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May 15, 1951
w. D. cANNoN
2,552,884
OSCILLOSCOPE SYSTEM
Filed Jan. 21, 1947
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May 15, 1951
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w. D. CANNON
2,552,884
OSCILLOSCOPE SYSTEM
ATTOFZ
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Patented May 15, 1951
2,552,884
UNITED STATS
ENT OFFICE
2,552,884
OSCILLOSCOPE SYSTEM
William D. Cannon, Metuchen, N. J., assigner to
The Western Union Telegraph Company, New
York, N. Y., a corporation of New York
I
Application lÍanuary 21, 1947, Serial No. '723,232
28 Claims. (Cl. 315-29)
l
2
This invention relates to improvements in os
Other and further objects of the invention re
side in the several unique circuit combinations of
cilloscope systems and in particular to oscillo
scopes intended for viewing high frequency elec
cathode ray tube, time base circuit, discharge cir
trical phenomena either periodic or transient in
cuit and signal amplifier which together provide
nature.
5 an oscilloscopio device of great utility for the ob
Practical oscilloscope devices of the cathode
servation of very rapid periodic and transient
ray type in general comprise four essential ele
phenomena.
ments, and these may be supplemented by addin
Oscilloscope time bases usually consist of a con
tional elements designed to serve special purposes.
denser charging circuit designed to provide a
The four essential parts are the cathode ray tube
With its associated power supplies, a time base,
or sweep circuit, for the purpose of moving the
cathode ray beam across the screen of the tube
in the forward direction, a discharge circuit for
the purpose of returning the beam to the start
ing point, and an amplifier designed to amplify
and control the Volume-of the signal current or
other phenomena under observation. This in
vention relates particularly to the time base cir
cuit, the discharge circuit, and the signal ampli
saw-tooth type of Wave in which a gradually ris
ing voltage during charge is applied to the hori
Zontal plates of the oscilloscope to deflect the
beam on its forward trace, while the more rapid
discharge voltage serves to return the trace to its
starting point. To secure distortionless delinea
tion of the Wave shape on the screen, the outlines
of this saw-tooth Wave should be as nearly linear
as possible and this is achieved ordinarily by
charging and discharging the condenser at a con
20 stant current rate.
fier.
One of the objects of the invention is to pro
vide an oscillograph time base of the constant
current type employing negative feedback to per
mit linear delineations at high frequencies and at
very high beam velocities.
For delineating very high
frequencies, the velocity of the beam and con
sequently the charging current of the condenser
become proportionately very high. The relation
ship between condenser capacity and charging
25
current is given by
Another object is to provide a time base which
2K =charging current in milliamperes (l)
100e
may be easily and positively synchronized with
the signal under observation and in which the
Where
beam velocity is independent of the synchroniz 30
V=volts per micro-second
ing potential.
C=capacitance in Mufarads
A further object is to- provide a time base op
erable at large ratios between the applied fre
At very high frequencies if the individual waves
quency and the sweep repetition. rate.
are to be adequately extended on the screen, volt
A still further object is to provide a time base 35 ages
varying at rates of several thousand volts per
in which the repetition rate is independent of the
micro-second are required. From Equation 1
applied voltage.
ì
Y
above, the charge or discharge of a condenser
as small as 25 ,LL/lf. at the rate of 6000 volts per
micro-second requires a constant current of 150
Still another object is to provide a time base
which utilizes a substantial percentage of the ap
plied voltage.
Another object is to provide a time base in
which the forward and return traces are both
substantially linear and may be used simultane
ously for delineating the same signal.
_
A further object of the invention is to provide
a signal ampliñer for use in connection with
either the signal or sweep deflection plates of the
oscilloscope which will transmit very wide fre
quency bands substantially free of frequency or
phase distortion.
Another object is to provide a signal amplifier
possessing high gain and high voltage output,
freedom from transient distortion, and which
permits easy adjustment of its amplifying char
acteristics.
40
milliamperes. Hence the importance of keeping
the condenser at a 10W value is evident, the mini
mum capacitance becoming that of the elements
ci the regulating vacuum tubes themselves in
addition to the capacitances of the associated
i circuit elements and wiring.
Since tube capaci
ties are quite significant in this frequency range,
a charging circuit should be chosen which per
mits the use of the smaller sizes of vacuum tubes
and circuit elements and so positions them that
50 the ñnal composite capacity is as small as pos
sible.
This specification illustrates a number of such
constant current charging circuits in which an
impedance consisting of resistance or inductance,
65 or both, in series with the space path of a triode
‘2,552,884
3
4
vacuum tube, or other tube triode connected, and
a source of D. C. potential regulate the charging
current to a small sweep condenser. By the
unique choice of circuits the spurious capacities
beam, a time base circuit is connected to the
plates 'I via condenser C6 and comprises a sweep
condenser Ct arranged to be charged through a
charging circuit including the battery I0, a tube
which lie in parallel to the sweep condenser are
minimized so that in certain of the circuits when
the sweep condenser has been reduced to zero,
the residual capacity may be reduced to as low
triode connected, having a plate II, grid I2, and
cathode I3), the inductance L1, and the resist
ance Rk. The inductance L1 when not required
V1 (which may be a triode or other type of tube
may be short-circuited by the switch I4 as indi
using standard vacuum tubes and cathode ray 10 cated. Associated with the grid circuit of the
tube are the series condenser Cg and the grid leak
tubes it has been possible to view satisfactorily
resistance Rg. The time constant of this combi
frequencies of 150 megacycles and higher. This
nation should be such that the voltage drop
impedance provides negative feedback via a con
across Cg does not Vary appreciably throughout
denser in the grid circuit. The series impedance
itself together with the large negative feedback 15 the time base cycle for the lowest repetition fre
quency considered.
which it produces serve to hold the condenser
To discharge the condenser Ct and return the
charging current to a remark-ably constant rate.
cathode ray beam to the starting point a discharg
The several embodiments of the invention can
ing circuit of conventional type is provided which
best be understood by reference to the accom
panying drawings in which:
20 comprises the gas tube V2 (provided with _plate
I5, grid I6 and cathode I‘I), a 'resistor Rs Afor reg
Fig. 1 illustrates a complete‘oscilloscope system
ulating the discharge current and to protect the
embracing a conventional type of oscilloscope
gas tube, a self-bias resistor R2 with bil-.passing
tube, a time base system illustrative of the in
condenser C4, and a regulating grid leak resist
vention, a conventional discharge circuit, and a
ance R1. The self-bias resistance Rz is adjusted
signal amplifier possessing certain of the special
to provide negative bias to the grid I6 such that
characteristics of the invention;
the tube will break ldown at the predetermined
Fig. 2 illustrates a novel combination of time
maximum voltage across the condenser Ct. For
base circuit and loliscl'iarge circuit;
purposes of synchronizing the sweep circuit with
Fig. 3 illustrates a 'second novel combination
30 the signal under observation, the grid circuit of
of time base circuit and discharge circuit;
the discharge tube is appropriately lassociated
Fig. 4 illustrates a third novel combination of
with the signal circuit which as illustratedV in
time base circuit and discharge circuit, especially
this case consists of a variable connection SC 'to
useful for very high frequency applications;
the self-bias resistor 51 of the output tube Vs
Figs. 5 and 6 illustrate the types of traces ob
of the signal amplifier. This circuit may include
tained on the oscilloscope screen at .diñerent fre
the isolating elements C3 and Re. The signal
quencies when using the time base circuits of the
amplifier .does not enter further into the opera
invention ;
tion of the sweep circuit and consideration of this
Fig. 7 represents a further improvement in
device will be deferred until 'after the various
time base circuits designed to produce exceptional
embodiments of the time base circuits have been
linearity in the charging rate;
explained.
Figs. 8, 9 and 10 are simpliiied figures provided
In Fig. 1 the charging circuit for the condenser
for use 'in connection with the explanation of the
Cl provides a substantially constant iiow ‘of cur
theory of the signal amplifier illustrated in Fig. 1;
rent to the condenser under control of th'e'vari
Fig. 11 gives a frequency characteristic of the
able resistor Rk. That this charging current is
improved amplifier;
substantially constant may be ‘proved by 'comput
Fig. 12 illustrates another version of the high
ing the value of the 'current at a few points in
frequency amplifier;
the charging cycle. An expression .for‘the Ycharg
Figs. 13 and 14 are simplified figures useful in
ing current may be derived as follows:
development of the theory of the ampliñer of
In the condenser charging circuit of Fig. 1,
50
Fig. 12; and
Figs. 15 and 16 illustrate typical responses of
as 25 auf. or even lower. With these circuits, and
the oscilloscope system to high frequency tran
sient waves.
In order to explain the operation of -the inven
tion, reference will nrst >be made to Fig. '1. The
ñgure includes a cathode ray oscilloscope >‘tube I,
which may be of conventional type kbut when used
for high frequencies should be of a design in
tended for use at these frequencies. The tube
possesses the usual elements consisting of the
cathode 2, grid 3 for controlling the intensity of
the beam, focusing electrodes 4 and 5, -a pair of
vertical deiiection plates 6, and a pair of horizon
tal deflection plates 1. II‘he tube receives the
requisite operating potentials from a vpotentiom
eter 8 connected to any suitable source of supply.
A ñlter 9, which may be of the resistance-ca
pacity type as shown, is included in series with the
where,
Eb: the total applied voltage.
ep, ek, and et are volt-ages across the elements as
indicated in the figure :at any instant of the
charging cycle.
