Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
BACKGROUND OF THE INVE~NTION
Conventional magnetic scan cathode ray tubes for use to
display pictorial images use a single lens means for focussing the electron
beam. No correction is applied to the beam to cause the beam to be in focus
over the entire display screen. Thus, as the electron beam is moved away
from the screen center, it becomes slightly defocussed with the greatest
amount of defocussing occurring at the areas of the screen that are
furtherest from the screen center.
For display of alphanumeric information, higher resolution is
required, and a bipotential lens means is generally used with a nominal
2 focussing voltage to focus the electron beam at screen center being about
3,000 or more volts. To dynamically correct the beam focus when using a
bipotential lens means when the eJectron beam is moved away from the
screen center, a voltage of about 500 volts is added to the existing voltage
on the bipotential lens means. The amplifier that is applyin~ this voltage to
the bipotential lens means must be insulated due to its, high voltage
~^ operation and more power is required to dynamically correct the focus.
V.S. Patent No. 3,603,839 employs several lens means for
focussin~ the electron beam and a second crossover of the beam is formed to
increasé the beam curr~nt through a shadowmask color cathode ray tube.
80 The vol~ages required to focus the second crossover are not of low value nor
is the lens means that effects the second crossover used
to correct for deflection defocussing.
SUMMARY OF THE INVENTION
The present invention relates to electron
discharge devices of the cathode ray tube type and more
particularly to applying a variable low voltage to a first
lens means to control the position of a second electron
beam crossover for dynamically correcting deflection
defocussing.
The present invention can be realzied in a
cathode ray tube by the use of unipotential lens means in
combination with bipotential lens means with the
unipotential lens means having variable low voltage
applied thereto to control the position of the focussing
of the second beam crossover relative to the bipotential
lens means to dynamically correct the focus of the beam at
any position on the display screen. ~ -
In accordance with an aspect of the invention
there is provided an electron discharge device comprising:
means for emitting an electron beam, means for forming the
emitted beam into a first crossover, a first lens for -
forming the beam from the first crossover into a second
crossover, a second lens for focussing the beam from the
second crossover onto a screen of the device, means for
developing, and applying to the first and second lenses,
relatively high voltages to enable their crossover-forming
and focussing functions, means for variably deflecting the
beam over the screen, means responsive to the deflection
means for developing a voltage that is related to the
amount of beam deflection and is substantially lower than
said lens-operating voltages, and means forming part of
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said first lens for causing said substantially lower
voltage to continuously control the location, relative to
the direction of beam travel, of the second crossover to
compensate for beam defocussing at the screen due to
varying beam deflection.
An object of the present invention is to provide
a cathode ray tube including low voltage control means for
dynamically correcting the beam focus.
Another object of the present invention is the
provision of a cathode ray tube which comprises
unipotential lens means in combination with bipotential
lens means with the unipotential lens means controlling
the second crossover of the electron beam along the
bipotential lens means.
A further object of the present invention is to
provide a cathode ray tube having dual unipotential lens
means with one of the unipotential lens means controlling
the second crossover of the electron beam therealong.
An additional object of the present invention is
the provision of a cathode ray tube having unipotential
lens means in combination with bipotential lens means with
the unipotential lens means having beam-limiting means to
shape the electron beam and control the current thereof.
Still a further object of the present invention
is to provide a cathode ray tube including unipotential
and bipotential lens means, the unipotential lens means
having variable low voltage applied thereto for
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contru~iing the second crossover of the electron beam rela~ive to the
bipotential lens means and the b~potential 1erls means having variable high
voltage applied tl~ereto for controllin~ the color of information that will be
displayed by the screen.
BRIEF DESCRIPTION OF THE DRAWINGS
The above objects and other objects, advantages and features
of the present invention will appear from the following detailed description
of embodiments thereof when taken in conjunction with the accompanying
drawings of which:
Figure 1 is a longitudinal cross-sectional view of a cathode ray
tube utilizing the present invention;
Figure 2 is a longitudinal cross-sectional view of an alte~rnative
embodiment of the present invention; and
Figure 3 illustrates the arrangement of electrodes of another
embodirnent of the present invention.
, DETAILED DESCRIPTION OF THE INYENTI(3N
.
Turning now to Figure 1, a cathode ray tube 10 includes a glass
envelope 12 which has a neck section 14 and a funnel section 16. An
electron beam forming structure is provided in neck section 14 which
~0 includes a cathode 18, a grid 20, a first anode 22, a unipotential lens which
comprises elements 24 and 26, a focussing electrode 28 and a bipotential
lens which includes element 26 and conductive coat~ng 30 on the inside
surface of funnel section 16.
' Cathode 18 is connected to ground or zero volts and it has a
heater coil 32 therein. Grid 20 is connec,ted to--50 volts and it has an
aperture 34 through which the electron beam 36 emanating from cathode 18
passes. Aperture 34 shapes electron beam 36 and determines the current
density thereof, whereas grid 20 acts on electron beam 36 to conver~e it
thereby causing it to form a first crossover Cl between grid 20 and first
0 anode 22.
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First anode 22 is connected to 1,000 volts and it has a beam-
forming aper~ure 38 through which electron beam 36 passes. The electric
field developed by anode 22 caLses eiectron beam 36 to diverge as it rnoves
into element 24 of the unipotential lens means. Elements 24 and 26 of the
unipotential lens means are connected to 2,000 volts. Element 24 has a
beam-forming aperture 40 through which beam 36 passes, and the electric
field of element 24 causes beam 36 to diverge as it moves therealong and
into focussing electrode 28.
