Note: Descriptions are shown in the official language in which they were submitted.
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DISPLAY TUBE FOR LIGHT SOURCE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a large-screen
display apparatus and more particularly to a display tube
for the light source as a constituent of picture elements of
a color display apparatus.
Prior art display tubes will be described hereinbelow
in conjunction with the drawings.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
display tube for light source in which the quantity of
thermoelectrons emitted from the cathode when only one data
electrode is turned ON, will be increased so that the
brightnass of the fluorescent display cell at that time is
not largely lowered below the brightness thereof when two
data electrodes are turned ON.
Another object of the present invention is to provide
a display tube for light source in which the flow of
thermoelectrons from a cathode is restrained so that other
than the predetermined fluorescent display cell 8 designated
as the picture element are not allowed to emit false light.
A further object of the present invention is to
provide a display tube for light source in which stray
electrons travelling from cathodes to the display screen la
are fully prevented.
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In accordance with one aspect of the invention there is
provided a display tube for light source having within a
vacuum envelope thereof: a display screen with fluorescent
display cells arranged thereon in a matrix; cathodes for
emitting electrons disposed corresponding to said fluorescent
display cells, a first control electrod2 with openinys
corresponding to said fluorescent display cells made therein
and positioned between said display screen and said cathodes;
second control electrodes disposed, corresponding to each of
said cathodes and oriented along the length of said cathode,
on a substrate which is located on the side of said cathodes
opposite to said display screen; and third control electrodes
disposed parallel to said cathode at both sides in the
direction of the column of said second control electrode;
characterized in that said second control electrodes
corresponding to said cathode and oriented along the length
thereof are provided two in number for each cathode, and there
are provided fourth control electrodes for reducing
fluctuation in brightness with each thereof disposed between
said two second control electrodes.
In accordance with another aspect of the invention
there is provided a display tube for light source having
within a vacuum envelope thereof: a display screen with
fluorescent display cells arranged thereon in a matrix;
cathodes for emitting electrons disposed corresponding to said
fluorescent display cells; a first control electrode with
openings corresponding to said fluorescent display cells made
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therein and positioned between said display screen and said
cathodes; second control electrodes disposed, corresponding to
each of said cathodes and oriented toward said cathode, on a
substrate which is located on the side of said cathodes
opposite to said display screen; and third control electrodes
disposed at both sides of said second control electrode;
characterized in that there are provided back shield
electrodes disposed between units, with a unit defined as
composed of said cathode, and said second con~rol electrode
and said third control electrodes corresponding to said
cathode.
In accordance with yet another aspect of the invention
there is provided a display tube for light source having
within a vacuum envelope thereof: a display screen with
fluorescent display cells arranged thereon in a matrix;
cathodes for emitting electrons disposed corresponding to said
fluorescent display cells; a first control electrode with
openings corresponding to said fluorescent display cells made
therein and positioned between said display screen and said
cathodes; second control electrodes disposed, corresponding to
each of said cathodes and oriented toward said cathode, on a
substrate which is located on the side of said cathodes
opposite to said display screen; and third control electrodes
disposed at both sides of said second control electrode;
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characterized in that there are provided side shield
electrodes in the space between said first control electrode
and the substrate of said vacuum envelope located between said
cathodes.
In accordance with yet another aspect of the invention
there is provided a display tube for light source having
within a vacuum envelope thereof: a display screen with
fluorescent display cells arranged thereon in a matrix;
cathodes for emitting electrons disposed corresponding to said
fluorescent display cells; a first control electrode with
openings corresponding to said fluorescent display cells made
therein and positioned between said display screen and said
cathodes; second control electrodes disposed, corresponding to
each of said cathodes and oriented toward said cathode, on a
substrate which is located on the side of said cathodes
opposite to said display screen; and third control electrodes
disposed at both sides of said second control electrodes;
characterized in that said substrate with said cathodes,
second control electrodes, and third control electrodes
provided thereon, is arranged to be an insulating substrate
floating above a back plate of said vacuum envelope, and said
first control electrode is formed to have a cross-section in a
U-shape and the edge portions thereof are extended so far as
to reach the vi~inity of said back plate.
