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Патент USA US2131892

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Oct. 4, 1938.
2,131,892
H. A. I‘AMS
‘ELECTRON DISCHARGE DEVICE
Filed Oct. 1, 1936
Hall
R
m,
INVENTOR
HARLEY A. IAMS
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ATTORNEY
2,131,892
Patented Oct. 4, 1938
um'rsp STATES PATENT OFFICE
2,131,892
ELECTRON DISCHARGE DEVICE
Harley A. Iams, Berkeley Heights, N. J.,.assignor,
by mesne assignments, to Radio Corporation
of America, New York, N. Y., a corporation of
Delaware
Application October 1, 1936, Serial No. 103,487
9 Claims.
The present invention relates to television
transmitting apparatus and particularly to ap
(Cl. 178-12)
tential slightly positive with respect to the second
anode. Thus if the potential of the second anode
is 1000 volts positive with respect to the cath
ode, the scanned element may be at 1001 volts
positive as the scanning beam passes from it to 6
adjacent elements, and it begins to collect second
ary electrons emitted from the adjacent elements
mosaic electrode consisting in general of an in
sulating sheet with a great number of discrete then being scanned, so that its potential gradually
falls. As soon as its potential falls below that
light-sensitive elements on the front surface form
10 ing a mosaic screen on which the optical image is of the second anode (1000 volts) it emits photo- 10
formed and a conductive coating or signal plate electrons under the in?uence of light from the
on the other surface, the front or illuminated sur-' object falling on the photo-sensitive surface of
face being scanned by a cathode ray beam from an the elements, and these photo-electrons are col
lected by the second anode. This emission of
electron gun having at least two anodes to pro
photo-electrons tends to make the potential of 15
,15 duce currents which ?ow through an output re
sistor connected between the signal plate of the the element rise, but the higher its potential, the
mosaic electrode and ground to generate the more secondary electrons emitted from other parts
of the screen does it tend to collect, to drive its
picture signals.
'
Now it has been found that parasitic signals potential more negative again. The ?nal po
tential of the element before again being scanned
.20 are developed superimposed upon the picture sig
nals taken from the signal plate. These parasitic is that potential it acquired by the previous
signals may take the form of base line wander at scansion, decreased by the secondary electrons
the line scanning or picture scanning frequency acquired by it ‘from the secondary electrons
or at both, or they may also develop an unnatural emitted from other parts of the screen and in
.25 shading of the re-created picture. Thus if the creased by the photo-electrons lost by‘ the ele- 25
true picture signals are regarded as consisting of ment under the in?uence of the incident light.
variations; corresponding to the brightness of the This ?nal potential may be of the order of 998
volts for an element illuminated with average
mosaic elements scanned; in an upward direc
tion from a base line corresponding to picture brightness. When the illuminated element is
scanned its potential is instantly restored to 30
_,30 black, the parasitic signals may have the effect again
1001
volts,and the resulting discharge of the
of causing the base line to assume a saw-tooth
form. The base line may fall relatively suddenly condenser constituted by the element and the
to a minimum value at the commencement of the signal plate causes in the circuit associated with
scanning of a line of the image and may rise the signal plate an impulse which is ampli?ed and
’
36
“35 steadily as the scanning of the line proceeds. In transmitted.
Assume now that the cathode ray beam scans
addition to this parasitic signal occurring at line
frequency, there may also be found a parasitic the screen in a series of approximately parallel
signal of similar general form occurring at the straight lines from left to right across the screen,
and starts a complete scan of the screen in the top
frame or picture frequency.
left-hand corner. Now when, in scanning any 40
40
The reason for this is believed to be as follows:
line, the beam‘ is on the left-hand end of a line
In the operation of the cathode ray trans
most of the secondary electrons emitted will ‘be
mitting tube, the average potential of the ele
ments of the mosaic screen is always in the collected by the second anode, but when the beam
the right-hand part of the line, there will
neighborhood of the potential of the second anode is on
a number of positively charged elements to 45
545 'of the ‘electron gun. These photo-electrically be
sensitive elements emit secondary electrons freely the left of the scanning beam, which collect
when struck by the scanning beam, and. the secondary electrons emitted from the elements on
paratus embodying cathode ray tubes.
