De¢.10,`1946.
,
, J.Q.EDSON ETAL
' 2,412,210
CATHODE RAY SWEEP CIRCUIT
Filed March 2l. 1942
2 Sheets-Sheet 1
A7' TORNEV
Dec? 1b, 1946.
2,412,210
J. O. EDSON ET AL
CATHODE RAY SWEEP CIRCÚIT
2 sheets-smet 2 v
Filed Marçh> 21. 19.42 I
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Patented Dec. 1Q, 1946
*UNITED STATES
orifice
2,412,210
CATHODE-RAY SWEEP CIRCUIT
James. 0. Edson,V Great Kills, N'. Y., William’ A. .
Edson, Chicago, Ill., and John B. Maggio, Summit, N. .1.,assignors to Bell-Telephone Labora
tories, Incorporated, New York, N. Y., a cor
poration of New York
_»
Application March 21, 1942, Serial-No; 435,688"
4 Claims.
(Cl. 315-26)
2
lf
larly those in whichA it is desired to provide bal
anced'saw-tooth voltagesV ona pair of horizontal
Either `of these pulses'may be used to effect-pro
duction of saw-tooth voltage waves in the output
circuit of the vacuum tubev’to‘which the multi
vibrator is suitably connected. For the purpose
deflecting'platesin .the oscilloscope;
of a balanced .circuit it is desirable'to make use
This invention relates-’to an improvement in
cathode ray oscilloscope sweep circuits, particu
The recognized‘advantage‘of such -balanced de
of bothV positiveand‘- negative voltage pulses at
iiectingvoltages is that their use eliminates the
impairment of definition of the electron spot
attendant onv Ithe application of an unbalanced
voltage to the sweep plates. There are numerous
patents which disclose circuits for the generation
the same time.
of balanced sweepvoltages. Among them may
and on the anodeîofthe trigger.V tube of an asym
metrical multivibratorY may. »bei transformed into
„be mentioned United States Patent 2,209,199`to
F. Gray, July'23; 1940; The use’ of vacuum tubes
tofamplify. the generated sweep voltage is also '
well-known, whether the amplified voltage is to
be, applied to staticf’deflecting plates or to the
terminals of a deflectingfcoil; An example of the
latter use. is disclosed inf W. O. Osbon’s United
Statesl Patent11‘,934,322, November '7,` 1933.
However, it does not appear that the circuits
known to the prior art include provision for the
choice of the- sweep voltage amplifying circuit
best adapted to the particular sweep frequency
selected.~ Such a provision becomes important
when it is desired to employ’with uniform ef
flciency and greatest economy of apparatus am
plified sweep voltages of frequencies varying from
the subaudible to the ultra-high.
Accordingly, another object »of the present in
vention is toprovide means including a pair of
vacuum tubes whereby the momentary voltage
pulses appearing
opposite' phase on the gridv
balancedlsaW-tooth voltages on the sweep plates
of the cathode ray oscilloscope.
Betweenground and thev cathode of the' .trigger
tube is the sweep frequency determining’ .circuit
comprising in parallel an' adjustable resistor and
an adjustable condenser. Across the .terminals of
this circuit there appears inthe operation of the
multivibrator a~~ saw-tooth voltage wave of fre
quency determined by the values of >capacitance
and resistance between cathode `and ground and
this saw-tooth Wave may be directly ampliñed as
desired. Where .a> balanced Voltage is to be de
rived from the -cathode-to-ground circuit, the
pai-r of amplifying tubes are supplied with a phase
inverting input circuit.>
'
Itis, therefore, aA further object of' the inven
tion to'provide switching means permitting the
selection of either vthe instantaneous grid and
Itis an object of the present invention Ito pro 30
vide a balanced cathode'rayv sweepucircuit includ
ing means for generatingLsweep voltages ranging
anode pulses above-mel'ltioned- or'the saw-tooth
in frequency from a few cycles .to’several mega
voltage between trigger cathodexandground as a
cycles per second, lcoupled with amplifying means
source from which to derive balanced voltages
for applying these voltages in balanced saw-tooth
for application to the sweepv plates of` theV oscil
form tothe horizontal deiiecting plates of a cath
ode ray oscilloscope and including provision for
selecting theamplifying circuit connection most
eiiicient for the desired frequency of sweep.
