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Jan» 4, 1949--
G. |_. FREDENDALL
T
V2,453,156
AUTOMATIC FREQUENCY CONTROL SYSTEM
T
.
¿y
.,
ÁTTOP/VEV
Jan. 4, 1949.
G. L. FREDENDALL
2,458,156
-AUTOMATIC FREQUENCY- CONTROL SYSTEM _
`
Filed July 29. 1944
2 Sheets-Sheet 2
Z/7
,
CONT/2u
V0.4 77465
007,007'
274
Wam' FaQ/w
2,458,156
Patented Jan. 4, 1949
UNITED smi-.a idn'i‘ixìi OFFICE
2,458,156
AUTOMATIC FREQUENCY CÜNTROL
SYSTEM
Gordon L. Fredendall‘, Feasterville, Pa., assigner
to Radio Corporation of America, a- corporation
of Uelaware
1
Application .lilly 29, 1944, Serial No. 547,230
l Claim. (Si. 25o-«36)
The present invention relates to' automatic
frequency control or phase control circuits and
particularly to novel apparatus for the syn
chronization of cathode ray deflecting circuits
in television receivers or the like.
In some locations, generally near the edges of
the service area of a television station, local inter
ference or weak signals, or perhaps both, impair
the accuracy of synchronization inv a television
receiver to such an extent that the horizontal
resolution is appreciably reduced. There may
also be failure of interlace and even sporadic fail
ure of synchronization. This invention aims to
provide an improvement .in synchronizing action
that will improve performance in’these marginal
locations without introducing comprising factors.
For signal conditions which are-at all satisfactory
ior reception, substantially the maximum yhori
zontal resolution. permitted by the television
channel may be realized in‘ a receiver embody
ing the present invention when allowance is made
for unavoidable noise effects `seen in the image
as beam modulation. Also, noise effects do cause
“tearing” of the picture in horizontal strips. Ap
preciable improvements» in lvertical synchroniza
tion is shown.
in accordance with this invention, these and
other desirable results'are attained by provid
ing improv'ements’inV previously known televi
sion receiving equipment in Íwhich synchroniza
tion of an oscillator'is to be obtained» by employ
ing an automatic frequency-'control' circuit re
sponsive to any change'in the time- relationship
0f the synchronizing’pulses with respect tosaw
2
Referring to Fig. 1 of the drawings, certain4
parts of a typical television receiver, modified-to
incorporate features of this invention, areshown‘
diagrammatically. The video ampliiier, D.v C.
restorer, sync separator, and the deflection gen
erators are shown.
A tube 5l serves as a video amplifier, the video
signals;7 from
the second detector of the receiver
(not shown) being impressed on the‘control grid
53 ci this tube by Way of a connection 54. The
output of the tube 5l includes a peaking ar
rangement indicated generally by reference char
acter 55. inasmuch as thisarrangement has been
employed in previously known television receivers; l
its functions and operation will not be described-4
in detail. rl‘he output to the image producing
device such as a Kinescope is indicated 4at »58. .
Usually, this connection will effectively terminate
at the control grid of the Kinescope. A. tube 59S-v
of the duplex type serves as a D. C. restorer and
also as a sync pulse separator and amplifier. l The .
cathode iii and the grid (52Y together with the.
cathode resistor 53 serves asv a diode. rectiiier.:
With its load resistor to perform the function `of
a D. C. inserter since the control grid circuit of
the image producing device is coupled/through.;
the resistor 53. The control grid S2 alsofcauses
the signals applied over a conductor 66 from the l
peaking circuits 55 to be rcpeatedzby wayof a
of the tube -.
