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Патент USA US2133882

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Oct. 18, 1938.
vv. K. zwoRYKlN -
2,133,882
TELEVISION SYSTEM
Filed Marcnso, 1955
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ATTORNEY
Patented 50ct. 18, 1938
. . 2,133,882
2,133,882
TELEVISION SYSTEM
Vladimir K. Zworykin,
Philadelphia, Pa., assign
or to Radio Corporati on of America, a corpora
tion oi’ Delaware
Application March 30, 1935, Serial No. 13,792
2 Claims.
(Cl. P18-7.2)
My invention relates to improvements in tele
vision systems and the method of operation
thereof.
‘
In developing picture signals for television
5 transmission, a scanning device >is exposed to
light from the view or object for transmission.
One form of scanning device for this purpose
comprises a'tube having a mosaic, photosensitive
screen upon which an image of the View is pro
10 jected through a suitable lens system. The tube
is provided with means for developing a ray of
electrons and directing the same at the screen.
The ray is deñected simultaneously in different
. directions to scan the screen, whereby the pic
15 ture signals are »developed for supplyto an am
pliñer and transmitter. In such a system, it has
been found that the cathode ray transmitter tube
operates most einciently under a given condition
of illumination by light from the View for trans
20 mission and, for this reason, manual adjust
ments have been made heretofore for the pur
pose of maintaining the tube at its most eiii
cient point of operation as the light intensity, to
which the photosensitive screen is exposed from
25 the view, might vary due to occurring changes at
the transmitting station such as a change in
light intensity from the view, or a change in
the distance between the transmitting tube and
¿o
the view.
With the foregoing in mind, it is one of the
objects of my invention to provide an improved
television transmitting system of the character
referred to in which means are provided for
automatically controlling the light intensity to
:5 which the scanning device is exposed from the
View, whereby the device is maintained substan
tially at its most efficient point of operation.
Another object of my invention is to provide a
system of the type described wherein electrical
0 means are utilized for correlating the sensi
tivity of the scanning device to the degree of
illumination of the object being scanned.
Other objects and advantages will herein
after appear.
'
the photosensitive screen of the tube and the
view- or object for transmission to control the
iight intensity to which this screen is exposed
from the View. An electrical eii’ect is developed
which varies with occurring variations in the
light intensity from the view, and is used to cause
openingor closing movement of the shutter de
vice, as might be required, to maintain the
value of light intensity on the screen substan
tially at the correct point for most-'efñcient op
eration of Athe tube.
My invention resides in the improved con
struction and method of operation of the char
acter hereinafter described andY claimed.
For the purpose of illustrating my invention',
several embodiments thereof are shown in the
drawings, wherein
-
Figure 1 is a simplified, diagrammatic View of
a television transmitting system constructed and
operating in accordance with my invention; and
Figs. 2, 3, 4, 5, 6 and 'I are views similar toY
Fig. 1, showing different modiñcations.
In Fig. 1, the reference numeral lli designates
a scanning device in the form of a cathode ray
tube of conventional design, comprising a tube
i2 provided with a mosaic photosensitive screen
lll and with means in the form of an electron
gun i6 for developing a stream or ray /I8 of
electrons and directing the ray at the screen.
The screen comprises a mica sheet provided on
the front face 2l! thereof with a large number
of minute, metallic, photosensitive elements,
spaced and insulated from each other.
The
screen is provided on the back face 22 thereof'
with a metallic layer to which a connection 2li is
made. In operation, an image of the object or
view 26 for transmission is projected by a lens
system 28 onto the photosensitive surface 2t of
the screen. In this way, individual, electrostatic
charges are developed over the surface yof the
screen, the value of the charge or charges at any
40
elemental area being proportional to the light
_ intensity on that area at the instant.
,
.
~The ray i8 of electrons is deñected horizon
ning device and the circuits associated therewith tally at a relatively high rate by coils 3U and 45
are utilized to generate an electrical eii'ect which is simultaneously deflected vertically at a rela
varies with occurring variations in the light tively low rate by coils 32, whereby the ray
intensity to which the device is exposed from v is caused to` scan the photosensitive surface of
the screen Hi. In this way, picture signals are
y the view for transmission. This eiîect is, in turn, developed
and supplied by the connection 2c to
utilized to control the light intensity to which
50
an ampliñer 3d and a transmitter 36. `
the scanning device is exposed from the view,
For
the
purpose
of
controlling
the
value
of
in the sense that the light intensity is made to
5
In accordance with my invention, the scan
decrease upon an increase in the electrical con
i trol effect and to increase upon a decrease in
such
eiîect.