.If it be assumed for the time being ‘that the
current is substantially constant for a `given value
of Re, the plate voltage ep can be represented
approximately by the equation
(3)
where, K is the plate impedance and u is the;am
plification constant of the tube, both .derived from
the Ep, Ip, Eg family of curves for the .particular
tube and approximate current being-considered.
This expression is derived from >Equation 49,
intensity control grid for the purpose of prevent
page 394 of the Principles of Electrical Engineer
ing modulation of the beam intensity by either 70 ing Series, Applied Electronics; prepared fby
the signal or sweep voltages which, at the high
Massachusetts Institute of Technology and pub
frequencies under consideration, may occur as a
lished by John Wiley -& Sons, New York.
result of the transfer of voltages 'through the ca
-pacity of the tube and wiring.
-`For providing the .horizontal .deflection of >the 75
Also, by inspection,
2,552,884
5
‘since Èc vremitir-1s constant throughout the time
6
constant. Charging currën't'w'il'l continue to flow
until the voltage across Ci has reached a specified
desired value, in the case of the example previ
ously mentioned, 200 Volts. At this instant the
gas tube V2 by virtueof the adjustment of >its
biasing elements R2 and C4 becomes conductive
to initiate the discharge of the condenser Ct and
hence to return the cathode ray beam to its start
`
lp-ïf+o+1>ßk
ing point. ‘The cycle then repeats itself under
The constant voltage drop Ec across `Cg is ñxed 10 control of the synchronizing potential.
by the maximum value of et and is taken at the
The charging current is maintained at an un
instant the condenser «Cr reaches its full charge
usually constant rate by virtue of the negative
and starts discharging. At this point in the cycle, ,
feedback through the network comprising the
the grid tends to become positive and hence by
resistor Rk, and the condenser Cg and resistor
permitting the ñow of grid current short-circuits 15 Rg in combination which as previously pointed
the grid leak Rg. eg therefore drops to zero.
out should possess a relatively high time constant.
Hence, when et: the maximum value of et, eg=0,
Rapid variations in the current are effectively
and Ec=ÍpRlc.
smoothed out by this means. IgThis effect may be
From (5) above,
furthered by means of the inductance L1 which
20 is located in series with the charging circuit and
may be introduced by opening the switch |14,
base cycle.
Y
`
Substituting (3) and (4) in (2)
thereby increasing the negative feedback and
(7)
To compute an example of the charging cur
rent, assume
Eb=40û volts, er (max.) :200 volts,
R1¢=50,000 ohms, p.=30, and K=8,000.
Then from (7), E¢=172~5 volts and from (6),
ip=3.45 mils for ef=200 volts
3.51 mils for er=100 volts
hence- giving an increased linearity.
The charging circuit comprising the tube V1
with associated circuit elements is suitable for
charging a sweep condenser at a constant rate
up to very high frequencies. However, the gas
tube discharging circuit illustrated in Fig. 1, be
cause of its deionization rate, becomes unsatis
30 factory at repetition rates in excess of about
30,000 cycles. In the next adjacent range of
frequencies, certain types of multi-vibrator cir
cuits employing hard tubes are satisfactory.
Figs. 2, 3 and 4 illustrate three classes of multi
The non-linearity in this case is only i 1.7% from
vibrator discharging circuits, on the left hand
the mean value, even when the sweep voltage
side of the lines A-A, operating in cooperation
reaches 50% of the applied voltage. If the value
with a constant current charging circuit located
of K and Il do not correspond exactly to ip as cal
on the right hand side of the lines A-A. In
culated, other values can be assumed until K and
these ñgures elements homologous with the ele
,L correspond to ip as expressed by the family of 40 ments of Fig. l are designated by like symbols.
tube data curves.
In Fig. 2 a charging circuit analogous to that of
The performance in regard to linearity'can be
Fig. 1 is illustrated but instead of the triode tube
appreciably improved, particularly for small
a triode-connected pentode tube is employed and
values of Rx, by including an inductance Li in
the resistance R”1<, to permit use of standard
series with the charging »circuit by opening the
parts and for convenience of adjustment, is
3.57 mils for er:
0 volts
switch I4. An inductance of appropriate value
along with the resistor Rk in series with the
charging circuit provides Áa higher impedance to
the variable component of the charging current
and hence an enhanced negative feedback which 50
divided into three parts. In addition to anode I l,
control grid I2 and cathode I3, the tube V1 con
tains screen grid l2’ and suppressor grid I2".
The resistance R”k, as shown, includes the fixed
elements I8 and I9 and the potentiometer 20.
together serve to largely suppress the variable
The sweep condenser Ct now comprises primarily
component of the charging current. The value
of charging current is :controlled by Rk as before.
This arrangement including the inductance is ad
vantageous and convenient where the sweep fre
the condenser Cn associated with the discharging
circuit but in addition includes the stray wiring
capacities indicated by the condenser Ctz shown
in dotted lines. Remaining elements of the
charging circuit are identical with the analogous
quency need be varied over narrow ranges only,
in which case switching means for varying the in
ductance is unnecessary.
In operation, assuming that the gas tube V2 is
non-conducting and the switch Id is closed, cur
rent flows from the battery I0 through the space
path of tube V1 and the resistor Rk to charge
the ‘condenser Cr. Starting at the point in the
cycle when Cn has just been discharged and et
equals zero, the development of the voltage et
serves to deñect the cathode ray beam across the
screen. Then ep will have a maximum value and
eg will have an appropriate negative value as de
termined by the I_R drop across Rk. A charging
current will then flow, whose magnitude may be
regulated by adjustment of Rr. As et increases,
the plate voltage ep decreases, but by virtue of the
feedback through the condenser Cg the negative
value of the grid voltage eg will decrease propor
elements of Fig. 1.
‘
The discharge function in Fig. 2 is provided by
the multi-vibrator circuit comprising the tubes
vV'2 and V3 which may forconvenience be en
closed in a common envelope as indicated.
Tube
V'z contains the control grid 22, anode 23 and
the cathode 2i which may also be common to
tube V3. Tube V3 contains the control grid 24
and anode 25. The two tubes V'2 and V3 are
alternately conductive so that the sweep con
denser Ct may be charged while tube V’z is non
conductive and may be discharged when this
tube Ibecomes conductive. The second tube
serves primarily to cause the tube V’2 to alternate
between the non-conducting and conducting con
ditions. Anode potential is supplied to anode 23
of tube V’z via the constant current charging
tube Vi from the potential source comprising the
tionately so that the charging current z'p remains 75 potentiometer R4 and condenser C5. Potential'
2,552,884
7.
8
to `the anode 25 of tube V3 is supplied from the
of condenser Ci; while the potentiometer R1 con
same -source via the resistor R5.
trols the discharge rate of condenser C2.
The repetition rate of the time base circuit
of Fig. 2 is only slightly affected by the D. C.
supply voltage. Hence a convenient method of
The anode of
tube V'z is coupled to the grid of tube V3 by the
sweep condenser Ct while the coupling in the re
verse direction between the two tubes is provided
by the condenser C2. A grid leak resistance R7
is -provided for tube V3. This resistance ,must be
of relatively low value since it is included in
series with the sweep condenser Cei. The grid
leak resistance for the tube V ’2 includes the re
sistor Re and the potentiometer R1 which is
ganged for operation in unison with the variable
portion 20 of the charging current regulating
controlling the beam velocity and the length of
the sweep on the screen is supplied by adjust
ing the D. C. plate voltage by means of the Do
tentiometer R4. This method is particularly
serviceable when no amplifier is used in connec
tion with the time base. A further advantage
of this independence of the supply Voltage lies
in improved steadiness of the screen pattern and
greater stability of synchronization even for large
resistance R'k.
Operation of multi-vibrator' circuits are Well 15 ratios of signal frequency to repetition rate.
Synchronization of the time base with the
understood by those skilled in the art. 1t should
signal under observation may be accomplished
suffice in the present case to point out the princi
pal actions in the cooperative functioning of the
tubes V’z and V3, along with the charging current
by injection of the synchronizing voltage into
the input circuit of tube V3 in any convenient
tube Vi, which provide an essentially linear for 20 manner. Only an exceedingly small amount of
energy is required. In fact, actual connection
ward trace for the cathode ray ibeam followed by
to the vertical deiiecting source or amplifier is
a rapid return trace. Operation of this circuit
usually unnecessary as suñicient energy to lock
organization is essentially as follows. Consider
the time base securely into synchronism for long
the instant in the cycle when condenser Cri has
periods of time is picked up when the synchro
just been discharged and begins to receive a
nizing lead is placed in proximity to the
. positive charge through tube Vi. At this instant
vertical deflecting source or amplifier. When a
tube V3 is conducting but tube V’2 is non-»con
Vertical deflection amplifier is used, the method
ducting due to a negative charge on condenser
shown in Fig. l of obtaining the synchronizing
Cz remaining from the »previous cycle. A con
stant current now flows through tube Vi to 30 voltage by means of the voltage drop across a
small resistance or impedance, such as 5l, lo
charge condenser Cu at a uniform rate to accom
cated in the cathode circuit of the last stage is
plish thedefiection of the cathode ray beam
satisfactory. La this way the synchronizing con
across the screen. At the same time the negative
trol potentiometer can be so arranged as to have
charge on condenser C2 is leaking off via the
resistances R1 and Rg and the space path of the . negligible effect on the amplifier characteristics
even when the amplifier is designed for the high
tube V3 until, at the end of the deflection, when
est frequency.