'
In one form of cathode ray transmitting tube
5 an optical image of an object of which a picture
is to be transmitted is formed upon a target or
second anode collects both the secondary elec
trons and the photo-electrons emitted by the
59 ‘ mosaic screen.
when an element is scanned by
the cathode ray beam, the secondary electrons
emitted .by the scanned element ?ow partly to
the second anode of the gun and partly to
neighboring elements on the mosaic'screen. and
5Q the scanned element becomes charged to a po
the part of the line then being scanned. Thus
there will be set up a field at the surface of the
screen which is more positive at the left-hand‘ 50
side‘ of the screen than at other points on its sur
face, and tend to attract electrons to the left
hand side of the screen. The effect of this field
is to cause the base line wander of the picture
signals at line frequency.
55
2
2,181,89Q
A similar effect will be produced as the beam’
moves down the screen from line to line, as the
upper part of the screen will tend to attract elec
trons emitted from the lower part‘and thus give
a base line wander of the picture signals at frame
frequency.
.
A further source of parasitic signals in a cath
ode raytransmitting tube such as that considered
above is in unequal secondary emission from all
parts of the mosaic screen. This unequalemis
sion results from the combination of the ?nite size
of the mosaic particles, the non-uniform distribu
tion of charges over the surface of the mosaic
screen, variable charges on the glass wall of the
15 tube, and the non-uniform electrostatic ?eld pro
duced by the second anode.
It is the object of the present invention to pro
vide means for removing or reducing these and
other parasitic signals.
According to the present invention a. cathode
ray tube having a target or mosaic electrode com
prising a mosaic screen of mutually-insulated ele
ments capacitively associated with a common sig
nal plate, an electron gun for directing a cathode
25 ray onto the screen, and de?ecting means for
causing the ray to scan the screen, is provided
with a compensating electrode system disposed
between said gun and said screen and out of the
path of the scanning beam and biased to produce
.30 transverse to the scanned surface of said screen a
potential gradient which serves to minimize para,
‘sltic signals generated in said signal electrode.
The biasing potentials necessaryfor this purpose
are usually small compared with the potential
.35 difference between the cathode and secondanode
of the electron gun..
The invention will now be described with refer
ence to the accompanying diagrammatic drawing
which shows in perspective a View of a transmit
40 ting tube of the kind previously referred to, incor
porating an embodiment of the, present invention.
Referring to the ?gure, the tube comprises a
highly evacuated envelope or bulb 5 having a
tubular arm or neck section enclosing a conven
tional type electron gun and a bulbous section
enclosing a parallelogrammic and usually rectan~
gular mosaic electrode of a well-known type. The
mosaic electrode is so mounted in the envelope
that an optical image may be projected on its.
front surface by a lens system i 9, and the illumi
nated surface scanned by the scanning beam from
the electron gun in the neck of the envelope.
The electron gun, of the conventional type, is
shown as comprising a cathode 3, a control elec
585 trode 5 connected to the usual biasing battery,
and ?rst anode ‘l associated with a second or beam
focusing anode ‘i3, preferably a conducting coat
ing on the inner surface of the envelope 5 near
the neck, which acts as a collector electrode for
60 electrons from the mosaic electrode. These
anodes are maintained positive with respect to
the cathode 3 by a battery 9 and the electron
stream leaving the ?rst anode ‘l is accelerated and
vconcentrated into an electron scanning beam
65 focused on the mosaic screen by the second anode,
which also collects any electrons emitted by the
mosaic screen. Beam de?ecting means, such as
the usual de?ection coils 2| and de?ection plates
22 sweep the beam in a horizontal and a vertical
,
70 plane to scan the mosaic electrode.
