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Патент USA US2410389

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Oct. 29, 1945.
E. NORRMAN
2,410,389
FREQUENCY DIVIDER
Filed Feb. 26, 1943
.
‘
INVEN TOR.
ErfyzSÚÀ/"o frm an,
W2# qw
2,4l0,38ä
Patented Oct. 29, 1946
UNirED :STATES PATENT oFF-ICE
2,410,389
'FREQUENCY DIVIDER
Ernst' Norrman, Delavan, Wis., assignor to George
W. Borg Corporation, Chicago, ~Ill.,a corpora
tion of Delaware
.Application February 26, 1943, Serial No. 477,237
l10 Claims. (Cl. 250-`-3G)
1
The present invention relates in 'general to fre
quency conversion apparatus, and more in _par
ticular- to so-called frequency dividers which are
employed to obtaina ‘desired lowjfrequency out
put from a. high frequency input. The object of
the invention is to produce a newvand improved
apparatus of this character.
The invention is useful, for example, in gener
ating standard frequency alternating current for
running the constant speed motor Aof `a watch
timing device.
In such a generator4 a source of
2
divider, for reasons which-need-not begone into
in detail. >For one thing, the standard îHar'tley
oscillator 4is not susceptible >to reliable control .at
a sub-multiple frequency by ,alternating currents
derived from >a crystal oscillator. Another diffi
culty arises from the fact that if it is attempted
to control a Hartley oscillator `ata sub-multiple
frequency fromla similar oscillator the controlled
oscillator tendsl to operate as an amplifier at the
control frequency.
.In this situation, I have discovered4 thatwith
suitable coupling arrangements which I have >also
devised a somewhat Vdifferent single tube oscil
lator can' be made to operate very satisfactorily
constant frequency alternating current is re
quired. A crystal oscillator has a substantially
constant frequency and'accordingly is very de
sirable for this purpose, but the frequency is far 15 as a frequency divider. The new oscillator ldif
fers from the standard Hartley'oscillator in sev
too high for. use in running a motor. However,
eral respects, as will be explained fully herein
by the usev of a suitable frequency Vdivider the
high crystal oscillator frequency (in the ,neigh
after in describing its construction and operation.
One feature which is important and which may
duced to a sub-multiple frequency of 100 cycles 20 be mentioned at this time is the wave shape of
the oscillator grid Voltage. VI have 'discovered
per seconder some other desired low frequency,
that for?satisfactory operation the positive half
and by suitable amplification ofthe low lfre
of the wave must bedecidedly limited inv ampli
quency output of _the frequency divider the re
tude, with a characteristic `flat top.
quired low frequency current for running the
According toanother feature of the invention,
motor may be obtained.
two somewhat Adifferent circuit arrangements are
Apparatusof the foregoing character, compris
employed, the one used in any case ,depending on
ing a crystal oscillator, frequency divider, and
4whether the oscillator is to divide by an oddor
amplifier, may be referred to as a constant fre
even number. l I have discovered that in the case
quency- generator, and has been used extensively
in connection with watch timing apparatus. ‘In ‘ of an‘oscillator which is -designed for odd divi
sion the4 best results-are obtained when a con
this known generator the frequency divider com
denser and leak resistor are used in the grid cir
prises a plurality of multivibrator stages >con
cuit, whereas inthe case of an oscillator designed
nected in _tandem and each operating at a fre
for even division these parts are omitted.
_
quency which is a sub-multiple of the frequency
,Theinvention and the various features thereof
at the preceding stage.
will be fully described hereinafter, reference be
VA frequency divider ,using multivibrators oper
ingV madek to ,the> accompanying'drawing, which
ates very satisfactorily. At each stage, however,
shows by means ofthe usual diagrammatic'cir
it requires two tubes or the equivalent, and since
cuit the apparatus and circuits involved.
the rate of division is rather-low (rarelyexceed
Referring to the drawing, the completeequip
ing 5 or 6), a considerable number of stages is , 40
borhood of 90,000 cycles >per second) can be re
required.
For these reasons the cost of a stand
ard frequency> generator using multivibrators is
rather high.
A Mspecific object of the present invention,
therefore, isa frequency divider using single tube
oscillators instead of multivibrators. Another
object is a frequency divider having a larger
division at each stage than has'been considered
practicable in frequency dividers using multi
vibrators.
