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Патент USA US2112279

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March 29, 1938.
K. HAGENHAUS
2,112,279
AUTOMATIC GAIN CONTROL CIRCUITS
Filed 'Sept. 10, 1936
2 Sheets-Sheet 2
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KURT HAGENHAUS
BY 3%
ATTORNEY
2,112,279
Patented Mar. 29, 1938
UNITED- STATES PATENT OFFICE
2,112,279
AUTOMATIC GAIN CONTROL CIRCUITS
Kurt Hagenhaus, Berlin-Siemensstadt, Germany,
assignor to 'I'elefunken Gesellschaft fiir Draht
lose Telegraphic in. b. H., Berlin, Germany, a
corporation of Germany
Application September 10, 1936, Serial No. 100,069
In Germany September 10, 1935
8 Claims. (Cl. 250-20)
In transmitters it is known that the differences the low-frequency amplitudes are always the
between loud and soft passages of a performance
can be decreased in order that disturbing noises
will not be too clearly noticed, while, on the other
5 hand, the transmitter will not be subjected to ex
cessive control, i. e., it is. not necessary to control
it in regard to the loudest sounds. In order that
in the receiver the intensity range will again be
obtained in its original form, it has been proposed
to expand at the receiver end the intensity range
by means of a control circuit.
Attention has al
ready been drawn to the fact that the control
curve for the intensity range at the receiver must
exactly correspond to that at the transmitter
where importance is to be attached to a true
intensity range. It was hitherto overlooked
that even in the case of corresponding control
curves, the intensity range control in case of
high-frequency receivers is not without faults.
In the drawings:
Fig. 1 shows a circuit arrangement employing
one form of the invention, and
Figs. 2 to 6 inclusive show respectively differ
ent modi?cations of the invention, and wherein
._ in each modi?cation the gain expansion bias is
applied to a radio frequency ampli?er.
According to one aspect of the invention, it is
proposed to employ, at the same time, gain con
trol preceding and following the control detector,
and an intensity range control.
In this way it is
accomplished that for transmitters differing from
each other, as regards intensity or due to fading
phenomena, no influence will be exerted upon
the intensity range control. This is due to the
35 fact that with gain control acting only upon
preceding tubes, the control potential, and hence
also the low-frequency potential which at a
de?nite degree of modulation is obtained in the
same manner as the control potential from the
40 high-frequency, does not remain constant, since
otherwise no controlling action occurs. However,
if also a subsequent stage is controlled in a known
manner, the low-frequency amplitude depends
only upon the degree of modulation of the re
spective transmitter.
Examples of embodiments of this aspect of the
invention are schematically shown in Figs. 1
and 2. In Fig. 1 there is placed in the output of
the high-frequency stage HF1, the detector Gs
50 which furnishes the gain control potential (after
?ltering out the low-frequency) for the preced
ing high-frequency stage (HF1) , and for the sub
sequent high-frequency stage (HFz). Conse—
quently, the receiving detector GE always utilizes
55 the same high-frequency amplitudes so that also
same at the same degree of modulation.
As a
result thereof, the intensity range control oper-i
ates by means of the detector GD which detects
the low-frequency energy, entirely independent CM
of the input potentials of the receiver.
In Fig. 2, the intensity range control operates
on the high-frequency stages. It would also be
possible to combine the arrangements of Figs. 1
and 2. Also other modes of structures are pos 10
sible, as the high-freequency stage I-IFz could for
instance be omitted, and a part of the gain control
and also the intensity range control could be
carried out in the low-frequency part. In this
case, the gain control potential may also be de 15
rived from the receiving detector. On the other
hand, the detector for the intensity range control
may be connected to the output of the detector
for the gain control.
In receivers which provide an intensity range 20
control in the audio-frequency network, for in
stance in order to expand the intensity range of
the reproduction while it is compressed at the
transmitter, there exists the danger of distortion
since the low~frequency amplitudes are very 25
large, and since for controlling the ampli?cation
it is necessary to operate on more or less bent
parts of the characteristics. This disadvantage
is overcome in accordance with another aspect of
the invention in that the intensity range con- 30
trol is carried out in the high-frequency stages
in which there is no gain control.
