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Description  |
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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=V0,
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:
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:
##EQU1##
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 1 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 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 o 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 combined voltage waveform provided to
display dot 7 at the intersection of segment electrode X5 and common
electrode Y2.
Reference is now made to FIGS. 23 through 26 wherein a second example of
inversion crosstalk is provided. A pattern is input to appear as display
20 (FIG. 23), but in reality appears as the pattern of display 19 (FIG.
24) due to inversion crosstalk. FIG. 25A shows a segment voltage waveform
provided at the display dot portion of segment electrode Y6. FIG. 25B
shows a common voltage waveform provided at the display dot portion of
common electrode Y2. FIG. 25C shows the combined voltage waveform which is
provided at display dot 7 at the intersection of segment electrode X6 and
common electrode Y2. FIG. 26 shows a combined voltage waveform provided by
electrodes Y2 and X5 to display dot 7 at the intersection of segment
electrode X5 and common electrode Y2.
The time period of switching between frame periods, i.e. before or after
the switching from F1 to F2 of FIG. 21 and FIG. 25 is known as the
inversion. As shown in FIG. 19 when the number of segment electrodes in
which the voltage applied to the segment electrode is an ON voltage before
and after the inversion (only the 6th segment electrode X6 in FIG. 19) is
less than the number of segment electrodes in which the voltage applied to
the segment electrode is an OFF voltage before and after the inversion
(the five segment electrodes X1 to X5 in FIG. 19), a rounded waveform as
is shown in FIG. 21B occurs at the time of inversion.
Therefore, when the pattern as shown in FIG. 19 is displayed, the rounded
waveform occurs in the common voltage waveform as shown in FIG. 21B at the
time of inversion.
Simultaneously, the voltage waveform applied to the segment electrode X6
(FIG. 21A) applied to display dots 7 on segment electrode X6 for changing
from an ON voltage to an ON voltage before and after the inversion,
generates a spike shaped voltage as shown in FIG. 21C, thereby increasing
the effective voltage making the display dark. On the other hand, for the
voltage waveform which is applied to display dots 7 of segment electrodes
X1 through X5 for changing from an OFF voltage to an OFF voltage before
and after the inversion, the rounded portion of the waveform as shown in
FIG. 22 occurs, thereby decreasing the effective voltage, thus lightening
the display.
Conversely, in display 20 (FIG. 23) the spike shaped voltage is generated
in the common voltage waveform as shown in FIG. 25B at the time of
inversion. Simultaneously, when the applied waveform changes from an ON
voltage to an OFF voltage before and after the inversion, a rounded
section (FIG. 25C) is generated in the voltage waveform which is applied
to display dots 7 on segment electrodes X1, X2, X3, X4 and X6, thereby
decreasing the effective voltage and further lightening the displayed
color. Additionally, when the voltage applied to the display dots on the
segment electrode X5, switches from an OFF voltage to an OFF voltage
before and after the inversion, a spike shaped voltage (FIG. 26) is
generated thereby increasing the effective voltage, darkening the
displayed color.
The above relationship is defined as follows. The number of segment
electrodes switching from an ON voltage to an ON voltage at the time of
inversion is a. The number of segment electrodes switching from an OFF
voltage to an OFF voltage at the time of inversion is b. The number of
segment electrodes switching from an ON voltage to an OFF voltage is c.
The number of segment electrodes switching from an OFF to an ON voltage is
d. Further, the number of ON dots on the common electrode (Y6, FIGS. 19
and 23) which is selected just before the inversion is N.sub.ON and the
number of OFF dots on the common electrode is N.sub.OFF while the number
of ON dots on the common electrode (Y1, FIGS. 19 and 23) which is selected
just after the inversion is M.sub.ON and the number of OFF dots on the
common electrode is M.sub.OFF.
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 representing the number of display dots on each common
electrode. Wherein,
##EQU2##
If the value of F is negative, at the time of the inversion, the rounded
waveform occurs when the non-selected voltage changes on the common
electrode. Conversely, if the value of F is positive, the spike shaped
voltage occurs in the direction of the ON voltage. The value the applied
voltage increases in accordance with the absolute value of F. This
introduces the display crosstalk as mentioned above.
The general crosstalk problem has been well known in the art. A method for
correcting crosstalk is also known in the art and is illustrated in
Japanese Laid-Open Patent Nos. 31825/87, 19195/85 and 19196/85. The method
consists of reversing the polarity of the voltage which is applied to the
liquid crystal panel a predetermined number of times per frame. This
method is known as the line reverse driving method.
However, this method has been less than satisfactory. The line reverse
driving method corrects only one mode of crosstalk (zebra crosstalk) of
the plurality of cross talk modes. As mentioned above, there are four
modes of crosstalk in the display relating to the mechanism which arise
due to changes of the voltage waveform. Accordingly, the crosstalk of the
display contrast is not completely removed.
