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Патент USA US2106207

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Jan. 25, 193s,
2,106,207
ACROSSLEY i-:r AL'
AUTOMßr-'I‘ICl VOLÚME CONTROL SYSTEM
Filed July 25,' _1935 '
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' EEBBEQETE E/NEWA,
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ATTORNEY.
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Patented Jan. 25V, 1938
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I_UNITED STATES
2.106.207
lPATENTA
, _ol-‘Fica
' _ _ i
AU'roMA'rIc vomlun CONTROL SYSTEM
Alfred .Crossley and Herbert E. Meinema, Chicago, \
Illa assignors to Johnson Laboratories, Inc., -
Chicago, Ill., a lcorporation of Illinois
_ a Application July z5, 1935, serlal No. 33,113
8 claims. (cl. 25o-_20)
This invention relates to improvements ‘in vacuum-tube» amplifying systems. More specifically,
high-frequency signals for the transmission of
intelligence.v Although the-arrangements of the
this invention relates to improvements ,in the _ present invention are applicable to vacuum-tube
means for automatically regulating the ampliñ5 cation of a vacuum-tube amplifying system.
amplifiers-of all types, they are Iof especial advan
'tage in the high-frequency amplifiers of radio re- 5.
' - An object of this‘invention is to provide anim-
ceivers.
proved method of amplification control which au-v
tomatically maintains the output level of a vac-
the output signal level remain substantially con- ‘
stant in spite of wide variations in the input signalv
In this case, it is usually desirable that
uum-tube amplifier substantially .constant in -voltage due to fading or to the. Widely different
10 spite of wide variations in the input voltage.
signal strengths whichare encountered in tuning 10
Another object of the present invention is to from one signal to another from a diiîerent source.
provide a system of automatic amplification» con- '_
trol which is responsive to relatively small changes
in the voltage at tire output of` a vacuum-tube
15 ampliñer.
»
The usual radio receiver consists of a high-fre
quencyamplifying system, a demodulator, and a
low-frequency amplifier. Since the demodulator» 15
performs most satisfactorily within a relatively
A further object of this invention is to provide
means whereby the control of amplification which
is automatically applied to a vacuum-tube ampliiler is'self-increasing.
Still another object of the present invention is
to provide an amplified control voltage for the
automatic regulation of the amplification of a
yvacuum-tubo amplifier, without the use of addi-
narrow range of signal levels, it is the _usual prac
tice to- regulate the amplification of the high
frequency amplifying system either manually or
automatically, in such a'way as to maintain the
signal at the demodulator substantially constant ‘ 20
despite large variations in the strength of the in
coming signal. If~ this operation is performed «
manually, constant attention on the part of the
tional vacuum tubes other than a demodulator.
user is vrequired to compensate for the relatively
.
25
An additional object of this invention is to rapid changes in the incoming signal strengtln 25
provide an automatic amplification control system Furthermore, whenever the receiver is adjusted to
which may be satisfactorily employed in conjunc- receive a different station the manual ampliñca
tion with the high-frequency amplifier of a radio tion control must be re-adjusted to produce the
receiver, to maintain the signal level at the de- desired output level from the new signal. These
»30 modulator substantially constant in'spite of wide requirements are objectionable in any receiver; 30
variations in the .input signal voltage. =
and are especially disadvantageous in the case of
Still a further object of the present invention is 'receivers intended for mobile use, as in automo
to provide an automatic amplification control sys- biles or motor boats.
tem which has a desirable input vs. output charVarious arrangements have been employed in
acteristic, but which does not prevent the full the past to Aautomatically vary the amplification 35
b: Ul utilization of the amplification of a vacuum-tube of the high-frequency amplifying system of a.
amplifying system.
_
Although a discussion of the principles underlying our invention is necessary to a full under4
radio receiver in accordance with changes in the
input signal level. ‘These arrangements are
usually operated by rectifying a portion of the-
_
»
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standing thereof, certain portions of this specifica- ` output voltage, and applying the rectified volt-T40
tion will be bestunderstood when taken in_con-
'age to a control electrode of one or‘more of the
ynection with the drawing, in which
Fig. 1 is _a graph showing the usual automatic
high-frequency amplifying vacuum tubes, there»
by regulating the amplification of the system in
amplification control characteristics under sev-
45 eral
different
sets of conditions;
and
Fig.
