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Dec. 10, 1946.
Y
'
L1. A. RAJcl-IMAN ET AL
y2,412,423
AUTOMATIG 'GÀINf‘ÓoNTRoL CIRCUIT
Filed April 29, 19.45
, 5 Sheets-sheet 1
:1144-. <4. _____ïï
um.
Gttorneg
Dec. 10, 1946.
` I
J. A. RAJCHMAN ET AL
2,412,423
AUTOMATIC GAIN CONTROL CIRCUIT
„Filed’April 29, 1943 `
s Sheets-sheet 2
È,
N
Dec. 10, 1946.
J. A. RAJCHMAN ET Al.
2,412,423
AUTOMATIC GAIN CONTROL CIRCUIT `
' Filed April 29, 1943
5 Sheets-Sheet 3
Patented Dec. l0, 1946
2,412,423
UNITED STATES PATENT OFFICE
2,412,423
AUTOMATIC GAIN CONTROL CIRCUIT
Jan A. Rajchman and Edwin A. Goldberg, Prince
ton, N. J., assignors to Radio Corporation of
America, a corporation of Delaware
Application April 29, 1943, Serial No. 485,040
20 Claims.
(Cl. Z50-41.5)
1
2
This application is a continuation-in-part of
our copending U. S. application, Serial No. 449,244,
filed July l, 1942, and assigned to the same as
the same multivibrator, whereby the electron
multiplier alternately is responsive to the signal
signee.
source and the control source.
The output of
the control amplifier is rectified and compared
This invention relates generally to electron 5 with a source of reference voltage. The combined
discharge devices and particularly to an improved
voltages are further amplified and regulated, and
method of and means for controlling the gain of
applied to the electron multiplier to control the
an electron multiplier or other photo-sensitive
gain thereof. A third embodiment of the inven
electronic amplifying device.
tion includes the utilization of either of these
One of the principal difficulties encountered
two methods to control the gain of a photo-elec
in the use of electron multipliers or other photo
tric cell and a photocell ampliñer.
sensitive amplifying devices is that of maintain
Among the objects of the invention is to pro
ing the gain of the device at a constant value
vide an improved method of and means for con
irrespective of changes in tube characteristics and
trolling the gain of an electron discharge device.
supply voltages. Richard L, Snyder, Jr. has de
Another object is to provide an improved method
scribed one method of gain control for electron
of and means for controlling the gain of an elec
multipliers in his U. S. Patent 2,198,233, granted
tron multiplier having only one electron stream.
April 23, 1940. The subject patent, however, re
Another object is to provide an improved method
quires a specially designed electron multiplier for
of and means for controlling the gain of an elec
efficient operation, whereas the instant invention
tron multiplier wherein a control frequency ap
is adapted to the automatic gain control of multi
plied to the multiplier is selected, rectified, com
pliers of all types.
`
pared with a source of reference potential, and
applied to the electron multiplier to control the
Briefly, one embodiment of the invention con
templates the control of any electron multiplier
gain thereof. Another object is to provide an
(for example, of the RCA type 931) which is
improved method of and means for controlling
the gain of an electron multiplier wherein a con
actuated lby a light beam modulated by some pre
trol voltage is intermittently generated by the
determined signal source. The output of the
electron multiplier, and compared with a source
electron multiplier may, if desired, be further
amplified and applied in a load circuit. In order
of reference potential and applied to the multi
to stabilize the gain of the electron multiplier, 30 plier as a gain control voltage. A further object
a second light source, which is modulated by any
is toprovide an improved method of and means
other predetermined frequency source, is also
for controlling the gain of a photo-cell ampli
focused upon the photo-cathode element of the
lier actuated by a photocell.
electron multiplier. The output of the multi
The invention will be described by reference
plier is applied to separate filters. One filter is 35 to the accompanying drawings, of which Figure 1
designed to pass only the signal frequency, while
is a schematic block diagram of one embodiment
the second filter is designed to pass only the
of the invention, Figure 2 is a schematic circuit
control frequency. The control frequency com
diagram of the principal features of Fig. 1, Fig
ponent is applied to a linear rectifier, and after
ure 3 is a schematic block diagram of a second
comparison with a source of reference voltage, is 40 embodiment of the invention, Figure 4 is a
further amplified and stabilized. The stabilized
schematic circuit diagram of the principal fea
control voltage derived from the last mentioned
tures of the modification of Fig. 3, and Figures 5
amplifier is applied to the electron multiplier to
and 6 are modifications of a third embodiment of
control the gain thereof.
