Television – Video display – Color sequential
Reexamination Certificate
1998-03-20
2001-08-28
Harvey, David E. (Department: 2614)
Television
Video display
Color sequential
C348S810000, C348S812000, C313S471000
Reexamination Certificate
active
06281947
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to color television systems and, in particular, to color television systems which use a single electron gun and do not use a shadow mask.
1. Background of the Invention
A conventional color television tube has three electron guns (i.e., one gun for the red image, a second gun for the green image, and a third gun for the blue image) and a shadow mask or aperture grill which serves to block the three electron beams produced by the guns from hitting the wrong phosphors on the face of the tube. While the shadow mask accomplishes this purpose, it causes many difficulties.
For example, approximately 80% of the total electron beam current produced by a gun hits the shadow mask, and is dissipated therein as heat. This heating causes the mask to expand and to eventually lose its registration with the tube's phosphors. The process is called doming, and results in an upper limit on the tube's brightness since as higher beam currents are used to achieve greater brightness, more heating and thus more doming occurs.
The mask also limits the resolution of the display, which depends on the number and size of the holes in the mask. There are plainly only so many holes that one can put in a mask and still keep it stiff. Also, as the hole size decreases, less of the electron beam reaches the phosphor, thus lowering the brightness.
Without a shadow mask these doming and resolution problems are eliminated. In addition, other drawbacks of conventional CRTs, e.g., x-ray emission from the mask as a result of electron bombardment, excessive weight, and relatively high cost, can be eliminated or reduced.
Efforts have been made in the past to remove the shadow mask in accordance with an approach known as “beam indexing.” This approach has had some technical success, but has failed economically except for highly specialized applications, such as radar screens.
The primary difficulty with beam indexing is that it requires high speed switching of the beam as it passes over each vertical phosphor line. In particular, the beam has to be turned on and off in a window of a few nanoseconds with an intensity precision of one per cent or better as it passes over the center of the phosphor line. A beam position sensing means is thus needed which is capable of determining the position of the beam to high accuracy to allow this critical timing to be right.
On-and-off switching and position sensing of this type turns out to be difficult to implement and very expensive. The only company known to have actually produced color television tubes in accordance with this approach is Sony Corporation. See “A New 30-Inch Beam-Index Color Cathode Ray Tube” by A. Ohkoshi et al.,
IEEE Transactions on Consumer Electronics,
CE-27, No 3, 433-443, Aug. 1981. This tube was never introduced into mass production due to its cost.
2. Description of the Prior Art
Beam-index type television systems are described in various patents and publications including: Justice, U.S. Pat. No. 3,030,439; Chatten, U.S. Pat. No. 3,041,391; Moore, U.S. Pat. No. 3,116,364; Alpers, U.S. Pat. No. 3,383,547; Jones, U.S. Pat. No. 3,406,251; Chen, U.S. Pat. No. 3,732,359; Thompson, U.S. Pat. No. 3,875,450; Strathman, U.S. Pat. No. 4,159,484; Seats et al., U.S. Pat. No. 4,240,073; Akazawa, U.S. Pat. No. 4,268,856; Kaku et al., U.S. Pat. No. 4,333,105; Weiss, U.S. Pat. No. 4,369,460; Midland, U.S. Pat. No. 4,408,223; Blank et al., U.S. Pat. No. 4,514,756; Midland et al., U.S. Pat. No. 4,527,192; Shinkai, U.S. Pat. No. 4,635,106; Turner, U.S. Pat. No. 4,635,107; Midland et al., U.S. Pat. No. 4,658,288; Takeuchi, U.S. Pat. No. 4,752,716; and Turner, J., “A New Beam Indexing Color Display Tube Using Direct Pick-Up of the Electron Beam—The Turner Tube,” IEEE Biennial Display Conference, 83-87, 1976.
A general discussion of cathode ray tubes can be found in
The Cathode-Ray Tube
by Peter A. Keller, Palisades Press, New York, N.Y., 1991.
The relevant portions of the above references and of the references referred to below are incorporated herein by reference.
SUMMARY OF THE INVENTION
To address the above problems in the prior art, the invention provides a system for displaying a color broadcast television signal which comprises a series of frames (e.g., 30 frames per second), each frame being composed of a series of lines (e.g., 525 interlaced lines per frame of which 483 lines form the visible image), said system comprising:
(A) a cathode ray tube which:
(i) does not have a mask;
(ii) has only one electron gun, the gun producing an electron beam;
(iii) has a faceplate which defines an x-axis (typically, the horizontal axis) and a y-axis (typically, the vertical axis);
(iv) has red phosphor stripes, green phosphor stripes, and blue phosphor stripes which are parallel to the x-axis and are organized into triads, the number of triads being at least equal to number of broadcast lines in a frame;
(v) has a plurality of beam positioning means which are parallel to the x-axis, one beam positioning means being associated with each triad, e.g., the beam positioning means is directly above (or below) the triad;
(B) two subsystems for performing line buffering, wherein:
(i) each subsystem is able to convert the red, green, and blue information of a line of the broadcast signal from the broadcast signal's parallel form into a serial form so that the red, green, and blue phosphor stripes of a triad can be scanned serially, the two subsystems working alternately on the lines of the broadcast signal, i.e., the first subsystem handles the first broadcast line, the second subsystem handles the second line, the first subsystem handles the third line, and so forth; and
(ii) each subsystem has an input state during which it receives and processes a line of the broadcast signal and an output state during which it outputs serial information, one subsystem being in the input state while the other subsystem is in the output state; and
(C) a control system which for each broadcast line:
(i) toggles the subsystems between the input and output states;
(ii) selects an appropriate beam positioning means for the particular broadcast line and then scans the electron beam along said selected means (i.e., scans the electron beam in a direction parallel to the x-axis) to obtain information regarding the beam's position in the direction of the y-axis, i.e., its “y” position, as a function of its scan position along said selected means;
(iii) stores the information obtained in (C)(ii) in a memory; and
(iv) serially scans the electron beam along the red, green, and blue phosphors stripes of the triad with which the selected beam positioning means is associated, using:
(a) the serial information of the line buffer which is in the output state to control the intensity of the beam as a function of its scan position along a phosphor stripe, i.e., the red serial information is used to control the intensity when the red stripe is scanned, the green information is used when the green stripe is scanned, and the blue information is used when the blue stripe is scanned; and
(b) the stored information of (C)(iii) to control the position of the beam in the direction of the y-axis as the beam is scanned along each stripe so as to align the beam with the stripe in the y-direction throughout the scan of the stripe.
A color television system of this type avoids the timing problem of the prior art beam index approach by scanning in the same direction as the phosphor lines, rather than across them. The control problem is then changed from a high speed synchronization problem to one of low speed position control along the phosphor stripes.
In accordance with the invention, it has been found that such low speed position control can be achieved without encountering the technical and economic difficulties which plagued the prior art beam index approach. As a result, the invention provides a practical way for satisfying the long standing need in the art for a mask-free, single gun, color television system which can be economically produced.
REFERENCES:
pate
Harris James Michael
Teter Michael P.
Corning Incorporated
Harvey David E.
Klee Maurice M.
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