System for driving a liquid crystal display device

Claims

What is claimed is:

1. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for compensating distortion of said voltage waveforms which occurs and varies according to the display pattern by detecting a voltage change within said matrix liquid crystal display device, determining an amount of distortion occurring as a function of said display pattern in one of said segment voltage waveforms and common voltage waveforms in response to said voltage change and generating a correction voltage based upon said voltage change, said correction voltage being added to the segment voltage waveform and common voltage waveform exhibiting said amount of distortion.

2. The matrix liquid crystal display panel of claim 1, wherein said compensation means includes detection means for detecting the sum of the segment voltage waveforms on said plurality of segment electrodes and producing a voltage sum in response thereto; and voltage addition means for adding said voltage sum to a group of said plurality of voltages to produce a plurality of correction voltages, said segment electrode driving means outputting a corrected segment voltage waveform in response to said corrected voltage.

3. The matrix liquid crystal display panel of claim 2, wherein the plurality of segment electrode is divided into at least a first group of segment electrodes, a second group of segment electrodes and a third group of segment electrodes;

said segment electrodes driving means includes at least a first segment electrode driver for driving said first group of segment electrodes, a second segment electrode driver for driving said second group of segment electrodes, and a third segment electrode driver for driving said third set of segment electrodes;

said voltage addition means providing a first correction voltage to said first segment electrode driver, a second correction voltage to said second segment electrode driver and a third correction voltage to said third electrode driver.

4. The matrix liquid crystal panel device of claim 3, wherein said first correction voltage does not equal the second correction voltage and the second correction voltage does not equal the third correction voltage.

5. The matrix liquid crystal panel device of claim 2, wherein said compensation means further comprises voltage differential means for receiving said voltage detection electrode voltage and a group of said plurality of voltages and outputting a voltage differential voltage waveform in response thereto, said voltage addition means receiving said voltage differential waveform and outputting a correction voltage in response thereto; and

said segment electrode driving means receiving said correction voltage and outputting a corrected voltage waveform in response thereto.

6. The matrix liquid crystal display device of claim 5, wherein said correction means further comprises a lighted dot count means outputting a dot count value in response to a DATA signal for amplifying the detected voltage sum in response to said count value, increasing the amplification value in response to an increase in the count value.

7. The matrix liquid crystal display device of claim 6, wherein said amplifier means includes a first through fourth resistors coupled in series, a first switching circuit coupled in parallel with said second resistor, a second switching circuit coupled in parallel with said third resistor and, a third switching circuit coupled in parallel with said fourth resistor, the count value being formed as an upper digit value, a middle digit value and a lower digit value, said first switching circuit being operated in response to the lower digit value, said second switching circuit being operated in response to said middle digit value and the third switching circuit being operated in response to said upper digit value, said first, second and third switching circuits being coupled in parallel to said voltage detection electrode.

8. The matrix liquid crystal display panel of claim 1, wherein said compensation means includes detection means for detecting the sum of the common voltage waveforms on said plurality of common electrodes and producing a voltage sum in response thereto; and voltage addition means for adding said voltage sum to a group of said plurality of voltages to produce a plurality of correction voltages, said common electrode driving means outputting a corrected common voltage waveform in response to said corrected voltage.

9. The matrix liquid crystal display device of claim 1, wherein said power circuit receives a first reference voltage and a second reference voltage; said power circuit means including voltage divider means for receiving said first reference voltage, and said second reference voltage and producing a first divided voltage, a second divided voltage, third divided voltage and fourth divided voltage; said first reference voltage and said second reference voltage, said second divided voltage and third divided voltage being input to said segment electrode driving means as said plurality of voltages; a first voltage correction means for receiving said first divided voltage and a second voltage correction means for receiving said fourth divided voltage outputting a second correction voltage, said first correction voltage, said second correction voltage and said first reference voltage and second reference voltage being input to said common electrode driving means as said plurality of voltages, said common electrode driving means outputting a corrected common voltage waveform in response thereto.

10. The matrix liquid crystal display device of claim 9, wherein said first voltage correction means has a circuitry identical to the circuitry of said second voltage correction means.

11. The matrix liquid crystal display device of claim 10, wherein said first voltage correction means includes a voltage input terminal, a current detection resistor coupled to said voltage input terminal and an inverting amplifier coupled across said current detection resistor.

