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Патент USA US3030598

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Aprll 17, 1962
E. H. HUGENHOLTZ
3,030,588
GATED PHASE LOCK FREQUENCY CONTROL SYSTEM
Filed March '7,|9l958
I. F. AMPLIFIER
(90° PHASE SHIFTER
I
1. F. AMPLIFIER)
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52
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53
63
3 ‘3%- H62
INVENTOR
EDUARD HERMAN HuaENHaLTZ
BY
-
AG NT
-
United States Patent ‘0 "ice
3,030,588
Eduard Herman Hugenholtz, Toronto, Ontario, Canada,
assignor to North American Philips Company, Inc.,
3,030,588
2
1
'GATED PHASE LOCK FREQUENCY
CON-FRUL SYSTEM
,
Patented Apr.- 17, 1962
and a phase discriminator is not capable of pushing the
controlled oscillator frequency towards the desired value.
In carrying out the control system in accordance with .the
present invention, the _LP‘. signal is fed through a gating
circuit to a phase discriminator circuit in which it is
compared with a component of the reference signal spec
trum to produce a control voltage. The gating circuit
‘Claims priority, application Canada Mar. 22, 1957
is maintained in its closed state and only opens whenthe
25 Claims. (Cl. 331—26)
.incoming I.F. signal is of a predetermined amplitude and
10 in a de?nite phase relation with the reference signal.
My invention relates to a tunable oscillator ‘locking
Further features and advantages of my invention will
system wherein ‘the oscillator is locked to a reference sig
become apparent as the description of my invention ,now
nal by means of an automatic frequency control (AFC)
proceeds with reference to the ?gures of the drawing .of
New York, N.Y., a corporation of Delaware
Filed _Mar. 7, .1958, Ser. No. 719,782
system employing, for instance, a reactance tube or other
which
equivalent means.
15
FIG. 1 shows a preferred embodimentof my invention,
In known systems the control voltage for the .AFC is
and
usually obtained by comparing the oscillator signal with
FIG. 2 shows a further embodiment thereof utilizing a
the reference signal as in a phase discriminator. When
modi?ed gating system.
the two signals applied to the phase discriminator means
‘Referring .now to vFIG. 1, wherein supply voltages have
‘in ‘synchronism, a direct current voltage is produced and 20 been omitted for simpli?cation, the
signal is fed into
phase lock is then possible, ‘through the medium of the re—
an ampli?er shown as ‘block 1. Theoutput ~.of.arnp_li?er.1
'actance ‘tube or other equivalent control means. If .the
signals are not in synchronism, .an alternating voltage .will
be produced ‘by ‘the phase ‘discriminator and locking does
not take _ place.
It ‘has been found desirable 'toprovide in a communica
tion system a facility for enabling the use of arplurality
of adjacent frequency channels of equal ‘width. vThis
may be accomplished by synchronizing'the oscillator of a
is fed ‘through condenser v3 to the control grid :of .a gat
ing ‘tube V1. "Va is normally maintained cutoff bymeans
of a negative bias applied to the grid thereof through the
medium of resistors 4, 19;, 15,, .12, 13 {and 18, and ter
minal '25 to which is applied a negative voltage. When
proper conditions exist ‘for phase lock, the bias is re
moved and gating tube V1 acts :as an ampli?er .and .the
ampli?ed
signal output from'Vl is fed to .a ?rst phase
transmitter to a harmonic of a stabilized low frequency 30 discriminator '21 in which his-compared with areference
‘(-i.e. T00 kc.'s._) signal and thus provide, in ‘this case, for a
number of channels whose center frequencies are displaced
‘100 kc.s.
,switch .23, to produce the phase lock voltage. The man
predetermined intermediate frequency maybe produced
phase discriminator. The IF. signal voltage developed
signal, suppliedby means ofinput terminalzd and reversal
ner in which the ‘bias voltage is removed from V1 will now
‘In such a system the harmonic spectrum of the stabilized
be described.
oscillator is mixed with the output of the controlled oscil 35
The ampli?ed ‘LF. signal from 1 .is also fed through a
lator ‘to provide an intermediate frequency ,(‘I.’F._). A
90° phase shift circuit 2 to tank circuit 9 .of .a second
by the frequency of the controlled oscillator "being dis
across circuit '9 is applied to ya .diode 14 by means of .a
;placediby the intermediate vfrequency above or below that
capacitor 2010 provide a positive voltage tending to neu
of the stabilized oscillator. These intermediate frequen 40 tralize the negative bias on V1 supplied at terminal 25.
cies can ‘be considered to vbe images of each other and will
Capacitors ‘16 and ,5 smooth out .the recti?ed voltages
be selected to the same degree'by a tuned circuit.
produced.
