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Патент USA US2404160

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July 16,1946.
-|-|_ BQUCKE
Filed June '14, 1939
2 Sheets-Sheet 1
F | 2 1191i
18 ’
A, F‘.
. gE
HEINZ Boucm';
July 16, 1946.
Filed June 14, 1939
2 Sheets-Shed 2
Patented July 16, 1946
r; 2,404,160
Heinz Boucke, Berlin-Charlottenburg 2, Germany,
by mesne
Patents ' .
Research Corporation, New York, N.’ Y., a cor-‘
poration of New York
Application J um: 14, 1939, ‘Serial No. 278,993
In Germany June25, 1938
11 Claims. (Cl. 179—171)
The present invention relates to improvements
mission characteristics of an ampli?er directly
and in proportion to changes of a ,charactertistic
of the oscillatory energy to be ampli?ed.
A further object is to control the time constant
of the smoothing ?lter in a- regulating channel
in electric control systems and methods of op
erating the same, more particularly to arrange
ments employed in ampli?ers for. oscillatory sig
nal energy which may be of low, medium and high
frequency for controlling a characteristic of the
‘ serving to transmit a gain control potential in
output energy in dependence upon variations of
an ampli?er directly in dependence upon the
the same or a different characteristic of the input
amplitude of the signals being ampli?ed.
energy to be ampli?ed. Control systems of this
- Still a further object is to control the time con
type serve various uses especially to improve the 10 stant of the ?lter in the regulating channel
ef?ciency and/or quality of the reproduction of .
sound or other oscillatory signal energy.
The most frequent use of control arrangements
of the above type in both high frequency and ‘low
frequency ampli?ers is in the form of automatic 15
gain or volume control (AVC) involving the em
ployment of a controlling potential obtained by
rectifying and averaging a portion of the signal
energy to be ampli?ed.
transmitting an automatic volume control poten
tial in "an ampli?erdirectly in proportionto the
degree or range of the automatic volumejcontrol.
Another object is to control the time constant
of the smoothing ?lter in the regulating channel
' for transmitting a volume control potential in
an ampli?er directly in proportion to the ‘ampli- '
tude ratio of different frequency or groups of
frequency’ components of- theloscill'atory signal
~ /
Automatic gain control systems serving to reg~ 20 energy to be ampli?ed. .
ulate the output volume in dependence upon vari
A further object is to control the time constant
ations of input signal strength and other ar
of the smoothing ?lter in the regulating channel
for transmitting a volume control potential in
rangements of this nature, such as automatic fre
quency control, band width control arrangements , an ampli?er directly in proportion .to the speed
in radio receivers, volume contraction and volume 25 or rate of change of the amplitude of the input
expansion systems in transmitters, receivers and ' signal energy applied to the ampli?er“
ampli?ers and Various other control arrange~
Still another object is to control the time con
ments, generally involve the use of a control po
stant of the ?lter in the regulating channel for
transmitting an atuomatic gain control potential
< tential or current obtained by averaging a portion
in an audio frequency ampli?er. directly in de
of the signal energy being ampli?ed such as by
recti?cation and subsequent ?ltering. The speed . pendence upon the adjustment of a frequency dis
criminating network adapted to modify the qual
of the regulating action in arrangements of this
ity of the sounds produced in a translating device
typeis determined by the time constant of the
energized by the ampli?erv output.
?lter employed for smoothing or steadying the
recti?ed potential.
A further object is to control the time constant
It has already been proposed heretofore to em
of the ?lter in the regulating channel for trans
ploy a plurality of control potentials acting with
mitting an automatic frequency control potential
different speeds or time constants to produce cer
in a radio. receiver equipped, with an automatic
tain desirable effects and advantages. Thus it
tuning arrangement, orin other Words to con
has been suggested toreduce the effect of short 40 trol the speed or quickness of action of the fre
quency control directly in dependence 'upon the
interfering impulses by momentarily reducing the
ampli?cation in a receiver equipped with auto
strength of the radio‘ signals being received.
matic volume control by the aid of an additional
Still a further object is to control the time con
control potential acting with reduced time delay.
stant of the ?lter in the regulating channel for
It is an object of the present invention to pro 45 transmitting a potentialor current in an audio
vide means for and a method of time constant , , frequency‘. ampli?er adapted to compress or ex
control in a regulating arrangement of the-above
pand the dynamic or intensity range of the audio
general character whereby-a desired variation or
signals being ampli?ed directly in dependence
upon the average signal amplitude. \
modi?cation of the characteristics of the output
energy in an ampli?er is obtained in‘a most e?i 60
cient and easy manner.