The mosaic electrode may be of the well-known
type and may be constructed in various ways. In
consisting of a multitude of oxidized silver glob
ules 26 which are in effect discrete and are there
fore insulated from one another, each made
photo-electrically sensitive by being coated with
caesium in accordance with the practice in make
ing photocells. Themetal coating on the back of
the mosaic electrode is connected to one end of an
output impedance 30 and to the input circuit of a
translating device such as the picture signal
ampli?er 32, the opposite end of the impedance 10
being connected to the positive terminal of the >
battery i5, usually through a ground.
In accordance with my invention I provide for
the mosaic screen a compensating electrode which
is adjacent the mosaic electrode but out of the 15
path of the optical image focused on the mosaic
screen and also out of the path of the cathode ray
scanning beam, and which at suitable bias poten
tial will suppress or eliminate parasitic signals
which otherwise occur. Preferably the compen 20'
sating electrode is close to the edge of the mosaic '
electrode and is insulated from it. I have found
that a compensating electrode at one side and
another at one end of the rectangular mosaic
electrode will suppress'much of the parasitic sig
nals at both line frequency and at picture fre
‘quency, but for more complete suppression I pre
fer to use a compensating electrode system of four
electrodes, 23, 2d, 25, and 26, two of which are
mounted along the two parallel sides of the
screen, and the other two along the top and bot~ -
tom edges. Incompensatingsfor parasitic signals
resulting from unequal secondary emission from
the mosaic particles, I prefer to sub-divide the
electrodes on two or more edges of the mosaic 35
screen. Thus two of the electrodes such as 23
and 26 may be divided as shown by the dotted
lines resulting in individual electrodes 23a, 23b,
23c, and 26a, 26b, and 250. Electrodes 24? and 25
may be left continuous or these may likewise be 60
sub-divided in similar manner.
-
Each of the auxiliary electrodes is connected to
a voltage divider 27, which serves as a source for
the bias potential for the electrodes, through a
lead and also through a resistor 28 which reduces
the capacitance of the mosaic electrode to ground.
The compensating electrodes may be biased pref
erably a few volts positive or negative with re
spect to the second anode it in compensating for
parasitic signals arising from unequal secondary
emission. The electrodes along any side of the @ill
mosaic screen may be further biased positively
or negatively with respect to each other to give
the desired compensating or suppressing ?eld
at the mosaic screen surface.
With the tube as illustrated, scanning prefer
ably takes place in a series of lines from side to
side of the screen beginning at the left-hand
top corner. The base line wander at line fre
quency may be corrected by biasing to a few
volts positive with reference to the second anode
the compensating electrode 2d which is near the
side of the screen on which the line scanning
ends, and at frame frequency by similarly biasing
the compensating electrode 23, near the bottom
of the target. In this way there is produced 65
along the surface of the mosaic screen a field
which compensates for the ?eld due to the
scanned elements, and minimizes the parasitic
signals. The positive electrode 2d at the right 70
hand 'end of each line of elements traversed by
the scanning beam during line scanning attracts
a preferred form it consists of a thin sheet of mica " the secondary electrons emitted by each scanned
I8 having on the back a continuous metal coating element and counteracts the eifect of the posi
$6 or signal plate is and on the front a mosaic screen tively scann‘ed elements in the line to the left 175
3
2,181,892
of the scanning beam. The positive electrode
said compensating electrode at'a potential with
23 at the bottom of the screen likewise counter
respect to said screen for producing in conjunc
tion with said collector electrode along the sur
face of said screen an‘ electrostatic ?eld by which
the effects of the ?eld due to the scanned ele
acts the e?ect of the positively oscanned elements
above the line of scanning. I have obtained good
results with a battery 9 of 250 volts, a battery ii
of 750 volts, and a bias on the compensating ' ments of the series are minimized.
