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Патент USA US2154484

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April 18,
Filed March 17, 1937
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Patented Apr. 18, 1939
David Arthur Bell, Great Baddow, Chelmsford,
England, assignor to Radio Corporation of
America, a corporation of Delaware
Application ‘March 17, 1937, Serial No. 131,325
In Great Britain April 29, 1936
- 2 Claims.
This invention relates to electrical frequency
dividing circuit arrangements and has for its
object to provide improved circuit arrangements
capable of producing from a given input fre
quency a divided output frequency.
According to this invention an electrical fre
quency dividing circuit arrangement comprises
two electron discharge devices, means for ap
plying an input frequency to be divided in par
allel to the input electrodes of said devices, a
circuit resonant to the required divided output
frequency included between the output electrodes
of said devices, cross coupling means being con
nected between the output electrodes of each de
vice and the input electrode of the other, but
said cross coupling being insufficient to cause
self-oscillation, and means for taking the di
vided frequency from the circuit included be
tween the output electrodes, the operating po
20 tentials applied to the electrodes of said devices
being such that current ?ows through each de-,
vice only once during each complete period of
the divided output frequency, there being no out
put in the absence of any input.
The invention is illustrated in and further ex
plained in connection with the accompanying
drawing in which Figure 1 shows, by way of ex
ample, one embodiment and Figs. 2 to 6 inclusive
are explanatory graphical ?gures.
Referring to Fig. 1 the arrangement therein
shown comprises two valves, shown as triodes I,
I 2, which have their cathodes 3, 4, connected to
gether and to the negative terminal of a source
22 of anode potential. Each of the two triodes
35 has its grid 5 or 6 connected through resistances
‘I or 8 to a common input coupling circuit shown
as a resistance-capacity coupling circuit 9, I0,
though any other form of input coupling arrange
ment, such as a transformer, could be employed.
40 The input wave whose frequency is to be divided
is applied at the terminals II, the common grid
‘ circuit being completed to the negative terminal
of the source 22 through a bias source I2 of such
magnitude that in the absence of incoming al
45 ternating voltage at terminals II the anode cur
rents of the valves are nearly zero. The triode
anodes I3 and I4 are cross-connected to the grids
6, 5, as shown, through condensers I5, I6 which
are sufficiently small to ensure that the system
50 will not oscillate of its own accord. The two an
odes I3, I4, are connected to opposite ends of a
parallel tuned circuit I'I, I8, which is tuned to
the desired sub-multiple (say one half) of the
input frequency applied at I I, the center point
55 I9 of the tuned circuit I'I, I8, ,being connected
(Cl. 250-36)
to the positive'terminal of the source 22 which
is shunted by a suitable condenser 20. Output
at the desired divided frequency (in the example
above mentioned, one half that applied at termi
nals II) is taken off from the ends of the circuit
I1, I8 to terminals 2|.
Consider an arrangement as shown in Fig. 1,
and ‘wherein the circuit I'I, I8, is tuned to one
half the input frequency applied at II. Then the
voltages applied to the two grids 5 and 6 will be 10
as represented graphically in conventional man
ner in Figs. 2 and 3 respectively. From these ?g
ures it will be seen that in such a case the ap
plied voltage is comprised of two components,
one a component 7‘ of the input frequency at ter 15
minals II,’ and the other a component 172 of
one-half this frequency. Since the valves have
their input circuits fed in parallel from the ter
minals II, the component I will be the same in
both cases but, since the valves are cross-con
nected to opposite ends of the circuit I'l, I8
(which is fed in opposition by the valves), the
components f/2 for the two valves will be in
phase opposition. Since the valves are so biased
that in the absence of input alternating voltage 25
at terminals I I, the anode currents are nearly
zero, anode current will ?ow in any valve only
at times when, as a result of input voltage at ter
minals II, the algebraic sum of the two com
ponent voltages on its grid is positive, the anode
current in any valve being zero when the net
voltage on its grid is negative. Fig. 4 shows in
conventional manner the anode current curve
which will result from the grid voltage compo
nents represented in Fig. 2, and Fig. 5 shows the 35
anode current curve corresponding to Fig. 3.
