Beam index type color cathode ray tube

Details Beam index type color cathode ray tube Beam index type color cathode ray tube

2000-02-09

2001-09-25

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

C315S010000

Reexamination Certificate

active

06294885

ABSTRACT:

BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a beam index type color cathode ray tube (CRT), and more particularly, to an improved beam index type color CRT capable of displaying images much more clearly by preventing a deterioration of the contrast of displayed images.
(b) Description of the Related Art
A shadow mask cathode ray tube (CRT) is generally employed as an image displaying unit for televisions, computer monitors, etc. because of its low cost and relative clear image quality.
However, the shadow mask CRT exhibits low beam current efficiencies because a large portion of the beam current is blocked from striking the phosphor and is absorbed by the shadow mask. Such beam current absorbed by the shadow mask forms high current areas on the shadow mask, which causes thermal expansion on the shadow mask, resulting in deterioration of color definition of the CRT.
Also, because the shadow mask CRT is susceptible to effects from the earth's magnetic field, an inner shield for intercepting the earth's magnetic field must be provided in the CRT.
To overcome these shortcomings of the shadow mask type CRT, beam index type color CRTs without a shadow mask and inner shield have been developed.
FIG. 1
shows a conventional beam index type color CRT. As shown in
FIG. 1
, the beam index type color CRT includes a panel assembly
10
consisting of a screen panel
20
(in which phosphor is deposited) and a funnel
30
, an electron gun
11
installed inside the funnel for emitting electron beams, a deflection yoke
12
mounted around a neck of the funnel
30
for deflecting the electron beams from the electron gun
11
, an index beam (an ultra-violet ray) condenser plate
13
mounted on the curved part of the funnel
30
, and photo sensor
14
for detecting and multiplying the index beam.
FIG. 2
shows an example of a conventional beam index type color CRT. As shown in
FIG. 2
, the beam index type color CRT includes a photo sensor
14
which detects the index beam which is generated from the beam index type color CRT upon impingement of the electron beam on index stripes thereof and responsively generates an index signal (an electric signal) depending on an amount of the detected index beam, a band pass filter (BPF)
20
for filtering a predetermined frequency of the index signals, a limiter
21
for limiting a predetermined amplitude of the index signals filtered by the filter
20
, a phase-locked loop (PLL)
22
for synchronizing an index signal to color selecting signals, a start-set controller
23
for setting an index starting signal in accordance with the index signal filtered by the band pass filter
20
, a ring counter
24
for counting each cycle of the filtered index signals, a color signal switch
25
for generating a color signal according to a index signal counted by ring counter
24
, a run-in area controller
26
for controlling a run-in area on the screen panel, an index processing circuit
27
for synchronizing the color signal with the index signal and producing a synchronized signal, and an amplifier
28
for amplifying the synchronized signal and sending the amplified signal to the electron gun.
As represented in
FIGS. 3 and 4
, in the conventional beam index type color CRT, the inner surface of the screen panel
31
has parallel triads of red, green, and blue color phosphor stripes
33
vertically arranged with a black layer
32
between the adjacent color phosphor stripes
33
. Index stripes
35
are provided on a transparent aluminum layer
34
which functions as a beam reflecting layer deposited on the triads of red, green, and blue (RGB) color phosphor stripes
33
and black layer
32
.
On the one hand, in order to obtain the index signal as well as color signal, the index stripes must be constantly exposed to the electron beam in the beam index type CRT.
That is, the electron beam scans the screen panel even when the generation of color signals are not required for a dark image construction, such as when displaying a night scene.
Since the electron beam must constantly scans the screen panel for generating an index signal, even when a color signal is not required for a portion of the display panel, the constantly scanning electron beam activates the red, green, and blue phosphors of the portion such that unintended light emissions of the phosphors lowers the contrast of a beam Index type color CRT.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the problems of the prior art.
It is an object of the present invention to provide an improved beam index type color CRT capable of obtaining a clear image by preventing the contrast of the image from being deteriorated, This is accomplished by the scanning the screen panel with an electron beam that is modulated on the basis of index data obtained from a previous image.
To achieve the above object, the inner shield of the present invention comprises an index signal controller for controlling input and output of the index signals, an index memory for temporally saving the index signals in units of a screen panel scene, and a switch for switching the index signals that is controlled by the index signal controller.


REFERENCES:
patent: 5138435 (1992-08-01), Shimada et al.
patent: 5343119 (1994-08-01), Takuma

Affiliated with

Also associated with

Rating

Beam index type color cathode ray tube does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Beam index type color cathode ray tube, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Beam index type color cathode ray tube will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2521940