30 condenser 58 on the control grid .69r
55. The grid and cathode elements lil and 62 rec-`
tify the peaks of the synchronizingpulses which
are applied to the cathode with'negative polarity,
and only the sync signals are passed by the con- -
denser 55 to the grid 59. The pulses appearing on
tooth waves used‘to control deflection;
the grid E9 are present in the plate circuit of the Y
A further object of the invention »is 4to provide
plate 'H which is coupled in- a vnovel .mannenx
an improved means forI synchronizing the de
hereinafter
described, tothe automatic frequency
flecting circuit or circuits of an image producing
controlled horizontal 0r vertical deflection cir-`
device.
A still further object of the invention is to pro 40 cuits.
The horizontal `deflection circuit ofthe image
vide an improved televisionv receiver.
producing device is fed in the usual manner fromA
ln accordance with the invention, a phase de
the secondary Sli of a transformer B5. A horizon
tector is coupled in a novelhmanner to a signal
tal saw-tooth generator 81 including a tube 88
source.
Other and more specific objects of the inven 45 applies a saw-tooth voltage to a high impedance
horizontal output tube 89. The plate circuit of
tion Will become apparent andl suggest themselves
this tube 89 is coupled to the horizontal deflect
to those skilled in therart to which the inven
ing means of the imageproducing device through
tion is directed upon reading the `following speci
the previously mentioned transformer 86.
iication and claim in connection With the accom
The details of the horizontal saw-tooth genera- »
panying drawing in Whicht
50
tor 3l and the function and operation of the hori
Fig. 1 is a circuit diagram of substantially the
zontal phase control 92 will now be described.
entire deflecting arrangement >of ay television re
The cathode 9i and anode 96 ofthe duplex. type
ceiver embodying the invention; and '
Fig. 2 is a schematic representation of Ya por
tube 88 are elements of the usual blocking oscil
tion of a television-receiver_embodying a modi 55 lator tube. The blocking >oscillator includes in
iication of theinventiom..
3
2,458,156
addition a feedback transformer 91, a condenser
99, which is charged and discharged, and a speed
control resistor |02 Which is in series with a re
sistor |03.
4
resistor IGI. As a consequence of capacitance
eilects in the tube |33, the resistors |6| and |62
are not necessarily oi equal value.
The blocking oscillator section of the tube 88
operates to produce pulses and is controlled from
the phase control 32 in a manner to be described.
The elements |03 and |38 of the tube 83 serve
as a discharge tube to generate a saw-tooth of
p
The condenser |2l|- serves to couple the plate
oi the tube |33 tothe cathode |64 of one of the
diode sections. The corresponding anode |36 is
joined to the cathode |67 of the other diode sec
tion, and this connection, indicated by reference
character |'||, serves as the output terminal of
voltage by charging and discharging a condenser 10 the phase detector 92. The D. C. return paths
|69. The adjustable resistor | | | serves as a Width
for the diode sections are provided by resistors
control. The saw«tooth voltage across the con
|14 and |75, having a common terminal which
denser ||J9 is applied through a condenser || 2
is grounded as shown, thereby providing a bal
to the grid ||4 of the high impedance horizontal
anced arrangement for the phase detector. The
output tube 89. The plate circuit of this tube 15 anode |69, corresponding to the last-named cath
includes the primary ||6 of the transformer 36
which also serves as a coupling impedance for
ode, is coupled by the condenser |26 to the cath
W ode ofthe tube |33.
applying voltage pulses to a iiiter composed of a
. The diode sections of the duplex diode |53
resistor |2| and a condenser |22 by way of a
function as peak detectors by selecting Values for
conductor ||9 and a condenser |23. This re 20 the resistors |34 and |75. The discharge paths
sistor |2| and condenser |22, in combination,
of the condensers |26 and |215 have a relatively
produce a Wave of saw-tooth form from the puls-es
long time constant.
