GB2060236A - Improvements in or Relating to Electrochromic Display Apparatus and to Timepieces Equipped with the Same - Google Patents

Abstract

An electrochromic display comprises a series of adjacent picture element electrodes and connections thereto so that, when a potential of predetermined polarity is applied between an adjacent polar, one electrode becomes coloured and the other as counter electrode. The apparatus may provide part of the time display in a quartz timepiece, showing seconds or other fractions of a minute. Element electrodes 11, 12, 13 carry electrochromic material and are based on a supporting substrate. By successive applications, schematically by switches 14, 15 of potentials of suitable polarity between pairs of adjacent electrodes any selected electrode may be coloured, associated with the removal of colouration (if present) at an adjacent electrode which at that time acts as a counter electrode. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Electrochromic Display Apparatus and to Timepieces Equipped with the Same This invention rleates to electrochromic display apparatus and to timepieces utilising such apparatus in their time displaying systems.

Electrochromic display apparatus is apparatus in which display is produced by electro-chemical redox reaction. Such apparatus may be of either of two general types namely the solid type and the liquid type. In an electro-chemical redox reaction (ECD) display apparatus of the liquid type EC, material (for example, heptyle-viologenbromide) dissolved in water or other electrolyte is held in a container between two sheets of substrate equipped with an electrode system comprising opposed electrodes. When a suitable voltage of the correct polarity is applied between two opposed electrodes, reduction reaction takes place at one of them, which acts as a display electrode, and colouring takes place in the EC material there.If a voltage of opposite polarity is applied between opposed electrodes oxidization reaction takes place and the EC material (if already coloured) returns to its original state, the colour being removed. In the solid type of ECD EC material, for example, tungsten trioxide, is deposited in thin film form on the display electrode (or electrodes if there is more than one) instead of being dissolved in the electrolyte. In the solid type colouration is produced and removed, by redox reaction, in much the same manner as in the liquid type of ECD apparatus.

Known electrochromic display apparatus has serious disadvantages and limitations. They involve the use of one or more counter electrodes in addition to display electrodes so as to enable voltage to be applied between a selected display electrode and a counter electrode opposite the same so as to produce colouration or to remove colouration. Even if only one counter electrode a sheet electrode -- is used in common for all the display electrodes, this necessitates the provision of two substrates (one for carrying the display electrodes and the other for the counter electrode or electrodes) with consequent complexity as regards the provision of wiring connections to the electrodes.Also, and more importantly, the response time of EC material is relatively long for, with most normally used EC material, it takes about a second for an applied voltage to produce colourisation and about the same time for an applied voltage of opposite polarity to remove it.

This last defect -- that of relatively slow response - makes an ECD display apparatus unsatisfactory for displaying time to a closeness of 1 second in a quartz timepiece or for use in any other equipment in which correspondingly frequent changes in the information displayed are required to be made. Indeed it is generally regarded as, in practice, impossible to use an ECD apparatus for displaying time to a closeness of 1 second in a timepiece.

The main object of this invention is to overcome these defects and limitations.

According to this invention an electrochromic display apparatus comprises a plurality of adjacent picture element electrodes and connections for the application thereto of potentials in such manner that, when a potential of predetermined polarity is applied between one of them and an adjacent other one, colouration takes place at the position of said one electrode and said other one acts as a counter electrode with respect thereto, while, at the same time, colouration (if already present) is removed from said other one. There is no additional counter electrode provided as such.

The invention is illustrated in and further explained with the aid of the accompanying drawings, in which: Figure 1, which is provided for purposes of explanation only, shows diagrammatically an ECD apparatus which is not in accordance with this invention; Figure 2 is a diagram illustrating the principle of the invention; Figure 3 shows a quartz timepiece time display arrangement in which the invention is employed in a seconds display. The term "seconds display" is used in this specification, and in the claims, in a broad sense to include any display of seconds not necessarily of every second.In Figure 3 the display is of 5 second periods; Figure 4 shows a display arrangement in which the invention is used to provide a day of the week display in a quartz timepiece; Figure 5 is a simplified circuit diagram of a quartz timepiece in which the invention is employed for providing a seconds display; and Figures 6 and 7 are explanatory waveform timing diagrams relating to the operation of the seconds display in the time display system of the timepiece illustrated by Figure 5.