^
»
'
More speci?cally, in accordance with my inven
tion, a cathode ray tube of conventional design
-is utilized to develop the picture signals„and an
adjustable shutter device is interposed between
light intensity to which the screen hi is ex
posed from the view. a shutter device in the form
of an- adjustable iris diaphragm 38 of. conven
tional design vis associated with the lens system
28. The opening in the diaphragm 38 is made
larger or smaller upon rotation of a gear 40
which meshes with a pinion 42 ilxed on a shaft
44 driven by a?D. C motor 46._» The motor 46 is 60
2
2,138,882
provided with separately excited ñeld coils 48,
bring it back to the point forv most eilicient oper- I
as represented in the drawings, and is also pro
vided with a suitable brake 50 which places a
ation.
relatively light, initial load on the motor.
_
The amplified picture signals from the ampli
ñer 34 are supplied by a connection 52 to the
grid of a relatively high impedance electron tube
54 of the type identiiied in the trade as “RCA
57". The tube 54 has a self-bias resistor 56 of
10 relatively high resistance. 'I‘his resistor is
shunted by a condenser 58 of relatively high ca
pacity. In operation, a D. C. voltage is devel
oped across the resistor 56 which varies sub
stantially ‘in accordance with occurring varia
15 tions in the average peak A. C. voltage on the
grid of the tube 54. This tube and its associated
circuits operate at a peak Voltmeter. An elec
trical effect, accordingly, is developed which va
ries with occurring variations in the light in
20 tensity to which the screen I4 is exposed from
the view. This electrical effect is ampliiied by a
control amplifier -68 to develop a voltage across
a resistor 62 in the output circuit of a tube 64
forming part of the amplifier.
The motor 46 is supplied from the amplifier 68
` through connections 66 -and 68, a battery 18 be
_ _ing connected as shown in the connection 68.
Adjustments are made initially so that when
the Value of light intensity to which the screen
30 I4 is exposed is substantially correct for most
ei'ñc1ent operation of the electron scanning de
vice I0, the potential difference Vm between the
potentials Va and Vb is substantially zero, or
at least so small as to prevent operation of the
35 motor 46 against the drag orload provided by
the brake 50. If illumination of the Ascreen I4
_should increase, the potential Va increases cor»
Y
In Fig. 2, the operating action is the same as
that in Fig. 1 except that the electrical control
effect is obtained from the second anode 'I2 of
the transmitting tube. The principle involved
resides in the fact that the photoelectric cur
rent, taken from the anode 12, varies proportion
ally to occurring variations in the degree of il
lumination of the screen I4. For the purpose of l0
adjusting the diaphragm 38, a solenoid ‘I4 is
utilized instead of the motor in Fig. 1. The sole
noid is connected by levers 16 and 18 to the ac
tuating member of the iris diaphragmv 38. A
piston 88 is connected as shown to-the solenoid,
.and is disposed within a cylinder 82 provided at
one end with a vent opening 84. A coil spring
86 is disposed between the piston and the other
end of the cylinder. Adjustments are made ini
tially so that the degree of illumination of the 20
screen I4 is correct for most eñ‘icient operation,
in which case the voltage across the lines 66 and
68 is sufficient to operate the solenoid so that
it holds the diaphragm 38 open *at the right
point, against the action of the spring 86 which
is compressed. If the degree of illumination of
the screen I4 drops below the desired point, the
potential across the lines 66 and 68 will drop cor
respondingly to lessen the downward pull of the
solenoid 14. The spring `86 is then eiîective to
cause movement oi.’ the lever 16 to open the dia
phragm 38 until illumination of the screen I4
is again sufiicient to cause the downward pull
of the solenoid 14 to balance the upward force
due to the spring 86. If the degree of illumina- A
tion of the screen increases beyond the point de
sired, the reverse action takes place. That is,
the potential across the lines 66 and 68 increases
respondingly to give a, Value to the potential Vm so that the downward pull of the solenoid 14 is
to cause rotation of the motor armature in the suilicient to further compress the spring 86, 40
proper direction to cause closing movement ci' whereby the diaphragm 38 is caused to close.