`
derived from the output of the tube 89, the latter
A D. C. ampliñer |82 ampliñes the control sig
being of such character that the saw-tooth cur
nal from the phase detector Which appears at
rent is produced in the horizontal deilecting coil 25 the point |'||. This amplifiedv control signal is
of the Kinescope. The condensers |23 and |23
applied to the grid resistor |03 of the blocking
correspond to the condensers 23 and 26, respec
tively, of Fig. l of a co-pending application of the
present applicant jointly with Alfred C. Schroe
scillator triode section of the tube 88. This outs
put is in the form of a signal Whichslowly Varies
when noise is present. The variation in this sig
der, Serial No. 547,355 and ñled July 81, 1944. 30 nal is added to or subtracted from the potential
Resistors |74 and |75 correspond to the resistors
normally appli-ed to the grid |83, this normal po
34 and 33 respectively of Fig. l of said appli
tential being variable at Willwithin chosen limits
cation. The filter' constituted by the components
by the speed control resistor |32.
|3|, |32, and |30, corresponds to the ñlter 39 of
The operation of the receiver of Fig. l With the `
Fig. 1 of the said application.
35 horizontal deflecting circuit arrangement as
The älter-resistor |33 has a critical value, for
shown, in accordance with the invention, will now
each receiver of a given design in which it isv
be described. Sync signals of opposite polarity
used. When this resistor is too large, th-e sides
with respect to ground are provided by the phase
of the image become scalloped, and when it is
inverter tube |33 by Way of the condensers |24
too small, the image as a Whole vibrates in the 40 and |26. These sync signals of opposite polarity
horizontal direction. There is an intermediate
range of values for Which the image is correct.
are superimposed on the saw-tooth Wave derived
A phase inverter tube |33 is coupled to the
output from the plate 1| of the tube 59 through
a coupling condenser |34.
The coupling con
denser |34 in conjunction with the grid resistor
45
from the tube 89 through resistors |83 and |88.
The sync signal which is applied through the con
denser |2|ì to the p-late |69 of the tube |53 is in
the -positive sense, while the sync signal applied
by Way of the condenser |24 to the cathode `|64
|36 of the tube |33 serves as la diii‘erentiating
is in the negative sense.
circuit to separate horizontal sync pulses from
the output of the tube 59. The pulses which are
applied to the grid |38 are of short time dura
tion which is desirable for application to the
phase control 92.
A phase inverter tube Ml is coupled to the
on the plate |69 and the cathode |64 are in phase
and the time relation is such that the sync sig
The saw-tooth Waves
nals are positioned on the return or re-trace por
tion of the saw-tooth. In normal operation, as
suming that disturbances such as noise are absent,
and with a pre-determined normal setting of the l
output of the tube 59 through a coupling con- ‘
denser |43 and a resistor |34. The resistor |43,
control |92, the sync signals are substantially at
the middle of the re-trace. Any change in the
in conjunction with a cond-enser |46, serves as
phase relation of the saw-tooth Wave and sync
an integrating circuit to obtain separation of `
pulses will cause an increase in the peak am
plitude of one composite .signal and a decrease
the vertical sync pulses Which are to be applied
to the vertical phase control designated gener
ally by a reference character |38. Inasmuch as
the action of the vertical sync circuits is similar
combined with one set of sync pulses extending
to the action of the horizontal sync circuits, a
either in a positive or negative sense.
detailed description will be given in connection
With tube |33, and it Will be .understood that
this description applies equally to the tube IM.
The voltages across the resistors I'lll and |15,
that is to say, on the diode side of the condensers
Pulses appearing on the grid |38 of the tube
|33 are applied in opposite phase by way of the
previously mentioned oondensers |24 and |28 to
a phase detector comprising a pair of diodes or,
as shown by way of example, a duplex diod-e |59.
Coupling is effected in a manner to provide posi
tive pulses on the plate and negative pulses sub
stantially of equal amplitude on the cathode of
in the peak amplitude of the other composite sig
nal, these composite signals being the saw-tooth
55
|24 and |26, include 'the D. C. voltage inserted by
the peak rectifier action of the diode Sections
of the duplex diode |59. The peaks of the sync
pulses are held at the same reference level, which
may conveniently be zero.
