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Патент USA US2133795

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Oct. 18, 1938.
L. E. BARTOLJ
j 2,133,795
INTERMEDIATE FREQUENCY AMPLIFIER
Filed July 28, 1934
17mg {£678,910 15 /17 L48
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Patented Oct. 18, 1938
2,133,795v
UNITED STATEd
PATENT OFFICE
2,133,795
INTERMEDIATE FREQUENCY AMPLIFIER
Loy E. Barton, Collingswood, N. J., assignor, by
mesne assignments, to Radio Corporation of
America, New York, N. Y., a corporation of
Delaware
Application July 28, 1934, Serial No. 737,357
12 Claims. (Cl. 250-20)
The present invention relates to high frequency the intermediate frequency ampli?er is provided
Cl
radio signal ampli?ers, and more particularly, it
relates to intermediate frequency ampli?ers for
superheterodyne radio receiving systems. The
invention has for its primary object to provide an
improved ?nal or output stage for a high fre
quency radio signal ampli?er such as an inter
for.
In a preferred embodiment of the invention, a
combined intermediate frequency ampli?er of the
pentode type, and detector of the diode recti?er
type, is provided as the output or ?nal stage of an
mediate frequency ampli?er.
intermediate frequency ampli?er which may be
used to drive directly an output power ampli?er
It is a further object of the present invention to
provide an output stage for an intermediate fre
quency ampli?er which is adapted to utilize a
ferred embodiment of the invention, is shown by 10
way of example in the accompanying drawing in
pentode electric discharge device having two ad
which
ditional diode anodes therein, as a combined inter
mediate frequency ampli?er and detector, and
15 means for providing automatic volume control
potentials.
It is a further object of the present invention
to provide separate automatic volume control po
tentials from two different sources, and in con
junction with the last stage of an intermediate
frequency ampli?er to provide ampli?ed auto
matic volume control potentials for preceding
tubes in the receiving system, and another auto
matic volume control potential for the last or
output stage of the intermediate frequency ampli
?er, directly.
stage. Such an arrangement, as the present pre
>
.
Figure 1 is a schematic circuit diagram of a
radio receiving system embodying the invention;
and
15
Fig. 2 is a similar circuit diagram showing a
modi?cation of a coupling means used in the cir-v
cuit of Fig. 1.
Referring to Fig. 1, 5 is a pentode type elec
tric discharge ampli?er device in the ?nal or out
put stage of an intermediate or high frequency
ampli?er for a radio receiving system‘, the signal
input circuits of which are indicated by the
block diagram 6. In a superheterodyne, this may
include the radio frequency ampli?er, ?rst de
tector, oscillator, and any intermediate frequency
It is a still further object of the invention to
ampli?er stages which precede the output stage.
provide a double diode pentode output stage for
an intermediate frequency ampli?er, wherein the
30 ampli?er portion of the pentode device is diode
cathode ‘I, a control grid 8, a screen grid 9, a
biased, that is, supplied with biasing potential
from the signal recti?er through one of the diodes,
and means providing initial negative bias on the
control grid of the pentode ampli?er, while a posi
35 tive or zero bias is provided on a diode-anode
utilized for detection in a conductively intercon
nected coupling network.
.
It is also an object of the present invention to
provide, with a single electric discharge device
40 of the multi-electrode type including ampli?er
and diode recti?er elements, a combined inter
mediate frequency and automatic volume control
ampli?er, a diode detector and a diode recti?er
AVC system.
In accordance with the invention, a coupling
45
system including the output stage, is providedbe
tween an intermediate frequency ampli?er and
an audio frequency ampli?er signal output stage,
which coupling system comprises a single electric
50 discharge device and circuit means in connection
therewith, whereby a signal sufficient to drive the
output audio frequency ampli?er stage effectively
is provided, while, at the same time, audio fre
The ampli?er device 5 is provided with a
suppressor grid I0, and an output anode I I, to- ,
gether with two diode plates or anodes I2 and
I3 associated with the cathode ‘I to provide there
with, a pair of diode recti?ers in the same en
velope with the pentode ampli?er elements.
