July 26, 1932.
1,869,331
S. BALLANTINE
AUTOMATIC CONTROL FOR AUDION AMPLIFIERS
Filed Nov. 5. 1927
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Patented July 26, 1932
1,869,331
UNITED sTATEs PATENT OFFICE"
STUABT IBAQLLANTINE, OF MOUNTAIN LAKES, NEW JERSEY, AÉSIGNOB T0 BOONNN
RESEARCH CORPORATION, 0F BOONTON, NEW JERSEY, A CORPORATION OF NEW
JERSEY
AUTOMATIC CONTROL FOR AUDION AMPLIFIEBS
Application ñled November 5, 1987. Serial No. 231,878.
REISSUED
This invention relates to an automatic fading in radio transmission by varying the
control for audion amplifiers, and more par amplification of the radio frequency ampli
ticularly to control methods and apparatus fier of a receiver in accordance with varia
for automatically maintaining the output tion of the input signal energy.
of an amplifier constant in the presence of
These and other objects of the invention
variations in the carrier Wave energy im will be apparent from the following speci 65.
pressed upon the input system of the am
plifier.
fication when taken with the accompanying
drawings in which
.
In the reception of radio signals, varia
Figs. 1, 2 and 3 are schematic views illus
tions in the electric field acting upon the col-. trating generic forms of the invention,
lector of the radio receiver arise from natu
Figs. 4, 5, 6 and 7 are dia ams showin
ral and fortuitous causes and are commonly certain characteristics of au ion tubes, an
called “fading”. Such variations are-natu
rally not amenable to control and the irreg
ular variation in the strength of the output
is very undesirable in broadcast telephone
reception and in other communications.
Similarly, in the transmission of signals over
Figs. 8, 9, 10, 11 and 12 are electrical dia
grams of amplifier circuits embodying the
invention.
In the drawings, Figs. 1, 2 and 3 are sche
matic diagrams representlng the invention
as embodied in apparatus for receiving the
land lines by means of carrier Waves, varia usual modulated carrier waves employed in
tion in the attenuation may cause marked radio broadcasting.
, 70
changes in the carrier Wave ener y which is
In Fig. 1, a conventional radio receiver is
impressed upon the amplifiers o the trans represented by the radio frequency ampli
mission line.
30
'
fier l, the detector 2 and audio amplifier 3.
In accordance with the present invention, The auxiliary system which provides an au
fluctuations in the output are suppressed or tomatic control consists generally of a radio
eliminated by automatically var ing the rate frequency amplifier 4, a rectifier 5 and a di
of amplification of the radio requency or rect current amplifier 6. The auxiliary sys~
carrier wave amplifiers in such a. way that, tem is in shunt with the receiver across the
as the signal strength increases, the ampli antenna and receives a portion of the incom
fication is reduced in amount sufficient to‘ ing carrier-Wave energy, from which is de~
maintain a constant out ut.
35
rived a direct current potential which is im
In the following speci cation and claims, pressed as a grid bias upon the radio ampli
the term “signal strength” has reference to lier 1 through the connect-ion 7.
,
the significant input energy which, in the
The use of a separate radio frequenc am
usual carrier wave systems of wired and plilier 4 and also of the auxiliary rectifier 5
1s not essential as the radio amplifier 1 of the
wireless transmission of signals, isthe car
'rier wave itself.
receiver and the detector 2 can be arranged
An object of the invention is to provide a to perform the functions of the corres ond~
40
method of and apparatus for automatically ing auxiliary elements, proper means ing
varying the amplification rate of an audion provided to filter out -alternating current
amplifier to suppress fluctuations in out ut components before impressing the output
due to variations in input energy. Furt er ‘jupon the direct current amplifier or upon
objects are to provide methods of and ap the grids ofthe radio frequency amplifiers.
50
paratus for suppressing fluctuations in the The resultant reduction in the parts required
output of an audion amplifier by automati -for the auxiliary system is of considerable
cally varying the grid bias of one or more economic advantage in certain practical4 ap
amplifying audions in accordance with va plications of the invention.
