EP0000594B1 - Elektro-optische Anzeigevorrichtung und Verfahren zum Betrieb dieser Vorrichtung - Google Patents

Elektro-optische Anzeigevorrichtung und Verfahren zum Betrieb dieser Vorrichtung Download PDF

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Publication number
EP0000594B1
EP0000594B1 EP78200048A EP78200048A EP0000594B1 EP 0000594 B1 EP0000594 B1 EP 0000594B1 EP 78200048 A EP78200048 A EP 78200048A EP 78200048 A EP78200048 A EP 78200048A EP 0000594 B1 EP0000594 B1 EP 0000594B1
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EP
European Patent Office
Prior art keywords
electrode
electrodes
signals
display elements
display device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
EP78200048A
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German (de)
English (en)
French (fr)
Other versions
EP0000594A1 (de
Inventor
Allan R. Dr.-Ing. Kmetz
Klaus Dr.-Phys. Müller
Terry J. Dr.-Phys. Scheffer
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
BBC Brown Boveri AG Switzerland
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BBC Brown Boveri AG Switzerland
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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/0102—Constructional details, not otherwise provided for in this subclass
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1343—Electrodes
    • G02F1/134309—Electrodes characterised by their geometrical arrangement
    • G02F1/134327—Segmented, e.g. alpha numeric display