In‘known control systems aphase discriminatorfistcom
‘To the center tap of the secondary winding of this sec
‘bined with a frequency discriminator in each of which
ond phasediscriminator is fed the reference signal applied
are compared the LF. signal and a component of the 45 at ‘terminal 24. ‘When the reference .and :the LP. tsignals
stabilized frequency spectrum to produce control vo'lt
fed to the second discriminator are in phase, .a further
ages. The frequency discriminator makes possible the
selection of the proper image. ‘The tuning of-the frequency
discriminator determines the component of the frequency
spectrum on which‘loc‘king may take place and is utilized
to ‘bring the IF. frequency toward the proper value. The
phase discriminator will then lock the controlled oscilla
positive voltage is produced ‘by diodes .10 and ‘11 :and adds
to the positive voltage across diode 14 produced by the
recti?ed .LF. signal. When this condition exists and the
IJF. signal is of suf?cient amplitude, the ;bias will be .re
the center .of the “frequency discriminator curve. _L0_cl<~
ing may also take place on a‘harmonicof the ‘LE, if suf
By means of phase reversal switch 23, it is possible to
provide for rphase lock on the selected LE. signal or its
moved from gating itube V110 allow ampli?ed I.~F.,si_gnal.to
be supplied to phase discriminator-.21.and;phase lock to
-t0r on the desiredfrequency.
takeqzplace. When the .LF. and referencenignalsapplied to
Disadvantages of the above type of system is that the
the second discriminator are in phase opposition, the-rec
frequency discriminator'has to be tuned quite close .to .the 55 ti?ed voltages produced thereby substantially neutralize
desired locking frequency in order to (prevent locking on
each other and the gatecircuit of ‘V1 remains closed.
?cient s‘ignalge'ts throughto the discriminator. 'Topre
image according to .the polarity versus change of the volt
‘vent this latter effect, greater selectivity in tuned circuits 60 age produced 'by discriminator .21.
would "have to ‘be employed with the consequence that
‘It should 'be noted that .the phaseshift circuit 2 .is out
misalignment and phase'shift could {possibly override the
side the actual control circuit and hence .does not ,lead
advantages to be gained thereby.
to instability.
The ‘present invention overcomes .the disadvantages
‘Referring now to EIG..2\wl1erein power supplies have
of therprior systems by use of a tunahlegate circuitwhich 65 been omitted ‘for simplicity reasons, the .LF. signal is
prevents the IF. signal ‘from reaching the phase discrimi
ampli?ed ‘by ampli?er Y50 and applied .to ,a further am
nator 'for all frequencies except those close to the de
sired'value. Furthermore, nophase‘loc'k ispossible except
pli?er tube V“). The IF. signal voltage developed at
the cathode of ‘V10 is fed ‘by means of capacitor 51 and
with IEF. signals above a predetermined strength. A
recti?er 52 to a phase discriminator 54 providing proper
frequency discriminator is not used and,'hence, a hunt 70 conditions "exit with regard ‘to recti?er ‘53 and-a gate con
ing'voltage must necessarily ‘be \super-imposede'on the 'con—
trol tube V13.
trol ‘loop as the combination of #a ‘tunable zgate circuit
The ampli?ed I.F. voltage at the anode of ‘V10 is fed
3,080,588
'
'
'
e
4
through a phase reversing switching system 55 to a tank
circuit 56 tuned to the frequency of the LF. voltage.
The LP. voltage developed across‘ tank circuit 56 is ap
plied to a recti?er circuit comprising diode 57, resistor 58
and a ?lter circuit consisting of resistor 59 and capacitor
60. Capacitor 61 in conjunction with resistor 62 produces
a phase shift of 90° in the 'LF. voltage between tank cir
cuit 56 and diode 57.
A negative delay voltage is applied, through the me
dium of input terminal 63, resistors 64, 58 and 59, to the
‘control grid of V13 to cause it to be normally non-conduct
mg.
.
A component of a stabilized reference signal is applied
through input terminal 65 to the control grid of a triode
ampli?er V12. Triode V12 has anode and cathode loads
constituted by upbypassed resistors 66 and 67 and con
sequently acts as a phase splitter. The reference signal
voltage developed across cathode resistor 67 is applied to
discriminator 54. The reference signal developed across
resistor 66 is applied by means of capacitor 68 to diode 12.