._
riations of the input signal energy. More
The diagram of Fig. 2 represents a radio
specifically, objects are to provide methods receiver suchV as shown in Fig. 1, and an aux
of and means for suppressing the effects of ^ iliary system comprising the rectifier 5 ‘and
15
1,969,381
prior art on account of the necessity for
direct current amplifier 6, the rectifier re the
lar
e curvature with the small signals then
ceiving amplified signal energy from the out available.
It is possible, however, as de
put of the receiver radio frequency amph
scribed in the copending a
er 1.
The diagram of Fig. 3 represents a further lantine and Hull, Serial
lication of Bal
o. 644,215, filed 70
8, 1923, patented 'January 8, 1929, No.
simplification of the general arrangement o_f June
1,698,668, to o tain a close approximation to
Fig. 1, the direct current amphíier 6 in this
case being connected across the detector
discontinuous action with certain rectifiers
2. The curve of Fig. 4 is a gra hical re re
sentation of the variation in t e ampli ca
ally higher than that obtained in the usual
first amplifying the signals sufficiently;
The method of operation will be described by
the
amplification being of an order materi
in connection with the system shown 1n Fig.
15
80
alloys containing about 70% to
bias of the ids varied through1positive and ferro-silicon
negative va ues. The values of g represent 80% silicon and about 30% to 20% of iron,
plifier audions. The relationship may e ex
pressed mathematically as:
Eg=A(Ec)Eo (1)
the contact point being iron pyrites (FeSz)
held in light contact with a sensitive spot in
the ferro-silicon. A rectifier of this type will
possess a critical point E which, when exceed
ed, will bring the rectifier into action. The
Eg, the precise formvof this function being
85
critical point may be adjusted to secure va
rious constant outputs. It will be noted that
where Eo is the impressed voltage due to the the response above the critical value is sub
stantially linear, and this feature is particu
wave
field or incomingusignal energy.
The grid bias is a notion of t _e voltage larly desirable in the systems of Fig. 3 to
determined by the characteristics of the rec
30
practice, i. e., say from ten to one hundred
tion in a four-stage one-way amplifier of the times that ordinarily empio ed.
A characteristic such as s own in solid line
type shown in my copending application Se
rial No. 629,702, filed April 3, 1926,_ as the in Fig. 7 may be obtained with commercial
the voltage across the intput o_f detector 2
for varying values of Ec, the direct current
bias on the grids of the radio frequency am
25
75
00
avoid distortion, but is not necessary in the
systems of Figs. 1 and 2 so long as the rise of
tifier 5 and direct current amplifier 6; that is t e characteristic curve above the vertical
voltage is suiiiciently steep.
Therniionic rectifiers of suitable design
The exact values attained b Eg'in view ma be employed in place of the ferro-silicon
EG=Í(E9)
(2) »
of
the simultaneous action of’läñuations (l)
and (2) may be found graphica y as shown
in Fi . 5. The intersections of the curves
give t e values of outputyoltages Eg, corre
s onding` to the various impressed voltages,
yielding the- Fig. 6 solid line curve of input
Eo versus output Eg for the whole system:
Ideal operation would give the_broken line
curve of Fig. 6, i. e., an increase in input en
ergy would produce a corres onding increase
in out ut until a critica output Eg is
reached); the output not increasing thereafter
with any increase in input energy; This
ideal relationship would obtain if t e recti
fier action was such as to furnish the relation
an iron‘pyrite or ferro-silicon and` metallic
contact rectifiers. I have found that the lack 100
of a sharp cut-off in the case of thermionic de
vices is due largely to the circumstance of the
applied voltages being near the same order of
magnitude as those corresponding to the
emission velocities of the electrons, energy IFS
due to thermal agitation and the voltage cor
responding to the work function of the metal,
and also to the Maxwellian distribution of the
velocities of the electrons. Without increas
ing the applied volta e, somewhat better ac Àlll)
tion may be obtained y decreasing the cath
ode temperature and providing a metallic
vapor of low work-function, such as caesium,
which emits copiously at low temperatures,
ship between positive lgrid bias Ec and recti .but in general the preferred method of ob
fier input Eg which is shown by the dotted
line in Fig; 5. Such a rectifier is diñicult taining a sharp cut-oíï is by raising the ap
voltages.