the iris diaphragm 38. 'I'his action continues 'This action continues, as will be well understood,
until sufficient light is cut off from the screen until the degree of illumination of the screen
I4 to bring the value of the potential Va back to
I4 is again such that the downward pull of the
the point whereat the potential Vm is at least solenoid 14 is balanced by the upward force due
45 low- enough to permit the brake 50 to stop the
' to the spring 86.
motor. If _illumination ofy the screen I4 should
'I'he piston 80 and cylinder 82 operate as a
decrease below the desired value for most em
dash-pot and, with the vent 84 at the proper size,
cient operation, the reverse action takes place. serve the same purpose as the brake 50 in Fig.
'I'hat is, the potential Va decreases and becomes .1 to provide a time-lag.
50 lessv than the potential Vb, whereby the polarity
In the system shown in Fig. 3, both the con
across the lines 66 and 68 is changed and the po-- trol electrical eiîects in Figs. 1 and 2 are utilized
tential Vm becomes at least Suillcient to cause to control the motor 46 for adjusting the dia
reverse -rotation of the motor to cause opening phragm 38. 'I'hat is, both the effects of varia
. movement ofthe diaphragm 38. This action tion of the peak picture signals and the photo
continues until the screen I4 is again exposed to electric current from the second anode 12 are
the “equired light 'intensity from the object for utilized for obtaining the automatic control of
light on the screen I4. In this ligure, the vari
mostv eiiicient operation, at which time the po
ous parts and connections corresponding, re
tential Vm again becomes zero, or at least de
spectively, to those in Figs. 1 and 2, are desig
Iii) creases to a value insufñcient to cause rotation
of the motor against the braking action of the nated by the same reference numerals as the lat
brake 50.
_
.
The brake 50 provides for sui‘llcient time lag
to prevent actuation of the diaphragm 38 for
every slight-momentary change in illumination
of the screen. I4.
'
From the foregoing it will be seen that varia
tion in the peak picture signals, with occurring
pliner 68.
‘Variations in illumination of the screen >I4, is
utilized to develop an electrical control eñect
which varies in a similar manner and operates
to control adjustment of a shutter device inter
jacent 4the screen I4y so that it is exposed to the
light emitted therefrom.- In this way, an elec
posed between the scanning device and the view,
76
ter. In Fig. 3, itis proposed to employ variable
,resistors 88 and 80, connected in the circuit as
shown, for the purpose of adjusting the ampli
tude'of the control amplifier 60. Also, the con
trol signalsl from the anode‘ 12 are ampliiled by
an ampliñer 8| before being supplied to the am
.
In Fig'. 4, the control electrical effect is ob
tained by supporting a photoelectric cell 82 ad
trical control eiïect'is developed which increases
whereby the value or degree of illumination of - when the degree of illumination 'of the screen
>the scanning device is changed accordinglyto , I4 exceeds that required for most efiicient op 7.
2,183,882
eration, and decreases when the degree o1’ illu
mination of the screen falls below the desired
value. The control current from the cell 92
is ampliiied by the control ampliíier SB and is
OW eiîective to cause operation of the motor ‘i6 in
the same manner and for the same purpose as
in Fig. l.
'
'
The arrangement and operating action of the
system shown in Fig. 5 is the same as that in Fig.
2 except that an additional connection 9d is made
from the output of the control amplifier 6E to
the control grid Bâ of the electron gun. The
polarities are such that as conditions change to
call for further opening of the diaphragm 38, the
15 blason the grid S5 is decreased to increase the
intensity of the scanning ray correspondingly.
When conditions change to call for closing of the
diaphragm 38, the bias on the grid St is increased
correspondingly to decrease the intensity of the
20 scanning ray.
In Fig. 6, the scanning device is represented
3
emits secondary electrons, so that the individual,
photosensitive elementsv _become more negative,
and the tube becomes correspondingly more sen
sitive.
A
When the degree of illumination of the screen
l# increases beyond the desired pointfth’e action
is just the reverse. That is, the potential on the
anode iid becomes more positive to cause’a cor
responding increase in the velocity of electrons
from the source M3.“ Since the electrons from 10
this source now strike the screen M at a greater
velocity, more secondary electrons are emitted
therefrom than primary electrons, and the mi
nute, photosensitive elements become less nega
tive. The sensitivity of the tube is thereby de
creased until it is again operating at the de
sired point.