In the signal appearing at the point |‘||, the
sync pulses are effectively balanced out, leaving
a signal containing only the saw-tooth wave com
ponents. The saw-tooth component is filtered
the tube |33. Equality of amplitude is readily
out by the previously mentioned filter composed
otbained by selecting a proper value .for the plate 79 of the elements, |36 to |32, and a D. C. control
2358356*
potential is obtained which‘is not a .fluctuating
saw-tooth Wave but is a very slowlyrvarying signal ‘
filter: If î'resistor ZMIhastOolaI-‘gefa value,'the;im=age‘will tend-'tto -bounce vinthe vertical~ direction;under“y the ‘influencefof f severe-N noise.
The -. lower :
when noise is present.. This .controllpotential‘ is“
limit-‘of value of the'resistor‘2il4>vvill7 inizgeneral, .,
amplified by the amplifier tube |82.- Injthe illus-'
berñXedVv bythe-'speed' ‘of-h pull-in considered "desir,
trative example, the average potential _"eXistin'g' .5'v able and the tightness of lock-in;desired.;Y
between the saw~toothwaves with‘the'peaks'of>
It is ydesirable inrthe' operationfof van automatic
the sync pulses at the same reference level' is zero
at the instant when the sync pulses occurî", If ai;
small phase displacement occurs betweenth'e'syri'c`
pulses and the saw-tooth waves, the peaks' Vofjthe.`
frequency controlled television received to . main-y A
tain `vafrea‘sonably constant plate voltage supply
|82f-'andf‘2ill (or thotwo'parts cfa.
duplex tube, if one ~is >used as shown) andfthe:
sync pulses continue to be maintained at vzero po“-A
tential, for example, but the average potential atH
the point lll is lowered'or raised,” depending'pnî
tubesy 881 295, and-'|91 when the gain- control.` of
the‘iL‘F?ampliñer (not shown) is varied. Ansi-J.l
whether the pulse moves to an advancedior to Ya4
V:constant~plate"«voltage is shown in ithe applica:-.>
fe`ctive-v arrangementy fori insuring a reasonably.V
retarded position in time relative to.th'e.saw- 15 tion”vof-"Gordonr LL FredendalL'- Serial No. 526,287; .
tooth wave. The feedback action issuch' that 'the
filediMarcl‘i‘flS;` 1944,` now. matured into ' Patent î.
change in speed of the oscillator tends to‘jredu‘ce';
Number 2,454g150?
the magnitude of the‘phase discrepancy between'
Referring‘toFi-g. 2î'of the drawings, a portion..
a saw-tooth cycle anda pulse that gave 'rise'to' sof a"te1e`visliorr'receiverk embodying the invention.
the increment in the control voltage.
in'm'odiñe'd -form `is disclosed. Reference characThe equilibrium position of the pulses isa func;
ter= `2 | 2 "denotes a'y transformer,l the.l primary’ßZ | 4 'î
tion of the settings of the speed control, for ex
of "Whichsis `V`furnished#with separated horizontal» i
ample, speed control 102; but is constrained to li'eand-'vertical ïsync `signals over a connection indie»,
somewhere on the return time of the saw=tooth2
«fcateollat-'215;k This» connection 2l5~ìmay corre
The suggested normal location given above was in
spond‘withf-or'beß-analogous to the circuit >of the
the middle of the return‘tizne’of-the saw-tooth.
