Circuit 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 layer sandwiched between said first substrate and said second substrate;

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes;

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device; and

said common electrodes intersecting said segment 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 electrodes, said multiplex driving means sequentially switching the selected voltage among the common electrodes, the compensation means receiving a data signal representative of the characters or pattern to be displayed, and producing a sign signal and strength signal, said multiplex driving means providing a common voltage waveform or a segment voltage waveform in which at least one portion of each waveform changes in a direction and size based on the sign signal and the strength signal.

2. The matrix liquid crystal display device of claim 1, wherein the compensation means is adapted to determine the number of dots in the ON state on the common electrode which is to next receive the selected voltage and to determine the value of the sign signal and strength signal based thereon.

3. The matrix liquid crystal display device of claim 1 wherein the compensation means comprises count means for receiving the data signal, substantively counting the number of dots in the ON state on the common electrode to next be selected, and outputting a count; first count holding means for the count from the count means, storing the count and outputting a stored count when a successive count is output by the count means; a second count holding means for receiving the stored count output from the first count holding means, storing the stored count value and outputting a second stored count when a successive stored count is output by the first count holding means; arithmetic means for receiving the first stored count and the second stored count and outputting a value I substantially equal to the difference between the count stored in the second count holding means and the count stored in the first count holding means and the sign signal; a pulse width control circuit for receiving the value I and producing a strength signal based at least in part on the absolute value of I.

4. The matrix liquid crystal display device of claim 3, wherein the time period during which the non-selected voltage is compensated in response to the value I.

5. The matrix liquid crystal display device of claim 3, wherein the voltage level of the non-selected voltage is compensated in response to the value of I.

6. The matrix liquid crystal display device of claim 1, wherein the multiplex driving means includes a plurality of voltage divider means and switch means.

7. The liquid crystal display device of claim 6, wherein said switch means selects a divided voltage from the plurality of voltage divider in response to the sign signal and strength signal.

8. The matrix liquid crystal display device of claim 3, wherein the multiplex driving means includes a plurality of voltage divider means and of switch means.

9. The liquid crystal display device of claim 8, wherein said switch means selects a divided voltage from the plurality of voltage divider means in response to the sign signal and strength signal.

10. The matrix liquid crystal display device of claim 7, wherein the period of the non-selected voltage is compensated in response to the value of I.

11. The matrix liquid crystal display device of claim 7, wherein the value of the non-selected voltage is compensated in response to the value of I.

12. The matrix liquid crystal display device of claim 1, wherein the multiplex driving means includes a plurality of voltage divider means, at least a first and a second voltage generator, and at least a first switch and a second switch.

13. The matrix liquid crystal display device of claim 12, wherein the first voltage generator and the second voltage generator generate a voltage of a value responsive to the sign signal and the strength signal, and the first switch and a second switch periodically select between a generated voltage and a divided voltage.

14. The matrix liquid crystal display device of claim 3, wherein the multiplex driving means includes a plurality of voltage divider means, at least a first and a second voltage generator, and at least a first switch and a second switch.

15. The matrix liquid crystal display device of claim 14, wherein the first voltage generator and the second voltage generator generate a voltage of a value responsive to the sign signal and the strength signal, and the first switch and the second switch periodically select between a generated voltage and a divided voltage.

16. The matrix liquid crystal display device of claim 15, wherein the value of the non-selected voltage is compensated in response to the value of I.

17. The matrix liquid crystal display of claim 14, wherein the first voltage generator and the second voltage generator each provide a voltage of a value responsive to the sign signal and the strength signal and the first switch and the second switch periodically select between a divided voltage and a generated voltage in response to the control signal, the duration of selection of at least one of said divided voltage and said generated voltage being selected at least in part in response to said strength signal.

18. The matrix liquid crystal display of claim 17, wherein the period and value of the non-selected voltage is compensated in response to the value of I.

19. The matrix liquid display device of claim 1, wherein the multiplex driving means includes a plurality of voltage divider means and at least a first and second voltage generator, the first voltage generator and the second voltage generator each producing a plurality of voltage waveforms each represented as an exponential function waveform of a maximum or minimum value, depending on the sign signal, responsive to the strength signal, the voltage waveform of each of the first and second voltage generators being combined with the output of the voltage divider means to produce a voltage for incorporation in at least one of the common voltage waveform and the segment voltage waveform.

