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Патент USA US3083351

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March 26, 1963
(5. WHITE ETAL
3,083,341
METHOD AND APPARATUS OF CONTROLLING GAIN OF AN AMPLIFIER
Original Filed April 16, 1954
4 Sheets-Sheet 1
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March 26, 1963
G_ WHITE ETAL
3,083,341
METHOD AND APPARATUS 0F CONTROLLING GAIN OF AN AMPLIFIER
Original Filed April 16, 1954
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March 26, 1963
(5. WHITE ETAL
3,083,341
METHOD AND APPARATUS OF CONTROLLING GAIN OF AN AMPLIFIER
Original Filed April 16, 1954
4 Sheets~Sheet 4
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FIG.
INVENTORJ‘
A TTOE/YEYS
nit-ed. ?tates Eatent
has
3,®8¥3,3@4l
Patented Mar. 26, 1963
1
2
3,083,341
tion. Another factor is that with all channel ampli?ers
in the system controlled by an automatic gain control,
the signals received from seismometer to seismo-meter
METHQD AND AlPl’ARA'i‘US 0F CGNTRGLLENG
GAEN OF AN Ali/ELIFHER
Gale White, Houston, and Edmond E). Jackson, Dallas,
Tern, assignors to Texas Instruments incorporated,
Dallas, Tex., a corporation of Delaware
Qontinuation of application Ser. No. 423,697, Apr. 16,
N54. This application inns 5‘, 1958, Ser. No. 743,516
24 Qlairns. (Cl. 336-132)
This invention relates to methods of controlling gain
and more particularly to methods of controlling the gain
of seismic signal ampli?ers whereby the desired type of
gain is obtained by modifying the operation of the auto
matic gain control section of the ampli?er and is a con
tinuation of application S.N. 423,697, ?led April 16,
1954, now abandoned.
Generally speaking, a seismic ampli?er equipped with
across the spread will be recorded as constant amplitude
traces on the seismogram. This is not always desirable
since the difference in the signal level received at the
various seisrnometers is sometimes of assistance in inter
preting the records. Also, for making velocity measure
ments in well bore-holes, a ?xed gain ampli?er is a pre
requisite for the equipment used by those performing
such surveys. Thus, ampli?er systems equipped only with
automatic gain control cannot meet the demands of sys
tems requiring ?xed gain ampli?cation. Further, time
varied gain is useful in areas where the signal decay
15 function with time is known and can therefore be used
in recording constant amplitude traces.
It is ‘accordingly a primary object of this invention to
provide seismic ampli?ers with an initial control to de
crease the sensitivity of the automatic gain control, and
automatic gain control is more satisfactory than either
the ?xed gain or the time varied gain ampli?ers due to the 20 consequently the gain, until the seismic signals are re
nature of the energy received in the seismic surveying
ceived at the ampli?er and cut off this initial control.
process. When an explosive charge is detonated, a por~
It is another object of this invention to provide means
tion of the waves generated travel in ‘a more or less direct
in conjunction with the automatic gain control to convert
path from the charge to the seismometers while another
the automatically controlled gain ampli?er to a ?xed
portion of the waves travel into the earth and are re
?ected back to the seismometers from layers where a
change of velocity occurs. At the interface between the
layers of different velocity material, only a portion of
25 gain ampli?er.
-
It is another primary object of this invention to provide
a summing and averaging circuit whereby all channel
ampli?ers in the amplifying system are controlled from a
the wave energy is re?ected back to the surface while the
master automatic gain control by the average signal level
remainder travels on towards deeper layers. These waves 30 ‘over the spread to obtain the variation in signal amplitude
are attenuated in traveling from the shot point to the re
arriving at the various seismometers.