2 is a schematic
wiring diagram“
` of . a por-
approximate accordance with the amplitude of
n
the
applied
input
also
signal.
tó a-low-frequency
In somel cases,amplifying
the control
vacis 45
tion of a radio receiving apparatus incorporating ' uum tube, the aim being to supplement the regu-_
our invention and- serving as an illustrative em- lation of amplification which is obtained in the
bodiment thereof.
l
high-frequency portion of the receiver.
' 5o
Vacuum-tube amplifiers of the type herein con-
The simplest forms of _automatic ampliñcation 50
templated are used in both low-frequency and » control systems decrease the amplification as soon
high-frequency communication systems. Low- as any output signal is present, the degree of
frequency amplifiers are commonly employed in reduction increasing as the output signal increases
l telephone systems. High-frequency ampliñers -in amplitude. ÁThese arrangements prevent the
55 are widely used in systems employing modulated full utilization of the high-frequency ampliflca- 55’
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2,106,207
tion of the receiver, since the amplification is re
duced by any signal at the output. `Further
more, the reduction in amplification does not
keep pace with the increasing input signal volt
point on, however, the output increases appreci
ably as the input increases. Curve D is the char
aeteristic of a system according to the presentl
invention, 'in which provision Vis made for both
age, with the result that the output level in- ~ delaying and amplifying the control voltage
creases appreciably as the input signal increases which is applied to the amplifying vacuum tubes.
in strength.
'
In this case, the outputv soon reaches its normal
The first of these objections may be overcome level, and is closely maintained at this level as
to a considerable extent by so 'delaying the op
the input increases many times. This curve '
eration of the automatic amplification control closely approaches the ideal curve, indicating
that there is no reduction in the amplification that the performance of the system‘of the pres
until the output signal exceeds a predetermined
The delay effect may be obtained in the
rectifier circuit, or an additional lbiasing voltage
15 which opposes the rectifier output. voltage‘may
. level.
_ be introduced by suitable means. In 'either case,
delaying the action of the 'automatic control per
mits the full sensitivity of the receiver to be
utilized.
.
The problem of decreasing the amplification
at a sufficiently high rate to keep pace with an
increasing input signal is especially acute in the
case of small receivers having only a limited
ent invention is very satisfactory.
Although the arrangements of the present in
vention may be applied to various types of ampli
fying systems, the embodiment shown in Fig. 2
as an illustrative example consists of a» three
stage high-frequency amplifier followed by a
diode rectifier. 'I'his type of amplifier is com
monly employed in radio receivers. The diode
rectifier may be used simultaneously as the con
20
trol rectifier and as- the signal detector or de
modulator, or a separate rectifier may be em
ployed as the demodulator.
Both forms are
number of high-frequency amplifying vacuum within the scope of the present invention.
25 tubes to which the control voltage may be ap
Referring to Fig. 2, high-frequency amplifying ‘
plied. The number of stages which, may be con
vacuum tubes I, 2 and 3, respectively, are cou
trolled is further limited by the fact that a vac ~pled in cascade by means of transformers 4, 5
uum tube which drives a' diode rectifier should and 6. Each transformer secondary is tuned to
.preferably be operated at a fixed bias voltage. `the signal frequency by variation of a capacitor
With only a limited number of vacuum tubes 1, or by variation of the effective inductance of 30
to be controlled, therefore, the only alternative the secondary itself. By-pass capacitors 8 fur
is to amplify tlie output voltage from the recti
nish a low-impedance path for all high-frequency
fier before applying it to the control electrodes of currents. Amplifying vacuum tube 3 has in its
one or more high-frequency amplifying vacuum plate. circuit, inductor 9 and resistor I0, Aand its
tubes.
î ,
plate 30 is coupled to the anode II of rectifier
Amplification of the control voltage has, prior
to the present invention, required either an ad
ditional vacuum tube or a substantial sacrifice
in the effective plate potential available for the
controlled amplifying Y vacuum tubes, or both.
The arrangements of the present invention, how
ever, provide for the amplification of the control
voltage without the necessity for an additional
vacuum tube and without an appreciable sacri
45 fice in effective plate potential on the controlled
amplifying vacuum tubes.
The advantage of
such an arrangement is obvious in any receiver,
and this is especially the case in receivers in
tended fo'r mobile service, where extreme com
vacuum tube
I2 by blocking capacitor I3.