The intermediate frequency ampli?er stage is
provided with a tuned input grid circuit I4 con
nected with the control grid 8 and a tuned out
put anode circuit I5 connected with the out
put anode II. The input and output circuits are
provided by the ‘tuned windings of suitable in 40
put and output coupling transformers I6 and II,
respectively, for the stage, the input transformer
I6 being utilized to couple the intermediate fre
quency ampli?er stage with the receiver 6.
The output transformer I1 is utilized to couple
the output circuit I5 to a diode recti?er circuit
I8 which includes the diode anode I2, the oath
ode ‘I, the tuned secondary I9 of the transformer.
I1, and a series circuit impedance in the form of
a resistor in two sections 20 and 2 I, connected be
tween the cathode and the low potential side of
the input coupling Winding I9, which connection
is shown in the present example, between the
quency detection and automatic volume control of
points A and B in the recti?er circuit.
the receiving system and of the output stage of
sistor or impedance 20-4 I is provided with ahigh 5.5
The re
2
2,133,795
frequency by-pass condenser 22 for intermediate
frequency currents.
r
‘ 5
.
'
T
~
point C and the common return lead 24. The tap
42 is adjustable to provide an initial bias on the
-
Modulated radio signals received in the circuit
M at intermediate frequency are applied to the
control grid 8 and ampli?ed to a high degree in
device 5, and are then applied to the diode
recti?er circuit I8 where the signals are demodu
lated or detected through the medium of the recti
?er device |2-‘|. The audio frequency and di
10 rect current components of the recti?ed signals
appear across the series impedance or resistor
20--2|.
The audio frequency or signal component is
utilized to drive an output ampli?er device 23
15 through a coupling network connected between
the point B which is the high audio frequency
potential point of the recti?er circuit, and a
common circuit return or ground lead 24.
The
coupling network in the present example includes
20 a tone-compensated, potentiometer, volume con
trol device 25 in series with which is a coupling
condenser 26, a ?lter resistor 21, and a second
?lter resistor 28.
The potentiometer device: has a variable vol
25 ume control contact 29 which is connected to the
control grid 30 of the output ampli?er device 23.
Signals ampli?ed therein are applied to a loud
speaker 3| through an output coupling trans
former 32.
Any suitable output coupling network may be
employed to apply the recti?ed signal or audio
frequency component to the output stage, al
though an impedance coupling network is at
control grid 8, that is, between the control grid
8 and the cathode ‘I, of any desired value such as
substantially 3 volts negative. The adjustment
of the potentiometer is not critical which per
mits the use of ?xed resistors for 40 and 4|. The
potential drop, it will be seen, is established
through the resistor sections 20, 40, and 4| and
the potential supplying the current through the 10
above namedsections is derived from the self
bias resistor 34 as the excess potential over that
established across the choke coil 35;
This, in the
present example, is initially substantially 40 volts,
that is to say, the point A is 40 volts more positive 15
than the point D. Current through the resistor
48 from the positive supply source also flows
through resistors 2|, 40, and 4|, thereby pro
viding potential across said last named resistors
20
and affecting the adjustment of the contact 42.
It will be seen also, that as recti?ed signal
current ?ows in the recti?er circuit l8 and
through the impedance section 20 an increasing
negative bias potential with respect to the oath
ode '| will be placed upon the control grid 8. 25
This results in a reduction of the anode cur
rent and of the potential across the self bias
resistor 34. This may continue until the po
tential across the resistor 34 falls to a value equal
to or less than the potential across the imped
ance 35. Stated in other words, the point A may
become equal in potential to or more negative
than the point D.
‘
present preferred, including the series poten
In such case, the ?xed potential across the
36 tiometer device and blocking or coupling con
impedance 35 predominates and causes current
to flow in an automatic volume control circuit
44 comprising the second diode anode I3 and a
series impedance element 45 to which the com
denser 26.
Between the point A and the common circuit
return lead 24, a self bias resistor 34 providing a
source of variable potential is connected in series
with a source of substantially ?xed potential.
