METHOD AND ARRANGEMENT FOR DRIVING LCD DISPLAYS

Abstract: Method for driving LCD displays which comprises a large number of display segments (2, 3) capable of being connected electrically to a number of so-called rear faces (6), and which is so arranged as to have a voltage applied between the pairs of segments and the rear faces concerned in order to produce the desired colour tone and/or grey scale on the display. It is thus possible by simple means to obtain the desired colour tone and grey scale on the LCD display in question. A rear face (6) common to a number of LCD segments (2, 3) is connected to a reference level, and the segments (2, 3) are driven individually at variable alternating voltages, the crossovers of which lie essentially on the reference level. The invention also relates to an arrangement for the implementation of the method.

Description: Method and arrangement for driving LCD displays The present invention relates to a method for driving LCD displays which comprises a large number of display segments capable of being connected electrically to a number of so-called rear faces, and which is so arranged as to have a voltage applied between the pairs of segments and the rear faces concerned in order to produce the desired colour tone and/or grey scale on the display. It is already familiar for LCD displays to be driven by connecting a low—frequency alternating voltage between the rear face and those segments which it is wished to activate. The segments which it is not wished to activate are connected to the rear face. If a display has a large number of segments, it will often be necessary to multiplex the drive. That is to say a large number of rear faces is used, in this way constructing an x— matrix with the rear faces as x and the segments as y . What will occur in this case is that a segment will be activated if the point of intersection in the matrix which corresponds to the segment exhibits a potential difference with the rear face in its vicinity. Each individual LCD requires a certain amplitude in the drive voltage in order to be activated. As the voltage is reduced from the nominal maximum level the densit inside the segment will reduce, which is manifested as a lightening of the segment. It is possible in this way to produce the desired colour tone or grey scale on the display by varying the voltage which is applied between the rear face and the segment. Problems arise where a number of segments are present, since the normal procedure involves switching the polarity between the rear face and the segment in order to create the necessary alternating voltage. It has even been found necessary to utilize one rear face per segment in order to obtain said desired function, which has had the effect of making the design complicated and more expensive. The principal object of the present invention is thus to make available a method which, amongst other things, will solve said problems. Said object is achieved by the application of a method in accordance with the present invention, which is characterized essentially in that a rear face common to a large number of segments is connected to a reference level and the segments are driven individually at variable alternating voltages, the crossovers of which lie essentially on the reference level. A further object of the invention is to produce an arrangement whose application is made possible by the implementation of said method. Said further object is achieved by means of an arrangement in accordance with the present invention, which is characterized essentially in that a large number of display segments of the LCD type are capable of being connected, each via its own connection, to a source of alternating voltage and to a common rear face intended for said large number of display segments, and in that means are provided for the individual variation of the alternating voltage for the optionally paired " display segments and rear faces in question. The invention is described below as a preferred illustrative embodiment, in conjunction with which reference is made to the drawings, in which: Fig. 1 shows a schematic perspective view of a display in accordance with the invention; Fig. 2 shows voltage curves for previously disclosed displays; and Fig. 3 shows voltage curves in accordance with the invention. The LCD display 1 illustrated schematically in Fig. 1 comprises a large number of display segments 2, 3 which exhibit in a previously disclosed fashion electrical connections 4,5 so arranged as to be capable of being connected to an appropriate so—called rear face 6 so as to permit a voltage to be applied between the pairs of segments and the rear faces 2, 6; 3, 6 in question via an electrical connection 7 leading to the rear face 6. In accordance with the invention a common rear face 6 for a large number of segments 2, 3 is arranged in pairs and in such a way as to permit the rear face 6 and the segments 2, 3 to be supplied with power and driven individually with a variable alternating voltage, as shown in Fig. 3, in order to produce the desired colour tone and/or grey scale on the LCD display segment 2, 3 in question. For this purpose the common rear face 6 for a large number of segments 2, 3 is connected in accordance with the invention to a constant voltage, for example 5 volts, relating to the reference level U6, thus enabling the reference level to be specified without restriction within a wide range of values. The crossovers for the respective alternating voltages, whose oscillations may exhibit curved form or the so—called square wave form, for example, are so arranged as to lie essentially on said reference level U6, unlike the previously disclosed technique, as illustrated in Fig. 2 in the form of curves for one example in which the alternating voltage B for the rear face 6 is caused to oscillate from a neutral level, for example 0 volt, to the desired voltage level, whereas the voltage for the respective segments S1 and S2 is caused to oscillate between the desired values, for example between 1 and 4 volts or between 2 and 3 volts, in order to produce a potential difference between the respective rear face and segments and in order to bring about a change in the tone on the display involving, amongst other things, the decomposition of the LCD liquid as a negative result. Thanks to the invention considerable freedom of choice is now provided for setting the reference level to the desired value, as illustrated in the drawings in Fig. 3, in addition to which it is now possible to utilize a single common rear face 6 intended for a large number of segments 2, 3. By applying voltages U2 and U3 of different values, for example such that the voltage varies between 4 and 6 volts and between 2 and 8 volts respectively for the segments 2 and 3, so that the potential difference between the segments connected in pairs and the rear face 2-6 and 3-6 exhibits the intended value, for example 1 volt and 3 volts, the liquid in each LCD display is caused to permit light to pass to a varying degree with the possibility of producing any desired tone and/or grey scale on the respective display segments 2, 3. Means are afforded by the proposed arrangement in accordance with the invention for the individual variation of the alternating voltage for the optionally paired display segments 2, 3 and the rear face 6, which can be executed in the form of previously disclosed components of this kind, in order to permit a certain amplitude to be achieved on the drive voltage so that each individual LCD segment can be activated at the desired time. As the voltage is thus reduced from the proposed selected reference level, a reduction will occur in the density of the segment 2, 3 in question, causing it to become lighter. An additional technical effect permitted by the invention is the possibility of applying different frequencies to the segments 2, 3, as is also evident from Fig. 3, for which the appropriate means are available. . The invention is not restricted to the- illustrative embodiment described above and illustrated in the drawings, but may be modified within the scope of the Patent Claims without departing from the idea of invention.

Claims: Pa t en t C l a i ms 1. A method for driving LCD displays which comprises a large number of display segments (2, 3) capable of being connected electrically to a number of so—called rear faces (6), and which is so arranged as to have a voltage applied between the pairs of segments and the rear faces concerned (2—6; 3—6) in order to produce the desired colour tone and/or grey scale on the display, c h a r a c t e r i z e d in that a rear face (6) common to a large number of LCD segments (2, 3) is connected to a reference level and the segments (2, 3) are driven individually at variable alternating voltages, the crossovers of which lie essentially on the reference level. 2. A method according to Patent Claim 1, c ha r a c t e r i zed in that different frequencies are applied to the segments (2, 3) in question. 3. An arrangement for the implementation of the method according to either of' the Patent Claims indicated above, c h a r a c t e r i z e d in that a large number of display segments (2, 3) of the LCD type are capable of being connected, each via its own connsctiorf4, 5; 7), to a source of alternating voltage and to a common rear face (6) intended for said large number of display segments (2, 3), and in that means are provided for the individual variation of the alternating voltage for the optionally paired display segments and rear faces (2—6; 3—6) in question. 4. An arrangement according to Patent Claim 3, c h a r a c t e r i zed in that means are provided for varying the frequency of the voltage for the segments (2, 3).

Inventors: BERGWALL GLENN, BERGWALL, GLENN
Applicants: MICRO E AB, MICRO-E AB
Application year: 1986
Main classification: G09G3
IPC codes: G02F1, G09G3