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Àug» 6, 1946
ML cAwElN
2,405,290
TELEVISION SIGNAL - AMPLIFIER
Filed March 29, 194s
3 Sheets-Sheet l
INVENTOR
Aug. 6, 1946. T
M. cAwElN '
TELEVISION SIGNAL AMPLIFIER
1 Filed March 29, 1943
3 Sheets-Sheet 2
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TELEVISION SIGNAL AMPLIFIER
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Filed Marsh 29, 1943
s sheets-Sheet s
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INVENToR
MADISON ¿cAwErN
Patented Aug.~6, 1946
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UNÃTED STATS
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2,405,290
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TELEVISION SIGNALAMPLIHER
\
Madison Cawein, Fort Wayne, Ind., assignor to
Farnsworth Television and Radio Corporation,
a corporation of Delaware
Application March 29, 1943, serial No. 480,978
1
~ 10 Claims.
(Cl. 178-7.5)
2
This invention relates to amplifiers and par
' grid adjusts itself to a direct current signal level
suchpthat the maximum positive peaks of one` oi
ticularly to amplitude discriminating amplifiers
for expanding non-linearly one of the compo
nents of a composite television signal.
the signal components produce a zero bias of the
‘
grid.-
According' to conventional television practice,
a carrier wave is modulated by both video and
necessary to amplify non-linearly one of the com
which is retained,
ponents and sometimes to simultaneously sup
press the other component. When the video
component is so amplified, itis possible to eilect
disadvantage of this latter type of limiter is that
plitudein order that the 'signal component which
is toibe suppressed have a voltage which will
elîect the cut-off of plate current in the tube at
the desired point of the signalfwave. For ex
diñers from the relative contrasts between other
parts of the picture. For example, it may be clesirable to deemphasize the contrast between the
darker parts of the picture while at the same
time to emphasize or accentuate the contrast
between the lighter parts of the picture. The
'gamma control may be accompanied by a separa
tion of the video signal component from the syn
ample, _where it ‘is desired to recover the 'syn
chronizing Vcomponent to the exclusion of video
componentv fromva" composite 'television signal
2 constituted in accordance with the present stand
ards adopted by RadioV lManufacturers Associa
tion in the United States,`the~ grid .voltage to
eiïect plate currentcut-oif should correspond to
chronizing component of the composite television
signal.
For the synchronous operation of the receiving
the television signals representing the black por
f tions of the picture. Wherever possible it is' de- '
439
one or moreampliñers for the demodulated sig
sired to recover. the video component to the ex
«- clusion of the synchronizing component >andto
amplify non-linearly` the video component for
the purpose of gamma control, it is desirable to
accomplish this result before the> video com
"le
this typeof limiter is that it can be used only
in cases where the direct current signal level of
the picture to be reproduced has been established. 45
input circuit of the tube in such a manner that
one of the signal components drives the potential '-
of Athe grid of the tube beyond lthe point of plate
current Acut-off and the other signal component
is` amplified in the output lcircuit o_f thetube.
This type of limiter can be arranged so that the
sirable to _separate the video signal component
from the synchronizing signal component in the
signal Wave derived from the detector Vofithe're
ceiver. Hence, for the operation of a limiter of
the grid cut-off xtype,'it is necessary to provide
nals in order to obtain the required amplitude in
the case of weaksignals. Also, where it is de
,
Another type of limiter employs a tube which
’
it requires television signals of considerable am
between some parts of the reproduced picture
is biased to effect plate current cut-ofi.r The 'com
posite television signals are impressed upon the
‘
' As .is well understood in the art, however, a
a gamma control such that the relative contrast
Numerous circuits have been devised for oper
ating limiter tubes. One expedient is to bias the
tube for saturation at a predetermined signal
level. The composite television signals are ap
plied to the input circuit of the tube so that one
of the signal components drives the tube to satu
ration while the other signal component is am
plified in the output circuit. A disadvantage of
'
tion and reproduce in ampliñed form, withoutk
substantial distortion, the signal component
television signal.'v At the receiver, it frequently is
press any desired one of the components-
'
ployed heretofore effect the desired signal separa
synchronizing components to form a composite
apparatus, it also is necessary to separate the
synchronizing and video components in such a
manner that the syncëhronizing component is re
tained and the video component is suppressed.
The separation of the two components of the
television signal may be accomplished by means
of limiter tubes. Such tubes may beV utilized to
separate the two signal components and to sup
'
Limiters of these two types and others em
ponent is amplified.-
.
