Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-10-12
2002-10-08
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S4770HC, C313S482000, C313S318010, C313S318050, C439S602000, C439S617000, C439S618000
Reexamination Certificate
active
06462466
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color cathode ray tube, and, more particularly, to a color cathode ray tube which can reduce deflection electric power and has improved focusing characteristics to increase the resolution of a display image on the color cathode ray tube.
A color cathode ray tube generally has a panel, a funnel connected to this panel, and a vacuum envelope comprised of a stem which is welded to the end of the cylindrical neck of the funnel. Disposed in the neck of the funnel is an electron gun assembly that emits three electron beams. Those electron beams are deflected by magnetic fields, which are generated by horizontal and vertical deflection coils of a deflection yoke mounted on the funnel, to be directed via a shadow mask toward a phosphor screen which is comprised of a three-color phosphor layer and provided on the inner surface of the panel. As this phosphor screen is scanned horizontally and vertically with the electron beams, a color image is displayed.
Of such color cathode ray tubes, a currently leading one is an in-line type which emits a line of three electron beams that pass the same plane of the electron gun, and, what is more, a self-convergence type which generates a pin-cushion magnetic field from the horizontal deflection coil of the deflection yoke and a barrel magnetic field from the vertical deflection coil and can converge a line of three electron beams on anywhere on the screen without any compensation circuitry is widely put to a practical use.
Generally, about 35% of the electric power consumed by a color cathode ray tube is horizontal deflection electric power, about 10% is vertical deflection electric power and about 45% is consumed by the deflection yoke. To decrease the power consumption of color cathode ray tubes, therefore, it is most effective to reduce the power consumption of the deflection yoke.
One way of reducing the power consumption is to make the neck to be attached to the deflection yoke thinner to place the horizontal and vertical deflection coils closer to the electron beams.
FIG. 1
shows a relationship between the outside diameter of the neck and the horizontal deflection electric power in a typical color cathode ray tube with a deflection angle of 90° and the neck's outside diameter of 29.1 mm. As indicated by a straight line
1
in
FIG. 1
, the horizontal deflection electric power is substantially increased in proportion to the neck's outside diameter, and making the neck's outside diameter to 22.5 mm can reduce the horizontal deflection electric power to about 80% of what is consumed in a case of the neck having an outside diameter of 29.1 mm.
With the deflection angle being the same, the overall length of a color cathode ray tube gets longer as the screen size becomes larger. In general, the overall length of a color cathode ray tube is made shorter by increasing the deflection angle which however results in increased deflection electric power. With the neck's outside diameter of 29.1 mm, for example, setting the deflection angle to 100° increases the horizontal deflection electric power to 135% of the power consumed when the deflection angle is 90°, as indicated by a point
2
in FIG.
1
. With the neck's outside diameter of 22.5 mm, however, even when the deflection angle is set to 100°, an increase in horizontal deflection electric power can be suppressed to 108% of the power consumed in the case of the deflection angle of 90°, as indicated by a point
3
in FIG.
1
.
The aforementioned increase in deflection electric power not only leads to an increase in consumed energy but also raises the following problems. Particularly, for a tube with a deflection angle of 90° and deflection electric power greater than 110% of the deflection electric power of the standard tube with the neck's outside diameter of 29.1 mm, the cost for the circuitry which maintains the reliability of the deflection power supply circuit, such as the breakdown voltage characteristic and temperature characteristic, is increased significantly. Further, the leak magnetic field from the deflection yoke increases, which requires an improvement on the performance of a device which suppresses this increase. Those two problems lead to an increase in the overall cost of the apparatus that drives a color cathode ray tube. Furthermore, as the amount of heat generated by the iron loss and copper loss of the deflection yoke increases, it is necessary to enhance the heat generating characteristic of the deflection yoke itself. This leads to enlargement of the deflection yoke and an increase in the number of members used therein.
In view of the above, it is desirable to suppress an increase in deflection electric power to 10% or less of the power consumption of the standard tube, and with a deflection angle of 100°, the outside diameter of the neck should desirably be set to 23.2 mm or smaller.
Reducing the neck's outside diameter limits the number of potentials to be supplied to the electrodes of the electron gun disposed in the neck so that the desired focusing performance will not be exhibited, resulting in an insufficient resolution.
In other words, the aforementioned, self-convergence in-line type color cathode ray tube generates non-uniform magnetic fields, a pin-cushion type horizontal deflection magnetic field and a barrel type vertical deflection magnetic field, the electron beams are affected by the deflection defocusing to form deformed beam spots on the peripheral portion of the screen, thus reducing the resolution. To overcome this problem, the self-convergence in-line type color cathode ray tube uses a dynamic focusing electron gun which changes the focusing voltage for the electron gun in synchronism with the deflection of the electron beams and apply the changed voltage to the multi-pole lens that is formed by the electron gun to thereby compensate for the deflection difference.
FIG. 2
shows a typical dynamic focusing electron gun. This electron gun comprises three cathodes KB, KG and KR for generating three electron beams in a line to cause light rays emitted from the three-color phosphor layer which constitutes the phosphor screen, three heaters HB, HG and HR for respectively heating the cathodes KB, KG and KR, an integral assembly of a first grid G
1
, a second grid G
2
, a third grid G
3
, a fourth grid G
4
, first and second segment electrodes G
51
and G
52
of a fifth grid G
5
and a sixth grid G
6
which are arranged in the named order from the cathodes KB, KG and KR toward the phosphor screen, and a shield cup C attached to the sixth grid G
6
.
A voltage obtained by superimposing a video signal on a DC voltage of about 150V is applied to the three cathodes KB, KG and KR via three respective conductive wires
7
provided at a stem
6
which seals the end portion of a neck
5
, and a heater voltage of about 6.3V is applied to the three heaters HB, HG and HR via two respective conductive wires
7
. A ground potential or a potential close to the ground one is applied to the first grid G
1
via one conductive wire
7
. A voltage of 500V to 900V is applied via one conductive wire
7
to the second grid G
2
and the fourth grid G
4
, which are connected together in the tube. A focus adjusting voltage of 6 KV to 9 KV which adjusts the focus states of the electron beams is applied via one conductive wire
7
to the first segment electrode G
51
of the fifth grid G
5
. A dynamic focusing voltage, obtained by superimposing a voltage which varies in synchronism with the deflection of the electron beams on a DC voltage of 6 KV to 9 KV, is applied via one conductive wire
7
to the second segment electrode G
52
which is connected to the third grid G
3
in the tube. The application of the dynamic focusing voltage changes the strength of the multi-pole lens formed between the second segment electrode G
52
and the first segment electrode G
51
and the strength of the main lens formed between the second segment electrode G
52
and the sixth grid G
6
, thereby adjusting the focus
Hoshino Fumitaka
Ichikawa Masatoshi
Koba Hiroyuki
Sugawara Shigeru
Takata Hidenori
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Nimeshkumar D.
Roy Sikha
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