Note: Descriptions are shown in the official language in which they were submitted.
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DISPLAY APPARATUS
The present invention generally relates to a display
apparatus for image reproduction, character display or the
like using a cathode-ray tube (hereinafter referred to
as CRT).
An in line shaped self convergence CRT system
(hereinafter referred to as non-uniform magnetic system) in a
television field causes considerable resolution deterioration
when electronic beams are deflected with deflection yokes.
Especially, the deterioration in picture scenes and their
circumferences is noticeable. Various proposals have been
made to settle this problem. A dynamic focusing system is
available to remove the difference in focusing, for example,
between the central portion of the picture scene and the
circumference portion. In order to remove the deflection
distortion in the circumference, there are an electromagnetic
correcting system as disclosed in Japanese Laid-Open Patent
Publication No. 57-84683, and an electrostatic system
represented by a DAF system.
Exceptional resolution deterioration is caused in the
deflection of an electron beam in a wide range, even if the
yoke is a uniform magnetic field deflection yoke. Especially,
the deterioration in the picture scene circumference is
exceptional. A proposal similar to the above description is
provided and introduced.
The above described Japanese Laid-Open Patent Publication
No. 57-84683 is complicated in construction and composition,
and is of high cost. The electrostatic system to be
represented by the DAF system is high in applied voltage, with
problems in terms of reliability and cost.
Accordingly, the present invention has been developed
with a view to substantially eliminating the above discussed
drawbacks inherent in the prior art and has for its essential
object to provide an improved display apparatus.
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Another object of the present invention is to provide an
improved apparatus in which the resolution deterioration in
the picture scene and its vicinities is corrected with a
prefocus lens portion of an electron gun to obtain an optimum
image, with the electronic beam shape being modulated with
parabolic wave forms of horizontal, vertical periods of the
parabolic wave forms and frequency components of the image
signals (hereinafter referred to as to a dynamic prefocus
system).
Still another object of the present invention is to
provide an improved display apparatus in which a moire
phenomenon caused by correlation between the electronic beam
spot and a shadow mask is removed so as to reduce the light
emission saturation phenomenon of the phosphor caused by
concentration of the electron beam spots.
In accomplishing these and other objects, the present
invention adopts a dynamic prefocusing system. In accordance
with one aspect of the present invention there is provided a
display apparatus including a CRT, said apparatus comprising:
a dynamic focus correction voltage generator, said dynamic
focus correction voltage generator generating a dynamic focus
correction voltage signal consisting of vertical and
horizontal cyclic parabolic waveforms and supplying said
signal to at least one main focus grid of the CRT; a
horizontal direction electron beam focusing determination
circuit, said horizontal direction electron beam focusing
determination circuit generating a horizontal direction spot
size signal in accordance with a high-pass component and
luminance component contained within an image signal input
thereto; a vertical direction electron beam focusing
determination circuit, said vertical direction electron beam
focusing determination circuit generating a vertical direction
spot size signal in accordance with a low-pass component
contained within said image signal input thereto; and an
electron beam focusing controller, said electron beam focusing
controller receiving said horizontal direction spot size
signal generated by said horizontal direction electron beam
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2a
focusing determination circuit and said vertical direction
spot size signal generated by said vertical direction electron
beam focusing determination circuit and outputting a signal in
response thereto; and a driving voltage generator, said
driving voltage generator receiving said dynamic focus
correction voltage signal and adding it to the output signal
of said electron beam focusing controller and supplying a
resultant added signal to at least one prefocus grid of the
CRT.
In accordance with another aspect of the present
invention there is provided a method of controlling a focus of
a CRT included within a display apparatus, said method
comprising the steps of: generating a signal consisting of a
vertical cyclic parabolic waveform and a horizontal cyclic
parabolic waveform and using the generated signal to control a
dynamic focus of the CRT by supplying the generated signal to
a main focus lens of the CRT; generating a horizontal
direction spot size signal generated in accordance with a
high-pass component and luminance component contained within
an image signal and a vertical direction spot size signal
generated in accordance with a low-pass component contained
within the image signal; combining the horizontal and vertical
direction spot size signals to form a combined signal; adding
the generated signal to the combined signal to generate a
signal which is applied to a prefocus lens of the CRT for
controlling a dynamic prefocus of the CRT.
As disclosed in laid-open Japanese Patent Publication No.