the invention. Similar reference numerals are
A second method of controlling the gain of an 45 applied to similar elements throughout the _draW- electron multiplier utilizes a multivibrator, or
ings.
similar device, Which alternately applies voltages,
Referring to Fig. 1', a source of signals l, which
from a signal source and a control source, to two
may be an oscillator having an output frequency
light sources which are focused upon the photo
'fa is connected to- a ñrst light source 2 which is
cathode of the electron multiplier, The output 50 focused upon the photocathode element of a con
of the electron multiplier is fed into a buffer
ventional electron multiplier 3.. The lig-ht source
amplifier, the output of which is connected to
2 may be any device such as, for example, a neon
the input circuits of a signal amplifier and a
lamp, which may be utilized to provide a modu
control amplifier.
The gain of the signal and
lated light beam. A control frequency source 4,
control amplifiers issynchronously controlled by 55 which may be an oscillator having an output fre
¿2,412,423
n
ô
ventional voltage regulator tubes 3l, 38, 39, 40,
¿I and ¿l2 (for example, RCA type X7R-150), are
connected across the various power supply cir
cuits to stabilize the potentials applied to the
various electrodes.
The rectified Voltage derived therefrom is
and applied to the input of a conventional D.-C.
amplifier I2. The voltages appliedA to the D.-C.
amplifier I2 may, if desired, be stabilized by the
use of conventional Voltage regulator tubes, such
as RCA type Vit-150. The amplifier output is
applied to the electron multiplier 3 to control the ‘
Y
Fig. 2 is a circuit diagram ofr one practical em
bodiment in which the collector electrode of the
electron multiplier is connected through a cou
ñrst amplifier tube I4 are derived from a source
of positive potential through conventional series
coupling resistors I9, 20 and 2i. A cathode re
sistor 22 is connected between the cathode of the
`
Y
In Fig. 3 the signal source I and the control
voltage source ¿l are connected to multivibrator
55, which alternately triggers the sources I and
4 to energize the signal light source- 2 and the
The cathode circuit of
amplifier tube ill is connected, through a second
coupling condenser 56 and a »series grid resistor
I'I, to the control electrode of a second amplifier
tube I8. Anode and screen potentials for the
multiplier 3. Potentials of both frequencies are
amplified by the tubes I4 and I8 and the signal
frequency is selected by the filter 'I and applied
to the signal output terminals 3. Potentials of
the control'frequency are Vselected by theñlter
8 and rectified by the diode 3 I. The rectified con
trol signals are then combined with the adjust
able bias Voltage derived from the battery 34
and the potentiometer 32 and applied to the grid
of the amplifier tube 33. After additional ampli
fication in the D.-C. amplifier tubes 54 and 35,
the control signals are applied to the multiplier
supply circuit to compensate for multiplier varia
tions.
` pling condenser I3 to the control electrode of a
the first amplifier tube I4 includes a resistor I5
connected between the cathode and ground. A
grid bias resistor I3 is connected between the con
trol electrode and ground. The anode of the
Y
' are focused on the photocathode of the electron
combined with a standard or reference voltage I I
first ampliñer tube I5.
'
The operation of the circuit of Fig. 2 is as fol
lows: Signal and control sources of different fre
quency modulate the light sources 2 and 5 `which
filter 8 tuned to pass the control frequency fc.
The output of the first ñlter ‘l is connected to the
` signal output terminals 3. The output of the
second filter 8 is connected to a linear rectifier
gain thereof.
.
potentials applied to the electron multiplier; Con- .
5, to the input circuits of a first filter l, tuned
to pass the ysignal frequency fs, and a second
I3.
