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Патент USA US3090842

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May 21, 1963
E. c. FLOYD
3,090,832
NOISE CANCELLATION CIRCUIT
Filed Jan. 30, 1961
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2 Sheets-Sheet 1
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ATTY.
May 21, 1963
E. c. FLoYD
3,090,832
NoIsE CANCELLATION CIRCUIT
Filed Jan. 30, 1951
2 Sheets-Sheet 2
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United States Patent O
3,090,832
er’
HCC
Patented May 21, 1963
1
2
3,090,832
Accordingly the principal object of this invention is to
provide an improved noise protection circuit for television
NGISE CANCELLATION CIRCUIT
receivers;
Earl C. Floyd, Westchester, lll., assignor to Admiral Cor
poration, Chicago, lll., a corporation of Delaware
Filed Jan. 30, 1961, Ser. No. 85,614
3 Claims. (Cl. 178-7.3)
Another object of this invention is to provide an im
proved noise cancellation circuit;
Still another object of this invention is to provide a
noise cancellation circuit employing a noise inverter tube
in which the conduction level of the noise inverter tube is
This invention relates in general to television receivers
and in particular to circuitry therein for improving the
visual display presented on the screen of a television re
continuously adjusted in accordance with signal level
10
changes;
Y
ceiver under adverse signal conditions.
A conventional television signal includes video informa
tion components for reproducing a visual indication of
the scene being televised, audio information components
A further object of this invention is to provide a noise
cancellation circuit for television receivers which not only
performs better than similar circuits of the prior art but
for reproducing the sound accompaniment and synchro
nizing components for controlling operation of the hori
A still further object of this invention is to provide a
noise cancellation circuit for a television receiver in which
zontal and vertical scanning circuits in the television re
ceiver. The video information and synchronizing com
the video amplifier output capabilities and the noise in
does so in a more economical manner;
verter cancellation ability are so apportioned as to prevent
over cancellation of noise pulses during weak signal recep
ponents of the television signal comprise amplitude modu
lations, whereas the audio components comprise frequency 20 tion;
modulations. The synchronizing components are sep
arated in amplitude from the video information compo
nents, being larger than any of the video information
components and occurring at relatively constant amplitude
levels. The television signal is subject to noise pickup
from many sources and often the noise components great
A feature of this invention resides in the provision of
a single tube envelope incorporating therein three inde
pendent triode tube sections, one for noise inversion and
cancellation, another for synchronizing signal separation,
and a third for development of an automatic gain control
potential.
Another feature of this invention lies in the provision
of means interconnecting the screen electrode of the video
These noise signals often interfere with thev proper
amplifier and the grid of the automatic gain control tube
synchronization of the circuitry in the television receiver
responsible for developing the horizontal and vertical 30 whereby the automatic gain control section of the receiver
is assisted in operation for both extremely strong and eX
sweep voltages. 'Ihe results of this type of interference
ly exceed the magnitude of the synchronizing components.
may be picture jitter, horizontal tearing, vertical rolling,
tremely Weak input signals to the video amplifier.
Further objects and features of this invention will be
etc. As is well known in the art, the vertical circuit is
>apparent upon reading of the specification in conjunction
most susceptible to disturbances of this type.
Most well designed television receivers have some sort 35 with the drawings in which:
lFIG. 1 represents a block diagram of a complete tele
of noise protection circuitry. In general there are two
vision receiver embodying the circuit of the invention; land
main methods of noise protection. One is noise gating
FIG. 2 represents a -schematic diagram of the circuit of
and the other is noise cancellation. In the noise gating
'the invention.