12. The matrix liquid crystal display device of claim 11, wherein said first voltage correction means further includes an operational amplifier coupled between said voltage input terminal and said current detection resistor, said operational amplifier operating in accordance with a first time constant and said inverting amplifier circuit operating in accordance with a second time constant.

13. The matrix liquid crystal display device of claim 11, wherein said voltage correction means further comprises delay means for delaying the time period during which the corrected voltage is output by said first and second voltage correction means.

14. The matrix liquid crystal display device of claim 11, wherein said voltage correction means further comprises a sample and hold circuit for sampling and holding the voltage output by said inverting amplifier.

15. The matrix liquid crystal display device of claim 11, wherein said voltage correction means includes an operational amplifier and transformer.

16. The matrix liquid crystal display device of claim 15, wherein said operational amplifier operates in accordance with a time constant.

17. The matrix liquid crystal display device of claim 1, wherein said power circuit receives a first reference voltage and a second reference voltage; and said compensation means includes a first current detection resistor serially coupled with said first reference voltage, first voltage differentiating means for detecting a change in voltage across said first current detection circuit and producing a voltage difference signal in response to a voltage change across said first current detection resistor, a first voltage addition circuit for adding said voltage change voltage and said first reference voltage and producing a first correction voltage, a second current detection resistor coupled in series with said second reference voltage, a second voltage differentiation means coupled across said second current detection resistor for detecting a voltage change across said second current detection resistor and outputting a voltage change in response thereto, a second voltage addition circuit for receiving said second reference voltage and said voltage change voltage and producing a second correction voltage; said common electrode driving means receiving said first correction voltage and second correction voltage and producing a corrected common electrode voltage waveform in response thereto.

18. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for detecting a voltage change within said matrix liquid crystal display device, determining an amount of distortion in one of said segment voltage waveforms and common voltage waveforms in response to said voltage change and generating a correction voltage based upon said voltage change, said correction voltage being added to the segment voltage waveform and common voltage waveform exhibiting said amount of distortion; said common electrode driving means applying a common electrode voltage waveform to each common electrode respectively, said compensation means detecting the voltage waveforms applied to at least two of said common electrodes, and said compensation means determining a voltage change between said two detected common voltage waveforms and portion of said two detected common voltage waveforms and a portion of said plurality of voltages and compensating said segment voltage waveforms in response thereto.

19. The matrix liquid crystal display panel device of claim 18, wherein said compensation means includes differential means for determining the difference between said subset of said plurality of voltage waveforms and said common voltage waveforms and outputting a differential voltage representative thereof and further comprising adding means, said adding means adding said differential voltage to a subset of said plurality of voltage waveforms to produce said correction voltage, said segment electrode driving means receiving said correction voltage and providing a corrected segment voltage waveform in response thereto.

20. The matrix liquid crystal display panel device of claim 18, wherein said compensation means includes differential means for determining the difference between a group of said plurality of voltage waveforms and said common voltage waveforms and outputting a differential voltage representative thereof and further comprising adding means, said adding means adding said differential voltage to a subset of said plurality of voltage waveforms to produce said correction voltage, said common electrode driving means receiving said correction voltage and providing a corrected common voltage waveform.

21. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for detecting a voltage change within said matrix liquid crystal display device, determining an amount of distortion in one of said segment voltage waveforms and common voltage waveforms in response to said voltage change and generating a correction voltage based upon said voltage change; said correction voltage being added to the segment voltage waveform and common voltage waveform exhibiting said amount of distortion, said voltage compensation means including detection means for detecting the sum of the segment voltage waveforms on said plurality of segment electrodes and producing a voltage sum in response thereto; and voltage addition means for adding said voltage sum to a group of said plurality of voltages to produce a plurality of correction voltages, said segment electrode driving means outputting a corrected segment voltage waveform in response to said corrected voltage, said compensation means including a voltage detection electrode mounted on said first substrate and disposed to be in facing relation with said plurality of segment electrodes and being capacitively coupled with said plurality of segment electrodes.

22. The matrix liquid crystal display panel of claim 21, wherein said detection means includes a voltage detection electrode mounted on said second substrate and disposed in facing relation with said plurality of common electrodes and being capacitively coupled with said plurality of common electrodes.