to obtain in practice 'for it demandsthe char plied
. Referring again to Fig. 4, it will be seen the
acteristic shown in dotted line 'in Fig. 7 _, that controlling
bias may be either positive
is, one 'in which there is no output until 'the or negative grid
and
thaton the positive side the
'as im ressed volta Eg increases to a critical control is somewhat better for a given change
`va ue E at whic the output- suddenly rises. in Ec than on the negative side. The positive
It is possible, however, to attain a practi control, while more effective, is under some
cal approximation to this requirement, as disadvantage due to the grid current which
shown by the, so 'd line curve of Fig. 7, is permitted to How in the radio frequency
which gives satisfactory operation in accord amplifier tubes. This extra conductance de
ance with this invention.
the selectivity and may in some cases
None of the known rectifier-s possesses a creases
lie
found
intolerable; in these cases the nega
critical region for low _impressed yolt tive control
may be used, the extra ran _e of
ngeamplitudes as all have a region of tran Ec required being obtained by suitable irect
sition 'iyhere it was customary tof operate in
115
120
130
i,see,asi
3
current amplification or increased rectifier emplo ed with condenser 22 to provide the
desire bias.
Practical embodiments of the invention as
It will be a arent that a thermionic diode
applied to radio receivers are shown in the (two electrodiig tube ma -be substituted for
circuit diagrams of Figs. 8, 9 and 10.
the crystal rectifier the laments being usu 70
The circuit of Fig. 8 is an embodiment of ally connected to the ground.
eflicienc
.
.
-
4
Y the schematic arrangement shown in Fig. 3,
The circuit of Fig. 10 illustrates the generic
but omitting the direct current amplifier of circuit of Fig. 3, the rectifier in this case
that system. The radio frequency amplifier
unit 1 may be of any suitab e design and is
being a thermionic triode. The radio fre
uency amplifier is not shown and the circuit 76
indicated aslcomprisxng a plurality of audi e ements which are substantially identical
ons 10 which with their interstage couphng
is
with those 'of Figs. 8 and 9 are identified
and tuning devices are arranged within a by the same numerals. The radio frequency
grounded shield 11. The grid returns of the transformer 13 supplies the thermionic de
several sta
are preferab y ~connected. to
the' tector 24 through the isolating condenser 21,
correspon ing filament circuits b radio-fre
80
the detector grid being biased by a battery
quency by-pass condensers 12, an . the several 25 through the grid-leak 26. The alternat
grid returns upon which the variable bias is ing current components of the output is
to be impressed are connected to the lead 7
transferred to the audio frequency unit 3 by
a low frequency coupling transformer 27.
The detector unit 2 of the receiver serves yThe plate circuit also includes a plate bat
also as the rectifier unit of the control sys~ tery 28 and a resistor 29 for passing the di
tem, and is coupled to the amplifier unit 1 by rect current component to the direct current
a transformer 13. The detector 14 is prefer amplifier unit 6. The resistor 29 is shunted
25 ably of the ferro-silicon and iron-pyrite type, by a condenser 30 of low audio frequency im
, and is connected across the transformer 13 i pedance, which condenser keeps the alterna t»
through the bias battery 15, by which the ing components from the direct current am
critical voltage of the rectifier 14 is adjusted, plifier
and also prevents the resistor 29 from
and thev resistor 16 which serves as a coupling interfering with the operation of audio trans
30 for the audible alternating current com
former 27 at audio frequencies. The detec
ponents of rectification. The audio fre uency tor plate battery 28 may be located between
20
35
40
from the automatic control unit.