_
Aníobject of the present invention, therefore,
is to provide,A in a'television system, an improved
signal separator, the operation of which is inde
pendent of the signal strength or the directA
current signal level,
_
`
’
Another object of the invention is to provide
an ampliiier for obtaining non-linear- distortion
of a portion of a composite television signal,-
whereby the distorted portion may beV separated
from other portions of the _television signal. _
_: Stilljanother object, ofthe invention is to pro
vide, in'a‘television receiver, an improved signal
limiter lwherein there is employed a yregenerative
voltage feed-back_'irom the output ¿circuit "cia
triade to _theginput çircuitiliereef.. whereby te
4
of a, cathode ray tube I3 for controlling, in a
conventional manner, the shading of the picture
to be reproduced.
The demodulated video and synchronizing
separate the synchronizing and video compo
nents of weak as well as strong composite te e
vision signals.
A further object of the invention is to provide
an improved non-linear feed-back amplifier
which is discriminatory of signal amplitude,
signals are coupled by means of a condenser I4
to the input circuit of a space discharge device,
such as a triode vacuum tube I5.» The input cir
whereby only the synchronizing component of
cuit includes the cathodefand the control grid
of the tube which are interconnected by resist
a composite television signal is ampliñed.
A still further object of the invention is to
provide a non-linearly distorting amplifier,
whereby the video component of a composite
television signal may be recovered‘in' 'such> form"
ance means.
This means comprises a series ar
rangement of a grid leak resistor I6 and a
cathode follower resistor I1, and the junc
tion4 point of these resistors is grounded. The
condenseris connected to the grid leak re
“sist'or portion-of the input circuit resistance ele
to eiîect a gamma control of a reproducedïpicture.
In accordance with the-~ present `Vinvention, -
there is provided a space discharge device suclrv
ment. There also is provided a variable resistor
I8 vconnected between the anode of the tube and
the ’cathode follower resistor Il. A battery I9
is connected through a resistor 2B to the anode
as a three element vacuum tube which employs
a self-biasing grid circuit. Th’ecathode'circ'uit
of the tube is made degenerative and‘thereîis“
coupled to the cathode a'direct current regenera
tube.
'
tive feed-back?circuit.- The arrangement is such 20 of Itthe
Will appear from subsequent -portions of the
that the regenerative component is large relative
description that there is developed at the cathode
tothe degenerative component so as to eiîect a
of the tube I5 a, square-topped impulsive voltage
discrimination in signal amplitude, Wherebyall
at the synchronizing signal frequency. This
signals of less than a predetermined positive
voltage
is applied to conventional synchronizing
amplitude are suppressed inthe 'outputcircuih 25 and scanning
control apparatus'ï‘l, the'purpose
Also‘the signals' which are reproduced in the
of which is to separate the horizontal and verti
output circuit are ampliñed in a non-linear man
cal synchronizing signals so as- to control the
ner with respect t0 the corresponding signals im
scanning generators. ’The horizontal` and verti
pressed upon the input circuit.' The magnitude
of the distortion varies directly> as a Lfunction 4of
the impressed signal7 amplitudeï
n
so
Whether the reproduced signals correspond
to the video or synchronizing components de
cal generators are connected‘to*4 the Yrespective
sets of deflector elements 22 and 23;»'whereby'the
usual defiections of the electronßbeamrmay be
eifected.l
‘
Y
The signal which appears in the output 'circuit
vision signal as it isimpressed upon the' input -cir 35 of detector vI I has afor'm‘ such as that illustrated
by the curve 2E of Fig. ‘3; This signalv consists
cuit of the‘ampli'i'ler;
Y
of video and synchronizing`> components vand va
For a betterI understanding of theV invention,
ries
in polarity so that the negative portions
together withl other’and. further objects-thereof,
thereof> constitute some‘ of the video signals'and
reference" 'is ‘ had tov the" following»` description
the positive'portions thereof constitute the-re-taken in connection with vthe- accompanying
mainder
of the video signals and the synchroniz
drawings, and its -scope will be pointedout inthe
ing impulses. If such a*l signal were applied to
appended ‘ claims. `
'
a prior art limiter, having a' tube'biased toy ei'r‘ect
1n the ^ accompanying >`drawingsâ
Fig; 1 is a> circuit diagram of» a'television re- _. plate current cut-on, the signal would have the
relation~ of the curve 25'iof Fig. 2, with respect
ceiver, partially schematic, embodying .the- pres
to the-plate current versus gridV volt'age'charac
ent‘linv‘ention, as-ernployedto recover the syn
teristic of the tube I5.