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3b
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing a prior art display
tube for light source;
FIG. 2 is an exploded perspective view of FIG. 1;
FIG. 3 is a plan view showing electrode structure;
FIG. 4 is a diagram schematically showing timing of
signals:
FIG. 5 is a plan view schematically showing a display
screen;
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FIG. 6 and FIG. 7 are diagrams schematically showing
potential in the vicinity of cathodes;
FIG. 8 is an explanatory drawing showing
relationships in the prior art between polarities of data
electrodes and scanning electrodes and the distribution of
, thermoelectrons from a cathode;
; FIG. 9 is a sectional view of a prior art display
tube for light source showing the flow of thermoelectrons
from a cathode;
FIG. 10 is a perspective view showing a substrate of
a display tube for light source according to a first
embodiment of the present invention;
FIG~ 11 is an explanatory drawing showing
relationships between polarities of data electrodes and
scanning electrodes and the distribution of thermoelectrons
from a cathode;
FIG. 12 is a sectional view showing the flow of
: thermoelectrons emitted from a cathode in a display tube for
light source according to a second embodiment of the present
nvention;
FIG. 13 is a sectional view showing a principal
portion of a display tube for light source according to a
third embodiment of the present invention: and
FIG. 14 is a sectional view showing a display tube
for light source according to a fourth embodiment of the
present invention.
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Description of the_Prior ~rt
FIG. 1 is a sectional view showing a prior art
display tube for light source disclosed, for example, in
Japanese Patent Application No. 62-256610, which was laid-
open on April 19, 1989, and FIG. 2 is an exploded
perspective view of the same. Referring to FIG. 1 and FIG.
2, reference numeral la denotes a display screen shaped in
the form of a flat plate and having sixteen fluorescent
display cells 8, lb denotes a frame body forming side faces
of a vacuum envelope of the display tube for light source,
8A denote accelerating anodes disposed so as to surrounded
the fluorescent surface of the fluorescent display cells 8,
14 denotes a planar electrode as a first control electrode
made in the form of a flat plate, and lc denotes a substrate
with such components as cathodes 4, second and third control
electrodes 10, 12, and their wiring leads 11, 13 disposed
thereon. The display tube for light source is contructed by
providing the planar electrode 14 in the space surround by
the frame member lb and by fixing the display screen la on
one end of the frame body lb and fixing the substrate lc on
the other end of the frame body lb.
The display screen la is provided with sixteen
fluorescent display cells 8 coated with phosphor and
arranged in a matrix (4 rows by 4 columns) thereon. Each
fluorescent display cell ~ is supplied with a high voltage
and adapted to emit light by being bombarded with electrons.
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In the planar electrode 14, there are made sixteen openings
15 arranged in a matrix (4 rows by 4 columns) corresponding
to the fluorescent display cells 8.
FIG. 3 is a plan view showing electrode structure on
the substrate lc, in which the horizontal direction is the
direction of the row and the vertical direction is the
direction of the column. In the center of the substrate lc,
there is made an exhaust hole 2 used as the passage of
exhaust air when evacuating the interior of the display tube
for light source~ There are four directly heated filament
cathodes 4 disposed above the substrate lc slightly spaced
from its surface. When a heater current is passed through
each cathode 4, thermoelectrons are emitted from the cathode
4.
On the surface of the substrate lc at the portions
corresponding to the cathodes 4, there are disposed eight
data electrodes, in an array of 2 rows by 4 columns, as the
second control electrodes for controlling thermionicemission
of the cathodes 4. Each data electrode 10, by being
supplied with positive or negative potential relative to the
potential of the cathode 4, controls thermionicemission of
each corresponding cathode 4. On the surface of the
substrate lc at both sides in the direction of the column of
each data electrode 10, there are disposed eight scanning
electrodes 12, in a matrix of 4 rows by 2 columns, as the
third control electrodes for controlling the moving
direction of the thermoelectrons emitted from the cathode 4.