90
95
amplifier unit 3 is connected across t e lre
resistor 29 and the filament as well as in
sistor 16; a variable tap being provided for the
the
position shown. The grid bias for the
regulating the alternating current input.
direct current amplifier 31 may be obtained
To rovide the variable direct current bias from the potential drop across resistor 29 due
free rom alternating current components, to battery 28, by means of a separate bias
the resistor 16 is by-passed by condenser 17 battery 32,l or by equivalent means. As
of low radio f uency impedance; and a fil
the plate circuit of the direct current
ter comprising t e resistor 18 and condenser shown,
amplifier
is supplied by a separate battery
19 is also connected across the resistor 16, the ` 33, but it is obvious that this may be common
variable bias lead 7 being brought to the junc with the other plate batteries. The direct
tion of filter elements 18 and 19. >The imped~ current
output is coupled to the grid returns
ance of the condenser 19 and other capacities by means
resistor 34, the lead 7 including
in parallel with it is low for the audio fre a battery of
20, if desired, for adjustment of
quency components. A battery 20 may be the mean bias.
60
85
105
110
provided` in the variable bias lead 7 to ro
The tetrode or four electrode tube is a very
vide the normal grid bias in the absence of a convenient
of direct current amplifier
signal, but this battery may often be omitted. as it ryields aform
considerable amplification with
The diagram of Fig. 9 shows an alternative low battery voltages.
method of substi
arrangement of the rectifier circuits. The tuting the tetrode forThe
the triode shown in 115
amplifier unit is not shown in this diagram Fig.
10 will be obvious to those familiar with
but may be of the type shown in Fig. 8. An audion
circuits.
isolating condenser 21 is arranged between the
55
The circuit diagram of Fig. 11 represents
detector 14 and the input transformer 13 to
prevent short circuiting of the detector out another embodiment arranged for negative
put circuit by the transformer secondary. control, that is, control by means of a nega
The ` detector output includes the bias bat tive bias on the radio frequency amplifier 1.
tery 15 and the resistor 16, the audio fre
120
The system is of the general type shown in
Fi . 2 - the radio receiver comprising the
quency unit3 being coupled to the resistor 16 ra
io frequency amplifier 1, detector 2 and
through a variable tap. This connection may
audio amplifier 3 and the control system com
prising
a separate rectifier 5 in parallel with
rect currentA drop across resistor 16 due to the
detector 2, and a direct current amplifier 6.
battery 15 does not provide the proper grid The
rectifier element or diode 35 is con
bias for the first tube of the audio amplifier.
M Under these circumstances, the grid leak 23 is nected across the transformer 13 through iso
include an isolating condenser 22 when the di
lating condenser 36, and the output circuit of
125
130
4
upon the detector stage‘or audio am
the rectifier includes a radio frelìpency choke placed
plifiers
in addition to or in place of the bias
37, battery 38 and resistor 39 w ich may be
radio frequency amplifiers.
about 25,000 ohms. The resistor 39 serves as onItthe
will be ap arent .that the invention is
a couplin to the direct current amplifier
unit 6 an a by-pass condenser 40 is shunted capable of wi e application with various
16
of audion amplifiers and that many
across the battery 38 and resistor 39 to keep types
circuits
may be devised for effecting control
radio frequency currents from am lifier 6; by the principles
which are described in this
the choke 37 preventing the con enser 40
specification.
from shorting the rectifier for radio fre
_
quency voltages. The battery 38 provides a I1. claim:
An audion amplifier including an audion
means for ad] usting the critical voltage of the for signal
wave amplification, an output cir
rectifier 35.
cuit,
and
means
sup ressing fluctuations in
The direct current amplifier element is said output circuit
ue to variations in the
shown as a tetrode 41 which has its control
strength
of
an
incomin
said means
grid cou led to the rectifier output through comprising a rectifier §01'signal,
incoming
signal
a grid bias battery 42. The usual batteries energy, and means for impressing upon
the
80
43, 44 supply the operating potentials and the grid of said audion a direct current bias
output is developed in a resistor 45 of about
20
e derived from said rectifier, said
100,000 ohm resistance which is shunted by volta
rectifier
being of the type having an approxi
a condenser- 46 of low reactance for audio mately linear
between direct cur
modulation frequencies. The variable bias rent output andrelation
radio
frequency
input above
lead 7 is connected to resistor 45 by an ad
a
critical
input
voltage.
justable tap, and preferably includes a bat
86
2. In combination, an audion, an output
tery 20 for placing a normal bias on the grids
circuit therefor, and means for suppressing 90
of the radio frequency am lifier 1.
fluctuations in said output circuit due to
It will be evident that this arrangement variations
'the strength of an incoming
may be used for positive control, i. e., with signal, saidin means
cdinprisingl a rectifier
the radio frequenc bias varying positively
a critical input voltage below which
instead of negative y, by omitting the direct having
substantially
no direct-current out ut is ob
current amplifier and connecting the bias lead tained, and means
for adjusting‘said critical
7 to the resistor 39 instead of to resistor 45
voltage.