?ecting layer and from ‘the re?ecting layer to the seismom
It is a still further object of this invention to provide
eter and, of course, the energy reaching the seismome-ters
a circuit with the ability to vary the gain of a number of
becomes smaller as the re?ections arrive from the deeper
ampli?ers with time from a master oscillator.
strata. Conversely, those waves traveling directly from 35
These and other objects of the present invention will
the shot point to the seisrnometer result in a compara
be apparent from the following description when taken
tively large signal. Even though these latter Waves
in conjunction with the accompanying drawings in which:
travel in the unconsolidated earth layer and consequently
FIGURE 1 is a block diagram of a two loop automatic
lower velocity layer, they generally arrive slightly before
gain control seismic ampli?er channel incorporating fea
the re?ections from the various strata because of the 40 tures for modifying the normal operation of the am
shorter travel path. Thus, the seismometers ?rst receive
pli?er;
energy at a high level which then decays rapidly as the
FIGURE 2 is a block diagram of the initial control
re reciions arrive from the deeper strata. The dispropor
circuit for decreasing the gain of the ampli?er channel
tion in magnitude between the waves traveling in the uns
of FIGURE 1 until the ?rst break energy is received;
consolidated earth layer or from shallow horizons to
FIGURE 3 is a block diagram and partial schematic
the seismometers and those re?ecting from the deeper
of a circuit for controlling the gain of a number of
horizons makes the use of a ?xed gain ampli?er unsuit
ampli?ers by the average signal level received over the
able for the basic reason that any gain low enough to
entire spread; and
allow the largest signals to be recorded on a chart of
FIGURE 4 is a block diagram illustrating a circuit for
reasonable width would be insu?icient to distinguish re 50 converting an automatically controlled gain ampli?er to
?ections at the tail end of the record. Also, an ampli?er
a time varied gain ampli?er.
system with its gain ?xed as a function of time is not
Describing brie?y the circuit of FIGURE 1, a two loop
always satisfactory for the reason that the signals from
automatic gain control ampli?er channel is shown similar
underlying strata may decay in accordance with a dif
to that described in co-pending application Serial No.
ferent time function from that time function preset on the
423,671, ?led April 16, 1954. When an explosive charge
ampli?er to increase the gain. Consequently, an auto
10 is placed in a shot point drilled in the earth and ?red,
matic gain control system is usually provided in making
seismic waves are generated which travel into the earth
seismic surveys to give the ampli?ers a high gain for small
to re?ecting layer 11 where they are reflected (in part)
signals and a low gain for large signals.
~
back to a seismometer 12 disposed on the surface of the
The feature of high gain with low amplitude input 60 earth. The signals detected at seismometer 12 are fed
signals, however, presents a problem since the seismic
to an input stage 13 comprised of any desired number of
ampli?ers are placed in operation before the explosive
ampli?er stages and then through ?lter 14. Filter 14 is
designed to pass only certain frequencies within the seismic
by the explosion arrive at the seismometers. Thus, any 65 frequency band and therefore consists of ?lters with vari
low ‘amplitude random noises detected by the seismom
able high cut-o?’ and low cut-01f characteristics to in_
charge is detonated and before any waves generated
eters appear at the ampli?ers and because of the automatic
crease or decrease the frequency ‘band passed as appears
gain control action, increases the sensitivity of the am
most advantageous. From there, the ampli?ed and ?l
pli?ers to a high gain level. Under these circumstances,
tered signal is applied to diode attenuator 15 in the ?rst
when the high level ?rst break energy from the seismic
70 AGC loop.
explosion arrives at the seismometers, the ampli?ers be
Diode attenuator 15, as described in the co-pending ap
come saturated and may not recover su?iciently to am
plication referred to above, consists essentially of two
plify the re?ections containing useful seismic informa
diodes in series with a high resistance and an arrangement
3,083,341
A.
'ator 1‘5 and therefore the grid bias voltage to ampli?er
3
to control the bias voltage on the diodes. The plate of
stage 16. The same action occurs in the second loop of
one diode is connected to the cathode of the other diode
the AGC system. The ‘low frequency band pass ?lter 32
at the output of the AGC loops blocks the high frequency
signal from the recording galvanometer but, since the
high frequency signal is much stronger than the random
noise signal and ‘has reduced the gain of the ampli?er, the
low amplitude random noise appears on the recording
while the remaining cathode and plate of the diodes re
spectively are connected into a Wheatstone bridge. A
positive source of D.-C. voltage is connected to the
Wheatstone bridge to bias the cathodes of the diodes in
the reverse direction for current how‘ and thereby create
a very high resistance. This positive bias voltage applied
galvanometcr as a straight line trace.
