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Патент USA US2411166

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Nov. 19, 1946.
Rl H_ QLSON
2,411,166
FREQUENCY MULTIPLIER
Filed Oct. 2, 1942
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Nov. 19, 1946.
R, |-|_ CLSON
2,411,166
FREQUENCY MULTIPLIE'R
Filed Oct. 2(1942
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Patented Nov. 19, 1946
Lilhltt
UNETED STATES PATENT OFPEQE
2,411,166
FREQUENCY MULTIPLIER
Roy H. Olson, Marion, Iowa, assignor to Collins
Radio Company, a corporation of Iowa
Application October 2, 1942, Serial No. 460,560
10 Claims.
(01. 250-36)
1
2
This invention relates to a frequency mu1ti~
plier, and more particularly to means for mini~
phase to the undesired variations in the harmonic
mizing undesired voltage variations at funda~
mental frequency.
put circuit as viewed from the tube to present
considerable capacitative reactance at the funda
One feature of this invention is that it provides
output. This is accomplished by causing the out
mental frequency.
an improved output for driving a class C ampli?er
In the particular embodiment of my invention
from a frequency multiplier, particularly where
illustrated in Figure 1, a tube lEl andxits asso
the frequency multiplier is operated at a higher
ciated circuits provide oscillations at a desired
order of multiplication as, for example, quad
fundamental frequency. The tube ii and its
rupling; another feature of this invention is that 10 associated circuits comprise the multiplier stage.
it minimizes or eliminates undesired frequency
The oscillator output is coupled to the grid circuit
components or variations in the desired multiple
of the multiplier stage and causes periodic pulses
frequency component in the output of the class C
of plate current in the multiplier stage,
being
ampli?er operating from a frequency multiplier
under conditions where such variations are trans
ferred by the circuit tuned at multiple frequency;
sufficiently biased to work as a class B or class C
15 ampli?er, in accordance with conventional multi~
plier practice. The output circuit of the tube E 1,
still another feature of this invention is that it
includes a tank circuit comprising the induc
enables the use of the same variable inductance
tance I2 and the condenser i3 in parallel, this
with different ?xed condensers for different orders
being tuned to any desired harmonic, as the
of multiplication from an oscillator of limited 20 fourth. This circuit, then, presents inductive re
frequency range without the output of a class C
actance to a lower frequency, as the fundamental,
ampli?er driven from the frequency multiplier
and to overcome this and cause the output circuit
containing undesired frequency components nor~
to present capacitative reactance at the funda
mally present due to the lower Q values in the
metal frequency, a, condenser M is connected in
frequency multiplier tank circuit at the higher 25 series with ‘the tank circuit. This condenser
multiplications such as quadrupling; and other
should have a capacity somewhat less than that‘
features and advantages will be apparent from
which would be required for series resonance at
the following speci?cation and the drawings, in
the fundamental frequency, preferably having a
which:
capacity such that its reactance exceeds that
Figure l is a circuit diagram of one embodiment 30 of the tank circuit at fundamental frequency by
a fraction of one over the order of multiplication,
of my invention; Figure 2 is a schematic repre
but is less than the order of multiplication at
sentation of decaying voltage oscillations; Fig
which the stage is operating times such tank
ure 3 is a schematic representation of plate cur
circuit reactance, less than four times in the
rent pulses in a multiplier stage; Figure 4 is a
schematic representation of the fourth harmonic
output of a multiplier stage with the peak Values
Varying periodically at fundamental frequency;
quadrupler here being described. I have found
in a particular case that best’ results are secured,
in a quadrupler, with a condenser having a ca
pacity of approximately one-third of that which
Figure 5 is a schematic representation of plate
would be required for series resonance with the
current variations at fundamental frequency, and
of voltage variations in the output circuit nor 40 tank circuit at fundamental frequency.
mally associated therewith; Figure 6 is a sche
Where it is desired to tune the tank circuit
matic representation of the undesired accentua
of the multiplier stage, as is usually the case,
tion of the variations of the positive peaks; and
best results are secured by tuning by inductance
Figure 7 is a schematic representation of the
variation where the condenser M is a fixed con»
output from a quadrupling stage embodying my 45 denser, as this tends to best keep the proper ratio
invention, showing elimination of variation in
of values between the circuit elements over a
the crest values of the positive peaks.
