US2441246A - Modified sweep circuit - Google Patents

Description

May 11, 1948. I w. A. MiLLER ETAL 2,441,246

' V MODIFIED SWEEP CIRCUIT Filed Nov. 2, 1945 I INVENTORS A 0 1 #iumvvfi 4/41/54. war K UUE I I Z g qa/ A JP/i/v fi: V2 WW 7' a M ATTORNEY Patented May 11, 1948 2,441,245 MODIFIED SWEEP cracurr William A. Miller, Port J efierson, and Eugene It.

Shenk, Brooklyn, N. Y., assignors to Radio Corporation of America, a corporation of Delaware Application November 2, 1943, Serial No. 508,702

The present invention relates generally to a method of and means for generating saw-tooth voltage waves. Circuits for generating saw-tooth voltage waves are generally referred to as sweep circuits because of the fact that the saw-tooth 5 saw-tooth voltage wave obtained from the cirvoltage wave is utilized to vary the voltage on cuit of the invention. The ordinate represents the horizontal deflection plates of a cathode ray voltage while the abscissa represents time. It is oscilloscope, as a result of which an electron desired that the saw-tooth voltage wave increase beam sweeps" or scans the fluorescent screen linearly from a normal value to a particular on the oscilloscope. point D at which it is desired that the voltage More specifically, the present invention proof the saw-tooth wave remain at rest for an invides a method of and a circuit arrangement for terval T from D to F, after which the voltage modifying the normally linear sweep or sawwave-form should again increase linearly from tooth voltage wave-form in such manner that the point F to point G with the same slope that it had voltage wave increases linearly to a particular between the point of origin and point D. It point or voltage value, then remains stationary should be noted that at point D the voltage of at this point or voltage value for a predetermined the saw-tooth wave increases rapidly by a value interval of time, and then increases again linear- M, then remains at rest for a period T until the ly for the normal duration of the saw-tooth voltpoint F is reached, after which the normally age wave. The present invention permits an linear increase in voltage of the saw-tooth wave adjustment of the particular point or Voltage is continued. It should be noted that the overall value of the saw-tooth voltage wave-form t linear increase in voltage of the saw-tooth wave 1 which the increase in voltage is stopped for the from e po n of Origin 110 Point Ggis the Same desired period of time. as would occur without the modification pro- Although it is known in the prior art to modid -Ced by the sudden increase in voltage at point fy the wave-form of a normally linear saw-tooth D and. the rest in the interval T. Before P generator, such known circuits hav modified th ceeding with a discussion of the circuit of Figsaw-tooth wave-form at the expense of a net in- 1116 2, it Should. at this time be noted that the crease or decrease of the final saw-tooth voltage, time T at which the voltage of the saw-tooth or have caused a change in the slope of that por- 30 Wave remains at re t corresponds in m i tion of the saw-tooth wave which follows the duration to the rectangular pulse'shown n line modified portion. By means of the present in- Z of Figure 2. It should also at this time be vention, however, we are able to produce a sawnoted that the time interval of the saw-tooth tooth wave which normally increases in value at voltage wave be w the P in f orl ln and a constant rate, and then stops increasing in 35 the Doiht G is qu 13 t e du at on of the me voltage value at some point in the saw-tooth tive pulse shown in line Y. The reasonior this wave for a, desired interval of time, after which 13 described in greater detail in 00111180131911 Wlth the saw-tooth voltage wave-form continues northe operation of the circuit diagram of Figure mally to increase with the same slope as before Referring to Figure 1,'there are shown a pair the stoppage 0f the wooth voltage wave. 40 of vacuum'tubesvl and V2 having their cathodes Moreover, by means of the present invention, the directly connected together and 1n circuit with a change in the saw-tooth voltage wave does not common cathode resistor R5. The o tube aifect either the duration or the amplitude of Vi is connected directly to f Its PQ the overall saw-tooth voltage wave Putting it is connected to a source of pos1t1ve polarizing in other words, the end result of the modified potential EB. The rid of e V2 15 connected saw-tooth voltage wave produced by the present through. a pair of resistors R6 and R1 to the invention insofar as duration or amplitude is concathode of the same tube. The junction P011117 cerned is the same as the saw-tooth voltage wave of the resistors R6 and R1 is connected. to terwould have been without the modification. minal A to which the input pulse of line Z of A more detailed description of the invention 0 Figure 2 is applied. The anode o tube 15 follows in conjunction with a drawing, wherein: connected through an adjustable resistor R2 to 7 Figure 1 illustrates, by way of example only, a-positive source EB. Between the anodes of the one circuit embodiment of the present invention two tubes VI and V2 there are provided "a res for producing a modified saw-tooth voltage wave R4, a pair of. diode V4 and V5, and a conde s having the above mentioned characteristics, and Cl, as shown. Another diode V6 is connected 4 Claims. (01. 250- 27) Figure 2 graphically illustrates the operation of the present invention by means of a series of curves X, Y and Z.