_
type of noise protection circuit, noise pulses above a cer
Referring now to FIG. 1, a television signal is received
tain amplitude are effective to immobilize the synchroniz
by antenna 5 and coupled to converter 6. Converter 6
ing signal separator circuit in the television receiver. The
theory is that it is better to lose output from the synchro- I is well known in the art and' includes a radio frequency
amplifier, a local oscillator, and a mixer for developing an
nizing signal separator for a brief interval of time, usually
intermediate frequency television signal. The output of
corresponding to a few horizontal lines, than to allow
large noise pulses therein which may prematurely trigger 45 converter 6 is coupled to an intermediate frequency
'amplitier 7 where the intermediate frequency signal is
the circuits responsible for developing the deflection volt
ages.
amplified. The intermediate frequency (IF) signal is fed
The noise cancellation technique is different in that it
is based on the principle that the noise signal may bere
moved from the television signal by algebraically combin
ing it with a similar though oppositely poled signal devel
oped responsive to the noise signal. This systemhas the
advantage of insuring that the synchronizing circuits of a
to video detector 8 which drives video amplifier 10. , Y
television receiver will not be immobilizedeven for short
periods of time, but will always remain operational.
While the theory of noise cancellation has been known
for some years, satisfactory results with circuits em
An audio circuit 9 is shown coupled to video detector
8 and includes a sound intermediate frequency amplifier,
a sound detector, a sound amplifier and a speaker. Audio
circuit 9 may be coupled instead to the video amplifier
output by use of suitable traps, as is known in the art.
Video amplifier ltl'ampliñes the composite video signal
55 from video detector 8 and is coupled to a synchronizing
signal separator l1 and an automatic gain control (AGC)
circuit 17. `Video amplifier 10 also drives the signal
input circuit (not shown) of picture tube 13. A portion
of the video detector signal is coupled to noise inverter
since it is a diñicult task to develop a noise cancelling cir 60 14, which is also coupled to video amplifier 10. Noise
bodying this theory have not been obtainable. All of the
circuits of the prior art have sulîered from various defects,
cuit Which will respond faithfully to the extreme Variations
in signal level and signal to noise ratios encountered in the
operation of a modern day television receiver. The cir
inverterv 14 operates, in a manner to be described Afully
hereinafter, to sense large noise impulses in the signal
from video detector 8 and to develop corresponding,
cuit o‘f the invention embodies a combination of elements
though oppositely poled, signals for application to the
cooperating in a manner such that the noise cancellation 65 output of video amplifier 10. Noise cancellation occurs
circuit operates faithfully over extremely wide variations
in signal level and signal to noise ratio. One of the
features of this circuit, aside from its excellent perform
ance, lie's in the use of a single tube envelope housing three
and synchronizing signal separator (sync separator) 11
is fed a relatively noise free signal.
The output of sync separator 11 is coupled to the
circuit 12 which is «responsible for generating
independent triode tube sections, respectively performing 70 vertical
deflection
voltages in conjunction with the vertical Wind
noise inversion and cancellation, synchronizing signal sep
ing on picture tube 13. The sync separator is also cou
eration, and automatic gain control voltage development.
3,090,832
3
¿à
pled to the horizontal and AFC (automatic frequency
control) circuit 15.
The horizontal oscillator (not shown) is of the free
arrangement is well known in the 4art and is commonly
l
.
running type and has a natural frequency of oscillation
called a “double time constant” coupling circuit for the
sync separator tube. Anode 51 of ysync separator 50* is
coupled to a low 'I3-{- supply voltage through a load re
close to the horizontal line »synchronizing frequency of
the television signal. The output of the oscillator feeds
sistor 48. Cathode 52 of tube 50 is connected to ground.
A resistor 49 is connected to the junction of anode 51
a horizontal outputV circuit »(-noty shown) >which is cou
and resistor `48 and in conjunction with resistor 48 com
prises a voltage divider arrangement for the sync sep
arator tube. Anode 51 is coupled to horizontal cir-`
pled to the receiver high voltage section 176. The AFC
circuit compares the horizontal oscillator -frequency with
the frequency of the horizontal line synchronizing com 10 cuitry (not shown) through a suitable coupling capacitor
55.