Diode load resistor I4 is connected between anode
i II and the junction of resistors 23 and 24.
The
direct-current grid returns- of amplifying vac
uum tubes I and 2 are connected through block 40
ing resistors I6 and I'l and through filter resistor
I_8 to diode anode II. High-frequency currents
from the diode circuit are prevented from reach
ing the grids of vacuum tubes I and 2 by by
pass capacitor I9.
The cathode 25 of vacuum tube I is connected
to the cathode 21 of vacuum tube 3. The cath
ode 28 of vacuum tube 2 is connected to the junc
tion of voltage-divider resistors 2I and 22. The
50 pactness, wide-range automatic amplification- cathode 21 of vacuum,tube 3 is connected to .
control and economical operation are essential ground through resistors 23 and 24. The direct
features of a satisfactory receiver. Furthermore, current grid'return of vacuum tube 3 is con
the arrangement of the present invention in
nected to the junction of resistors vI‘I and I8.
cludes provision for» obtaining a desirable delayed - 'I'he input signal to the amplifier is applied to
operation of the automatic amplification control, Vprimary 26 of coupling transformer 4.
permitting the full ‘sensitivity of the receiver to
be efficiently utilized.
`
'I'he performance characteristics of various
forms of automatic amplification control systems
are shown graphically in Fig. 1. Curve A repre
sents the ideal form, the output rising rapidly to
the normal level and thence remaining constant
atthis level. This characteristic is not attained
in any simple arrangement. Curve B shows the
performance of a simple control system in which
a portion of the output signal is rectified and
Vacuum tube I2 is a duplex diode, and in
cludes a second diode anode 33 which in connec
tion with cathode I5 is employed as the demodu
lator, the audio-frequency voltage being devel
oped across resistor 34, connected betweendiode
When no input signal is present, an initial bias
voltage for vacuum tubes I, 2 and 3 is developed 65
across resistor 23. The values of resistors 2|
-and 22 are so chosen that the’ cathode 28 of vac-*_
A very large input-e uum tube 2 has the same potential relative to
is
preceding
required amplifying
to produce normal
tubes. output„and normal ground as the cathode 25 of vacuum tube I. In
70 output is reached very graduallyas the inputin
the absence of a signal, there is no appreciable
creases. Curve C represents the performance of voltage across resistor i4.
When a signal is applied to. primary 2S and
a system similar to that of curve B, except that
a delay effect has been introduced to prevent the amplified by vacuum tubes I,>2 and 3, and it ex
automatic controi-v from4 operating i until the. out
„ceeds the negative delay- _voltage on the diode
used to control the amplification of one or more
75 put almost reaches its normal level. From this.
C1)
anode 33 and cathode I5. The amplified signal
is fed to diode anode 33, through blocking capaci
tor 32.
anode II due to the voltage drop across resistor
2,106,207.
`- 23, it will be rectified by vacuum tube- n. as.
soon as rectification takes place, a direct-current
l voltage appears across resistor Il. This voltage
»
according -to` Fig. .2, the following components
and constants will be found satisfactory. It will
.be understood. however, that any lof these values
may be altered, and theyare not to be taken as
in any way' limiting the scope of the present
adds to the initial bias on vacuum tubes I, 2-and
l, thereby tending to reduce their mutual con-'
' ductance and hence their ampliñcation.- A de- y
invention.
.
vf' creaseïin voltage drop across'resistor 23 occurs
when the platel currents of vacuum tubes I and
I. 3 decrease due to the increasing negative grid
ylo
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Type or value
bias ßwhich is being applied to these vac
'I‘his change in the voltage' drop
uum tubes.
I'
Reference
numeral
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.Type78
_
,
Typ@ 78
.
TypeßB? (pentode portion)
across resistor 23 decreases the initial bias volt
which is applied to'the grids yof vacuum
Type 6B7 (diode portion)
tubes .I, 2 and V3, but simultaneously the delay
0. 4 mi‘ilihenry
5000 ohms
0.1 microiarad
ase
voltage on diode anode II is decreased and per
>
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16
_ 200 micromîcrofarnds
i. 0 megohm
._ mits the development of a larger control voltage
0. l-megohm
across resistor Il. The nét result, if this were
the only .means for automaticallyy regulating the
'_y amplification of the system. would be a per
20 fomance characteristic substantially like that
represented by curve C of Fig. l.