Two examples of this phase of the invention are
schematically shown in Figs. 3 and 4. In Fig. 3,
the control detector Gs for the gain control is
connected to the output of the high-frequency
stage HF1. Following the ?ltering out of the low
frequency potentials, the control potential acts
upon the high-frequency stage I-IF1. But these‘
low~frequency potentials are applied to the detec
tor GD which serves for the control of the in
tensity range. This control is carried out at the
high-frequency stage HFz, and provides expansion
of gain thereof.
In the example according to Fig. 4, the low
frequency produced in the receiving detector GE
is applied to the detector Go for the control of
the intensity range. The output of this detector
is connected to the high-frequency stage HFz.
The recti?er Gs provides the usual AVC action.
According to another aspect of the invention,
at one or several stages of a high-frequency re
ceiver a gain control, or control of the intensity
range is carried out. This phase of the inven
tion has advantages in receivers in which a lim
2
2,112,279
ited power reserve is available.
The gain con
trol and also the intensity range control each
require a reserve of power in order that they be
fully e?‘ective. Hence, both together can only
be used in larger receivers. The construction
now to be described affords the possibility of still
utilizing the advantages of both controls. In
general, the intensity range control will only be
connected at local reception, or to receive signals
10 from powerful transmitters not subject to fading‘
phenomena, while, on the other hand, for dis
tance reception more importance is to be attached
to compensating the fading phenomena, since in
this case the intensity range control would act
in a false manner, in view of the changing input
3. In a radio receiver of the type including at
least two radio frequency ampli?ers in cascade,
an audio demodulator, an audio ampli?er and a
reproducer, an automatic volume control circuit
responsive to the signal output of the ?rst radio
ampli?er for controlling the gain of the latter,
and an automatic gain expansion circuit, re
sponsive to the audio component of detected sig
nals, for controlling the gain of the second radio
ampli?er in a sense opposite to the gain control 10
of the ?rst radio ampli?er, said volume control
circuit including a recti?er connected to the
?rst radio ampli?er output circuit, and said ex
pansion circuit including a device for rectifying
the audio component of the recti?ed output of 15
potentials.
Examples embodying this aspect of the inven
said recti?er.
tion are schematically shown in Figs. 5 and 6.
least two radio frequency ampli?ers in cascade,
In Fig. 5, following the high-frequency stage HF,
20 a detector Gs is connected for the gain control
to correct for fading, and which controls the
high-frequency stage. Instead thereof, the con
trol could also be carried out at the receiving de
tector GE. The low, or audio, frequency energy
25 appearing in the output of the receiving detector
will be detected in the detector GD.
This control
potential will only then be applied to the high
frequency stage HF, when the switch S is in the
downward position.
The detected audio com
30 ponent is used for expansion of the R. F. am
pli?er gain.
Figure 6 differs from Figure 5 in that the audio
frequency potential for the intensity range con
trol is derived from the detector Gs, and detected
in the detector GD. In accordance with the posi
tion of the switch S, a gain control potential, or
a potential of the intensity range control, is ap
plied to the high—frequency stage HFz. In this
example a gain control is always carried out at
the high-frequency stage HF1, so that at the
right hand position of switch S, a complete gain
control will be effected.
Also, other modes of construction are possible
in which, for instance, at an audio-frequency
45 stage, an intensity range control, or an additional
gain control, are carried out at will. The ar
rangement could, also, be such that the switch
ing is carried out automatically in accordance
with the input amplitude.