The manner in which the gating is controlled will now
be explained. As was stated previously, the LP. signal
voltage developed across cathode resistor 69 of tube V1
is applied to diodes 52 and 53 which are poled to conduct
in opposite directions.
Considering the condition wherein triode V13 is non
conducting due to the negative bias supplied via terminal
63, i.e. the LF. signal amplitude and phase is incorrect for
3. The system as set forth in claim 1 wherein the signal
representative of said reference signal supplied to said
phase discriminator may be reversed in phase to provide
for locking on the image of the signal representative of
said oscillator frequency.’
4. Apparatus for producing a control voltage repre
sentative of the phase difference between a signal fre
quency voltage and the frequency of a reference signal
voltage comprising a phase discriminator, means supply
ing a signal representative of said reference signal to said
phase discriminator, normally closed gate means adapted
to supply said signal frequency voltage to said phase dis
criminator to produce a control voltage which varies with
the phase difference of said signal frequency voltage and
said representative signal and means responsive to said
last two mentioned signals to produce a voltage elfective
to open said gate when predetermined phase and ampli
tude relations exist between said last two mentioned
signals.
5. The system as set forth in claim 4 wherein said
gate means comprises a vacuum tube ampli?er normally
biased to cut off.
6. The system as set forth in claim 4 wherein said gate
means comprises biased recti?ers.
7. A system as set forth in claim 4 wherein a hunting
25
voltage is superimposed on said control voltage.
8. Apparatus for producing a control voltage repre
sentative of the diiference frequency between the fre
quency of a tunable oscillator and a component of the
‘locking, diodes 52 and 53 are therefore blocked because
of their series relationship to the direct current path of 30 harmonic frequency spectrum of a stabilized oscillator
comprising means to select said difference frequency and
V13. The LP. signal on capacitor 51 is blocked due to
apply it to the input of an ampli?er which is normally
the recti?er action of diode 52 which conducts to render
the junction between capacitor 51 and diode 52 negative
biased to cutolf, means supplying said difference frequency
with respect to the junction between diode 52 and ca
to a circuit tuned thereto, means rectifying the voltage
pacitor 71. Under these conditions the intermediate fre 35 produced across said tuned circuit, recti?er means produc
ing a voltage representative of the phase and amplitude
quency signal developed across resistor 69 is blocked
from discriminator 54.
relations of the difference frequency and said component,
means adding the voltages produced by recti?cation and
, Consider now the condition wherein the LP. signal sup
utilizing the product, obtained thereby, to neutralize the
plied to tank circuit 56 is of the required amplitude and
phase as compared to the reference signal developed across 40 bias on said ampli?er when proper phase and amplitude
relations exist between said difference and component fre
resistor 66, a voltage is built up across diode 57 which
quencies, to supply ampli?ed difference frequency to a
substantially neutralizes the negative bias supplied to V13.
phase discriminator wherein it is compared with said
Diodes 52 and 53 are unblocked and the LF. signal is ap
component frequency to produce said control voltage.
plied to discriminator 54 where in it is compared with
9. Apparatus for maintaining a predetermined dif
the reference signal developed across resistor 67 to provide 45
ference frequency between the oscillation frequency of a
a control voltage at terminal 72 capable of maintaining
the required phase lock.
tunable oscillator and a reference oscillation comprising
a normally closed gate means adapted to supply one of
Reversal of switch 55 facilitates the locking of the
controlled oscillator with respect to either image of the
said oscillation frequencies to a phase discriminator,
LF. signal produced by mixing the output of the oscil 50 means normally supplying the other of said oscillation
lator with a reference frequency spectrum.
frequencies to said phase discriminator, means selectively
supplying said ?rst mentioned oscillation and a signal
It will be apparent from the foregoing that I have pro
representative of said reference oscillation to a recti?er
vided a phase lock control system which offers advantages
circuit to produce a control voltage effective to open said
over those of the prior art. ‘It should be noted that var
ious modi?cations may be made, such as substitution of 55 gate when predetermined amplitude and phase relations
exist between said ?rst oscillation and said representative
tube or’ recti?er types, elimination or increase of ampli
signal, and means utilizing the output voltage of said
?cation etc., without departing from the spirit and the
phase discriminator to control the frequency of said tuna
‘scope of my invention.
.
ble oscillator.