plate ‘-'|| ofthe -tube~59 'of Fig. 1. Push-pull horie ~«
When the amplitude of noise is sufficiently great,
zontaleA and v‘verticat sync- pulses ~ required by the ‘
some noise peaks tend to beheld at'zero-‘potential
by the action of the diodes ofy the l"duplex diodel
tube |59. The potential at the point |`|| tends
to fluctuate about zero, if the Vdistribution of the
noise is random. Under such circumstances, the
D. ' C. component ‘is zero.' It‘is 'important Lhereïto
note that the waveforms -of noise> and saWj-tooth
do not appear at 'the'jun‘ction of the diodes as dise
tributing components’ of ' the" control' voltage;
Variations in the` difference" between the-“in-4
stantaneous A. C. axes”v of the'Vv two saw-'tooth
waves'would >appear at’the'point l|1| in’ the :ab=
sence of the filter‘lBU-iEZ. The function “ofthe
nlter is Athe removal ofthe higher frequencyîcome
horizontal andyertical phaseldetectors -2|‘|"ar1d"~
2 | B“ are derived * from » the» transformer 2 |‘2 by`>-
meansfof-‘hig'hepass‘Re-C filter network 2|9 and 'ï
a lowßpassR-C filter network- 22 0,
Tl'i'efhorizon-tal'sync control- will first bede-v
scribed'isi-nce; as uwas-'stated in connection with
:Fig~ l‘ofV the drawings, the principal features of ‘
the vertical sync controlare analogous and therefore‘a ‘detailedl description of it need not be given.
Thefphase-detectorZ l1 comprises apair of diodes -
or;fin~the<«interest of economy,y a duplex diode 222V
comprising s independent diode »sections 223 and‘
2245V The' high-‘pass lfilterw‘ìlâ-is designed in- ac-l
cordance with Well-known~- principles and com
ponents of the control voltage and the transmis
prises-twosections; each composed of a condenser
sion only of the very low frequency components.
and'resistor. Condenser 226 and resistor 22? >pro
In. the absence of noise, the§latter are atruein
vides sync pulses in the positive‘sense to the'diode
dication‘that a readjustment ‘in the phase of 'the
section 2'23. Condenser 228 and resistor 229 pro
oscillator is necessary for the maintenance of ac
vide a sync pulse in the negative sense to the di
curate synchronism. Low frequency components
ode section 224. Condenser` 233 corresponds in
are indications of a drift in circuit constants or
function and location to the condensr |26 of Fig.
small changes in the frequency of the transmitted
50 1. Condenser 234 corresponds in function and 1o
sync pulses.
cation to the condenser |24 of Fig. 1.
The vertical deflection circuit and vertical de
Resistors 236 and 237 are grounded at their
flection control shown by Fig. 1 of the drawings
point of connection to cause the diode sections to
are similar to and operate in the manner already
serve as peak detectors. In order that a control
discussed in connection with the horizontal de
signal representing the phase difference between
flection circuit. The adjustable resistor |90
sync signals and the saw-tooth deflection wave
serves as a size control and corresponds to the
may be developed at the point 239, the saw-tooth
size control i l l. The adjustable resistor |92
deñection wave is fed by way of a connection 24|
serves as a speed control and corresponds in func
to the zero ground potential point, provided at
tion to the adjustable resistor |02. The adjust
v the junction of the resistors 229 and 221. 'The
able resistor |93 serves as a vertical linearity con
arrangement from the condensers 233 and 234
trol. A condenser lîlä is charged and discharged
may be the saine as the arrangement shown on
to provide a voltage wave which controls the plate
Fig, 1 of the drawings from the condensers |24
current of a tube i9?. This plate current in the
and |26 through the horizontal deflection trans
primary of transformer |98 serves to drive a saw
former 86 shown on Fig. 1 of the drawings. The
05
tooth wave of current through the vertical de
connection '24| corresponds to the connection | I9
flection coil (not shown).
of Fig. 1. Inasmuch as the arrangement of Fig.