reasonable band of frequencies. The output of
The output of higher order multiplication
stages, particularly quadrupling stages where
the multiplier stage is coupled to the input cir
cuit of a succeeding tube 15, and since it is the
higher values of effective reactance to resistance 50 crest values of the positive peaks of the harmonic
ratio is used in the tank circuit or ‘Where the
oscillations which are leveled 01f, this succeed
decay of the circuit is high, has heretofore con~
ing tube must be sufficiently biased so that its
tained periodic variations‘ at fundamental fre
operation is not affected by the negative harmonic
quency which could not be minimized or elimi
peaks. That is, there is still variation in the
nated. I have found that these periodic unde-‘ 55 negative peaks of the harmonic output, as will
sired variations can be completely eliminated or
be more fully described later, but operating the
minimized to a negligible value by combining
succeeding stage with the proper cutoff value
with the harmonic output another voltage vary
eliminates any difficulty with these variations.
ing at fundamental frequency and being sub
In the particular circuit shown, the induct
stantially equal in amplitude and opposite in 60 ance l6 could have a value variable between
2411,166
4
3
oscillator arrangement employed, or the oscil- .
about 40 and 60 microhenries, and condensers I‘!
and I3 values of about 800 mmf., providing for
some variation of the oscillator frequency in the
neighborhood of one megacycle. Conventional
values would be used for the coupling condensers
I9 and 20, the grid leak 2|, and the radio fre
quency choke 22 connected'to the plate voltage
this specification and the accompanying claims,
supply.
the theory of operation of the present invention,
lator and multiplier stage combined in a single
tube. Moreover, as the word “plate” is used in
it is intended in a broad sense covering any anode
element as a screen grid operating as an anode.
Figures 2 to 7 are intended as illustrative of
The tube It is illustrated as a triode,
and this will be described in connection with a
as type 801 having cathode, grid and plate ele~
10 quadrupler.‘ When the periodic energy pulses at
ments Illa, lilb and I00.
oscillator fundamental frequency energize the
The output of the oscillator is ‘coupled through
tank circuit in the multiplier output, fourth har
a condenser 23, which may have a value of 500
monic oscillations are induced, and the peak val
mmf., to the input circuit of the tube II, here
ues ‘of these oscillations decrease, as is illustrated
in Figure 2. This ?gure is not intended as an
illustrated as a type 802 pentode having an in
directly heated cathode element I Ia, control, .
screen, and suppressor grid elements Ilb, H0,
and Ild, and a plate element He. The grid leak
24 should have a value considerably higher than
that usually associated with such a tube, prefer
accurate representation, since the peak variations
follow an exponential decay curve; but it does
illustrate what happens when a very brief energy
pulse is admitted periodically to a tank circuit
ably between 50,000 and 200,000 ohms. The by 20 of reasonably good Q tuned to four times the
energy frequency. The decay per oscillation is
given by the formula
have conventional values, as .002 mi. and 20,000
ohms.
Where the multiplier stage is to operate as a
quadrupler, the inductance I2 may have a value
variable between about 9 and 14 microhenries, 25 where R'is the resistance and L the inductance
of the circuit. Since t=1/F, and since
and the condenser I3 a value of about 110 mmf.
for this inductance. These values may, of course,
be varied with relation to each other; but the
tank circuit must be tuneable through a band of 30 substituting gives
frequencies four times that of the oscillator, the
pass condenser 25 and screen grid resistor 26 may
D=e_2_Lt
band having a corresponding range.
It will be
D=e
understood that, in accordance with conventional
Q
practice where the transmitter is intended to op
Using this formula, the decay for a given num
erate in a number of different hands, a plurality 35 ber of cycles would be K times the power in this
of condensers I3 of different values may be pro
formula, so that where the circuit is tuned to
vided and selectively connected into this circuit.
the fourth harmonic, the amount of decay in the
These may provide different multiples of the same
‘crest values of the positive peaks, before another
frequency, or the same multiple of widely dif
energy pulse is received, is given by the formula
ferent fundamental frequencies. Condenser M, 40
t 41
‘in. connection with a tank circuit having a Q of
about 50 and the values stated, would have a
D=e Q
In a quadrupler where the tank circuit has a
Q of 50 at the harmonic frequency, it will be
" seen that the decay for four cycles, in accordance
with the above formula, is from whatever the ini
tial crest value was to .777 of such value. This
ate value may be used to connect the plate to a
is a substantial change, amounting to about 20%
plate voltage source 28.
