Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-07-30
2003-11-11
Hjerpe, Richard (Department: 2674)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S089000, C345S209000, C345S214000, C345S690000
Reexamination Certificate
active
06646628
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal projector apparatus capable of modulating light from a light source by means of a plurality of liquid crystal panels and projecting synthetic light transmitted or reflected by the liquid crystal panels as a color image, and particularly to a liquid crystal projector and an adjusting method thereof that prevent luminance variation from occurring in each frame on a display screen of such a liquid crystal display.
Television receivers and the like have been spread which form a liquid crystal projector with a light source such as a lamp and a plurality of liquid crystal panels or spatial light modulators to project a color image on a screen or the like.
Such a liquid crystal projector generally separates white light emitted from the lamp into three primary colors by means of a dichroic mirror, modulates light of each of the three primary colors by means of a liquid crystal panel, and thereafter combines the three pieces of light with each other by means of a dichroic prism or the like. Then the liquid crystal projector projects the combined light onto a screen or the like via a projection optical lens to thereby form a large screen.
FIG. 5
is a plan view of a configuration of a three-panel-type liquid crystal projector apparatus formed with one liquid crystal panel for each of the R, G, and B colors (hereinafter referred to simply as a liquid crystal projector).
The liquid crystal projector apparatus shown in
FIG. 5
condenses light emitted from a lamp
21
via an IR/UV cutoff filter in a light source optical system
30
, and thereafter performs color separation.
The light source optical system
30
comprises two microlens arrays
31
a
and
31
b
each having a set of microlenses, a polarization beam splitter
32
for aligning a plane of polarization of light, and a condenser lens
33
.
A white luminous flux that has passed through the light source optical system
30
first enters a dichroic mirror
34
for transmitting the red light R. Then, the dichroic mirror
34
transmits the red light R and reflects the green light G and the blue light B. The red light R transmitted by the dichroic mirror
34
is changed in traveling direction by 90°, for example, by a mirror
35
, and then guided to a liquid crystal panel
37
R via a field lens
36
R.
In the meantime, the green light G and the blue light B reflected by the dichroic mirror
34
are separated by a dichroic mirror
38
for transmitting blue light.
Specifically, the green light G is reflected and thereby changed in traveling direction by 90°, for example, and then guided to a liquid crystal panel
37
G via a field lens
36
G. The blue light B passes through the dichroic mirror
38
, thus traveling in a straight line, and then guided to a liquid crystal panel
37
B via a relay lens
39
, a mirror
40
, a relay lens
41
, a mirror
42
, and a field lens
36
B.
After being subjected to spatial light modulation by the liquid crystal panels
37
R,
37
G, and
37
B, the pieces of light of the RGB colors enter crossed dichroic prisms
43
as a light combining means to be spatially combined with each other. Specifically, the red light R is reflected by a reflection plane
43
a
and the blue light B is reflected by a reflection plane
43
b
in a direction of a projection lens
44
. The green light G passes through the reflection planes
43
a
and
43
b
, whereby the pieces of light of the three colors are combined with each other on a single optical axis.
Then, the projection lens
44
projects a magnified color image onto a screen
45
hung on a wall, for example, or a flat screen formed as a rear projector.
The R, G, and B liquid crystal panels
37
employed in the liquid crystal projector as described above generally have a transparent opposite electrode Pf and pixel electrode Pu with liquid crystal intermediate between the opposite electrode Pf and the pixel electrode Pu, as shown in
FIG. 6. A
thin-film transistor TFT serving as a switching device is formed by semiconductor techniques in part of the pixel electrode Pu in a divided pixel unit.
A gate of each thin-film transistor TFT is connected to a gate bus line Lx formed in a stripe manner in a line direction. A source of the thin-film transistor TFT is connected to a source bus line Ly arranged in a direction orthogonal to the gate bus line Lx.
A drain of each thin-film transistor TFT is connected to a transparent pixel electrode Pu divided for each pixel. A liquid crystal capacitance Cis is formed between an opposite electrode Pf and the pixel electrode Pu with liquid crystal intermediate between the opposite electrode Pf and the pixel electrode Pu.
Generally, the source bus lines Ly are sequentially selected in a horizontal direction by an X drive circuit to supply a display signal for one line, and the gate bus lines Lx are sequentially selected in a vertical direction, whereby a signal voltage for each pixel at an intersection of a source bus line Ly and a gate bus line Lx is supplied via a thin-film transistor to charge the liquid crystal capacitance Cis. Display information is thus written to modulate light passing through each liquid crystal pixel and thereby generate an image.
Incidentally, an auxiliary capacitance Cs as indicated by a dotted line is often formed for the purpose of compensating for leakage current between the source and the drain electrodes.
In some cases, black stripes are provided to the opposite electrodes Pf to minimize leak of light passing through portions other than the pixel electrode portions.
As described above, the liquid crystal panel (hereinafter referred to as the LCD panel) comprises an X shift register for sequentially selecting the source bus lines in a line direction to supply a video signal to be written; and a Y shift register for selecting the gate bus lines Lx to take in the supplied signal sequentially in a horizontal direction. Thus, active matrix driving is performed so that the video signal is written to each pixel in dot sequence or line sequence and the written signal is retained by a capacitance C (Cis+Cs) for a period of one field.
The driving of each LCD panel by direct-current voltage tends to cause electrochemical reaction in liquid crystal material and alignment layer material and at their interface, which results in faulty display. Therefore, in order to prevent application of the DC voltage to each pixel electrode of the LCD panel, an image signal with a field cycle whose polarity is reversed between positive and negative with a Vcom voltage as its center DC level is supplied, as shown in FIG.
7
.
Thus, the TFT type LCD panel employs a reversal driving method, in which the LCD panel is driven on the basis of an FRP signal for reversing signal polarity, and a display signal reversed in polarity at least in each field period is supplied to each pixel.
In the case of simple field reversal driving, it is difficult to perfectly balance the driving at the time of positive polarity and the driving at the time of negative polarity, and thus variation of transmitted light in each field generally results in a flicker occurring at half a frame frequency.
Hence, the signal to each LCD panel is reversed in each frame, and line-sequence reversal driving, which applies signals opposite to each other in polarity between adjacent lines, is performed to reduce variation of the luminance signal on each field screen.
Thus, when the Vcom voltage for setting the center direct-current level is set at an appropriate value for each LCD panel and line reversal for reversing polarity in each line is performed, luminance variation is reduced and thereby flicker is made less noticeable. However, when gray frames in which white and black are repeated in every two lines continue, a flicker or change in brightness in each scanning line still occurs because white is more noticeable than black.
Even in the case of dot reversal, which supplies a display signal reversed in polarity for each adjacent pixel in a horizontal direction, luminance variation remains, and the
Endo Hiroaki
Nagata Yuji
Shirochi Yoshiki
Dinh Duc Q
Frommer William S.
Frommer & Lawrence & Haug LLP
Hjerpe Richard
Kessler Gordon
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