US2604591A - Saw-tooth voltage generator - Google Patents

Description

Jul? 2 1952 I w. BEACH SAW- TOOTH VOLTAGE GENERATOR Filed Oct. 28, 1946 INVENTOR H. W. BEACH NGE fol

ATTORNEY Patented July 22, 1952 UNITED STATES PAT ENT OFFICE 1 SAW-TOOTH VOLTAGE GENERATGR fibroid-W. Beach; Fort Wayne, ma; assignbr; by me's'ne assignments, to Fa'rnsvi' oith Research 7 jcorporationgacorporation elf-Indiana Argue-Mien October- 2'8, 1946', Serial-No.- 706,255

This invention relate .to saw-tooth Wave gen erato'rsan'd particulariy to generators can'f ible' qf producing 'a'pflsh-phll volteg'fof saw tootiiw ave form" having good linearity. and" relatively high voltage; I v i In order todeflect theel'ectrofi beam of al cath ode my tube it'is'necessaivte ir'npie'ss up'eh the deflecting System56]. sweep" voltage" varying o'dica11y.betv/een maximum 6. rr'iinirhu'riifaiiip if tilde? limits in a predetermined mann r? In oscil loscop-es, television" tubes aiiiii'the like; the "wave form of such a sweepfivoitlagefgiierally"has'the shape offfa' saw'='tb0'th. Ordinarily the" voltage variation of th'ef sweep"Wave'isr'eQUiieH tDTbe as linear as possible'i, o

Many devices for "generating" ari'eiectroii b'ain' deflecting Voltage naveheretoforebeenu vised; In general, these 10'! such devices which arecib'able of generating saw-tooth v'lavesfha viifg good linearity are incapable ofpioducingi'thes' Waves at 'aiiyappre'ciable voltage. Su "uevicesme' gen; er'aily satisfactory for employment with ca'thod'e the deflectingsysteinwom'p -se'a plurality of el'ongated'electrode slocated'ardund the path of mam, ofa 'plui alityfof iiiipeda e devices sucH 4 Cla-ims. (Cl. 250 27) networks of 'the'charac't'ei described"b'i Treason of their inability to ro-auee a s wcuivitag' relativelyhigh voitageif'.

present inventionijto 'piovi'de'aifdv generate? capablefoffproducingia;"substantially linear saw;

tooth" Waveof' appreciable? voltage magn tude:

'An' oth "er objectoff'the'inventio eretm; can :b1

* ducting-under the eoiitfrof a uses; to couple the gei ergtqr' t1 the deflectin condensers which must be used to couple' the orator to the defiecting' sfvsteiii are-of comparama hi hj values in order to have"siiia1]' react} 1 coimibn'ents bu lki',

ances'." No't' o'r'fli' are" sue therehyutiliz-ing considerable space m'uie eon-1pment, but also by reason of thei frlativelvhigh' Values effect an a preciable distortion ffofn Ii Ii- Therefore? wis stiu another bject o'f'the iii ven't'io'n to' provide; in 'com'uneuosfl with a" saw: tooth wa'vei generator capable of Wave having goodline ag e a novel coupliiig arrangement betvien the generator and the electron beam deflecting sys' tern;

In'accordan'ce with the present invenudn there is' provided af vacuum'wube having at least an" anodega'ca'th' de' and "a control g'rid'wh'ih' is con"- nectedin'thecircuit withothei' components for developing 'a' substantially linear 'saw-tooth" voltage-wave'of considerable 'ainia'lifud-e. Th anode" and the cathode of this tube 'ar' connected re specti'vely' through individual circuits iricl udin'g' impedance devices to a source of spacecurrent." Conduction Of SDELCe-Ibl'iifi'ent" through the tube and the impedance devices 'coiinctedinthe o'u-t put circuit, thereof is varied in'tiin' according" to asaw-tooth' functio'n' un'd'efth'e' 'contioi "offasimilarly" varying voltage impressed upon the control 'giidj Thefvoltage' for'iinpissionfub n" the control" grid is u'eriveu y from" a; circuit having" a capacitiverea'ctanc'e of a magnitude depending unon' the frequency at which'it isdesiredto"geiiplied with "charging current througi'fah' iinia'ed.