The ?xed potential source is provided in the pres
ent example, by a choke coil or impedance device
35 forming part of a bleeder or voltage supply
means between positive and negative direct our
rent supply terminals 36 and 31. The remainder
of the voltage supply means is provided by a‘ re
sistor section 38, and the common circuit return
lead 24 is connected to a terminal D between the
impedances 35 and 38. A suitable audio and
50 radio frequency by-pass condenser 39 is provided
in parallel with the series connected impedances
34 and 35..
'
The voltage supply‘ arrangement is such that
the potential across the choke coil or impedance
35 is in opposition to the potential established
in the self bias resistor 34. Normally, with no
signal, in a circuit of the character shown, and
with an RCA 2B7 tube utilized as the device 5,
about 150 volts may be provided by the impedance
60 device 35 and substantially 190 volts by the re
sistor 34, the latter having a resistance of about
40,000 ohms.
'
Initial bias potential for the control grid 8 is
‘derived from the opposing sources 34 and 35,
65 through a tap connection G between the sections
20 and 2| of the series diode circuit impedances
and a potentiometer device connected therefrom
to the common circuit return lead 24. The po
tentiometer device comprises two impedance sec
70 tions 40 and 4| between which is connected a
movable tap 42 having a circuit connection with
the input circuit I 4 and the control grid 8
through a bias potential supply lead 43.
F7,5
It will be seen that the present connection
provides a series circuit in shunt between the
mon circuit return lead 24 is connected at one
end 46 and to which automatic volume control 40
leads 4‘! are connected for supplying variable
biasing potentials to the preceding circuits (not
shown) in the receiver 6.
The double diode pentode device therefore may
supply delayed automatic volume control po 45
tentials, the potentials being derived through the
second diode anode and a suitable diode circuit
impedance device for coupling to the preceding
receiver circuits. Since this type of automatic
volume control system per se, is not part of
the present invention and is described and
claimed in my copending application Serial No.
640,946, ?led November 3, 1932, and assigned
to Radio Corporation of America, further de
scription is believed to be unnecessary.
Suitable values for the resistor sections which i
have been found to be satisfactory are as fol
lows: section 20-03 megohm; section 40—2
megohms; section 4l-—5 to 10 megohms. Other
suitable values may, however, be used for the V60
various impedance or resistor sections to provide
any desired potentials for the operation of the
device 5 as a variable grid bias, variable anode
current, signal and automatic volume control
ampli?er. It will further be seen that the device 265
5 is controlled directly by the AVG potential de
rived from the impedance 20 so that in effect it .
becomes a self controlled automatic volume con
trol intermediate frequency ampli?er and an
ampli?er for automatic volume control poten
tials applied to the preceding circuits of the
receiver through a second diode circuit.
Furthermore, the additional biasing potential
is derived from the signal current recti?ed by
the diode |2—-'| so that the ampli?er is of the
70
3
2,133,795
diode-‘biased type. At the same time there is
provided a ?xed initial bias which is effec
tive to bias the ampli?er when the signal cur
tion with an ‘input signal‘ of a predetermined
rent is zero or in the absence of an appreciable
the potentiometer or tapped resistance connec
tion 40-4! with the point C to the'common cir
cuit return lead 24 is necessary in order that
the control grid 8 may receive an initial po
tential which, otherwise, in the absence of a
signal, would be zero. This is for the reason
received signal.
It will be seen that the detector or rectifier
circuit I8 is connected with the cathode and
with the control grid 8 in a conductive network.
This circuit arrangement tends to provide a
ll) negative potential on the detector diode anode
I2 with respect to the cathode because of the
initial potential drop in the impedance section 20
of the network. This would normally provide a
delay in detection which is not desired in the
circuit of the present example. Accordingly, a
positive potential with respect to cathode is ap
plied to the diode anode l2 through a variable
control impedance 48 connected between the
point B on the diode recti?er or detector circuit
and a source of positive potential such as the
anode circuit [5 for the device 5. The positive
connections indicated in the diagram are made
to the terminal 36 or any other suitable point
of connection on the resistor 38. These con
nections are omitted in the diagram for the pur
pose of simplifying the same.
