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Патент USA US3087130

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April 23, 1963
N. w. BELL
SIGNAL coNTRoLLEb oscILLA'roR
3,087,121
Filed June 29, 1961
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United States Patent Oliîce
3,Ü87,l2l
Patented Apr. 23, 1963
1
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$587,121
negative feedback around the variable frequency signal
source, the frequency of the signal generated thereby
SIGNAL CONTROLLED GSCELLATOR
Norton W. Bell, Monrovia, Calif., assigner to Consoli
dated Eiectrodynamics Corporation, Pasadena, Calif.,
a corporation of Catifornia
Filed .lune 29, 1961, Ser. No. IZÜÑSS
8 Claims. (CE. 331-11)
varies in a direct manner with changes in the magnitude
»of the control signal applied thereto.
Accordingly, the present invention provides apparatus
for developing an output signal the frequency of which
is variable over a frequency range extending from zero
frequency in direct proportion to the magnitude of the
control signal applied thereto.
This invention relates to apparatus for generating a
The above `as well as other features of the present in
signal of yariable frequency and, more particularly, to 10
vention may be more clearly understood by reference to
apparatus for generating an alternating current output
the drawing, the single FIGURE of which represents in
signal having a frequency which is directly proportional
block diagram form a preferred embodiment of the present
to the magnitude of a direct current input signal applied
invention.
thereto.
As represented in block diagram form, the present in
Apparatus for generating a signal having a frequency 15
vention includes apparatus for generating an output signal
which varies directl-y with the magnitude of -a control
having a frequency which is equal to a difference in fre
signal applied thereto have found many different uses in
quency between the signals generated Iby a variable fre
the field of electronics. One such use is in the area of
low level signal integration. Generally, signal integra
quency signal source represented as a voltage controlled
tor systems for integrating lo-w level signals employ a 20 oscillator 1l) and a íixed frequency signal source rep
resented by the oscillator 12. To produce the output sig
voltage controlled oscillator the output of which is
nal, the present invention as represented in the drawing
coupled to a frequency counter. In such systems, the sig
includes a modulator 14, which -may be of a balanced
nal to be integrated is -applied to the voltage controlled
-rnodulator type, producing a signal having frequency
oscillator. As the magnitude of a signal increases, the
frequency of the signal generated by the voltage con 25 components of the sum and difference between the fre
quencies of the signals -generated by the voltage con
trolled oscillator likewise increases. Since the counter
trolled oscillator 10 and the oscillator 12.
«totals the number of cycles of oscillation, this total is
proportional to the integral of the input signal at any
To develop the output signal having a frequency equal
to a difference between the signals generated by the volt
In general, in integrator systems of the type described 30 age controlled oscillator l() and the oscillator 12, the
present invention as represented in the drawing includes
above, to accurately integrate a signal, it is necessary
a low-pass filter 16.
that the frequency of the oscillator be proportional to
As described briefly above, the presen-t invention con
the magnitude of the signal being integrated. Thus, as
templates means for selectively contro-lling the frequency
vthe magnitude of the signal increases from zero to some
finite value and returns to Zero, the frequency of the signal 35 of the output signal by controlling the frequency of the
signal generated by the variable frequency signal source.
generated by the oscillator should increase from zero to
To accomplish this, the present invention includes means
a maximum frequency that is directly related to the maxi
time.
mum magnitude of the signal and then return to zero
for selectively controlling the magnitude of the voltage
frequency. Generally, lhowever,
signal applied to the input of the voltage controlled oscil
variable oscillators
which operate down to zero frequency are nonlinear and 40 lator 10 such that the frequency of the signal generated
have poor drift characteristics. Thus, when utilized they
are in in-tegrator systems such as that described above,
the count stored in the counter may not represent an ac
curate measure of the integral of the signal wave form.