2. A cathode ray transmitting tube comprising
electrode of about 5 volts positive with reference
to the second anode I3. I have also found that
resistors 28 of a value of about 100,000 ohms, are
10 suitable.
a planar mosaic electrode including a mosaic
screen of mutually insulated photo-electrically
sensitive elements each capable of holding an 10
For suppressing parasitic signals resulting from
non-uniform secondary emission from the mosaic
screen I have found it desirable to bias the auxil
iary electrodes either positively or negatively in
electrostatic charge and a common signal plate
back of said screen and capacitively associated
with said elements, scanning means including an
electron gun for directing a scanning beam to said
such a manner that the transmitted picture when
715"'re-created'is
of uniform shading? It has been
screen and a collector electrode in front of said
screen, a plurality of’ compensating electrodes'ad
jacent and distributed along the edge of said
screen and out of the path of the scanning beam
and means to maintain each of said compensating
electrodes at a potential which will equalize the 20
e?‘ect of the charges on said photoelectrically
found that some tubes of this type are more'sub
ject to parasitic signals of this nature than to
parasitic signals resulting in base line wander.
20 I thus provide the potentiometer 21 which sup
' plies either positive or negative potential sources
sensitive elements produced by scanning said
as desired for the suppression of parasitic signals
due to inequalities of secondary emission over the
mosaic surface.
The auxiliary or compensating electrodes may
25
screen.
-
3. A cathode ray transmitting tube comprising
a parallelogrammic mosaic electrode including a 25
mosaicscreen of mutually insulated photo-elec
be’ used also to generate corrective signals which
maybe mixed with the signals from the signal
trically sensitive elements each capable of hold
ing an electrostatic charge and a common signal
plate back of said screen and capacitively asso
ciated with said elements, scanning means includ 30
ing an electron gun for directing a scanning beam
to said screen to liberate secondary electrons
from said elements and a collector electrode in
front of said screen, compensating electrodes
adjacent one side and one end of said screen and
means to maintain each of said compensating
ture signal ampli?er.
It is obvious that the compensating electrodes electrodes at a potential which will produce an
- 23, 24, 25,'and 26 of the ?gure may be replaced electrostatic ?eld which in combination with the
by compensating electrodes attached to the walls ' electrostatic ?elds produced by the collector elec
of the bulbous portion of the tube | and arranged trode and the charged elements of the screen will
between the cathode ray gun in the neck portion insure the uniform distribution over the surface
plate either directly or after ampli?cation. For
example the auxiliary electrodes, fed from a suit
30 able bias potential source through a high re
sistance may be connected through a condenser
to the mosaic electrode conductive coating, or to
a tapon the impedance which is connected to the
signal plate and across which the picture signals
35. are developed, or to a suitable point in the pic
of the screen of secondary electrons produced by
and the mosaic electrode assembly, that the elec
trodes-may be in the form of wires let in through
the glass walls, and that they may be perpen
dicular to the glass, or may be arranged parallel
scanning said screen.
4. A cathode ray transmitting tube as claimed
in claim 3 having a plurality of compensating
to the sides of the screen, as long as they are in
proper relation to the screen and are given suit
mosaic screen.
.
5.,A cathode ray transmitting tube comprising
able positive or negative biasing potentials.
What I have indicated the preferred embodi
ment of my invention of which I am now aware
50 and have also indicated only one speci?c appli
cation for which my invention may be employed,
it will be apparent that my invention is by no
means limited to the exact forms illustrated or
55 the use indicated, but that many variations may
be made in the particular structure used and the
purpose for which it is employed without depart
ing from the scope of my invention as set forth
in the appended claims.
