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Патент USA US2135599

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Nov. 8, i938.
H. o. PETERSON
2,135,599
AUTOMATIC VOLUME CONTROL CIRCUIT
Filed Sept. 14, 1935
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INVENTOR
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HAROLD o. PETERSON
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QMW
ATTO R N EY
Patented Nov. 8, 1938
2,135,599
UNITED STATES PATENT OFFICE
, v
2,135,599
AUTOMATIC VOLUME CONTROL CIRCUIT
Harold 0. Peterson, Riverhead, N. Y., assignor to
Radio Corporation of America, a corporation of
Delaware‘
Application September 14, 1935, Serial No. 40,568
5 Claims.
My present invention relates, in general to
automatic gain regulation circuits adapted for
use in connection with signal ampli?ers and radio
receivers, and more particularly the invention
5 relates to automatic volume control ‘circuits uti
lizing diodes as signal detectors and gain control
devices.
Diode recti?ers are often utilized at the present
time as signal demodulators of radio receiving
'10 systems. Such .diode‘ devices are, also, suitable
for use as signal recti?ers in connection with
automatic volume control circuits in order to
maintain a substantially constant signal ampli
tude at the demodulator input circuit. In the
15 ‘past a common diode device has been used both
for the signal detection and automatic volume
control recti?er functions. However, many of
these past devices have been constructed so as
torequire the diode anode to be maintained nor
20 - mally at a negative direct current potential with
respect to the cathodes of the signal transmis
2
sion tubes whose gain was under control.
According to one of the main objects of my
present invention, a diode recti?er device is uti
lized'to demodulate the received signal, and si
dicated diagrammatically a circuit organization
whereby my invention may be carried into effect.
Referring now to the accompanying drawing,
which shows the present invention embodied in a
receiver of conventional construction, it will be
observed that the numeral I designates a signal
collector device. This device may be the usual
grounded antenna, or it may be a loop antenna;
dipole or even a radio frequency signal distribu
tion line. The collected signals, which signals 10
may be in the broadcast range or any of the short ,
wave ranges, are impressed on the tunable input
circuit 2 of the radio frequency ampli?er tube 3.
The tube 3, shown as a screen grid tube of the
indirectly heated cathode type, has its cathode 4 15
grounded, and it will be understood that the
screen grid and plate of the tube are connected
to suitable sources of positive direct current po
tentials. Such sources are not shown, but those
skilled in the art are-fully aware of the fact that 20
these sources may be of the battery type; or they
may be embodied in the usual bleeder resistor
connected across the ?lter output of a 60 cycle
alternating current recti?er.
' A grounded electrostatic shield 5 is shown dis
multaneously to rectify signal energy for the
posed between the signal collector l and the input
production of a gain control voltage which is used
to decrease the gain of the signal ampli?ers as
coil of the tunable circuit 2, and it will be under~
stood that the numeral 6 designates a tuning
device which is used to tune the radio receiver
the received signal amplitude increases, the diode
at =
(Cl. 250-20)
25
anode being normally maintained at a potential
through the desired operating frequency range.
which does not becomenegative, and which spe
ci?cally is positive, in direct current potential
with respect to the cathodes of the controlled
The signal demodulator, or detector, is a triode
of the indirectly heated cathode type, which may
be, for example, a tube of the 37 type, and is des
ignated by the numeral 1. To provide a diode
detector device the grid and plate of tube 1 are 35
tubes.
,
Another important object of the present in
vention may be said to reside in the provision of
a'radio receiving system wherein a signal trans
mission tube has its normal negative grid bias
provided by the conjoint and opposing action of
40‘ negative and positive direct current voltage
sources, and wherein the normal negative grid
bias is increased, as the rec-eived'signal amplitude
increases, by a diode signal recti?er whose anode
is normally maintained positive with respect to
45 the cathode of the controlled tube.
Still other objects of the invention are to im
prove generally the simplicity and [efficiency of
radio receivers utilizing automatic volume con
trol, and more especially to provide such radio
50 receivers with diode signal detectors in such a
manner that the receivers are not only reliable
and efficient in operation, but economically
manufactured and assembled.