Polarities relative to ground of the vertical sync
1 may be used, it is not believed that further de
pulses appearing at the vertical phase detector
tailed illustration of these features is necessary.
|99 should be such that positive pulses are ap
plied to the plate 29d and negative pulses to the 70 The saw-tooth wave is derived, for example, from
a discharge tube under control of a blocking os
cathode 292. The limits of the value of resistor
cillator tube which functions in the manner ex
29e, which is the damping resistor in the filter
combination 2%, 298, and 204, in general need
not be as restricted as the value limits of the
plained in connection with tube 88 of Fig. 1 of
the drawings. The output of the discharge tube
corresponding resistance |30 in the horizontal 75 appearing in its plate circuit is supplied through
2,458,156 l
7
the medium of a transformer to the horizontal
defiecting coil (not shown). The output of the
discharge tube may, it will be understood, be of
.An automatic frequency control system com“v
prising a pair of peak rectiñers, a source of sig
nals of sawtooth wave form, a source of separated
a wave form which is suitable to provide a cur
pulses providing high and low frequency pulses,
rent wave of saw-tooth form in the horizontal
deflecting winding.
a transformer connected to said source of sep
arated pulses, means for applying sawtooth wave
Y
The synchronizing peaks, applied in opposite
form signalsto said rectiñers with like polarity
at each rectifier, means including a high pass
sense by the connection 2M and the saw tooth
wave voltage are combined in a manner previously
filter for applying pulses `of high frequency to
explained in Fig. l of the drawings to provide a 10
said rectiñers from said transformer with oppo
control signal at the point 239.
.
site polarity at each rectifier, means for utilizing
vThe principal difference between the vertical
the output of said pair of peak rectiñers for con
and horizontal control circuits in this modifica
trolling said means for applying sawtooth wave
tion lies in the design of the Yñlter 220 which
form signals, a second pair of peak rectiñers,
passes the vertical sync signals Since the details 15 means for applying low frequency sawtooth wave
of the ñlter 229 conform to normal practice,„and
form signals to said second pair of peak rectiñers
the choice of constants of the filter can readily
with like polarity at each rectifier, means includ
be made by those skilled in the art,.a detailed
ing a low pass filter for applying low frequency
description will not be given. It is to be `noted
pulse signals to said second pair of rectiñers from
that the capacity arms of the positive and nega
said transformer with opposite polarity at each
tive portions of the filter are grounded at 269. 20 rectifier, and means for utilizing the output of
The saw-tooth voltage from the vertical discharge
said second pair of'rectifiers for controlling said
tube is applied over a connection 272 to each half
« means for applying low frequency sawtooth Wave
of the phase detector by resistors 274 and 216.
form signals.
As a consequence of the balanced nature` of »
GORDON L. FREDENDALL.
both vthe horizontal and vertical control circuits 25A
in accordance with this modification of the Iin
REFERENCES CITED
vention, there are no troublesome reactions be
Thev following references are of record in the
tween horizontal and vertical circuits.A Economy
file of this patent:
.
of design is also a feature of the invention in this 30
UNITED STATES PATENTS
form since only the single transformer 2| 2 is
Number
`
Name
Date
required for both the horizontal and vertical cir
cuits. This feature of economy is of considerable
2,132,654
Smith __________ __ Oct. 11, 1938
importance in television receivers designed for
2,201,978
Bedford __________ __ May 28, 1,940
household use which, to be available generally to 35 2,209,507
Campbell _________ __ July 30, 1940
the public, must be sold at a modest price.
2,227,815
Toulon __________ __ Jan, 7, 1941
Various alterations may be made in the present
2,250,284
Wendt ___________ __ July 22, 1941
invention without departing from the spirit and
2,275,460
Page> ____________ __ Mar. 10, 1942
scope thereof, and it is desired that any and all
2,339,536
Wendt ____________ __ Jan. 18, 1944
such alterations be considered within the purview 40 2,358,545
Wendt ___________ __ Sept. 19, 1944
of the present invention as defined by the here
inafter appended claim.
2,361,255
,
Having now described the invention, what is
claimed and desired to be secured by Letters
Patent is the following:
’
r
Zworykin ________ __ Oct..24, 1944
FOREIGN PA'I’ENTS
Number
45
118,660
Country
'
Date
Australia ________ __ July 13, 1944
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