4
circuits of the A.-C. amplifier and the biasing
quency fc, is connected to a second light source
5, which may be of the same type as the first
light source 2. The second light source 5 is also
focused upon the photocathode element of the
electron multiplier 3. The collector electrode cir
cuit of the electron multiplier 3 is connected,
through a conventional A.-C. feedback amplifier
control light source 5, respectively.
The light
from the two sources 2 and 5 is focused upon
the photocathode of the electrode amplifier 3.
The output of the electron multiplier 3 is applied
to the input circuit of a D.-C. amplifier 5I. The
output circuit of the D.-C. amplifier 5I is con
nected to the input circuits of' a second D.-C.
amplifier 52 and a third D.-C. amplifier 53. The
output circuit of the second D.-C. amplifier 52
is connected to the signal output terminals 29.
`
40 The switching multivibrator 50 is also connected
second amplifier tube I8 and ground. A grid re
to the second D.-C. amplifier 52 and the third sistor 23 is connected between the control elec
D.-C. amplifier 53 to control intermittently-and
trode of the second amplifier tube I3 and ground.
alternately the gain thereof in synchronism with Y 1
A feedback circuit, comprising the series resistors
the energization of the first and second light
24 and 25 connected in parallel with the series
capacitors 26 and 2ï, is connected between the 45 sources 2 and 5„whereby the signal and control
frequencies are alternately and intermittently
anode of the second amplifier tube I8 and the
amplified. The output of the third D.-C. ampli
cathode of the first amplifier le. Anode potential
is applied through serially connected choke coils
fier 53 is combined with a source of reference '
Vpotential II in the same manner as in: Figs. 1
lf3 and 44 and a series resistor 45. Screen poten
tial is applied throughV the choke coil ¿i3 and 50 and 2, and is applied to the input of a fourth`
D.-C. amplifier I2. The output of the fourth
screen resistor 55. lThe anode of the second
D.-C. amplifier I2 is applied to the electron multi
amplifier tube I8 is coupled, through a coupling
plier -to control the gain thereof. The control
condenser 28, to the input of the signal frequency
.voltage source e, in this modification, may be
filter "I, which may be of any well known type
either A.-C. or D.-C. since the signal and con
designed to effectivelyV limit the output at the
trol sources are not applied to the multiplier cir
terminals I! to the signal frequency component.
cuit at the same time, and since D.-C. amplifiers
The anode of the second amplifier tube I8 is also
are used throughout.
'
coupled'through the coupling capacitor 23 to the
Fig. 4 is a circuit diagram of. another practical
input of the control frequency ñlter 8, which is
also of conventional design. The output of the v60 embodiment of the system in which the electron
multiplier 3 is provided with biasing potentials
control frequency filter 8 is coupled, through a
derived from the bleeder resistor 36. The collec
coupling capacitor 30, to the anode of a diode 3|.
tor electrode of the electron multiplier 3 is con
The rectified output of the diode 3l is combined
nected to the control electrode of a first D.-C.
with an adjustable D.-C. potential derived from
a potentiometer 32, and is applied to the control 65 amplifier 5I. The anode of the first D.-C. ampli
electrode of a D.-C. ampliner 33.
A source of
reference potential 34, which may be a battery,
is connected across .the terminals of the poten
tiometer 32. The output of the first D.-C. ampli
fier tube 33 is further amplified by second and 70
third D.-C. amplifier tubes 54 and 35, respectively,-
fier 5I is connected through a first coupling re
sistor BI to a first control electrode of the second
D.-C. amplifier 52 and a first control electrode Y
of a third D.-C. amplifier 53.Y Signal output is
applied to the output terminals 29 >from'across
a cathode resistor 62 in the cathode circuit of
the second D.-C. amplifier 52. Control potentials
arederived from the third amplifier tube 53 from
sistance 36, which supplies the operating voltages
across aresistor 63 in the cathode circuit -of the
for the electron multiplier 3. Separate sources
of potential are preferably provided for the anode 75 tube 53.V These control potentials are applied
and is applied to the terminals of a bleeder re
2,412,423
to the anode of a diode 3|- land are coinbinedwith
the reference voltage, derived fromv the- poten
tiometer‘32. The-resulting voltage is ampliñedby
the> 13h-C. amplifiers 54, 35 and 66- in the same
control potentials» from one of said Separated
signals, and applying said `control potentials to .