23. The matrix liquid crystal display device of claim 21, wherein said detection means comprises a second voltage detection electrode disposed on said first substrate at a position spaced from said first voltage detection electrode, said second voltage detection electrode being disposed in facing relationship with said plurality of segment electrodes, said second voltage detection electrode producing a second voltage output, said addition means adding said voltage output to said voltage sum and said group of said plurality of voltages.

24. The matrix liquid crystal display panel of claim 23, wherein the plurality of segment electrodes is divided into at least a first group of segment electrodes, a second group of segment electrodes, and a third group of segment electrodes;

said segment electrode driving means includes at least a first segment electrode driver for driving said first group of segment electrodes, a second segment electrode driver for driving said second group of segment electrodes and a third segment electrode driver for driving said third set of segment electrodes;

said voltage addition means providing a first correction voltage to said first segment electrode driver means, a second correction voltage to said second segment electrode driver means and a third correction voltage to said third electrode driver means.

25. The matrix liquid crystal panel device of claim 24, wherein said first correction voltage does not equal the second correction voltage and the second correction voltage does not equal the third correction voltage.

26. The matrix liquid crystal panel device of claim 23, wherein said first voltage detection electrode is disposed in a co-linear non-overlapping relation with said second voltage detection electrode.

27. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for compensating for distortion of said voltage waveforms which occurs and varies according to the display pattern by detecting a current change within said matrix liquid crystal display device, determining an amount of distortion in one of said segment voltage waveforms and common voltage waveforms in response to said current change and generating a correction voltage based upon said current change, said correction voltage being added to the segment voltage waveform and common voltage waveform exhibiting said amount of distortion.

28. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode, said common electrode driving means applying a common electrode voltage waveform to each common electrode respectively, and

said power circuit means including voltage compensation means for compensating for distortion of said voltage waveforms which varies according to the display pattern detecting means for detecting the voltage waveforms applied to at least two of said common electrodes, and said compensation means determining a voltage change between said two detected common voltage waveforms and a portion of said plurality of voltages and compensating said segment voltage waveforms in response thereto.

29. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for compensating for distortion of said voltage waveforms which varies according to the display pattern, said compensation means including detection means for detecting the sum of the segment voltage waveforms on said plurality of segment electrodes and producing a voltage sum in response thereto; and voltage addition means for adding said voltage sum to a group of said plurality of voltages to produce a plurality of correction voltages, said segment electrode driving means outputting a corrected segment voltage waveform in response to said corrected voltage.

30. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for compensating for distortion of said voltage waveforms which varies according to the display pattern said power circuit receiving a first reference voltage and a second reference voltage and detecting said distortion; said power circuit means including voltage divider means for receiving said first reference voltage, and said second reference voltage and producing a first divided voltage, a second divided voltage, third divided voltage and fourth divided voltage; said first reference voltage and said second reference voltage, said second divided voltage and third divided voltage being input to said segment electrode driving means as said plurality of voltages; a first voltage correction means for receiving said first divided voltage and outputting a first correction voltage and a second correction means for receiving said fourth divided voltage outputting a second correction voltage, said first correction voltage, second correction voltage and said first reference voltage and second reference voltage being input to said common electrode driving means as said plurality of voltages, said common electrode driving means outputting a corrected common voltage waveform in response thereto.

31. A matrix liquid crystal display device for displaying characters or a pattern comprising:

a first substrate;

a plurality of common electrodes being formed on said first substrate;

a second substrate;

a plurality of segment electrodes being formed on said second substrate;

a liquid crystal sandwiched between said first substrate and second substrate;

power circuit means for generating a plurality of voltage waveforms;

segment electrode driving means for receiving at least a portion of said plurality of voltage waveforms and producing a voltage segment waveform in response thereto, said segment electrodes receiving said segment voltage waveforms and exhibiting either a lighting or non-lighting state in response thereto;

common electrode driving means for receiving at least a portion of said plurality of waveforms and producing in response thereto a common voltage waveform, said common electrodes receiving said common voltage waveform and exhibiting one of a selected and non-selected state in response thereto, said common electrode intersecting said scanning electrodes to define a matrix having a dot at each intersection, the dots being in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrode; and

said power circuit means including voltage compensation means for compensating for distortion of said voltage waveforms which varies according to the display pattern, said compensation means including detection means for detecting the sum of the common voltage waveforms on said plurality of common electrodes and producing a voltage sum in response thereto; and voltage addition means for adding said voltage sum to a group of said plurality of voltages to produce a plurality of correction voltages, said common electrode driving means outputting a correction common voltage waveform in response to said corrected voltage.