Y
ponentsin the television signal and provides correction
The junction of video amplifier load resistors 35 and
voltages to hold the horizontal oscillator at the line syn
chronizing frequency. This arrangement is well Iknow-n
`37 is connected to grid 73 of AGC tube 70 through a
resistor 60. Grid 73 is connected, through a ñxed re
in the art.
^
High voltage section 16 develops the horizontal sweep 15 sistor 61 and a variable resistor 62, to ground. Variable
voltages for the deñection windings of picture tube 13
resistor `62 is labelled AGC Set and is utilized to ad
as well as the high voltage direct current necessary for
just the automatic gain control level for the individual
operation of the picture tube. High voltage pulses, oc
television receiver in accordance with the strongest sig
curring at the horizontal. sweep rate, are, fed to AGC
,nal which said receiver is to receive. Another con
circuit 17 to develop what is commonly called a gated 20 nection -to «grid 73 exists from B+, through resistor 56,
through variable -resistor v57, and through a fixed resistor
or keyed AGC control voltage. High voltage section 16
59. A ‘lower portion of variable resistor '57, which is
is also coupled to» horizontal and AFC' circuit 15 to
provide the necessary pulses for the automatic frequency
the contrast control in the receiver, is bypassed by a
.capacitor 5S. Additionally, the upper terminals of re
'control' section to stabilize the horizontal oscillator at the
25 sistors 59 and i6() are joined, this junction also being
proper frequency.
The AGC voltage developed in AGC circuit 17 Vis
connected to the video amplifier lload resistors. A con
coupled to the converter 6' and also to the IF amplifier
nection to »grid 73 also exists, through a resistor 63, Vto
the screen grid 324 of video amplifier 30.
v
7. Noise inverter circuit 14 is :coupled to the ‘I-F ampli
AGC tube 70 has its anode «71 coupled through a ca
ñer AGC potential. IIt should be noted that the lead con
necting video amplifier 10 with AGC circuit 17 actually 30 pacitor 74 to high Volta-ge section 16 (not shown in this
íigure). Anode 71 is also connected to a pair of inte
comprises two individual coupling paths as will be ap
-grating networks comprising resistor 75 and capacitor .
parent by reference to FIG. 2.
' Winding 20 is tuned lby parallelly connected ca
pacitor 21 and comprises a portion of the ylast inter
76, and resistor 7S and capacitor 79, respectively. The
junction between 4resistor 78 and capacitor 79, llabelled
mediate frequency transformer (not shown) in the inter 35 RF-AGC, is connected to converter `6, shown in FIG. ~1.
The junction of resistor 75 and capacitor 76, labelled
mediate .frequency amplifier 7 of FIG. 1. Winding 20
is connected to ground at its lower terminal and to a
IF-AGC, is _connected to IF amplifier 7 in FIG. 1. This
‘latter junction feeds a network comprising resistor 77,
diode detector 22 at its upper terminal. A series of
resistor 68, and capacitor 69, lwhich is coupled to junc
.tuning coilsV 23, 24 and 25 are utilized in a conventional
manner so that a negative -going composite video signal 40 tion 44, previously mentioned. Junction 44 V_is also con
is coupled -to control grid 33 `of video amplifier tube 30.
nected, through a resistor l65, to a Noise Set variable
resistance control'166. One end of this control is con
This composite video signal is developed across the cir'
nected to ground through a resistor 67, and the other
cuit comprising winding 25 and tapped resistor 26.
end to the grid of the horizontal output tube (not
Tapped -resistor 26 is required since the video detector
must also 4feed the cathode of the noise inverter tube, 45 shown) in horizontal and AFC circuit 15 of FIG; l.
The latter connection is through a resistor 64. A de
which constitutes a heavy load. Therefore only a por
scription of the operation of the circuit now follows.
tion of the composite video signal is coupled to the
cathode by virtue of tapped resistor 126.