20. The matrix liquid display device of claim 1, wherein the multiplex driving means includes a plurality of voltage divider means and at least a first and second voltage generator, the first voltage generator and the second voltage generator each producing a plurality of voltage waveforms each represented as a ramp function waveform of a maximum or minimum value, depending on the sign signal, responsive to the strength signal, the voltage waveform of each of the first and second voltage generators being combined with the output of the voltage divider means to produce a voltage for incorporation in at least one of the common voltage waveform and the segment voltage waveform.

21. The matrix liquid crystal display device of claim 19, wherein the voltage generator includes a variable resistor, an operational amplifier, a plurality of switching power sources and switching control means.

22. The matrix liquid crystal display device of claim 4, wherein the segment voltage waveform is compensated in response to the value of I.

23. The matrix liquid crystal display device of claim 22, wherein said compensation is one of varying the value of a portion of the segment voltage waveform, varying the period of a portion of the segment voltage waveform, and varying both the value and period of the segment voltage waveform.

24. The matrix liquid crystal display device of claim 22, wherein said compensation is by at least one portion of the segment voltage waveform being one of an exponential or ramp function waveform of a maximum or minimum value, as determined by the sign signal, responsive to the strength signal.

25. The matrix liquid crystal display device of claim 3, wherein said compensation is by at least one portion of the segment voltage waveform being one of an exponential or ramp function waveform of a maximum or minimum value, as determined by the sign signal, responsive to the strength signal.

26. The matrix liquid crystal display device of claim 25, wherein the multiplex driving means receives the strength signal and provides a voltage output for compensating the selected voltage.

27. The matrix liquid crystal display device of claim 25, wherein the multiplex driving means including a plurality of voltage divider means, at least a first switch and a second switch, the first switch and the second switch each selecting between voltages of the plurality of voltage divider means in response to the strength signal.

28. The matrix of liquid crystal display device of claim 26, wherein said compensation is one of varying the value of a portion of the selected voltage, varying the period of a portion of the selected voltage, and varying both the value and period of the selected voltage.

29. The matrix liquid crystal device of claim 26, wherein said compensation is by at least one portion of the selected voltage being one of an exponential or ramp function waveform of a value determined by the strength signal.

30. The matrix liquid crystal display device of claim 26, wherein said compensation is one of varying the value of a portion of the segment voltage waveform, varying the period of a portion of the segment voltage waveform, and varying both the value and period of the segment voltage waveform.

31. The matrix liquid crystal display device of claim 26, wherein said compensation is by at least one portion of the segment voltage waveform being one of an exponential or ramp function waveform of a value determined by the strength signal.

32. 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 common electrodes being formed on said first substrate;

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

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes; and

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device by the portion of said liquid crystal sandwiched layer at an intersection of said segment electrodes and said common electrodes without crosstalk, the common electrodes intersecting with the segment electrodes to define a matrix having a dot at each intersection, the dots being either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrodes said multiplex, driving means sequentially switching the selected voltage among the common electrodes, the compensation means receiving a data signal representative of the character or pattern to be displayed, and the compensation means including a count means for substantively counting the number of dots in the ON state on the liquid crystal display and producing a count, a count holding means for storing the count and a strength signal, the multiplex driving means receiving the strength signal and producing a voltage output for compensating at least one of the non-selected voltage and the segment voltage waveform in response to the strength signal.

33. 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 layer sandwiched between said first substrate and said second substrate;

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes; and

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device by the portion of said liquid crystal sandwiched layer at an intersection of said segment electrodes and said common electrodes without crosstalk, the common electrodes intersecting with the segment 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 electrodes, said multiplex driving means sequentially switching the selected voltage among the common electrodes, the compensation means receiving a data signal representative of the character or pattern to be displayed, the compensation means producing a sign signal and a strength signal representative of the difference between the sum of the number of dots in the ON state of the present and next common electrodes to receive the selected voltage and the number of dots on each common electrode, said multiplex driving means compensating at least one of a non-selected voltage and a segment voltage waveform in response to said sign and strength signals.

34. The matrix liquid crystal display device of claim 33, wherein said compensation is by at least one portion of at least one of the non-selected voltage and the segment voltage waveform being one of an exponential or ramp function waveform of a value determined by the strength signal.

35. The matrix liquid crystal display device of claim 33, wherein said compensation is by one of varying the value of a portion of one of the non-selected voltage and the segment voltage waveform, varying the period of a portion of one of the non-selected voltage and the segment voltage waveform, and varying both the value and period of one of the non-selected voltage and the segment voltage waveform.

