US2224005A - Electrical transmission circuit - Google Patents

Description

Dec. 3,1940. I A. w. VANCE 2324,0025

ELECTRICAL TRANSMISSION CIRCUIT Filed May 31, 1935 2 Sheets-Sheet lv -A ail i VVC q O} E m LE S INVENTOR t s HrihurWVan'c A. W. VANCE ELECTRICAL TRANSMISSION cmcun Filed May 31, 1935 2 Sheets-Sheet 2 i l l'lh'l l 'I'l WitnessE' INVEN'I'OR Arthur W Vance 117' 7'0 NEY Patented D... s, 1940 v .11; v 2,224,005

U I 'r TAT S, PATENT Radio. Corporation of America, a corporation of Delaware Application May 31, 1935, Serial No.'24,199

8 Claims. (Cl; 178-75) My invention relates to electrical transmission ploying a transformer in which the step up ratio circuits which include transformers and particof the transformer is such as to give 'asubularly to circuits for supplying a deflecting voltstantially undistorted voltage wave of maximum age to electrostatic deflecting plates in cathode amplitude. r p x ray tubes. Other objects; features and advantages of my r51? In deflecting a cathode ray electrostatically, it invention will appear from the following-dc I is the usual practice to supply a saw-tooth voltscription taken in connection with the accomage to the deflecting plates through a power panying drawings in which,

tube and a transformer, :the transformer being Figure 1 is a schematic diagram which isreemployed'to-step up the voltage for 'obtaining ferred to in explaining theinvention; 10!

maximum deflection. The transformer is prac- Figures 2, 3, 4 and 5 are curves which are retically open-circuited on the secondary'exce'pt ferred to in explaining the-invention;

for the slight capacityof' the deflecting plates Figure 6 is a circuit diagram of one, emb0d-- which is negligible compared to the distributed iment of my invention; Z: j capacity of the transformer secondary. The ef- :Figure'lis a diagram :Which isreferredtoein .fect of this distributed'capacity in conjunction explaining the operation of the circuit shown? with the transformer leakage reactance is to in Figure 6; and I spoil the shape and ratio of the saw-tooth volt- Figures 8 and 9 are circuit diagrams of other; age appearing across the secondary. Because of embodiments of my invention. 0 this, there is a definite limit to the number Before considering a specific-circuit for com I of secondary turns, and, therefore, the secondpensating for the exciting curr'entof a transary inductance, which must not be exceeded if former, the problem as a whole' -will be conthe eifect of the distributed capacity is tobe sidered with reference to Fig, 1 in which 'Leand v kept small enough to be harmless. Lsrepresent the inductance values of the mi- 2 Since the transformer is to step up the voltmary and secondary, respectively, of a perfect age, it follows that there is'al'so a definite limit transformer. The power tube 'is considered a' to the number of primaryturns and, therefore,' constant resistance generator: of impedance Rp to the primary inductance whereby the primary and internal voltage E, the voltage E'being grid. inductance is so low that an exciting current. volts times the amplification factor of the-tube; of appreciable value must be i1supplied to the The set-up'ratio or turns ratio of -the trans- 3O transformer. Of course, if the primary inducformer is I tance could 'be made very high, the exciting curda turns rent would:be negligiblen I N- T An object of my invention-is 0 provide an im- Y v Pmmary turns 1..

proved method of and means for transferring a Then g V non-sinusoidal voltage wave through a transi former. IP- 2 A further object of.1myiinvention is to provide an improved electrostatic deflecting circuit The instantaneous voltages across the pri- 40 of the type employing a step-up transformer. mary and secondary are Vp and lfs, respectively. 40