modulation of the harmonic oscillations at fun
The output of the multiplier tube i I is con 50 damental frequency; and this modulation is an
neoted through a coupling condenser 29 to the
undesired-variation which goes through with the
capacity of about 830 mmf. This condenser value
is not sharply critical, although the closer it is
held to the calculated value, the more complete
ly undesired positive peak variations are elimi
nated. A radio frequency choke 27 of appropri~
grid circuit of the tube I5, here schematically
harmonic oscillations and is produced rather
than eliminated by the tuned tank circuit.
illustrated as a triode, although in commercial
practice this would normally be a multi-element
Where the multiplier stage is being operated
tube, the present representation being intended 55 with an angle of ?ow of about 180 degrees, the
as a generic one.
This tube 15 might comprise
plate current pulses are as illustrated in Figure 3.
If a situation is conceived where these plate cur
part of another multiplying stage, again multi
plying the output of the tube I I ; or it might com,
rent pulses delivered energy to the tank circuit
prise an intermediate stage between the multi
without any variation in the plate voltage at fun
plier and the power ampli?er of a transmitter. 60 damental frequency, that is, where the tank cir
If operating as another multiplier stage, another
cuit presents zero impedance at fundamental fre
type 802 might be employed with circuit con~
quency, there would be a situation like that illus
nections similar to those of the tube I I; and if as
trated in Figure 4, with the harmonic oscillations
an intermediate ampli?er, a beam power tube
30 swinging about a ?xed voltage base line here
such as a type 813 tube might be used. In either 65 indicated as 3|, with upper and lower envelope
case, it is essential that this stage be operated
curves 32 and 33 resulting from the decay modu
as a class C ampli?er, that is, that the control
lation effect. Because of the decay action, the
grid be provided with su?icient negative bias that
bottom or minimum point of the modulation
the negative grid voltage peaks are all below the
curve 32 occurs approximately at the point of
cutoff level.
70 zero plate current flow, and the positive peak of
It will be understood that the preceding detailed
this modulation envelope occurs approximately
description of the circuit of Figure 1 is intended
at the point of zero plate current flow 90 degrees
as illustrative only, since this invention may be
in phase after maximum current, Figures 3 and 4
showing the relationships in this regard over two
embodied in any number of different circuits.
Different type tubes might be used, a different
75
cycles.
>
'
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,
‘
5
2,411,166
The plate voltage, however, does vary at the
fundamental frequency, this being illustrated in
current is substantially independent of plate
voltage, and the control grid current is negligible,
the plate current is- given by the formula
Figure 5 where the line 34 indicates current flow
in the output circuit at fundamental frequency,
the amplitude shown in Figure 5 being approxi
where Eg is the control grid voltage, Esg the
mately in correct relationship to the harmonic
screen grid voltage, [.Lsg the voltage ampli?cation
oscillations 36 shown in Figure 4. Under output
circuit conditions heretofore employed, the out
factor of the screen grid, k the tube constant,
and a, a constant between 1 and 2 and normally
put circuit presents inductive reactance to the
about 1. An explanation of the theory behind
fundamental frequency, and therefore plate volt
this formula, and of‘ the relationship between
age variations, indicated by the line 35, are ap
current harmonics at various frequencies, is
proximately 90 degrees ahead of plate current
contained in an article by Terman and Ferns in
flow. It should be noted that, even though a by
pass condenser has heretofore been frequently
the March, 1934, Proceedings of the Institute of
used in the output of a multiplier stage, this con 15 Radio Engineers, volume 22, No. 3, and will not be
gone into here.
denser has always had such a large capacity (in
Where the voltage applied to the grid of the
order to provide low impedance to ground) that
tube consists of ‘a ?xed negative bias Ec- and an
the reactance of the output circuit has always
alternating potential of crest amplitude Es and
been inductive, even when such a condenser was
employed.
angular velocity w, as is the case in a frequency
The result of combining the crest voltage varia
multiplier stage actuated by an oscillator, this
formula becomes
tions illustrated in Figure 4 with the plate volt
age variations at fundamental frequencies has
always heretofore resulted in accentuating the
By Fourier analysis, the components of the
positive peak variations of the harmonic oscilla 25
plate current at various frequencies can be de
tions, as illustrated in Figure 6, giving an unde
termined for various angles of current ?ow.