‘
a'
'
3. In an electrical system, the combina
tion
with an audion having input and output.
gous arrangement ut adapted for positive circuits,
of means for suppressing fluctua
control. The symbols are for the most part tions in said
output circuit due to variations _' _ '
uniform with those of the preceding figure in the strength
of an incoming signal in said `
and the parts have the saine functions. In input circuit, said means comprising a. recti
this case the filaments of the rectifier and dì fier of the type having an approximately
rect current amplifier tubes are at ground linear relation between direct-current out 105'
potential with those of the radio fr uency
as shown.
y
The circuit of Fi . 12 illustrates an analo
‘
40
amplifier, thus permitting the use o coin
' 100“
ut and radio frequency input above a critical .
input voltage, and means for varying the ‘ .
nion “A” batteries. Also a triode has been critical voltage of said rectifier.
60
55
shown instead of the tetrode in the direct
4. The combination with a receiving sys
current amplifier. It will also be obvious tem comprising an audion, of>_means ener 110
that if the output tap is shifted from resistor gized by said audion for impressing a vari
45 to resistor 39 the control changes from able bìas on said audion, said means includ
sitive to negative.
Although the use of a rectifier having a ing a rectifier, and voltage-biasing means for
rectifier.
i
sharp cut-oí, and in some cases having a sub said
5. The combination with an audion, of 115
stantially linear characteristic above the cut means for biasing said audion by a direct
off voltage, is particularly desirable for close current voltage, means for automaticall
regulation and good quality, it will be ap varying said bias voltage in accordance wit
parent that some improvement in volume the strength of an incoming_signal, at least
control may be had with rectifiers having one of said means including a 'rectifier having 120
other characteristics.
a critical working voltage, and means where
In general the use of a separate rectifier by said critical voltageinay be adjusted.` '
for control purposes is prefera le to using the
6. In a
stem for “ the transmissionL o
regular detector of the receiver for both pur-' modulated signals, the combination with an
poses. The reasons for this have been given. audion amplifier for amplifying said signals, iis
A goed combination is a linear detector at 2, and means automatically cont?ollingi'the
and a linear rectifier at`5 with a cut-off char gain of said amplifier in- accordance with the
acteristic. A linear rectifier at 5 without a strength of received signals, of a demodula
cut-ofi` characteristic is less useful for con tor, and means to suppress all _output from
v130
trol purposes with a characteristic of the type
shown in Fig. 4. The variable bias may be said demodulator until the amplified signals
necesa:
Y5h4 "
impressed thereon reach a predetermined
critical value.
7. The invention as set forth in claim 6,
wherein said last means is adjustable to con
5 trol the predetermined value of amplified
signal strength below which no demodulator
output is obtained.
»
8. In a receiver for modulated carrier
waves, the combination with a signal fre- ‘
1° quency amplifier, and a demodulator having
an ,audio frequency response substantiall
proportional to the strength of impresse
signal volta es of a linear rectifier for recti
fying ampli ed signal voltages to produce a
direct current voltage for automatically con
trolling the ain of said amplifier, and means
for suppressin the direct current response of
said rectifier or impressed signal voltages
below a predetermined value.
9. The invention as set forth in claim 8,
wherein said means is adjustable to control
the predetermined amplified signal value
below which no gain control voltage is de
veloped by~ said rectifier.
10. In a receiver for modulated carrier
waves, a signal frequency amplifier, means
for producing audio frequency and direct
current voltages by rectification of amplified
signals, means actuated by said direct cur
3° rent volta e to control the gain of said am
plifier, an means suppressing the develop
ment of audio frequency and direct current
voltages for im ressed amplified voltages
below
11.'
redetermmed values.