In View of the above, the present invention provides
apparatus for generating a signal which is controllable
thereby is directly proportional to the magnitude of an
externally developed signal. To provide the desired con
trol, the present invention includes means for develop
ing a signal proportional to the frequency of the signal
generated by the oscillator 12 as well as a signal propor
over a frequency range extending from zero frequency
tional to the frequency of the signal generated by the
voltage controlled oscillator iti-these signals being con
and is directly proportional to the magnitude of the con
tinuously added at a summing network 18 with the exter
trol signal applied thereto.
nally developed signal.
in particular, to develop- a signal proportional to the
To accomplish this, the present invention in a basic 50
fixed frequency signal generated by the oscillator 12, the
form includes means for generating a variable frequency
present invention `includes a frequency discriminator rep
output signal having a frequnecy which is equal to a fre
resented at 20. The frequency discriminator 20 pro
quency difference between signals generated by a fixed
duces a -direct current voltage signal having a magni
frequency signal source -and a variable frequency signal
source. To selectively control the frequency of the out 55 tude which is directly proportional to the frequency of the
fixed frequency signal. As represented, the voltage signal
put signal such that it varies directly »with the magnitude
produced by the discriminator 20 is applied to an input
of the control signal, the present invention includes means
terminal 22 of the summing network 18.
for selectively controlling the frequency of the signal
To develop a signal proportional to the frequency of
generated by the variable frequency signal source. Briefly,
the frequency control means of the present invention in 60 the 4signal generated by the voltage controlled oscillator
iti, the present invention includes a frequency `discrimi
cludes means for adding the control signal with a negative
nator 24. In particular, the frequency discriminator Z4
feedback signal which is proportional to the frequency
acts as a negative feedback network between the output and
of the variable frequency signal and a direct current
input of the voltage controlled oscillator l0. The frequency
signal which is proportional to the fixed frequency signal.
ln particular, due to the negative feedback provided 65 discriminator 2.4 produces >a voltage signal which is pro
portional to the frequency of the signal generated by
by the present invention, when a control signal of zero
the voltage controlled oscillator 10 and, as represented,
magnitude is applied at the input of the variable fre
is of opposite polarity relative to the direct current volt
quency signal source, the frequency of the signal gen
age signal produced by lthe discriminator 20. As repre
erated by the variable frequency signal source is equal to
the lixed frequency generated by the fixed frequency sig 70 sented, the negative feedback voltage signal developed
by the discriminator 24 is applied to .an input terminal
nal source. This results in an output signal of zero fre
quency.
Further, since the present invention provides »
26 of the summing network 18.
Accordingly, a nega
3,087,121
3
4
tive feedback loop is produced which includes the volt
age controlled oscillator lil, the discriminator 24, and a
direct current amplifier represented at 28. Due to this
negative feedback loop, the voltage appearing at the
input terminal 26 of the summing network 1S tends to be
equal to the sum of the voltage signals developed at the
by said variable frequency signal source; a fixed fre
quency signal source for generating a signal having a
fixed frequency; means including a frequency discrimi
nator -coupled between said fixed frequency signal source
.and the input of said variable frequency signal source for
ldeveloping a direct current signal having Va magnitude
input ~terminals 22 and 30.
which is proportional to the fixed frequency signal, said
Thus, a nearly zero voltage
signal is normally developed at an output terminal 32 of
direct current signal being of opposite polarity to said
the summing network 18.
In view of this, when no input signal is applied at
input terminal 30, the voltage developed by the frequency
discriminator 24 tends to equal that developed by the
frequency discriminator 20. When the frequency dis
negative feedback signal; means for adding said direct cur
rent signal and said negative feedba-ck signal at the input
of said variable frequency signal source such that said
variable frequency sourcel in the absence of an externally
developed input signal to its. input is caused to generate
a signal having a frequencyr substantially equal to the
ponents, the frequency of the signal generated by the volt 15 fixed frequency signal; means coupled to said fixed fre
age controlled oscillator 10 hence tends to equal the fre
quency signal source and said variable frequency signal
quency -of the signal generated by the oscillator 12. When
source for producing `an output signal having a frequency
this occurs, the frequency of the output signal passed by
substantially equal to a -diderence between .the fixed. fre
the low-pass filter 16 is equal to zero frequency.
quency and the frequency of the signal generated by said
Further, when the loop gain of the negative feedback 20 variable frequency signal source; and means forA apply
loop is high, the drift or change in the output frequency
ing an externally developed direct current input signal
of the voltage controlled oscillator 16 with no change in
to the input of said variable frequency source to selec
input depends wholly upon the- drift of the direct current
tively vary the frequency of said output signal.