A further bject of 'my'inventionjis to p Since it is desired that a saw-tooth voltage vide an improved electrostatic-deflecting circuit wave be impressed upon the deflecting plates in which the effect of exciting current in indicated at l in Fig. 1, it i's -assumed that a s pp transformer o e d I saw-tooth voltage of pe'akamplitude V and e-' lirtherjobject. f'my Invention is to riod T is impressed across the primary. This r provide an electrostatic deflecting circuit emvide animprovedmethodof and means for-im-' Voltage is represented by the curve in Fig pressing a substantially perfect saw-tooth volt- It equation is J age wave upon cathoderay tube deflecting plates. v

' jAstill further object'; of my invention'is to e 0 where t is the time measured from the beginning of the period. Also Evaluating C such that the wave shall have no D. C. component:

The D. C. component will be zero if V t J; 'pdz j; -K H- 1 V153 Vi T 1 VT3 VT2 r. We 101; sr-a- Let Then T c= for no D. C. component, and

'V t EXT' t) which has the wave form shown by the curve in Fi 3.

From an inspection of Fig. 1 it is apparent that p p+ p Then which has the wave form shown by the curve in Fig. 4.

From the last equation it is apparent that the voltage applied to the grid of the output tube must contain two components in order to impress a pure saw-tooth voltage upon the deflecting plates, one component for the output voltage, and another component for the internal drop in the output tube caused by the transformer exciting current.

The transformer ratio N for maximum defiection with given values of L5 and Rp may now be determined as follows:

From an inspection of Fig. 4 it is apparent that E is a maximum when t=T. Let Em equal this maximum value. Substituting in the last equation To determine the value of the secondary voltage Vs:

Substituting in the equation for V a 6 Et Since Ls, RIP, T and Em are fixed, deflection is greatest when V5 is greatest. To determined the transformer turns ratio N which will give maximum value of Vs,

We may compare the value of the primary inductance Lp with the tube impedance Rp when the above condition for maximum deflection exists as follows:

Ls=N L Substituting in the equation for N 6 N LI 6L, TR, N TR,

F 41a E-J. and R T Em=V+V=2V which shows that at the peak value of E the peak value of the saw-tooth component equals the peak value of the integral component.

The preceding calculations have shown that for given circuit constants there is one particular transformer ratio that will produce maximum deflection of the cathod'erayr It is'no'w of interest to. determine ihow far the optimum transformer ratio may be" departedafrom. with out materially changing themaximum value of the deflecting voltage. I

-In Fig. 5 the maximum deflectingl voltage'vs is plotted against a quantity: which is a function. of N. It will be seen that the-curve is rather sharply peaked so that:-if"'N 'is ilessthan about 7 10 0.5 times the optimum value:,or, greaten .than

about 2 times said value, there is a,.'decidedreduction in the value of V5 as compared withits peak value. X

Referring now to Fig. 6, an embodimentof my invention is shown applied to the horizontal de- I fleeting circuit ofu'a. television receiver. The receiver. comprises a cathode ray tuberllqoi well known construction having a cathode3,,a co'ntrol electrode 4,- a first'anodeG, a secondanode-l I and afluorescent screen 8.; A pairof deflecti plates 9 are located inside the tube for deflecting the cathode ray inone planer I I As will be described :hereinafter,- asaw-toothvo-ltagewave is impressed upon the deflecting plates 9 through ",atransformer -I I having .a primary l2 and a secondary I3. The deflecting.

" plates 9 are connected across the secondary l3 through blocking condensers l 4c-.and l6, and

the second anode 1 is connected to the Ymid- Y 0 point of a resistor I! connected across the de 'flectingplates. By employ g this. particular circuit the deflecting plates 9 are. maintained at the same direct current potential as the second anode 1 and they are varied above and below the second anode potential equal amounts during deflection whereby the'electrostatic focusing of the cathode rayis lnot impaired.