.
he invention as set forth in claim 10,
wherein said rectification means has a linear
response for impressed signal voltages above
. the predetermined value.
f
12. The combination in a receiver for car
40 rier wave signals, of an audion amplifier, _
a linear rectifier upon which the am lified
si nal voltage is impressed, means inc uding
said rectifier for im ressin a variable gain
control bias on saidJ ampli er, said rectifier
45 having a critical input voltage below which
no rectified output obtains, and means for
adì'usting
said critical input voltage.
n testimony whereof, affix my signature.
STUART BALLANTINE.
DISCLAIMER
1,869 331.-Stuart Ballantine, Mountain Lakes, N. J. Aan'roiii'ric CONTROL Foa
ÁUnioN AMrLIriiias. Patent dated July 26, 1932. Disclaimer filed October 12,
1933, by the assignee, Boonton Research Corporation. u
Hereby enters this disclaimer to the subject matter comprising claim 1, which
claim 1 reads as follows:
.
0
_
_
“1. An audion amplifier includin an audion for signal wave amplification, an
" output circuit, and means suppressing uctuations in said output circuit diie to vai-_ia
tions in the strength of an incoming signal, said means comprising. a rectifier for in
coming signal energy, and means for impressing upon the grid of said audion a dir_ect
current bias voltage derived from said rectifier, said rectifier being of tlie‘ty e having
an approximately linear relation between direct current output and radio requency
input above a critical input voltage.”
[Oficial Gazette November 7, 1933.]
necesa:
Y5h4 "
impressed thereon reach a predetermined
critical value.
7. The invention as set forth in claim 6,
wherein said last means is adjustable to con
5 trol the predetermined value of amplified
signal strength below which no demodulator
output is obtained.
»
8. In a receiver for modulated carrier
waves, the combination with a signal fre- ‘
1° quency amplifier, and a demodulator having
an ,audio frequency response substantiall
proportional to the strength of impresse
signal volta es of a linear rectifier for recti
fying ampli ed signal voltages to produce a
direct current voltage for automatically con
trolling the ain of said amplifier, and means
for suppressin the direct current response of
said rectifier or impressed signal voltages
below a predetermined value.
9. The invention as set forth in claim 8,
wherein said means is adjustable to control
the predetermined amplified signal value
below which no gain control voltage is de
veloped by~ said rectifier.
10. In a receiver for modulated carrier
waves, a signal frequency amplifier, means
for producing audio frequency and direct
current voltages by rectification of amplified
signals, means actuated by said direct cur
3° rent volta e to control the gain of said am
plifier, an means suppressing the develop
ment of audio frequency and direct current
voltages for im ressed amplified voltages
below
11.'
redetermmed values.
.
he invention as set forth in claim 10,
wherein said rectification means has a linear
response for impressed signal voltages above
. the predetermined value.
f
12. The combination in a receiver for car
40 rier wave signals, of an audion amplifier, _
a linear rectifier upon which the am lified
si nal voltage is impressed, means inc uding
said rectifier for im ressin a variable gain
control bias on saidJ ampli er, said rectifier
45 having a critical input voltage below which
no rectified output obtains, and means for
adì'usting
said critical input voltage.
n testimony whereof, affix my signature.
STUART BALLANTINE.
DISCLAIMER
1,869 331.-Stuart Ballantine, Mountain Lakes, N. J. Aan'roiii'ric CONTROL Foa
ÁUnioN AMrLIriiias. Patent dated July 26, 1932. Disclaimer filed October 12,
1933, by the assignee, Boonton Research Corporation. u
Hereby enters this disclaimer to the subject matter comprising claim 1, which
claim 1 reads as follows:
.
0
_
_
“1. An audion amplifier includin an audion for signal wave amplification, an
" output circuit, and means suppressing uctuations in said output circuit diie to vai-_ia
tions in the strength of an incoming signal, said means comprising. a rectifier for in
coming signal energy, and means for impressing upon the grid of said audion a dir_ect
current bias voltage derived from said rectifier, said rectifier being of tlie‘ty e having
an approximately linear relation between direct current output and radio requency
input above a critical input voltage.”
[Oficial Gazette November 7, 1933.]