' vA well known single tube oscillator is the so
_called Hartley oscillator, employing a tuned plate
circuit and la grid circuit'- inductively coupled
thereto. The standard vHartley oscillator, how
'ment therein shown is a standard frequency lgen
erator which may be used, for example, to supply
alternating current for running a small motor at
constant speed. ` Theprincipal component parts
of the generator are a‘crystal oscillator, athree
stage frequency divider, and _a power amplifier.
The crystal oscillator and power amplifier arefof
known construction. The invention relatesV to
the combination of these elements with the fre
50 quency divider and more -in particular» to the
‘frequency divider per-se, as previously indicated.
The `frequency of the crystal oscillator is
rassumed to be 590,000 cycles per second,~as indi
cated in the drawing. The three yoscillators
ever,_ is entirely unsuited for use as a frequency 55 -which comprise the three-stage frequency divider
3
2,410,389
divide, respectively, by 10, 10 and 9, and oscil
late at frequencies of 9,000y 900 and 100 cycles per
second, respectively. This arrangement, giving
an output frequency of 100 cycles per second, is
the resistors 44 and 45 are preferably 50 M ohms
and 500 M ohms, respectively. There is a con
denser 46 (capacity .05 mf.) in the grid circuit,
shunted by the leak resistor 41 which preferably
satisfactory for the intended purpose, although
it will be understood that the invention is not
limited to the employment of any speciñc fre
quencies. By selecting a different oscillator fre
has a value of 100 M ohms.
cuit, being supplied with anode potential through
biasing resistor.
The power amplifier comprises the tubes I4
and I5, which may be of any suitable type, and
includes the output transformer 50. The con
quency, or by adjusting one or more of the oscil
ductors 5I and 52 constitute the output circuit,
lators at the frequency divider to divide differ 10 which may leadrto a small synchronous motor.
ently, or both, various other output frequencies
The ampliñer is of the push-pull type and the
may be obtained.
grids of the tubes are controlled from the third
Describing the equipment more in detail, the
oscillator stage of the frequency divider, as indi
reference character I0 indicates a suitable space
cated in the drawing. In this connection it will
discharge device, which may be a type 6J7 15 be noted that the oscillator transformer has a
pentode. This tube functions as a combined
third winding 43. Windings 42 and 43 together
oscillator and ampliûer tube. The control grid
have the same number of turns as winding 4I,
and the screen grid are coupled to the crystal,
whereby equal and opposite voltages to ground
as shown, by means of condensers. The screen
are available for application to the grids of tubes
grid functions as the plate or anode in this cir 20 I4 and I5. The resistor 55 is the usual grid
the resistor Il, which may have a value of 500
The apparatus having been described, the oper
M ohms. The control grid is connected to ground
ation of the complete standard frequency gen
through the resistor I9, which may have a value
erator will now be explained.
of one megohm. There is a reactance coil 20, 25 ' The operation of the crystal oscillator and am
value about 20 milli-henrys, which is connected
pliñer stage I0 is well known and need not be
in series with the crystal I6, and the oscillator is
described in detail. Suffice it to say that by
tuned to the exact frequency by means of the
the operation of the crystal oscillator section of
condenser I 8. The control and screen grids func
the tube I0 iluctuating currents having a fre
tion also in the amplifier. The suppressor grid 30 quency of 90,000 cycles per second are set up in
is connected to the cathode as shown, and the
the plate circuit of the amplifier section of the
plate is connected to the plus B lead through
tube, whereby fluctuating voltages of the same
the resistor 2l, which may have a value of 500
frequency are made available at the plate for
M ohms.
application over the control circuit to the grid
The first oscillator stage of the frequency di 35 of the tube II of the first oscillator stage of the
vider comprises a space discharge device I I, which
frequency divider. The crystal oscillator may be
may be a type 6F8 triode. Explaining the oscil
tuned to the exact frequency of 90,000 cycles per
lator circuits brieñy, the cathode is grounded,
second by means of the condenser I8.