Considering now the circuit :for generating the saw-tooth deflecting voltage, impulses are gener ated by means of a relaxationoscillator l8 such as the blocking 'oscillator illustrated. The blocking oscillator comprises-an electric discharge tube 19 having a cathode 2l, acontrol .grid22 and a plate 23. The plate 23 is supplied with'voltage from a'suitable source such as a battery 24, this voltage being applied to the plate through a resistor 26 and the primary 2! of a'transformer 28. A- grid leak resistor 29 is connected between the control grid 22 and'th e cathode 2|; Also a grid condenser 3| in series with'i'a winding 32 of the transformer 28 is connected between the grid 22 and the cathode 2| wherebythe p-latecircuitof transformer winding. 33 to the input circuit of an electric discharge tube '34 which may .be of the screen grid type'having a ,'cathode 36,".a controli. I grid 31, ascreen grid38 andaplate 39. I I '7 65 The control grid 3! is maintained at a negalvtive bias which is high enough to bias the tube almost to cut-oft. This negative bias may be applied in any suitable way aszby means'of a biasing battery or by means of the self-biasing rev sistor 4| and a shunting condenser 42'shown in 1 the drawings- I s In" the. plate circuit of'the tube 34 ithereis' a condenser 43 across which a saw-tooth voltage is" to be produced. .This condenser is connected' be- '35 tween the plate 39. and the cathode-36, ,in th.

- indicated by the curve 63. I the two voltages appearingiacross the resistor 59 particular circuit shown, the "connection" tol the? cathode 36 being through the self-biasing re-- sist'or 4l. The plate 39 is maintained at a positive potential by means of a connection through a'resistor44 of highiresistance'value' to the posi- 5 I tive' terminal of. the battery 24. The resistance of theplate resistor 44 is high enough tocause the condenser 43 to be charged substantially linearly toproduce the gradually changing :por-

tionof the saw-tooth voltage-wave. :Each Volt- 10 age impulse produced by the oscillator I8 is impressed upon the control grid 31 in the positive direction whereby thetube is made highly con-" 'ductive and the condenser suddenly dischargessaw-toothr l I As previously explained, the voltage having a substantially perfect saw-tooth wave form which appears across the condenser 43 cannot-be aptherethrough to produce the steep portion of-the f plied directly to the input circuit of the-power tube "46 which supplies the transformer ll because ef the exciting current taken by the trans-'-' former. Therefore, an electric discharge tube 41 and: an associated circuit are provided for the purpose of providing a voltage having both a saw tooth component and an integral component to the input circuit of the power tube 46. The- I tube 41 may be of the screen grid type having a cathode 48, a control grid 49, ascreen grid 5| anda plate 52. A negative bias having a suitable value for making'the tube 41 operate as an ordinary class A amplifier is applied to the grid 49 -:through a grid-resistor 53. by any. suitable means such asla self-biasing resistor 54 and a shunting condenser 56.v The plate 52 of the tube 5.: I

is connected through a plate resistor 51 to the positive terminal of the battery 24. In-accordance with my. invention, a network.

consisting of a condenser 58 andia variable, re-.

sistor 59 in series is connected between the plate- 52 and the cathode 48, in the particularembodiment shown,'the connection to the cathode being through the self-biasingresistor'54. a

By referring to Fig. 7, where Rp represents the plate impedance of the tube 41 it will be seen that if a saw-tooth voltage 6| is impressed upon the input circuit of the tube 41there will be a resulting flow of saw-tooth plate current which will; cause a saw-tooth voltage 62' to appear across the resistor 59. The saw-tooth plate current 501 flowing into the condenser 58 will charge the condenser'to cause a voltage to appear thereacross which is the integral of the saw-tooth Voltageas" Therefore, the sumof andthe condenser 58 is a voltage having the Wave form shown in Fig. 4; and by properly adjusting the value of the resistor 59 the relative magnitudes of thetwo components may be made such 60:-

as to cause a perfect saw-tooth voltage to appear across the secondary I3 of the transformer; It will be understood that the plate impedanceR is very high compared with the impedance of the network 5859 so thatthe plate current is subv stantially independent of the Voltage across thenetwork; The power tube 46 may be of the three electrode type having a cathode 64, a grid 66 and a plate 61., The grid 66 is maintained at a suit- I I able-negative bias for causing the power tube to 70 operate as an ordinary class A amplifier. Inthe circuit illustrated this bias is obtained by means of a self-biasing, resistor 68 shunted by a condenser 69, the bias being applied through agrid.