Horizontal and vertical deflection coils 42 of conventional
1~ design are provided on envelope 12 and they are operated by deflection
signals being generated by conventional X and Y deflection circuits 44.
Signals are derived from deflection circuits 44 and transmitted to focus
arnplifier 46 of conventional design and the output from focus amplifier 46 is
connected to focussing electrode 28. The voltage of the signals from focus
amplifier 46 and being applied to focussing electrode 28 vary between 0--100
volts and the level of the voltage depends on the deflection that is being
applied to the electron beam 36 by deflection coils 42. As the deflection of
electron bean~ 36 moves away from the tube axis, the voltage on focussing
electrode 28 will vary and this will cause the electric-field of focussing
20 electrode 28 to vary thereby causing electron beam 36 to converge at a
second crossover C2 within element 26 dependin~ on the voltage on
focussin~ electrode 28. Thus, the unipotential lens forms an image of the
second crossover C2 between the unipotential lens and the bipotential lens.
Conductive coating 30 is connected to a high voltage, e.g.
18KV., and conductive coating 30 is also engaged with a conventional
fluorescent screen 48 that is formed from a P4 black and white phosphor so
~hat screen 48 is also connected to 18KV. The second crossover C2 of beam
36 is focussed onto any displayable location on fluorescent screen 48 by the
bipotential lens. Screen 48 can of course use other phosphors to provide
81~ whatever color that is desired.
Thus, in accordance with the present invention, correction for
deflection defocussing is effec~ed by changing the voltage on focussing
~26~
electrode 28 which controls the position of the second crossovcr C2 of the
electron beam relative to the unipotential lens means. The position of the
second crossov~r is very sensiti~re to the strength of ~he unipotential lens
means; hence a low dynamic correction voltage is required which is close to
ground potential. In this regard, focus amplifier 46 need not have high
voltage requirements and require insulation therefor which constitutes cost
and power savings in dynamic focus correction amplifier design and
construction.
Figure 2 illustrates an alternative embodiment wherein like
reference characters are used to identify like elements. In this Figure 2
embodiment, a second unipotential lens is used instead of a bipotential lens.
Elements 24 and 26 of the first unipotential lens and element 50 of the
second unipotential lens as well as conductive coating 30 are connected
together and to 18KV. Focussing electrode 28 of the first unipotential lens
means is connected to the output of focus amplifier 46 and the voltage from
amplifler 46 can range between 0-200 volts in the same manner as described
in conjunction with the embodiment of Figure 1. Electrode 52 of the second
unipotential lens is connected to zero volts. The operation of the cathode
ray tube is the same as that of the cathode ray tube of Figure 1.
2 ~ Figure 3 illustrates another embodiment of the electrode
arrangement of the present invention wherein like reference characters are
also used to identify like elements. In this Figure 3 embodiment which is
identical in construction as the electrode arrangement of Figure 1 except
that elements 24 and 26 of the unipotential lens are connected to focus
amplifier 46 which applies 100-500 volts thereon and electrode 28 has à
fixed voltage of 5,000 volts connected to it. Thus, instead of using electrode
28 for dynamic focus correction to electron beam 36, the unipotential lens
can be operated at its high voltage operating mode, e.g. 5,000 volts, to
reduce beam aberrations and electrodes 24 and 26 can be operated at a low
~1~ voltage and adjusted for deflection defocussing. Electrodes 24 and 26 are
therefore the focussing electrode means and they receive varying correcting
voltage from focus amplifier 46.
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Screen 48 can be formed from a conventional penetron
phosphor which ernits red and green colors or any desired colors. Conductive
coating 30 in the cathode ray tubes of Fig-lres 1--3 can be selectively
connected to either 18KV or 12KV via switch means 54 in order to display
the information in a red color when conductive coating 30 is connected to
12KV and in a green color when conductive coating 30 is connected to 18KV.
The color can vary between red, orange, yellow and green depending on the
voltage that is applied to conductive coating 30 and hence to screen 48.
Switch means 54 can take any desirable form such as electronic or manual.
'0 In the cathode ray tube of ~igure 1, switching the voltage on
conductive coating 30 from 18KV to 12KV or vice versa via switch means 54
will also require changing the voltage at the same time on focussing
electrode 28 to assure proper correction for defocussing of electron beam
36. The voltage will likewise have to be changed on focussing electrodes 24
and 26 in the cathode ray tube of Figure 3 when conductive coating 30 is
changed from 18KV to 12KV or vice versa to assure proper correction for
defocussing of electron beam 36. In the case of the cathode ray tube of
Figure 2, switching the voltage on conductive coating 30 from 18KV to 12KV
or vice versa via switch means 54 will notrequire refocussing of the beam at
~1~ the second crossover. Thus, no change of the voltage of focussing electrode
28 in the cathode ray tube of Figure 2 is required when the voltage is
switched on conductive coating 30 from one voltage level to the next,
whereas the change of the voltage on focussing electrode 28 in the cathode
ray tube of Figure I is required, when such voltage level change occurs.
While ~he unipotential and bipotential lens means have been
disclosed as being electrostatic, magnetic lens means can be used in their
place to achieve the same result.
It can readily be discerned from the foregoing that the
application of a low variable voltage to a focussing electrode of a
8~ unipotential lens means controls the position of a second crossover of 1:he
electron beam thereby dynamically controlling the focus along adjacent lens
means.
While embodiments of the present invention have been shown
and described, it will be a~aren~ ~o ~hose skilled in the art that changes and
modifications may be made withou~ departing from the present invention in
its hroad aspects. The appended claims are therefore intended to cover all
such changes and modifications as fall within the true spirit and scope of the
present invention.
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