to the diodes remains until a signal is fed through the
‘With the gain of the ampli?er thus clamped down by
AGC loop and converted into a positive D.—C. voltage to 10
the high frequency signal, the ampli?er is not saturated
balance in whole or in part the constant bias voltage
by the initial high energy level seismic signals. Instead,
on the diode cathodes. The balance voltage to the Wheat
stone bridge is provided by amplifying signals through
ampli?ers 16 and 17, feeding the ampli?ed signals through
phase splitter 18 to produce two voltages of opposite
polarity, rectifying the voltages in recti?er 21, and then
' these signals are ampli?ed through the two loop AGC
and recorded by the recording galvanometer 33 as a ?rst
15
pears at lead 35 which is connected to low frequency
ampli?er 50. Since the signals passing ?lter 32 are within
theseismic frequency band, they are of a low enough
frequency to be accepted at ampli?er 50 and ‘are accord
controlling the .grid of cathode follower 22 by means of
the recti?ed D.-C.- voltage. The current flow in cathode
follower 22 causes 1a voltage drop across a resistor in
series with the cathode of the follower tube and deter
break. Any signal recorded by galvanometer 33 also ap
20
ingly ampli?ed. The output of the .low frequency ampli
?er St)‘ is recti?ed by means of recti?er 51 to a negative
D.-C. voltage and applied to the grid of ampli?er 43
as the balance voltage reduces the bias voltage on the
through a time delay circuit 52. The negative D.-C.
diodes, the diodes offer less resistance to current ?ow.
voltage biases ampli?er 43 to cut-off and thus removes
It follows then that since the two diodes are in series with
a resistance, a voltage divider is formed in which the 25 the high frequency signal from the two AGC loops al
lowing the normal AGC operation to take hold and main
voltage drop across the resistance of the diodes varies
mines the balance voltage applied to the bridge. Thus,
tain the output of the seismic signals at a constant ampli
in accordance with signal through the ampli?er and which
tude. It should be noted that although the high frequency
in turn provides the grid bias control for the ampli?er
signal is fed to a number of channels, there is only one
in ampli?er stage 16. More particularly, both diodes of
the diode attenuator 15, together with their series resist 30 return path to cut off the high frequency signal. The
cut-off path is so chosen that the high frequency sensi
ance, form a voltage divider network in which the voltage
tivity reducing signal remains on all of the channels until
drop across the diodes varies in accordance with the out
the seismic signal has arrived at the farthest channel in
put signal of the ampli?er 16as impressed on the divider
time from the shot point. Further, a sensitivity control
network through stages 17, 18, 19, 21 and 22. This vary
ing voltage across the diodes of attenuator 15 is used ‘as 35 58 is connected between oscillator 40 and the high fre
quency leads to the channels to prevent the gain control
the grid bias or gain control of the ampli?er 16. The
eifect of this circuitis to provide a constant amplitude
output signal regardless of the amplitude of the input
signal. This effect is multiplied by a second AGC loop
identical to the ?rst and consisting of the components
designated by the numerals 23-30.
7
Considering now FIGURES 1 "and 2, the two circuits
signal to each channel from falling below the preset level.
As indicated above, ampli?er 41 feeds the signal from
oscillator 40 to both ampli?ers 43 and 46.
A, second
bank of channel ampli?ers is provided with initial gain
control by feeding the high frequency signal from arn
pli?er 41 to ampli?er 46, attenuator 47, ampli?er 48
‘and connecting the signal into ‘the other channels by
lead' 49. A single lead cut-off path 56, similar to path
ampli?ers when a large signal is received as well as to 45 35,v detects the low frequency signals at galvanometer
33 and applies these signals to a low frequency ampli?er
keep random noises from being recorded on the seismic
53. The output of ampli?er 53 is recti?ed by recti?er
record. The output of a high frequency oscillator 40,
54 to a negative D.-C. voltage and applied to the grid
which is of considerably higher amplitude than the ran
of ampli?er 46 through a time delay circuit ‘55 to bias the
dom noise signals detected by the seismometer, is ampli
ampli?er to cut-off. By duplicating this arrangement, it
?ed in ampli?er 41 and then fed to ampli?ers 43 and 46.
is apparent that the sensitivity of any number of chan
The high frequency signal is ?rst ampli?ed in ampli?er
nels can be controlled by the high frequency signal from
43, and from there, it is reduced inarnplitude in attenu~
oscillator 40. Provision is made through a time delay
ator 44 and again ampli?ed in ampli?er 45 before being
circuit 57 to also bias ampli?er 41 to cut-oft".