'
‘The embodiments of the invention in which an exclu
10. Apparatus for maintaining a predetermined dif
sive property or privilege is claimed are de?ned as fol 60
ference frequency between the frequency of a tunable
lows:
‘
oscillator and that of a component of the harmonic fre
1‘. ‘In a frequency control system wherein the frequency
quency spectrum of a stabilized oscillator comprising
of a tunable oscillator is adapted to be locked with that
means to select said predetermined di?erence frequency
of a reference signal, a phase discriminator, means feeding
and apply it to a normally inoperative ampli?er, means
a signal representative of said reference signal to said
supplying said difference frequency to a tuned circuit
phase discriminator and gate means adapted to open and
selective thereto, ?rst recti?er means producing a ?rst
feed. a signal representative of said oscillator frequency
direct current voltage representative of the amplitude of
to said phase discriminator when said oscillator frequency
said difference frequency produced across said tuned cir
approaches substantially a desired value, wherein said
gate means is controlled by a voltage produced by applica: 70 cuit, second recti?er means comparing the amplitude and
tion of said representative signals to a common recti?er
phase of said difference frequency produced across said
tuned circuit with the amplitude and phase of said com
means.
'
-
_ 2. The system as claimed in claim 1 wherein a hunt~
ponent to produce a second direct current voltage, means
ing voltage is superimposed on the output voltage of said
adding said ?rst and second direct current voltages to
75 produce a third direct current voltage and means utiliz
phase discriminator. _
3,030,568
"5
6
ing said third direct current voltage to control the opera
tion of Said ampli?er to supply ampli?ed difference ‘fre
provide for ‘locking on the image of the signal represen
tative of said oscillator frequency.
quency to a phase discriminator wherein it is compared
with said component frequency to produce a direct current
voltage is superimposed on said con-trol voltage.
voltage which is utilized to maintain said predetermined
difference.
voltage 'is superimposed on said control voltage.
11. Apparatus as claimed in claim 10 ‘wherein said
ampli?er is normally ‘biased ‘beyond cutoff.
12. Apparatus as claimed in claim 10 wherein means
is provided for reversal of ‘the phase of one “of said fre
'17. A'system as set ‘forth in claim '5 wherein a hunting
118. A system ‘as set forth in claim 6 wherein a'hunting
‘19. Apparatus as claimed in claim ‘11 wherein means
is provided for reversal :of the phase of one of said ‘fre
quencies to ‘provide for frequency control on the image
of ‘said difference frequency.
20. Apparatus for controlling the frequency of signals
from a controllably variable signal :source by signals
from a reference signal source comprising ?rst zsignal com
ble oscillator with respect to a reference frequency com
;paring means for comparing signals from said reference
prising means ‘to selectively amplify a signal representative 15 signal source with signals representative of signals from
of said tunable oscillator frequency, means comparing the
said controllably variable signal source, gating means
ampli?ed signal with respect to phase and amplitude with
responsive to said representative signals and said ?rst
that of said ,reference frequency to produce a ?rst direct
signal comparing means to [pass said representative sig
current control voltage, gate means adapted to supply
nals when a predetermined relationship exists between
said representative signal to a phase discriminator wherein 20 said representative signals and signals from said reference
it is compared with said reference frequency to produce
signal source, and second signal comparing means for
a frequency control voltage, and switch means under con
comparing the signals from said gating means with the
trol of said ?rst control voltage and adapted to open said
signals from said reference signal source for transmitting
gate when predetermined amplitude and phase relations
control signals to said controllably variable signal source.
exist between said reference and representative signals, 25 21. Apparatus for controlling the frequency of signals
said frequency control voltage being utilized to maintain
from a controllably variable signal source by signals from
the frequency of said tunable oscillator with respect to
a reference signal source comprising gating means adapted
said reference frequency.
to receive signals from said controllably variable signal
14. In a frequency control system including a tunable
source, signal comparing means for comparing signals
quencies to provide for .frequency control on the image
of said difference frequency.
13. Apparatus for controlling the frequency of ,a'tuna
oscillator the frequency of which is to be controlled, a 30 from said reference signal source with signals from said
source of reference oscillations, means mixing the output
controllably variable signal source, said gating means
voltage of said tunable oscillator with said reference
being responsive to said signal comparing means to pass
oscillations to produce a difference frequency voltage,
the controllably variable signals when a predetermined
means selecting said difference frequency voltage and
relationship exists between the signals from said con
supplying it to a recti?er having a load circuit, a nor 35 trollably variable signal source and said reference signal
mally closed gating circuit consisting of a normally blocked
source, and a phase discriminator responsive to the sig
direct current switch having a pair of diodes in series cur
nals from said gating means and said reference signal
rent carrying sense therewith, a ?rst capacitor connected
source, said phase discriminator transmitting signals to
between the extremities of said series connected diodes,
control said controllably variable signal source.