Definitions

  • the present invention relates to an electro-optical display device for displaying symbols consisting of separately controllable display elements according to the preamble of claim 1 and to a method for controlling such a device.
  • a display device of the aforementioned type in which partial electrodes are provided on the front panel, one of which, in the absence of a supply line, cannot be acted upon by electrical signals.
  • the result of this is that no electrical field can form in the electro-optically activatable medium located between this partial electrode and the opposite rear electrodes and can influence the medium.
  • Such display devices are designed for the principle of the twisted nematic liquid crystal and must therefore be provided with polarizers and surface treated.
  • an electro-optically activatable medium which absorbs light when it is in the field-free state and transmits light when signals are present at the front and rear electrodes, the differential voltage of which is greater than a transition voltage at which the medium is light lets through, bright symbols appear on the display surface on a dark background.
  • a display device is known in which each partial electrode surface of the front electrode is congruent with the surface of the display element.
  • the liquid-crystalline medium located between the partial electrodes of the front and back electrodes of a symbol is optically activated by electrical activation of the corresponding electrodes and scatters the incident ambient light, so that a viewer can read the activated symbol.
  • Such display devices are designed to take advantage of the dynamic scattering effect of liquid crystals and have a high energy consumption because they are driven with relatively high voltages.
  • This display device is also not always to be used advantageously for electro-optical media, the activation of which is based on a different physical effect, since these devices also display bright symbols on a dark background, for example when using a cholesterol guest-host substance. This is not always advantageous, since the symbol shown is optimally readable if it is present like the letters of a newspaper as a dark marking against a light background. The invention seeks to remedy this.
  • the invention achieves the object of providing a display device of the aforementioned type in which dark symbols are displayed on a light background by actuation with low voltages and without the use of polarizers, and in which the control is also carried out by a simple, low-energy method.
  • the display device even with illumination with unpolarized light and with control with comparatively low voltages, extremely high-contrast representations of the displayed symbols on a light background can be achieved. It is particularly advantageous here that the device can be controlled using the same integrated circuits that are used in the very common rotary crystal display device.
  • FIG. 1 shows on the left side the top view of the electrode pattern of the front electrode applied on a transparent front plate and on the right side the electrode pattern of the rear electrode applied on a back plate of a possible embodiment of the display device according to the invention.
  • a, b, ..., g, h are the partial electrodes of the front and i, j the partial electrodes of the rear plate.
  • Leads extend from the electrodes to the connection lugs a ", b", ..., i “, j" located on the edge of the front panel.
  • the lines between the electrodes denote recesses A, A ', B, B', through which the partial electrodes covering the front and rear plates almost completely are electrically insulated from one another.
  • the thick black lines A 'and B ' indicate the delimitation of partial electrodes caused by the recesses in the area of a display element belonging to a symbol to be displayed.
  • each of these display elements is completely covered by a corresponding partial electrode of the front panel on the one hand and completely by the area of the counter electrode j of the rear panel on the other.
  • the limitation of each display element is given by the overlap area of the corresponding partial electrode of the front panel and the partial electrode j of the rear panel.
  • the front plate has a further partial electrode h, the surface of which does not coincide with any of the display elements.
  • the connecting lugs i ", j" of the two partial electrodes i, j of the rear plate are attached to the front plate.
  • This front plate can, for example, be plugged into a standardized connection piece, so that each electrode of the display device can be easily controlled.
  • the contact from the leads of the electrodes i and j of the rear plate to the connection lugs i "and j" can be carried out in a simple manner, since the leads of the electrodes i and j are also guided to the edge of the backplate and are directly opposite the associated connection lugs.
  • the electrode h of the front plate completely covers the supply line of the partial electrode j of the rear plate and the electrode i of the rear plate completely covers the supply lines of the partial electrodes a, b, ..., g of the front plate, whereby the part of the partial electrode that is to be understood as the supply line does not coincide with the area of the display elements. This prevents the feed lines from becoming visible when the device is in operation.
  • FIG. 3 A simplified representation of the display device according to FIG. 1, the partial electrodes being connected as a two-part matrix, is shown in FIG. 3.
  • the two partial electrodes i and j of the rear plate are represented by two horizontal lines and the partial electrodes a, b ..., h of the front plate by eight vertical lines. The intersections of these lines correspond to those areas of the display device where the corresponding front and rear electrodes overlap and a local electric field can be applied.
  • the display elements a ', b' and c ' are activated in such a way that they remain dark, ie that the liquid crystal layer in question is field-free, while the remaining liquid crystal layer forming the background is in a sufficiently strong electric field so that a light background is present.
  • the electrode j is operated with a pulsed DC voltage signal Ug of the amplitude 2V and in a 50% cycle, while a continuous DC voltage signal U 9i of the potential V is applied to the second partial electrode i of the backplate.
  • the front plate-side electrodes a, b, c of the display elements a ', b', c ' are operated with the same pulsed DC voltage signal U S1 , which is applied to the rear plate-side electrode j. All other electrodes on the front plate side d, e, f, g and h are operated with a pulsed direct current signal Us which is 180 ° out of phase with the signal at the electrodes a, b, c and j and has the same amplitude as this.
  • the voltage level V is selected so that it lies above a critical voltage U e at which the cholesteric phase of the liquid crystal completely changes into the nematic phase. This voltage is hereinafter referred to as the “transition voltage”. No further reorientation of the liquid crystal can take place above the transition voltage and the feature characterizing the electro-optical property reaches a saturation value.
  • the method for driving the display device described above has the advantage that the same integrated circuits that are usually used when driving nematic rotary cells can be used.
  • the only additional elements are a simple logic inverter and a voltage divider.
  • FIG. 6 shows the means for driving a known nematic rotary crystal display.
  • a DC voltage U is applied to an integrated circuit IC, from which 50% pulsed signals U a , ..., Ug reach the front electrodes a, ..., g and a signal U B p to the rear electrode BP of a liquid crystal cell D.
  • FIG. 7 shows the means for controlling the display device according to the invention according to FIG. 1. These means include the same integrated circuit IC, but this time the DC voltage 2U is present. However, part of the signal U SP is now phase-shifted to the front electrode h and another part in an inverter I (for example one of the type RGA CD 4041 A) by 180 ° and then applied to the back electrode j.
  • an inverter I for example one of the type RGA CD 4041 A
  • the other back electrode i is supplied with a continuous DC voltage V, which can be generated, for example, in a simple voltage divider R ', R " .
  • a further method for controlling the display device according to the invention is specified below.
  • a simplified addressing scheme of this method is shown in FIG All signals are unipolar pulse trains with a 50% pulse-pause ratio and an amplitude U.
  • the display signals a ', b' and c ' have the same signals on both the front and rear electrodes, so that
  • the display elements d ', e', f 'and g' are given phase-shifted pulses on the front and on the back electrode, so that the potential difference is a bipolar square wave voltage of the amplitude U and is without a DC component.
  • U is greater than the transition voltage U c , these indicators are present elements in the nematic state, absorbing little light.
  • the partial electrode i of the rear plate which covers the leads of the front electrodes, is operated at a higher frequency, preferably a harmonic to the frequency of the signals applied to the electrodes of the front plate.
  • the potential difference between the overlapping areas of the front electrodes and the rear electrode i then has the shape shown in FIG. 8.
  • U the pulse-pause ratio
  • U the pulse height
  • the front electrode h is operated like the partial electrodes a to g. Therefore, the liquid crystal layer of the entire background is in the nematic state, while only the display elements a ' , b', c 'are in the light-absorbing cholesterol state.
  • this method Since the higher-frequency signal is tapped, for example, in clocks from the frequency chain of the means used to control conventional rotary crystal displays, a particular advantage of this method is that no two voltage sources, the levels of which have to be carefully coordinated with one another to avoid harmful DC components, are now necessary. In addition, this method can also be used for liquid crystals with transition voltages greater than 7.5 V in commercially available integrated circuits operated at 15 V voltage.
  • FIG. 10 shows the minimum voltage difference U necessary for setting and maintaining the nematic phase of a cholesteric liquid crystal in a display device (controlled as described above) as a function of the frequency f of the higher-frequency signal applied to the partial electrode i.
  • a liquid crystal with a transition voltage of 7.5 [V] is provided. Below 20 [Hz] the flickering of the display cannot be eliminated even when the voltage is raised.
  • the energy consumed is greatest at the locations of the display where the high-frequency voltages are present, because of the capacitive losses, it is advisable to reduce the areas of these locations. This can be done, for example, by changing the electrodes according to FIG. 9.
  • the leads of the electrodes a, ..., g of the front panel and corresponding to the electrode i of the rear panel are kept as small as possible. It is also possible to lead the leads of the electrodes a, ..., g to opposite edges of the front panel.
  • the display device according to the invention is not only limited to cells with liquid-crystalline guest-host substances, it can also be used, for example, for the use of electro-phoretic suspensions as an electro-optically activatable medium, and above all because such substances cover the entire display area an electrical potential must be present in order to maintain or set a fully defined optical state. It is particularly advantageous here that, for example, the 7-segment display of a number can be switched without the feed lines to these segments becoming visible.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Geometry (AREA)
  • Mathematical Physics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Devices For Indicating Variable Information By Combining Individual Elements (AREA)
EP78200048A 1977-07-29 1978-06-19 Elektro-optische Anzeigevorrichtung und Verfahren zum Betrieb dieser Vorrichtung Expired EP0000594B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CH939777A CH617281A5 (ja) 1977-07-29 1977-07-29
CH9397/77 1977-07-29