chronizing component from- a composite tele
This would be the case in the present ampli-A
vision signal;
fier if it were not for the'regenerativefeed-back
Fig. 2 is a graphic representation of typical
provided. It is seenthat the tube has a
television signalsin relation to the plate~ cur 50 voltage
zero grid-to-cathode' bias' corresponding' to 'the
rent versus grid voltage characteristic of a'vacu
maximumY positive peaks vof the signal; If’the
um tube;
~
signal applied to the input circuit ofthe'tube
Fig. 3 illustrates typicalV television signal volt'
is relatively weak,Y the‘iarnplitude is-insuii‘icient
ages appearing in the circuits of Fig. 1 which are
to carryv the grid sufficiently' negativeV to' effect
55
of assistance in explaining the operationl'of-l the
cut-01T of the' plate >current below the VbasesV ci
illustrative embodiment of the invention; and
the pedestals of the synchroniaingimpulses. The
Fig. 4 is a circuit diagram of a television re
result produced in such a >case vis >illustrated in
ceiver, partially schematic, embodying the pres
Fig. 2 in which the curve 26 represents the plate
pends upon the polarity of the composite tele
ent invention as employed tof recover the video
component from a composite television-*signal
in a form suitable for Veffecting a gamma-«control
of the reproduced picture.
Y
_
N ,
current derived from a weak »signal‘applied‘ to
a‘signal limiter of the grid cut-off type. Thus,
separation of the video and synchronizing sig
nals by such a device is impossible, unless the sig
Referring now more particularly to> Fig; 1 of
the drawings, there is shown> schematically-_a
nal strength is increased by amplification before
superheterodyne receiver embodying-the present
the signal is applied to the limiter.
invention in a preferred form. Thetelevision
Y y
_ i Á
'
, The apparatus in accordance ¿with the present
signals which are interceptedV by an antenna I0
are ,converted into an intermediate,` frequency
invention combines the amplifying ¿and limiting
operations in the circuits associatedv with'av single
video signals andthe synchronizing impulses are
tube then would' nuctuate'asiiiustrated‘pyftrie
three-element tube. Assume for the~ moment
and demodulated by conventional radiantvenergy
when a compositeftelevision signal having
receiving apparatus I I , labeled inthe drawings ¿as 70 that,
theY
form
of theï'curve 24'of
3Tis1appl'ied'to
“Frequency converter, L'. F. amplifier, detector.”
the
input
circuity
of`the'ftube
I
5*,"l
the'` feed-back
The rectified television signals consisting Aof the
circuit is inoperative.V The ' anodefvol'tage‘ ->ofthe
ampliiiediby a video amplifìerfIZ.` . Theampli
fled yideo signals are impressed upon the'grid _
curve" 21 and the‘cathode' voitagè‘as‘ shown by
...2,405,290
6.
Vthe curve 28. _The _ranges ofvariation of the
nal strength.
@anode and cathode voltages are substantially dif
.maximum amplitude variation under these, con
ferent by reason of ' the constants selected for
-the resistors Il and .29. Satisfactory operation
V.using the tube of the 6J 5 type has been secured ï
with the resistor I1 having a value of a few thou
sand ohms and the resistor 25 `having a value
- ofapproximately twenty-five times the value cf
ditions.
.
cathode increases as the amplitude of the signal
increases in a positive direction. 'I'he amplitude
of the positive anode potential decreases as the
amplitude of the signal increases in a positive
direction. >As would Ibe expected, the voltage
_ developed in the cathode follower resistor Il has
a degenerative eiiect upon the input circuit of
.
«
’
.
,
,
,_
signal component will be positive and the syn
chronizing signal lcomponent will be negative.
By the action of the amplifierthe positive Video
signals will be amplifiedA in the output circuit of
the tube distorted in amplitude and the negative
synchronizing signals will be suppressed. Also,
since ,the magnitude of the distortion of the
amplified Video signals depends upon the ampli
tude of these signals, the signals representing
.
`Actually, however, a portion of the anode volt
age is applied to the cathodeiof the tube by means
of a direct current coupling comprising ‘the vari-.
able resistor I8. This feed-back voltage has a
regenerative effect upon the input circuitof the
-
` i5 in reverse polarity to that described, the video
The amplitude of the positive potential of the
the-tube I5.
,
It is evident that,> if the composite television
signal is applied'to the input circuit of the tube
the resistor Ii. When using circuitelements
having these constants, the .battery I9 has a po
tential of 300 volts.