Referring to Figure 1 the ECD apparatus therein diagrammatically shown has a substrate 1 with a pattern of transparent display electrodes 2 on one side of it, the pattern being chosen in dependence on the nature of the display requested. For example, in a display of the digital or numeric type required to display any numeral from 0 to 9, the pattern would consist of seven socalled segment electrodes so positioned in relation to one another in manner well-known per se that, by selective energisation of different combinations of the segment electrodes any of the desired numerals can be displayed. 3 is electro-chemical (EC) material which is deposited in film form on each of the display electrodes. 4 is a protective coating or layer also deposited on 2. 5 is another substrate on the opposite side of the whole structure and upon the inner side of which is a transparent counter electrode 6 on the inner face of which is deposited a layer 7 of the same EC as that used for the layer 3. 8 is a spacing member for holding the various parts of the structure in their required relative positions and 9 is an electrolyte filling. The spacer 8 may be, for example, of glass or of the material known as Teflon (Registered Trade Mark) and, in a typical case, may have a thickness of 0.5 to 1.00 mm.

This spacer is between the two substrates. 10 is epoxy bonding material moulded in position as shown and serving to act as an external supporting and enclosing member.

If the ECD display apparatus was of the liquid type the construction would be similar except that the electrolyte would be one containing EC material and therefore the thin film deposits of 3 and 7 of EC material would not be necessary and would be omitted.

With an ECD cell apparatus as above described, colour will appear where a display electrode 2 is made negative in potential in relation to the opposed counter electrode and conversely, if a display electrode is made positive with respect to the opposed counter electrode, colouration (if present) will be removed. In the case of a solid type ECD apparatus e.g. one using tungsten trioxide as the EC material, there could be a pattern of counter electrodes like the pattern of display electrodes, each display electrode being opposite a counter electrode.If this were done, the application of potential of one polarity between a display electrode and the opposed counter electrode would produce colouration at the display electrode and no colouration at the opposed counter electrode while the application of potential of the opposite polarity would cause colouration at the said counter electrode and no colouration at the said display electrode.

An apparatus as shown in Figure 1 or as above described would have the defects already mentioned, including the need to provide two substrates and the limitations due to slowness of response.

Figure 2 diagrammatically illustrates the present invention in principle. As will be clear later it avoids the disadvantages above mentioned.

Referring to Figure 2 this shows three display picture element electrodes 11, 12 and 13 with EC material which are supported by a transparent substrate e.g. of glass. Suppose, for purposes of explanation, that the element 1 shown at the left in Figure 2, is already exhibiting colour (though it is equally possible to suppose that it is not). If, by closing the switch 14, the element 11 is made positive with respect to the adjacent element 12, oxidisation reaction will occur at 11 and the colour (if already present) will be removed. At the same time reduction reaction will take place at the element 12 and colour will be exhibited at that element. The visual effect of closing switch 14 is therefore to transfer the exhibition of colour from the element 11 to the element 12.If, now the switch 14 is opened and the switch 15 closed to make element 12 positive with respect to element 13, the redox reactions occurring will be such as to remove colour display at 12 and produce colour display at 13. As will now be seen the principle employed is to use each of the different elements for two purposes, each being used at one time as a display electrode and at another time as a counter electrode, the reaction produced, at any time, at a picture element acting to provide a colour display being opposite to that produced at another picture element electrode which, at that time, is acting as a counter electrode so that, when. colour is produced at one element it is removed at another. In this way, colour display can be effected in an ECD display apparatus. The apparatus may employ, for example, W03 as the EC material.

In Figure 2, which is purely diagrammatic a battery is shown between each pair of adjacent elements. This, however, is only to simplify the explanation. In practice, of course, only a single battery could be used, the required changes in the applied potentials being effected by suitable switching circuitry.