The novel features which I believe to be char
55 acteristic of my invention are set forth in par
ticularity in the appended claims; the invention
itself, however, as to both its organization and
method of operation will best be understood by
reference to the following description taken in
60. connection withthe drawing in which I have in
strapped together, and the resulting diode out
put electrode is connected to the cathode 8
through a path which includes the signal input
coil 9, the coil ID, the condenser ll, resistor R2
and the visual indicating meter, or milliammeter 40
l2. The condenser l3, connected between the
high alternating potential side of coil 9 and
ground, tunes coil 9 to the operating signal fre
quency which is to be detected. A heating bat
tery A is connected across the heater element 14 45
of diode 1, and the positive terminal of the heat
ing source A is connected to the ungrounded side
of resistor R2 through the choke coil l5, which,
of course, has ?nite resistance.
The audio frequency utilizing network, which 50
may comprise one or more stages of audio fre
quency ampli?cation followed by a reproducer or
other signal indicator, has impressed upon it
the demodulated signal energy through a path
which includes the audio frequency transformer 55
[6. The primary winding ll of transformer 16
has one side thereof connected to the junction
of coils 9 and ID through a path which includes
coil l8. The resistor R6 is connected in shunt
with winding H, the condenser (9 being con 60
2,135,599
' 2
nected in series with winding I ‘I and resistor R6.
The by-pass condenser 20 connects the resistor
side of coil l8 to ground, and the side of resistor
R6 adjacent condenser 19 is connected to ground
through a path which includes resistor R4 and
resistor R5.
may be applied to any of the additional signal
transmission tubes preceding theg?nal signal de
modulator. Thos'eskilled in the. art will, in gen
eral, understand the operation of the automatic
volume control arrangement shown herein. Nor
The junction of resistors R4 and R5- 4 mally,'and in the absence of received signals, the
is connected to the positive terminal of heating automatic volume control arrangement is not
source A through a path which includes resistor "functioning. ‘When the desired signals are re
R1 and lead 2|. Coil l0 and condenser I l resonate - ceived, the AVG network begins to increase the
10 to the frequency of the carrier being recti?ed
negative biason the signal grid 4’. As the signal 10
by the detector, This affords a low impedance amplitude increasesfthe gain control bias in
path for the carrier frequency. The resistance Re I creases, and'in‘this way the gain of the signal
is low compared to the primary impedance of ‘transmission tube 3 is decreased. In other words,
transformer l6. Consequently, the alternating duringperiods when no signals are received the
15 and direct current impedances of the diode load
circuit are substantially equal. This is a desirable
condition for diode operation when signalshaving
nearly 100% modulation are received. _
The gain control direct current voltage derived
20 from the recti?ed signal energy is impressed upon
the signal input grid 4’ of ampli?er 3 through
a path which includes the ?lter resistor R3 and
lead 22. The lead 22 is denoted by the reference
4 letters AVC to designate that this is the auto
25 matic volume control circuit, and the network
comprising resistor R3 and condenser 23 functions
to suppress ?uctuating current components in
the gain control voltage.v
30"
’
‘
gain of the signal transmission tube 3 is a maxi 15
mum, and the receiver is in a highly sensitive
condition. The cold electrode of the diode de
tector ‘! is maintained normally;that is to say in
the absence of desired signals, at a positive po
tential with'respect to the grounded cathode 4'.
This positive potential may be, for example, of.
the order of 0.47 volt, and is supplied from the
positive terminal of the heating’ source-A. The
latter has a voltage of about 6 volts. This heat
ing source not only supplies heating current to‘
the ?lament of the detector 1, but, also, impresses
a potential-across the resistors R1 and R2. The
approximate voltages at the'ungrounded sideof'
,
Signal energy is impressed between the signal
grid 4' and cathode‘ 4 of ampli?er V3’by virtue
of’ the connection of the signal grid 4' to the
high alternatingpotential side of input circuit
2, and the signal byepass condenser 3’ connected
between the low alternating potential side of in
353 put circuit 2 and ground. The desired signal
energy-is transmitted to the tuned input‘circuit
9 of the diode demodulator I through the signal
transmission network generally denoted by the
numeral 30. Thisnetwork 30 may comprise one,
or more, additional stagesv oftunable radio fre-,
quency ampli?cation. In such case the tuning
condenser 6, thetuning condenser l3, and the
tuning condensers of the additional transmission
stages may all be uni-controlled in the'wellknown
451; manner so that allsignal stages are simultane
resistor R2, and at the junction ‘of resistors R1
and Rs'are shown in the drawing? Thus, the 30"
junction of resistors R1 and 1251s at approximately
0.5 volt, and the ungrounded side of resistor R2
is at a potential of 1.5 volts. There is consider
able voltagev drop across coil l5 due to its re
' sistance.