sirable amount of fundamental frequency in the
Where a. is 1 and the angle of ?ow is about 180
output of the stage. By making the total re
degrees, the ratio of the fundamental crest value
actance of the tuned output circuit capacitative,
however, the phase of the voltage variation 35 30 to that of the fourth harmonic will be found to
be about 12.5. Whether this ratio is derived
at fundamental frequency is shifted approxi
theoretically by this formula, or by direct meas
mately 180 degrees, so that it is out of Phase
urement and analysis of the plate current, this
rather than in phase with the crest or positive
relationship and the circuit Q can be used, in
peak value variations of the harmonic oscilla
connection with the particular decay being en
tions 30. This tends to reduce rather than to in
countered, to provide a formula for the amount
crease such undesired positive peak variations
of capacitative reactance necessary.
The
caused by the decay modulation effect, and if
voltage developed at a given harmonic K is, of
the amplitude of the voltage variation 35 is prop
course, a function of the current flow at that
erly adjusted and the phase relation is exactly
correct, variation in the’ positive peaks will be 40 harmonic times the impedance of the tuned cir
completely eliminated and the positive crest '
cuit at that harmohic, so that
values of the harmonic oscillations 30 will all be
equal, as shown in Figure 7. In practice, the
phase relations will not be exactly correct, since
the crest value of the envelope 32 and 33 will
not necessarily occur 90 degrees out of phase
with the crest value of the plate current pulse
where Q is the reactance-resistance ratio of the
tank circuit at the harmonic frequency, and XL
is the reactance of the inductance at the funda
mental frequency.
The voltage at the fundamental frequency is
also equal to the current times the impedance,
practice, however, and positive peak variations ‘of 50 and is given by the formula
the harmonic oscillations reduced to a negligible
EFT-I
amount. It will be noted that there is consid
erable variation in the negative peaks of the har
where X0 is the reactance of the condenser [4.
monic oscillations illustrated in Figure 7, but
Since
the peak value of the variation of this
these are completely wiped out by biasing the 55
fundamental voltage above and below its center
grid of the succeeding tube to such a point that
line should be equal to one-half the total decay
the cutoff level is above all of these negative
of
the harmonic oscillation peaks,
peaks, as for example, on line 36 in Figure '7.
The amplitude of the voltage variations at fun
34.
The theoretically perfect result illustrated
in Figure '7 can be very closely approached in
IG-FXC)
damental frequency (illustrated as 35) can be 60
adjusted to equal the positive peak voltage varia
tions of the harmonic oscillations by varying the
Equating the two functions which are equal to
value of the condenser l4, and thus the amount
Er, with a negative sign before one to indicate
of capacitative reactance, since the voltage devel
proper phase relation, solving for Xe, we have
oped in the output circuit is a function of the 65
current and the reactance through which it flows.
l—~e Q 1K
K2
While I have determined that the capacity of
the condenser should preferably be such as will
provide a reactance somewhat greater but less
X““[(—2‘—)TKQ+T€2Ti]XL
If Q is taken as 50, a value which may be
than the multiplication factor times the induc 70 normal in practice, andthe angle of ?ow is 180
degrees, so that the ratio of Ix to I is as 1 is to 12,
tive reactance of the tank circuit at fundamental
frequency, therequired capacitative reactance in
any given case can be mathematically deter
and where K is 4 (quadrupling), the portion of
the equation in the large parenthesis will be seen
mined.
to work out to a fraction over 3.
4
This is con
In a pentode vacuum tube, when the plate 75 ?rmed by the experimental determination that
2,41 1,166
the capacity of the condenser It should be sub
stantially less than that which would provide
series resonance at the fundamental frequency,
.preferably such that the capacitative reactance
provided by the condenser l 4 is about three times
and X1. is the reactance of the tank circuit induc
tance at said fundamental frequency.
5. Apparatus of the character claimed in claim
1, including means for varying the period of said
pulses, and wherein said tank circuit includes a
variable inductance.
6. The method of minimizing undesired periodic
variations, at fundamental frequency, in the posi
tive voltage peaks of the harmonic output of a
the inductive reactance of the tank circuit at
the fundamental frequency.