connected by lead 34 into the AGC ampli?er loops as
To convert the ampli?er channel from an automatically
shown in FIGURE 1. In like manner, this ampli?ed high 55
controlled gain ampli?er to a ?xed gain ampli?er,
frequency signal from oscillator 40 is connected into other
switches 20 and 28 shown in FIGURE 1 are simply
ampli?er channels as shown by the multiple leads in FIG
moved from switch position 1 to switch position 2. With
URE 2.
the switches 28 and 28 in position 2, a path for the high
The highfrequency signal mixes with any low ampli
tude random noises detected by the seismometer and this 60 frequency signal from oscillator 40 vis provided through
each AGC loop by the high pass RC ?lters 19 and 27
mixed signal is ampli?ed in ampli?er 16. From ampli?er
‘and, as before, this high frequency signal reduces the
116, themixed signal divides into two paths, one leading
sensitivity of the control loops to prevent random noise
to ampli?er 17inptl1e ?rst AGC loop and the other to
signals from opening up the gain of the ampli?ers ‘and
the.’ second AGC loop. The action of the AGC loops
from appearing on the seismic record as a noisy trace.
being identical, only the action of the ?rst loop on the
However, as low frequency signals (such as would be
mixed signal will be described here. After the signal is
combined-providea means for initially controlling the
sensitivity of the AGC loops to prevent saturation of the
ampli?ed by ampli?er 17, the high frequency component
passes through high pass RC ?lter 19‘ while the lower
frequency random noise component passes throughphase
splitter 18, switch 20lbeing in the closed position. The
signals again mix ahead of recti?er 21 and are there
recti?ed and the D.-C. voltage applied to the grid of
cathode follower 22. The voltage produced in the cath
ode follower is used to reduce the sensitivity of the AGC
loop by decreasing the bias voltage on the diode attenu
received from making velocity measurements in a bore
hole) are received at the channel, the open switches
prevent the low frequency signals from completing a cir
cuit through the phase splitters 18 and 26 and are there
fore ampli?ed straight through ampli?ers 16 and 24
:and output ampli?er 31 to the recording galvanometer.
The low frequency signal, picked up by lead 35, biases
ampli?er 43 to cut-off and removes the high frequency
signal from the channel as described above. With the
3,083,341
5
6
high frequency signal removed and the low frequency
signal prevented from passing through the control loop,
prevent random wind noises from appearing on the seis
the channel operates merely as a ?xed gain ampli?er.
Considering now FIGURE 3 in conjunction with FIG
URE 1, a circuit is provided for ‘averaging the signals
received at the seismometers across the spread and mak
ing all channels track from a master gain control. In_
this circuit, the gain of all channels is controlled by this
average signal to give an indication of the variation in
signal amplitude received at each seismometer. As in 10
signal is ampli?ed through the channel, the high fre
the circuit for ?xed gain ampli?cation, the high frequency
signal from oscillator 40 is ampli?ed in ampli?er 43,
reduced in amplitude by attenuator 44 and ‘again ampli
?ed in ampli?er 45 before being fed to the AGC loops
mogram as a noisy trace. When a low frequency seismic
quency signal is removed by a negative D.-C. voltage
applied to the grid of ampli?er 43 through lead 35, low
frequency ‘ampli?er '50, recti?er 5i and a time delay cir
cuit 52. To provide time varied gain control, switch 39
is closed to position 2 and this same low frequency signal
[fed to a low frequency ampli?er 75 by lead 3S. Ampli
?er 75 ampli?es the signal and feeds it to a starting
circuit 76. Starting circuit 76 consists of a recti?er to
provide a positive voltage to the grid of an ampli?er tube.
A resistor is connected in series with the cathode of the
ampli?er tube to ground and a condenser is connected
by lead 34. Switches 20 and 28 are in switch position 2 15 across the resistor. As current ?ows in the ampli?er
thereby opening the circuit and preventing the low fre
tube due to the recti?ed voltage, the voltage drop across
quency signals from taking over the control of the AGC
the resistor charges the condenser. The discharge path
loops. The high pass RC ?lters 19 and 27 provide a
of the condenser is connected to the grid of modulator
path for the high frequency signals from oscillator 40
77, the modulator being connected in the output path of
through the gain control loops to reduce the sensitivity of 20 oscillator 49 and feeding into the AGC loops of an 11
the channels.