`
Video amplifier 30 comprises a pentode type tube hav
ing an anode 31, a cathode 32, a control grid 33 and a 50
screen grid 34. The last grid, that is the suppressor
lgrid, is not indicated with ka separate reference numeral
since it plays 4no part in the invention and is assumed to
be connected in a conventional manner. Cathode 32 is
grounded and anode 31 is connected to B-I- through a
tuned circuit comprising capacitor 28 and coil 27, a
=Omitting the function of the noise tube 40 and the ~
4‘audio circuit, the television intermediate frequency sig
nal is detected by video detector 22, which develops «the
composite video signal. ' This signal is fed to control
grid 33 of video ampliiier 30. As is indicated by dia
gram 100, this composite signal is negative going and
may contain Vspurious noise pulses of relatively large am
plitude. The signal is amplified by video amplifier 30
and coupled to sync separator 50 Iand AGC tube 70.
The “double `time constant” input circuit of sync sepa
rator 50 acts to pass only the extreme portions of the
peaking coil 29, and a load resistance combination. 'llhe
load resistance combination comprises resistor 35 which is
signal, that is the synchronizing components. These
parallelled by serially connected resistors 36 and 37. A
resistor 38 is connected to the junction of resistors 36 »and 60 components are separated in sync separator 50 and
coupled to «the horizontal and vertical circuits, respec
37 andthe anode of noise >tube 40. B-l- for screen grid
tively. 'I‘he amplified composite video signal is'coupled
34 is »supplied through -a fairly large resistor 80. >A
to .the grid of the AGC 'tube 70, ‘the anode of which
capacitor 81 bypasses the screen grid to ground.`
is subjected to a gating or keying pulse, indicated by
NoiseV tube 40 includes `an anode l41, a cathode 42
waveform 100. This type AGC circuit is well known
65
and a control grid 43. Cathode 42 is connected to
tapped resistor 26 which is used to select a portion of
the composite video signal. Control grid 43 is connected
in the art and is commonly called gated or keyed AGC.
'I‘lre high voltage pulses of waveform 100 occur in syn
chronism withV the synchronizing components of the sig
nal fed to grid 73. The cathode 72 of AGC tube 70 is
to a junction 44. A capacitor 39' couples the anode
of noise tube 40 to sync -separator tube 50. The entire 70 connected to a source of low B+ and hence the Vtube is
coupling circuit comprises capacitor 39 and resistor 45,
normally cut-off. However, ¿during the occurrence of
to the junction of which is connected the parallel com
synchronizing components, a high voltage pulse is fed
bination of resistor 46 and capacitor "47. The other end
to Ithe anode 71 of AGC 'tu-be 70, driving the tube con
of this combination of resistor 46 and capacitor 47 is
duc-tive. The magnitude of the conduction current drawn
connected to gridr 53 of sync separator tube- 50. This 75 -by AGC tube 70 is determined by the magnitude of the
3,090,832
5
synchronizing components in the composite video signal.
This circuit is elïective to produce negative potentials
at the points labelled IF-AGC and RF-AGC which po
tentials vary in accordance with the magnitude of the
incoming signal.
If the composite signal is large, grid 73 is driven heav
ily .positive and a large current .flows through tube 70,
resulting in a large negative control voltage being de
veloped across the integrating networks. Conversely,
grid 43 to an -additional control source which is capable
of following variations in the levels of the received tele
vision signals. Connection of Igrid 43 through the cou
pling circuit to the IF-AGC potential provides this vari
able potential.
Ideally, noise tube 40 should have a large ampliiica
tion factor as well as a high plate current capability.
However, triode tubes having these characteristics are
not generally available and therefore means are pro
if Ithe signal is small the opposite eiîect -occurs and a cor 10 vided :to match the capabilities of the video amplifier
respondingly smaller control voltage is developed. The
developed AGC potentials are «fed back to converter 6
tube with the capabilities of the noise inventer tube. This
means comprises circuitry for coupling the output of the
video amplifier tube to the noise tube anode at a reduced
level. ’Ihe combination of elements performing this
and IF amplifier 7 to control :the gain of these .portions
of the television receiver. Thus, under normal signal
conditions, the magnitude of the input signal to video 15 function are resistors 35, 36 and 37.