Publications (2)

Publication Number Publication Date
EP0000594A1 EP0000594A1 (de) 1979-02-07
EP0000594B1 true EP0000594B1 (de) 1981-04-22

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EP78200048A Expired EP0000594B1 (de) 1977-07-29 1978-06-19 Elektro-optische Anzeigevorrichtung und Verfahren zum Betrieb dieser Vorrichtung

Country Status (5)

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US (2) US4281902A (ja)
EP (1) EP0000594B1 (ja)
CH (1) CH617281A5 (ja)
DE (1) DE2738679A1 (ja)
HK (1) HK76185A (ja)

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JPS576882A (en) * 1980-06-16 1982-01-13 Hitachi Ltd Liquid crystal display element
US4451122A (en) * 1980-12-29 1984-05-29 Beckman Instruments, Inc. Multicompartment electro-optic display device
US4547773A (en) * 1983-01-19 1985-10-15 National Research Development Corporation Character display panels and panel devices
US4741604A (en) * 1985-02-01 1988-05-03 Kornfeld Cary D Electrode arrays for cellular displays
DE3516298A1 (de) * 1985-05-07 1986-11-13 Sartorius Gmbh Verfahren zur ansteuerung einer fluessigkristallanzeige mit funktionsfehler-erkennbarkeit
SE447519B (sv) * 1985-05-14 1986-11-17 Micro E Ab Forfarande samt anordning for att driva lcd-displayer
US5730133A (en) * 1994-05-20 1998-03-24 Dynamics Imaging, Inc. Optical functional mamoscope
EP2458017B1 (en) 2005-11-29 2017-03-15 Cambridge Enterprise Limited Markers for breast cancer
TW200941076A (en) * 2008-03-31 2009-10-01 Ind Tech Res Inst Color cholesteric liquid crystal display devices and fabrication methods thereof
US8269801B2 (en) * 2008-09-24 2012-09-18 3M Innovative Properties Company Unipolar gray scale drive scheme for cholesteric liquid crystal displays
US8217930B2 (en) * 2009-08-27 2012-07-10 3M Innovative Properties Company Fast transitions of large area cholesteric displays

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US3647280A (en) * 1969-11-06 1972-03-07 Rca Corp Liquid crystal display device
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US3841083A (en) * 1971-03-01 1974-10-15 Time Computer Self-illuminated liquid crystal timepiece
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Also Published As

Publication number Publication date
HK76185A (en) 1985-10-18
DE2738679A1 (de) 1979-02-08
DE2738679C2 (ja) 1987-12-23
US4281902A (en) 1981-08-04
US4241344A (en) 1980-12-23
CH617281A5 (ja) 1980-05-14
EP0000594A1 (de) 1979-02-07

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