It is believed that the foregoing is a correct
explanation of the theory and a correct mathe
matical determination of the Various factors con 10 frequency multiplier, comprising combining
therewith an alternating voltage of said funda
sidered. Whatever the theory and mathematics
mental frequency substantially equal in amplitude
may be, however, there is no question that un
but opposite in phase to said periodic variations.
desired variations, at fundamental frequency, in
7. The method of minimizing undesired periodic
the positive peaks of the harmonic oscillations
are minimized to the point of substantial 15 variations, at fundamental frequency, in the posi
tive voltage peaks of the harmonic output of a
elimination by the use of a condenser in series
frequency multiplier, comprising combining
with the tank circuit and with a capacity low
therewith an alternating voltage of said funda
enough to provide a reactance substantially ex
mental frequency substantially equal in amplitude
ceeding that of the tank circuit at the funda
but opposite in phase to said periodic variations,
mental frequency.
,
and eliminating the negative peaks of the com‘
While I have shown and described certain
bined voltages.
embodiments of my invention, it, is to be under
8. The method of minimizing undesired periodic stood that it is capable of many modi?cations.
variations, at fundamental frequency, in the
Changes, therefore, in the construction and ar
rangement may be made without departing from 25 positive voltage peaks of the harmonic output
of a frequency multiplier, comprising using the
the spirit and scope of the invention as disclosed
current at said fundamental frequency to create
in the appended claims.
an alternating voltage substantially equal in am
I claim:
plitude but opposite in phase to said periodic
1. A frequency multiplier of the character de
variations, combining said alternating voltage
scribed, including: a tube having at least cathode,
with the harmonic voltage, and eliminating the
grid, and plate elements; means for causing
negative peaks of the combined voltages.
periodic pulses of plate current at a certain fre
quency; and an output circuit connected to said
plate, said circuit including a tank circuit tuned
9. A frequency multiplier of the character de
scribed, including: a tube having at least cathode,
to a multiple of said frequency and a condenser 35 grid, and plate elements; means for causing
in series with said tank circuit, said condenser
having a capacity such that its reactance at said
frequency is at least one divided by said multiple
periodic pulses of plate current at a certain fre
quency; an output circuit connected to said plate,
said circuit including a tank circuit tuned to a
multiple of said frequency and a condenser in
greater, but less than said multiple times, that
which would provide series resonance with the 40 series with said tank circuit, said condenser have
ing a capacity such that its reactance at said fre
tank circuit at saidfrequency.
quency is greater than that which would be re
2. A frequency multiplier of the character de
quired to provide series resonance at said fre
scribed, including: a tube having at least cathode,
quency; a second tube having at least cathode,
grid, and plate elements; means for causing
periodic pulses of plate current at a certain fre 45 grid and plate elements; a grid circuit for said
second tube coupled to said output circuit; and
quency; and an output circuit connected to said
means providing a negative bias on the grid of
plate, said circuit including a tank circuit tuned
the second tube such that the negative peaks of
to four times said frequency and a condenser in
the grid voltage variations’ are all below cut-oif
series with said tank circuit, said condenser hav
~
ing a capacity such that its reactance at said fre 50 level.
10. A frequency multiplier of the character de
quency is substantially three times that which
scribed, including: a tube having at least cathode,
would provide series resonance with the tank cir
grid, and plate elements; means for causing
cuit at said frequency.
periodic pulses of plate current at a certain fre
3. Apparatus of the character claimed in claim
1, further including: a second tube having at 55 quency; and an output circuit connected to said
plate, said circuit including a tank circuit tuned
,least cathode, grid, and plate elements; a grid
to a multiple of said frequency and a condenser
‘circuit for said second tube coupled to said output
in series with said tank circuit, said condenser
circuit; and means providing a negative bias on
having a capacity such that its reactance Xe at
the grid of the second tube such that the negative
peaks of the grid voltage variations are all below 60 said frequency is substantially equal to that deter
cut-off level.
4. Apparatus of the character claimed in claim
2, wherein said condenser has a capacity such
that its reactance Xe at said frequency is sub
stantially equal to that determined by the formula 65
mined by the formula
’
where K is said multiple, Q is the ‘reactance
resistance ratio of the tank circuit at the multiple
frequency, Ik divided by I is the ratio of the crest
values of the multiple and fundamental fre
where Q is the reactance-resistance ratio of the 70 quency current components, and X1. is the reac
tank circuit at the multiple frequency, I4 divided
tance of the tank circuit inductance at said
fundamental frequency.
by I is the ratio of the crest values of the multiple
and fundamental frequency current components,
ROY H. OLSON.
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