In this type circuit it is highly desirable that the AGC
detector 22 is held relatively constant as a result of this
control voltage track the incoming signal accurately. As
AGC action.
is Well known in the art, when a rapid transition is made
A portion of the composite video signal is coupled to
from a strong signal to a weak signal or vice versa,
cathode 42 of noise inverter tube 4t). This signal is
both the AGC circuit 'and the sync separator circuit may
negative going and tends :to drive the noise tube conduc
not respond quickly enough and the result may be mis
tive. However, noise tu-be 40 is maintained at cut-oilr
synchronization in the television receiver. To assist the
by virtue of the negative potential impressed on grid
sync separator circuit, andato a limited extent -the AGC
43, from the .grid circuit of the horizontal output tube
(not shown). This negative potential is substantially
circuit, a circuit described in Patent No. 2,927,156-, is
25 sued to Robert Jones, is u-tilized. Briefly, the connec
constant for all signal conditions.
v Grid 43 of noise tube 41) thus has a constant negative
tion of screen grid 34 of video ampliñer tube 30 to B+
potential applied thereto to maintain it nonconductive
rthrough resistor `80 helps keep the signal to «the sync
for all video and synchronizing information components
separator near the value »to which it is held when the
of the composite television signal. Grid 43 is also con
-AGC circuit »is effective. The screen grid draws current
nested through a network previously described to the 30 in proportion to the conduction'current flowing in the
lF-AGC control potential which varies in accordance
video ampliiier. -If an extremely weak Ásignal is Áfed to
with signal level. The Noise Set control 66 is adjusted
the control kgrid of the video ampliiier the conduction
so that the potential on grid 43 is sutiicient to hold
current therein increases.
This increase 'in conduction
noise tube 50 nonconductive for all negative signals ap
current is ysensed by the screen `grid which, due to its
plied to cathode 42 except those a predetermined amount 35 connection to B-f- through resistor 80, suffers =a voltage
or more in excess of the amplitude of the synchronizing
drop. Thus the screen grid potential lfalls as it draws
portions of the composite television signal. Upon oc
more current. This ldecline in screen grid potential in
currence of such large signals, noise tube 40 is driven
effect shifts the transfer characteristic of the video arn
conductive as cathode 42 becomes negative with respect
pliñer tube in a direction which tends to maintain the
to grid 43. Assuming a waveform substantially as shown 40 level of the sync tips in the output signal at the level
at 100, the Waveform applied :to cathode 42 Will be as
to which they are normally held by fthe AGC circuit.
shown at 102. However, only the portions below dashed
Thus the sync separator 4is protected from large, rapid
line 102’ will be effective to cause conduction in tube 40.
changes in input signal level. By maintaining the in
Waveform 101 indicates the ampliñed composite video
put signal level to «the sync 4separator iixed, the -arnpli
signal and the noise pulses therein. For normal signal
tude of any noise -fed thereto is minimized. Thus during
levels to video »ampliiier 30, the maximum amplitude
this critical transient interval the noise inverter is also
of noise pulses in the video amplifier output is limited
assisting in performing its cancellation lfunction.
by cutoiî of the tube. Noise pulse in excess of those
Lt will be recalled that the screen ygrid of they video
causing cutoff in the grid circuit are clipped. The out
ampliiier is also connected to the control grid of the
50
put signal trom video lamplilier 30 is algebraically added
AGC tube .through a resistor `63». This connection greatly
across resistor 38 to the output signal of noise tube 40,
enhances the response of the AGC circuit, which cir
resulting in cancellation of the noise pulses. The result
cuit controls the conduction level of the noise inverter
is a waveform substantially as shown by 193. This noise
tube. Assume va'large input signal to the video ampli;
free waveform is coupled by the coupling network pre
tier. The video arnpliiier will ‘be cut oiî lby the sync
viously indicated to grid 53 of sync separator 50 where 55 components and the screen grid will cease drawing cur
the synchronizing components are separated. Thus, the
rent. This results in a rapid increase in the screen volt
noise pulses are prevented from entering the synchroniz
age, which increase is immediately reflected at »the AGC
ing signal separator circuit and hence can produce no
rtube
control grid, thus insuring rapid development of
deleterious eiîects upon the horizontal and vertical cir~
AGC
voltage. This AGC voltage reduces »the gain of
60
cuitry of the television receiver.