condenser Cu has attained its maximum voltage
rl‘he time base circuits herein described pro
the grid of tube V’2 becomes positive and the
duce output voltages of ample magnitude for
tube starts to conduct. At this instant a nega
tive potential is passed via condenser Cm to the 40 the deflection of the cathode ray beam in most
work. However, if needed, an amplifier of the
grid of tube V3 to cause it to become non-con
type shown in Fig. 1 but of smaller gain may be
ducting and this action in turn sends a positive
introduced between the time base generator and
charge through condenser C2 to the grid of tube
the deflection plates. In the circuits shown in
V’g. These latter actions are cumulative in driv
ing the grid of tube V’z positive at a very rapid - Figs. l and 2 and in the subsequent figures as
well, one side of the sweep condenser is ground
rate to permit current to flow through this
ed. This may require that supplemental center
tube to discharge Cn and thus return the cathode
ing means for the deflection plates 1 of the oscil
ray beam to the starting' point. As current
losco-pe tube be added. Such arrangements may
ceases to flow in condenser Cn, tube Vs be
be of conventional types well known in the art.
comes conducting at the same cumulative rate
to again charge C2 negatively and interrupt the
current now through the tube V’2. The cycle
now repeats itself to start a second deflection of
the cathode ray beam.
Synchronization of the applied signal may be
accomplished by connecting the grid 2d of tube
Additionally, supplemental amplifiers if provided
between the time base generator and the deflec
tion plates may be of the phase inverting type
arranged to transfer the sweep impulses from
the grounded circuit to the ungrounded or center
grounded deflection plates.
'
Vs to a suitable point in the signal circuit via
The usual precautions necessary in high `fre
the isolating elements Re and C3 and conductor
quency work in respect to shielding and avoid
SC, as in Fig. l‘.
ance of wiring and other stray capacities should
The upper frequency limit for which the cir GO be observed in the design and operation of these
cuit of Fig. 2 may be employed is determined by
high frequency time base circuits. Further, best
the minimum capacitance of condenser ACn but
results will be obtained from an oscilloscope tube
proper functioning of the multi-vibrator device
which has a small spot and is particularly de
places the minimum value for this condenser
signed for high frequency use. This may in
at approximately 5 fici. The repetition rate is
volve relatively small physical sizes, short leads
controlled by condenser Cu and C2 in combina
and separated terminals. An internal shield for
tion which preferably are ganged to a common
the tube is desirable. To prevent undesirable
control. Condensers for this service are usually
modulation of the intensity of the beam by the
of fixed types controlled by multi-point switches
sweep or signal voltages, the filter section 9 is
so that the capacity steps are inconveniently 70 indicated in series with the intensity control grid
large. For the intervals between steps the ve
3 of the cathode ray tube I in Fig. 1. As an addi
locity of the forward trace may be controlled
tional precaution, sometimes desirable, the in
by the tapered double potentiometer containtensity and focusing elements 3, 4 and 5, may
ing resistances Ri and 2li. ït is evident that
be by-passed to the cathode or to ground by
the `potentiometer 2G controls the charging rate 75 means of small condensers connected at the
2,552,884
tube base pins. These precautions are particu
larly desirable at the higher frequencies.
10
the circuit of Fig. 3 is the same as in Fig. 2. The
capacity or” the sweep condenser Ct may be re
duced to zero leaving only stray wiring and tube
of the circuit of Fig. 2 is determined by the size
capacities as the minimum. This minimum with
of the condenser Cu which while serving as an
the type of tubes indicated may be of the order
element of the sweep condenser Ct also per
of 25 ,fi/Lf. This circuit is somewhat superior to
forms an essential function >in the operation of
that of Fig. 2 .and may be used at frequencies
the multi-vibrator and because of the latter may
extending to approximately 20 megacycles.
not be reduced below a certain limit. Fig. 3
A time base circuit somewhatmore specialized
overcomes this limitation through the choice of 10 in character which may be built for observing
a somewhat diiïerent circuit which relieves this
frequencies to at least as high as 150 megacycles
condenser of its multi-vibrator function. In
is illustrated in Fig. 4. This circuit is very sim
this figure a charging circuit identical with that
ilar to that oí Fig. 3 and its method of operation
of Fig. 2 charges the sweep condenser Cr. The
is identical, but in order to reach higher fre
discharge function is accomplished by a multi 15 quencies the tubes chosen are types which will
vibrator circuit which is identical with that of
carry higher current but without increased capac
Fig. 2 except that the voltage transfer from
ity to ground, and the circuit elements chosen
the anode-cathode circuit of tube V’z to the grid
are almost all of the fixed type in order to avoid
24 of tube V3 is accomplished by means of the
the larger ground capacities which accompany
self-bias` resistor R2 and the condenser C1. The 20 the variable types. A limitation of this circuit
time constant of the condenser C7 and the grid
as shown, therefore, is that the elements may not
leak R1 Should be suñiciently large to prevent
be adjusted in order to vary the frequency range
variations in grid potential during the period
covered. The system may be built with Variable
of the longest repetition rate used.
elements for use at other than the highest fre
Operation of the circuit of Fig. 3 is essentially 25 quencies.
similar to that previously outlined in connection
All three tubes used in this circuit are prefer
with Fig. 2, differing only in certain minor re
ably of the pentode type and selected further for
spects. This mode of operation will be described
the low capacity of the elements to ground. The
as a series of steps .as follows:
tube V1 contains anode ll, control grid i2, cath
As previously noted, the upper frequency limit
For the starting condition:
Y
1. Condenser Ct has just discharged and is
ready to receive a positive charge via tube V1.
2. Tube V’z is non-conducting due to a nega
tive charge remaining on condenser C2 from the
previous cycle.
30 ode I3, and scr-een grid i2', all connected as
shown, but the suppressor grid i2” in the par
ticular tube shown (GAGT) preferably remains
disconnected. The tube V”2 includes anode 23,
grid 22 and cathode 2l, and also the screen grid
22’ and suppressor grid 22” triode connected as
indicated. The tube V”3 is also triode connected
3. Tube V3 is conducting.
4. The grid of tube V3 is at cathode potential.and contains the anode 25, cathode 2l, control
For the charging condition:
grid 24, screen grid 2d’ and suppressor grid 24".
1. A constant current flows through tube V1
In the charging circuit for the condenser Ct
to charge condenser Ct to thereby deflect the 40 an inductor L1 replaces the resistor Bk. An induc
cathode ray beam.
tor L2 is addedV in series with the battery supply
2. The negative charge on condenser C2 is leak
ing off via resistors R1 and Re and the space path
of tube V3.
Condition `at completion of charge:
1. The negative charge on condenser Cz hasV
leaked oiî until the grid of tube V’a retains only
a small negative potential.
'
2. Tube V’z starts to conduct.
3. Passage of current through tube V’z and
resistor R2 rapidly renders the cathode of tube
Va positive with respect to its grid (in vie-w of '
condenser C7) so that tube Vs becomes non
conducting.
4. As current through tube V3 diminishes, a
heavy positive charge passes through condenser
circuit of tube V”s and an inductor Ls is vadded
in the grid leak circuit of tube V”2. These induct
ances have been found to contribute appreciably
to linearity of both the forward and return traces.
In the operation of ‘this circuit the return trace
is suiiìciently linear that it» may be satisfactorilyw
used for viewing purposes and, because of its high
velocity, especially high frequencies may be delin
cated. Both traces Vof vthe sweep circuit may be
used torprovide simultaneously on vthe screen a
long section covering a number of Cycles of sig
nal during the forward -trace together with .a
spread out section covering a smaller'nurnber of
cycles cf signal during the- more rapid return
trace. Velocity ratios of l to 3 are convenient
for this purpose. If desired, either trace may be
C2 to the grid of tube V’2.
5. Conditions l and 4 above cause tube V’z to
blanlred out by means or blanking out circuits
become rapidly conductive to discharge condenser
well known to those skilled in this art, thus per
C1; via the space path of tube V'z and the resistor 60 mitting observation of a single trace.
`
Rz.
As in the case of‘Fig. ,3, the condenser Ct may
For the discharging condition:
.
l. The declining potential across the discharg»
ing condenser Ct returns the cathode ray beam
to its starting point.
2. As the discharge rate of condenser Ct
declines, the IR drop across resistor R2 declines
‘ and the cathode of tube V3 becomes less positive
with respect to its grid.
3. Current starts to Jflow through tube V3. ,
be reduced so as to provide a minimum capacity
made up solely of the capacity ofY tube V”2
together with the capacity of the wiring and
oscilloscope plates. For the same reason the con
denser Cg should be maintained as small as pos
sible. A ñlter circuit comprising theinductor 26
shunted by the resistor 2ï in conjunction with
stray wiring capacities as indicated is desirable
in order to prevent signal or other frequencies
picked up at the oscilloscope tube from reacting
4. A negative charge passes via condenser C2
to the grid of tube V'z t0 render that tube non
_ on the time ‘oase circuit.
f
conductive.