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The size oE the data electrode 10 is made smaller
than that of the scanning electrode 12. Of the eight data
electrodes 10, two each arranged in the same column are
connected together to each of four wiring leads 11 arranged
in the direction of the column, and of the eight scanning
electrodes 12, two each in the same row are connected
together to each of the four wiring leads 13 arranged in the
direction perpendicular to the wiring leads 11, that is, in
the direction of the row. The wiring leads 11 and the
wiring leads 13 are laid down with an insulating layer
interposed therebetween so as not to come into contact with
each other. These data electrodes 10, scanning electrodes
12, wiring leads 11, and wiring leads 13 are formed on the
substrate lc by printing.
Operation will be explained below. Referring to
FIG. 3, Sl, S2, S3, and S4 indicate scanning signals applied
to two each scanning electrodes 12 in the same row, and Dl,
D2, D3, and D4 indicate data signals applied to two each
data electrodes 10 in the same column. FIG. 4 is a timing
chart of the application of the signals S1 to S4, and D1 to
D4. FIG. 5 is a diagram showing arrangement in a matrix of
the fluorescent display cells 8 formed on the display screen
la. Light emitted from each of the fluorescent display
cells 8 is controlled by applying the signals S1 to S4, and
D1 to D4.
The operation for controlling the emission of light
will now be described.
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i ON (positive)/OFF (negative) control of each of the
data electrodes 10 and ON (positive) /OFF (negative) control
of each of the scanning electrodes 12 are performed at the
timings of the data signals and scanning signals as shown in
FIG. 4~ There are four phases of periods in the
combinations of the ON/OFF states of the scanning electrode
12 and the ON/OFF states of the data electrode 10 (i.e.,
where the state of the scanning electrode 12 and the data
electrode 10 are ON and ON, ON and OFF and ON, and, OFF and
OFF, respectively). The light emitting condition of the
fluorescent display cell in each period will be described
below. FIG. 6 and FIG. 7 are schematic diagrams showing
states of potential in these four periods.
~ Where both the scanning electrode 12 and the
data electrode 10 are in the ON state, the field in the
vicinity of the heated cathode 4 becomes positive under the
field of the data electrode 10 and the scanning electrode 12
and hence thermoelectrons are emitted. The emitted
thermoelectrons are deflected under the field of the
scanning electrode 12 and accelerated by the planar
electrode 14 to advance to the corresponding fluorescent
display cell 8 and bombard the fluorescent display cell 8.
Then, the electrons coming into contact with the phosphor
material cause the fluorescent display cell 8 to emit light
(FIG. 6 ~ ).
~ Where the scanning electrode 12 is in the ON
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state and the data electrode 10 is in the OFF state, since
the data electrode 10 is disposed closer to the cathode 4,
the field of the data electrod~ 10 affects the cathode 4
more strongly. Hence, in this case, the field in the
vicinity of the cathode 4 becomes negative so that the
thermionicemission from the cathode 4 is suppressed and the
fluorescent display cell 8 does not emit light
(FIG. 7 ~ ).
~ Where the scanning electrode 12 is in the OFF
state and the data electrode 10 is in the ON state, although
the data electrode 10 is positive, both the scanning
electrodes 12 formed on both side of the data electrode 10
are negative, and moreover, the size of the scanning
electrode 12 is larger than that of the data electrode 10,
and hence the field in the vicinity of the cathode 4 becomes
negative so that the thermionicemission from the cathode 4
is suppressed and the fluorescent display cell 8 does not
emit light (FIG. 6 ~ ).