and the plate is connected to the plus B lead
The first stage oscillator II of the frequency
through the resistor 25, the value of which may 40 divider has a frequency of 9,000 cycles per sec
be 50 M ohms. There is a tuned circuit com
ond and is driven or controlled at exactly that
prising the inductance 29 and the condenser 28
frequency by voltages transmitted from the plate
which is connected between the plate and ground
circuit of tube I0 by way of the condenser 22
by means of the condenser 21. This condenser
and resistor 23 to the grid of tube I I.
preferably has a value of .001 mf. and is shunted 45
The second stage oscillator I2 of the frequency
by the 100 M ohm resistor 26. The inductance
divider oscillates at a frequency of 900 cycles per
29 is one Winding of a transformer the other
second. It is controlled at exactly that frequency
Winding 30 of which is connected to the control
by voltages developed across the tuned circuit
grid of the tube through the l0 M ohm resistor
28-29 of the ñrst stage oscillator and trans
V24. The ratio of primary turns to secondary 50 mitted
to the grid of tube I 2 through the re
turns is preferably about 4 to 1, as indicated.
sistor 35.
In order to control the oscillator Il from the
The third stage oscillator I3 of the frequency
preceding stage the control grid of tube II is
divider oscillates at a frequency of I00 cycles per
coupled to the plate circuit of tube I0 by means
of - the resistor 23 and the condenser 22.
second and is controlled at that frequency by
The 55
voltages developed across the tuned circuit 36-32
resistor 23 preferably has a value of 150 M ohms,
while the capacity of the condenser 22 may be
of the second stage oscillator and transmitted
by way of resistor 45 and' grid condenser 46 to
100 mmf.
A
’
the grid of tube I3.
The second oscillator stage of the frequency
The push-pull ampliñer I 4--I 5 ampliñes the
divider comprises the space discharge device I2, 60 100 cycle output of ‘the third stage oscillator, said
which may also be a type 6F8 triode. This
output comprising equal and opposite voltages to
oscillator is similar to the first stage oscillator
ground which are developed in the winding 4I
except for diiferent values of some of the circuit
and windings 42 and 43 of the oscillator trans
elements. Thus the coupling condenser 3l pref
former. These voltages control the operation of
erably has a value of .01 mf. The ratio of turns 65 the amplifier in known manner, with the result
in transformer winding 32 to the turns in the
that alternating current having a frequency of
secondary winding 33 is 2 to 1. The resistors 34
100 cycles per second is transmitted over the out
and 35 preferably have values ofY 50 M ohms and
put circuit 5I-52.
one megohm, respectively.
The foregoing is a more or less general descrip
The third oscillator stage of the frequency di 70 tion of the operation. Attention will now be di
vider comprises the space discharge device I3,
rected more particularly to the features of the
which may be another type 6F8 triode. The
oscillators in the frequency divider hereinbefore
coupling condenser 40 preferably has a value of
mentioned and other features which are desir
.1 mf. The turn ratio between the transformer
able or essential to satisfactory performance.
windings 4I and 42 is 2 to 1, and the values of 75
The tuning of the oscillators may first be con
.25410;389
sidered. .Thezoscillator I2, for example,'oscillates
„undericontrol at a frequencyof 900`cycles per
second. It 'may `rbe- tuned to Vthat frequency, but
-is preferably'tuned- to a‘some'what -lower fre
quency. ».The tuning isaccomplished by selecting
a. condenser 36~-of~the proper capacity ,fand by
adding a small trimmer-condenseras indicated, if
required. f'I/'he frequency to which the oscillator
should be tuned for the best results is determined
by ascertaining‘the'upper and .lower limits of the
natural -or uncontrolled frequency which the os-4
The tuned circuits at theseveral :oscillators
shouldeach have va rather high inductance to ca
pacityv ratio, and for this purpose iron‘cores’are
used in the oscillator transformers.