amplifier 28 and the discriminators 20 and 24. Since
2. Apparatus for generating an output signal having a
criminators> are of the same type and include similar com
the discriminators 20 Iand 24 are of the same type and of 25 frequency which is directly proportional to the magni
similar components, their drifts, which are due to changes
tude of an externally developed input signal -applied
in temperature, cancel. Thus, since the drift for direct
thereto comprising: a controllable frequency signal source
current amplifiers may be made quite small, the. overall
for generating a signal .at its> output which has a fre
ydrift of the system as described may be negligible. Also,
quency substantially proportional to vthe magnitude of a
due to the negative feedback loop, neither of the oscil 30 control signal applied `at its input; means for producing
lators 10 or 12 need be stable since any change in the
said control signal including >means coupled to the output
yfrequency of the signal generated by the oscillators 10' and
of said controllable signal .source for developing a nega
12 is -compensated for by the negative feedback loop.
tive feedback signal having a magnitude .which is pro
Further, the voltage controlled oscillator 10 need not
portional to the frequency of the signal generated by said
vbe linear since non-linearities are reduced by the negative 35 controllable signal source, a fixed frequency signal source,
feedback.
means for producing a voltage signal proportional to the
In operation, due to the negative feedback signal pro
frequency of the signal generated by said fixed' frequency
vided by the discriminator 24, when an input signal is
source, and combining means coupled to the input of said
applied to the input terminal 30, the frequency of the
signal generated by `the voltage controlled oscillator is
rapidly increased thereby resulting in an increase in the
voltage developed by the discriminator 24, which in turn
balances the increase in voltage appearing at the sum
ming network 18. Accordingly, the voltage appearing
40
controllable signal source for continuously adding the
externally developed input signal with the voltage signal
and the negative feedback signal to produce said control
signal; and means responsive to the signal generated by
said fixed frequency source and the signal generated by
said controllable signal source for producing the output
at the output terminal 32 of the summing network 18 is 45 signal having ‘a frequency equal to a difference between
again reduced to Zero magnitude. However, due to the
increase in the frequency of the signal generated by
the voltage controlled oscillator 10, the output signal now
the fixed frequency and the frequency of the signal gcn
erated by said controllable signal source.
3. Apparatus for ygenerating an alternating current out
put signal having a frequency directly proportional to
f2, thi-s frequency being directly proportional to the mag 50 the magnitude of an externally >developed input signal
nitude of the signal applied at the input terminal 30.
applied thereto comprising: a voltage controlledv oscilla
Accordingly, when the present invention is utilized in
tor for generating a signal at its output which has -a fre
the low level signal integrator system as briefly described
quency proportional to the magnitude of voltage signal
above, an increase in the voltage applied at the input
applied at its input; means coupled between the output
terminal 30 is reflected directly as an increase from zero 55 and input of said voltage controlled oscillator for de
frequency inthe output signal developed by the present
veloping a negative feedback voltage at the input of said
invention. As represented, the output signal m-ay, in that
voltage controlled oscillator, the magnitude of said nega
embodiment, be applied to a frequency counter 34 which
tive feedback voltage being proportional to the >frequency
accurately counts the number of oscillations of the sig
of the signal generated ‘by said voltage controlled oscil
nal generated »by the present invention to store a count 60 lator; a Ifixed 4frequency oscillator for generating'a signal
which is an accurate measure of the integral of the wave
having a fixed frequency; means coupled between said
>form of the signal applied at the input terminal 30.
fixed frequency oscillator and theinput of said voltage
What is claimed is:
controlled oscillator for developing a voltage signal hav
1. Apparatus for generating »an alternating current
ing a magnitude which is proportional to the fixed fre
output signal having a frequency which is directly pro 65 quency, said voltage signal being of opposite polarity to
portional to the magnitude of an externally developed
said negative feedback signal; means coupled -to the in
input signal applied thereto comprising: a variable fre
put of said voltage controlled oscillator for adding the
has a frequency equal to -the difference between f1 and
quency signal source for generating an alternating cur
voltage signal, the negative feedback signal, and an ex
-rent signal at its output having a frequency which varies
ternally developed input voltage to develop a resultant
as a function of the magnitude of a signal applied to» its 70 voltage signal; means for applying the resultant voltage
input; means including a frequency discrirninator cou
signal to the input of -the voltage controlled oscillator;
pled between the output and input of said variable lfre
modulation means coupled between the Output of said
_quency signal source for developing a negative feedback
voltage controlled oscillator and said fixed frequency
signal, the magnitude of said negative feedback signal
oscillator for developing a signal including a signal com
being proportional to the frequency of the signalgenerated 75 ponent having a frequency equal to a difference between
3,087,121
6
the frequency of the signal generated by said voltage con
trolled oscillator and the fixed frequency; and a low-pass
filter coupled to said frequency modulator for passing
said signal component and yrejecting undesired signal corn
ponents.