In the present
example, the resistor 48 may be of a value of 5 to
10 megohms and is reduced in resistance value
until the potential at point B is substantially
equal to that at point A or is preferably some~
what positive so that the diode anode i2 is at
substantially zero potential or positive with re
. spect to the cathode ‘I.
This connection also provides means for reduc
ing the distortion in the diode recti?er when
connected to the succeeding stage through im
pedance coupling means as shown. This is for
the reason that an increasing positive poten
tial may be placed upon the detector anode to
40 cause an initial flow of current in the recti?er
circuit as described and claimed in my copending
application, Serial No. 695,555, ?led October 28,
1933, Patent No. 2,078,994, issued May ll, 1937,
and assigned to Radio Corporation of America.
45
It will be seen that the detector circuit is
arranged to receive the signal output from the
pentode ampli?er portion of the device 5. With
maximum signal input the signal voltage may
reach a peak of 150 volts on the diode I2 pro
vided that an ef?cient coupling means is em
ployed between the pentode output circuit [5
and the detector or recti?er circuit I8.
In the
present example,,an intermediate frequency cou
pling transformer having tuned primary and
secondary windings is shown. The coupling may,
however, be provided by other means such as
combined capacity and magnetic means as indi
cated in Fig. 2 to which attention is now di
rected.
60
It will be seen that in the diode recti?er cir
cuit I8 is provided with a tuned inductance 5!}
while the output anode circuit I5 is provided with‘
a similar inductance 5!, which provide windings
_ which are loosely magnetically coupled.
The
electrical coupling between the circuits i5 and I8
is completed through a direct capacity coupling
means or condenser 52, preferably between the
high potential ends of the inductances, so that
70 combined magnetic and capacity coupling is pro
vided in such proportions that a relatively strong
signal is applied to the detector diode. The pre
ferred receiver arrangement is such that the
maximum output swing on the detector diode
may be obtained at about 30 to 50% modula
value.
"
‘
‘
Referring again to Fig. 1, it will be seen that
that with no signal, the recti?ed signal current 10
in the detector circuit I8 is zero.
To cause an
initial potential on the grid 8, in the absence
of signals, the network 20, 4|], and M is pro
vided across the potential source between points
A and D.
1.5
From the foregoing description, it will be seen
that the coupling network, provided between the
cathode, control grid and the diode plates of a
double diode pentode device is conductive. The
network comprises a pair of series connected 20
impedance elements 2|] and 2| preferably re
sistors, in the diode recti?er or detector circuit,
the anode end or terminal (A) of which is con
nected to a common circuit return lead, through
a self bias resistor and means providing a ?xed v25
source of potential, and the diode anode end or
terminal (B) of which is connected to said com
mon circuit return lead through an impedance
coupling network providing a variable output
connection for an audio frequency ampli?er 30
stage for the receiving circuit substantially in
shunt to the detector output circuit impedance
2D-—2l.
Intermediate between the ends of the detector
circuit impedance 20—2l, a tap C is provided be 35
tween the sections, providing a direct current
path from the tap point C to the common circuit
return lead 24, which may be the ground or
chassis return circuit.
‘
By utilizing a circuit embodying the invention
as described in connection with the present ex
ample, ampli?ed automatic volume control po
tentials may be obtained from the output stage
of an intermediate frequency ampli?er which,
at the same time, provides detection or demodu- 1+
lation of the signal and diode automatic volume
control of the intermediate frequency output
stage directly, all in conjunction with one elec
tric discharge device of the double diode pentode
type, such as an RCA 2137 tube.
Such a system, therefore, provides for the re
duction in the number of tubes employed in the
receiver without sacri?cing the gain and con
trol functions including bias and plate potential V
supply from a common source, as is desirable
in a receiver for good quality of reception. The
present system provides a relatively high value
of signal potential from the pentode amplifier
section, and is adapted to provide a relatively
high signal output to the output stage, while the
operation of the automatic volume control is
reduced to preferred or desirable limits by suit
able tapping-in on the network between the de
tector diode anode and the cathode. The re
sistor sections 4i and 43 are then provided to
establish a desired initial potential on the con
trol grid of the ampli?er and the resistor 48 is
provided to control the potential on the detector
diode anode whereby the network is balanced for
the reception of signals and for the effective con
trol of the receiving system in response to signals.