The fact that the oscillator gridvoltage should
have a wave shape characterized‘bya low »arn
plitude flat-topped positive halfl wave has’ pre
viously beenv mentioned. At the oscillator I2 the
required wave shape is secured by means of the
high resistance 34 in the grid circuit. When the
grid- swings positive it starts to draw current, but
the resistance 34 is so high relative to the internal
resistance of the tube .(cathode to grid) that the
major part of the .total voltage in the-grid circuit
lected which is higher thantheA lower frequency
limit by approximately one-third- .of the total 15 is developed across vthe resistor'34 andthe .poten
tial of the grid» relative to the cathode is limited
range between the Aupper and .lower limits, and
to a low value. Similar resistors are used in the
`the oscillator-is then tuned> to this frequency.
grid circuits. ofthe .other oscillators> in the fre
To illustrate the foregoing, I have found- that
quency divider. .This is «an important -feature,
if other factors are properly .takencare of„.as ywill
be explained presently, the >oscillator ~ I2.may 20 since it is impossible to .properly control .the os
cillators at the desired- sub-multiple frequencies
have >a natural frequency ranging from the lower
unless the resistors ,are presentin the grid cir
limit of about 820vcyc1esper second to the .upper
cuits.
limit of about 915 cyclesper second and still :be
The ratio of .the control voltage to the oscil
vsusceptible to controla-t 900. cycles persecond
lator grid voltage is »also of paramount impor
from the preceding 9,000-cycle oscillator. This
tance. Considering the oscillator I2 again, .the
is a range of 95 cycles. One-third of 95._cycles is '
grid voltage is thevoltage generated in the sec
approximately 32 cycles, which when added to
ondary winding,33,due„to its coupling lwith the
820 cyclesgives 852 cycles per second as .the
primary winding 32. It is the coupling. between
proper frequency to which the oscillator should
30 these two windings, one in the‘plate circuit and
be tuned.
the other in thegrid circuit, that makes thetube
The'reason for tuning to .the lo'w side of the
oscillate. By the term “control voltage” I mean
range is two-fold. The operative natural fre
the voltage that is .transmitted from the preceding
quency range extends farther belowthe operating
stage and applied to the grid of tube I2 .to cause
frequency of 900 cycles per second than it does
above it, and the changes which may be expected I it to .oscillate .at exactly .the -desired frequency.
This voltage is transmitted. over a circuit to ground
to occur in time, such as changes in condenser
which includes the resistor35, the resistor34
capacity or variations in resistance of the re
and the winding 33, the latter .having such a 10W
sistors, tend to increase the natural frequency
resistance that it may be neglected. >The gridfof
of the oscillator.
The condenser 3! is the coupling condenser 4 U the tube I2 being connected to the junction of
resistors 35 .and 34, these resistors operate as a
through which power is delivered from the plate
voltagedivider or potentiometer and the ratio of
circuit of oscillator I2 to the tuned circuit corn
resistance 35 to resistance 313 determines what
pri‘sing condenser 36 and inductance 32. Where
proportion of the` total voltage available will .be
as a large condenser on the order of 2 mf. in ca
pacity is generally used at this point, I -Yhave 45 effective at the grid of the tube.
Now. I have found that for the best results the
found it desirable to use a condenser of much
control voltage ,should be approximately 15% of
lower capacity in order 'to' limit the amo-unt of
the grid voltage. The desired ratio is secured by
power transferred. ~Otherwise too high a voltage
a proper proportioning of the factors which affect
appears across the tuned circuit,.and> it is very
difiicult to properly proportion the `other circuit .50 it, but mainly by selecting a resistor 35 havingfthe
`proper resistance value.
elements. YIt will be' >noted‘that the'condensers
In stating that the best results are secured
such as' 3l have different capacity'values depend
when the control voltage is 15% of the grid
ing on the frequency of the oscillators to which
cillator may have and besusceptibleto controlat
900 cycles per-second. A frequency-.is then 'se
they belong. Condenser 3i has a-capacityof -.0l
voltage, I mean that with this ratio of control
mf., condenser 2'I has a capaci-tyof .G01-mf., while
voltage to grid Voltage the oscillator may _be
condenser 40 has‘a capacity Yof .l mf. ’These
-values are notl critical, but it is important to ruse
such values that the described limiting effect `is
tuned to any frequency within _a maximum fre
quency range and still be susceptible to control
at the desired frequencyof 900 cycles per second,
and that if the ratio is changed substantially >in
secured.