The 4anode voltage has a greater «
zo
the darker .portions of the picture are distorted
less than the signals representing the lighter por
tions of the picture. Consequently, it is seen
that the ampliiier embodying the present inven
tion is also susceptible of operation, whereby to
eñîect a gamma control of the reproduced picture.
Such a use for the ampliiier embodying the
instant invention is illustrated in Fig. 4. Circuit
elements corresponding to similar `elements of
Fig. 1 are given identical reference characters in
i tube and, by means of a suitable adjustment of 25
the two iigures.` The demodulated composite tele
the resistor> I 8, the regenerativecornponent is
vision signals are impressed upon the input cir
made large relative to the degenerative compo
cuit of the tube I5 in such a mannerthat the
nent.
.
video signals are of positive polarity and the
.The result produced by the regenerative feed
synchronizing signals are of negative polarity.
.back voltage is an amplitude distortion or expan '30
The
output circuit including the resistor I1 is
. sion of the signal applied to the input circuit of
connected to the input circuit of the video am
the tube I5. Also, by reason of the described com
, pliñer I2... Also theldemodulated >signals, are im-bination of regenerative and degenerative com
ponents which have materially diiierent ranges 35 pressed upon a synchronizing and video signal
separator 33 which may be of the type illustrated
of variation, there is produced a net feed-back
in Fig. 1, if desired.
v voltage to the input circuit which is non-linear
. with respect to the signal voltage. The eifect of
The operation of the distortion amplifier as a
.device for effecting a gamma control of the re
the feed-.back voltage is much greater in the
region of the positive signals than it is in the» 40 produced picture is believed to be obvious in view
of the detailed description of its operation as a
region of the negative signals. Consequently, the
limiter.
By reason of the described polarity of
~positive portions of the signals are expanded
the composite television signal as applied to the
' more than the negative portions.
input circuit of the amplifier tube I5 of Fig. 3,
Also, by reason of the direct current coupling '
the video component appears in the output cir
between the output and input circuits of the tube, 45 cuit-in a non-linearly distorted form. Such a
a portion of. the positive potential _of the battery
signal, when applied to the grid of the cathode
I9 appears as a steady direct current voltage at
ray tube I3, controls the reproduction of the pic
the cathode. The effect of this arrangement
ture in a manner to vary the contrast in the light
is to shift the average bias ofthe tube further
and dark portions of the picture.
toward the point of plate current cut-oli.
50
While there has been described what at present
f Thus, when a signal such as that represented
is
considered the preferred vembodiment of the
by the curve 25 of Fig. 2 is impressed upon the
invention,k
it will be obvious to those skilled in
resistor IS of Fig. l, the resultant expanded sig
the art that various changes and modifications
nal applied to the input circuit of the tube by the
may be made therein without departing from the '
apparatus in accordance with this invention is
invention and, therefore, it is aimed in the ap
represented :by the curve 29 of Fig. 2. It is seen
pended claims to cover all such changes and
that the synchronizing signal portions have been
modifications as fall Within the true spirit and
amplified considerably more than the video sig
scope of the invention.
nal portions. Also, it is seen that the bases of
~ What is claimed is:
the pedestals of the synchronizing impulses coin-` 60
cide approximately with the point of plate cur
rent cut-oli. Such signals produce plate current
in the tube I5, having the form illustrated by
the curve 35.
Thus, the video signals are sup
pressed completely in the output circuit.
The Voltage ñuctuations actually occurring at
the anode of the tube I5 are represented by the
curves 3I of Fig. 3. Similarly, the actual voltage
1. Apparatus for effecting a non-linear ampli- Y
fìcation of a composite televisionsignal including
video-'and synchronizing components comprising
- a single vacuum tube having input and output
circuits, means for impressing said composite
television signal upon said input circuit, a re
generative feed-back connection between said
output and input circuits to eifect a non-linear
amplitude distortion of said amplified signal, and
means including said feed-back connection to
are illustrated by the curves 32. Either or both 70 reproduce in said output circuit onlyone of said
of these twoV voltages may be utilized for synchro
composite television signal components.
nizing purposes. However, it is preferable to
2. In a television receiver, means for receiving
use the voltage derived from the cathode for the
a composite television signal including video and
reason that it does not vary in its maximum
fluctuations occurring at the cathode of the tubel
amplitude appreciably with variations of the sig
synchronizing components, an ampliñer tube hav
75 ing input and output circuits, means for im
l2,405,290
'7
pressing said received television signal .upon the
input circuit of said ampli'iier tube in such ‘a
manner that said video component is positive and
said synchronizing component is negative, means
for regeneratively coupling said input >and out
putcircuits to produce in the‘output circuit of
said amplifier tube non-linearly distorted video
signals, and means including said coupling to
effect a gamma control of a picture reproduced
8
including saidcoupling to `reproduce said syn
chronizing lcomponent in said output circuit to
thev exclusion of said video component.