A system for driving a liquid crystal display which would solve the uneven
contrast of the display by changing a portion of a driving voltage
waveform applied to a liquid crystal panel in accordance with the
characters and the designs displayed is known from Japanese Patent
Application No. 63-159914. This system amends the unevenness in contrast
by changing a portion of the driving voltage waveform in accordance with
the display characters or designs. However, this system suffers from the
disadvantage that it does not include a parameter related to an ambient
temperature or the temperature of a liquid crystal display. Because the
liquid crystal display characteristics depend on temperature, proper
amendment of the voltage waveform and resulting display cannot be effected
over a wide range of temperatures.
Reference is first made to FIG. 83 wherein the power circuit for producing
a voltage waveform which corrects the uneven horizontal cobwebbing display
as known in Japanese Patent Application No. 63-159914 is provided. A
plurality of resistors 6101 through 6105 are serially connected and a
voltage V0N and V5N is supplied at the end of the resistors providing a
series of voltage dividers thereof and an operating voltage V.sub.op
defined as V0N-V5N. The voltage at the end of each respective resistor
6101 through 6105 is defined as V1, V2, V3, V4 and V5N. A respective
Voltage follower circuit 6106 through 6109 is provided at the end of
resistors 6101 through 6105 to reduce the impedances of voltages V1, V2,
V3 and V4.
Voltage V0N and V5N are operated on by mirror-like structures. A constant
power source 6110 is provided at voltage line 6170 and across a pair of
resistors 6112, 6128 provided in series which serve to divide the voltage
output by constant power source 6110. The divided voltage is a reference
voltage. An inverting amplification circuit 6116 receives as one input the
divided voltage from the voltage divider provided by resistor pairs 6112,
6128. At its other input, circuit 6116 receives the voltage V1 produced by
voltage follower circuit 6106, input to reversible amplification circuit
6116 through a resistor 6117. A resistor 6118 is coupled to a resistor
6117 at the input of amplification circuit 6116 at its one end and at the
output of amplification circuit 6116 at its other. Amplification circuit
6116 produces an inverted voltage V1 which has been biased by the
reference voltage. A resistor 6122 is coupled to the output of
amplification circuit 6116 and resistor 6118 at one end and a diode 6124
at its other end which is coupled to a voltage line 6171 carrying voltage
V0N. Resistor 6122 and diode 6124 comprise a circuit for keeping the
output voltage of reversible amplification circuit 6116 at a level no
greater than V0N. A voltage follower circuit 6126 receives th output of
reversible amplification 6116 and outputs voltage V0U.
Similarly, a constant voltage power source 6111 is coupled to a voltage
line 6170 and across pair of resistors 6113, 6129 coupled in series to
provide a divided reference voltage. An inverting amplification circuit
6119 receives the divided reference voltage at one input and the voltage
V4 output by voltage follower circuit 6109 input through a resistor 6120
at a second input. A resistor 6121 is connected to resistor 6120 at the
input to inverter amplification circuit 6119 at its one end and the output
of amplification circuit 6119 at its other end. Inverting amplification
circuit 6119 outputs an inverter voltage V4 based on the reference voltage
produced between resistor 6120 and 6121.
A resistor 6123 coupled to the output of inverting amplification circuit
6119 is coupled to a diode 6125 to form a circuit for preventing the
output voltage of amplification circuit 6119 to be greater than V5N. A
voltage follower circuit 6127 receives the output of amplification circuit
6119 and outputs a voltage V5L.
Reference is now made to FIG. 84 in which a graph representing the voltages
produced based on the correction suitable at 25.degree. C. using the prior
art construction and the ideal correction at a higher temperature, as a
function of V.sub.op, is provided. Voltage V0U based on the correction
suitable at 25.degree. C. is denoted by graph line 6151. The voltage V5L
based on the correction suitable at 25.degree. C. is represented by the
line 6152. These voltages are to be compared with the representation of
the ideal voltages based on experimental data shown in FIG. 82 in which
the ideal voltage represented at each temperature is provided. Lines 6131
and 6132 on the graph represent voltages V0U and V5L at a temperature of
50.degree. C. Points 6133 and 6134 denote voltages V0U and V5L at a
temperature of 25.degree. C. Points 6135 and 6136 represent the respective
voltages V0U and V5L at a temperature of 0.degree. C. As can be seen from
comparing the graphs in FIG. 82 and FIG. 84, the voltages V0U and V5L
differ greatly from the ideal except at the temperature of 25.degree. C.
As shown in FIG. 84, on which line 6135 from FIG. 82 representing the
ideal voltage V0U at 0.degree. C. has been added, when V.sub.op changes
from Point X to Point Y with a change of temperature, the prior art
arrangement produces an excessive correction voltage represented by Point
A, while the ideal value of the correcting voltage is represented by Point
B. Accordingly, this illustrates how the prior art has been unable to
control the voltages over a wide range of temperatures.
Accordingly, a mechanism for driving a liquid crystal display which
overcomes the limitations of the prior art by correcting for crosstalk
over a wide range of temperatures is desired.
SUMMARY OF THE INVENTION
A mechanism for driving a matrix liquid crystal display having two
substrates and a liquid crystal layer formed therebetween in accordance
with the invention is provided. A group of common electrodes is formed on
one substrate. A group of segment electrodes is formed on the other
substrate. The common electrodes intersect the segment electrodes,
providing display dots on the liquid crystal display at each intersection.