said device as bias voltages to control the velocity
of said electron stream. and hence the gain of
mannerV as described- heretofore for the circuit Cil said multiplier.
of Fig. 2. The output current of the last D.-C.
amplifier -tube 66 flows through the bleeder re
sistance 36, to controll the gain of the electron
multiplier 3. Similarly, the potentials applied to
2. The method of controlling the. gainof an
electron multiplier device` comprisinggenerating
separate. light beams. modulated at different` fre
quencies, simultaneously applying said light
the anode circuits and- electron multiplier elec 10 beams.` to said multiplier to producev a common
trodes are stabilized by conventional voltage
electron stream therein, deriving. combined. sig
regulator tubes such as the type VBL-150, as in
nals from said multiplier, separating signals» of
the circuit of Fig. 2.
~
diiîerent frequency components, deriving control
A conventional multivibrator circuit 50 is con
potentials from one of said separated signals,
nected to a second control electrode of the second 15 andr applying said control potentials to said de
D.-C. amplifier tube 52 and applied-` toY trigger
vice as bias voltages to control the velocity of
the signal source l. The» multivibrator is also
connected to the second_control electrode `of the
third D.-C. ampliiier 53 V`and applied to trigger
the control voltage source ll, whereby the signal
and control channels are alternately and inter
mittently energized and conditioned. The multi
vibrator circuit 50 may be of any suitable type
known in the art, for example, the circuit de
saidl electron stream and hence the gain of said
multiplier.
`
.
3. The method of controlling the gain of an`
_electron multiplier device comprising generating
separate light beams, one of said beams providing
signal intelligence and another of said beams pro
viding a control signal, alternately applying said
light beams to said multiplier,` deriving from said
scribed in the' Review of Scientiiic Instruments, 25 multiplier combined signals each characteristic
vol. 9, July 1938, at page 222.
of a different one of said alternately applied
Thus, the operation of the circuit of Fig. 4
light beams, separating said signals, deriving con
is» as follows: Modulated light is alternately ap
plied- tothe electron` multiplier 5tv by the keying
action of the» multivibrator on the signal source
l andthe controlV source 4. Simultaneously, the
D.-C. ampliiiers A52 and 53 are keyed by the multi
vibrator 5o to synchronize their operation with
the signal and control sources. The signal out
put is> derived from the terminals 2Q of the cath
ode» resistor 623m circuit with the amplifier 52.
Control> voltages- from across- the cathode resis
tor 63 in circuit with the amplifier 53 are. rectified
by thediode 3ll and combined with the adjustable
bias voltage derived from` the battery 34 through
the voltage divider .32.. The combined voltages,
which include signals representative of Variations
in the characteristics of the multiplier, are am
pliñed and applíedto the multiplier supply circuit
to compensate for such multiplier variations.
Fig. 5 is similar to Fig. 1, with the exception
that a conventional photocell Bl and variable
gain amplifier 6.9 are substituted for the electron
multiplier 3. The operation is generally the
same as that of Fig. 1.
trol potentials from one of said separated signals,
and applying said control potentials to said de
30 vice as bias voltages to control the. velocity of
said electron stream and hence the gain of said
multip-lier.
4'. A circuit for controlling the- gain of anr
electron multiplier device including means for
generating separate distinctively modulated light
beams, one of said beams providing signal in
telligence and another of said beams providing
a controly signal', means for applying said light
beams to said multiplier to produce a common
electron stream therein, means for deriving from
saidl multiplier combined signals each character
istic of the’distinctive features of said light beams,
means for separating said signals, means respon
sive to one of said separated' signals for deriving
control potentials therefrom, and means for ap
plying said control potentials to‘said device as
bias voltages to control the velocity of said elec
tron stream and hence the gain of said multiplier.