A more speci?c object is to control the time
constant of the smoothing ?lter'in a regulating
channel transmitting a controlling potential or
With the‘foregoing and other objects which will
‘become apparent. as ,7 the ‘following description
proceeds, in view the invention contemplatesthe
provision of meangto render the: time to estab- '
lish a control effect upon changes of a variable
current to an element adapted to vary the trans- “characteristic of the ampli?er; or of the. energy
being ampli?ed, or any other cause. hereinafter
a discharge impedance I4in parallel or shunted
' referred to as “attack” time and/or the time to
across the condenser as shown in the example
illustrated, but may be of more complex. con
struction as will be understood. The charging
remove the control effect after cessation of the
cause, hereinafter called “recovery” time directly
impedance may be constituted partly or entirely
by theiinternal impedance of the current source;
that isjin'the example shown thesimpedance of
by automatically adjusting an element of the ?l
the secondary winding of the transformer II] or
ter 0r smoothing network arranged in the chan
;by the impedance of the'recti?er I I. The charg
nel transmitting the control potential.
The invention both as regards its design and: 10 ing and discharge impedances preferably al
though not ‘limitatively consist of ohmic resis
arrangement of circuit elements as well as“func-,
tion and operation will become ‘moregapparent, "tors. ~"Th'ey’may'lbe entirely or in part inductive
reactances. *The‘ch‘arging resistance in conjunc
from the following detailed ‘description taken‘
tion “with the “discharge resistance determines
with reference to the accompanying drawings
essentially'the attack time of the regulation while
formingpart of this speci?cation and wherein:
?the‘recove'ry time is essentially determined by the .
Figure 1 shows for the sake "of illustration 12.
.well known recti?er and ?lter circuit forproduc- , *sizeof‘the discharge resistance and the smooth
ing a control potential by averaging a1 portion .of' 5 ~ ing‘ condenser.
The variation of the time constant of the ?lter
the signal energy to be controlled,
Figure 2 illustrates one vwayof controlling ‘the 20 is.eifected according .to the. invention by ,varying
the impedance valuesofone or. more of.the.ele
time, constant or speed of the controlling action
ments . I2, I3 . and I 4, thus .involvingthe variation
in a purely electrical manner proposed'by the
dependent upon the same or another character
istic of theampli?er or the energy tobe amplified,‘
of one .or .more capacity, resistance :and/or .in
ductance elements. vFor ,thisnpurposewany. one of ’
Figure-ashows a ?lter circuitsuited for use in
a low frequencyvsuch as anaudio ampli?er for 25 the known devices-‘maybe (employed such . as ar
obtaining volume compressionor expansion with
rangements for v.step-by-step variation -.of .. a
the time constant or speedof the control action
depending-upon the-degree- or range of .gain' .con
pacity, a resister, or inductance element “by
means of suitable-switching» arrangements .or .by ‘
gradualadjustmentof. one .onmoreof these .values
Figure, {4, illustrates ~. an .exempli?cation of a 30 in anysuitable manner. rArgradualiadjustment
may be effected bymecham'cal .orelectrical means
such as by the emplo-ymentpf{electronic valves
serving} as variableimpedances .orby means» .of-a
’ variable ., speed . gain control \. in _ dependence upon
the rate of change of-the. inputsignalamplitude‘
applied to aniampli?er,
magnetic reactor provided - with Ian-auxiliary
Figures 4A and 4B illustrate furthergexempli
?cations. ofr-variable gain control systems embody;
' ing the principles of the invention.
.Figure 5 is :acircuit diagram illustrating: an
exempli?cation for variable : speed gain ‘control
According to theimprovements ofjthe present
invention the control of-the?lter .time-lconstant
or the speed of the control .actionin arr-ange
ments 10f the .aforementioned character 'is
in dependence uponthe tonecontrol adjustment
4.0 e?ectedrautomatically and. in- dependence upon ' a
. in, an ampli?er,
---Fig,ure;6 :isa circuit diagramillustrating anar
ran'gement for obtaining variably delayed-auto
variable characteristic ‘.or :adjusting operation. in
matic gain .control :depending . upon- the average
trol of the .timenconstant of the ?lter in the
regulating channel causes 'a variation —.of the
thereceiver or ampli?er. 'In case'thatthe con
amplitude _' oreinput:signalstrength. applied to an
45 average 7 value of ' the-control potential, suitable
compensating ‘ means tcmayzbev employed‘. to 'elimi
nate this defect! partly or entirely.
Figure '7 . shows‘ ~a~.circuitl diagram ...for::a :radio
receiver illustratinga variably delayedautomatic
frequency .control depending ‘upon the..strength.
ofa receivedradiesignal.