BACKGROUND OF THE INVENTION

The present invention relates to a liquid crystal display device, and in particular, to a circuit for driving a matrix liquid crystal display device.

Matrix liquid crystal displays are known in the art. Reference is made to FIGS. 1 through 3 in which a conventional matrix liquid crystal display is provided. A liquid crystal panel generally indicated as 1 is composed of a liquid crystal layer 5, a first substrate 2 and a second substrate 3 for sandwiching the liquid crystal layer 5 therebetween. A plurality of common electrodes Y1 through Y6 are oriented on substrate 2 in the horizontal direction and a plurality of segment electrodes X1 through X6 are formed on substrate 3 in substantially the vertical direction to form a matrix. Each intersection of common electrodes Y1 through Y6 and segment electrodes X1 through X6 forms a display dot 7. Display dots 7 marked by the hatching indicate an ON state, and the blank dots 7 indicate an OFF state. The dot structure of liquid crystal panel 1 is limited to a six by six matrix for simplicity however, in exemplary embodiments the number of dots of liquid crystal panel 1 may be much greater.

The voltage standard method is conventionally used for driving the prior art matrix liquid crystal display device. A selected voltage or non-selected voltage is sequentially applied to each of common electrodes Y1 through Y6. The period required to apply the successive selected voltage or non-selected voltage to all the common electrodes Y1 to Y6 is one frame.

Simultaneous to the successive application of the selected voltage or non-selected voltage to each common electrodes Y1 through-Y6, an ON voltage or OFF voltage is applied to each segment electrode X1 through X6. Accordingly, to turn a display dot 7, the area in which one common electrode intersects one segment electrode, to the ON state, an ON voltage is applied to a desired segment electrode when the common electrode is selected by providing a selected voltage to the desired common electrode. Similarly if the display dot is turned OFF, the OFF voltage is applied to the desired segment electrode.

Reference is now also made to FIGS. 2 and 3 in which examples of the actual driving waveforms (waveform of the applied voltage) applied at the electrodes are provided. FIG. 2A shows the segment voltage waveform applied to segment electrode X5 over time. FIG. 2B shows the common electrode waveform applied to common electrode Y3 over time. FIG. 2C shows the voltage waveform applied for producing the ON state at display dot 8, the intersection of segment electrode X5 and common electrode Y3.

FIG. 3A shows the segment voltage waveform applied to segment electrode X5 over time. FIG. 3B shows the common voltage waveform applied to common electrode Y4 over time. FIG. 3C shows the voltage waveform applied to the display dot at the intersection of segment electrode X5 and common electrode Y4 to produce the OFF state.

In FIGS. 2 and 3, F1 and F2 indicate the frame period. ##EQU1## wherein;

V0-V1=V1-V2=V

V3-V4=V4-V5=V

V1-V5=n V

(n is a constant).

Accordingly, by changing the polarity of the voltage which is applied to display dots 7 during frame periods F1 and F2, alternating driving is accomplished. It follows that whether the display dot 7 is ON or OFF depends on whether the ON voltage or OFF voltage is applied to the desired segment electrode when the selected voltage is applied to the intersecting common electrode corresponding to the desired display dot. This driving method is the voltage standard means used in the prior art.

The prior art structure and driving method has been less than satisfactory. When matrix liquid crystal display 1 is driven by the above conventional voltage standard method, the uniform rectangular waveforms illustrated in FIGS. 2 and 3 are not actually applied to display dots 7. Distortions in the applied waveforms occur. A first reason for the distortion is that each display dot 7 has an inherent electrical capacity based on the area of each dot 7, the thickness of the liquid crystal layers, the dielectric constant of the liquid crystal materials and so on. Secondly, both the common electrode and segment electrode are formed of a transparent conductive film having a surface resistance of about several tens of ohms as well as fixed electrical resistance. Therefore, even if the uniform rectangular waveforms as shown in FIGS. 2 and 3 are applied by the driving circuit, the waveform which is actually applied to the display dots becomes deformed and cross talk results. As a result, it becomes necessary to generate the difference of the effective voltage of the waveform which is applied to each display dot, resulting in the generation of contrast cross talk.