~ Where both the scanning electrode 12 and the
data electrode 10 are in the OFF state, the field in the
vicinity of the cathode 4 becomes negative so that the
thermionicemission from the cathode 4 is suppressed and the
fluorescent display cell 8 does not emit light (FIG. 7
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In the described manner, the emission of light in
each of the fluorescent display cells 8 is controlled at
will by combination of the potential of the data electrode
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10 and the scanning electrode 12. since, here, the
potential of the data electrode 10 and the scanning
electrode 12 is controlled by the data signals Dl - D4 and
the scanning signals Sl - S4, it is made possible to have
each of the fluorescent display cells 8 emitting light or
not at will by controlling these signals.
Now, when two data electrodes 10, as adjoining two
control Plectrodes, are simultaneously ON, two adjoining
fluorescent display cells 8 corresponding thereto emit
light, and when only one data electrode 10 is ON, only one
of the fluorescent display cells 8 emits light. The
difference in the light emission in the fluorescent display
cells 8 between these cases is shown in FIG. 8 (a) and FIG.
8 (b), wherein four fluorescent display cells 8a, 8b, 8c,
and 8d controlled by ON/OFF states of the corresponding two
data electrodes 10a and 10b and two scanning electrodes 12a
and 12b are shown. When the data electrodes 10a and 10b are
both turned ON (positive potential) and the scanning
electrode 12a is turned ON (positive potential),
thermoelectrons from the cathode 4 are deflected by the
field of the scanning electrode 12a as shown in FIG. 8 (a)
and bombard the corresponding two fluorescent display cells
8a and 8b causing these two to emit light.
On the other hand, when only the data electrode 10b
and the scanning electrode 12a are ON, the thermoelectrons
are deflected so as to bombard only one fluorescent display
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cell 8b, as shown in FIG. 8 (b), causing the same to emit
light. In this way, by controlling the states of potential
developed also by the other scanning Plectrodes 12a and 12b
and the data electrodes lOa and lOb, one to four of the
fluorescent display cells 8a to 8d can be selectively caused
to emit light.
Since the prior art display tube for light source is
constructed as described above, when only one each
electrode, i.e., the data electrode lOb and the scanning
electrods 12a, are turned ON, the data electrode 10a is held
negative, and this causes the region of thermionicemission
on the cathode 4 to reduce to about one half as shown in
FIG. 8 (b). Hence, there has been the probability of
fluctuation in brightness of the fluorescent display cell 8b
between a case of both the data electrodes lOa and lOb being
turned ON and the other case of only the data electrode lOb
being turned ON. There has also been the probability of
such difference in brightness, though slightly, from the
tolerance of assembling such as positioning of the
electrodes or from the fluctuation of an input voltage.
Further, while the data signals Dl to D4 and scanning
signals Sl to S4 as shown in FIG. 4 are being applied to the
data electrodes 10 and the scanning ~lectrodes 12 as shown
in FIG. 6 and FIG. 7, if the polarities of adjoining sets of
the electrodes 10 and 12 are as shown in FIG. 9, then the
thermoelectrons emitted from one of the cathodes 4 flow
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normally as indicated by the arrow P, pass through the
opening 15 in the control electrode 14, and bombard the
predetermined fluorescent display cell 8 tQ cause it to emit
light. However~ there has been the probability of a portion
of the emitted thermoelectrons flowing also in the direction
of the arrow Q and straying into other adjoining openings
15, whereby other than the predetermined fluorescent display
cells 8 are caused to emit false light.
Furthermore, there has been the probability of the
electric field of a high voltage of the anode 8a penetrating
through the gap between the frame body lb and the planar
electrode 14 and reaching the vicinity of the cathode 4,
thereby causing electrons emitted from the cathode 4 to pass
through the gap and reach the fluorescent display cells 8 at
the circumference of the display screen la and cause them to
emit false light.
A preferred embodiment of the present invention will
be described below in detail with reference to the
accompanying drawings.
Referring to FIG. 10, reference numeral ld denotes a
substrate, and on the substrate ld, there are disposed
cathodes 4, data electrodes lOa, lOb as second control
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electrodes, scanning electrodes 12a, 12b as third
control electrodes, and electrodes 21, located between
the data electrodes 10a and 10b~ and between the scanning
electrodes 12a and 12b as fourth control elec-trodes
supplied with potential at a predetermined level for
reducing ~luctuation in brightness. Above the substra-te
lc, there are provided a planar electrode 14 as first
; control electrode and a display screen la with
predetermined spacings between one another, and these
are contained in a frame body lb as in the prior art.