'In Figure *2 there .'.is shown a vwayaofeele'ctric
control of the‘ time-:constant- of ‘the-?lter orthe
Like reference characters identify. :like $616. 50 speed of .' action not la control - potential lei ;trans
mitted through I the ?lter in ;:.proportion. to .an
other. auxiliary:controlzpotentialvet. .Therezis .pro
Referring .Eigurecl, there
vided for this purposela'vacuum tube; Iizsuchaas
mentsthroughout-thedi?erent'viewsi of the draw
. is .shown; a combined . recti?er rand,‘ ?ltenrgircuit
a triode or a tube of any otherssuitablezcon
of well a known. construction for. producing a_'con-‘ 55 struction vserving; as a variable impedance shunted
.trol potential. from‘ aportion of \thetmain zsignal
across: the - output: or: discharge resistance‘ ' I 4. The
energy to be ampli?edor translated. ,The.;en
ergy extracted from the mainrsignalpircuitsuch'
impedance f-of ‘ the tube). is variedin accordance
as .a . receiver .or . ampli?er- is :applied - by :way . of
.grid‘ or other control"elementinra‘imanner well
with vthe controlling potential let applied :to'the
input terminalsv a-;-b: andtal coupling transformer 60 understood, resulting . in a’ ‘variation i of '1 the “tube
It] to a rectifier. suchcasadiode recti?erIIrcon
nected across the transformer secondary inseries
with an impedance I2: and .alcondenser :I3. A
‘further impedance I4 is; shunted across :thexzon
impedance and. in'turn‘of- the recovery-:timezcon- .
I .stant‘of the ?lter.
In? agsimilar; mannerithe .-re- ,
sistance I 2 may be‘controlledft'o adjust itheiattack
time constant or ‘the. speed with 'whichrthe con
denser . I3. The ‘control - or regulating {potential 65 ‘trolie?ect is.established. Other variable‘ imped-v
ances suited ; for electrical 'orimechanical :control
_ 6r is derived vfrom‘the - opposite _ends -of the-im
‘ may .be' used ‘ for'lthe" purpose 'of‘the inventioniin
pedance I4 and serves toinfluencea regulating
device by way of. the output'lterminals-ic—d1isuch
as. an element. adapted to. control ,theiamplifying
place‘? of‘ the ' valve I 5‘ aslis readilyunderst'oo'd.
Inthe following there will bei-described several
gain; the ‘band ’width, tuning adjustment, oriany 70 exempli?cations illustratingtheieffects " and ad
other characteristic of thereceiver or ampli?er
»in' a'manner well known in the. art.
vantages of a time constantcontrol'_'as'proposed
by the invention.
. ‘
I "Thei'?lter' for; smoothing the-icontroliipotential
According 1 to i one ilembodiment, ithevv time‘ con
lei-1v comprises in. general-'a ‘smoothing- condenser
I3 in series with a charging impedance I2 and
?stant ma‘y’bei automatically‘controlled in depend
ence upon the degree or range of automatic regu
2,404,160 I
lation in an- ampli?er especially for controlling
in systems for automatic volume compression and
expansion in dependence upon the relative'am
plitude of different frequencies or groups of fre
quencies of the oscillatory signal energy to be.
ampli?ed. .Thus, vit has been found advanta
geous to operatively connect the variable resistors
for influencing the charging and discharging pe-i
the intensity range of the ampli?cation such as
for volume compression and expansion. As is
known, in arrangements of this latter type the
attack and the recovery time constants are chosen -
by a compromise on the basis of the fact that if
the time constants‘ are too low non-linear dis
tortion will result, while with time constants be
ing too high dynamic distortion will occur in the
riods such as shown in Figure 2 with artone con
trol device in such a manneras to increase the
The non-linear 10 ?ltering action or decrease the speed of the con
output signal of the ampli?er.
distortions increase with increasing degree of
trol with increasing relative strength of the lower
regulation. Inasmuch as the degree of regulation
sound frequencies. This dependence may also bev
is usually not ?xed, but may be chosen by op
accomplished in a purely electrical manner asis'
erating an adjusting knob or’ the like,» it is pro
understood from the above.
posed to decrease'one or both time constants of 15
According to a further feature of theiinvena
the ?lter in the regulating channel automatically
tion, the time constant is rendered dependent
with the decrease of the degree of regulation. In
upon. the frequency‘ distribution of the audio or
other low frequency signal to be amp-li?edby
this manner a desired minimum of both dis
dividing the ‘signal ‘band into two groups;_one.