I claim as my invention:
.
1. In a signal ampli?er stage, the combination
with an electric discharge ampli?er device hav
ing a cathode, a diode anode associated there
to
4
2,133,795
with to provide a recti?er, and a control grid,
of a conductive coupling impedance circuit net-1
work interconnecting said anode, cathode and
control grid to supply to said control grid a. por
tion of the recti?ed signal as a biasing potential
from said recti?er, means for applying an initial
impedance element for applying signal variable
biasing potential to said control grid from said
negative biasing potential to said control grid
between the cathode and ground, and a poten
tiometer resistance in circuit therewith in said
last named connection between the signal input
circuit and said impedance element for impress
ing an initial negative biasing potential on said
through a portion of said network, and means
connected in circuit with said anode for pre
10 venting the application of said negative potential
thereto.
'
recti?er circuit, said diode anode, cathode, and
control grid being thereby conductively con
nected together, means including a source of
?xed potential and a self bias resistor in series
2. In a signal ampli?er stage, the combination
control grid, and separate means for impressing
with an electric discharge ampli?er device hav
ing a cathode, a diode anode associated there
15 with to provide a recti?er, and a control grid
of a conductive impedance circuit network inter
an initial positive potential on said diode anode.
connecting said anode, cathode and control grid
to supply to said control grid, a signal controlled
biasing potential from said recti?er, means for
20 applying an initial negative biasing potential to
said control grid through a portion of said net
work, and means connected in circuit with said
anode for preventing the application of said
negative potential thereto, said conductive net
25 work including a series resistance element in
circuit between the anode and the cathode, a
shunt resistance element connected between a
tap on said series resistance element and a po
tential supply point in said network more nega
30 tive than said cathode, and said grid being con
' 6. A radio signal receiving system in accord
ance with claim 5 further characterized by the 15
fact that the control grid is connected to a tap
point on said series impedance element between
the terminal ends thereof and an impedance
coupling element is connected in circuit with a
terminal end of said impedance element more 20
adjacent to the diode anode.
'7. A radio signal receiving circuit in accord
ance with claim 5 further characterized by the
fact that a signal variable source of potential
is connected in circuit with said impedance ele 25
ment more adjacent to the cathode, an imped
ance coupling element is connected in circuit
with said ?rst named impedance element more
adjacent to the diode anode, and the control grid
is connected to an intermediate potential point
nected with a tap on said last named shunt
with respect to said connections on said imped
resistance element.
ance element.
3. In a radio signal receiving system the com
bination with an electric discharge ampli?er de
35 vice having a cathode, a control grid, and at
least two diode anode electrodes associated with
the cathode, of a recti?er circuit including a con
ductive impedance coupling network between
said elements, means for maintaining said con
trol grid initially negative and one of said anodes
initially positive with respect to said cathode,
and means for maintaining one of said anodes
more positive than the other of said anodes with
respect to said cathode.
4. In a radio signal receiving system, the com
45
bination' with an electric discharge ampli?er de
vice having a cathode, a control grid, and a di
.
8. In a radio signal receiving system, the com
bination with an electric discharge ampli?er de
vice having a cathode, a control grid, an output 35
anode, and a diode recti?er anode associated
with the cathode, of a signal input circuit con
nected with said control grid, a second signal
input circuit- coupled to the output anode and
connected between said diode anode and the
cathode, said last named circuit including a po
tential drop producing impedance element con
nected adjacent to the cathode, means providing
an intermediate tap connection between the
signal input circuit and said impedance element
for applying signal variable biasing potential to
said control grid from said recti?er circuit, said
ode anode electrode associated with the cathode,
last named means including a portion of a sec
of means providing an electrical impedance cou
ond impedance element connected between said
tap and ground for said system, said diode an
ode, cathode and control grid being thereby con
ductively connected together, means for impress
ing an initial negative biasing potential on said
control grid and separate means for impressing
50 pling network conductively coupling said elec
trodes for the flow of direct current and includ
ing a resistance element and a signal input cou
pling means between said anode and cathode,
said control grid being connected with a point
55 intermediate the ends of said resistance element,
means for maintaining the anode and cathode at
substantially the same positive potential with
, respect to ground in the absence of signals, and
means in circuit with said grid for maintaining
60 said grid initially negative with respect to said
an initial positive potential on said diode anode. ,
9. In a radio signal receiving system, the com
bination with an electric discharge ampli?er
device having a cathode, a control grid, an out
put anode, and a detector diode anode associated
with the cathode, of a detector circuit connected
between the detector anode and the cathode, and
cathode, and means for causing said grid poten
tial to vary in response to and under control of ‘including at least two resistor elements in series
recti?ed signal currents ?owing in said resistance adjacent to the cathode, means connected in said
detector circuit between the detector diode an
element.
