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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 è 29 44%1.¿_ e2' 52 à 55 en" ' ' .1.0. EDSON - /NvE/vrons: mAfosoN , B?JßMAGG/o jm@ ' 7' TORNEI’ 2,4l2,2l0 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.