FIG. 11 is an explanatory drawing showing a difference
in emission of li~ht between the periods where both data
electrodes are turned ON and where one data electrode is
turned ON in a display tube for light source with the
electrode arrangement as described above.
Operation will be described below.
In the region of thermionicemission on the cathode
4, when both the data electrodes 10a, 10b are turned ON
and the scanning electrode 12a is turned ON, the
thermoelectrons are deflected as shown in FIG. ll(a),
virtually in the same way as in the case shown in
FIG. 8(a), whereby corresponding two fluorescent display
cells 8a, 8b are both bombarded by the electrons to emit
light. On the other hand, when only one data electrode
10b and the scanning electrode 12a are turned ON, the
region of thermionicemission on the cathode 4 includes
the portion corresponding to the fourth control elec-trode
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21, and therefore, it is expanded, as shown in FIG. 11(b),
to virtually two times larger than that in the prior art.
As a result, the thermoelectrons from such a wider
region are deflected to bombard one fluorescent display
cell 8b causing it to emit light. Hence, its brightness
becomes much higher than that in the prior art as shown
in FIG~ 8(b), reducing the difference in brightness
between this and that of the fluorescent display cell 8b
in the case where the fluorescent display portions 8a,
8b are both allowed to emit light, and thus an
improvement is obtained such that the difference in
brightness is made virtually undetectable by vision.
Similarly, when using other fluorescent display cells
8c, 8d separately from or jointly with the fluorescent
display cells 8a, 8b to selectively cause one to four of
them to emit light, it becomes possible to reduce the
difference in brightness by holding the fourth control
electrode 21 ON and thereby obtain a well-balanced and
good image display.
Such a fourth control electrode 21 also has a
performance to reduce the fluctuation in brightness
resulting from a tolerance of electrode positioning or
assembling.
FIG. 12 is a drawing showing a second embodiment of
the present invention. Referring to FIG. 12, reference
numeral 22 denotes a back shield electrode provided on
the substrate lc. Defining a unit as composed of one
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cathode 4, two data electrodes 10 as second control
electrodes positioned under and facing the cathode 4,
and two scanning electrodes 12 as third control
electrodes disposed on both sides in the direction of
the column of the data electrodes, four back shield
electrodes 22 are disposed between each two adjoining
units of four such units. The back shield electrode 22
are, for example, formed out of carbon by screen-printing
on the subs-trate lc. Other components correspondiny to
those shown in FIG, 3 are denoted by corresponding
reference numerals and duplicated explanation thereof is
omitted here.
Operation will be described below.
In the present embodiment, as described above,
there are disposed the back shield electrodes 22 between
each of adjoining units. Hence, by keeping the
potential of the back shield electrode 22 at a zero or
negative potential level at all times, the
thermoelectrons emitted from the cathode 4 in one unit
likely straying into the adjoining unit are affected by
the zero or negative potential of the back shield
electrode and thereby deflected as shown by the arrow P'.
Thus, it does not occur that the thermoelectrons emitted
from the cathode 4 of one unit stray into the opening 15
in the planar electrode 14 corresponding to other units
as was the case in the prior art, and therefore, the
probability of emission of false light at the
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fluorescent display cells 8 in other units due to such
stray electrons can be thus eliminated. As a result,
each of the adjoining units e~fects the emission of
light on the fluorescent display cell 8 by its own
thermoelectrons and a good image display is ensured.
FIG. 13 is a dr~wing showing a third embodiment of
the present invention. Referring to FIG. 13, reference
numeral 23 denotes a side shield electrode, and these
side shield electrodes 23 are provided between the
control electrode 14 and the substrate lc being erected
between the cathodes 4, 4. The side shield electrode
23 may be electrically connected at its top edge to the
control electrode 14 or isolated therefrom to connect
to an earth line instead.