an' ce device conne'eted in "seriesthe'revvith'. This i impeuanee'uevice'is coupled to the control grid and cathode of the vacuum tube in such a mannei -fth at at an times-"during 'the cvcIe a' substan I tiaiiyconstaiit peter-ism difference is maintained acrossthe impdaiic'e devic'el Pe'riodicall y the capacitive reaemhe pir'cuit is" odispharged be rendered-con through" a 'cireui't" whieiifmeiv series of relatively produced comparatively no distortion" short time-spaced impulses. The anode and cathode of the tube are coupled to a load circuit such as a deflecting system, the mid point of which maybe connected to a' datum potential such as ground.

In accordance with an additional feature of the instant invention, the vacuum tube may be coupled to the load circuit by means of one or more glow discharge devices such as neon tubes. In one such arrangement these discharge devices may be connected in series between the anode of the tube and one terminal of the load circuit in which case the cathode is coupled to the other terminal of the deflecting system and the impedance between this latter-terminal and the mid point of the load circuitserves as the cathode follower impedance for the'tube.

For abetter understanding of the invention together with other and further objects, thereof, referenceis made to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appendedclaims. v

In the accompanyingdrawing:

Fig. l is a circuit diagram of apparatus embodying one form of the invention, particularly adapted for operation at a relatively high frequency; and- Fig. 2 is a circuit diagram of apparatus emb'odying another form of the invention which includes a novel coupling arrangement and which is particularly well suited fo'r operation at a relatively low frequency.

Reference will be made first to Fig. 1 wherein the apparatus disclosed is arranged particularly for operation at a relatively high frequency of the order of 15,000 cycles per second, forexample. The saw-tooth wave generator includes a vacuum tube I I which preferably is a pentode. The anode of this tube is connected through an impedance device such as a resistor I2 to the positive terminal of a source of space current, diagrammatically illustrated as a battery I3. The negative terminal of this battery is connected to ground. The cathode of the tube is connected through an impedance device such as a resistor I4 to ground. In order to generate a balanced push-pull saw-tooth voltage the resistors I2 and I4 should be of approximately the same values. The suppressor grid I5 of the tube II is directly connected to the cathode. The screen grid I6 of this tube is connected to the anode. The control grid I1 is connected to a capacitive reactance circuit which includes a capacitance I8. At the relatively high frequency specified, a part, at least, of this capacitance may be the inherent capacitance between the control grid I! and ground. v

anode serves as the major portion of the capacitance I8. The cathode of the tube 24 is connected to ground through a resistor 25 which is by-passed by a condenser. 26. The suppressor grid 2'! of the tube 24 is connected to the cathode. The screen grid 28 of this tube is connected through a resistor 29 to the positive terminal of There is provided for the capacitive reactance circuit including the capacitance I 8, a circuit for supplying charging current thereto. This circuit comprises a resistor lflconnected between the positive terminal of the battery I3 and the anode of a diode 2|, the cathodeof which is connected in series with a resistor 22 and the capacitance I8. A condenser 23 is provided to couple the cathode of the tube'I I'to the terminal of the resistor 22 which is connected to the cathode of the diode 2|.

The capacitive reactance circuit also is provided with a discharging circuit. This circuit includes a vacuum tube 24 which preferably is a pentode. The anode of this tube is directly connected to the ungrounded terminal of the capacitance I8. The capacity to ground of the the battery I3 and is by-passed to ground by a condenser 3|. The control grid 32 of the tube 24 is coupled by a condenser 33 to one terminal of a source of synchronizing impulses which are of positive polarity relative to ground. The other terminal of the impulse source is grounded.

Theanode of the tube II is coupled by a condenser 35 to one terminal of a load circuit shown diagrammatically by resistors 36 and 31 of substantially equal values. The cathode of the tube I I is coupled by a condenser 38 to the other terminal of the load circuit. The junction point between the load circuit resistors is connected to ground. This arrangement provides a load circuit which for alternating currents has a balanced impedance relative to ground. For example, in a successfully operated embodiment of the invention, the resistors I2 and I4 had values of 10,000 ohms and the resistors 36 and 31 had values of 15,000 ohms. Thus, from both the anode and the cathode of the tube II, the effective alternating current load circuit impedance to ground was 6,000 ohms, each 10,000 ohm resistor being effectively coupled in parallel with one of the 15,000 ohm resistors.