53-105168, published September 13, 1978 in the name of Kouzou
Tateishi, when a cathode-ray-tube having an electron gun is
used so that auxiliary acceleration, focusing electrodes are
provided on the cathode side of the accelerating electrode or
on the main lens side, rectangular or similarly shaped
electronic transmission apertures are formed in each of a
control electrode, an accelerating electrode and an auxiliary
accelerating electrode, the above described control electrode
is arranged so that the major axis direction of the electronic
transmission aperture can become vertical to the main scanning
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2b
direction of the electron beam, the electronic transmission
aperture of either the above described accelerating electrode
or the auxiliary acceleration focusing electrode are arranged
so that the major axis direction thereof can become orthogonal
to the major axis direction of the electronic transmission
aperture of the above described control electrode, the
electronic transmission aperture of the other electrode is
arranged so that the major axis direction can become parallel
to the major axis direction of the electronic transmission
aperture of the above described control electrode, or when a
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cathode-ray-tube having an electron gun is used so that an
auxiliary acceleration, focusing electrode is arranged on the
cathode side of the accelerating electrode or on the main
control electrode, a round shaped or a rectangular electronic
transmission aperture is formed at each of the control
electrode, accelerating electrode and auxiliary accelerating
electrode, the dynamic voltage is applied to the auxiliary
acceleration focusing electrode so as to reduce the
deterioration of the resolution with the voltage for
correcting the focusing shift and astigmatism distortion in
the picture scene vicinity portion being piled.
At the same time when the high frequency components are
many through the detection of the frequency components of the
reproducing image signal, the electron beams are made long
vertically. When the low frequency components are many, the
electron beams are made long horizontally. Higher fidelity,
higher acuteness and higher resolution of the reproduced
images may be achieved across the whole picture scenes without
the moire phenomenon being caused.
The present invention corrects the focus shift of the
electronic beam spot of the picture scene and its vicinity
portion, and reduces astigmatism by the above described
construction. The present invention controls the shape of the
electron beam spot in accordance with the frequency component
of the image signal across the whole picture scene, so that
the bright point shape on the fluorescent screen can be
selectively determined. An electron beam bright point of high
current density is obtained and the light emitting saturation
of the phosphor can be removed.
In the drawings:
Fig. 1 is a perspective exploded view showing an electron
gun electrode construction of a CRT of a first embodiment of
the present invention;
Fig. 2 is a perspective exploded view showing an electron
gun electrode construction of a CRT of a second embodiment of
the present invention;
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Fig. 3 is a spot shaped, control, dynamic prefocus
driving circuit diagram of an electron beam in the first
embodiment of the present invention;
Fig. 4 is a dynamic prefocus driving circuit diagram in
the second embodiment of the present invention;
Figs. 5(a) to (j), show signal wave-form charts of the
construction of Fig. 3 in the first embodiment of the present
invention, and
Figs. 6(a) to (j), show signal wave-form charts of the
construction of Fig. 4 in the second embodiment of the present
invention.
The present invention reduces the peripheral focus
deterioration due to a large image scene, by the flattening
operation by a dynamic prefocus driving circuit composed of
five blocks to achieve improvements in the fidelity, acuteness
and resolution of the images across the whole picture scene.
(Embodiment 1)
One embodiment of the present invention will now be
described with reference to the drawings.
Fig. 1 shows the electrode construction of a CRT to be
used in the present circuit. Secondary electrodes are two in
number. They are both rectangular and in the shape of the
electron beam transmission aperture. The major axes of the
respective rectangles are orthogonal. It is characteristic
that the spot shape of the electron beam by the voltage
applied to the electrode can be controlled (Japanese Patent
Publication No. 61-6970).
First, a dynamic astigmatism correcting voltage
generating portion 19 will be described in Fig. 3. Image
signals of the terminal 10 pass through a vertical saw tooth
wave generating circuit 11 and a vertical parabolic wave
generating circuit 12 to form vertical parabolic waves. The
same image signals pass through a horizontal pulse wave
generating circuit 13, a phase shift control circuit 14, and a
horizontal parabolic wave generating circuit 15 to obtain the
horizontal parabolic waves. The vertical parabolic waves of
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the outputs of these circuits and the horizontal parabolic
wave of the outputs of these circuits are added at a first
adding circuit 16, and are inputted into a V G2S driving
voltage generating portion 59.
A horizontal direction electron beam shaped detecting
deciding portion 29 is composed of a high-pass component
detecting circuit 21, a brightness signal component detecting
circuit 22 and a second adding circuit 23. An image signal on
the terminal 10 passes through the high-pass component
detecting circuit 21, and signals equivalent to the outline
among the image signals are outputted. The same image signal
passes through the brightness signal component detecting
circuit 22 and signals equivalent to the brightness among the
image signals are outputted. Both the above described outputs
are added by the second adding circuit 23 and are inputted to
an electron beam form control circuit 49. The signal decides
the spot size in the horizontal direction and at the same
time, has a level adjusting function.
A vertical direction electron beam form detection
deciding portion 39 is composed of a delay line 31 and a
subtracting circuit 32 ~or delaying the image signal by lH.
A signal of the difference between the original signal and the
signal delayed by lH is made by a subtracting circuit 32, and
is inputted to an electron beam form controlling circuit 49.
The signal decides the spot size in the vertical direction
and, at the same time, has a level adjusting function.
In the electron beam shaped control circuit 49, signals
for a horizontal direction electron beam from the detection
deciding portion 29 and signals for the vertical direction
electron beam from the detection deciding portion 39 are
inputted. They are converted into signals for controlling the
electron beam form to input the output signal into a third
adding circuit 51.