`5. A circuit for controlling the gain of an
electron multiplier device including means for
generating separate light beams, means for mod'
Fig. 6 is similar to Fig. 3, with the exception
that the photocell Sl and variable gain amplifier
ulating said beams at diiiferent frequencies, means
69 are substituted for the electron multiplier 3.
for
simultaneously applying said beams to said
The operation is generally the same as that of
multiplier to produce a common electron stream
Fig. 3.
therein', ymeans for deriving combined signals
The variable gain ampliñers of Figs. 5 and 6
from
said multiplier, means for separating said
may be of any type known in the art wherein the
signals, means responsive to one of said separated
gain is controlled by a gain control voltage de
signals for deriving control potentials therefrom,
rived from associated apparatus.
and
means for applying said control potentials
The systems disclosed in Figs. 5 and 6 differ 60
to said device as bias voltages to control the
from previously disclosed devices in that the in
velocity of said electron stream and hence the
stant systems employ a common photocell and
gain o_f said multiplier.
photocell. amplifier for both the control. voltage
6. A circuit for controlling the gain of an elec
and the signal voltage components.
tron multiplier device including means for gen
We claim as our invention:
65 erating separate light beams, one of said beams
l. The method of controlling the gain of a
electron multiplier device comprising generating
separate distinctively modulated light beams, one
of said beams providing signal intelligence and
yproviding signal intelligence and another of said
beams providing a control signal, means for
alternately applying said light beams to said
another of said beams providing a control signal, 70 multiplier, means for deriving from said multi
plier combined signals each characteristic of a
applying said light beams to said multiplier to
different
one of said alternately applied light
produce a common electron stream therein, de
beams, means for separating said signals, means
riving from said multiplier combined signals each
responsive to one of` said separated signals for
characteristic of the distinctive features of said
deriving
control potentials therefrom, and means
light beams, separating said signals, deriving 75
for applying said control potentials to said de
2,412,423
of said emotion stream and hence _thegain 9i
vice as _bias voltages to control the velocity of said
electrongstream andhence the 4gain of said,V mul
Saidmultiplier..
tiplier.
photo-sensitive
_
_
_
_
_
»
.
A'lcircuit of the type described in claim 6,
including means for modulating atleast one of Si
saidlight'beams.
_
__
_
V_8. A circuit of the type. described in claim 5,
including means for deriving a gain controlled
signal from said multiplier. _
_
9. A circuit of the type described in claim 6,
including means for deriving a gain controlled
signal from said multiplier.
_
_
_
___
_
_
_.
_
_-
__
`>14.,"1`he method of controlling the gain „of a
amplifying d device ì Vcomprising
generating separate distinctively modulated light
beams, one of said beams providing signalin
telligence and another of said beams providing
a control signal, applyingsaid light beams to
said device to produce a common electronic cir
cuittherein, deriving from said device combined
signals characteristic of thev distinctive features
of said light beams, separating said signals, '
_
deriving control potentials from one of said lsep-_
10. A circuit for controlling the gain of .an
i arated signals, and applying said control. pOlìen
tials toV said device as bias voltages to controlk
15
generating separate _light beams, one of said
the Yvelocity of saidl relectron stream‘and hence '
electron multiplier device including means for
beams ,providing signal intelligenceand another
the gain of saidY device.
of said beams providing a control signal, means
l
»_
_
t
n
>l5. The method of controllingy the gain of a
including a multivibrator for alternately apply
ing said light beams to said Amultiplier, means
for deriving from said multiplier rcombined sig
photo-sensitive amplifying device comprising
generating separatev light beams modulated at
diffeiyent frequencies, simultaneously applying
nals each characteristic of a diñerent one of
Vsaid alternately applied light beams, means in
cludingV said multivibrator for separating said
signals, means responsive to one of said separated
said light beams to said device to produce a com
mon electronicV circuit therein, deriving combined
signals for deriving control potentials therefrom,
and means for applying said control potentials
signals Vfrornsaid device, separating signals of ,dif
ferent frequency components, VAderiving control po
25 tentials from one o-f said separated signals, and
applying said control potentials to said Vdevice
to ‘said device as bias voltages to control the
velocity of said electron stream and hence the
gain of said multiplier.