Velocities corresponding vto voltage variations
5. Condenser Ct again begins to charge.
of 7,000 volts per microsecond are readily ob
Control of the repetition rate .and velocity for 75 tainable with the ciruit of Figli. Voltage varia
iafaözgesc
1,12
.~ employ fratios >of ¿signal _; frequency ;to;.1repetition
.: tions i at least .as .high . .as L9,000 . volts Aper _micro
rate of theordenof severalithundred, or.;by._using
high velocitiesnat low repetition-:rates verysfshort
creasing the plate voltageand. at the same time
transientsmaybe spreadiout .as muchas desired.
`making appropriate vadjustments in Re and L2.
4Depending upon the type of oscilloscope tube and Us it is possible '.alsoftoadjustthe sWeepî frequency
l.toa-.rate much higher. than'thesignal frequency.
:theaccelerating voltage used, this latter figure
.This‘feature has particular utility in` the viewing
.corresponds to a Velocity approaching 1,500. miles
of very short but vslovvly periodic transients.
perzsecond for the cathode ray beam. across the
:second can be obtained for Yshort .periodsby in
Hence the transient itself may be Well> spreadbut
voscilloscope screen` For the higher velocities,
care must be taken to reduce the wiring and l0 Y. on the screen but theinterveningidle. period ex
eluded. vAll Vof the foregoingmay be :accom
Ashielding capacitances to a minimum.
. plished while using either the forward or return
>A low impedance input circuit is desirable for
.the-tube V'fa. .Sufficient voltage for synchroniz
ing 'purposes may be obtained by merely bringing
`traces or both, and .With complete absenceofm
stability or flicker.
vThe-single tube charging circuits for thetime
the. input loop circuit 28 into the vicinity of the '
'.signalcircuit. Regulation of the time base cir
cuit over a limited frequency range may be ac
basesystenisoflî‘igs. 1 to 4 provide sufficient
linearity for all ordinary oscilloscopio Work.
However, when 4a greater- degree of linearityis
...complished'by-variationof the resistor R2 and
.the condenser Cv. As previously noted, these
:variable elements lie; at groundpotential so that
needed for oscilloscopio use or fors-any othery con
»stant current application, the- linearity may' ‘be
yfurther improved by the introduction of a sec
ond tube V’1 in series »with the tube '-Vl ¿nf-Figs.
144. This portion of the circuit will nowï-be as
indicated in Fig. 7. The secondy tube is provided
Atheir .presence does not introduce shunting ca
pacity nor does .the handling introduce disturb
ing variations in frequency.
’The values of the various elements used in
the time base circuits of Figs. l to 4 are depend- í
ent-inpon the range of frequency under observa
tion. ,Howeven in order that adequate informa
tionmay be conveyed for the practice of the in
with resistor R’g and condenser C’g correspond
ing to the like elements Rg and Cg of the first
tube. The cathode impedance Rk is common to
both tubes and, as before, may include induct
ance. I have discovered that the presence of
vention, suggested values for each of the ñgures
are specified in the following table of preferred
the second tube will compound the stabilizing
negative feedback effect of the ñrst tube, in fact,
values. .It isunderstood that all of these values
are subject to variation'and that "substitutions
it can be proved that for the same Rk the non
`may 'be made inthe Atype of vacuum'tubes.
linearity can be reducedv by a factor of ,i+1 if a
_
.5 mcg.
10U-200 ohms.
50,000 ohms... 50,000 ohms... 50,000 ohms.
30,000 ohms... 30,000 ohms. ._ 7,500 ohms.
_
>2,000 ohms..
>2,000 ohms. . .............. __
500 ohms .... ._
1
25,000 ohms. _ _
25,000 Ohms. _ _
GAB? _______ _.
GAB? _______ _.
meg _______ ._
.
5 me
6
6F8-G ______ . _
second identical tube is inserted in series with
To illustrate'the order of linearity which may
'be'obtained with the time base circuits previously 60 they tube V1 as indicated inlilig. 7.
For use in connection with an oscilloscopeat
described when operating at high frequencies,
high frequencies amplifiers capable of amplify
the oscillograms of Figs. 5 and 6 have been in
cluded.
Fig. 5 represents a distorted Wave at a
ing Very Wide frequency bands with negligible
distortion are necessary in connection with the
frequency of 40 megacycles. As will be noted,
three cycles of the Wave are delineated by the 65 signal deflection plates and less frequently also
‘forward trace for each cycle delineated by the
in connection with the horizontal deflection
plates. To meet these requirements an amplifier
V‘more rapid return trace. Fig. 6 illustrates the
has been devised which possesses substantially
forward and return traces of a sine wave at 125
megacycles. l
constant amplifica-tion and linear phase shift over
A remarkable feature of these time base cir 70 a band of frequencies having a Width of seven
niegacycles or greater. In this specification at
cuits is their stability, freedom from disturbing
tentîon will be givenY particularly to an amplifier
variations and the firmness or tenacity of syn
of this class designed to amplify a band of y_fre
chronizm of the sweep function with-the applied
quencies ranging from the neighborhood of .one
vrsignal. 'This property-greatly augments the util
“ity of the device, e. g. it is readily possible to 75 cycle up to seven megacycles. However,`by the
2,552,884
13
14
same methods the amplifier may be arranged to
accommodate a band of frequencies of like
for the stage will be uniformly increased for the
entire band. In the present case R’c is about
width located at frequencies very much higher in
twice as large as Re to permit an approximate
the spectrum.
doubling of the output voltage. This increase
In order to explain the particular advantages (Il in output, however, does notV necessarily result
of the amplifier of this invention it will be neces
in any appreciable increase in gain because any
sary to examine briefly present practices in the ' improvement in this direction will have been ab
design of broad band amplifiers for operation at
sorbed by the negative feedback. Advantages of
high frequencies. Fig. 8 shows the equivalent
the amplifier are, rather, that high voltage out
circuit of a resistance-capacitance coupled am
puts may be obtained uniform over a very wide
pliñer stage at high frequencies where the ele
ment and wiring capacitances become important.
band of frequencies, providedan adequate input
v Equivalent total capacitances to ground include
larger voltages are vailable inasmuch as the prod_
uct of band width and output voltage is a design
constant for a particular amplifier tube. Other
significant advantages are that since the correct
voltage is applied.
three components; Cg', wiring to ground; Cpk,
plate to cathode; and Cgk, grid to cathode. The
resistor Re represents the necessary interstage
coupling or load impedance. At high frequen
For bands of lesser width,
ing networks are at ground potential and do not
shunt the signal circuits, it is possible to use
cies the coupling impedance as a whole degen
erates into a composite shunting capacitance
order to obtain a fiat frequency characteristic,
more complex networks, as desired, to meet any
requirement. For example, the networks may be
arranged to be adjustable for the separate cor
rection of amplitude and phase and to correct for
both high and low or for intermediate frequencies.
Further, as is weil known, the negative feedback
` to lower the low frequency output voltage to the
which accompanies thn use of the cathode net
same degree by reducing the coupling resistance
works increases the stability of the amplifier and
reduces the tendency to transient oscillation in
whose impedance diminishes with increasing fre
quency, with consequent falling off in voltage
output to the succeeding stage. With the high
frequency output thus limited it is customary in
to a value which approximates the shunting re
actance at the upper frequency cut 01T. With
the networks.
The vertical deflection amplifier shown with
in a wide band amplifier will be of the order of 30 the cathode ray oscilloscope in Fig. 1 possesses
an exceptionally fiat response from one cycle to
1000 ohms, and with the plate current relatively
about seven megacycles, and good transient re
fixed it is seen that a limit is quickly reached to
sponse. These two requirements are somewhat
the available output voltage for the stage.
incompatible and usually cannot be met at the
Hence in wide band amplifiers it is necessary to
accept low voltage outputs and low gains per 35 same time without sacrifice of some band width.
The best transient response requires that the
stage. This loss in gain may be recovered to
frequency response fall on’ gradually at the up
some degree by the introduction of inductances
per end of the frequency band, whereas an am
which tune to the capacities so as to present
plifier which has a ñat frequency response to the
a more favorable coupling impedance. However,
ordinary pentode tubes this coupling impedance
such inductances occupy positions in the circuit
having high impedance with respect to ground
40
‘ and as they contribute further shunting capacity
highest possible frequency and then falls off
rapidly, will 'have an inferior transient response.
Curves showing the relation between frequency
they quickly become self-limiting in their bene
ñts. An amplifier designed according to these
principles is disclosed in Patent No. 2,370,399.
The present amplifier greatly improves upon
the former practice in that it actually achieves
response and transient response are given in-a
an effective reduction of the tube element ca
valid for high frequenciesf
pacities to> ground, rather than a compensation,
The three stage amplifier of Fig. 1 uses nega
tive feedback over the last two stages and indi
vidual feedback in each of the three stages. In
the ñrst stage only individual feedback was nec
essary since in view of the low signal level, dis
tortion was small. With such a design difficulties
are avoided due to instability and in the making
of adjustments for various response conditions.
The individual feedback for each stage was ac
complished by the use of networks in the cath
ode circuit of each tube which permits the fre
so that the high frequency coupling impedance
remains large and the low frequency coupling
impedance may accordingly be raised to a high
value.
This improvement is accomplished
through the introduction of impedance networks
in the cathode circuits of the tubes where they
are essentially at ground potential and do not
shunt the signal circuits. These networks pro
duce cathode feedback to cause a considerable
redistribution of the circuit values.
