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Патент USA US2133075

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Oct. 11, 1938.
Filed Feb. 12, 1934
‘101% HA x20 W/C‘K
M ‘
Patented Oct. 11, 1938
Frank Blythen, Hayes, and John Hardwick, West
Drayton, England, assignors to Electric and
Musical Industries Limited, Hayes, England, a
company of Great Britain
Application February 12, 1934, Serial No; 710,802
In Great Britain February 13, 1933
3 Claims.
The present invention relates to cathode ray
tubes such for example as are used in television
Such a tube may comprise a heated cathode, a
5 control electrode, means for accelerating the elec—
tron ray and bringing the electrons to a focus on
a ?uorescent screen and means for de?ecting the
ray over the screen.
The received picture signals are applied be
10 tween the control electrode and cathode, to vary
the negative potential of the grid in relation to
the cathode, and serve to increase and decrease
the intensity thereof whilst the ray is swept, by
the de?ecting means, over the screen in harmony
(Cl. 178-—'7.5)
and means for increasing the amplitude of sig
nals representative of the darker portions of the
object as compared with signals representative of
the lighter portions of the object.
An embodiment
with reference
of the invention
to the accompanying
will now be
drawing in which
Fig. l is a circuit diagram of television receiv
ing' apparatus arranged in accordance with the
present invention,
Fig. 2 is a graph of the light intensity-grid,
voltage characteristic of a known form of cathode
ray tube, light intensity being plotted as ordi
nates ‘and grid voltage as abscissae, and
Fig. 3 is a graph of the anode current-grid volt- E15
15 with the scanning device at the transmitter.
In such tubes it is found that the light inten
sity-grid voltage characteristic is‘ very curved,
the rate of change of light intensity being con
siderably greater for less negative grid potentials,
voltage being plotted as ordinates and grid‘volt
20 that is higher light intensities, than for more
signals are applied to the grid circuit of a screen- ‘20
age characteristic of a thermionic valve, anode
age as abscissae.
Referring now to Fig. 1, the received picture
negative grid potentials, that is lower light inten
grid valve I, the anode circuit of this valve being
sities. ‘It is usually necessary to bias the control
coupled to the control grid circuit of a cathode
ray tube 2. The positive potential applied to
the screening grid 3 relative to the cathode 4
grid relatively to the cathode in such a way that
a picture signal of maximum amplitude in the
25 “black” direction reduces the intensity of the
ray substantially to zero and when this is done
it is found that, owing to the curvature of the
of the valve l and the value of the anode resist- 25
ance 5 are both lower than usual. By suitably
biasing the control grid 6 of the valve l relative
characteristic, gradations of intensity in the
to the cathode 4, the shape of the anode current
grid voltage characteristic of this valve, shown
in Fig. 1, can be made complementary to the 30
shape of the light intensity-grid voltage char
acteristic of the cathode ray tube 2, shown in
Fig. 3, so that the signals applied to the grid 1
darker parts of the reproduced picture are masked
30 whilst, in the lighter parts, they are unduly ac
It is an object of the present invention to re
move or reduce the errors introduced by a non
linear characteristic in a cathode ray tube.
It is a further object to provide a method of
transmitting and receiving images. of objects
wherein picture signals are distorted, either at the
transmitter or at the receiver, before being ap
plied to a non-linear reproducing device such as
40 a cathode ray tube, in such manner as to com
pensate, at least partially, for the non-linear
light intensity-modulating voltage characteristic
of said reproducing device.
Yet another object of the present invention is
45 to provide television receiving apparatus com
prising a cathode ray tube or a like reproducing
device having a non-linear light intensity-modu
lating voltage characteristic and means for dis
torting picture signals, before application to said
50 device, in such manner as to compensate, at least
partially, for the non-linearity of said device.
Yet another object of the present invention is
to provide television transmitting apparatus com
prising means for generating picture signals cor
55 responding to the light and shade of the object
of the cathode ray tube 2 are distorted, signals
in ‘the “black” direction appearing in the anode 35
circuit of the tube 2 at greater intensity than
signals in the “light” direction.