Operation will be described below.
First, the data signals Dl to D4 and the scanning
signals Sl to S4 as shown in FIG. 4 are supplied to the
data electrodes 10 and the scanning electrodes 12 as
shown in FIG, 6 and FIG. 7. Supposing now that these
electrodes 10, 12 have obtained polarities as shown in
FIG. 13, the thermoelectrons emitted from one cathode 4
are allowed to flow normally in the direction indicated
by the arrow P and further to pass through the opening
15 in the control electrode 14. Thereby, the
fluorescent display cell 8 corresponding to the opening
15 is bombarded by the electrons and emit light.
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Meanwhile, some of the -thermoelectrons emitted from
the cathode 4 moving -toward another opening 15 are
deflected by the effect, for example, of zero potential
or negative potentlal of the side shield electrode 23
and flow in the direction of the arrow R, and thereby,
caused to pass through the opening 15 and be lead onto
the same fluorescent display cell 8 as above via the
normal rou-te. Consequently, all the thermoelectrons
emitted from the cathode 4 are concentrated on the
designated fluorescent display cell 8 causing the same
to emit llght effectively. Thus, deterioration of
brightness at the predetermined fluorescent display cell
8 due to straying electrons or emission of false light
at other fluorescent display cells 8, can be prevented
for certain.
FIG. 14 is a drawing showing a fourth embodiment of
the present invention. Referring to FIG. 14, reference
numeral 24 denotes an insulating substrate provided
within the vacuum envelope in a manner floating above a
back plate lc. The insulating substrate 24 is formed
out of a ceramic plate, a glass plate, or the like. On
the insulating substrate 24, there are provided the
cathodes 4, the data electrodes 10, and the scanning
electrodes 12 in the same arrangement as in the previous
examples. Reference numeral 14A denotes a first control
electrode which as a whole has a square form and its
circumferential portions are bent so -that the thus made
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bent pieces 14b -together with the control elec-trode 14A
have a cross-section in a U-shape.
The firs-t control electrode 14A also has openings
15 made therein. The edge portion 14b of the first
control electrode 14A is arranged to extend pas-t the
periphery of the floating insulating substrate 24 as
far as the vicinity of the back plate lc.
Although not shown in the drawing, leads from the
cathodes 4 and electrodes 10, 12, and 14A are arranged
to be taken out on the back side of the back plate lc
through a cut made in the edge portion 14b of the first
control electrode 14A, a cut groove made in the back
plate lc, or the like. The first control electrode 14A
is provided with zero potential or negative potential.
Operation will be described below.
First, a heater voltage is applied to the cathode 4
: so that thermoelectrons are emitted therefrom and a
voltage, for example, at 8 XV is applied to the anode
8A. Thereby, electric field of the high-voltage is
developed within the vacuum envelope between the
fluorescent display cell 8 and the first control
electrode 14A, around the anode 8A as the center. At
this time, the electric field partly tends to penetrate
into the vicinity of the cathode 4 taking the route
passing through the minute gap between the edge poxtion
14b of the first control electrode 14A and the back
plate lc and the minute gap between this Eirst control
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electrode 14A and the periphery of the insulating
substrate 24.
However, since -the route is passing through such
minute gaps and the route itself is bent and long, the
high-voltage potential is sufficiently attenua-ted on the
midway of the route, so that it hardly reaches the
vicinity of the cathode 4. As a result, the stray
electrons passing through this route from the cathode 4
to the anode 8A and the fluorescent di.splay cell 8 can
be prevented and hence there is no probability of
emission of false light at the fluorescent display cells
8~ .
Although the above described embodiments were all
of a four-dot type in which one cathode 4 makes four
fluorescent display cells 8 emit light. The same
effects as obtained from the above described embodiments
can be obtained even if the device is of a two-dot type
in which one cathode 4 makes two fluorescent display
cells 8 emit light.
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