Asa consequence of these potential relations,
the AVG action does not, in the absence of desired
signals’, maintain the signal grid 4' highly nega
tive’;' on the other’ hand, it maintains the signal
grid!’ at a relatively small negative potential
with respect to‘ the grounded cathode 4, and rather
close to zeroidirect current potential, with there
sult‘that during periods ofitim'e'when‘no signals
are impressed upon‘the collector 'Lthe signal
ampli?ers are in condition to produce maximum
ampli?cation of the received signals. This fol
ously tuned to a desired signal frequency. .
The receiver may be of the superheterodyne.
type. In such a case the network 30 may com
prise additional signal frequency ampli?er stages,
50 followed‘ by the usual ?rst detector and local
oscillator circuits for the production of a de
sired intermediate, frequency. The ?rst, detector
lows by virtue of the fact that the cold electrode
of the diode »'| is normally maintained at a posi-'-'
tive potential with respect to the grounded oath-'
ode 4.
'
'
'
503
That is to say, while the junction point of re:
sistors R1 and Rs'is at approximately +0.5 volt,
output will be followed by one, or more, stages the signal grids of the controlled ampli?ers are
of intermediate frequency ampli?cation, A sec-' not positive by'this amount, but in fact are at a
55 ond converter can beused to change the ?rst small negative potential with respect to the
I. F. (say 300 kc.) to a second I. F. (say 50 kc), grounded ‘cathodes of the controlled signal trans
and the latter will be ampli?ed before detection. mission tubes. This is explained by the fact that
In that case the demodulator 1 functions at inf when the cathodes of the signal transmission
termediate frequency; Of course, the condenser tubes are heated to an electron emitting condi
l3 in the case where the receiving system is of the tion, electrons leave the cathodes at such high
superheterodyne type is ?xed in value to tune velocities that they impinge upon the signal con
a the input circuit of the detector to the desired trol grids adjacent them. This causes a certain
intermediate frequency. Reference is made to amount of recti?cation action, the recti?ed grid‘ 7
so
the application'of J .~B. Moore, ?led December 8,
1933, and having application Serial No. 701,435,
Patent No. 2,078,769, April 27, 1937, which shows
a radio receiving system of the superheterodyne
type with‘ which an automatic volume control
“ arrangement of the present type may be em
ployed.
~
While the present circuit diagram shows the
AVG voltage applied to only‘ one of the signal
transmission tubes of the receiving system, it will
be clearly understood that the gain control biasv
currents flowing through the path including re
sistors R3, R4, R5 and then to ground. Normally,
this recti?ed grid ‘current would maintain the
signal grids of the controlled transmission tubes
at a negative potential with respect to- their
cathodes in the absence of received signals. This
negative potential is reduced very slightly'b'y the 70
opposition of ‘the positive voltage of 0.5 volt ex
isting at the junction of resistors R1 and B5.
In this condition the control grid bias of these
tubes assumes a value between _0.5 and -1‘.2
volts.- This assumed bias happens to be of a value 75
2,135,599
at which these tubes have approximately maxi
mum gain.‘ As received signal strength is in
creased irom zero, the junction of resistors R6
and R4 decreases in positive potential, goes
through zero potential, and then increases in neg
ative potential. The bias of the controlled tubes
is practically unchanged until the potential of
the junction of Re and R4 reaches a negative value
61
equal to the negative value assumed by those grids
in the no-signal condition. As the signal strength
is further increased the grid bias of the con
trolled tubes will be the same negative potential
, as that of junction Re and R4 since for such in
creasingly negative values, no current will be
drawn by the grids of the controlled tubes. From
this point on, the gain is progressively decreased
as the signal amplitude increases. In this way
the signal amplitude at the input circuit of de
tector l is maintained substantially uniform in
spite of a wide range of signal amplitude variation
at the collector I. It will be recognized that the
action described above is a form of delayed AVC.
The junction of resistors R6 and R4 is at positive
potential for zero signal; and is at a negative
potential for signals of such strength that the di
rect current voltage drop in R4 is greater than the
?xed bias on R5. R3 is normally between ten
times and one hundred times as great as R4 and
R5.
Also R3 is great compared to the internal
30 resistance between grid and cathode of the con
trolled ampli?er tubes when the grids are oper
ated at potentials such that grid current ?ows.
