Active matrix type liquid crystal display apparatus used for...

Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix

Reexamination Certificate

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Details

C345S096000

Reexamination Certificate

active

06239779

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display apparatus preferably applicable to a projection-type display system or a projector, and more particularly to an active matrix type liquid crystal display apparatus capable of suppressing a drive frequency in a row signal electrode drive circuit and realizing an excellent AC driving of the liquid crystal elements, thereby improving the quality in the liquid crystal video display. Furthermore, the present invention relates to an improvement of video display quality robust against adverse influence of the wiring resistance etc.
Conventionally, transmission-type liquid crystal display apparatuses are adopted in many of projection-type display systems and projectors. On the other hand, reflection-type liquid crystal display apparatuses have been recently used to attain a higher aperture rate under the severe requirement of high densification of pixels and also to realize higher resolution as well as higher brightness.
In both cases, improvement of the display quality and reduction of the costs are strictly required.
FIG. 8
shows a fundamental arrangement of a conventional active matrix type display apparatus employed in the transmission-type and reflection-type liquid crystal display apparatuses.
In
FIG. 8
, Di (i=1,2,3, - - - ) represents a plurality of row signal electrodes and Gj (j=1,2,3, - - - ) represents a plurality of line scanning electrodes. The row signal electrodes Di (i=1,2,3, - - - ) and the line scanning electrodes Gj (j=1,2,3, - - - ) are arranged in a matrix pattern on a substrate. An active element circuit, consisting of a switching transistor
1
and an auxiliary capacitor
2
, is formed at respective intersections formed by the row signal electrodes Di and the line scanning electrodes Gj. A plane pixel electrode
3
is provided on each surface dissected by the row signal electrodes Di and the line scanning electrodes Gj. Each pixel electrode
3
is connected to a connecting point between the switching transistor
1
and the auxiliary capacitor
2
in each active element circuit. A liquid crystal orientation film (not shown) is provided on the upper surface of the pixel electrode
3
.
The liquid crystal orientation film and a common electrode film
4
are provided on a glass substrate (not shown), which is positioned in a confronting relationship with the substrate for the above-described active elements. A liquid crystal
5
is sealed tightly in a clearance space between these opposed substrates, so as to form a light modulating section.
Each row signal electrode Di is driven by an analog switch
6
-i connected to this row signal electrode Di. A plurality of analog switches
6
-i (i=1,2,3, - - - ) are associated with a horizontal shift register
7
to form a row signal electrode drive circuit
8
. Each line scanning electrode Gj is driven by a line scanning electrode drive circuit
9
. The row signal electrode drive circuit
8
and the line scanning electrode drive circuit
9
are disposed along the sides of the light modulating section.
More specifically, in the row signal electrode drive circuit
8
, the horizontal shift register
7
is activated in response to a horizontal reset signal (i.e., HRST) and a horizontal shift clock (i.e., HCLK) sent from a drive timing pulse generating circuit (not shown). The activated horizontal shift register
7
successively turns on and off analog switches
6
-i (i=1,2,3, - - - ) to supply a video signal Sig of each horizontal scanning period to a corresponding row signal electrode Di.
The line scanning electrode drive circuit
9
is formed by a vertical shift register which is activated in response to a vertical reset signal (i.e., VRST) and a vertical shift clock (i.e., VCLK) entered from the drive timing pulse generating circuit (not shown). The activated vertical shift register successively applies a select pulse to each line scanning electrode Gj to successively turn on each switching transistor
1
for one horizontal scanning period.
Accordingly, the video signal supplied to the row signal electrode Di charges the auxiliary capacitor
2
via the switching transistor
1
connected to a currently selected line scanning electrode Gj. The electrical potential (i.e., the voltage) of the pixel electrode
3
varies in accordance with the charging of the auxiliary capacitor
2
. Thus, each pixel region of the liquid crystal
5
is independently activated in response to the voltage of the pixel electrode
3
so as to realize a pixel-by-pixel modulation of the reading light irradiated to the light modulating section.
FIG. 9
shows the relationship between horizontal scanning signals (1,2,3, - - - ) included in the video signal Sig of the non-interlaced scanning type (i.e., the ordered scanning type) and application of the selection pulse to each line scanning electrode Gj (i=1,2,3, - - - N) in the line scanning electrode drive circuit
9
.
As apparent from
FIG. 9
, to realize the AC driving of the liquid crystal element
5
, the polarity of the video signal Sig is alternately inverted in synchronism with the start timing of each vertical scanning period (i.e., frame period) so that the video signal Sig has opposed electrical potentials with respect to a predetermined reference potential between two neighboring vertical scanning periods. Respective line scanning electrodes Gj (i=1,2,3, -) are successively turned on in response to the selection pulse corresponding to each horizontal scanning period. Each pixel signal is supplied to each row signal electrode Di by closing the corresponding analog switch
6
-i during the turning-on duration of each line scanning electrode Gj.
As a result, the light modulating section forms the frame video at the end of each vertical scanning period, so as to obtain the projection light of the pixel-by-pixel modulated frame video.
As described above, the liquid crystal display apparatus forms the frame video based on the video signal Sig of the non-interlaced scanning type. In other words, it was difficult to realize the similar video display by performing the horizontal scanning of the video signal of the interlaced scanning type (i.e., the jump-over scanning type). This is because the AC driving of approximately 30 Hz is definitely necessary for activating the liquid crystal, as understood from
FIG. 9
wherein the polarity of the video signal Sig is inverted in synchronism with the start timing of each vertical scanning period.
However, Japanese Patent No. 7-32473 (publication of the examined patent application) discloses a liquid crystal display apparatus capable of realizing a high-quality video display by using the video signal of the interlaced scanning type. According to this prior art, the activating method of the line scanning electrodes is characteristic.
FIG. 10
shows a fundamental arrangement of the liquid crystal display apparatus disclosed in Japanese Patent No. 7-32473. Both the light modulating section and the row signal electrode drive circuit
8
are formed in the same manner as those disclosed in FIG.
9
. However, a line scanning electrode drive circuit
10
is formed by a vertical shift register whose stage number is approximately a half of the total display line number. Output terminals of the line scanning electrode drive circuit
10
are connected to the odd-number line scanning electrodes Gj (j=1,3,5, - - - ). There are a plurality of analog switches
11
-p (p=1,2,3, - - --), each selectively connecting an even-number line scanning electrode Gj (j=2,4,6, - - - ) to one of two neighboring odd-number line scanning electrodes Gj (j=1,3,5, - - - ) in synchronism with the start timing of each field period.
According to this apparatus, the switching of the analog switch
11
-p (p=1,2,3, - - - ) is performed in response to the video signal Sig of the interlaced scanning type. More specifically, a switching control signal O/E (i.e., odd/even field signal) is supplied to each analog swi

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