With cathode feedback, the corresponding
equivalent circuit is shown in Fig. 9, the three
capacitances nowv Ibeing separated by the re
spective cathode impedances Zk, and Re being
paper,
“Picture Transmission by Submarine
Cable,” by J . W. Milnor7 A. I. E. E. Transactions,
1941, pp. 105-08, Fig. 3. Although applied to low
frequencies, the curves of the paper are equally
quency and phase characteristics to be readily
controlled at any part of the frequency rangeby
means of simple adjustment of these networks.
Before describing the amplifier in greater de
tail a discussion of the effect of this type of feed
increased to a new‘value R’c. Actually each of
these new capacitances is an equivalent capaci 05 back upon the inter-element capacities will be
undertaken.
A
tance evaluated for the particular tube condi
Referring again to Fig. 8, the effect of each of
tions, and include the effects of space charge and
the capacitances Cgf, Spk, and Cgk on the frequency
feed back through the inter-element capaci
characteristic will be examined separately. The
tances. With the shunting capacities thus re
stage gain (complex) for the Cg' portion of the
duced the coupling resistance can be increased
total shunting capacity at frequency ,f is
`> `
until it is again equal to the shunting reactance
(accompanied if necessary by an increase in the
@_il'ßß
4
plate voltage supply so as to maintain rated plate
ETH/„iacp
. (8)
current) with an accompanying increase in avail
where gm is the mutual conductance for the
able output voltage. Hence the output voltage 75
2,552,884
l5
16
‘With cathode feedback, Fig. 9, the correspond
stage gain vis
ducing the gain of the stage which in theory
may be treated more or less separately.
It is
further evident that, under specified conditions,
negative feedback may be introduced into the
amplifier without loss in gain. These conditions
are: (a) The elements C’k and R’k of the cath
ode networks must bear the relationship to Cpk,
If Zk is assumed to be a resistor R’k and a con
Cgf and Cgi; when considered alone as expressed
denser C’k in parallel, as in Fig. 10.
in Equations l1, 18 and 21, and, (b) the plate
gmR’c
10 resistance Re of Fig. 8 must be increased to R’c
n
1+Í°"__R'¢Cg’ Ñ
(10)
in Fig. 9 by the factor indicated in Equations
1 _i. gmß_l£__
13.
1+jwR/kC/Íc
Calculation of C’k for practical conditions
from Equations 11, 18, and 21 give values of ca
15 pacitance many times larger for Equation «1l
than for Equation 18 or 21. Hence the value of
(l1)
C’k is principally determined by Cgf. This is be
cause due to the cathode feedback the tube ele
ment capacities are in effect reduced and ycon
20 sequently the required capacity in shunt with
R’k to compensate for the effects of Cpk and
Cgk on the frequency and phase characteristics
(12)
of the stage are rendered much smaller in value
than the corresponding capacity required to com
Hence the importance of keep
ing Cgf, which is made up principally of wiring
and stray capacitances, to a minimum is evident.
then
The composite value of C’k, must compromise
@Q_ gmRc
somewhat from that determined from the indi
E_l-i-jwRcCgf
(14) 30 vidual Equations 11, 18, and 21 along with modi
ñcation of Rc in accordance with Equation 13,
Equation 14 is the same as Equation 8; hence
to provide the same gain as without feedback and
under the conditions of Equations 11 and 13 the
it is not possible to obtain all of the indicated
gain is identical for no feedback and for cath
improvement. However, the final capacity is
ode feedback.
35 Astill quite small in value `and so allows consid
Similarly, for the capacitance Cpk in Fig. 8,
erable opportunity of modifying the frequency
@__
gmRc
.
and phase characteristics by further modifica
E_1+jwR.c„,
(1")
tions in the Zk networks.
and letting
25 pensate for Cgf.
and in Fig. 9, the corresponding gain is,
EÜ-
_lâ-œ-~ l
l
gmR C
(gm‘ì'jwopk) +jmR/ccpk
(1e)
From the foregoing, it can be seen that a net
40 work Zk in the cathode circuit of the various
stages has .important properties in modifying the
lfrequency and phase characteristics of an ampli
When Zk is a condenser and resistor in parallel
fier. Increasing or decreasing the composite
value of C’k gives respectively a gradually rising
as before,
or falling characteristic with frequency.
gmRt.
45
The networks Zi: lcan have many forms. 'I'hey
may be simple frequency or phase regulating net
works as shown in Fig. 1 or they may be filter
sections or transmission lines with or without
50
reflections to modify the frequency and phase
characteristics. More complicated networks can
be added to Zk to affect the characteristics in
a particular region.
The frequency character
istic can be ‘made as flat as desired over the use
55
ful range usually by simple adjustments, or the
phase characteristics can be readily modif-led.
In making these adjustments in Zk, the network.
can be made as complicated as one wishes with
out adding the harmful additional capacitances
60 to Cg', Cpk, or Cgk that would result if complex
networks were introduced into the plate or grid
circuits.
Particular emphasis should again be placed
For the capacitance Cgk, by a similar method
upon the property of the amplifier of Fig.
it can be shown that the gains of Figs. 8 and 9
1 in providing high voltage output for an ex
65
are again identical when we make
tremely wide band frequencies. The amplifier
of Patent 2,370,399 has already been referred to.
The practice of improving the linearity of ampli
fiers by means of negative feedback is also com
70 mon, but in the past so far as I am aware this
expedient has always been accompanied -by a
substantial reduction in gain and in Voltage out
From the foregoing it is evident that in the
put. This is in contrast to the amplifier of Fig.
amplifier of Fig. 8 each of the shunting ca
1«~which not only avoids the addition of shunt
pacitances Cpk, Cgf and Cgk has a share in re 75 ing capacities,v but through the use of cathode
2,552,884
17
of relatively simple form, each designed to cover`
feedback causes an effective reduction in inter->
a separate portion of the frequency range han-->
nal tube capacities to further reduce the losses
dled by the amplifier. The tube V4 impedance,
at the upper frequency end of the range. The>
principal shunting capacity remaining is that. of
network comprises inductor 63, resistor 64 and
the inter-stage wiring to ground and the effect
the condensers 65 and 66. For the intermediate
of this capacity on the amplifier frequency and
tube V5, condenser 61 only is provided as a cath
ode network. In the output stage the parallel
phase characteristic, up to the limiting frequency
of the amplifier, may be conveniently compen
connected resistor 68 and inductor 69 in series
sated by design and adjustment of the compen
with condenser 16 is provided. A circuit includ
sating networks located in the cathode circuit. 10 ing condenser 15 and resistance 16 connect the
With the shunting capacities minimized the plate
anode of tube V6 to thecathode of tube V5 to
load impedance may be increased to at least
permit negative feedback over these last two'l
twice the value indicated by customary design
stages. In the output stage of the amplifier, a
practice, so that reduction in output caused by
so-called series peaking network comprising in
the negative feedback can be compensated. By 15 ductor 'Il and condenser 12 and a shunt peaking
increasing the voltage of the battery supply
network including inductor 13 and condenser 14
source this impedance may be still further in
creased to provide very substantial increases in
are provided.
These networks serve to sustain
the upper end of the frequency characteristic of
output while retaining constant attenuation and
the amplifier.
linear phase shift over the entire frequency band. 20
The plate coupling resistors for each stage are
‘ In Fig. 1 an amplifier is indicated only in the
in all cases much larger than would be provided
circuitof the vertical deflection plates. Ordi
on the basisv of the usual design formulae for
narily an amplifier is not required in the hori
wide band resistance coupled amplifiers thereby
zontal deiiection plates inasmuch as the time
providing substantially increased voltage output
base circuit itself produces substantial output 25 for each stage. Likewise, the high impedance
voltage. However, if an amplifier is required in
output circuit for the ñnal stage serves to pro
this circuit it may to advantage be of the type
vide a large voltage to drive the oscilloscope
illustrated. This is particularly true in such ap
plates. The peaking networks used in the out
plications as circular sweeps where the charac
put stage are provided principally to compensate
teristics of both deflection circuits Vshould be 30 the input capacitance of the oscilloscope tube
identical in respect to both attenuation and
since it is not possible to effectively compensate
phase shift. 'I’here are also advantages of
this capacitance by means of the cathode net
economy and simplicity if the amplifier equip
works. The usual care in minimizing wiring
ment of the oscilloscope is limited to the one
capacities and in isolating the rather large cou
35 pling condensers should be followed in the de
type.
A detailed description of the amplifier of Fig.
sign of this amplifier for high frequencies. `
1 follows: In order to provide substantial gain
In the ñgure, no means for adjusting gain has"
three stages employing tubes V4, V5 and V6 are
been illustrated. One means for doing this
illustrated. These tubes may be conveniently of
without adding harmful shunting capacities is
the types 6AC'1 for the first two stages and 6AG’1 40 to adjustably connect the input conductor 62 to
for the output stage. However, other equivalent
the cathode resistor of a preceding cathode fol
types of tubes may be substituted if desired.
lower stage.
The three tubes possess, respectively, cathodes
The frequency characteristic of the amplifier
36, 40 and 56, anodes 3l, 4I and 5|, control grids
is illustrated in Fig. 11. It will be noted that
32, 42 and 52, screen grids 33, 43 and 53, and
the gain is substantially constant from approxi
suppressor grids 34, 44 and 54. Input potentials
mately one cycle to 7 megacycles where a gradual
are supplied to grid 32 of the first stage of the
downward slope is provided. Irregularities tend
amplifier over conductor 62. The three tubes
to occur at the very lowest frequencies unless
are »provided respectively with plate coupling im
substantially perfect regulation is provided in
pedances 35, 45 and 55 and grid resistors 36, 46 50 the anode voltage supply.
and 56.