It has been found that -when 'the condenser-V3I , 60 either direction the frequency range is,correspondingly narrowed. This may be illustrated
for example, is made of low enoughv` capacity to
by the results of tests on. the 900-cyc1e.oscillator
substantially limit the,»power transferred to the
I2. It was previously -mentioned that. this oscil
associated tunedcircuitit hasta considerablezef
lator may have a natural .or ,uncontrolled fre
fect on the tuning of the tuned circuit, and any
quency ranging from 820 cycles per secondto 915
change-which might occur inthe capacity of ,the
cycles'per second,.but it will be understood. now
condenser would change. the oscillator frequency
that. it has this large frequency range only when
appreciably. It is desirable to eliminateas many
the control Voltage bears the, optimum relation
changeable factors as possible, and `accordingly
tothe .ì grid voltage. .I have found that ?if the
the condenser 3| is shunted by the high yresistance
resistor 3'I. When this shunt is used the ca 70 control voltageV is raised to 30% of „the grid
`voltage, the natural frequency range .within which
pacity of condenser 3| can change by as much
.the oscillator may be tuned becomes approxi
as 20% without causing failure of .the oscillator
.mately'825 cycles to 880 cycles, while if thecon.
to'divide properly. Asimilar shunt resistance 25
-trol >voltage.is. decreased .to v',7.1/¿% of the „grid
is connected around vthe conden'serîlatthe os
cillator I I.
'
'
voltagethe frequency rangebecomes approxi
2,410,389
7
mately 870 cycles to 920 cycles. kThese values
-show a considerable narrowing of the range and
indicate the importance of maintaining the ratio
of control voltage to grid voltage within fairly
close limits and as near to the best ratio as is
practicable.
The same ratio is used at all the
oscillators of the frequency divider.
Attention has already been directed to the fact
that a, condenser is used in the grid circuit at the
oscillator I3, which divides by 9.
8
said Iirst resistor, and means for transmitting
control voltages over said control circuit to con
trol said oscillator at a frequency which is a sub
multiple of the control voltage frequency, the
said resistors having values which are so related
to each other that the control voltage impressed
on said grid over said control circuit is not less
than 10% nor more than 30% of the voltage im
pressed on said grid by said grid circuit due to lts
I have dis 10 coupling with the tuned plate circuit.
covered that in the case of an oscillator which
divides by an odd number the insertion of a
condenser of the proper capacity in the grid
circuit approximately doubles the natural fre
4. In a frequency divider, a first oscillator, a
second oscillator, each oscillator comprising a
single space discharge device having cathode,
grid and plate elements, each oscillator also com
quency range within which the oscillator may be 15 prising a direct current plate circuit including a
tuned. In the case of an oscillator which divides
resistor, a tuned circuit which is connected to the
by an even number, however, the use of a grid
plate by means of a condenser, and a grid circuit
condenser is of no avail and actually decreases
conductive to direct current, which is inductively
the range. Accordingly, at any stage where odd
coupled to the tuned circuit, the tuned circuit of
division is required the grid condenser is used, 20 the second oscillator being so adjusted that the
b'ut is omitted at other stages.
second oscillator is adapted to oscillate at a fre
In the description certain types of tubes have
quency which is a sub-multiple of the frequency
been speciñed, and actual values have been given
of the íirst oscillator, and means for coupling the
for various parts such as condensers and re
second oscillator to the first oscillator comprising
sistors, but it will be understood that this has
a resistor connected from the junction of the
been done merely by way of example and to assist
condenser and tuned circuit at the first oscillator
in the understanding of a concrete embodiment
to the grid of the second oscillator.
of the invention and the principles which govern
its operation.
l
5. In a frequency divider, an oscillator com
The invention having been described, that 30 prising a space discharge device having cathode,
grid and plate elements, a ñrst plate circuit in
which is believed to be new and for which the
cluding a source of current, a second plate cir
protection of'Letters Patent is desired will be
cuit excluding said source and including tuning
pointed out in the appended claims.
I claim:
elements and a condenser, a grid circuit conduc
1. In a standard frequency generator, a crystal 35 tive to direct current which is inductively cou
pled to said second plate circuit, a second oscil
oscillator having a constant high frequency, a
lator comprising a similar space discharge de
frequency divider comprising a plurality of single
vice and having similar plate and grid circuits,
tube oscillators, each oscillator comprising a space
except that the second plate circuit is tuned to
discharge device having inductively coupled plate
and grid circuits, means for coupling said oscilla 40 a diiierent frequency, and means for coupling the
second oscillator to the iirst oscillator comprising
tors together in tandem relation, said means com
a connection which is conductive to direct current
prising a conductive connection from the plate
extending between the grid of the second oscil
of each oscillator except the last to the induc
lator and the first plate circuit of the first oscil
tively coupled grid of the next oscillator, tuning
means in said single tube oscillators whereby the 45 lator.