a second capacitor coupling said difference frequency 40 22. Apparatus for controlling the frequency of signals
voltage to the common junction of said diodes, a circuit
from a controllably variable signal source by signals
connection between the end of said series circuit remote
from a reference signal source comprising ?rst signal
comparing means for comparing signals from said refer
from said switch and a phase discriminator, means sup
plying a signal representative of the reference oscillation
ence signal source with signals from said controllably
to said phase discriminator to produce a frequency con 45 variable signal source, gating means responsive to said
trolling voltage on the presence of said difference fre
first signal comparing means and to said controllably vari
quency in said phase discriminator and means supplying
able signals to pass the controllably variable signals when
said representative signal to said recti?er means to pro
a predetermined phase and amplitude relationship exists
duce in said load circuit in conjunction with said differ
between the signals from said controllably variable signal
ence frequency voltage a direct current voltage effective to
source and said reference signal source, ‘and second signal
open said switch when predetermined phase and ampli
comparing means for comparing the signals from said
tude relations exist between said reference and difference
gating means with the signals from said reference signal
frequency voltages.
source for transmitting a control signal to said controllably
15. In a frequency control system including a tunable
variable signal source.
oscillator the frequency of which is to be controlled, a 55
23. Apparatus for controlling the frequency of signals
source of reference oscillations, means mixing the output
from a controllably variable signal source by signals from
of said tunable oscillator with said reference oscillations
a reference signal source comprising gating means adapted
to produce a di?ference frequency voltage, means supply
to receive signals from said controllably variable signal
ing said difference frequency voltage to 1a recti?er having
source, signal comparing means for comparing signals
a load circuit, means supplying a signal representative of 60 from said reference signal source with signals: from said
said reference oscillations to said recti?er to produce in
controllably variable signal source, said gating means
conjunction with said difference frequency a gate control
being responsive to said signal comparing means to pass
voltage which varies with the phase and amplitude re
the controllably variable signals when a predetermined
lationship between said reference and difference frequency
signals, a phase discriminator adapted to produce a fre 65
quency control voltage for said tunable oscillator, means
supplying said difference and representative frequency
phase and amplitude relationship exists between the sig
nals from said controllably variable signal source and
said reference signal source, and a phase discriminator
responsive to the signals from said gating means and said
voltages to said frequency discriminator, and gate means
reference signal source for transmitting signals to control
actuated by said gate control voltage effective to prevent
said controllably variable signal source.
the application of one of said voltages to said phase dis 70
24. Apparatus for producing a control voltage repre
criminator in the absence of a predetermined gate con
sentative of the phase difference between a signal fre
trol voltage value.
quency voltage and a reference frequency voltage com
16. The system ‘as set forth in claim 2 wherein the
prising gating means responsive to pass said signal fre
signal representative of said reference signal supplied to
quency voltage when opened, signal comparing means
said phase discriminator may be reversed in phase to 75 responsive to said reference frequency voltage and to said
3,030,588
'
8
7
signal frequency voltage via said gating means when
opened for producing said control voltage representative
of the phase di?erence between said signal frequency volt
age and said reference frequency voltage, and control
means for opening said gating means when a predeter
mined condition is present, said control means being re
means for opening said gating means when a predeter
mined condition is present, said control means being re
phase of said signal frequency voltage and said reference
frequency voltage for producing a second control signal,
sponsive to the relative phase of said signal frequency
said control means opening said gating means when the
sum of said ?rst and second control signals is a predeter
mined value.
voltage and said reference frequency voltage.
‘
25. Apparatus for producing a control voltage repre
sentative of the phase difference between a signal fre 10
quency voltage and a reference frequency voltage com
prising gating means responsive to‘pass said signal fre
quency voltage when opened, signal comparing means
responsive to said reference frequency voltage and to said 15
signal frequency voltage via said gating means when
opened for producing said control voltage representative
of the phase difference between said signal frequency volt
age and said reference frequency voltage, and control
sponsive to the strength of said- signal frequency voltage
for producing a ?rst control signal and to the relative
References Cited in the ?le of this patent
UNITED STATES PATENTS
' 2,468,350
Sunstein ____________ __ Apr. 26, 1949
2,521,058
2,521,789
2,666,136
Goldberg ____________ .._ Sept, 5, 1950
Grosdoff ____________ .._ Sept. 12, 1950
Carpenter ___________ .._ Jan. 12, 1954
FOREIGN PATENTS
148,588
Australia ____________ __ Oct.
10, 1952
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