The tubes also are supplied with self
bias resistors 31, 41 and 51, respectively. De
coupling filters 38, 48 and >58 are provided for
A frequency response which falls off at the rate '
shown in Fig. 11 will possess a somewhat inferior "
transient response.
'
For distortionless amplifi- `
cation of transients somewhat greater slope w
the screen grid circuits of the three tubes re
spectively while a similar filter 39 is provided for 55 should be provided. Fig. 15 illustrates a tran-V
the plate circuit of the initial stage. As a means
sient response oscillogram when a wave front of ‘
of preventing inter-stage feedback either at low
approximately .1 mierosecond was applied to the '
or high frequencies a large condenser 6| shunted
input of the amplifier. It will be noted that the
by a small non-inductive condenser is inserted
wave front is steep and free of oscillations. The l
across the plate voltage supply circuit. Con 60 central timing wave in the figure has a frequency
denser 45 couples the anode of tube V4 to the grid
of 1.05 megacycles.
of tube V5 while condenser 59 similarly couples
In Fig. 16 is shown a similar transient response> tube V5 to tube Vs. Potentials for synchroniz
oscillogram when the networks were adjusted so
ing the oscilloscope sweep circuit may be readily
that the frequency characteristic has approxi
tapped to points on the grid-cathode resistor 36
mately 2 db amplitude rise at the upper end of «
of tube V4, or preferably may be obtained as
the frequency response curve. The oscillations
shown from a cathode resistor such as 51v for
following the wave indicate that both amplitude ;
tube Vs.
'
and phase distortion are present.
Compensating impedances which are prefer 70 _In the amplifier illustrated in Fig. 1, numerical 1
ably adjustable in some degree shunt the self
values are given for the various elements. It J
bias resistors of each of the three tubes to pro- "
should be understood that these are for a particu
vide selective negative feedback. These im
lar case, that is, an amplifier possessing the broad
pedances may be relatively simple or may con-V
band characteristic illustrated in Fig. 11. ’Other
sist of ~complex networks but asillustrated are 75 combinations of elements may produce the samef
2552581814
i9
20
approximate result. The values given, therefore,
andthe tap on R”k.
are merely illustrative and intended only to serve
as a guide in the construction of such amplifying
devices.
As. indicated in the frequency characteristic of
is indicated in Fig. 1_4. If RW;l is returned :to
ground, it should b_e noted that there is no vin-v
crease in the> time >constant R"gC, due tothe in
troduction ofv cathode feedback.
To illustrate the incorporation of this method,
of low frequency compensation into an amplifier'
such as' that disclosed in Fig. 1 `whichv is provided`
Fig. 11, the amplifier of Fig. 1 provides faithful
amplification down to a frequency of approxi
mately one cycle. This low frequency ûdelity is
method. of connection;
also with high frequency compensation, Fig. 12
has been provided. This amplifier corresponds
essentially tothe final twol stages of the ampl-iñer
of Fig. 1 including tubes V5 and V6. Circuit ele
ments bearing like designations in the two figures;
a consequence of the negative feedback employed,
aided further by the choice of values for the de
coupling network 33 of the plate circuit of tube
Yi. Further expedients for improving the low
frequency range of this amplifier may readily be
introduced. An amplifier of the same general
character as that of Fig. 1 is illustrated in Fig.
12> which possesses both high frequency and low
frequency compensation. An approach to the
method of low frequency compensation will be
illustrated in connection with Figs. 13 and 14.
Referring to Fig. 13, a single stage amplifier is
have they same significance but it should be un
; derstood that the numerical values of these ele
mentsmay differ from those given in Fig. l. In
Fig. 12 the grid resistor-.46 of tube V5 connects
to a variable tap 46' on the cathode resistor 41
after the manner illustrated in Fig. 14, while the
entire resistance is shunted by a high frequency
compensating network Ni. Similarly, the grid re
sistor 5G of tube Ve is connected at tap 56’ to the
cathode resistor 51v which is'in turn shunted by
the network N2. The cathoderesistorsill and 5,1
schematically shown as a vacuum tube with an
ode, cathode and control grid elements and hav
ing a mutual conductance gm. The circuit ele
ments include a cathode resistor R”k, a grid re
sistor RX’g, a grid condenser C, appropriate anode
and grid batteries, and a plate resistor R”c
through which the plate current Ip flows. By the
are now of larger value than would be used for>
considerations of high frequency compensation
alone. The large amount of negative feedback
which follows tendsk to reduce the gain per stage
o_ver the entire frequency range. However, this
method shown previously, it can be shown that
the relationship between output voltage En and
the input voltage E may be represented by the 30 is vagain compensated byA increasing the plate cir.
following expression:
cuit resistor 45 and 5_5 by the factor (,1-i-gmR”k),
while the plate supply voltage should beiincreased
@lqgm Rl l e Ril c
accordingly. It is apparent, therefore, that the
(22)
E ._ R Il g ( 1
m R Il
C
amplifier of Fig. l2, incorporates both high fre
quency and low frequency compensation to pro
or, expressed in operational form for transientre
videV anY exceptionally wide bandwidth along with
a high order of amplification.
sponse.
While the specific amplifier examples illustrated
Eo-gmR/rgRl/c.
p1
l
p+R".C<1+g..Rf/k>
in Figs. 1 and 12 were designed' for the ampli
ñcation of wide frequency bands extending, from
near zero frequency up to.7 megacyclesvor‘higher.
their use is also envisaged for amplifying bands
(23)
where 12:71», and 1 is the Heaviside Operator.
Solving,
E0 gmRHgRl/c. _Iï
t
of corresponding width but having boundary fre.
quencies located at very much higher positions
1
45 in the spectrum. The conversion `from alow pass
Without
E_]__f_gm1ìllk
feedback, R”k=0,
e R/lgC(1_|_gmR/lk)
and the transient re
to
sponse becomes
principally by changing the character of the
cathode networks and; the interstate coupling cir'
E>-gmR :Re Ruso
(25')
corresponding
amplifier
is
accomplished
cuits, including the capacitances Cgi, Cpii and'Cgk,
50 from low pass to band pass varieties after the
Where R. is. the appropriate value of plate load
resistance
a band pass
to R"k=0. Hence,
when negative feedback is added the time con
stant R”gC is increased by the factor (1+gmR"k)
with a corresponding many fold increase in gain i
at the very low frequencies where the response is
manner familiar to designers of filter and like
network structures. In general the band pass
design may be obtained from the low pass design
by substituting resonant'circuits for the coils'and
anti-resonant circuits for, the condensers, all
tuned to the center of the- desired band. Such
amplifiers are serviceable also for many purposes
normally deficient. The amplifier characteris
other than the one illustrated, for example, vas
tic is thus extended linearly to a value nearer to
video amplifiers, and as intermediate amplifiers'
zero frequency. As in the case for high frequency
response, the wide band gain can usually be re 60 in micro-waveI applications.
Likewisethe constant current charging circuit
stored to the original before feedback was added
described in connection with oscilloscope time
by increasing the plate resistor by the factor
bases has multiple uses in the supply of constant
current to circuits of rapidly varying impedance,
That is when R”c= (1+gmR”k) R in the equations 65 or in suppressing rapid fluctuations, such as
ripples, in. a supply source.
above, the gain becomes equal for both cases. If
It should now be apparent that this invention
it is desired to omit the grid biasing battery R”g
provides the two essential.` and cooperating ele
may be tapped at R9 along R”k at a point which
ments for the operation of cathode ray oscillo
will avoid the excessive grid bias that-occurs when
a large value of Rf’k is used. The increase in 70 scopes in the observation of both periodic
and transient phenomena requiring. faithful»
time constant is then
amplification over very wide frequency bands and
1+gmR”k
.
primaD
_Rn
'C
(26)
where R9 is the part of R”ii between the cathode
oscilloscopio delineation at extremely high beam
velocities. By means of;v amplifiers designed` ac.
cording to the inventiona.very'widev variety of
attacca?.
211i
electrical phenomena maybe' applied .at 'high'
22
necting said grid and cathode and a condenser~
voltage and without distortion tothe signal de
connected in shunt to .both said resistor and im
iiection plates of an oscilloscope. In combination
pedance.
.
therewith the unique time base circuits, particu
8. A system for providing a constant ñow of
larly those of Figs. 3 and 4, provide ample beam 5 direct current to a rapidly varying load compris
velocity for the detailed delineation of these
ing a space discharge device including an anode,
phenomena on the oscilloscope screen.
'
i
cathode, and control grid, a source of current in
series with said load and the space path of said
ticular embodiments, these specific illustrationsspace discharge device, an impedance connect
are for the purpose ofrconveying adequate in 10 ed in series with said load and adjacent to said
formation for the practice of the invention. It
cathode, and negative feedback means for main
should be understood that the invention may be
taining constancy of said current iiow including
practiced in divergent methods and is not at all
a resistor connecting said grid and cathode and
to be restricted to the specific embodiments il-a condenser shunting both said resistor and im
lustrated, but is to be limited onlyby the scope _ 15 pedance, the time constant of said resistor and
of the claims.
.
.
condenser in combination exceeding the period
What is claimed is:
of the average of said load variations.