Referring. now to the operation of the embodiment of the invention shown in Fig. 1, assume that the conditions which obtain in the various circuits of the apparatus are those corresponding to the start of a cycle of the sawtooth voltage wave to be developed. Under these conditions the tube 24 is in a non-conducting state and the tube II is in a state of minimum space current conduction. The capacitance I8 is in a state of minimum charge. The voltage of the anode of the tube II is at its maximum .positive amplitude and the voltage at the cathode of this tube is at its minimum positive amplitude. The control grid I1 is at its maximum negative potential relative to the cathode of the tube II.

Charging current flows at all times through the diode 2I and the resistor 22 into the capacitance I8. As the cycle progresses and the capacitance I8 accumulates a charge. the ungrounded terminal thereof increases in positive voltage relative to ground. .The effect of the impression of this increasing positive voltage upon the control grid I! of the tube II increases the magnitude of the space current flowing in this tube. As this current traverses the cathode-connected resistor I4; the voltage of the cathode is increased positively relative to ground. This increasing positive cathode voltage, when impressed by the coupling condenser 23 upon the upper terminalof the resistor 22, serves to maintain a relatively constant potentialdiiference across this resistor, irrespective of the state of charge of the capacitance I8. By this means the magnitude of the charging current is maintained relativelyconstant.

As is well khowm ordinarily the rate of change of the charging current flowing in a capacitive reactance circuit is in accordance with an exponential function so that, as the charge accumulated by the capacitance increases, the rate of current flow decreases. ,However by means of the described coupling'of the resistor 22 to both the controlgrid-and the cathodecf the 5. be 1. I. .the chargingv current. I and. therefore. h voltage of the. capacitance It varies. at. a relatively. slow ratecsubstantially according to a.

linear function. Since: the voltage of the ca-.

pacitance l8 controls the space current conduction in the tube H, the voltages which. are developed atthe anode and cathodev of this tube vary in a substantially linear manner. These voltages are,-of course, of opposite phase. and. therefore, are suitable for impression upon the terminals of the output circuit resistors 36 and 31 so as to supply this circuit with a push-pull voltageiwhich'is balanced relative to theig'rounded mid point ortthe load circuit. Inasmuch, as one-half of the output circuit voltage is derived from the anode of the tube H and'the other half from the cathode o1 this tube, the effective magnitude oi this voltage is substantially'double the voltage-which could bev obtained from only one of these electrodes in a more conventional manner. At the end of the relatively slow change of the generated output voltage, one of the p'osi-' tive impulses-derived from the source 34 is impressed upon the control grid 32 of the tube 24, thereby rendering this tube conducting. There is provided by these means a relatively low impedance discharging circuit for the capacitance l8. Accordingly-the capacitance is discharged through the tube 24 and the resistor -25 at a relatively rapid rate to end the cycle. The apparatus iunctio'ns in the manner-' described'from this point for each succeeding cycle.

The diode 2|, by reason or its unilateral conducting characteristic, is effective to enable highervoltage operation that if itwer'e' not used;

At the peaks of the savv to'oth voltage'cycles the combinedualternating and unidirectional voltages at the'cathode offthe diode may b'e'considerably greater than the vo'ltagef'of the bat tery l3 and; consequently, the diode-anode. The diode, functions to permit this combined cathode voltage to1 develop, thereby extending the linear operating range of the saw-tooth Wavev generator. H vv Reference'will' new be'made to Fig. z'wherein another embodiment of the invention is disclosed. The circuit arrangement'in' this embodiment of the invention, is particularly well: suited for operationj'at relatively low frequencies of the order of 60' cycles per second, for example. Circuit components .in thisjilgure whichcorr'e spond to circuit components in Fig.1 have been given similar characters of reference; 'In' general, the arrangement. of the apparatus is much the same as that'p'reviously disclosed. x

However-{in view of the relatively low', operating frequency the. inherent capacity of the con-' trol grid I! of the tube II to ground is inadequate to effect the generation of the desired saw-tooth voltage wave.' In this instance, therefore, a condenser'39 is connectedbetween the control grid I! of the tube ll and ground in the capacitive reactance circuit. Also a small condenser 4| is connectedv between thescreen grid ISYof this tube and thepositive terminal of the'battery [3' and, in some cases, hasbeen found to be-helpiul.