4. Apparatus for generating an output signal having a
frequerf'cy which is directly proportional to the magnitude
of an externally developed »input signal applied thereto
6. Apparatus defined in claim 5 including means cou
pled between the output of said controllable frequency
signal source and said fixed »frequency signal source for
developing an output signal having a frequency which is
substantial-ly equal to the difference between the frequency
of the signal `developed by said controllable frequency
signal source and the fixed frequency.
7. Apparatus for generating a |variable frequency out
put signal having a frequency which is directly propor
comprising: a controllable frequency signal source for
generating a signal at its output having a frequency sub 10 tional to the magnitude of an input signal applied there
to comprising: means for generating at an output ter
stantially proportional to the magnitude of a signal ap
minal an output signal having a frequency equal to a
plied Iat its input; means coupled between the output and
frequency `difference between signals generated by a vari
input of said controllable frequency source for develop
able yfrequency signal source and a fixed frequency sig
ing a negative feedback signal at the input of said con
nal source; and means for selectively Varying the fre
trollable frequency source, said negative feedback signal
quency of said output signal by varying the frequency of
having a magnitude which is proportional to the frequency
of the signal generated by said controllable frequency
source; a fixed frequency signal source for generating a
signal having a fixed frequency; means coupled to said
the signal generated by said variable frequency signal
source, the frequency varying means including negative
feedback means coupled between the input and output
fixed frequency source for developing a ‘direct current 20 of the variable frequency signal source, means for de
signal at the input of said controllable frequency source
which is proportional to the fixed frequency, said direct
current signal being of opposite polarity to said negative
feedback signal; means for adding »said ‘direct current sig
nal and said negative feedback signal to an externally
developed input signal to produce a resultant signal; and
amplifying me-ans for applying said resultant signal to
the input of said voltage controlled oscillator 4to cause said
Voltage ‘controlled oscillator to generate a signal having
a frequency which is directly proportional to the magni 30
tude of said externally developed input signal.
veloping at `the input of the variable frequency signal
source a signal having a magnitude proportional to the
signal generated by the fixed frequency signal source, and
means for applying the input signal to the input of the
variable frequency signal source.
8. Apparatus for gener-ating an output signal having
a frequency which is directly proportional to the mag
nitude of `an input `signal applied thereto comprising:
means for generating a fixed frequency signal; means
for generating a variable frequency signal; means for
developing an output signal having a frequency which is
«equal to a difference between the fixed frequency and
5. Apparatus for developing an alternating current sig
the variable frequency signals; and means for selectively
nal having a frequency which is directly proportional to
controlling the Ifrequency of said output signal to be di
the magnitude of an input signal applied thereto corn
prising a controllable frequency signal source for gen 35 rectly proportional to the magnitude of an input signal
applied to said means for generating said variable fre
erating a signal at its output having a frequency which is
quency signal including means for developing a first di
substantially proportional to the magnitude of a signal
rect current signal proportional to the frequency of the
applied to its input, negative feedback means coupled
fixed frequency signal, means for developing a second
between the output and input of said controllable fre
`direct current signal proportional to the frequency of
quency signal source, a fixed frequency `signal source for
the variable frequency signal, said `second direct current
generating a 'signal having a fixed frequency, means cou
signal being of opposite polarity relative to the first di
pled to said fixed frequency signal source for developing
rect current signal, and means coupled to the input of
a direc-t current signal having a magnitude which is di
rectly proportional to the fixed frequency, said direct cur 45 said means for generating the variable frequency signal
for adding `said first and second direct current signals.
rent signal having a polarity which is opposite to the nega
tive feedback signal, and means for adding the direct
No references cited.
current signal with the negative feedback signal at the
input of the controllable frequency signal source.
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