9. In a sweep circuit for the deflection plates
l. In an oscilloscope system, a sweep condenser,
of a cathode ray oscilloscope having a sweep con
a circuit for cyclically charging said condenser, '
and means for rendering constant the charging 20 denser connected in parallel to said plates and
a charging circuit for said sweep condenser
rate> of said condenser 'comprising a negativeY
adapted to provide a rising voltage during
feedback circuit having a time constant llonger
While the inventionY has been Ydisclosed in par- ’
than the cyclic period.
charge;
the improvements which comprises
means for rendering constant the rate of rise of
2. In an oscilloscope system, a sweep condenser,
a circuit for cyclically charging said condenser, 25 said voltage including a constant current circuit
in series with said condenser, said constant cur
means for rendering constant the charging rate v
rent circuit comprising in series connection a
of said condenser comprising a negative feed
source of direct current, a vacuum tube having at
back circuit having a time constant longer than
least an anode, a cathode, and a control grid, an
thev cyclic period, and means for discharging
30 impedance connected in circuit adjacent to said
said condenser at a constant rate.
cathode, a grid resistor connecting said grid to
3. A condenser, means for supplying a definite
said cathode, and a grid condenser connected in
charge to said condenser, and means for render
shunt to said grid resistor and said impedance,
ing constant the charging rate of said condenser ‘
said grid resistor and grid condenser having a
comprising a negative feedback circuit having a
time constant longer than the charging period.
time constant longer than the period of chargel
4. In an oscilloscope system, a sweep condenser,
a charging circuit forcharging said condenser to
of said sweep condenser, and a discharging cir
cuit for said condenser.
10. In a sweep circuit for the deflection plates
a predetermined voltage, and means for render
ing constant the voltage rise across `said con
of a cathode ray oscilloscope having a sweep con
denser during charge comprising a negative 40 denser connected in parallel to said plates‘and a
charging circuit for said sweep condenser provid
feedback circuit having a time constant longer ing a rising voltage during the 4charging cycle;
than the charging period.
the improvement which comprises means for
>5. A system for providing a constant flow of
rendering constant the rate of rise of said voltage
direct current to a load circuit, which comprises a space discharge device including an anode, 45
cathode, and control grid, a» source of`V currentA
in'series with said load and the space path of '
said space discharge device, an impedance con
including a constant current circuit in series with
said condenser which comprises in series connec
n_ected in series with said load and adjacent to
trol grid, an impedance connected in circuit ad
tion a source of direct current, a vacuum tube „
having at least an anode, a cathode, and a con
said-cathode, and negative feedback means for V50 jacent to said cathode, a grid resistor connecting
said grid to said cathode, and a grid condenser
maintaining constancy of said current ñoW in
cluding a resistor connecting said grid and cath
connected in shunt to said grid resistor and said ,Y
ode and a condenser connected in shunt to both
impedance, said grid resistor and grid condenser
having a time constant longer than the periodof
6. A system for providing a constant flow of 155 charge of said condenser, and discharging means '
for said condenser including a multivibrator1 de
direct current to a rapidly varying'load'com- '
v1ce comprising two vacuum tubes Veach vhaving
prising a space discharge device including at'
anodes and control grids, condensers intercon
least an anode, cathode, and control grid, Va source
necting respectively the anode of each tube to ,_
of ‘current in series with said load and the space
path of said space discharge device, an induct 60 the control grid of the other, one of' saidI con-v
densers serving as said sweep condenser.
ance connected in series with said load and ad
l1. In aV sweep circuit forV the deflection Yplates
jacent to said cathode,- and negative feedback
of a cathode ray oscilloscope having a sweep 'con-means for maintaining constancy of said cur
said resistor and impedance.
denser connected in .parallel to said plates anda
rent'iiow including a resistor connecting _said
grid and cathode anda condenser connectedîin 65 circuit for cyclically charging said’ sweep _con-' ._
denser; the improvement which comprises means ‘f
shunt to both said resistor and' impedance.
` '
for rendering constant the rate of rise of -voltage
’7. A system for providing a constant flow of
across said condenser during charge including a' C
constant current circuit in series with said con
cathode, and control grid having the space path 70 denser which comprises in series connection a
source of direct current, a vacuum tube having '
of said space discharge device rin series with said
at least an anode, -a cathode, and a control grid, ,`
source, an impedance connected in series with
an impedance connected in circuit adiacentïto "
said load and adjacent to saidV cathode,A and .neg- "
direct current from ‘a variable source comprising 1
a Vspace discharge device including an anode,
ative- feedback means for maintaining~ constancy .
of *said current flow -includingawesistor‘con
said
toV said
cathode,
’ cathode,
a grid
' a grid
resistor
'- condenser
connecting
connected
saidl grid
' in "
mariages-4t
23"
24
shuntrto sai'd grid resistor and said impedance,
andídischarging saidîcondenser., both. of s'ai’dicir#V
and al. discharging. circuiti~ for» said' sweep.' con
denser including at least one space dischargeides-vice also having-.anA anode, a cathode, anda con
trolpgrid.»,. ant impedance' connected;v in circuit ad
cuits including?A negative: feedback means’ having.
jacent. to. said? last'fmenti'oned‘ cathode. a. grid:
resistor connectingy said last-mentioned grid,- to.
saidlast mentionedzcathode; anda grid condenser'
connected in shunt' to said grid resistor‘and said
time; constants' of. the: same order: as the cyclicl'
period.
17. In. an oscilloscope system, a sweep con--
denser, separate circuitsv for cyclically> charging>
and discharging said' condenser, and meansf'or.v
rendering- contant thercharging rateïof said con
denser,”` comprising a negative feedback circuity
impedance, said grid resistors andgrid condens 181; having; a» time constant. longer than the cyclic'
ers: for; each tube respectively` having time con
period, and additional means for: rendering con-v
stants.- longer- than theA period of the. phenomena
stant the discharge rate> of said condenser.
under.' observation on the oscilloscope screen.
18. In lan oscilloscope system, a sweepl con
12”. In a sweep.> circuit for the deilectionfplates,denser, a circuit for cyclically charging-.and dis
of a: cathode .ray oscilloscope having a- sweepvcon
denserrconnected'in parallel. tosaid plates. and a.
charging circuit for said sweepAv condenser
adapted-to»provide’al voltage rising to'a maximum
at.the.-end of charge; the improvements’ which
comprisesmeans for rendering` constant the rate -
of risefof said voltage including a- constant cur
rent circuit in series with said condenser which
comprises in series connection a source of direct
current, alvacuum tube having at least an anode,
arcath‘ode, and a control grid, an impedancecon
nectedë in circuit adjacent to said‘ cathode, a grid
resistor connecting said grid to said cathode, and
agrid condenser connected in shunt to said grid
resistor. and said impedance, said. grid resistor
and. grid condenserV having a time constant longer
than the period of the. phenomena under observa~
tion` on- the» oscilloscope screen, said- maximum
chargez voltage being` at least 50 per cent of the
voltagefofr the-source.
13É In a sweep' circuit fory the horizontal de- .
flection plates of aV cathode ray oscilloscope hav
ing a sweep condenser connected in parallel to
said plates and a charging circuit for said sweep
condenser adapted to provide a rising deflection
voltage;
the improvements which comprises'
means. for rendering constant the rate of rise of
saidvoltage including a constant current circuit.
in serieswith. said condenser which comprises a
source of direct current having a voltage not
larger than twice the final deflection voltage.
14. In an oscilloscope system, a sweep con
denser, a circuit for cyclically charging said..
sweep condenser, means for rendering constant
the charging rate of said sweep condenser com
prising a negative feedback circuit having a timev
constant longer than the cyclic period,` and
meansfor discharging said sweep condenser com»
prising; a pair of alternately conductive vacuum
tubes, each tube including at least an anode and
control grid, condensers joining the anode of>
each tube to the grid of the other, respectively,y
one of'said condensers and said sweep condenser
being-- common..
l5.A In an oscilloscope system, a sweep con
denser, a circuit for cyclically charging saidv
sweep condenser, means for rendering constant
the charging rate of said sweep condenser com
prising a negative feedback circuit having a time
contsant longer than the cyclic period, and means
for discharging said sweep condenser comprising
v chargingv said 'sweep condenser, meansrfor rendeltf
ing constant the charging rate of said sweep con»v
denser comprising in series therewith aniimped
ance and. aiìrst space Vdischarge device`y including
a cathodenand. control grid», a> grid resistory con»V
nected betweensaid` cathode :andgrid, and aconf
denser'` connected'between said grid and: the end
of said'impedance distant from said cathode„saidl
grid resistor and condenser havingv a timeë con-f
stant- at least-asA long as thecharging cycleffor the
~ sweep condenser, and means for‘dischargingsaidf
sweepcondenser comprising a. second and third;
space discharge device 'eachhaving at least.- an;
anode, cathode-- and control grid, said; cathodesi
being connected to» one vend' of a common cathode:
resistor, grid resistorsjoining the- grids> and ca»
thodes of each‘tuberespectively, said second space
discharge- device- in combinationv vvith-y said> ca
thode resistor being adapted .to'shunt said: sweep
condenser, a. condenser` joining» the grid of the>
secondA to» the» anode-’of the third‘discharge de
vice. and a grid.A condenser joining the grid of
the third spaceidischa-rge device to the distant end.>
of said. cathode. resistor, the grid condenser and..
grid resistor for the-,third space dischargefdevice.