Low frequency seismic signals are then
number of channels through attenuator 78 and leads simi
lar to lead 34. When the condenser discharges, a large
voltage is applied to the grid of modulator 77 which
56. The output of ampli?er 50 is recti?ed to a negative
decreases in accordance with the discharge character
D.-C. voltage by recti?er 51 and fed through a time delay 25 istic of the condenser. ‘Thus, a large high frequency
circuit 52 to the grid of ampli?er 43 where the grid is
signal ‘from oscillator 46‘ is applied to the AGC loops
biased to cut-off.
to decrease the gain for the ?rst high energy level seismic
Switch 37, however, is now closed in switch position 2
waves and, as the ‘discharge voltage of the condenser
and these same low frequency signals are picked up by
decreases, the high frequency control signal to the AGC
lead 36. The low frequency signals are fed by lead 36 30 loops decreases to allow a higher gain for the smaller
to a recti?er 60 where they are recti?ed to a positive
seismic signals. If the time decay of seismic energy at
D.-C. voltage. By a similar arrangement, low frequency
"a given prospect is known, the discharge characteristic
signals from an n number of channels are recti?ed to
of the condenser can be so chosen that the seismic signals
‘ampli?ed straight through the channel and are picked up
by lead 35 and routed to the low frequency ampli?er
positive D.-C. voltages by recti?ers 61, 62 and 63. The
will be recorded as a very nearly constant trace regardless
recti?ed D.-C. voltages ‘are summed and averaged in a 35 of the signal amplitude.
circuit comprised of resistors 64, 65, 66 and 67 connected
To summarize a basic two loop automatic gain con
in parallel and the parallel resistances connected in series
with a resistor 68 equal in resistance to the sum‘ of the
parallel resistances. Thus, a voltage divider is formed
in which the D.-C. voltages are summed in the parallel
resistances 64-67 and the average voltage level taken by
trol seismic ampli?er channel is provided with a high
frequency signal and a high frequency path through the
control loops together with means to switch the low fre
quency path out of the control loops. Then by using
the low frequency seismic signal or the-high frequency
oscillator signal in various modi?cations, the gain of the
the drop across resistor 63.
The ripple in the recti?ed D.-C. voltage across resistor
ampli?er can be controlled according to the desired type
68 is smoothed out in condenser 70 and the voltage fed
of gain.
through resistor 69 to the grids of modulators 71, 72 45
Although the present invention has been shown and
and 73, modulators 71, 72 and 73 being connected in
described in particular embodiments, nevertheless Various
series with the output of oscillator ‘40. The positive volt
changes and modi?cations obvious to one skilled in the
age from the summing and averaging circuit drives the
art are within the spirit, scope and contemplation of
grids of the modulators more positive in accordance
the invention.
with the average ‘amplitude of the low frequency signals 50
What is claimed is:
and therefore controls the output of the oscillator. The
1. A gain control system for an ampli?er comprising
modulated high frequency signal is connected with leads
similar to lead 34 which then apply the control signals
to an 12 number of channels as indicated in FIGURE 3.
High pass RC ?lters such as filters 19 and 27 of FIG
URE 1 permit the high frequency control signal to pass
through the control loops and, by varying the resistance
high frequency signal generating means, means to feed
said high frequency signal'to the input circuit of said
ampli?er, means to sample the high frequency com
55 ponents of the output signals of said ampli?er, means
to rectify said sample, means operative responsive to
said recti?ed sample to control the degree of ampli?ca
of the diode attenuators, set the gain of each ampli?er
tion of said ampli?er means as an inverse function of
channel equal to every other channel. With ‘the gain of
the value of said recti?ed sample, and means operative
all channels controlled by the average signal level over 60 responsive to frequency components of said output sig—
the entire spread, it can be seen that a larger signal
nals of said ampli?er lower than the frequency of said
detected at one seismometer will be recorded with a
larger amplitude than :a neighboring seismometer receiv
ing a smaller signal. Therefore, the amplitude of the
high frequency signals to change the amplitude of said
high frequency signals fed to the input of said ampli?er.