Figure 3 illustrates an embodiment wherein the above described principle of the invention is used in a quartz timepiece to display time. In Figure 3 the display is arranged to provide a display of time in hours and minutes together with seconds at 5 second intervals. The hours and minutes are displayed by 7-segment numeral displays (the time shown is 1 2 h 34 min). This hours and minutes display is in a surround consisting of twelve 5-second display elements 1 6 to 27 in an apparatus in accordance with this invention and between successive pairs of which suitable potentials are successively applied so that they successively exhibit colour, each for 5 seconds. In Figure 3 element 1 7 is indicated as coloured.In other words the colour display for displaying seconds is caused to occur successively, using the principle above described with the aid of Figure 2, at the elements 16 to 27, element 16 being coloured over the period extending from an exact minute to five seconds past, the element 1 7 being coloured over the period extending from five seconds to ten seconds past... and so on. After the exhibition of colour by the display element 27, for indicating fifty-five seconds to zero seconds, the cycle is repeated starting with colour display by the element 16. Obviously the number of elements used for seconds display is not necessarily twelve, the number chosen being determined by the closeness of time display required. Thus six elements would enable seconds to be displayed to a closeness of 10 seconds and sixty would enable seconds to be displayed to a closeness of 1 second. Obviously also the seconds displaying elements need not be arranged in a surround. They could be in any other convenient arrangement.

Figure 4 illustrates an embodiment, also for use in a quartz timepiece, for displaying days of the week. Here there are seven elements, 28 to 34, marked with abbreviations (Su, Mon ... Sa) of the day names. These elements successively display colour, one on each successive day, to indicate the day. In Figure 4 the day indicated is Tuesday. Instead of using mere colour displaying elements, as illustrated in Figure 4, for the different days and identifying the days by the adjacent abbreviations, the elements could themselves be used to identify the days, e.g. by providing a different day identifying mask over each element or by shaping the EC material of each element differently so that, when any one of them is exhibiting colour, it does so in a pattern which itself identifies the day to which it relates.

Thus element 30 (for example) would display the letters Tu in colour. An ECD display apparatus similar to that described above with reference to Figure 4 for displaying days of the week, but of course with a larger number of picture elements (31) may be provided for displaying the date in the month.

Many modifications in the arrangement of the display are possible. For example, for time display by a quartz watch, hours could be displayed by a ring of twelve elements, positioned like the hour figures of an ordinary timepiece face, and causing them successively to exhibit colour, each for one hour and minutes could be displayed by a concentric ring of sixty elements caused successively to exhibit colour, each for one minute. A seconds display could also be provided for in any of the ways already described with reference to Figure 3. Again, in a watch in which a seconds display is not required but in which it is required to show that the watch is running, this may be done by providing two colour exhibiting elements of EC material and causing them to exhibit colour alternately, for example every second. Such a pair of elements could be provided anywhere on the watch face dial.They could, if desired be positioned to serve as a colour (as shown in Figure 3) between a numeric display of hours and minutes.

The invention can also be used to provide an apparently moving cursor or indicator in other forms of analog type display.

As will now be appreciated the characteristic feature of the invention lies in using the different elements in a display both as a display element and as a counter element, one and the same element being used at one time to display colour and at another time to act as a counter electrode for another element which, at that time, is serving as a display element.

The invention has important practical advantages. It eliminates the need for providing separate counter electrodes solely for that purpose. It simplifies wiring connections. It enables all the electrodes with their wiring to be disposed on one substrate, so that there is one substrate instead of two. Also the response to applied potential changes is relatively rapid because the removal of colour from one element is accompanied simultaneously by the display of colour by another. This last advantage is important because, without the invention, the response in an ECD display device, is, as already stated, relatively slow.

Figure 5 is a block diagram of the driving circuitry of one form of quartz timepiece e.g. a wrist watch with a display including an ECD seconds display in accordance with this invention.

Referring to Figure 5 reference 128 is a quartz crystal vibrator circuit constituting the time base of the watch. To give a typical practical figure, it might have a frequency of 32,768 Hz. 129 is a frequency divider consisting of a cascade of flipflop circuits (if the frequency of 128 is as just stated there would be fifteen of them) providing a 1 Hz output frequency. 130 and 131 are counters.

Counter 1 30 is a 60-counter counting minutes and 131 is a 12-counter counting hours. These counters provide BCD signals including signals every minute, every ten minutes, every hour and every ten hours in manner well-known per se.