Graph X of Figure 2 illustrates the type of between ground and the Junction point between diode V and condenser Cl. A third vacuum tube V3 having a resistor R3 between its grid and cathode and a condenser C2 between its anode and cathode is connected from a point between the two diodes V4 and V5 to another source of positive potential +E. The positive voltage obtainable'from source +E is less .th'an that obtain able from source"+Ee. The grid of-tubeV3 is connected through a condenser to terminal B to which a negative rectangular wave pulse general-L ly of the form of graph Y of Figure 2.is.supp lied.

The operation of the circuit of Figure lin its three essential steps in the operationriot-the-zcom-iplete cycle will now be describedzi St'artingvwith; the quiescent condition before: the application of any pulse to either terminalsA Or-B, the-vacuum tube Vi will be non-conducting while the vacuum tubes V2 and V3 will be conducting;

the second essential step in the cycle of operations; with the 'applicationiot-z a: negative :rectangular wave pulse-Yrto terminal B the-vacuum tube V! will still be non-conducting, the.vacuum tube V2 will. still be conducting; while the-vacuum tube V3' will be.- irrthe .non conducting gcondition because of the applicationrcf i as negativeinput pulse to. its grid: Mathexthirdessentialstep'of the :cycle' of operations; with thenegative-rectangular-wave :pulse .Y still :applied :to terminal B and with the negative rectangular wave input pulse 2 .applied to terminal. -A-,- theevacuumetube VI will become conducting; while.-. the vacuum tubes V2 and V3 will be .non-iconducting; The vacuum tube-V3 .will remain non-conducting until the end "of the rectangular wave-pulse .Y applied to terminal B;

Considering thezoperatioir of Figured .inmore detail, with particular-reference to the :various circuit elements,: the vacuum tube .V-l will be.non-. conducting and thervacuumtubes V2:and vawin be conducting'during the quiescent condition-,- that' is; prior" to'; the-application. of" negative pulses, toi either: of the; terminals; A: and: B. In this. quiescent: condition; it; will be: seen that thee grid: of: tube: V2? has no bias. applied thereto; as a resultiiottwhichrcurrentwill-iiow from the positive: source;+EB;throug-h resistor R2 and through the vacuum tube VZEtoground through the common'zbias resistorR'o'. The :flow of current through: resistorz R5" will produce an IR drop therein which applies :suifi'cient negative bias to the gridoftubeVl -to :cut-ofi-thefiow of anode current in thisrtube; Inasmuch-as; the negative rectangular wave .pulsehasnot .beenapplied to terminal B in thiszquiescent condition of operation, there will be rnmbias onathezgrid'of tube V3 andthis tube wi'llialso'- be conducting. As aresult of the status: of.these'sthree-.-tubes, in this particular conditiomof: operation; there willbe a fiow ofcurrent fromrtheapositive.source +-Ee through resistors: RI: and; R4=- in: series, through di'ode V4 and throughzvacuumtube- V3 to the source- +E. Source =E'Zastbefore mentioned, has a-positive valuelessF than that of source-EB. As a result of'th'is; a charge; will build. up on condenser C2,- but this'chargeWilLbe oii small value dueto the factthat thesvalue of resistors RI and R4 taken togetherrisilargezcompared to the -internal impedance f: the-pvacuum tube V3. This residual charge will always. be on the conidenser C2 and is. indicated. by. thesmall positive amount 'on' the ordinateeabove the reference: line 0' in graphiX of: Figure-2.- This .ordinate: represents the voltage. on. the condenser C2; and. is labeled 'Eca- It 'wilLthus-beenseen.thatthe saw:-

tooth sweep voltage starts with a small positive potential. In the next essential step in the operation representing the condition with only the negative pulse applied to terminal B (note graph Y of Figure 2), this negative pulse will bias the tube V3 to anode current cut-ofi, as a result of which the charge on condenser C2 will start to build up'li-nearly'."