The load'circuit comprises the series connection oftwo resistors 42 and 43-.- The junction point between these resistors is--groundedas in the previous case. and the otherterminal o f ;the resistor 43 is directly coupled to the cathode. of the tube H. No other cathode follower resistor is connected to the cathode of this tube. In

addition, the anodeof-theqtube II is coupled to theother terminal of the resistor 4-2 through one.- or more glow discharge devices 44. These components may. be, neon tubes, voltage regulatortubes or the like. In such an arrangement the load circuit may be balanced relative to ground for alternating currents by making resistors l2 and 42 of 10,000 ohms and resistors 43 of'5,000 ohms. Resistors l2 and 42 are effectively coupled in. parallel for alternating currents so that the impedance of the load circuit to. ground from the anode of tube H- is 5,000 ohms to match the impedance of the load circuit to ground from the cathode of; the tube.

The operation of the apparatus illustrated in Fig. 2 is substantially the same as the described operation of the apparatus ofFig. 1. The-condenserv 39 is charged at a relatively slow rate through the circuit Which includes the resistor 22. The voltage across. the condenser 30,, when.

impressed upon the. control grid ll of 'the tube ll, causes this tube toronductmore, -space current at ,a rate which increases substantially linearly. In this case, the space current ismade to-traverse the load-resistor 43 by reason of its direct coupling tothe cathode of the tube ll. Nevertheless, as in the previous. instance, .the voltage at the cathode of this tube increases with an increase in the space. current conduction by the -tube'soas to.;maintain a substantially constant voltagedrop across the charging resistor 22.; The condenser 30' is, -discharged.at a relatively rapid rate; through the space discharge pathpi, thetube 24 as'in the case previously de-. scribed. I v

v'llhe decreasing voltage at. the anode or "the tube ll caused byjthe increasingcurrent con"- ducted byfthe tube is impressed upon the ungrounded terminal o-fthe load resistorM'fthrough thefglow discharge devices 44. "All of such devices have, the characteristic that once a predetermined threshho-ldTvoltage is exceeded the impedanceof'the tube's, remains practically constant. Oo-nsequjently,jthe anodevoltage which is impressed upon the load circuit is not distorted by'reason of having to traverse the glow discharge? devices 44; Linearity of the saw-tooth voltage wave which is impressed, upon the load circuit, therefore, is preserved.

Such a coupling arrangement'is particularly useful when operating at relatively low freq uen cies. When conventional capacity coupling is employed it is necessary 'at'such' frequencies to use a 'relativelyhigh value of 'capacitance'so that the reactance may be keptsmall. Such co-ndensers are bulky andfor this reason, are not. generally desirable; "Smaller [condensers have largerfreactances' fandftliereby introduce a disto ori infthe 'voltageimpressed upon the load circflinfwhereby, the desired high order or 1111-,

earity is not obtainedf Thus, it apparentthat 7 a SaW tl3h' wave 'hav'i'ng the desired linearity characteristic.- 7 The provision of impedance devices connected -'respectively to both the anode and cathode of the tube enables the production of the s'aw -tooth wave in a push-pullmamier and also at considerable voltage magnitude. I While there has been described what at pres'. entis considered the preferred embodimentci the invention, it will be obvious to those skilled in the art that various'changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and modifications'as fall within the true spirit and scope of the invention.