132 and 133 are decoders which receive the BCD signals and convert them, in manner also wellknown per se, into numeric signals suitable for operating seven segment numeral display devices for displaying hours and minutes as shown in Figure 3. The outputs from the decoders are fed, as indicated, each to one input of a different one of a group of AND gates 134 of which only three are shown. These gates serve for selecting and operating the display devices for digitally displaying hours and minutes of time. The other inputs of the AND gates 134 are fed as will be described later herein.The output from each AND gate 134 is used as a control signal for a different switch 1 35 (in practice an electronic switch, though not so shown) in a group of such switches each acting as a switch for supplying operating voltages to elements in an ECD display device 136 which is as shown, is not itself in accordance with this invention since it has display elements (indicated by the letter W and a common counter electrode (indicated by the letter c).

The times TW and TE for applying voltages to the picture elements in the display 136 and employed to cause writing into and erasing from the display, will now be described with the aid of Figure 6. Line (a) of Figure 6 shows pulses occurring every 60 seconds and taken from the minute counter 1 30. These pulses are fed to a mono-stable multi-vibrator or counter 137, which produces therefrom pulses of predetermined length TW, as shown in line (b) of Figure 6 each time it is triggered or turned on by a pulse (a). If 137 is a mono-stable multi-vibrator the length of the writing in time is determined by the time constant (capacitance-resistance values) thereof.

If 137 is a counter, the length of the writing-in time is determined by the period of the clocking signal supplied thereto and the number of pre-set counts. 1 38 is a timer circuit for determining a pulse of length TM as shown in line (c) of Figure 6. It is produced in manner similar to that used for producing the time TW. The actual display memorising time is the time interval between TM and To. 139 is a further timer circuit to which the pulse TM is applied. It determines the display erasing time TE (see line (d) of Figure 6) and operates similarly to 137 but is triggered by the trailing or "turn off" edge of the pulse TM.

Referring back to Figure 5, 140 is an OR gate to the inputs of which the TW and TE pulses are supplied and the output from which is fed to the remaining inputs of the AND gates 134. Writing in, erasure, and memorising are controlled by the switches 135 each of which is connected between a different writing in or picture element W in the display device 136 and earth. Two further switches 141, 142, respectively controlled by the TW and TE pulses from 137 and 139 are employed to supply voltage +V or --V to the common counter electrode C of the numeric display device 136. Thus, in order to write-in to a selected picture element, a switch 135 is closed, and simultaneously, a switch 141 is also closed for the time TW. After that, all the switches 135 are opened.Then voltage +V is applied to the counter electrode of the device 136 through the closed switch 141. Reduction reaction occurs at the selected picture element and colour is displayed there. Thereafter the display begins to be memorized. Next, when the predetermined memory time has elapsed the switches 135 and 142 (in readiness for the next picture element display) are closed and voltage --V is applied to the counter electrode C of 136 through switch 142 to erase the picture element last previously displayed in colour and memorised. In this manner, by means of the apparatus in Figure 5 as so far described, numeric or digital display of time in hours and minutes, with a change of the time displayed every minute, is carried out by the ECD display device 136 with its display picture element W and its common counter electrode C.

The apparatus in Figure 5 not yet considered and which operates in accordance with this invention to display intervals of time shorter than a minute - for example every 10 seconds - by means of picture elements which act sometimes as display elements and at other times as counter electrodes, and which do not co-operate with a common counter electrode, will now be described. Figure 7 is a time chart which is employed to explain the operation of this part of the apparatus.

It will be assumed for convenience of description in what follows, that it is required to display the passage of time at 10-second intervals by means of six EC colour display elements disposed in a surround enclosing the numeric display of hours and minutes in the fashion shown in Figure 3, though, of course, other intervals of time may be chosen and other arrangements of the display adopted.

Referring again to Figure 5, 143 is a timer circuit similar to 137 and 138 and fed with a clock signal of 1 Hz taken from the output of 129.

This clock signal is shown by line (e) of Figure 7.