A voltage waveform circuit produces a voltage waveform for driving the
liquid crystal. A waveform compensation circuit changes the voltage
waveform in accordance with the pattern of drawings or characters to be
displayed in the liquid crystal display device produce the desired display
and in accordance with the ambient temperature and temperature of the
liquid crystal display.
Accordingly, it is an object of the present invention to provide an
improved circuit for driving a liquid crystal display.
Another object of the invention is to provide a voltage waveform driving
circuit for a liquid crystal display which amends the driving voltage
waveform to compensate for variations in the display of the liquid crystal
display due to variations in temperature.
Still other objects and advantages of the invention will in part be obvious
and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the construction hereinafter set forth, and the scope of
the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to the
following description taken in connection with the accompanying drawings,
in which:
FIG. 1 is a perspective view of a liquid crystal display and pattern in
accordance with the prior art;
FIGS. 2A-2C and 3A-3C are graphs of ideal waveforms of the voltage applied
to the liquid crystal panel for forming the display pattern of FIG. 1;
FIG. 4 is a perspective view of the liquid crystal panel and actual display
pattern of FIG. 1;
FIGS. 5A-5C and 6A-6C are graphs of waveforms of the voltage actually
applied to the liquid crystal panel when forming the display pattern of
FIG. 1;
FIG. 7 is a perspective view of a liquid crystal panel having another ideal
display pattern:
FIG. 8 is a perspective view of a liquid crystal panel showing the actual
display condition when the display pattern of FIG. 7 is formed;
FIGS. 9A-9C and 10A-10C are graphs of waveforms of the voltage actually
applied to the liquid crystal panel when forming the display pattern of
FIG. 7;
FIG. 11 is a perspective view of a liquid crystal panel wherein another
ideal display pattern is formed;
FIG. 12 is a perspective view of the actual display when the display
pattern of FIG. 11 is formed;
FIGS. 13A-13C and 14A-14C are graphs of waveforms of the voltage actually
applied to the liquid crystal panel for forming the display pattern of
FIG. 11;
FIG. 15 is a view showing the actual display when the display pattern of
FIG. 16 is formed;
FIG. 16 is a perspective view of a liquid crystal panel wherein another
ideal display pattern is formed;
FIGS. 17A-17C and 18A-18C are graphs of waveforms of the actual voltage
applied to the liquid crystal panel for forming the display pattern of
FIG. 16;
FIG. 19 is a perspective view of the liquid crystal panel wherein another
ideal display pattern is formed;
FIG. 20 is a perspective view of the actual display condition when the
display pattern of FIG. 19 is formed;
FIGS. 21A-21C and 22 are graphs of waveforms of the voltage actually
applied to the liquid crystal panel at the time of forming the display
pattern of FIG. 19;
FIG. 23 is a perspective view of a liquid crystal panel wherein another
ideal display pattern is formed;
FIG. 24 is a view showing the actual display condition when the display
pattern of FIG. 23 is formed;
FIGS. 25A-25C and 26 are waveforms of the voltage actually applied to the
liquid crystal panel at the time of forming the display pattern of FIG.
23;
FIG. 27 is a block diagram of the liquid crystal display device constructed
in accordance with the present invention;
FIG. 28; is a schematic diagram of a liquid crystal unit constructed in
accordance with the invention;
FIG. 29 is a timing chart for the control signal and the data signal in
accordance with the present invention;
FIG. 30 is a block diagram of a compensation circuit in accordance with the
present invention;
FIG. 31 is a circuit diagram of the power circuit in accordance with the
present invention;
FIG. 32 is a perspective view of a liquid crystal panel wherein a display
pattern is displayed;
FIGS. 33A-33C are graphs of the voltage waveform applied to form the
pattern of FIG. 32;
FIG. 34 is a partial exploded view of the waveform of FIG. 33B;
FIG. 35 is a block diagram of a liquid crystal display device in accordance
with a second embodiment of the invention;
FIG. 36 is a block diagram of a compensation circuit in accordance with the
second embodiment of the invention;
FIG. 37 is a circuit diagram of a power circuit in accordance with the
second embodiment of the invention;
FIGS. 38A-38C are graphs of the voltage waveforms applied for forming the
pattern shown in FIG. 32;
FIG. 39 is a partial exploded view of the waveform of FIG. 38B;
FIG. 40 is a block diagram of the liquid crystal display device in
accordance with a third embodiment of the invention;
FIG. 41 is a circuit diagram of a power circuit constructed in accordance
with the third embodiment of the invention;
FIG. 42 is a block diagram of a liquid crystal display device in accordance
with a fourth embodiment of the invention;
FIG. 43 is a circuit diagram of a circuit constructed in accordance with
the fourth embodiment of the invention;
FIG. 44 is a graph of an experimental function waveform;
FIG. 45 is a graph of a ramp voltage waveform;
FIG. 46 is a schematic diagram of a function waveform generating circuit
constructed in accordance with the invention;
FIG. 47 is a block diagram of a liquid crystal display device constructed
in accordance with a fifth embodiment of the invention;
FIG. 48 is a circuit diagram of a power source constructed in accordance
with the fifth | | |