2. A gain control system as de?ned in claim 1 where
traces recorded side by side will not appear with the 65 in said means operative responsive to frequency com
same amplitude but instead give an indication of the varia
ponents of said output signals of said ampli?er lower
tion in signal level received at each seismometer in the
than the frequency of said high frequency signals to
spread.
change the amplitude of said high frequency signals
FIGURE 4 in conjunction with FIGURE 1 illustrates
changes the amplitude of said high frequency signals as
a block diagram circuit for providing time varied gain 70 a desired function of time.
for a seismic ampli?er. As described in the other meth
3. A gain control system as de?ned in claim 1 wherein
ods for controlling gain, the output of a high frequency
said means operative responsive to frequency components
oscillator 40 is fed through ampli?er 43, attenuator 44
of said output signals of said ampli?er lower than the
and ampli?er 45 and applied to each channel in the
frequency of said high frequency signals to change the
ampli?er system to reduce the gain of the channel and 75 amplitude of said high frequency signals reduces the am
3,083,341
8
7
plurality of ampli?ers in unison and as a function of the
plitude of said high frequency signals by a ?xed amount.
4. A signal ampli?er having automatic gain control
‘average amplitude of the‘ low frequency output signals
high frequency signal to said input circuit of said signal
averaging the amplitudes of said frequency ‘components
to change the amplitude of said high frequency signals fed
of all of said plurality ‘of ampli?ers comprising means
which comprises signal amplifying means having an 11'1"
generating high frequency signals, means to feed said
put circuit, ?rst means for deriving a ?rst voltage propor
tional to the high frequency components of the output of 5 high frequency signals to the input of each of said plu
rality of ampli?ers, means in each of said plurality of
said signal amplifying means, second means for deriving
ampli?ers to sample the high frequency output signals of
a second voltage proportional to the low frequency com
that ampli?er, means in each of said plurality of ampli
ponents of the output of said signal amplifying means,
?ers to rectify said sample of said high frequency output
means for rectifying said ?rst and second voltages, means
operative responsive to said recti?ed voltages to control 10 signals, means ‘in each ‘of said plurality of ampli?ers
operative responsive to said recti?ed sample of said high
the gain of said signal amplifying means, means to gener
frequency output signals to control the gain of that am
ate a high frequency signal, means to feed said high
pli?er, means sampling the frequency components of the
frequency signal to the input circuit of said signal am
output signals, of each of said plurality of ampli?ers lower
plifying means, band pass ?lter means to receive the out
than the frequency of said high frequency signals, means
put from said signal amplifying means and pass only s1g
averaging the amplitudes of said’ sampled frequency com
nals of a frequency lower than said high frequency signal,
ponents of the output signals of all of said plurality of
and means operative responsive to the output of said
‘ampli?ers, and means operative responsive to said’ means
?lter means to render inoperative said means to feed said
amplifying means.
a
to the input of said plurality of ampli?ers as an inverse '
5. A signal ampli?er having automatic gain control
function of said average amplitude of said frequency
'COIIIPOIICIltS.
as de?ned in claim 4 wherein said ?rst means and said
second means for deriving ?rst and second voltages pro
13. An automatic gain control for a multi-channel am
portional to the high and low frequency components of
the output of said signal amplifying means-are connected
in parallel.
pli?er system comprising a plurality of ampli?ers, a low
frequency pass ?lter receiving the output of each said
ampli?er, ?rst sampling means to sample the output of
each said ?lter, rectifying means to rectify each said
‘
6. A signal ampli?er having automatic gain control
as de?ned in claim 5 wherein switch means is provided
in series with said second means for deriving ‘a second
voltage proportional to the low frequency component of
the output of said signal amplifying means.
sampled signal, means to sum and average said sampled
30 signals from all said recti?ers, means to generate a high
frequency signal, means to ‘modulate said high frequency
‘signal with said averaged signal, means to feed said modu
lated signal to the input of each said ampli?er, second
which comprises space discharge ampli?er means, means
sampling means to sample the'output signal from each
to sample the ampli?ed signal, phase splitting means to
transform said sampled signal into two voltages of oppo 35 said ampli?er, means to rectify said second sampled sig
nal, and attenuating means operative responsive to Said
site polarity, rectifying means to rectify 'said voltages,
‘second recti?ed signal to control the grid bias of said
attenuating means operative responsive to said recti?ed
ampli?er.