A suitable apparatus for the gener-ation of re
current pulses of the desired frequency of recur
rence is an asymmetricalV multivibrator using
hard vacuum tubes such as that disclosed, for
loscope.
It has been found possible to use the same pair
of amplifying tubes for the utilization of either
source of sweep voltage, providing, of course,
_ these’ tubes with‘the input and output circuits
appropriate »to the source selected. The switch
ing means, later >to be described, simultaneously
select the sweep voltage sourceland the amplifying
example, in United States Patent 1,978,461, Octo
ber 30, 1934, to P. L. Hoover et al. The generation 45 circuit adapted thereto, thereby.` attaining an
by this device of recurrent pulses is dueto the
mutual interactions of the .two vacuum tubes
which are commonly called the amplifier 4tube and
other -object of the invention, namelyVto provide
a circuit capable of.` utilizing with the greatest
economy .of apparatus lany source of sweep volt
age Iobtainable from a multivibrator.
the trigger tube,- respectively. In the operation
How these objects are attained by `the present
of such -a multivibrator, momentary voltage pulses 50
invention will be clearly shown in the following
of short duration in comparison with vtheir period
of ` recurrence appear simultaneously but with
description thereof with the aid- of> the accom
opposite polarities on the anode and on the grid
panying drawings in »all-ofwhich like parts are
designatedfby the samenumerals or letters, and
of»` the multivibrator trigger tube, the anode pulse
being negative,l while the grid pulse is positive. 55 in which:
`
'2,412,210
3
4
Fig. 1 is a diagram of a complete circuit of
R21 included between cathode 20 and tap 23.
the invention;
When the multivibrator circuit is in operation,
condenser 22 is only fractionally discharged in
connection of the amplifying tubes of Fig. 1
each cycle and with the circuit elements recited
adapted to utilize simultaneously pulses of 5 above, the time required for this fractional dis
opposite polarity arising on grid and -anode of a
charge can be reduced to the order of 0.01 micro
multivibrator trigger tube;
second. This interval of partial discharge is ap
Figs. 2A and 2B are representations of ~the grid
proximately one-tenth the period of recurrence
voltages, plate currents and plate voltages in the
determined by the described adjustment of con
circuit of Fig. 2;
10 denser 22 and tap 23. After this discharge
Fig. 3 is a schematic circuit illustrating the
through the temporary conductance of tube 3,
connection of the amplifying tubes of Fig. 1
condenser 22 is recharged comparatively slowly
adapted to amplify saw-tooth voltages in the
from battery I8'. A saw-tooth wave is thus gen
cathode-to-ground circuit of a multivibrator
erated which could be applied to the horizontal
trigger tube;
deflecting plates of the cathode ray oscilloscope,
Figs. 3A and 3B are representations of the grid
one of said plates being connected to point L1 of
and plate voltages in the circuit of Fig. 3.
switch S1, that is, to the cathode 2U of tube 3,
For the sake of simplicity, beam power tubes
the other of said plates being grounded. Of
24 and 25 of Fig. 1 are represented by triodes
course, such a saw-tooth voltage is unbalanced,
similarly identiñed in Figs. 2 and 3.
20 and the means to transform it into a balanced
Fig. 2 is a schematic circuit illustrating the
Referring to Fig. 1, multivibrator I comprises
ampliñer 2 and trigger tube 3, suitably a beam
power tube and a pentode, for example a 6Y6G
voltage employed by the present invention will be
later described.
The charge-discharge cycle of condenser 22
and a 6AC7, respectively. Control grid 4 of tube
2 is connected to ground through grid leak 6U as
shown (0.5 megohm) and through condenser 5 to
anode 6 of tube 3 and to contact H1 of switch
S1. Anode 'l of tube 2 is directly connected to
grid 8 of tube 3 and to contact H1’ of switch S1.
Cathode 9 and beam-forming plates I0 of tube 2 30
may be made to occupy time intervals varying
from one-tenth to one-ten millionth of a second.