Observation has demonstrated that deformation of the voltage waveform being applied to the display dots occurs based upon relationship dependent on the pattern of the characters or drawings which is displayed by the liquid crystal display device. Secondly, the change of the effective voltage based on the deformation of the voltage waveform which is applied to the display dots causes the contrast crosstalk.

1. The First Mode (zebra crosstalk)

Reference is now made to FIGS. 1, 4, 5, and 6A through 6C wherein zebra crosstalk is depicted. For simplicity of explanation, the common electrodes Y1 through Y6 are sequentially selected from the first common electrode Y1 to the sixth common electrode Y6, again returning to the first common electrode Y1. Additionally, liquid crystal panel 1 is a positive display wherein the greater the effective voltage applied to the display dots 7, the darker the display dot. A scale is provided in FIG. 4 to indicate relative darkness. This type of display is used for each explanation unless otherwise indicated.

If the display of FIG. 1 is desired and the inputs of FIGS. 2 and 3 are provided, the crosstalk of the display contrast as shown in FIG. 4 actually occurs in the liquid crystal display device 1. As can be seen, segment electrodes X1 through X4 receive identical inputs. The segment voltage waveform at the display dots portion of segment electrodes X1 through X4 is shown in FIG. 5A, the common voltage waveform applied at the display dot portion of the common electrode Y3 is shown in FIG. 5B. The voltage waveform applied at the display dots located at the intersections of segment electrodes X1 through X4 and common electrode Y3 is shown in FIG. 5C. The voltage waveforms applied to the four display dots will differ from each other slightly. However, this slight difference can be ignored here.

A spike shaped deformation of the voltage waveform occurs at the non-selected voltage level of the common voltage waveform as shown in FIG. 5B. The relationship between the direction and the size of the spike shaped voltage and the display pattern is as follows. Generally, when the selection of the successive common electrode moves from the nth common electrode to the (n+1)th common electrode, the number of segment electrodes to which the ON voltage is successively added is a, the number of segment electrodes to which the OFF voltage is successively applied is b, the number of segment electrodes to which a voltage is applied by switching from the ON voltage to OFF voltage is c and the number of segment electrodes to which the voltage is added by switching from the OFF voltage to ON voltage is d. The number of ON dots 7 on the nth common electrode is N.sub.ON. The number of OFF dots 7 on the nth common electrode is N.sub.OFF and the number of ON dots 7 on the (n+2)th common electrode is M.sub.ON while the number OFF dots on the (n+ 2)th common electrode is M.sub.OFF. The relationship between the segmented electrodes and common electrodes is as follows:

N.sub.ON =a+c,

N.sub.OFF =b+d

M.sub.ON =a+d,

M.sub.OFF =b+c

N.sub.ON +N.sub.OFF =M.sub.ON +M.sub.OFF =K

K is a constant and equal to the total number of display dots on each common electrode Y.

A value of I equal to the difference in ON dots between successive segment electrodes is defined as follows: ##EQU2## so, when the value of I is negative, the direction of the spike shaped voltage is in the direction of the ON voltage. On the other hand, where the value of I is positive, the direction of the spiked shaped voltage is in the direction of the OFF voltage. The size of the spike increases in accordance with the absolute value of I.

In other words, when the number d of segment electrodes in which the applied voltage switches from the OFF voltage to ON voltage is larger than the number c of segment electrodes in which the applied voltage switches from the ON voltages to OFF voltage, the spike shaped voltage occurs on the common voltage waveform in the direction of the ON voltage. In contrast thereto, when the sign of I, which is the difference between c and d, changes the spike shaped voltage occurs in the direction of the OFF voltage. Additionally, the value of the spike shaped voltage corresponds to the absolute value of I.

As shown in FIGS. 5A and 5B, when the relationship between the change of the segment voltage waveform and the direction of the spike shaped voltage of the common voltage waveform on the non-selected voltage are in-phase, a rounded corner occurs in the voltage waveform of the voltage applied at the display dots (FIG. 5C). The longer the in-phase period, the smaller the effective voltage value of the applied waveform, resulting in the displayed color becoming very light.