electrodes along said side and said end of said
,
Having now particularly described and ascer
a parallelogrammic mosaic electrode including a
mosaic screen of mutually insulated photo-elec
trically sensitive elements and a common signal
plate back of said screen and capacitively asso
ciated with said elements, scanning means in
cluding an electron gun for directing a scanning
beam to said screen, a plurality of compensating 55
electrodes adjacent and distributed along the
sides and edges of said screen and means to main
tain each of said compensating electrodes at a
potential with respect to said screen for producing
in conjunction with said collector electrode along
tained the nature of said invention, and in what
the surface of said screen an electrostatic ?eld by
manner the same is to be performed, I declare
which the e?ects of the ?eld due to the scanned
that. what I claim is:
elements of the said screen are minimized and
the distribution of secondary electrons over the
65
surface of the screen made more uniform.
‘
1. A cathode ray transmitting tube comprising
65 a mosaic electrode including a mosaic screen of
mutually insulated photo-electrically sensitive
6; A cathode ray transmitting tube comprising
elements and a common signal plate back of said ' a target electrode adapted to receive an optical
screen and capacitively associated with said vele
image, a. collector electrode in front of said target
ments, scanning means including an electron gun electrode, and scanning means including an elec
70 for directing a ,scanning beam to said screen tron gun for directing a scanning beam over F
and‘a collector electrode in front of said screen, said target in a series of parallel paths, a com
a compensating electrode mounted out of the pensating electrode mounted out of the path of
path of the scanning beam and adjacent one the scanning beam and adjacent one end of the
. end of the paths followed by the scanning beam paths followed by the scanning beam, and means
in scanning aseries of said elements maintaining to maintain said compensating electrode at a
@
arsaeea
predetermined potential with respect to said tar
get electrode for producing in conjunction with
said collector electrode along the surface of said
screen an electrostatic ?eld by which the effects
of the ?eld due to scanning the target electrode
in one direction are minimized.
7. A cathode ray transmitting tube, comprising
a parallelogrammic target electrode adapted to
receive an electron image, scanning means in
cluding an electron gun for directing a scanning
beam to said target electrode to liberate second
ary electrons from said target electrode and a
collector electrode in front of said target elec_
trode, compensating electrodes adjacent one side
and one end of said target electrode, and means
to maintain each of said compensating electrodes
at a predetermined potential with respect to said
target electrode for producing in conjunction with
said collector electrode along the surface of said
2% target electrode an electrostatic ?eld by which
the effects of the ?eld due to the scanning of said
target electrode are minimized and the distribu
tion of secondary electrons produced by the scan
ning beam on said target electrode over the sur
face thereof made more uniform.
- '
V
8. A cathode ray transmitting tube comprising
' a target electrode adapted to receive an optical
. image, a collector electrode in front of said target
electrode, and scanning means including an elec
tron gun for directing a scanning beam over said
target in a series of parallel paths, a compensat
ing electrode mounted out of the path of the
scanning beam and adjacent one end of the paths
followed by the scanning beam, and means to
maintain said compensating electrode at a posi
tive potential of approximately ?ve volts with
respect to said target electrode for producing in
conjunction with said collector electrode along
the surface of said screen an electrostatic ?eld
by which the effects of the ?eld due to scanning
the target electrode in one direction are mini
mized.
10
9. A cathode ray transmitting tube comprising
a parallelogrammic target electrode adapted ‘to
receive an electron image, scanning means in
eluding an electron gun for directing a scanning '
beam to said target electrode to liberate second
15
ary electrons from said target electrode and a
collector electrode in front of said target elec
trode, compensating electrodes adjacent one side
and one end of said target electrode, and means
to maintain each of said compensating electrodes 20
at a vpositive potential of approximately ?ve volts
with respect to said target electrode for producing
in conjunction with said collector electrode along
the surface of said target electrode an electro
static ?eld by which the effects of the ?eld due 95
to the ‘scanning of said target electrode are mini
mized and the distribution of secondary electrons
produced by the scanning beam on said target
electrode over the surface thereof made more
uniform.
HARLEY A.
.
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