Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
2000-06-26
2003-04-22
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C313S443000, C313S420000, C313S413000
Reexamination Certificate
active
06552484
ABSTRACT:
TECHNICAL FIELD
The present invention relates to deflection yokes used to adjust electron beam deflection in cathode ray tubes. In particular, the present invention pertains to conductive plates which may be used to replace or augment the deflection yokes used in cathode ray tubes.
BACKGROUND OF THE INVENTION
The invention relates to cathode ray tube (CRT) apparatuses having a display screen, an electron gun system to generate at least one electron beam, and a deflection unit (or deflection yoke) for deflecting the electron beam(s) in accord with a changing pattern.
In monochrome CRT's the electron gun system generates one electron beam which is directed onto the display screen, whereas color display tubes use electron gun systems which generate three electron beams which converge on the display screen.
Referring to
FIG. 1
which depicts a conventional cathode ray tube (CRT) apparatus including a vacuum envelope
10
which commonly resembles a trumpet shaped vacuum envelope having a narrow neck portion
12
and a wider portion which includes a display screen
14
. Toward one end of the narrow neck portion
12
lies the electron gun system
16
. At the opposite wider end of the envelope lies the display screen
14
which includes phosphorescent materials which radiate light when struck by electrons emitted from the electron gun system
16
.
The deflection yoke
20
, (also, referred to as a deflection system or deflection unit) commonly positioned about the narrow neck portion of the envelope, is designed to deflect the electron beam(s) emanating from the electron gun system
16
. The deflection yoke
20
is used to deflect the electron beam from its normal undeflected straight path, so that the beam impinges upon selected points on the display screen
14
to provide visual presentations. By varying the magnetic (or deflection) fields created by the deflection yoke
20
in a suitable manner, the electron beam(s) can be deflected upwards or downwards and to the left or to the right over the display screen. By simultaneously modulating the intensity of the beam a visual presentation of information or a picture can be formed on the display screen. A common example is the display of video images.
In three beam electron gun systems
16
the three deflected beams which correspond to different colors (for example, red, green, and blue (RGB)) are deflected such that the three beams each converge at the display screen
14
to produce the appropriate color in a manner known to those having ordinary skill in the art.
The shape and intensity of the magnetic deflection fields created by a deflection yoke vary throughout the CRT and along a distance the electron beam must travel. One typical field pattern is known as a “barrel” field, an example of which is shown in
FIG. 2
as a cross-section perpendicular to the CRT axis. As is well known in the art the field is called a “barrel” field because the separation between field lines
5
is greater near the center regions of the deflection field. The field depicted in
FIG. 2
results in a so-called North/South (NS) distortion “pin-cushion of otherwise horizontal lines. Another common field pattern is the so-called “pin-cushion” field depicted in FIG.
3
. As is also well known, the field is called a “pin-cushion” field because the separation between field lines
5
decreases near the center regions of the deflection field. The field depicted in
FIG. 3
results in a so-called NS barrel distortion. These and other field variations are known and used by practitioners having ordinary skill in the art in the design and application of suitable deflection yoke's
20
.
Many different coil configurations are used to establish the desired deflection field at each location within the vacuum envelope
10
. Typical examples of coils known in the art are saddle coils (
FIG. 4
a
), which are used in opposing pairs, and toroidal coils (
FIG. 4
b
).
A common type of deflection yoke comprises two sets of deflection coils positioned about the display enabling deflection of the electron beam in two directions which are transverse to each other. By way of example, a first set of saddle coils uses two coils which are arranged on oppositely located sides of the neck portion of the vacuum envelope. Another set of saddle coils can be oriented relative to the first set of coils by orienting them at 90° about the neck portion of the vacuum envelope. Such an arrangement is commonly referred to as a saddle-saddle (or S-S) coil arrangement (after the “saddle” shape of the deflection coils). One set of coils (the vertical deflection coils), when energized deflects the electron beam in a first (vertical) direction. Another set of coils (the horizontal deflection coils), when energized deflects the electron beam in a direction transverse to the first direction. The sets of deflection coils upon energization, generate a dynamic magnetic multi-pole field comprising at least a dipole component and a multi-pole component. Alternatively, the vertical set of saddle coils may be replaced with a so-called toroidal coil to form a hybrid coil arrangement called a saddle-toroidal (or S-T) arrangement. Still other applications may not use saddle type coils at all, instead using pairs of toroidal coils (in a toroidal-toroidal (T-T) arrangement).
Using a saddle-saddle arrangement as an example, the two sets of deflection coils are energized to produce two substantially orthogonal deflection fields. Inside the vacuum envelope the fields are substantially perpendicular to the path of the undeflected electron beam(s). A cylindrical core, comprised of material having a very high relative permeability (e.g., on the order of 1000), positioned to closely engage the sets of deflection coils (in a saddle-saddle configuration) is used to concentrate deflection fields generated by the coils and to increase the flux density in a deflection area. Also, an insulating liner is positioned between the two sets of coils to prevent electrical shorting between the coils.
With continued reference to
FIG. 1
, a cross section view of a saddle-toroidal (S-T) configuration is shown. A vacuum envelope
10
including a neck portion
12
, an electron gun system
16
for producing at least one electron beam, and a display screen
14
are shown. Also shown is a S-T type deflection yoke
20
including a pair of saddle deflection coils
21
a
&
21
b
positioned about the neck
12
of the envelope
10
. The deflection yoke
20
also includes an electrical insulation layer
25
positioned between the saddle coils
21
a
,
21
b
and a toroidal coil
23
. The toroidal coil
23
is commonly wrapped around a ferrite core
24
.
In order to satisfy certain requirements regarding picture quality, the (dynamic) magnetic deflection fields are often strongly modulated. For example, as is known in the art, the stringent convergence requirements in three inline color television systems necessitate, different polarities and different magnitudes of magnetic multi-pole components along the axis of the yoke from gun side to screen side. “Line” field is synonymous with horizontal field because this field results in forming lines by pushing electrons from left to right on screen. “Field” is same as “vertical” because vertical deflection refreshes the whole field (i.e., whole screen) after all horizontal lines are scanned. Further, in systems where the electron beam(s) must negotiate a large deflection angle (such as in wide screen applications), it is particularly difficult to achieve the required deflection field modulations using only the two sets of deflection coils. In some cases this can only be achieved at very high cost, in other cases the required field modulation is simply not possible to achieve using two sets of coils.
Many approaches have been tried to solve the complex problem of adjusting the deflection field to achieve the desired field modulation at each point in the CRT. One approach has been to include a variety of “helpers” which modify the deflection field in ways which are not possible with present art defl
Fitch Even Tabin & Flannery
Hodges Matt
Patel Vip
Sony Corporation
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