36. 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 layer sandwiched between said first substrate and said second substrate;

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes; and

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device by the portion of said liquid crystal sandwiched layer at an intersection of said segment electrodes and said common electrodes without crosstalk, the compensation means includes count means for substantially counting the number of dots in the ON state of the common electrode to next receive the selected voltage and outputting a count in response to the data signal, a first count holding means for storing th count and outputting a stored count in response to the next count output of the count means, a second count holding means for storing the stored count of the first count holding means and outputting a second stored count in response tot he next stored count output by the first count holding means, arithmetic means for receiving the first stored count and the second stored count and outputting a value F equal to the difference between the sum of the first and second stored counts and the number of dots on a common electrode to produce a sign signal and a strength signal.

37. 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 layer sandwiched between said first substrate and said second substrate;

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes; and

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device by the portion of said liquid crystal sandwiched layer at an intersection of said segment electrodes and said common electrodes without crosstalk, the common electrodes intersecting with the segment electrodes to define a matrix having a dot at each intersection, the dots existing in either an ON state or an OFF state depending on the voltage applied to the intersecting common and segment electrodes, said multiplex driving means sequentially switching the selected voltage among the common electrodes, the compensation means receiving a data signal representative of the character or pattern to be displayed, the compensation means producing a strength signal represented by a value Z' equal to the sum of the number of dots in the ON state of the next common electrode to receive the selected voltage and a constant times the difference between the number of dots in the ON state in the next and present common electrodes to receive the selected voltage, said multiplex driving means providing compensation to the selected signal of the next common electrode of a period representative of Z'.

38. The matrix liquid crystal display device of claim 37, wherein the compensation means includes count means for counting the number of dots in the ON state on the common electrode which is to next receive the selected voltage, first count holding means for storing the count and producing a first stored count value in response to the next count output by the count means, second count holding means for receiving the first stored count value and producing a second stored count value in response to the next first stored count value output by the first holding means, an arithmetic means for receiving the first stored count value and the second stored count value and producing the value Z', pulse width control means for receiving the value Z' and producing a strength signal representative thereof, the multiplex driving means receiving the strength signal, and providing a voltage for compensating the selected signal of the next common electrode in response to the strength signal.

39. 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 layer sandwiched between said first substrate and said second substrate;

multiplex driving means for providing a common voltage waveform including a selected voltage or a non-selected voltage to said plurality of common electrodes and providing a segment voltage waveform including an ON voltage or an OFF voltage to said plurality of segment electrodes; and

compensation means for compensating at least one of said common voltage waveform or said segment voltage waveform based upon said pattern or said characters to be displayed in said liquid crystal display device by the portion of said liquid crystal sandwiched layer at an intersection of said segment electrodes and said common electrodes without crosstalk, the common electrodes intersecting with the segment 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 electrodes, said multiplex driving means sequentially switching the selected voltage among the common electrodes, the compensation means receiving a data signal representative of the character or pattern to be displayed, the compensation means producing a first strength signal and a first sign signal representative of a value I equal to the difference between the number of dots in the ON state on the common electrode presently receiving the selected voltage and next to receive the selected voltage; a second strength signal and a second sign signal representative of a value F equal to the sum of the number of dots in the ON state on the common electrode presently receiving the selected voltage and next to receive the selected voltage less the number of dots on the common electrode, a third strength signal representative of value equal to a value T equal to the number of ON dots on the liquid crystal display and a fourth strength signal representative of value Z equal to the number of ON dots of the common electrode, in response to the data signal and the multiplex driving means providing a voltage output for compensating the non-selected voltage during alternating periods in response to the first strength and sign signals and the second strength and sign signals and further in response to the third strength signal, and compensating the selected voltage in response to the fourth strength signal.

40. The matrix liquid crystal display device of claim 39, wherein the first and second strength signal compensate the period of a portion of the non-selected voltage and the third strength signal compensates the value of a portion of the non-selected voltage and the fourth strength signal compensates the period of a portion of the selected voltage.

