Driving circuit for supplying tone voltages to liquid...

Details Driving circuit for supplying tone voltages to liquid... Driving circuit for supplying tone voltages to liquid...

2000-02-09

2004-06-08

Awad, Amr (Department: 2675)

Computer graphics processing and selective visual display system

Plural physical display element control system

Display elements arranged in matrix

C345S095000, C345S210000

Reexamination Certificate

active

06747624

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an LCD (liquid crystal display) panel driving circuit. In recent years, the LCD has rapidly been widespread as a display unit for television and office equipment for ordinary home use. The reasons behind this are that the LCD is thin and lightweight as compared to a CRT and the display quality is not very inferior to that of the CRT can be obtained.
BACKGROUND OF THE INVENTION
FIG. 1
is a schematic view showing the key portions of a conventional LCD panel driving circuit. The driving circuit comprises n units of selectors
11
(
1
),
11
(
2
), . . . ,
11
(
n
); n units of operational amplifiers
12
(
1
),
12
(
2
), . . . ,
12
(
n
) each operating as a buffer amplifier; and n units of output-polarity selection switches
13
(
1
),
13
(
2
), . . . ,
13
(
n
). Wherein n is a multiple of 2.
Of the selectors
11
(
1
),
11
(
2
), . . . ,
11
(
n
), for instance, odd-numbered selectors are dedicated to positive-polarity output, and even-numbered selectors are dedicated to negative-polarity output. Input into each of the selectors
11
(
1
),
11
(
3
), . . . ,
11
(n−1) dedicated to the positive-polarity output are, for instance, 6-bit data for positive-polarity output and a positive tone voltage. Input, on the other hand, into each of the selectors
11
(
2
),
11
(
4
), . . . ,
11
(
n
) dedicated to the negative-polarity output are, for instance, 6-bit data for negative-polarity output and a negative tone voltage.
Of the operational amplifiers
12
(
1
),
12
(
2
), . . . ,
12
(
n
), half of them are operational amplifiers dedicated to positive-polarity output, and the remaining half are dedicated to negative-polarity output. Output voltage from the selectors
11
(
1
),
11
(
3
), . . . ,
11
(n−1) for positive-polarity output respectively loaded into each of the non-inverted terminal of the operational amplifiers
12
(
1
),
12
(
3
), . . . ,
12
(n−1) for positive-polarity output.
Output voltage from the selectors
11
b
,
11
d
, . . . , and
11
n
for positive-polarity output is respectively loaded into each non-inverted input terminal of the operational amplifiers
12
b
,
12
d
, and
12
m
for negative-polarity output.
The output-polarity selection switches
13
(
1
),
13
(
2
), . . . ,
13
(
n
) are connected to output pads
14
(
1
),
14
(
2
), . . . ,
14
(
n
) respectively. The output pads
14
(
1
),
14
(
2
), . . . ,
14
(
n
) are electrically connected to a LCD panel not shown herein.
Effects of an LCD panel driving circuit are explained below together with each switching operation of the output-polarity selection switches
13
(
1
),
13
(
2
), . . . ,
13
(
n
). However, it is assumed that k is an integer of 1 or more than 1 for convenience in description. When
2
k
−1-th data D
2
k
−1 has a positive polarity, the data D
2
k
−1 is inputted into a
2
k
−1-th selector.
The
2
k
−1-th output-polarity selection switches are electrically connected towards positive polarity (the broken line shown in FIG.
1
). Therefore, the positive-polarity driving voltage output from the
2
k
−1-th selectors is output to
2
k
−1-th output pads via the
2
k
−1-th operational amplifiers and the
2
k
−1-th output-polarity selection switches.
Here,
2
k
-th data D
2
k
acquires a negative polarity and is inputted into
2
k
-th selectors. Therefore,
2
k
-th output-polarity selection switches are electrically connected towards negative polarity (the broken lines shown in FIG.
1
). Therefore, the negative-polarity driving voltage output from the
2
k
-th selectors is output to
2
k
-th output pads via the
2
k
-th operational amplifiers and the
2
k
-th output-polarity selection switches.
Namely, the driving voltages of
2
k