To provide for this very wide range of sweep fre
quencies, condenser 22 is made variable from
about 4 microfarads for a sweep frequency of the
order of 10 cycles per second Ito complete discon
nection where only a distributed capacity of some
10 micrornicrofarads shunts potentiometer 2|.
to ground. Screen grid I2 of tube 2 is at a poten
tial, 150 volts positive to ground provided by bat
tery I3. Battery I3 also supplies power to anode
Coarse adjustment of sweep frequency is made by
variable condenser 22; fine adjustment by vary
ing the setting of tap 23. At the lowest frequency
all, at the highest some 5000 ohms, of the re
sistance of potentiometer 2| is in series between
are connected together and through resistor I I
‘I of tube 2 through resistor I4.
.
In tube 3 of multivibrator I screen grid I5 and
suppressor grid I 6 are connected to each other
and to a source of poten-tial 150 volts positive to
ground and cathode 20. When with suitable am
plification the voltage appearing across condenser
- ground which lmay be supplied from separate bat
22 is applied to the horizontal plates of the oscil
tery I‘I as shown or, if preferred, from battery 40 loscope, sweep of the electron spot takes place dur
I3. Anode 6 of tube 3 is suppliedfrom Z50-volt
ing the charging fraction of the cycle, flyback
during discharge.
battery I8 through resistor I9. Cathode 20 of
tube 3 is connected to ground through a portion
During discharge of condenser 22 there simul
(selected by tap 23) of potentiometer 2I in par
taneously appear voltage pulses on grid 8 and on
allel with variable condenser 22. Cathode 20 is
anode 6 of tube 3. The duration of these pulses
at the same time connected to point L1 of switch
is that of the partial discharge of condenser 22.
S1.
These pulses, negative on anode 6, positive on
Suitable values of resistances and capacitances
grid 8, may themselves be transformed into saw
in the above-described circuit are as in the fol
tooth voltage waves applicable to the horizontal
lowing table, wherein C4 is the capacitance of
plates of the oscilloscope and so are available
coupling condenser 5; R11 is the resistance of
alternatively with the voltage across condenser
cathode resistor I I, etc.
22 as a control of electron spot movement.
Double-pole double-throw switch Si in the po
:C5-0.1 microfarad
sition
shown in full line on Fig. 1 connects anode
C22-4 microfarads to 10 micromicrofarads
6 and grid 8 of tube 3 to the input circuits of am
R11-_100 ohms
plifying tubes 24 and 25, respectively. These am
R14-500 Ohms
plifying tubes are suitably beam power tubes such
R19-800 ohms
as the RCA-807. Point H1 of switch S1 leads from
R21-0.5 megohm
anode 6 through stopping condenser 26 to grid
It will be recognized that the above circuit is 60 27 of tube 24, while point H1’ leads from grid 8
that of an asymmetrical multivibrator. For a de
through condenser 28 to grid 29 of tube 25. Con
scription of the operation of such a circuit ref
densers 28 and 28 have suitably each a capaci
erence may be made to United States Patent
tance of 0.1 microfarad. Tube 24‘ is provided With
1,978,461 above-mentioned, or to the article en
a grid leak 30 of approximately 250,000 ohms re
titled “Trigger circuits,” by H. J. Reich, in “Elec
~ sistance. Bias voltage for the grid 2'I is provided
tronics,” August 1939, page 14. Since the multi
by cathode resistor 3l (say, 50 ohms) by-passed
vibrator circuit is in itself no part of the pres
by condenser 33a of large capacity (say, 20 micro
ent invention, it will be sufficient hereinto point
farads). Beam-forming plates 34 of tube 24 are
out the recurrent voltages appearing in its oper
joined to cathode 32, and screen grid 35 derives
ation.
70 from battery 35 a potential of 250 vvolts above
A recurrent saw-tooth voltage appears across
ground. For grid 29 of tube 25 a negative bias is
the terminals of variable condenser 22, in the
obtained across cathode resistor 31, by-passed by
cathode circuit of trigger tube 3, the frequency
condenser 336, between cathode 4I and ground.
of recurrence of this voltage being determined by
Elements 31 and 33h are of the sameÍvalues aS
the simultaneous values of C22 and. the portion of 75 elements Bland 33a, respectively. Cathode `4I
2,415.2;210“
6
Under these conditions, the negative. voltage.