'
'Ihe values of operating potentials, resistance
and capacity may be substantially as designated`
in Fig, l. These values, however, are not critical,
and may be varied over a substantial range, as
as being in the form `of a cathode ray tube of
might be required.
conventional design in which the mosaic, photo
From the foregoing it will be seen that I have
provided an improved television transmitting sys
tern and method of operation thereof in which
adjustments are automaticalLv made as the de
gree of illumination of the scanning device might
vary due to change in illumination of the object,
or change in the distance of the transmitting
tube from the object, and that in this way the
sensitive screen ida is two-sided.
That is, the
25 minute, metallic elements,l represented-anse, pass
through the supporting mica sheet, and are pho
tosensitive on the side removed from the electron
gun. In operation, an image of the view is
projected onto the photosensitive surface of the
screen ida through a wire mesh- iûD which is
maintained at a potential positive with respect
to the potential of the screen illu. The principle
involved res’tles in the fact that the sensitivity
` of the tube varies upon variation in the potential
on the anode IBD. The control electrical eiîect
is obtained, as in Fig. 2, from the second anode
72a, and is supplied to the control amplifier $0.
The potential on the anode lilo is dependent upon
the voltage across the resistor md in the output
circuit of the amplifier Si?.
In operation, adjustment of the potentiometer'IBS is made to bias the anode 109 to the point
for most emcient operation. Ii the degree of
illumination of the screen Ilia decreases below
this point, the voltage across the resistor |04
charges to cause the potential on the screen |00
to become more positive with respect to the
potential on the screen ma. In this way, the
sensitivity of the tube is increased until the
point is reached whereat the tube is again oper
ating most efiìciently. If the degree of illumina
tion of the screen 98 increases beyond the desired
point, the automatic control action is just the
reverse. That is, the potential on the anode |00
becomes less positive with respect to the poten
tial on the screen Ida to decrease the sensitivity
of the tube, until conditions are again restored to
the point for most eñicient operation.
In Fig. '1, the transmitting tubé" is ’shown as
w being provided with an auxiliary source of elec
trons, designated generally by the reference nu
meral I 08, and comprising a iilament- l IU, a grid
H2, and an anode HB. By this means, electrons
in the form of a spray are directed at the screen
iE to supply a bias thereon. In operation, as the
degree of illumination of the screen M decreases
below the point for most eñicient operation, the
15
'
system is maintained at substantially the point
for most emcient operation thereof.
.
It will be understood that modiñcations, other
than those disclosed, are possible without de
parting from the spirit of my invention or the 85
scope of the claims.
`
I claim as my invention:
1. In a television system, a cathode ray trans
mitter tube comprising a screen which is so sen
sitized that it emits electrons when an image 40
is formed thereon, said tube also comprising an
electrode positioned to collectk said electrons and
further comprising means for producing a cath
ode ray, means for scanning said screen by said .
cathode ray whereby picture signals are devel 45
oped, a connection including an impedance unit .
between said collector electrode and said ray
producing means, a shutter device for controlling
the intensity of said image, and means including
a direct current ampliñer connected between said 50
impedance -¿mit and said shutter for decreasing
the intensity of said image in response to an in
crease in the `voltage drop across said impedance
unit.
'
2. In a television system, a cathode ray trans 56
mitter tube comprising a screen which is so sen
sitized that it emits electrons when an image
is formed thereon, said tube also comprising
means for producing a cathode ray, means for
scanning said screen by said cathode ray where 80
by picture signals are developed, means for pro
ducing an electrical eiîect which varies in re- ’
spense to occurring variations in the intensity of
said image, a shutter device for controlling the
intensity of said image, means for controlling said 65
shutter device in accordance with said electrical
eiïect in the sense that the shutter device is
control signals, which in this case are taken from
the second anode 12 and supplied to the control
ampliner Se, are effective to cause the poten
tial on the anode HB to become less positive,
caused to close in response to an increase in the
whereby the velocity oi electrons from the source
I 88 decreases correspondingly. The screen It
then collects more primary electrons 'than it
tensity of said image.
VLADEHIR. K. ZWORYKIN.
intensity of said image, and means for simul
taneously increasing the intensity of said cath
ode ray in response to an increase in the in
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