_
30
_ 11. A circuit for controlling _the gain of an
photo-sensitive amplifying device comprising
generating separate light bçeams, one of said
beams Vproviding signal intelligence and another
oi' said beams providing a control signal, alter
nately applying said light beams to said device,
deriving from said device combined signals each
electron multiplier device including means for
generating separate lightI beams, means for mod
ulating said beams at different frequencies, means
for simultaneously applying said beams to said
multiplier to’ produce a common electron stream
therein, means for deriving combined signals
from said amplifier, filter means for separating
characteristic of a diiîerent one of saidalter
nately applied light beams, separating said sig- '
nals,_deriving control potentials from one of said
said signals, means responsive to one of said
-separated signals for deriving control potentials
as bias voltages to control the velocity of saidV
electron stream and hence the gain of said device.
16. The method of Ycontrolling, the gain of a-
40
separated signals, and applying said control po-V
therefrom, and means for applying Said control
tentials to said device as bias voltages to control
potentials ,to said device as_-bias voltages to
the velocity of _said electron stream and hence
~ controlthe velocity of said electron stream and
hence the ygain of said multiplier.
12. A circuitrfor controlling the `gain of an
electron multiplier device including means for
generating separate light beams, means for mod
ulating said beams at dinerent frequencies,
means for simultaneously applyingsaid beams to
the gain of' said device.
`
1'?. A circuit for controlling the gainof a pho
to-sensitive amplifying device including means
for generating Vseparate l distinctively modulated
light beams, one of said beams providing signal
intelligence and another of said beams: providing '
a control signal, means for applying said light
Y said multiplier to produce aV common` electron 50 beams to said device to produce a common elec- .
stream therein, means for deriving combined
signals from said multiplier, filter means for sep
arating said signals, meansincluding a source
of reference potential and responsive to one of
said separated signals for deriving control po
tentials therefrom, and means for applying said
control Ipotentials to said device as bias voltages
to control the velocity of 4said electron stream
and hence the gain of said multiplier.
`
13. A circuit for controlling the gain'of an
electron multiplier device including means for
tronic circuit therein, means for deriving from
said-’device combined signals each character
istic of the 'distinctive features of said light beams,
means for separating said signals, means respon-_
generating separate light beams, onel ,of> said
beams providing signal intelligence and another
for generating separate lightbeams, means for
sive to one of said separated signals for deriving '
control potentials therefrom, and means for ap
plying said control potentials to said device asV
bias voltages to control the velocity of said elec-`
tron, stream and hence the gain Vof said device.
18. A circuit for controlling the gain of a pho
to-sensitive amplifying device including means
modulating said beams at diîerent frequencies,
means for simultaneously applying said `beams to
including a multivibrator for alternately apply-v 65 said device to ,produce a common electronic cir-1
cuit therein, means for deriving combined signals
ing said light beams to said multiplier, means
for deriving from said multiplier combined sig
from said device, means for separating said sig-V
Inals, means responsive to one of said separated '
nalspeach characteristic of a different one of said
signals for deriving control potentials therefrom,
alternatelyapplied light beams, means includ
and means_for applying said control potentialsv
ing said multivibrator for separating said signals,
to said device vas bias voltages to control the
means ?including a source of reference potential
of said beams providing a control signal, means `
and responsive'to one of said separated signals
for deriving control potentials therefrom, and
means for. applying Vsaid control potentials to
velocity of saidelectron stream and hence thev
Y gain of said'device.
~
i9. A circuit for controlling the gain of a pho
said'device as_bias voltages to control the velocityV 76 to-s'e'nsitive amplifying -device including meansY
9
for generating separate light beams, one of said
beams providing signal intelligence and another
10
_
potentials therefrom, and means for applying
said control potentials to said device as bias volt
ages to control the velocity of said electron stream
for alternately applying said light beams to said
and hence the gain of said device.
device, means for deriving from said device com 5
20. A circuit, of the type described in claim 19
bined signals each characteristic of a different
including means for modulating at least one
one of said alternately applied light beams, means
of said light beams.
for separating said signals, means responsive to
JAN A. RAJCHMAN.
one of said separated signals for deriving control
EDWIN A. GOLDBERG.
of said beams providing a control signal, means
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