As the voltage across resistor 2l decreases,
' -however, the left-hand terminal of resistor I4
l. 0 megohm
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_
0. 0l microiarud
20
750 ohms
25,000 ohms
750 ohms
750 ohms
Vacuum tubes 3 and yI2 are shown above as
being combined in a-single type 6B? vacuum tube, 25
tube 2 is at a_ which contains a diode portion and a pentode
25_ Since the cathode 28 of vacuum
, _substantially fixed positive potential relative to
portion with a common cathode, since the cath
becomes less positive with respect to ground.
Y ground, the effective negative' bias on grid> 3| of
vacuum vtube 2'increases.
This increase is in
addition 'to the bias _voltage developed across
diode load resistor Il. These two arrangements
30 .combine
to produce a very desirable self-increase
in_ _the overall' degree of- amplification control,
so'that the performance of the system is similar
‘ to that represented by curve D of Fig. l.
.
, The operation of the system willbe better un
, >derstood by noting that, in effect, vacuum tube I .
odes of these vacuum tubes are connected to
gether in a preferred embodiment. Separate 30
vacuum tubes may be used if desired, or any
other suitable types may be substituted._ Fur
thermore, any ofthe other vacuum tubes may
be of the multi-function type, the portions not
used in the arrangements shown in Fig. 2 being I
35
used for any other desired purpose, as for ex
ample as a first stage of low-frequency amplifl- '
acts as a direct-current ampliiier. Resistors 23
and 24 are in the direct-current plate circuit of
vacuum tubes I and 3, and any change in the
cation.
_
.
Having thus described our invention, what we
claim is:-
_
1. In a ra'dio receive
a multi-stage amplifier
direct-current voltage _ongrlds 29~ changes they. including plural amplifying vacuum tubes, a first
plate current of the tubes, and produces a mag
niñed change in the voltage across resistors 23
and 24. The amplified voltage change is utilized
in two distinct ways to produce a greater degree
45 o_f amplification control, with the result that the
range of input signal amplitudes which may be
means for automatic control of the amplification
of a first and ajsecond of said -vacuum tubes, and
a second `means for controlling the amplification
of said second- vacuum tube, said second means
including plural resistors inthe cathode circuit
tube _whereby
'said first
said _first vacuum
ì
handled by the receiverwithout overloading the ' . _of
vacuum tube acts additionally as a'direct-current
output tube is substantially increased', This amplifier to increase the degree oi’v control exerted
desirable in receivers for
>"feature- is“ especially y
Y
mobileservice, where great variation in the fieldl .
upon said second vacuum tube by- said first -con
strengths of the signals is commonly encoun
trol means.
tered.
means for automatic amplification control includ
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It will be understood that vacuum tube I2 may
l' be replaced by any other suitable type of recti
l55 `ñer,
asfor example a copper-oxide rectifier. ’ In
~ alpreferred embodiment, inductor 9 is resonantv
' '- at a frequency approximately midway between
the extreme vfrequencies to which the system may
' `be tuned, and its resonance characteristic is
60 broadened by means of resistor III. _ It will be
that any other suitable"
’ understood,l however,
meansyïmay be employed for coupling amplifying
vacuum tube 3 to rectifier I2. The arrangements
of the present invention may be applied _to am
plifiers having more or less than three stages
-without departing from the scope thereof, the
'increased control voltage being applied to one
or more amplifying vacuum tubes, some or all of
which may be .the intermediate-frequency am
plifiers in a superheterodyne type of receiving
apparatus; and the increased control voltage may
also be applied to tubes »which are subsequent to
_the demodulator, within the scope of this inven- I
tion.
. -
5 wv1n an 'embodiment‘iof the present inventionV
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f 42. In , a multi-stag
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vacuum-tube amplifier,
ing a diode rectifier coupled to the output of said _
ampliñerand having/a direct-current connection
from its negative output terminal to a' control
electrode of at least a first and a'second vacuum
tube of said amplifier, means for successively de
laying and increasing the effect of said automatic
ampliñcation control. including Aa, connection be coy
tween the .cathode of said first vacuum tube and
the cathode of a third vacuum tub'e; a connection
between the cathode of Vsaid diode rectifier and the
cathode of said third vacuum tube; a connection
includinga first and a second resistor vbetween
Athe cathode of said third vacuum >tube and
ground; Aa connection between the junction of
said first and second`resistors`and the positive
terminal of a third resistor in the output circuit
of said diode rectifier; and means for maintain
ing the cathode of said second vacuum tube at
substantially the same potential relative to
ground as that of the cathode' of said ñrst vacuum
' tube when no
amplifier..