The valve I is used also to rectify an incoming
carrier modulated with picture signals. This is
done by arranging the valve, in the manner illus- 40
trated, as a grid-leak recti?er.
When the distortion introduced by the cathode
ray tube 2 is compensated for in the manner de
scribed, the negative bias upon the control grid
1 of the cathode ray tube 2 may be made less 45
than is usually necessary whilst still obtaining
good reproduction of black portions of a picture.
As a consequence of this, an increase in modula
tion does not produce such an increase of back
ground brightness as results from working with 50
higher values of bias. Any change that remains
may, however, be compensated for by biasing
the grid 1 of the cathode ray tube 2, as shown,
from the D. C. potential drop along the anode re
sistance of the distorting valve.
For the reception of a carrier frequency of
about 40 megacycles the following arrangement
is satisfactory:
A selector circuit 8 tuned to the carrier fre
quency to» be received has one terminal connected
to the cathode 4- 0f the screen-grid valve l and
the other terminal connected through a con
denser 9 of 25 micromicrofarads shunted by a
resistance ID of 10,000 ohms. The screening grid
10 3 is maintained at a potential of 40 volts relative
to the cathode 4 and the vanode H is connected
through a resistance 5 of 10,000 ohms to a point
at 200 volts relative to the cathode 4. The end
of the resistance 5 remote from the anode H is
15 connected to the cathode l2 of the cathode ray
tube 2 and the other terminal of the resistance
5 is connected through a high frequency choke
coil I4 to the control grid ‘I of the cathode ray
tube 2.
A receiver of this kind is of particular advan
tage for the-reception of motion picture ?lms
because it is common practice in the ?lm indus
try to develop ?lms in such manner that detai
in bright portions of the picture is brought out,
25 or ampli?ed, as it were, relatively to the detail
in the darker or more opaque portions of the
pictures. This is done because pictures projected
upon av screen from ?lms developed in this way
appear more natural to the eye. Therefore it is
30 essential that, when ?lms of this kind are trans
mitted, the receiver should not still further em
phasize detail in bright portions of the picture,
normally non-linear light intensity modulating
voltage characteristics which comprises the steps
of applying from an amplifying system to the
control circuit of the electro-optical reproducing
device controlling signals and modifying the sig
nals prior to applying the same for control pur
poses by operating the amplifying system upon
that portion of its anode current-grid voltage
characteristic which has a curvature substan
tially complementary to the curvature of the 10
light intensity modulating voltage characteristic
of the electro-optical reproducing device.
2. The method of compensating for distortion
in reproducing electro-optical images upon the
viewing target of a cathode ray tube having nor
mally non-linear light intensity modulating volt
age characteristics which comprises the steps of
amplifying and non-linearly detecting control
ling signals to provide an output characteristic
complementary to the non-linearity of the cath- -
ode ray tube and applying the ampli?ed detector
signals to the control circuit of the cathode ray
tube to modulate the electron beam developed
in the tube whereby a substantially linear re
sponse is obtained.
N) in
3. In a television system wherein a non-linearly
responsive cathode ray tube having a control cir
cuit is used to produce electro-optical image rep
resentations andwherein a grid leak multi-grid
thermionic tube having input and output cir '30
cuits is arranged to receive upon the input cir
cuit signals ‘representative of the electro-optical
as would be the case if distortion of the received
signals is not effected as is described herein.
Although it is preferred to carry out the cor
effects, the method steps of operation which
comprise non-linearly detecting the received sig
rection of the picture signals according to the
linearity of the cathode ray tube and feeding the
detected signals from the output circuit of the
thermionic tube through a frequency discrimi
nating path to the control circuit of the cathode
ray tube so that electro-optical image represen
tations are substantially linearly reproduced.
present invention at the receiver, in some cases
the correction may be effected before transmis
We claim;
1. The method of compensating for distortion
in reproducing electro-optical images upon the
viewing screen of a cathode ray tube having
nals in a manner complementary to the non
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