Inthisrstep in the cycle of operation, tube V2 is still conducting and tube VI non-conducting. At some later time, when it is desired to stop. the increase in voltage on the condenser C2, for-a desired period of time, representing the third essential step in the cycle of operation of Figured;there-isapplied to terminal A a negativeinputpulse'of a magnitude sufficient to cut off the flow of anode current through tube V2. (Note graph Z'of Figure 2.) The application of a negative input pulse to terminal A causes the tube V2 to be non-conducting as a result of which the flow of current through R5 produced by the current flow in tube V2 :ceases, thus per,- mitting tube V! to conduct. Si-nce the negative input pulse applied to terminal-B ,-is,.of longer duration. than: that applied toterminal A it-will. be seen that in thisparticular step. in-the-cycle of op erations, tub es. V2 -.and- V3 are non-conduct.- ing while tubeVl :is conducting... Undenthis condition of operation, .in which .tube Vl. is. conducts ing, there will be a flow of current;thr,ough-v re: sistor RI,- in. .turn causing .a; decreaseinthevoltage applied. to the anode :of diode. V4 through resistor. R4. Thevoltage now availableonihe anode of diode. V4 .is..less .p,ositive .than .the volt-lage on the cathode .oi. the. same, ,diodapas are.- sult of which thediode. V4 will..cease.conduct-. ing, thus stoppingthe. building- .up...of.ithe char e on the condenser. 0.2.;over. the. path. which. in.- cluded the diode Va and .resistorsRA and; Rliin series- At .the. same .time that diode vfceased conducting, there .will. be. a sudden rise .in. the potential of the charge oncondensencfrepr sented by the. amount LMJin graph .Xilof Figu e 2. due to the fact that whentubeVZ'ceasescouducting there. is a. rise: in. potential applied; to the circuitincluding resistor R2; condenser; G! dicdevfi and .condenserCZLinseries. This risein potential makes diode. V5. conduct .andjcharses condensers. C2 1 and 01 in, .series. Condenser C2 willremain charged, to thesuddenly. increased amount represented bypoint Din graph X-oi Fig.1 ure 2,. for thetimecinterval-T correspondingto the. duration, of the. negative input pulse applied to terminal ,A. (note. Figure. 2.) When the neg! ative input .pulse. applied to.v terminal .A.. ceases, vacuum. tube V2; will again. conduct. and, bias vac-um tube VI. to -the. noneconducting state.

During. the time interval of the. negative. input pulse Z applied to terminal.A-,.it will .benotedthat the charge onv condenser 02. remains. constant. as represented by the horizontal line betweenpoints D and F on graph Xof Figure .2. The .-fiow otcurrent through V2. after the termination of, the negative input pulse. applied. to terminal A will now reduce thevoltage available in .the path .in: cluding R2, Cl and diode Veto a-positivevalue less than. the value, of source..+E, asaresultof which, the a diode V5 will cease conducting. and condenser Ci. will discharge through. diode. V6. The time required for. thesudden increase-.in voltage on condenser CZduring the time-interval when diode- V5 is conducting depends upon the time constantof thecircuit including resistor.R;2 and condensers Cl .and 02 while the amount of sudden increase in voltage on condenser G2: de-

pends upon the ratio of O2 to CI and upon the value of R2 When diode V5 becomes non-con ducting, simultaneously therewith diode V4 becomes conducting to reestablish a charging path for condenser C2 through diode V4 and resistors R4 and RI in series. The reestablishment of this charge path for condenser C2 causes the charge on condenser C2 to increase linearly from point F to the end of the cycle of operations represented by point G in Figure 2. It should be noted that except for the time interval T, the saw-tooth grave is linear and represented by a single straight In the design of the circuit of Figure 1, the time constants and values of the various elements are such that the height M of Figure 2 representing the sudden increase in voltage on C2 atpoint D and the rest period T during which the charge on condenser 02 remains constant are in the same ratio as the height of the saw-tooth wave at time G and the duration of the complete saw-tooth wave represented by the time of the negative input pulse on graph Y.

It will" be noted that the time T during which the saw-tooth wave is modified and during which the charge on condenser C2 remains constant depends upon the position of the negative pulse Z supplied to terminal A and its duration. By moving the position of the pulse applied to terminal A, we can thus modify the saw-tooth wave at any desired point in its cycle in accordance with graph X of Figure 2.

One use of the present invention, given by way of example only, is in connection with a radio locating and detecting system employing antenna lobe switching. In such a system, pulses of radio frequency energy are sent out in all four quadrants of a circle and it is important to distinguish on the oscilloscopes between pulses received during the different quadrants of the lobe switcher. By means of the present invention, one is able effectively to displace on the oscilloscope one received pulse with respect to another received pulse in an opposite quadrant. For an example of an antenna lobe switching system of the prior art, reference is made to Lindenblad application, Serial No. 454,661, filed August 13, 1942, and to Miller copending application, Serial No. 473,801, filed January 28, 1943, U. S. Patent 2,422,361, issued June 1'7, 1947.

What is claimed is:

1. The method of generating a modified sawtooth wave by means of a circuit including a condenser, which eomprises linearly charging said condenser to a desired point in the charge cycle, suddenly increasing the charge on said condenser by a desired amount, maintaining constant the charge on said condenser for a predetermined interval of time after the sudden increase of the charge, and then again linearly charging said condenser at the same rate as before.