tortionand time delay of the regulating action
is ensured for the different ranges or degrees of 20 group comprising the lower frequencies andthe
other group comprising the medium and high
frequencies. Separate regulating potentials are
An arrangement of this type is illustrated by
produced from each frequency group and com
the circuit diagram according to Figure 3. In the
latter, the smoothing impedances l2 and I4 are
bined in opposition to producea di?erential con
trol potential. The latter will be equal to? zero
constituted by variable resistors, preferably of the
rotary or any other suitable type arranged for
if both groups of frequencies are of substantially
uni-control by means of a single operating ele
equal amplitude and will assume increasing nega
tive or positive values depending on which of the
ment or knob indicated at H, whereby both re--v
group of lower and higher frequencies predomi-v
sistances may be increased or decreased simul
taneously thereby correspondingly varying the at 30 nate over the other. 'By the aid of the thus ob
tack and recovery time, respectively, for the con
tained auxiliary control potential (8t) which, if
trol potential. In the example shown, the corn-v
desirable, may be converted into a control cur-.
mon operating element ‘(I'D is extended to si
rent, theltime constant of the control potential
multaneously adjust an element for controlling
proper (er) is then regulated by varying the mag
the degree of regulation such as a potentiometer
nitude of the charging and/or discharge resist-'
16 connected across the output terminals and 35 ance in. any of the above described'manners.
serving to control the magnitude of the control
Thus; the control according to Figure 2~may be
potential er and in turn the degree or range of
effected by shunting an electron valve acrosslthe' -
the automatic gain control. In this manner the
speed of regulation is automatically varied in di
dischargeiresistance and controlling the grid of
the valve by the auxiliary (6t) potential obtaine
rect proportion to the degree or range of the
in the manner described above.
An arrangement of the latter type is shown in
In certain cases it may be advantageous to in
Fig. 4A, wherein separate energy portions are
crease the time constants or to decrease the speed
derived from the secondaries 20' and 22' of trans
of the regulating action with increasing degree
former 2i? and applied to diode recti?ersl I’ and
or range of regulation in the interest of a better
H” by way of a‘loW-pass ?lter l2’, I3’ and a
?ltering action and in view of the fact that for
high-pass ?lter i2", 13”, respectively. The rec
small degrees of regulation the dynamic delay is
ti?ed potentials developed by the diode‘load re
less disturbing than with the higher regulating
sistors H'and- M" are combined differentially to
60 produce a vcontrol potential et. The latterv is
If the degree of regulation is varied by a step
applied to the grid of tube I 5 for varying the time
switch, the resistors 12 and 14 may be constructed
constant of the ?lter l2, l3, M for the gain conand adapted thereto in a manner well understood. ' trol potential er to obtain a variably delayed con_
According to another embodiment, the time
trolling action dependent upon the amplitude
constant may be varied in dependence upon the
ratio between the low and high frequency com
averageQvolume of the signal being received or
ponents of the signal energy being ampli?ed.
regulating action.
ampli?ed. Thus,'if the average signal strength
The variation of the discharge resistance in '
is high, the inherent distortion of the ampli?er
the above described manner may entail a varia
will be high also in which case it is recommend
tion of the absolutemagnitude of the control
able to increase the time constant for the regu 60 potential and in turn a change of the degree of
lation in order to prevent a further increase of
regulation; that is, the latter will‘ become less ,
the over-all distortion. The control of the time
if the recovery time is decreased. Since, how
constant or smoothing action in dependence upon
ever, in general the recovery time in automatic
the average signal strength may be effected for
volume compression and expansion systems is
instance by varying one or more of the ?lter ele
65 chosen substantially higher than the attack ,
ments, in ‘particular the charging and/or dis
charge resistance automatically together with the
time-about 30 to 100 times the former—'the dis
charge resistance will be about 30 to 100 times
adjustment of a volume control regulator in a
desired sense. An arrangement of-this type may
greater than the charging resistance whereby
be derived from Figure 3 by replacing the poten
tial divider I6 by the usual variable volume con
minimum of 1A of its normal value, the total
potential will vary only about 10 to 20%. The
trol resistor employed in ampli?ers such as in
radio receivers and similar ampli?er systems,
Another exempli?cation of the invention con
may ‘also be eliminated by simultaneously de-v
even‘ with the recovery time being reduced to a
effect on the magnitude of the control potential
creasing the discharge resistance and/or the re- »
sists in varying the attack and/or recovery time 75 sistance of the recti?er by shunting. avariablev
?erand-?lter circuit'l l to M byway of input ter-. '
‘ ' resistance across: the'latter or in any other suit
able. manner.
vIn Fig. 43, there is shown a system of this
type for varying the time constant of a con
trol potential in dependence upon the average
minals a-g-bv and the secondary ll of a trans
former 29. The regulatingtube t5 shunted across"
the discharge resistance i4 is controlledby the
. auxiliary control potential et whose half waves
volume. of the. signal energy being transmitted
or‘ ampli?ed. There is shown in block dia
corresponding to the periods of intensity increase
gram form an ampli?er l5’ of a radio receiver
or the like embodying a volume control resis
control'potential et-is-producedbymeansof asec- .