voltage to control the degree of conductivity of said
14. A master automatic gaincontrol a's de?ned in claim
space discharge ampli?er means, a high frequency pass
?lter in parallel with said phase splitting means, a high 40 13 wherein said means to sum and ‘average 'said sampled
signals, includes a plurality of resistors in parallel and
frequency signal generating means, means to feed said
another resistor in series therewithequalin value to the
high frequency signal to said space discharge ampli?er
sum of the values of said plurality of resistors.
means, a low frequency pass ?lter to receive the output
15. A master automatic gain control as de?ned in'claim
from said space discharge means ampli?er, and feedback
means to sample the output signal from said low fre 45 13 wherein means are provided to feed said high frequency
7. An automatic gain control system for an ampli?er ’
signal unmodulated to each said ampli?er, and means are
provided to derive from the output of a low frequency
p'ass'?lter a signal to block said unmodulated high fre
quency pass ?lter and to use same to block said high
frequency signal.
_
8. An automatic gain control ampli?er as de?ned in
quencysignal.
claim 7 wherein means are provided to amplify said high
16. An automatic gain control as de?ned in claim 13
frequency signal before same is fed to said ampli?er 50
wherein a circuit composed of a'phase'splitting means and
tube and said feedback means functions to‘bias'said
a switch means in series ‘therewith arranged in parallel
means to amplify high frequency signals to cut-off.
with a high frequency pass ?lter is interposed between
9. An automatic gain control ampli?er as de?ned in
said second sampling means and said means to rectify
claim 7 wherein switch means is provided in series with
said phase splitting means.
'
55
10. An automatic gain control comprising an ampli?er,
a low frequency pass ?lter receiving the output of said
ampli?er, ?rst sampling means to sample the output of
said ?lter, a circuit including a condenser, means for
charging said condenser by said sampled signal, high fre
quency generating means, means to modulate the gener
ated high frequency signal ‘by discharge of said condenser,
means to feed said modulated high frequency signal to the
input of said ampli?er, second sampling means to sample
the signal from the output of said amplifier, means to rec—
tify said second sampled signal, and attenuating means
operative responsive to said recti?ed second signal to ‘
said second sampled signal.
17. The method of controlling as a'desired function
of time the gain'of an ampli?er having an automatic gain
control circuit, which method comprises introducing into
the ampli?er at its input signals of a frequency higher
than the highest frequency of the signals of interest to ‘be
ampli?ed, blocking said signals of interest from said au
tomatic gain control circuit, initiating attenuation of said
high frequency signals in accordance with said desired
function of time at about the time said signals of interest
are applied to said ampli?er.
18. The method of controlling as a desired function of > -
time the gain of an ampli?er having an automatic gain
control circuit, which method comprises introducing into
the ampli?er at its input signals of a frequency higher
10 wherein means are provided to feed a second high 70 than the highest frequency'of signals of interest to be
ampli?ed, blocking said'signals of interest from said auto
frequency signal unmodulated to said ampli?er and means
matic gain 'control circuit, adjusting the ‘amplitude of
are provided to derive from the output of a low frequency
said high frequency signals fed to the input of said am
pass ?lter a signal to block the unmodulated high fre
quency signal.
pli?er to the value ‘at which said automatic gain control
12. A gain control system for varying the gain of a '7 circuit’ sets the gain of said ampli?er at a desired initial
control the grid bias of said ampli?er.
11. An automatic gain control as de?ned in claim
3,083,341
level, and initiating attenuation of said high frequency
signals in accordance with said desired function of time
at about the time said signals of interest are applied to
said ampli?er.