and' beam-,formingr plates- 42 are connected toi-
pulse arriving at grid 21 drives tube 24 momen»
tarily to cut-olif.' Since the inductancev 48 is
traversed by- constant current,v the current ex
Grid leak 38 is similar togr-id'leak 302
»
Anodes 43 of tube 24 and 44 of tube 2'5’are con-v Ul tinguished in tube 24‘appears as a momentary‘in'»crease in- the charge of condenser` 45. After pas
nected, respectively, to the'mid-points of doub e
sage of the Voltage pulse condenser 46 discharges
pole double-throwA switch S2. While switches Si
at aconstant rate through inductance/49`. Arc.
and-S2 are shown-*widely separated'inFig~1, they
cordingly,- the voltage between anode 43.- and
are in actual assembly joined together'so' that
ground> undergoes a saw-tooth variationwith
when Si selects Athe input connection` to anode 6i
timersteeply» rising during the existence of the
andl grid 8, as shown, switch S2 at the same time
negative pulse on grid 27 and thereafter. morev
connects grids 43 and 44 to the output circuits
gether directly to ground and' screen grid~39- isA
made> positive to' ground byY 250-vo1t battery 40.'
slowly falling toward thev previously steady value
about to` be described;
until. another steep rise is provokedby a new gridr
‘,When Sz'is in the-positionshown in full lines,
pulse.
Simultaneously, the positive voltageA pulse on
each of anodes 43' andÍ 4-4- is connected to an in~I
ductance shunted' by a capacitance and through
these to the positive terminal of Z50-volt b-attery
45,. the negative terminalY of which is grounded.>
grid 29 of tube 25 renders this-tube momentarily
more highly conductive. Since constant current.
from battery 45 flows“ also in this circuit,.the cur.
As used' for the purpose of> this» invention, con
densers 46 and 41 areeach variable between ap
rent of tube 24 increases at the expense ofv the
charge of condenser 4T. ~A fractional discharge of
proximately 2000 micromicrofarads and the dis
tributed capacity of the associated inductance.
The inductances 48‘and 49iare each variable from
20'henriesY to 0.1 henry. The highest sweep fre~
quency is, of course, associated- with the lowest
simultaneous values of condensers 4S and- 4'1- and
of inductances 48 and 49. The circuit just de
scribed is preferred when the sweep frequency eX
ceed'sV 100 kilocycles per second.
In the alternative pair of simultaneous switch
positions, L1 and L1' of Si, In and'Lz’ of Sz, cath
ode- 20 of'tube 3 is connected'through condenser
25 to grid 2l' of tube 24 of which anode 43- is con«
nectedy to a. phase inverting circuit comprising
condenser 5l!> inv series with resistances 5l'and'52 35
to ground. Condenser'älì may appropriately be of
this condenser takesplace duringV the existence of
the positive pulse on grid 29 and after passage of
the pulse condenser 4l recharges at a constant
rate through inductance 49. The anode to ground>
voltage of tube 25 varies, therefore, in the same
way as the corresponding voltage of tubei24vv but Y
in opposite phase thereto.
The variations of grid voltage e1, anode current
i1, and anode voltage epi of tube 2,4 are graph
ically shown in Fig. 2A; corresponding voltage`
and current variations of tube 25 e2„i2 and epz
are shown in Fig. 2B. It will be clear that'plates`
A and A’ of the oscilloscope connectedy respec
tively to anodes 4?;v and 44 receive balanced saw
tooth voltage waves of magnitude determined by
the choice oi tubes 24 and 25'and their> associated
circuit elements and’of frequency determined by
the adjustment of the cathode circuit of multi'
0111 nii'crofarad capacity, while resistances 5I and
52" are‘, respectively, 1 megohm and 0.1 megohm.
In this alternative circuit conductor53` connects
f
as shown the junction of resistances 5l and 52 40 vibrator tube 3.