In addition, means are shown in Fig. 43 to
compensate for the effect of the discharge re
duce the auxiliary control potential by electrical
are suppressed by a recti?er 23. The auxiliary
ondi recti?er circuit comprising atertiary winding
tor it’ of well known design and acommon oper 10 22 of the transformer 2&3, recti?er 23,,v smoothing
condenser.“ and resistance 25v and having at
ating member indicated vat'll’ for simultaneously
tacky and recovery time constants which are low
adjusting the volume control, the discharge re
er than the time constants for the mainccontrol
' sistor l4 and the charging resistor I2 of a smooth
potential er; A condenser 26 and resistance 29
ing ?lter in the circuit producing the control or
connected across the resistance 25 serve to pro
regulating potential 6r.
di?erentiation, i, e. a potential Let) varying ac
cording to the rate of change of the recti?ed and
sistor M on the amplitude of the. cpntrol poten
?ltered potential, the former being impressed
tial er‘by the provisionof a further variable re
sistor' 1:8’ shunting the recti?er U and arranged
upon the recti?er 28 in series with coupling Ire-r.
for unicontrol with the remaining resistors as
sistance 29 supplying the auxiliary grid. control
shown. In an arrangement of this type, the time
constant of the ?lter I2, I3, I4 is decreased as
potential e1; for the electronic resistance I5. ,If
desired a ?xed bias may be applied. to the grid in
the» volume is decreased and vice versa.
a manner well known.
Still another application of the invention-con?
thermore, the arrangement 'is such, as indicated 25
sists in the control of the time constant of a po
by the arrows, that the current shunted around‘
tential serving to effect automatic tuning.‘
the recti?er ll decreases as the discharge‘ re
radio receiver independence upon a control po
sistor“ and, in turn, the control potential‘er
tential varying according to the signal strength
are decreased” Accordingly, the recti?er output
current. will be increased, resulting in increased 30. which may be obtained in a manner ‘similar as in
automatic volume control systems; According to
potential drop across resistor l4 and compensa
tion ofthe decrease or the control potential 61".
According to another embodiment of the in
vention the time constant‘ for the regulating po
a preferred. arrangement, this control is- effected
in such a manner that during strong fadings
. the’ time constant of the tuning control poten
tential or- current is varied in dependence upon 35 tial isincreased to a considerable extent. In this '
manner the: tuning will be maintained for a cer
A the speed or‘ rate of change of the intensity vari
tain period; although the transmitter may be
ations of human speech or a musical selection.
blanketed by the noise level, and though a strong '
In the latter case, slow intensity variations will
neighboring transmitter may tend to pull’over
cause a more ei?cient ?ltering-resulting in a de
crease ofdistortion. In order to carry out the 40 the. tuning adjustmentdue- to theautomatic tun
ing action. The ?lter for the regulating potential
desired control of the time constant or ?ltering
in accordance with’ the rate of change of the
amplitude variations a special auxiliary poten-'
in this case is controlled by the control poten
tial in such. a manner that the time-constants
to establish and remove the control effect are in
This auxiliary potentialmay be obtained by 45 creased during several seconds. This may be
accomplished in an: easy manner by the provision
producing a regulating potential. varying ac
or? high ohmic smoothing impedances shunted
cording to the intensity changes of the. original .
by electron valves serving as impedance elements
sound" or other signals and to derive from this
in the manner described hereinabove. As a re
potential a further potential by electrical. dif
sult, the tuning will be maintained constant dur
ferentiation which will thus‘ vary according to
ing-short and strongfading periods but will only
the rate of change of the original regulating po
be switched. over to a neighboring transmitter in
case of. prolonged and strong drifts or fading
The auxiliary control potential may be utilized
to control the time constants by controlling one
tial is required representative. of this relation.
or morerelectron valves in a manner understood
from‘. the ‘above; The auxiliary control potential
is applied to the. discharge resistance preferably
in-such amanner that during the. half waves
corresponding to increasingiintensity, the discharge resistance‘ is reduced, while duringthe
half waves corresponding- to the. periods of de
creasing intensity 2, control ofthe charging re
sistanceonly takes place; This. is accomplished.
by applying the respective portions'of the aux
iliary‘ potentials to each of theregulating re
ter equipped- with means for adjusting the car-1
rier‘ amplitude in proportion to the amplitude of
the modulating (audio) signal to improve the
transmission e?iciency.