50
What is claimed is:
1. In a radio receiver of the type including at
least two radio frequency ampli?ers in cascade,
4. In a radio receiver of the type including at
an audio demodulator, an audio ampli?er and a
reproducer, an automatic volume control circuit
responsive to the signal output of the ?rst‘ radio
ampli?er for controlling the gain of the latter,
an automatic gain expansion circuit, responsive
to the audio component of detected signals, for
controlling the gain of the second radio ampli?er
in a sense opposite to the gain control of the
?rst radio ampli?er, said expansion circuit in
cluding a recti?er for rectifying the said audio
component, and means for applying the recti?ed
audio component to the second radio ampli?er. 30
5. In a radio receiver of the type including a
radio frequency ampli?er network, a demodula
tor, an audio frequency ampli?er network and a
reproducer, means responsive to variations in
modulated signal carrier amplitude for automati
cally controlling the carrier transmission effi
ciency through the radio ampli?er network in a
sense to maintain the carrier amplitude at the
demodulator input substantially uniform regard
less of fading at the radio ampli?er network in
put, and additional means, responsive to an in
crease in the audio component amplitude of the
modulated signal carrier, for increasing the said
transmission e?iciency.
6. In a radio receiver of the type including a 45
radio frequency ampli?er network, a demodula
tor, an audio frequency ampli?er network and a
reproducer, means responsive to variations in
modulated signal carrier amplitude for automati
cally controlling the carrier transmission e?i 50
ciency through the radio ampli?er network in a
sense to maintain the carrier amplitude at the
an audio demodulator, an audio ampli?er and a
demodulator input substantially uniform regard
reproducer, an automatic volume control circuit
responsive to the signal output of the ?rst radio
ampli?er for controlling the gain of the latter,
less of fading at the radio ampli?er network in
and an automatic gain expansion circuit, re
ulated signal carrier, for increasing the said
transmission e?iciency, said ?rst means including
sponsive to the audio component of detected
signals, for controlling the gain of the second
radio ampli?er in a sense opposite to the gain
control of the ?rst radio ampli?er.
2. In a radio receiver of the type including at
least two radio frequency ampli?ers in cascade,
an audio demodulator, an audio ampli?er and a
65 reproducer, an automatic volume control circuit
responsive to the signal output of the ?rst radio
ampli?er for controlling the gain of the latter,
an automatic gain expansion circuit, responsive
to the audio component of detected signals, for
controlling the gain of the second radio ampli?er
in a sense opposite to the gain control of the ?rst
radio ampli?er, said volume control circuit in~
cluding a signal recti?er, and said expansion cir
cuit including a recti?er connected to the output
75 of said signal recti?er.
35
put, additional means, responsive to an increase
in the audio component amplitude of the mod
a carrier recti?er, and said additional means in
cluding a recti?er for said audio component.
60
'7. In a radio receiver of the type including a
radio frequency ampli?er network, a demodula
tor, an audio frequency ampli?er network and a
reproducer, means responsive to variations in
modulated signal carrier amplitude for automat
ically controlling the carrier transmission ef?
ciency through the radio ampli?er network in a
sense to maintain the carrier amplitude at the
demodulator input substantially uniform regard
less of fading at the radio ampli?er network in 70
put, additional means, responsive to an increase
in the audio component amplitude of the modu
lated signal carrier, for increasing the said trans
mission e?iciency, said ?rst means including a
recti?er upon whose input is impressed modu 75
2,112,279
lated carrier energy, and said additional means
deriving its audio component input from said
recti?er output.
8. In a radio receiver of the type including a
radio frequency ampli?er network, a demodula
tor, an audio frequency ampli?er network and a
reproducer, means responsive to variations in
modulated signal carrier amplitude for automat
ically controlling the carrier transmission e?i
10 ciency through the radio ampli?er network in a
sense to maintain the carrier amplitude at the
3
demodulator input substantially uniform regard
less of fading at the radio ampli?er network in
put, additional means, responsive to an increase
in the audio component amplitude of the modu
lated signal carrier, for increasing the said trans
mission ei?ciency, vsaid radio ampli?er network
comprising at least two ampli?er stages in cas
cade, said ?rst means controlling the gain of the
?rst stage, and said additional means controlling
the gain of the second stage.
KURT HAGENHAUS.
10
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