7.' An amplifier for alternating current signals
comprising a vacuum tube having an anode, a
cathode and a control grid„a resistance element
connected between said grid and said cathode,
means for impressing said signals upon a portion
of said resistance element, and means including
10 a resistor for impressing upon another portion
from said video signals. '
of said resistance element a potential derived
3. -Apparatus for separating lthe video and syn- ,
from said anode, whereby to increase the `poten
chronizing components of a composite television
tial of said grid with respect to said cathode suf
signal comprising a vacuum` tube having an
ficiently to suppress in said output circuit signals
anode, a cathode and a control grid, an input
of less than a predetermined positive amplitude.
circuit including said cathode and said grid, an
8. An amplifier for alternating currentsignals
output circuit including said Ycathode and said
anode, means comprising a direct current cou
pling including a resistor between ,said anode and
said cathode to effect a non-linear regenerative
feed-back from said output circuit to said input
circuit, and means including said coupling to re
produce said synchronizing component in said
output circuit to the exclusion of said video
component.
4. Apparatus for separating the video and syn
chronizing components of a composite television
signal comprising, a vacuum tube having -an
anode, a cathode and a controlV grid, an input
Y circuit including said cathode and said grid, an
comprising a vacuum tube having an anode, a
cathode and a control grid, a series connection
of a grid leak resistor and a cathode follower re
sistor, means for impressing said signals upon
said grid leak resistor, and means rincluding a
variable resistor for impressing upon said cath
, ode follower resistor a potential derived from said
anode to increase the potential of said grid with
respect to said cathode, said anode-derived po
tential having a> magnitude determined by said
variable resistor whereby to suppress in said out
put circuit signals of` less than a predetermined
positive amplitude.
.9.. A combined signal limiter and ampliñer for
output circuit including said cathode andsaid 30 separating
the synchronizing component from a
anode, means comprising a direct current cou
composite
television
signal including video and
pling between said anode and "said cathode to
synchronizing components comprising a single
effect a regenerative Yfeed-back-from said output
space discharge device having input and output
circuit toY said input circuit, and means includ
means responsive to signals having
ing said coupling to reproduce said synchroniz 35 circuits,
greater than predetermined amplitudes for auto
ing component in said output circuit to the ex
matically biasing said input circuit to effect out
clusion of said video component.
put current cut-off of negative portions of said
5. Apparatus for separating the videoV and
signals,
means coupling said output and input
synchronizing components of a composite tele
vision signal comprising a vacuum tube having 40 circuits responsive to signals having lesser than
said predetermined amplitudes for regenerating
an anode, a cathode and a control grid, an input
circuit including said cathode and said grid, an
output circuit including said cathode and said
anode, a resistor connected to said cathode in se
ries with said input and output circuits, a direct
current coupling including a resistor between
said anode and said cathode, and means includ
ingV said coupling to reproduce said synchroniz
ing component in said output circuit to the exclu
sion of said video component.
6. Apparatus for separating the video arid
synchronizing components of a Composite tele
vision signal comprising a vacuum tube having
an anode, a cathode and a control grid, an in
put circuit including said cathode and said grid,
an output circuit including said cathode and said
Lanode, self-biasing means in said input circuit
including a condenser in series'with said input
circuit and a leak resistor in shunt with said in
put circuit, a resistor connected Vto said cathode
in series with said input and output circuits, a
direct current coupling including a resistor be
tween said anode and said cathode, and means
said last named signals, and means including
said coupling means, to eiiect said output current
cut-oit of the video component of said last
., named signals.
Y
l0. A combined signal limiter and amplifier for
separating the synchronizing component from a
composite television signal including video and
synchronizing components comprising a vacuum
tube having input and output circuits, means in
cluding a condenser in series with said input cir
cuit and a resistor in shunt with said input cir
cuit and responsive to large amplitude signals for
automatically biasing said input circuit to effect
output current cut-off of negative portions of
said signals, means including a resistor cou
pling said output and said input circuits for re
generating small amplitude signals, and means
including said coupling to effect said output cur
rent cut-off of the video component of said small
amplitude signals.
MADISON CAWEIN.
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