In Figures 5 to 7 there are shown speci?c prac
tical applications of‘the, invention described in
sistors byway of arecti?er suppressing the un
The above described arrangement for produc
ing a.- control potential vdependent on the low
(audio) frequency signal amplitude and control
of the time constant depending upon the rate of
change of the signal strength variations, may
be used in a broadcast transmit
the: f.oll'owinsr .1
Figurezi shows an arrangement for controlling
In, Figured of the drawings there is. shown an
the time constant for a gain control potential
example for‘ influencing the recovery time con
stant by means of a- eontrolpotential dependent 70 in dependence’ upon the’ adjustment of a tone ~
control device inan- audio frequency ampli?er.
upon the speed'or rateoi increase of the signal
intensity. The'regulating. potential proper err is
The signal currents obtained from any source,
such as a'radio receiver, microphone, pick-up
produced in thesame manner asshown. in the
previous ‘illustrations by applyinga portion of the»
device,-v etc., are appliedto the ampli?er 32‘by
signal’ energysuch-as-sound ‘currents to. a recti- - \ way of the input terminals c—,f. The output-of
, 2,404,160
the ampli?er serves to energize‘ a translating de
antenna circuit comprising an antenna 51 and
ground connection 58 and having its output con
vice suchas a loud speaker 34 by way of a cou
pling transformer 33.
The primary winding of
nected to a translating device such as an image
receiver or loud speaker 59 as shown in the draw
the transformer 33 is shunted by a tone control
circuit comprising in a known manner a variable.
resistor 35 and a condenser 35 in series and serv
ings. ~ The receiver is equipped with a system for
automatic frequency control known per se and
ing to adjust the relative amplitudes of the low
indicated in the drawings only to an extent‘v as ‘is
and high audio frequencies resulting in a varia
deemed necessary for an understanding of the
tion of the quality of the reproduction in a man
ner well understood. A portion of the audio 10
A portion of the intermediate'frequency en
signal energy is extracted by means of a tertiary
ergy extracted from the tuned circuit 60 is‘ ap
winding 37 of the transformer 33 and averaged
plied to the grid of an ampli?er valve Gland the
by means of recti?er 38 and smoothing ?lter
ampli?ed signal energy impressed upon the'tuned
comprising ‘a variable charging resistor 40,
output transformer 63. The‘ opposite ends of
charging condenser“, and discharge resistor 42,.
15 the. secondary winding of ' the latter 'are >‘con
nected each to one terminal of a recti?er such as
to produce a control potential 6r impressed upon
a gain control element of 'the ampli?er 32 in .a
manner well understood from the above. The
{tone control resistor 35 and the smoothing re
sistor 40 are arranged for uni-control by the aid 20
of a common operating element indicated at 40’
such as by the employment of resistors of the
rotary type mounted upon a common shaft. In
this manner both resistors are simultaneously
varied in the direction of or opposite to the ar v25
rows as indicated, in such a manner that with
the adjustment of the tone control for accentua
tion of the low signal notes the attacktime is
increased, as is permissible for the low signal
diode recti?ers 64 and 65, respectively,uthe re
maining terminals of the recti?er being con
nected through a pair of equal resistances 66 and
61 in series and shunted by smoothing condensers
66’ and 61', respectively. The center tap'of vthe
secondary winding 53 is coupled on the onehand
to the high potential end of the primary‘ wind- '
ing and to the junction of the resistors‘66 and
61 through a high frequency choke 0011 on the
other hand, whereby in a' known manner the
sum and the difference of the primary and sec
ondary potentials ‘of the transformer 63 are
recti?ed and combined in ‘opposition producing
frequencies, resulting in an improved smoothing. 30 a difierentialpotential between the outer‘ ends of
action and in turn in increased freedom from
‘the resistances 56 and 61 which potential ‘varies
directly in proportion to and depending on the
Referring to Figure 6 illustrating a system for
sense of detuning of the transformer 63 rela
time constant control in an ampli?er with auto
tive to the impressed signal frequency. ' This
matic volume compression, the audio frequency ‘
tuning control potential is then applied'by'way
input is applied to the. ampli?er 43 by way of
input terminals c—f and the ampli?ed signal
of circuit connections 68 and 69 to a reactance
control element of the receiver 56 such as the
local or heterodyne oscillator suited to effect‘ a
tuning control in such a manner as to automati
energy applied to a translation device such as a
cutting device for phonograph recording con
nected to the output terminals g-h. A portion 40 cally adjust the intermediate signal frequency
of the output energy is a applied to the primary
to coincide with the center resonance frequency
of a transformer 44 having two secondary wind
of the intermediate frequency amplifier of the
ings 45 and 5B. 5 The secondary 45 serves to
According to the present
improvements ' there
energize a recti?er 46 and ?lter comprising charg
ing resistor 41, smoothing condenser 48, and dis- 2 45 are provided a pair of variable impedances in‘ the
charge resistor 49 to produce a control potential
form of electronic tubes 16, TI shunted across
the resistors 65 and 61, respectively, and ‘serving
for automatic control of the time constant for'
e1- applied to a gain control element of the am
pli?er 43 for compression of the signal intensity
range, in a manner well known in the art. There '
the frequency control potential in dependence
is further shown an electron tube impedance 55 A
upon the carrier amplitude or average‘ strength
shunted across the charging resistance 4'! and
serving to control the- charging period of the
purpose the grids of the valves 16 andjg‘l'l “are
of the radio signals being received. For "this
smoothing condenser 48. For this purpose'the
grid of the valve 55 is controlled by an; auxiliary
potential er varying according to‘the average sig
nal strength and produced by means of a recti
?er 5|, smoothing condenser 52 and discharge
resistance 53 energized by the secondary winding
the attack time for the ‘compression control with
cuit elements.-
potential er is derived from the ends of the re‘
sistance 13 shunted by a smoothing condenser
14, while a further ?xed bias is applied ‘to‘jthe
grids of the tubes 16 provided by a suitable‘ source
such as a ‘battery 15 and acting in oppositionto
the recti?ed potential drop developed across
,' I‘
.65 smoothing resistance 13.