the receiver prior to the video detector and biases the
noise inverter tube lback strongly to prevent cancella
tion'of thel sync pulses. Conversely, upon receipt of a
cel noise pulses before they reach the synchronizing sig
very Weak signal (large conduction current in the video
nal separator. However, in the presence of large varia
tions in signal strength a fixed noise Ítube bias is unde 65 amplifier), the screen voltage falls quickly and this change
It should be obvious .to those skilled in the art that for
normal signals, a ñxed Noise Set level will suñice to can
sirable. If the signal is excessively strong, noise tube 40
may be driven conductive responsive tothe synchronizing
components and result in cancellation of these compo
nents. This of course will result in complete loss of
is communicated Ito the AGC tube which results in a
smaller developed control voltage. Hence the noise in
verter can respond quickly- ‘to >rapid signal level changes,
thus greatly improving its noise cancelling -ability in
synchronization in the television receiver. If the signal 70 these critical areas.
The connection of the control grid ofthe noise tube
is weak and noisy, the signal to noise ratio will be de
to a source of control potential which varies in accord
creased by .the video ampliñer -gain characteristic and
ance with the signal level also prevents over cancella
result in incomplete, if any, noise cancellation by noise
tion of noise pulses in the video signal which lgive rise
tube 40.
This situation is obviated by connecting noise inverter 75 to white spots in the displayed picture. These white
3,090,832
S
spots are the result of holes being cut into the video
said reference components being »greater Vin amplitude
information when the cancellation pulse is larger than
Ithe noise pulse. Over cancellation occurs in the pres
ence of extremely strong signals in »which the -sync tips
nal being subject to `undesired spurious noise lcomponents
come very close to «the cut-oit portion of the Video am
plifier transfer characteristic, kIn such case, noise pulses
extending Ibeyond the sync tips are clipped and hence
are not materially iarger, in the output circuit of the
video amplifier, than the sync'ltip portions. These noise
pulses however are not clipped or compressed when they
are coupled to the cathode of the noise tube, land give
rise to large cancellation signals. The algebraic can
than said information components, said television sig
of greater amplitude lthan said reference component-s; a
video amplifier including ya cathode, ya control grid, a
screen grid and an anode; means for »applying said nega
tively oriented composite video signal between the cath
ode and control grid of said Yvideo amplifier; a source
of positive potential; a tapped load resistance'connected
between said video amplifier anode 'and said source of
potential; a noise inverter tube »for inverting and can
celling said spurious noise components including an Ian
ode, a cathode and a control grid; a resistor connected
lbetween the tap on said video amplifier load resistance
cellation of the positive going noise pulse with the nega
tive Igoing cancellation pulse at the anode of the. noise
tube may result in over cancellation and consequent chop
and the anode of said noise inverter tube for coupling
ping into the video portion of the signal. This effect is
the output of said video amplifier at reduced level to `
substantially eliminated «by adjusting the noise tube con
said noise inverter anode; direct current means coupling
duction level in accordance with the incoming signal
said negative going composite video signal to the cath
strength so that Y'for strong signals the noise tube is much
ode of said noise inverter tube at reduced level; means
less sensitive, that is it is more di-?ìcuflt to drive into con 20 for applying a constant negative direct current bias po
rtential to the control grid of said noise inverter tube
duction.