41. The matrix liquid crystal display device of claim 39, wherein the compensation means includes a first count means for counting the number of dots in the ON state on the common electrode to next receive the selected voltage and outputting a count value in response to the control signal, a first count holding means for storing the count value and outputting a first stored count in response to the control signal, a second count holding means for storing the first stored count and outputting a second stored count in response to the control signal, first arithmetic means for comparing the first stored count and the second stored count and producing a value representative of I, a second arithmetic means for receiving the first stored count and the second stored count and producing an arithmetic value representative of F, switching means for receiving the first and second arithmetic values during alternating periods and producing the first and second sign signals and first and second pulse signals, a pulse width control means for receiving the first and second pulse signals and producing a first or second strength signal, a second count means for counting the number of dots in the ON state on the liquid crystal panel and for producing a second count, third count holder means for storing the second count and producing the third strength signal, a second pulse width control means for receiving the first stored count value and producing a fourth strength signal in response thereto.

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.

______________________________________ During frame period F1, selected voltage = V0, non-selected voltage = V4 ON voltage = V5, OFF voltage = V3 During frame period F2, selected voltage = V5, non-selected voltage = V1 ON voltage = V1, OFF voltage = V2, ______________________________________

wherein;

V0-V1=V1-V2=V

V3-V4=V4-V5=V

V0-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+1)th common electrode is M.sub.ON while the number OFF dots on the (n+1)th common electrode is M.sub.OFF. The relationship between the segmented electrodes and common electrodes is as follows: ##EQU1##

K is a constant and equal to the total number 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 veritical 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 electrode Y3. Similarly, FIGS. 18A through 18C show each voltage waveform applied at segment electrode X5, common electrode Y2 and the combined voltage waveform applied at display dot 7 at the intersection of segment electrode X5 and common electrode Y2.

The non-selected voltage level of the common voltage waveform during the displaying of the pattern of display 14 having many ON dots varies in the ON voltage direction as shown in FIG. 13B. Conversely, the non-selected voltage level of the common voltage waveform of display 15 having few ON dots varies in the OFF voltage direction as shown in FIG. 17B.

Where there are many ON dots, the variation is caused because each of common electrodes Y1 through Y6 is electrically connected to the segment electrode to which the ON voltage is applied through the condenser of display dots to a greater extent than to the segment electrode to which the OFF voltage is applied. The reason for this phenomenon is unclear, but it may occur due to a lack of sufficient output impedance of the power circuit relative to the load of the liquid crystal panel. The relationship for the generated voltage shift is described below.

For all display dots 7 of displays 14 and 15 T is the number of ON dots and L is the number of OFF dots. A value T' is defined as T'=T-L when T' is positive, the non-selected voltage level varies in the ON voltage direction. On the other hand, when T' is negative the non-selected voltage level varies in the OFF voltage direction. The size of the variation increases in accordance with the absolute value of T'.

Where the pattern includes many ON dots 13 as shown in display 14, the difference between the OFF voltage and the non-selected voltage becomes large and the difference between the ON voltage and the non-selected voltage becomes small. Therefore, comparing the voltage waveform (FIG. 14A) which is added to display dots 7 on segment electrode X5 of display 15 (FIG. 12) having no ON dot 13, with the voltage waveform FIG. 13A which is added to display dots 7 on segment electrode X6 having ON dot 13, illustrates that the effective combined voltage which is applied to display dot 7 on the segment electrode X5 is larger for the portion marked by the hatched area (FIG. 14C), thereby making the display dots on the segment electrode X5 dark when they should be blank.

Similarly, where the display has few ON dots 13 such as display 15, the difference between the ON voltage and the non-selected voltage becomes large, and the difference between the OFF voltage and the non-selected voltage becomes small. Therefore, comparing the voltage waveform which is provided to display dots 7 by segment electrode X6 including ON dot 13, and the voltage waveform which is provided to display dots 7 on the segment electrode X5 having no ON dot 13, the effective voltage which is provided to the display dots on the segment electrode X6 is larger than that of electrode X5 for the period marked by the hatched area (FIG. 17C) resulting in a dark display dot on segment electrode X6.

4. The fourth mode (inversion crosstalk)

Reference is made to FIGS. 18 through 21 in which inversion crosstalk is illustrated. A desired pattern is input to a display 17 (FIG. 19), but in reality appears as the pattern on a display 18 (FIG. 20) due to inversion crosstalk. FIG. 21A shows a segment voltage waveform provided at the display dot portion on segment electrode X6. FIG. 21B shows a common voltage waveform provided at the display dot portion on common electrode Y2. FIG. 21C shows a combined voltage waveform which is provided to display dot 7 at the intersection of segment electrode X6 and the common electrode Y2. FIG. 22 shows the co