Referring to Figure 7, there is shown an exem
pli?cation of the invention embodiedjin a system
for automatic frequency. control commonly used
in radio receivers. The rectangle 56 collectively
indicates a receiver ‘preferably of the super
heterodyne type having its input excited by an
60 by way of transformer l0 to a rectifyin‘g'cir
cuit comprising recti?er ‘H shunted by smoothing '
resistances 12 ‘and 13 in series. ~ Thercont'ro‘l
50 of the transformer 44. vA source of potential
54 such as a dry battery or the equivalent serves
to provide a ?xed bias for the tube 55, whereby
a reduction of the tube resistance is started after
the signal amplitude exceeds a _ predetermined
value. In this manner it is possible to reduce
increasingrsignal strength, in particular when a
predetermined signal strength ‘is reached which
may be chosen by suitably proportioning the .eir
simultaneously controlled by a potential etpro
duced by applying another portion of intermedi
ate frequency energy extracted from‘ the'circuit
In an arrangement of‘ the aforedescribedtyliie ‘
the regulating‘time constant for the automatic
frequency adjustment will be normal as-long as
the signal strength remains within a predeter
mined limit, in that the ?xed negative grid bias
for the valves 15 and 11 provided by the battery
15 iscompensated by the potential?drop ‘across
resistance‘ 13. "If the signal strength decreases
below this limit the valves 15 and 11 will .be
blocked by the negative ‘bias 15, whereby the ‘dis
automatic gain control means to effectcompr‘es
sionofthe intensity range of the ampli?edaudlo
through the resistances éli-vand E'Eonly insuch a
5 manner that with proper design of the circuit the
1 potent-ialat the condensers 66' and 6.1‘ will retain
1 its value for a certain period. Thus, during rapid
signals, ?lter means in the gain control‘circuit,
meansfor producing an auxiliary potential vary
ing in accordance with theaverage signal ampli
fading periods the receiver will be in the exact
tude, further means for controlling the time con
stant of said ?lter means by said auxiliary po
1 tuning adjustment when the signal strength
‘ again begins to rise.
' 6;. In an audio frequency ampli?er comprising
5 charge of the condensers 55' and ?'l‘jtakes, place
In other words, the speed
tential, whereby the time constant is decreased
‘ ofthe automatic frequency control (AFC) action
3 is varied in direct proportion :toth'e variations 10 as the signal strength is increased, and‘ delay
means to limit the control of the time constant
of the strength of- the signals being received.
of said ?lter to signal amplitudes in excess of a
It willlhe evident from the above that. the in
predetermined minimum level;
‘ ventionris not limited to the speci?c circuits and
7; In an audio frequency'ampli?er comprisin
'_ ‘ ‘arrangements of parts. and‘ methods disclosed
"herein for illustration but that the underlying 15 automatic. gain control means for. compressing
the intensity range of the ampli?ed audio signals,
idea and prineipleof the invention are susceptible
?lter means in the gain control circuit comprise
' l of ‘numerous. modi?cationsand variations coming
ing impedance elements and an electron dis
1‘ within its broader scope and spirit as de?nedhy
charge device opcratively connectcd'vvith' atleast
-1 the appended claims. The speci?cation‘ and
i drawings are to: be regarded accordingly in an 20 one of i said impedance elements; means to pro
vide a ?xed bias for said electron device, means
: illustrative rather than in a limiting sense.
for producing an auxiliary potential varying in \
1-. In; atranslation system for oscillatory signal
proportion to the, average signal amplitude, and
meansto applyadditional variable bias tosaid
electron device by said auxiliary potential to con
trol the time constant of said, ?lter means; said
fixed bias being of such polarity and magnitude
that the time constant is decreased when the
' l cnergy,: means for producing an auxiliary poten
' 1 tial. lay extracting and averaging- a pQl‘tion of the
{energy being translated, means to utilize said
auxiliary potential to automatically control a con-,7
‘ dition ofxthe- energy being translated; and further
Signal amplitude increases beyond a predeteré .