ode and the resistor elements providing electri 65
5. In a radio signal receiving system, the com
65
cal coupling with the output anode, a signal in
bination with an electric discharge ampli?er de
vice having a cathode, a control grid, an output put circuit connected between said control grid
anode, and a diode recti?er anode associated with and a point intermediate said resistance elements,
the cathode, of a signal input circuit connected said control grid, cathode, and detector diode
anode being thereby conductively connected to
70 with said control grid, a signal transmission cir
cuit connected between said diode anode, and the gether, means providing a common circuit re
cathode, and including an impedance element turn lead for said system, a self bias resistor and
a source of ?xed potential in series between the
adjacent to the cathode, said circuit being cou
cathode and said return lead, the positive ter
pled to the output anode, means providing a con
75 nection betweenthe ‘signal input circuit and said minal of said ?xed source being connected with 75
70'
2,133,795
5
said return lead, a resistor in circuit with said
11. In an intermediate frequency ampli?er a
control grid adjacent to the connection between
?nal ampli?er stage comprising an electric dis
charge device having a cathode, a control grid,
said series resistance elements, a second resistor
in series therewith between the control grid end
of said ?rst resistor and the common return lead,
and means for impressing a positive potential on
said detector diode anode connected with said
detector circuit between said series resistance ele
ments and said coupling means.
10. In a radio signal receiving system the com
10
bination with an electric discharge ampli?er de
vice having a cathode, a control grid, an output
anode, and a detector, and a diode anode asso
ciated with the cathode, of a detector circuit
connected between the detector anode and the
cathode and including at least one resistor ele
ment connected adjacent to the cathode, means
connected in said detector circuit between the
detector diode anode and the resistor elements
providing electrical coupling with the output an
ode, a signal input circuit connected between said
control grid and a point on said resistance ele
ment, said control grid, cathode, and detector di
ode anode being thereby conductively connected
25 together, a common circuit return lead, a self
bias resistor and a source of ?xed potential in
series between the cathode and said return lead,
the positive terminal of said ?xed source being
connected with said return lead, and a resistor
in circuit with said control grid, said resistor
being connected between said point of connec
tion for said input circuit with the resistance ele
ment and said return lead.
a screen grid, a suppressor grid, an output anode
and two separate diode anodes associated with
the cathode, a self-bias resistor in circuit with
the cathode, a ?lter choke coil between the self
bias resistor and the control grid providing a
potential in opposition to that provided by the
self-bias resistor, and a diode recti?er associated 10
with the cathode and interconnected by conduc
tive connection with the control grid, and means
in said conductive connection for preventing the
application of a biasing potential to the control
grid from being applied to the diode anode.
12. In a superheterodyne receiver a combined
intermediate frequency ampli?er and detector
stage comprising an electric discharge ampli?er
device having a signal grid, a cathode and an
auxiliary anode adjacent to the cathode pro 20
viding a diode recti?er, means forimpressing in
termediate frequency signals on said diode rec
ti?er, a diode output impedance in circuit with
said recti?er having an intermediate tap there
on, means for applying a positive potential to 25
said tap including a series connected poten
tiometer resistor connected at one end with said
tap, and means providing a variable tap connec
tion for said signal grid on said potentiometer
resistor.
LOY E. BARTON.
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