Reference is now made to FIG. 6 which illustrates the change of the segment voltage waveform and the direction of the spike on the common voltage waveform when the waveforms are out of phase. FIG. 6A shows the segment voltage waveform applied at the display dot portion of the segment electrode X5 of display 10. FIG. 6B shows the common voltage waveform applied at the display dot 7 portion of the common electrode Y3. FIG. 6C shows the combined voltage waveform which is applied to the display dot at the intersection of segment electrode X5 and common electrode Y3. As shown, where the relationship between the change in the segment voltage waveform (FIG. 6A) and the direction of the spike shaped voltage of the common voltage waveform of the non-selected voltage (FIG. 6B) are out of phase, a spike shaped voltage is generated in the combined voltage waveform applied to the display dots 7 (FIG. 6B), thereby increasing the effective value of the applied voltage. The longer the out of phase period, the larger the effective value, resulting in a darkening of the displayed color. Therefore, display dots 7 on segment electrodes X1 to X4 become light, and the display dots on the segment electrode X5 become dark regardless of the applied ON state or OFF state voltages. The darkness of display dots 7 on segment electrode X6 become a color of intermediate degree between the above on segment electrodes X1 to X4 and those on X5.

2. The Second Mode (horizontal crosstalk)

Reference is now made to FIGS. 7 through 10 in which a desired pattern is illustrated. FIG. 7 illustrates a display 11 on which a horizontal crosstalk pattern is displayed. Display 11 is the same as liquid crystal panel 1. The actual contrast crosstalk generated by display 11 is shown by display 12 of FIG. 8.

Display dot 7 acts as a capacitor. The capacity of this capacitor has a different value in the ON state than in the OFF state. The value of the capacitance in the ON state is larger than the capacitance in the OFF state. This occurs because the liquid crystal 5 acts as an anisotropic dielectric and the resulting alignment change occurs between the ON state and OFF state. Accordingly, the capacitance of all dots 7 on common electrode Y2 having many ON dots 13 is larger than that on common electrode Y4 having a few ON dots 13. Since common electrodes have the same circuit resistance, the rounded waveform generated in the voltage waveform of common electrode Y2 becomes larger.

FIG. 9A shows the segment voltage waveform over time applied at the display dot portion on the segment electrode X1 of display 11. FIG. 10B shows the common electrode waveform over time applied at the display dot portion on the common electrode Y2. FIG. 9C shows the combined voltage waveform over time applied to dot 7 at the intersection of segment electrode X1 and common electrode Y2.

FIG. 10A shows the segment voltage waveform over time applied at the display dot portion on the segment electrode X1 of display 11. FIG. 10B shows the common voltage waveform over time applied at the display dot portion on the common electrode Y4. FIG. 10C shows the combined voltage waveform over time which is applied to the dot at the intersection of segment electrode X1 and common electrode Y4.

As can be seen from a comparison of FIG. 9B and FIG. 10B the waveform of common electrode Y2 which has many ON dots is more rounded when a change from the non-selected voltage to selected voltage occurs. This area is marked by the hatched area. As can be seen by comparing FIG. 9C with FIG. 10C the voltage effective value of the waveform which is applied to dots 13 on common electrode Y2 also decreases by the hatched area. Accordingly, the color produced at each display dot 7 of common electrode Y2 having many ON dots 13 becomes very light. Thus, if the number of ON dots on each common electrode is represented by Z, the larger the value of Z of the common electrode, the lighter the displayed color.

3. The Third Mode (vertical crosstalk)

Reference is now made to FIGS. 12 through 17C in which vertical crosstalk is illustrated. The pattern of display 14 is actually displayed as display 15 due to vertical crosstalk. the segment voltage waveform applied at the display dot portion on segment electrode X6 is shown in FIG. 13A. The common voltage waveform applied to the display dot portion on the common electrode Y2 is shown in FIG. 13B. The combined voltage waveform which is applied at the display dot at the intersection of segment electrode X6 and common electrode Y2 is shown in FIG. 13C. Further, FIGS. 14A through 14C show each voltage waveform on segment electrode X5 and common electrode Y2 and the voltage waveforms which are combined to form the actual waveform at the display dot at the intersection of segment electrode X5 and common electrode Y2.

A second example of vertical crosstalk is now described. The segment voltage waveform applied at the display dot portion of segment electrode X6 is shown in FIG. 17A. A desired pattern is input to produce the pattern on display 15. However, due to vertical crosstalk a pattern such as that of display 16 results. The common voltage waveform applied at the display dot portion of common electrode Y3 is shown in FIG. 17B. FIG. 17C shows the combined voltage waveform which is applied to the display dot at the intersection of segment electrode X6 and common ele