; meansicr' automatically varying the speed of
potentialin. direct do? 30 mined minim-um level
an ampli?er’ for oscillatory signal energy,
nendencc, upon variations ‘of a dine-rent condition
the steps of controlling a condition 01”: theam
; qr the energy- being; translated.
pli?ed energy accordance with a characteristic
.2. In a
ion system fo1"oscil1a.torysig'—
of the energy to be ampli?ed, and. automatically
cal cncrey" in “ding an amplifier, means com
Y prising rectif: ris- and?lter means fer-producing 35 varying the speedof control'in‘direct accordance
with variations of a different characteristic of
1 adauX'iliarv-pctential by extracting andavcraa
said energy.
ins a portion; cf-thc energy being translated; said
‘ control-l of: said all. iliagry
; ?lter means; ccmprising a network of impedance '
. elements, means» to utilize said auxiliary Pete-c
tial for- CQIltl‘Olling-thd gain; of. said ampli?er,
means for producing a further auxiliary poten
terfering noisewaves of relatively short, period
compared to the signal Waves, or toselective 'sig- '
nal fading conditions, said range controller in
cluding a variable gain ampli?er in'said; circuit
and a control circuit including a variable‘ im
3 tial varying-inproportion to variations of a dif
j ferent condition of the energy being ampli?ed,
;~and~mcans toutilizc said further auxiliary poten
1 tial. for, controlling the magnitude of atlcast one
1 of. the impedance elements,‘ of-said nltcr means
Ina translation system for oscillatory signal
' ludinegan ampli?er, meanscomprisine
5 cccrsw-nc
g; and ?lter means. for producing an aux,
. iliary' potential. by extracting and. ayeragiue a
9. In combination with a range controller in
a signal wave transmission circuit subject to in
pedance, for automatically adjusting the gain of
said ampli?er" to, make the amplitude range of
the signals in its output a desiredifunction-ofithe
‘ means comprising»- a. network of impcdanccclcr
signal amplitude- range, in its uncut,v means to
improve the operation of said range controller
comprising. means for automatically varyingthe
value of said variable impedance» to adjust the
time. constant oi said control circuit in accord
5 mcnts. anclcctronic device 0.perativelyfconnccted
ance with the rate of variation of the- Waves-lap:
‘ with at least. one of said impedance elements,
plied to. the input of said ampli?er.
1 pcrtioncf the'cnersy heingttranslat?d; said-?lter
. means tc-utilize said. auxiliary potential for con-
‘ trcllinertlae gain of said ampli?er, means for Pro
ducins a. further auxiliary potential varying- in
. - .
10.. In a transmission system, a. rectifier e er,
55 gized from said system to produce a control volt
age, meansfor controlling a transmission char
‘ proportion to variaticnsci a different. condition
acteristic. of said system-in accordanceivith said
3 oi the» cnereyhcine ampli?ed, and further means
controlvvoltagc, a ?lter connecting said recti?er ‘
to. said control means for partiallysmoothing; out
i to control the. impedance. of said electronic device
‘ in accordance. with said further- auxiliary poten 60 variations in said. controlvoltage, means for- ad
J'usting the. time. constant of the-?lter,,~and- said
tial, to vary the, time constant of, said ?lter. means
adjusting means being automatically actuatedin
1 in dependence upon. variations of, said condition
dependence on adi?erent. characteristic oi sig
4. In a, system‘ as claimed
claim. wherein
said further auxiliary potential varies with the
rate of. change oithc Signal amplitude. variations,
whereby the speed 0iv the gain. control-is varied in
j direct proportion to the rate of. chance. ci. the.
‘ signal amplitudevariaticns.
5.. In asystcmas claimed in claim 3., wherein
‘ said further auxiliary potential varicsaccording ~
. to the relativeamplitudcs of high audlcw fre
l quency: components of. the. energy being. trailer
‘ lated'zwhereby the speed of gain control is‘ dc.
creased with increasing relative strength of the
low frequency components.
nals emanating: from said system.
1.1,. In a. transmission system. a recti?er ener
gized from saidsystem to, produce a control-volt.’
age, means for controlling. a-._transmissicn charac
teristic of said system'in accordancdWith said
control voltage, a ?lter. connecting said ., recti?er
to. said controlv means tor partially Smoothing,- out
variations in said control voltage; and means‘ op
erciting.-v automatically in dependence on; - varia
tions, in a di?‘erent. characteristic. 0: signals in
said system. ior'adiusting the ?lter; time constant.
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