What is claimed is:

1. A saw-toothvoltage generator comprising, a vacuum tubehaving an anode, a cathode and a control grid, a source of space current for said tube, a circuit including first and second impedance devices connected respectively to said anode and said cathode'for coupling the space discharge path of said tube to said source of current, a circuit having capacitive reactance means and including a charging impedance device connected in series with said capacitive reactance means for supplying charging current thereto, one'terminal of said charging impedance device being coupled to the control grid of said tube and the other terminal being coupled to the cathode of said tube, whereby a substantially constant potential difierence is maintained between the terminals of said charging impedance device and as a consequence the rate at which current is supplied to said capacitive reactance means is maintained substantially-"constant, means for periodically discharging said capacitive reactance means aload circuit for said generator including the series connection of said second impedance device and a third impedance device, and means maintaining a constant voltage drop thereacross for limiting amplitude range of current flow connectedibetween' the anode of said vacuum tube and said third impedance device.

2. A saw-tooth voltage generator comprising, a first vaccum tube having an anode, a cathode and a control grid, afs'ource of space current for said tube, a circuit including first and second impedance devices connected respectively to said anode and said cathode for coupling the space discharge 'path of said tube to"respective terminals of said source'ofcurrent, a capacitive reactance circuit including a condenser and a resistor connected in series therewith for supplying charging current thereto, one terminal of said resistorobeing coupled to the control grid of said'tube and the other terminal being. coupled to the cathode of said tube, whereby a'sub stantially constant potential difference is maintained between the terminals of said resistor and as a consequence the rate at which current is supplied to said condenser is maintained substantially constant, means including a second vac-,

uum tube for periodically discharging said'condenser, a load circuit for said generator including- 31A saw-tooth voltage generator comprising; a first vacuum'tube having an anode, a cathode and a control grid, at sourceiof space current for said tube, acircuit including first and second impedancedevices connected respectively to said anode and saidcathode fortcoupling the space discharge path of said tube to respective terminals of said source of current, a capacitive reactance circuit including a condenser and a resistor connected in series therewith for supply-1 ing charging curr'ent'thereto, one terminal of said resistor being coupled to the control grid of said tube and the'other terminal beingcoupl'ed tothe cathode of said tube, whereby a substantially constant potential difference is maintained between the'termin'als' of said resistor and as a consequence the rate atwhich current is supplied to said condenser; is maintained substantially constant, meansoincluding a second vacuum tube connected to said capacitive reactance circuit and periodically being rendered conducting to, discharge said condenser, a load circuit for said generator including the series connection of said second impedance device and a third impedance device, and means including a plurality of serially-connected glow discharge tubes for coupling the anode of said first vacuum tube to sai third impedancedevice. V r 7 4. A saw-tooth voltage generator comprising,a first vacuumtube having an anode, a cathode and a control grid, asource of space current for said tube, a circuit including first and second resistors connected respectively to said, anode and said cathode for coupling the space discharge path of said tube to respective terminals of said source-of current, acapacitive reactance circuit including a condenser and a chargingresistor connected in series therewithior supplying charging currentithereto at a relatively slow rate, one terminal 'of said charging resistorbeing coupled to the control grid of said tube and the other terminalcoupledto" ,the' cath ode-of said tube, whereby a substantially constant potential'difference is maintained between the terminals of said charging resistor and as a consequence the rate at which current is supplied to said condenser-is maintained substan tially constant, lrneans including a secondvacuum tube-havingits space discharge path connected, in parallel with said condenser and periodicallyibeing rendered conducting to discharge said condenser at a relatively rapid rate, a load circuit for said generator including the series connection of. saidisecond resistor and a third resistor,- and,,,means including] a plurality f of serially connected glow discharge tubesfor c0u-' third resistors" 1 pling the anode of 'saidfirst' vacuum tubeftojsaid REFERENCES orrnn s The: following references are or" record in the file of this patent; V s UNITED. STATES PATENTS Number Name.' I f-Date' 2,232,075 Newsam Feb. 18; 1941 2,254,344 Andrieu Sept L 2, 1941 2,412,063 Rosentreter v 1-946 2,412,064" Moe' I Dec.-3,1946 2,426,256 Zenori.. Aug. 26,1947 2,439,324 -Walker A r? 6, 1948 3,452,024 "-"Johnson Feb'f15', 1949

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