2. The method of generating a modified sawtooth wave by means of a circuit including a condenser, which comprises linearly charging said condenser to a desired point in the charge cycle, suddenly increasing the charge on said condenser by a desired amount, maintaining constant the charge on said condenser for a predetermined interval of time after the sudden increase of the charge, and then again linearly charging said condenser at the same rate as before, the ratio which the amount of said sudden increase in charge on said condenser bears to said predetermined time interval being the same as the ratio which the total maximum charge on said condenser bears tothe total time it takes for said condenser to reach said maximum charge.

3. A generator of modified saw-tooth waves comprising first and second vacuum tubes each having a cathode, a grid and an anode, a direct connection between the cathodes of said two tubes, a common cathode resistor for said two tubes one terminal thereof being grounded, separate resistive connections from the anodes of said two tubes to a source of positive undirectional polarizing potential, a connection from-the grid of said first tubeto ground, a resistive connection from the grid of said second tube to its cathode, whereby said second tube normally draws current and biases said first tube to anode current cut-01f, a circuit between the anodes of said two tubes, a condenser connected between said circuit and a second source of positive unidirectional potential, the positive potential of said last source'being smaller in magnitude than the positive potential of said first source, a vacuum tube shunting said condenser, a connection for supplying to said vacuum tube a negative pulse of suilicient magnitude to render said last vacuum tube nonconducting, to thereby enable a charge to build up on said condenser over a circuit including the anode resistive connection of said first tube, and a circuit for supplying a negative pulse to thegrid of said second tube of a duration less than that of said other negative pulse and of a magnitude suflicient to bias said second tube to cut-off, as a result of which said first tube becomes conducting for the interval of said smaller duration negative pulse, and the shape of the saw-tooth wave produced by 'said generator is modified.

4. A generator of modified saw-tooth waves comprising first and second vacuum tubes each having a cathode, a grid and an anode, a direct connection between the cathodes of said two tubes, a common cathode resistor for said two tubes one terminal thereof being grounded, separate resistive connections from the anodes of said two tubes to a source of positive unidirectional polarizing potential, a connection from the grid of said first tube to ground, a resistive connection from the grid of said second tube to its cathode, whereby said second tube normally draws current and biases said first tube to anode current cut-ofi', a circuit between the anodes of said two tubes, comprising the series connection of a resistor, a first diode, a second diode and a first condenser, said first resistor of said series connection being directly connected to the anode of said first tube, while said first condenser is directly connected to the anode of said second tube, the cathodes of said two diodes being directly connected together, a third diode connected between ground and the junction point of said second diode and first condenser, a second condenser connected from the cathodes of said first and second diodes to a second source of positive unidirectional potential, the positive potential of said last source being smaller in magnitude than the-positive potential of said first source, a third vacuum tube having its anode connected to one terminal of said last condenser and its cathode connected to the other terminal thereof, a connection for supplying to the grid of said last vacuum tube a negative pulse of suificient magnitude to bias the tube to anode current cut-off for the duration of the pulse to thereby enable a charge to build up on said second condenser over a path including the anode resistive connection of said first tube and the resistor and first diode of said series connection, and a circuit for supplyal -negative pulsewto ine gnidsof said: second tube ofeawduration lesethan that of said other pulse end-eta magnitude sumcient to bias said second tube to. cut-off, as a result of which said firststube beoomes'oondueting andzproduces -anlR drop imitswanode oircuitof sumcient value as to interrupt the ehargingpath fer-said second condenser fer :the intewal ofesaid-smaller duration negabiveepulse, saidsecond -condenser having its change suddenly increased when-said charging 10 path :is-interrupted,ever a, pathincluding the second-diode, thefiflrst condenser and the anode resistive connection of said second tube; after which the 'ohaf-rge on-the second condenser remainsoonstant :for the: time during. which said second. tube is out off, said second tube again drawing 'ourrent upon the termination of said smaller duratimi-negative pulse, as a result of which saidlfirst tube becomesnon-conduoting and the charge on saidsec'onw condenser again builds up to a ts-maximum value, the termination of said 8 longer duratiom negative ipulse' permitting saidth-ird tube to draw current and 'dischargeseidsecondmondenser.

WILLIAM-A. EUGENE R; REFERENCES CITED The following references are of recordm me file of this I patent:

UNITED STATES PATENTS Number Name Date 1,955,332 Iams Apr. 17, 1934 2,075,140 Schlesin er Man-30; 1937 23188395 Swedlund July 27, 193'? 2,122,499 Stocker Ju1y5; 1938 $275,460 Page Mai". 10, 1942' 2,300,189 W011? Oct. 27, 1-942 2,312203 Wallace Feb. 2391943 2,347,608 Vance Apr. 18, 1944'

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