110) are respectively interconnected by connection lines (120) (Figure 7).  10. Display device according to one of claims I to 9, characterized in that the first plate comprises P groups of Q electrodes in which the Q homologous electrodes of the P groups are respectively connected by connection lines (120) and R electrodes (160) interposed between the P groups of Q electrodes, while the second plate carries R groups of T electrodes (210 ) respectively superimposed on the R electrodes (160), and in which the T homologous electrodes of each of the R groups are interconnected by connection lines (220), as well as P electrodes (260) respectively superimposed on the P groups of Q electrodes (figures 8 and 9).  He. Display device according to one of Claims I to 10, characterized in that to display an angular position of the needle α between two real positions α 0 and α 1 materialized by electrodes, the external control means alternately control the display of the positions α 0 with a duty cycle of α 1 - α and α 1 with a duty cycle of α - α 0.  α 1 - α 0 α 1 - α 0