19. The method of varying the gains of a plurality of
if)
as to provide a desired ?xed initial value of gain in said
ampli?er before signals of interest are applied to Said
ampli?er and to provide a different desired ?xed value
of gain in said ampli?er after said signals of interest are
applied to said ampli?er, which method comprises intro
ducing into ‘the ampli?er at its input signals of a frequency
level of signals of interest at the outputs of all of said
higher than the highest frequency of said signals of inter
plurality of ampli?ers, each of said ampli?ers having a
est to be ampli?ed, blocking said signals of interest from
separate automatic gain control circuit and each receiv
said automatic gain control circuit, adjusting the ampli
ing different signals of interest to be ampli?ed, which 10 tude of said high frequency signals to the value at which
method comprises introducing into all of said plurality
said automatic gain control circuit sets the gain of said
of ampli?ers at their inputs signals of a frequency higher
ampli?er at said desired ?xed initial value and thereafter
than the highest frequency of said signals of interest,
removing said high frequency signals from the input of
blocking said signals of interest from said automatic gain
said ampli?er at about the time said signals of interest
control circuits, sampling said signals of interest at the 15 are applied to said ampli?er,
outputs of all of said plurality of ampli?ers and thereafter
23. The method of controlling the gain of an ampli?er
controlling the amplitude of said high frequency signals
having an automatic gain control circuit in such manner
ampli?ers in unison and as a function of the average
as an inverse function of the average amplitude of said
as to provide a desired ?xed value of gain in said ampli
?er before signals of interest to be ampli?ed are applied
plurality of ampli?ers.
20 to said ampli?er and to provide a different desired ?xed
20. The method of varying the gains of a plurality of
value of gain in said ampli?er after said signals of inter
ampli?ers in unison and as a function of the average level
est are applied to said ampli?er, which method comprises
of signals of interest at the outputs of all of said plurality
introducing into said ampli?er at its input signals of a
of ampli?ers, each of said ampli?ers having a separate
frequency higher than the highest frequency of said sig
automatic gain control circuit and each receiving different 25 nals of interest to be ampli?ed, blocking said signals of
signals of interest to ‘be ampli?ed, which method com
interest from said automatic gain control circuit, and
prises introducing into all of said plurality of ampli?ers
changing the amplitude of said high frequency signals at
at their inputs signals of a frequency higher than the
the input of said ampli?er at about the time said signals
highest frequency of said signals of interest, ‘blocking said
of interest are applied vto said ampli?er.
signals of interest from said automatic gain control cir 30
24. The method of controlling the gain of an ampli?er
signals of interest sampled at the outputs of all of said
cuits, adjusting the amplitude of said high frequency sig
having an automatic gain control circuit in such manner
as to provide a desired ?xed initial value of gain in said
nals to the value at which the automatic gain control
circuits of each of said plurality of ampli?ers set the
gains of said plurality of ampli?ers at a desired initial
ampli?er before signals of interest to be ampli?ed are
applied to said ‘ampli?er and a different desired ?xed
level, sampling said signals of interest at the outputs of 35 value of gain in said ampli?er after said signals of interest
all of said plurality of ampli?ers and thereafter control
are applied to said ampli?er, which method comprises in—
ling the amplitude of said high frequency signals as an
troducing into said ampli?er at its input signals of a fre
inverse function of the average amplitude of said signals
quency higher than the highest frequency of said signals
of interest sampled at the outputs of all of said plurality
of interest to be ampli?ed, blocking said signalsof interest
of ampli?ers.
21. The method of controlling the gain of an ampli?er
40 from said automatic gain control circuit, adjusting the
having an automatic gain control circuit in such manner
as to provide a desired ?xed value of gain in said ampli
?er before signals of interest to be ampli?ed are applied
amplitude of said high frequency signals to the value at
which said automatic gain control circuit sets the gain
of said ampli?er to said desired initial value, and there
after changing the amplitude of said high frequency sig—
to said ampli?er and to provide a different desired ?xed 45 nals at the input of said ampli?er at about the time said
value of gain in said ampli?er after said signals of inter
signals of interest are applied to said ampli?er.
est are applied to said ampli?er, which method comprises
introducing into the ampli?er at its input signals of a
References Cited in the ?le of this patent
frequency higher than the highest frequency of said sig
UNITED STATES PATENTS
nals of interest to be ampli?ed, blocking said signals of 50
interest from said automatic gain control circuit and re
moving said high frequency signals from the input of
said ampli?er at about the time said signals of interest
are applied to said ampli?er.
22. The method of controlling the gain of an ampli?er 55
having an automatic gain control circuit in such manner
2,286,106
Ritzmann _____________ __ June 9, 1942
2,329,558
2,397,830
Scherbatskoy _________ __ Sept. 14, 1943
Bailey ________________ __ Apr. 2, 1946
2,554,905
2,663,002
Hawkins _____________ __ May 29, 1951
McManis ____________ __ Dec. 15, 1953
2,723,387
Slavin _____ __, ________ .. Nov. 8, 1955
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