Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1998-05-26
2001-03-06
Shankar, Vijay (Department: 2778)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S098000, C369S044230, C369S112040
Reexamination Certificate
active
06198465
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system for producing a liquid crystal driving signal and an optical disc reproducing system provided with the system for producing a liquid crystal driving signal.
Recently, the DVD (Digital Versatile Disc) having a large capacity larger than that of the compact disc has been proposed. Since the DVD has a high density, the tilt angle margin of the disc at the reproducing thereof is small. Therefore it is desirable to provide a control means for adjusting the tilt angle in the reproducing system.
The assignee of the present invention proposed a system for correcting the wavefront aberration by using a liquid crystal panel, the aberration is caused by the inclination of the thickness of the disc, in the Japanese Patent Application Laid Open Publication 9-128785.
FIG. 6
shows an optical disc reproducing system using the principle disclosed in the publication. A laser beam emitted from a laser
1
is reflected from a half mirror
2
, passes through a liquid crystal panel
3
and applied to an optical disc
5
by an objective
4
to form a spot on the disc.
A laser beam reflected from the optical disc
5
passes through the objective
4
, liquid crystal panel
3
, and half mirror
2
, and condensed on a photo-detector
7
by a condenser lens
6
. Thus, a pickup is composed.
A tilt sensor
8
is provided adjacent the pickup for detecting the tilt angle of the disc
5
. The tilt sensor
8
has one light emitter and two photo-detectors which receive light reflected from the disc
5
. Outputs of the two photo-detectors are applied to an adder
10
which produces a difference of the outputs as a tilt error signal. The error signal is fed to an A/D converter
11
.
A CPU
17
applies a control signal based on the error signal to a gain adjuster
13
. The gain adjuster
13
adjusts the amplitude (gain) of a standard signal fed from an oscillator
12
in accordance with the control signal. The standard signal has, for example, a duty ratio of 50%. The adjusted standard signal is applied to the liquid crystal panel
3
as a driving signal. The gain adjuster
13
comprises a plurality of adjusting devices, each of which is connected to each electrode piece of the liquid crystal panel so as to adjust the tilt angle of the disc
5
as described hereinafter.
FIG. 7
a
is a sectional view of the liquid crystal panel
3
, and
FIG. 7
b
is a plan view of the panel. The liquid crystal panel
3
comprises opposite transparent glass substrates
301
a
and
301
b
, transparent electrodes
302
a
and
302
b
evaporated on the substrates
301
a
,
301
b
, orientation films
303
a
and
303
b
, and liquid crystal
303
sealed between the orientation films.
At least one of the electrodes
302
a
and
302
b
comprises a plurality of electrode pieces
302
c
arranged in matrix as shown in
FIG. 7
b
. Each of the electrode pieces
302
c
is connected to a corresponding gain adjuster
13
.
FIG. 8
shows a molecule M of the liquid crystal
304
. The molecule M has a refractive index of n1 in the optical axis and a refractive index of n2 in the direction perpendicular to the optical axis. Namely, the liquid crystal is a double refraction crystal having different refractive indexes in direction. For example, the liquid crystal is nematic liquid crystal.
FIGS. 9
a
to
9
c
show various directions of molecules M when applied voltage is changed.
FIG. 9
a
shows the direction when no voltage is applied.
FIGS. 9
b
and
9
c
shows directions when alternating voltages e
1
and e
2
are applied (e
1
<e
2
).
As shown in figures, the direction of the molecule changes from the horizontal direction to the vertical direction.
Each of
FIGS. 9
a
to
9
c
shows the state when equal voltages are applied to all electrode pieces of the liquid crystal
3
so that the directions of the molecules in each figure is the same. However, if the voltage applied to each electrode piece is different from that of other pieces, the direction necessarily changes. Thus, the refractive index of each molecule can be changed between n1 and n2.
When the refractive index of the liquid crystal is changed, the light beam passing through the liquid crystal changes in the optical path of the difference given by the following formula.
Optical path difference: &Dgr;n·d
where &Dgr;n is the change quantity of the refractive index and d is the thickness of the liquid crystal.
This means that a phase difference obtained by the following formula is given to the light beam passing through the liquid crystal.
Phase difference: &Dgr;n·d(2&pgr;/&lgr;)
where &lgr; is the wavelength of the light beam.
Therefore, it is possible to correct the wavefront aberration caused by the inclination of the disc by controlling the refractive index n of each part of the liquid crystal so as to cancel the aberration generating in the objective
4
.
However, in the liquid crystal driving signal producing system, it is a problem to realize the controlling of the amplitude of the liquid crystal driving signal.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a novel system for producing a liquid crystal driving signal.
According to the present invention, there is provided a system for producing a driving signal for a liquid crystal panel, for correcting a wavefront aberration in an optical system for an optical disc, the liquid crystal panel having a plurality of unit electrodes.
The system comprises an oscillator, a low pass filter for limiting a frequency band of an oscillating signal produced from the oscillator, and control means for producing a control signal for setting a cutoff frequency of the low pass filter so as to change an amplitude of the output signal of the low pass filter in accordance with a refractive index at each of the unit electrode of the liquid crystal panel.
The system further comprises a level shifter for shifting the level of the oscillation signal from the oscillator, a tilt sensor for detecting a tilt of the optical disc and for producing a tilt signal, the control means is provided for producing the control signal dependent on the tilt signal so as to correct the wavefront aberration.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.
REFERENCES:
patent: 5526058 (1996-06-01), Sano et al.
patent: 5793735 (1998-08-01), Oono
patent: 5949393 (1999-09-01), Sakai et al.
patent: 0 537 904 A2 (1991-10-01), None
Japanese Patent Application Publication No. 9-128785, by Otaki Masaru et al., dated May 16, 1997.
Abstract of Japanese Patent Application Publication No. 9-128785, by Otaki Masaru et al., dated May 16, 1997.
Araki Yoshitsugu
Furukawa Jun-ichi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Pioneer Electronic Corporation
Said Mansour M.
Shankar Vijay
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