The V G2S driving voltage generating portion 59 is
composed of the third adding circuit 51 and a V G2 voltage
generating circuit 52. A voltage V G2S controlled by the
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third adding circuit 51 is applied to an auxiliary
acceleration focusing electrode G2S (4 of Fig. 1).
Figs. 5(a) to (j) show signal wave-form charts of the
above described operations. Figs. 5(a) to (j) use
asymmetrical shafts in Fig. 1. The beam spot form in the
focus is controlled in the electron beam shape.
By the use of the above described prefocus driving
circuit, the deflection distortion and the geometric
distortion of the electronic beam by the non-uniform magnetic
deflection are improved. Further, the vertical direction and
horizontal direction frequency component of the image signals
are detected. The electron beam form is controlled (the
formation of the vertical length beam spot and the horizontal
length beam spot are freely effected so that the brightness
point shape on the fluorescent screen can be selectively
determined) so that a display apparatus of higher acuteness,
higher resolution can be obtained.
(Embodiment 2)
A second embodiment of the present invention will be
described hereinafter with reference to the drawings.
The electrode construction of a CRT to be used in the
circuit of the presen~ invention will be described in Fig. 2.
The second electrodes are two in number. They are both round
and square in the shape of the electron beam transmission
aperture. It is characteristic that the focusing of the
electronic beam spot can be controlled by the voltage to be
applied to the electrode. The dynamic focusing voltage
generating portion 60 will be described in Fig. 4. The image
signals of the terminal 10 pass through a vertical saw tooth
wave generating circuit 11 and a vertical parabolic wave
generating circuit 12 to form vertical parabolic waves. The
same image signals pass through the horizontal pulse wave
generating circuit 13, the phase-shifting control circuit 14,
and the horizontal parabolic wave generating circuit 15 to
obtain the horizontal parabolic waves. The vertical parabolic
waves of the output of the vertical parabolic wave generating
circuit 12 and the horizontal parabolic waves of the output of
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the horizontal parabolic wave generating circuit 15 are added
by the first adding circuit 16, and are inputted to the V G2S
driving voltage generating portion 59.
The horizontal direction beam focusing detection deciding
portion 29 is composed of the high-pass component detecting
circuit 21, the brightness signal component detecting
circuit 22, and the second adding circuit 23. The image
signals of the terminal 10 pass through the high-pass
component detecting circuit 21, and signals equivalent to the
outlines among the image signals are outputted. The same
image signals pass through the brightness signal component
detecting circuit 22, and signals equivalent to the brightness
in the image signal are outputted. Both the above described
outputs are added by the second adding circuit 23 and are
inputted to the electron beam focus control circuit 63. The
signal decides the spot size, and at the same time, has a
level adjusting function.
The vertical direction beam focus detection deciding
portion 62 is composed of the delay line 31 and the
subtracting circuit 32 for delaying by lH the image signals.
Signals of difference between the original signals and the lH
delayed signals by the subtracting circuit 32 are made and are
inputted to the electron beam focus control circuit 63. The
signal decides the spot size and, at the same time, has a
level adjusting function.
In the electron beam focusing control circuit 63, signals
for the horizontal direction beam focus detection deciding
portion 61 and the signals for the vertical direction beam
focus detection deciding portion 62 are inputted. They are
converted into the electron beam focusing signals to input the
output signals into a third adding circuit 51.
The V G2S driving voltage generating portion 59 is
composed of the third adding circuit 51 and a V G2S voltage
generating circuit 52 so as to apply a voltage V G2S
controlled by the third adding circuit 51 to the auxiliary
acceleration focusing electrode G2S (8 of Fig. 2).
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By the use of the above described dynamic prefocus
driving circuit, the difference in focus between the central
portion of the picture screen and its vicinity portion is
removed. Further, the vertical direction and horizontal
direction frequency component of the image signal is detected
to control the focusing of the electron beam, so that a
display apparatus of higher acuteness and higher resolution
may be obtained. Figs. 6(a) to (j) show signal wave-form
charts of the above described operations. Figs. 6(a) to (j)
use a symmetrical shaft of Fig. 2 as a CRT. The beam spot in
focus changes with respect to the increase or decrease in the
beam current.
As is clear from the above described embodiment, the
present invention improves the focus shift of the electron
beam around the picture screen of the CRT, and further
controls the focus of the electron beam in accordance with the
component of the image signal across the whole picture screen,
so that a display apparatus of higher fidelity, higher
acuteness and higher resolution can be obtained.
As is clear from the above described embodiment,
according to the present invention, the focusing shift,
astigmatism distortion of the electron beam causing the
picture scene peripheral portion to be accompanied by a
flattening of the large picture scene CRT, are reduced or
prevented. The spot shape of the electron beam is controlled
in its vertical length, and horizontal length in accordance
with the components of the image signals across the whole
picture scene, so that a display apparatus of higher fidelity,
higher acuteness and higher resolution of the images can be
obtained.
Although the present invention has been fully described
by way of example with reference to the accompanying drawings,
it is to be noted here that various changes and modifications
will be apparent to those skilled in the art. Therefore,
unless otherwise such changes and modifications depart from
the scope of the present invention, they should be construed
as included therein.
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