Ina practical circuit embodying the invention tubes
whereby said noise inverter tube is. only driven conduc
40, 50 and 70 are all contained in one tube envelope.
tive for signals of greater amplitude than said reference
This tube -arrangement makes for a very economical pack
components; separating means coupled tothe anode of
Isaid noise inverter tube yfor separating said periodic ref
age of excellent perfomance. The Noise Set control
is not required lonce the circuit parameters have been
erence component-s; a gain control tube having a cath
established, it being replaced Iby iiXed resistors. The cir
cuit as [described utilizes Ikeyed AGC, but non-gated AGC
ode, a control `grid and an anode; direct current means
yfor coupling said load resistance of said video 4ampliiier '
'
to the control grid of said gain control tube; an inte
It is understood 'that numerous modifications in the 30 grating network connected -to ,the anode of said gain con
trol tube; means ‘for applying high Voltage pulses fto the
circuits «shown may be made without departing from the
anode of said gain control tube in synchronism with said
true spirit and scope of the invention as defined in the
periodic reference components on its control grid for driv
following claims.
'
mayalso be employed.
What i-s claimed is:
,
1. In combination in a television receiver including
means for producing 1a composite video signal having in
ing said tube conductive -in accordance with the ampli
tude of said reference components,v said integrating net
=work developing a negative control potential varying as
:a function of the amplitude of said reference components;
means, including a resistor, coupling the screen grid elec
ponents being greater »in magnitude than said information 40 »trode of said video ampliiier to said source of poten
tial; means connecting the »screen grid electrode of said
components, said television signal being subject to un
' formation components and periodic reference components
from a received television signal, said reference com
desired spurious components of greater magnitude than
video amplifier to the control grid of said> gain control
ftube for coupling variations in the videoamplitìer con
duction current to the control grid of said gain control
resistor therefor; means for applying said composite sig
nal -to said video ampliñer; a noise inventer tube Afor in 45 tube; means coupling said integrating network to the con
rver-ting and cancelling ysaid spurious components includ-V
trol Igrid of said noise inverter tube for automatically
ing an anode, a cathode and a control grid; «a resistor
yadjusting the conduction level .thereof `in accordance with
signal level changes, whereby said noise inverter tube is
connected Ibetween a point intermediate the ends of said
video ampliiier load resistor and said »anode lfor coupling
driven conductive by spurious noise components ot
the output [of said video amplifier to said noise inverter 50 greater amplitude than said reference components and
cancels said spurious noise components present in the
'anode at reduced level; means lfor -coupling said com
output of said video ampliiier tube thus producing a sig
posite video signal to said cathode at a reduced level;
means -for applying a constant direct current bias to said
nal free of said spurious noise components for said sepa
control grid whereby said noise inverter tube only con
rating means.
t
ducts on signals of greater magnitude .than said reference
3. In a television receiver as set forth in claim 2 where
components; control voltage means coupled to said video
in said noise inverter tube, said separating means, and
amplilier load resistor for developing a control voltage
said ‘gain control tube, individually comprise independent
in yaccordance with »the magnitude of said reference com
electron discharge devices included in a common evacu
ponents; means in said video amplifier, and responsive to
ated tube envelope.
'
the conduction current in said video ampliñer, coupled 60
References Cited in the ytile of this patent
to said control voltage means for conveying information
regarding changes in said conduction current thereto; and
UNITED STATES PATENTS
means for coupling said control voltage to said control
2,797,258
Denton _____________ __ June 25, 1957
lgrid whereby fthe conduction level of said noise inverter
Sonnenfeldt _____ .._,_____ Feb. ll, 1958
rtube is automatically ladjusted as the level of said com 65 2,823,257
said reference components; a video amplifier and a load
2,841,646
Thomas _______________ __ July 1, 1958
2. In combination inV a television receiver including
means =for producing a negatively yoriented composite
2,868,873
Splitt ________________ __ Ian. 13, 1959
2,927,156
Jones ---__ ___________ __ Mar. 1, 1960
video signal having information components and periodic
2,945,090
Scott ________________ __ July 12, 19.60
reference components from a received television signal, 70
2,950,344
Gibson ______________ __ Aug. 23, 1960
posite video signal varies.
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