The leading edge of a pulse (line (fl of Figure 7) occurring every 10 seconds is used as a trigger to determine the time TWE for writing into or erasing a colour display by a seconds display picture element. The means for determining the time TWE includes a further timer circuit 144 for producing pulses of width TWE and which is fed from 143. The output from 144 shown by line (g) of Figure 7 is fed to one input of each of six AND gates 146. 145 is a shift register with parallel outputs. It receives as one input, a pulse occurring every 60 seconds taken from 130 and a clocking signal occurring every 10 seconds and taken from the output of 143.The shift register 145 provides a six bit output with the bits occurring in succession at 10 second intervals, each pulse bit being 10 seconds wide as indicated by the lines (h) and (/1 to (m) in Figure 7. Thus one cycle of operation is accomplished in sixty seconds. The bit output leads of the register are connected respectively to the remaining inputs of the AND gates 146.

Accordingly the outputs of the AND gates 146 are made successively of HIGH level for a time TWE at intervals of 10 seconds, the phase of the output signal from the top AND gate 146 shown in Figure 5 being 10 seconds in advance of that from the next lower AND gate which is in turn 10 seconds in advance of that from the next lower AND gate ... and so on, the complete cycle taking 60 seconds and repeating every sixty seconds.

These output signals, thus relatively phased, are used respectively to control switches (in practice electronic switches) 147-1, 147-2 to 147-6 and 148-1, 148-2 to 148-6 closing associated pairs of switches, such as 147-1 and 148-1, or 147-2 and 148-2 together and successive pairs being closed at 10 second intervals for the time TWE.

The six colour displaying 10-second display elements are represented by their electrodes 1491, 149-2 to 149-6 and are in a ring on the same side of a substrate (not shown) there being no common counter electrode. The outputs of the switches 147 are respectively connected to the different element electrodes 149 as are the outputs from the switches 148. The positive terminal of a battery of voltage V is connected to the input terminals of the switches 147 and its negative terminal is connected to the input terminals of the switches 148.

Thus suppose, at some particular time, element 149-1 has voltage applied thereto to cause it to display colour. The voltage applied to element 149-6 will, at that time, be such as to cause it to act as a counter electrode with respect to element 149-1 and will not display colour. This state of the display is memorised and will be maintained for the required time.

After ten seconds, the next operation of the switches 147 and 148 will occur and switches 147-2 and 148-2 will produce a potential difference V between the element 149-2 and the element 149-1 with the result that colour will disappear from element 149-1 and the element 149-2 will display colour... and so on. Thus the visual effect is to cause the exhibition of colour to shift round the ring of colour display elements, shifting from one element to the next every ten seconds.

Obviously intervals of time other than 10 seconds may be adopted as may be required by suitably increasing or reducing the numbers of picture elements and switches and suitably modifying the circuitry to suit. If, as is, of course, much to be preferred, electronic switches such as transistors are employed, the whole apparatus may be embodied in an integrated circuit (I.C.) structure and thus be made very small, of low power consumption, and well suited for use in a timepiece of small dimensions, such as a wrist watch.

The use of the invention to provide an ECD display for part of the time display (the seconds display) in a quartz timepiece has many advantages some of which have already been mentioned. The advantage, given by such use of the invention, of relatively quick response is particularly important. In general ECD displays, as at present in use, do not have a quick response, a slow response speed being a general characteristic of known ECD displays because of the defect that the writing-in and erasure of colour do not occur at the same time. More particularly, in order to display individual seconds in a timepiece using a known ECD display, it is necessary to effect both writing in and erasure of colour within one second. However, with known ECD display arrangements, it takes about a second to write in colour and about the same time to remove it.It has therefore been regarded, hitherto, as impossible to use an ECD display to display time to a closeness of one second. But, with this invention in which writing in and erasure are accomplished at the same hime, the visual response time is reduced to about half so that what has hitherto been regarded as impossible is made possible and time can be displayed to a closeness of one second. There is another great advantage provided by this invention. If seconds are displayed numerically or digitally (as by 7 segment numerals) the number of On/Off switchings of the numeral segments required is about 3 x107 per year.However the greatest number of On/Off switchings which can be satisfactorily effected by a conventional ECD display is only about 1 x 1 0. Accordingly, even if a conventional ECD is used to display seconds, the life of the display device is much reduced and its useful life is generally less than about four months. If, however, in accordance with this invention, a plurality of seconds display picture elements are suitably disposed and successively operated to accomplish one cycle to indicate the passage of a minute, this very important defect is avoided because each picture element is switched On/Off only once per minute. In other words, only about 5 x 104 On/Off switching operations per year are required. Therefore the defect of shortened useful life is avoided and an ECD display, operating in accordance with this invention, may be expected to have a satisfactory useful life of about twenty years.