Tubes 24y and 25 may be balanced in output by
and condenser 2S. Tubes 24 and 25~are thus con
suitable choice of their grid biases. Their outputs
nected’ as' a well-known phaseV inverting circuit
are proportional to the duration of the voltage
described, for example, in United StatesA Patent
pulses and to the capacities of condensers 46' and
2,246,168 to R; B. Dome', June 17, 1941. At the
same time anodes 43 and 44' are connected to bat
Since’ the pulse duration is approximately a>
constant fraction of the period of sweep, con
stancy of output of tubes 24' and 25 is effected
45 4'?.
tery 45 through the 2 megohm resistances 54 and
55, respectively'. This arrangement of the input
and output circuits of tubes
and 25 is suitable
for sweep frequencies below 100 kilocycles per sec
ond. In either position of switches S1 and S2, an- >
odes 43 and 44V are'connectedl through condensers
56v and 5l to horizontal deflecting plates A and A',
respectively, of- cathode ray oscilloscope CRO.
Plates A and A’ are connected to ground through
resistances 58 and 59; respectively, which resist
by adjusting the capacities of condensers 46. and
41, increasing these capacities as the sweep fre
quency is decreased.
rIfhe circuit above-described is in principle suit
able for any value of sweep frequency. However,
at sweep frequencies below 10()> kilocycles per
second, inductances 48 and 49 must be incon
veniently large to serve the purpose of main
densers A56 and'51 may conveniently each be of
taining constant current in their respective cir
cuits from battery 45. Therefore, for the lower-
0.01 microfarad capacitance.
TheA operation of the circuit preferred for the
sweep frequencies it is convenient to make usc
of switches Si and S2 to throw tubes 24 and 25
ances are each suitably 10> megohms, while con
60 into the phase inverting circuit shown inv Fig. 3.
I-Iere by suitable choice of resistors 5i and 52,
plained by reference to Fig. 2. Here tubes 24 and
voltage e2’ on the grid of tube 25 may be- made
25 are symbolically represented by triodes. The
equal but opposite to voltage e1’ iny the grid of
negative voltage pulse arriving at grid 21 of tube
tube 24. Resistors 54> and 55 are appropriately
24 is represented by e1 of Fig. 2A; the positive
pulsesimultaneously arriving at grid 29 of tube 25 65 each 2 megchms insuring the equality in magni
tude of the output Waves amplified with respect
by e2.of"Fig. 2B'. In the multivibrator circuit de
to grid voltage waves e1’ and e2’ which, as above
scribed; trigger tube 3 has unity gain so these
described, are themselves of saw-tooth form aris
pulses are numerically equal but of opposite sign.
ing between cathode 20 of tube 3 and ground.
Each of the inductances 48 and 49 is so chosen
higher sweep frequencies is more readily eX
that its reactance is very large at the sweep fre
quency to be used. In this way, as taught by R. A.
Helsing in United States Patent 1,442,147, Janu
ary 16, 1923, inductances are employed to main
tain constant currents in the circuits supplied
75
from battery 45.
Figs. 3A and 3B respectively exhibit as functions
of time the grid and plate voltages of tubes 24
and 25, respectively. Plates A and A' of the
oscilloscope connected to anodes 43 and 44, re
spectively, are now, as in the connection pre
viously described for the higher sweep frequen
2,412,210
7
cies, supplied with saw-tooth waves balanced to
8
with which is a cathode resistor, a pair of am
ground.
,
plifying vacuum tubes havingeach at least an
While the phase inverting circuit utilizing the
anode, a control grid and a cathode, switching
saw-tooth voltage across condenser 22 is not
means coupling in a ñrst switch position the
theoretically limited to the lower sweep frequen Ul control grids of said amplifying tubes in push-pull
cies, it is not desirable to use this circuit for the
relationship individually to the anodes of said
frequencies of sweep much greater than 100 kilo
first and second tubes and coupling in a second
cycles per second. The saw-tooth voltage avail
switch position said amplifying tubes in phase
able at the cathode of the trigger tube of the
inversion relationship, the control grid of one
multivibrator does not exceed 10 or 15 volts. At
of said amplifying tubes being connected in par
least 200 to 300. volts are required for horizontal
allel with the cathode resistor of said second
deñection of the oscilloscope. Hence, a phase
tube.