input voltage is applied to said
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2,106,207
y A ` 3. In a radio receiver. including a multi-stage
high-frequency vacuum-tube amplifier and a di
ode detector-rectifier, means for automatically
regulating the amplification of said amplifier inaccordance with changes in the direct-current
output of said diode detector-rectiñer, said
means including a direct-current connection
between the anode of said diode detector
rectifier andA a
control electrode of at least
10 a first and a- second vacuum tube of said amplifier;
a connection between the cathode of said first
vacuum tube and the cathode of a third vacuum
tube; a connection includinga first and a second
resistor between the cathode of said third vac
output of a multi-stage high-frequency vacuum
tube amplifier and having a direct-current con
nection from its anode to a control electrode of
at least a first and a second vacuum tube of said
amplifier, said means'including a. connection be
tween the cathode of said first vacuum tube and
the cathode of a third vacuum tube; a connection
including` a first and a second resistor between
the cathode of said third vacuum tube and
ground; a, connection between the junction of
said first and second resistors and the positive>
terminal of a third resistor in the output circuit
of said diode rectifier; a connection between the
cathode of said 4third vacuum tube and the cath
ode of said diode rectifier; and means for main
taining the cathode of' said second vacuum tube
uum tube and ground; a connection between the
junction of said first and second resistors and the
positive terminal of a third resistor in the output _ at substantially the same potential relative to
circuit of said diode detector-rectifier; a con . ground as that of the cathode of said first vacuum
nection between the cathode of said third vacuum tube when no input voltage is applied to said radio
20 tube and the cathode of said diode detector-recti
. receiver.
fier; and means for maintaining the cathode of
6. In a radio- receiver, plural high-frequency
said second vacuum tube at substantially the amplifying tubes and a detector, means including
same potential relative to ground as that of the - a diode rectifier for automatic control of the
cathode of said first'vacuum tube when no input amplification of at least some of said vacuum
25 is applied to said radio receiver.
tubes, and means whereby one of said controlled
4. In a -radio receiver, a multi-stage high-fre - tubes acts additionally as a direct-current ampli
quency vacuum-tube amplifier. the last vacuum fier to increase the degree of control exerted upon '
vtube of which has its cathode in common with at least one other of said vacuum tubes by said
the cathode of a diode rectifier coupled to -the automatic control means.
.
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30 output of said amplifier, and means for automati
cally regulating the amplification of said ampli
fier in accordance with changes in the direct
current output of said diode rectifier, said means
including a direct-current connection between
7. In a radio receiver, plural high-frequency 30
amplifying 4tubes and a detector-rectifier, means
for automatic control of the amplification of at _
vleast some of said vacuum tubes, and means
whereby one of said controlled tubes acts addi
tionally as a direct-current amplifier to increase
the degree of control exerted upon at least one
tube of said amplifier;»a .connection between the .other of said vacuum tubes by said automatic _
cathode of said first vacuum tube and' the cath
control means. ode of said last vacuum tube; a connection in
8.'In a multi-stage amplifier, plural amplifying
40 cluding a first and a second resistor between the
vacuum tubes, means for automatic control of 40
cathode of said last vacuum tube and ground; a the amplification of at least some of said vacuum
connection between the junction of said first and tubes including a. rectifier coupled to the output
second resistors and the positive terminal of a of said amplifier, and means whereby one of said
third resistor in the output circuit of said diode controlled tubes, in the presence of an input sig
the anode of said diode rectifier and a control
electrode of at least a first and a second vacuum
_ rectifier; and means for maintaining the cathode
of said second vacuum tube at substantially the
same potential relative to ground as that of the
cathode of said first vacuum tube when no _input
voltage is applied to said radio receiver.
-50 _5. In a radio receiver, means for successively
delaying and increasing .the rang/,e of the amplifi
cation control `of a diode rectifier coupled to the
_nal to said amplifier exceeding a pre-determined
minimum value, acts additionally as a direct-cur
rent amplifier to increase the degree of control
exerted upon at least one other of said vacuum
tubes by said automatic control means.
ALFRED cRossLEY.
HERBERT E. MEINEMA.
45
50
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