Claims (18)

Claims

1. An electrochromic display apparatus comprising a plurality of adjacent picture element electrodes and connections for the application thereto of potentials in such manner that, when a potential of predetermined polarity is applied between one of them and an adjacent other one, colouration takes place at the position of said one electrode and said other one acts as a counter electrode with respect thereto.

2. A solid type apparatus in accordance with claim 1 with electrochromic material deposited on the picture element electrodes thereof.

3. A solid type apparatus in accordance with claim 1 with electrochromic material in the electrolyte provided therein.

4. An electronic timepiece having, as part of its display, a portion consisting of an apparatus as claimed in any of claims 1 to 3.

5. A timepiece as claimed in claim 4 wherein a portion of the timepiece display is a seconds display consisting of an apparatus as claimed in any of claims 1 to 3.

6. A timepiece as claimed in claim 5 wherein the seconds display apparatus has 60 element electrodes and displays seconds at one second intervals.

7. A timepiece as claimed in claim 5 wherein the seconds display apparatus has an integral fraction of 60 elements and changes its display at intervals of a corresponding integral fraction of a minute.

8. A timepiece as claimed in claim 4 wherein a portion of the timepiece display is a day of the week display.

9. A timepiece as claimed in claim 4 wherein a portion of the timepiece display is a date in a months display.

10. A timepiece as claimed in any of claim 4 to 9 wherein a portion of the timepiece display is a seconds display consisting of an apparatus as claimed in any of claims 1 to 3 with the element electrodes thereof arranged in a surround enclosing another portion of the display displaying hours and minutes digitally.

11. A timepiece as claimed in claim 4 and having included in its display an apparatus as claimed in any of claims 1 to 3 with only two electrodes which alternately display colouration when the timepiece is in operation.

12. A timepiece as claimed in any of claims 4 to 10 wherein, to effect simultaneous colouration of one element electrode and removal of colouration from another, there are employed element driving voltage pulses the lengths of which are predetermined to cause memorisation, by the display of each item of information displayed thereby substantially until the next item of information is to be displayed thereby.

1 3. A timepiece as claimed in any of claims 5, 6 or 7 wherein the seconds display is driven by circuitry substantially as herein described with reference to Figure 5 of the accompanying drawings.

14. Electrochromic display apparatus substantially as herein described with reference to Figures 2 to 7 of the accompanying drawings.

1 5. A driving method for an electrochromic display device utilizing electro-chemical redox reaction, wherein the colour of an nth picture element is produced by using an mth (m*n) picture element already coloured as a counter electrode, the colour of the said mth picture element being removed at the same time as that in which the nth picture element is coloured ...

and so on, the elements being coloured in turn when using a previously coloured electrode as a counter electrode.

16. A driving method as claimed in claim 15 wherein the electrochromic display device includes n picture elements and in which, when a first picture element is coloured following the colour production of an nth picture element, the colour of the said first picture element is produced by using the nth picture element as a counter electrode, colouration of each successive picture element being cyclicly produced.

1 7. A driving method as claimed in claim 16, wherein n picture elements are utilized for displaying either hour, minute, second, day of the week or date.

18. A timepiece utilizing an electrochromic display device, wherein hours and minutes are displayed digitally, and seconds are displayed by transmitting at least more than two symbols indicating pre-determined time width.

1 9. An electrochromic timepiece as claimed in claim 1 8 wherein, when transmitting n (n2) symbols indicating seconds, and in order to write an mth (m < =n) symbol not already coloured, the said mth picture element is coloured by using the coloured (rn-i )th picture element as a counter electrode, and at the same time, the colour of the (rn-i )th picture element is removed, the action being repeated to provide a seconds display cyclicly.