inverting amplifier with upwards ofv 26 decibel
2. In a cathode ray sweep circuit including a
gain _would be required. Its frequency range
multivibrator generating a plurality of recurrent
would be such that at least the tenth harmonic
voltages of :controlled frequency of recurrence,
of the highest sweep frequency would have to be
means for deriving balanced saw-tooth voltage
passed with negligible phase or amplitude dis
waves from said recurrent voltages comprising a
tortion. With tubes available at present, such
pair of amplifying vacuum tubes, an input cir
an amplifier would require a phase inver-ter and
cuit and a ñrst and a second output circuit for
at least two or three high-power push-pull stages. 20 each of said tubes, and switching means select
Generating the sweep voltage directly at the
ing in a ñrst switch position the ñrst output cir
plates of the cathode-ray oscilloscope by utiliz
cuit for each of said tubes and simultaneously
ing the positive and negative pulses already avail
coupling said input circuits individually to the
able in the multivibrator circuit eliminates this
ampliñer and the attendant increased drain on
sources of a first and a second recurrent voltage
the power supply circuits.
.
The signal to be explored by means of the de
scribed sweep circuit is amplified as desired by
of said multivibrator, and selecting in a second
switch position the second output circuit for each
of said tubes and simultaneously coupling the in
put circuit of one of said tubes to the source of
the push-pull amplifier of Fig. 1 and applied to
a third recurrent voltage of said multivibrator
vertical plates B and B’ of the oscilloscope. The 30 and the input circuit of the other of said tubes
sweep cycle may be synchronized with this signal
to the second output circuit of said one tube.
3. In a cathode ray sweep «circuit including a
by any well-known means, for example, through
multivibrator generating a plurality of recur
the synchronizing ampliñer of Fig. l comprising
rent voltages and comprising a first and a second
a tube, suitably a 6AC7, the anode of which is
connected through a stopping condenser to anode 35 vacuum tube, said second vacuum tube having at
1 and grid 8 of tubes 2 and 3, respectively. The
least a control grid, a cathode and an anode,
grid of the synchronizing tube is itself supplied
through switch S3 from any desired external
means for deriving balanced saw-tooth voltage
waves from said multivibrator comprising a third
and a fourth vacuum tube having each at least
the ampliñed signal to be examined. The use of 40 a control grid, a cathode and an anode, an input
a synchronizing tube in such a connection is well
circuit for each of said third and fourth vacuum
tubes, coupling between the control grid of said
understood and requires herein no detailed de
voltage source or from a power supply or from
scription.
From the foregoing description of the inven
tion, it will be readily seen that means are pro
vided whereby the horizontal deflecting plates of
the cathode ray oscilloscope are in all cases sup
plied with saw-tooth potentials balanced to
ground and all the recurrent voltages made avail
able by the operation of multivibrator l are made ;
use 0f with the maximum economy of apparatus
together with means for selecting the source of
recurrent voltage and amplifying circuit therefor
best suited to the frequency desired for the sweep.
second tube and the control grid of said third
vacuum tube, coupling between the anode of said
second vacuum tube and the control grid of said
fourth vacuum tube, and output circuits for each
of said third and fourth vacuum tubes, said out
put circuits each comprising in parallel connec
tion an inductance and a capacitance.
,
4. In a cathode ray sweep circuit, the method
of providing balanced saw-tooth sweep voltages
of desired frequency which comprises generating
in the foregoing illustrate a satisfactory embodi
ment of the present invention, it is to be under
stood that those familiar with the art may find
a plurality of recurrent voltages of controlled fre
quency of recurrence, at least two of said recur
rent voltages being opposite in phase to each
other, selecting for sweep frequencies greater
than a chosen frequency said two recurrent volt
ages of opposite phase and transforming said tWo
other and equally useful tubes and circuit ele
voltages into equal and oppositely phased volt
While the tubes and circuit constants described ,
ments and employ such without ceasing to use 60 ages of saw-tooth form, and selecting for sweep
this invention.
frequencies of and less than said chosen fre
What is claimed is:
quency a third recurrent Voltage and transform
l. In a circuit including a cathode ray oscillo
ing said third voltage by phase inversion into
scope provided at least with a pair of sweep plates,
equal and oppositely phased voltages of saw-tooth
means for generating balanced saw-tooth volt
form.
ages on said sweep plates including a multivibra
WILLIAM A. EDSON.
tor comprising a ñrst and a second vacuum tube,
JAMES O. EDSON.
said ñrst and second tubes having each at least
_an anode, a control grid and a cathode in circuit
JOHN B. MAGGIO.