For this reason the grids of the controlled stages
V21 C11
become less negative only very slightly for
changes in the potential of the junction of R6
and R4 as long as the potential of this junction is
such that grid current will ?ow through R3. As
soon as this junction becomes suf?ciently negative
so that no grid current ?ows through R3 there
40 is no potential drop in R3, and, consequently,
from then on to much more negative Values of the
3
to the grid of said transmission tube in a sense
such that the said normal negative grid bias is
increased as the received signal amplitude in
creases.
2. A radio receiving system including a con
trolled electronic transmission stage, a diode de
tector with its anode and cathode both normally
at positive potentials with respect to the cathode
of the controlled electronic transmission stage, a
load circuit and network connected to the diode
so as to obtain modulation frequency output as
Well as direct current output, the direct current
output being connected in series with a ?xed
source of positive direct current potential and a
series resistor between the grid of the con
trolled electronic transmission stage and the
cathode of the latter whereby the grid of said
stage will normally assume a substantially con
stant potential negative with respect to the oath
ode of said stage until the received signal reaches
such a value that the negative direct current out
put of the diode exceeds the above mentioned
series ?xed source of positive potential.
3. In a signaling system having at least one
signal transmission tube, a diode, means for nor- a,
mally establishing the anode and cathode of the
diode at positive potentials with respect to the
transmission tube cathode, means for deriving
from'the recti?ed output of the diode a direct
current voltage, means including a source of 30
substantially constant positive potential and a
source of negative potential in circuit with the
transmission tube grid circuit for establishing a
normal negative bias on said transmission tube,
said direct voltage deriving means being con
nected to the transmission tube grid circuit in
such a manner that said normal negative bias
value is increased when the magnitude of the
derived voltage exceeds that of the positive poten
tial.
4. In combination with a signal transmission
40
junction it will be found that the grids have the
tube, means including opposed positive and nega
same potential as the junction of Re and R4.
tive direct current voltage sources for establish
ing a normal negative bias on the signal input
electrode of said transmission tube with respect 45
to the cathode thereof, said sources being inde
pendent, and the negative source comprising a
network included in circuit with said input elec
trode and through which network current ?ows
for signals below a predetermined amplitude, a
The voltage supplied at the junction of coil l5
and R2 could be supplied by a tap on a bleeder
resistance across a recti?er output deriving
power from the main supply. Likewise, the usual
alternating current power supply bleeder resistor
may be used to supply the positive potential in
dicated at the junction of R1 and R5.
While I have indicated and described a system
for carrying my invention into effect, it will be
apparent to one skilled in the art that my inven
tion is by no means limited to the particular or
55 ganization shown and described, but that many
modi?cations may be made without departing
from the scope of my invention,-as set forth in
the appended claims.
What I claim is:
1. A radio receiving system of the type includ
ing a signal transmission tube followed by a sig
nal recti?er of the diode type, means for estab
lishing a normal negative grid bias for said trans
60'
mission tube by the conjoint and opposing action
of'indep'endent negative and positive direct cur
rent voltage sources, said negative voltage source
comprising a circuit in the grid circuit of the
transmission tube and through which grid cur
rent ?ows in the absence of signals of a desired
70 amplitude, means for preventing the recti?er
anode from assuming a direct current potential
which is negative with respect to the cathode of
said transmission tube, and means for applying
the direct current voltage output of said recti?er
diode signal recti?er, means electrically associat~
ed with the?rst said means for preventing the
diode anode from assuming a negative potential
with respect to the transmission tube cathode,
and additional means for applying the direct cur
rent voltage output of said recti?er to the input
50
55
electrode of said transmission tube in a sense to
increase said normal negative bias as signal am
plitude increases.
5. In combination with a signal ampli?er of a 60
radio receiving tube, a diode recti?er for the out
put of said signal ampli?er, means coupled to said
recti?er for utilizing the modulation component
of the recti?er output, means for deriving a direct
current voltage from the recti?ed output of said
recti?er, means for normally maintaining the 65
diode anode and cathode at a direct current po
tential which is positive with respect to the oath
ode of said ampli?er, and additional means for
applying said direct current voltage output of the
recti?er to the input electrodes of said ampli?er
in a sense to decrease the gain of the ampli?er as
the received signal amplitude increases.
HAROLD O. PETERSON.
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