6. In a. frequency divider, a ñrst oscillator, a
same are caused to oscillate at progressively lower
second oscillator, each oscillator comprising a
frequencies which are sub-multiples of the fre
single space discharge device having cathode,
quency of said crystal oscillator, and means for
grid and plate elements, each said oscillator also
amplifying the output of the last oscillator.
2. In combination, an oscillator comprising a 50 comprising a plate circuit including a source of
direct current, a tuned plate circuit excluding
single space discharge device, a transformer hav
said current source, and a grid circuit inductively
ing three windings all connected in series, the
coupled to the tuned plate circuit, a condenser
number of turns in the first winding being equal
.connecting the tuned plate circuit of each oscil
to the number of turns in the second and third
windings, a tuned circuit including the ñrst wind 55 lator with the associated plate, a resistor connect
ing the tuned plate circuit of the iirst oscillator
ing -coupled to the plate of said device, a grid
vwith the grid circuit of the second oscillator, and
circuit for said device including the second wind
a resistor connected in shunt of said condenser
ing, a push-pull amplifier comprising two space
at the ñrst oscillator, whereby a positive bias is
discharge devices having their cathodes con
nected to the junction of the said ñrst and second 60 placed on the grid of the second oscillator.
7. In a frequency divider, an oscillator com
windings, and grid circuits for the space dis
prising a space discharge device, a tuned circuit
charge devices of said amplifier, one including
coupled to the plate of said device, a grid circuit
the said first winding and the other including
the second and third windingsM
for said device coupled to said tuned circuit,
3. In a frequency divider, an oscillator com 65 whereby current changes in said tuned circuit
produce grid voltages in said grid circuit, a high
prising a space discharge device having cathode,
resistance in said grid circuit, a control circuit
grid and plate elements, a tuned plate circuit
extending to the grid of said device, a high re
including an inductance and a condenser in
parallel therewith connected between said plate
sistance in said control circuit, said resistances
and cathode, a grid circuit including a resistor 70 being connected together at said grid and means
for transmitting control voltages over said con
connected directly to said grid and a second in_
trol circuit to control said oscillator at a fre
ductance connected to said cathode, said second
quency which is a sub-multiple of the frequency
inductance being inductively related to said i'irst
of said control voltages, the values of said re
inductance, a control circuit including a second
resistor connected> directly to said grid and to 75 sistances being so proportioned that the control
2,410,389
9
voltage impressed on said grid by said control
circuit is not more than 30% of the voltage irn
pressed on said grid by said grid circuit.
8. In a frequency divider, an oscillatoi` com
10
high resistance connected in shunt of said cou*
pling condenser to limit the effect which said
condenser has on the tuning of the tuned circuit.
9. A frequency divider as claimed in claim 4,
wherein the tuned circuit in each oscillator coni«
prising a space discharge device including cath
prises an inductance and a capacity connected in
ode, grid and plate, a, tuned circuit, a condenser
parallel, and each inductance has an iro-n core
coupling said tuned circuit to the plate of said
to give a relatively high ratio of inductance to
device, said condenser having a capacity so re
capacity.
lated to the resonance frequency of said tuned
10. A frequency divider as claimed in claim 4,
circuit that the power transferred to the tuned
wherein the condensers which connect the tuned
circuit is substantially limited, a circuit including
circuits in the ñrst and second oscillators to the
said cathode and grid inductively coupled to said
plates of such oscillators have capacities which
tuned circuit, means for transmitting control
are inversely proportionate to the frequencies of
voltages to the said grid to control said oscillator
at a frequency which is determined by said tuned 15 such oscillators, and the capacity o-f each con
denser is 10W enough to substantially limit the
circuit, said frequency being a subqnultiple of
power transferred through it to the associated
the frequency of said control voltages, a control
tuned circuit.
circuit over which said control voltages are trans
ERNST NORRMAN.
mitted terminating directly at said grid, and a
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