Y having, a. timeV constant atleast as. long- as- theì
sweepcondenserv charging cycle.
19. In an oscilloscope system, a, sweep con--
denser, a circuit for. cyclically charging and' dis
charging-said.sweep-condenser, means for render-'
ing; contsant the'chargingrate ofv said sweep4 con
denser comprising> in series therewith an indue-f»
tance and a first. space discharge device includ-v
ingacathodeland control grid, agrid-resistor con#
nected. between `said cathode and grid, _ and ' a. con-Á
. denser connected between said grid and the end
of said inductance distant fromsaid cathode, said
grid;y resistor and- condenser having a time con
stantat- least as.- long. as the charging cycle for
the sweep condenser, and- means-'for discharging.
f said sweep4 condenser at alinear rate comprising
a second andthird- space disch-arge> device each,
having at least» an anode, cathode and controll
grid,v said cathodes being connected to one- end`
of, a.. common cathode resistor, an inductance
joining, the grid and cathode'of said second‘space
discharge device,v a gridv resistor joining -the grid
and, cathode of saidy third space discharge de-.
vice,.said,second» space discharge device in combi-f»
nation with. said» cathode resistor being adapted
to. shunt. said sweepy condenser; a condenser
joining theY grid- of the _secondf to the anode;
of. thethirddischarge device anda grid condenser
and control grid, said cathodes being joined to
joiningthe. grid» ofthe: third space discharge de
gether to one end of a common resistor, a con-I
vicev to the distant end of said cathode resistor,
denser connecting the anode of one tube to the 70 the, grid. condenser and grid'. resistor >for the vthird
grid of the other, said sweep‘condenser joining
space discharge device having. a. time constant.
the anode of the. other tube to the other end
atleast as.A long as the. sweep- condenser charg
a pair of alternately conductive vacuum tubes,
each tube including at least an anode, cathode
of said common resistor.
16. In an oscilloscope. system, a. sweep con
ing. cycle.
20... In. an. oscilloscopev system, a»V sweep com;
denser, separate circuits for cyclically charging. 75 denser, a. circuit. for cyclically charging.. andadis-> ,
'#25
52,552,884
"'26
charging said sweep condenser at a controllable
and a source of' voltage, ’means for discharging
repetition rate, means for rendering constant the
charging rate of said sweep- condenserncomp'ris
ing >in, series therewith Aav variable impedance vand
said condenser includingin shunt thereto the
space path of'said second space discharge de
vice, and'means comprising said third space dis
a first space discharge device including a cathode
charge device for rendering said second space dis
-and control grid, agrid resistor-connectedbe
charge device conductive,` said third space dis
charge device having anv element also connected
tween said cathode and grid, and a Vcondenser
connected between vsaid grid andthe end of
said impedance distant from said'V cathode,
Vtoi said source of voltage and means for deter- «
inating the charge applied to lthe sweep con
denser after a‘predetermined time interval com
prising a variable grid resistor joining the grid
means for rendering constant the charging rate
of-said condenser, and means for discharging said
condenser at a controllable repetition rate, both
of said means including negative feedback cir
mining said maximum voltage` independently of
said grid resistor» and condenser having. a 10 the charging repetition> rate comprising means for
varying the voltage of said source.
n l l
,
time constant at least as long as the charging
24. InV an oscilloscope system for continuously
‘cycle for the sweep condenser,_ and means for '
discharging said sweep condenser comprising a
observing a repeated signal, a sweep condenser,
second space discharge device, an'anode, and a
circuits for _cyclically/»charging and discharging
cathode and control grid, and means for term :15 said condenser, saidlcharging circuit including
" and cathode of said second space discharge device,
said second space discharge device being adapted 20 cuits having time constants of the same order as
to shunt said sweep condenser, said repetition
the period of said repetition rate, the periods of
rate thus being controlled jointly by said variable
. said repetition rate and of said signals having a
impedance and said variable grid resistor.
ratio of not less than 50.
21. In combination in an oscilloscope system,
25. In an oscilloscope system for continuously
a first space discharge device, a second and a 25 observing a repeated signal, a sweep condenser,
third space discharge device each having an
circuits for cyclically charging and discharging
anode, cathode and grid, Ya variable sweep con
said condenser, said charging circuit including
denser, a circuit for cyclically charging and dis
means for rendering constant the charging rate
charging said sweep condenser at a controllable
' of said condenser, and means for discharging said
repetition rate, means for rendering constant the 30 condenser at a controllable repetition rate, both
charging rate of said sweep condenser compris
of said means including negative feedback cir
ing in series therewith a variable resistor, the
cuits having time constants of the same order as
space path of said first space discharge device and Y the period of said repetition rate, the periods of
a source of voltage, means for discharg
said repetition rate’and of said signals having a
ing said sweep condenser including in shunt
ratio of not less than 100.
,
thereto the space path of said second space dis
26. In an oscilloscope system, a pair of vacuum
charge device, a second _resistor connecting the
tubes each of which has, at least, an anode,
cathode and grid of said second space discharge
cathode, and control grid, a sweep condenser, a
circuit for cyclically charging said sweep con
device, said latter device being subject to the
control of said third space discharge device, a 40 denser which includes in series therewith, in
second Variable condenser joining the grid of
order, an impedance and the space paths of said
said second to the anode of said third space dis
' pair of vacuum tubes, grid resistors connected
charge device, and means for varying said repeti
between the grids and cathodes of each of said
tion rate comprising means for jointly control
tubes, and negative feedback means for rendering
ling the capacitance of said two variable con 45 constant the charging rate of said sweep con
densers in combination with means for jointly
denser which comprises grid condensers con
controlling said two variable resistors.
l
nected from the end of said impedance distant
22. In combination in an oscilloscope system,
from said tubes to the grid _of each tube respec
a ñrst space discharge device, a second space dis
tively, the grid resistor and grid condenser com
. charge device, a third space discharge device, a
bination for each tube having a time constant of
the same order as the cyclic period.
sweep condenser, a circuit for cyclically charging
said condenser to a predetermined maximum
27. A system for providing a constant flow of
voltage, means for rendering constant the charg
direct current to a variable load circuit, which
ing rate of said condenser comprising in series
comprises a pair of vacuum tubes each of which
therewith an impedance, the space path of said
has, at least, an anode, cathode and control grid
first space discharge device and a source of volt
and an impedance, a source of current in series
age, means for discharging said condenser in
with said load, and, in order, the space paths of
cluding in shunt thereto the space path of said
said pair of Vacuum tubes and said impedance,
grid resistors connecting the grid and cathode
second space discharge device, and means com
prising said third space discharge device for
of each tube, and means for maintaining con
rendering said second space discharge device
stancy of said current flow which comprises nega
conductive, said third space discharge device hav
tive feedback condensers connected between the
distant end of said impedance and the grid of
ing an element also connected to said source of
voltage, and means. for predetermining said
each tube respectively, the condenser and resist
maximum voltage comprising means for varying 65 ance in combination for each tube having time
the voltage of said source.
constants of the same order as the variations in
load.
23. In combination, a first space discharge de
28. A system for providing a constant iiow of
vice, a second space discharge device, a third
direct current to a load circuit, which comprises
space discharge device, a condenser, a cir
cuit for cyclically charging said condenser to 70 a pair of vacuum tubes each having, at least, an
a desired maximum voltage at a controllable
anode, cathode and control grid and an im-Y`
repetition rate, means for rendering constant
pedance, a source of current in series with said
the charging rate of said condenser com
load, and, in order, the space paths of said pair
prising in series therewith an impedance, the
of vacuum tubes and said impedance, grid re
space path of said ñrst space discharge device 75 sistors connecting the grid and cathode of each
2,5525884
27
Y.
tube,A and> means` for mainißainirig` constancyv of
said,Í currentVv flow which> comprisesl condensers
conneçtìed¿- between the.»dista,nt~end ofV said. im.- _
.pedajnce vand: the gridrof,.e2u4:h»tuberespectively.y
WILLIAMD< CANNON.
_A
Y
_Y
5
l
REFERENCESCITEU
The following. references arefof record-'in the
me 01.13115; vparent;
Number
2,085,100
` 2,174,234
2,180,365
Name
Date
2,394,891
Bowie» __________ __ Feb.- 12; 1946
2;4O'Z~,8984v
Norgaard _______ __ Sept; 17», 1946
2,452,213
10
Knowles-eil ali-___--- June >29,1937
Name.
'
Datel» 1',
Browne ___________ __ Juneîlô;` 1942
Bode ________ ______ Mar'.\30,»1943
Livingston ______ ___ Aug,A 14„1945
2,410,745
2,426,256
A
UNITED ` STATES ` PATENTS
'28
Numberv
2;286,8942,315,040`
2,382,243Y
2,473,915
Pugsiey __________ _ Nov.
_ Zener ----------- -- AugSontheimer ...... __ Oct.
Slepian et- a1. ____ __ June
OTHER- REFERENCES
A
5, 1946
26,1947
26, 1948
21, 1949
.
_
»
Sò0ync.“Cur1îentLStabilizers? Proc. I.,R.,E-.'..pp,
Cawein_.___. ______ __ Sept. 26,A 1939
41510 417,vv01.¿32, N0. 7, July 1944;.
Norton _________ __Y- NOV. 21, 1939 u,
y
Y ,
I,
ff‘