Since the outputs from the two valves are fed
in phase opposition to the tuned circuit I‘I, I8,
the effective current to the said circuit will be
as represented in conventional manner in Fig. 6, 40
This is obviously a distorted wave of frequency
f/2, and by virtue of the well known selective
properties of a tuned circuit, the voltage de
veloped across the tuned circuit Il, I8 will be
considerably nearer the sinusoidal wave form
than the current fed to it. It will have been
noted that in Figs. 2 and 3 the components f/2
are shown as, sinusoidal, and in view of the
action (just mentioned) of the tuned circuit I1,
I8, this assumption is true to a reasonable de
gree of approximation; small distortions in the
wave form applied to the grids 5, 6, are not of
seriousimportance. The circuit will operate to
give an approximately sinusoidal output of fre
quency .f/ 2 when fed with a frequency f, and al 55
though the wave form of the input voltage wave
at terminals II will have some effect on the dis
vices in parallel, a circuit resonant to a desired
sub-multiple of the frequency of said source, said
tortion of the output Wave form at terminals 2|,
circuit being interposed between the output elec
any reasonable input wave form of frequency i
will result in an output of frequency f/ 2.
trodes of said discharge devices, cross-coupling
The factor of division in the above example is 2,
but the invention may be employed to obtain
division by any other even number, though as the
number becomes greater the output becomes less.
10 For division by the factor 2 the normal negative
bias applied to the valve grids 5 and 6 is, as
above stated, such as to reduce the normal anode
current to zero or thereabouts.
Where division
by a larger number is required the negative bias
15 should be so adjusted that the grids become posi
tive only once in each cycle of the divided fre
It will be seen that the output circuit is bal
anced with respect to the input circuit both as
20 regards coup-ling through the valves and coupling
through the anode-grid cross-coupling means in
cluding the condensers l5. Hence the interaction
between the input frequency and the divided out
put frequency circuits is reduced to a minimum.
In other words, the output contains a very slight
component of the input frequency, and, the im
pedance presented to the source of input fre
quency energy has a high value.
Although, regarded purely as a diagram, Fig. 1
30 resembles the well known “multi-vibrator” type
of circuit, the invention is obviously fundamen
tally and ‘inherently different from a multi
I claim:
1. A frequency divider comprising two electron
discharge devices, each having a cathode and
input and output electrodes and circuits connected
thereto, a source of alternating current input
energy coupled to the input circuits of said de
means between the output electrode of each de—
vice and the input electrode of the other, said
cross-coupling means having an impedance value
su?icient to prevent self-oscillation in said elec
tron discharge devices, a source of operating
potentials having a negative terminal connected
to the input electrodes, an intermediate tap con
nected to the cathodes, and a positive terminal
connected to the output electrodes of said devices,
said positive terminal connection including a cen
ter tap on said resonant circuit, and means for 15
maintaining the value of said source such that a
substantial current flow through each device is '
permitted only once during each complete period
of said sub-multiple frequency.
2. An electrical frequency dividing circuit com 20
prising a pair of thermionic valves, each having
a cathode, an anode and a control grid, cross
coupling condensers connected one between the
anode-of one valve and the control grid of the
other, and another between the anode of said 25
other valve and the control grid of said one valve,
said cross-coupling condensers being too small to
cause self-oscillation, a parallel tuned circuit con
nected at one end to the anode of one valve and
at the other to the anode of the other, means for
applying an input frequency to be divided in par
allel to the control grids of said valves, means for
applying anode potential to said valves through
a center point on said parallel tuned circuit, and
means for taking the required divided output fre
quency from across said tuned circuit, said tuned
circuit being resonant at said required divided
output frequency.
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