−1-th data lines acqure a positive-polarity driving voltage based on positive-polarity data D
2
k
−1, whereas the driving voltages of
2
k
-th data lines acquire a negative-polarity driving voltage based on negative-polarity data D
2
k.
The data D
2
k
−1 and data D
2
k
invert polarity at a prespecified cycle in the previous stages of the
2
k
−1-th and
2
k
-th selectors. The data D
2
k
-
1
with negative polarity is input into the
2
k
-th selectors. The data D
2
k
with positive polarity is input to the
2
k
−1-th selectors. The
2
k
−1-th output-polarity selection switches are electrically connected towards negative polarity (the solid line in FIG.
1
). The
2
k
-th output-polarity selection switches are electrically connected towards positive polarity (the solid line in FIG.
1
).
Therefore, the negative-polarity driving voltage output from the
2
k
-th selectors is output to
2
k
−1-th output pads via the
2
k
-th operational amplifiers and the
2
k
−1-th output-polarity selection switches. Each positive-polarity driving voltage outputted from the
2
k
−1-th selectors is output to
2
k
-th output pads via the
2
k
−1-th operational amplifiers and the
2
k
-th output-polarity selection switches.
Namely, the driving voltages of the
2
k
−1-th data lines acquire negative-polarity driving voltage based on negative-polarity data D
2
k
−1, whereas the driving voltages of the
2
k
-th data lines acquire positive-polarity driving voltage based on positive-polarity data D
2
k
. Therefore, a positive-polarity driving voltage based on the positive-polarity data D
2
k
−1 and a negative-polarity driving voltage based on the negative-polarity data D
2
k
−1 are alternately loaded to each driving voltage of the
2
k
−1-th data lines at a prespecified cycle.
Further, a negative-polarity driving voltage based on the negative-polarity data D
2
k
and a positive-polarity driving voltage based on the positive-polarity data D
2
k
are alternately loaded to each driving voltage of the
2
k
-th data lines at a prespecified cycle.
The positive-polarity driving voltage based on the positive-polarity data D
2
k
−1 and the negative-polarity driving voltage based on the negative-polarity data D
2
k
−1 are opposite in polarity, but has the same level. The same is true with respect to the negative-polarity driving voltage based on the negative-polarity data D
2
k
and the positive-polarity driving voltage based on the positive-polarity data D
2
k.
The reason why AC driving is performed such that a positive-polarity driving voltage and a negative-polarity driving voltage are alternately loaded to an identical pixel at a prespecified cycle as described above is because inconvenience of degradation in a liquid crystal under the situation where a voltage with the same polarity is kept on being loaded to an identical pixel should be avoided. However, screen flicker occurs due to AC driving. To suppress the flicker, in the LCD, driving voltages opposite in polarity are loaded to adjacent data lines, and voltages opposite in polarity are loaded to adjacent pixels.
In the above-described conventional type of LCD panel driving circuit, each driving voltage of the
2
k
−1-th data lines is prepared with each output voltage from the
2
k
−1-th operational amplifiers and each output voltage from the
2
k
-th operational amplifiers. Further, each driving voltage of the
2
k
-th data lines is also prepared with each output voltage from the
2
k
−1-th operational amplifiers and each output voltage from the
2
k
-th operational amplifiers.
Therefore, even when there are offset voltages in the
2
k
−1-th and
2
k
-th operational amplifiers, an offset difference does not occur between each driving voltage of the
2
k
−1-th data lines and each driving voltage of the
2
k
-th data lines. Similarly, even when there are offset voltages in the
2
k
+1-th and
2
k
+2-th operational amplifiers, an offset difference does not occur between each driving voltage of the
2
k
+1-th data lines and each driving voltage of the
2
k
+2-th data lines.
However, when an offset voltage in the
2
k
−1-th operational amplifier and that in the
2
k
&

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