resistor II. The; network 53:59 is scoupled to the input circuit of the power tube 46 through a coupling condenser 12. A suitable positive voltage is applied to th plate 61 through a choke coil 13, the primary 12 of the transformer I I having its lower terminal.

connected to the cathode 64 and its upper terminal connected to the plate 61 through a blocking condenser 14.

It should be understood that my invention is not limited to use in a cathode ray tube deflecting circuit. In a transmissionline or cable which must transmit a saw-tooth wave, it is sometimes necessary to match impedances by means of a transformer which introduces distortion because of the exciting current required. In such a circuit an integral voltage component may be supplied to the transformer by means of a network such as described above for the purpose of avoiding the distortion.

Instead of obtaining the integral component by means of the condenser and resistor network shown in Fig. 6, it may be obtained by means of a network such as shown in Fig. 8. In Figs. 6

and 8 like parts are indicated by the same reference numerals. The portion of the circuit shown in Fig. 6 to the right of the dotted line 15 may be replaced by the circuit shown in Fig. 8. The distinction between the two circuits is that a low impedance tube 8!, such as a 2A3 type, supplies current to a network in the plate circuit which includes an inductance coil I1 and a resistor 18 connected in series. The impedance of the coil 71 is large compared with that of the resistor 13 whereby a saw-tooth voltage impressed upon the grid of the tube 8! causes a saw-tooth voltage to appear across the inductance coil 11 and an integral voltage component to appear across the resistor 18. The reason for this is evident from the fact that a saw-tooth voltage applied across an inductance coil causes current to flow therethrough having a wave form which is the integral of the saw-tooth. This current flowing through the resistor 18, of course, causes a voltage of similar wave form to appear across the resistor.

The saw-tooth voltage component preferably is taken off a potentiometer 19 shunted acrossthe inductance coil 11.

A voltage wave having saw-tooth and integral components may be obtained by various other circuits. For example, as shown in Fig. 9, the condenser 58 may be replaced by a tuned circuit 8283 of the character described and claimed in my copending application Serial No. 744,533, filed September 18, 1934, and assigned to the same assignee as this application. Also, the saw-tooth component and the integral component may be produced by two separate tubes and combined later in a common circuit instead of being produced and combined in the same network.

The values of certain elements in the circuits shown in Figs. 6 and 8 are indicated in ohms, megohms, microfarads, and henries. It should be understood that these values are given merely by way of example and may be varied within wide limits. The values indicated are for a circuit designed to produce voltage saw-teeth occurring at the rate of approximately 8000 per second.

It will be apparent from the foregoing description that various other modifications may be made in my invention without departing from the spirit and the scope thereof and I desire, therefore, that only such limitations shall be imposed thereon as are necessitated by the prior art and are set forth in the appended claims.

I claim as my invention:

1. In a cathode ray tube deflecting circuit for impressing a voltage of substantially pure sawtooth wave form upon a pair of deflecting plates, a pair of deflecting plates, a transformer having a primary and a secondary, the in ductance of said primary being so low that an exciting current of appreciable value must be supplied to the transformer, means for coupling said deflecting plates across said secondary, an electric discharge tube having an input circuit and having an output circuit coupled -to said primary, and means for impressing a Voltage upon said input circuit which has two main components, one of said components having a sawtooth wave form, and the other component having a waveform which isan integral of said sawtooth component.

2. In a cathode ray tube deflecting circuit for impressing a saw-tooth voltage upon a pair of deflecting plates, a pair of deflecting plates, a transformer having a primary and a secondary, the inductance of said primary being so low that an exciting current of appreciable value must be supplied to the transformer, said secondary being coupled across said plates, an electric discharge tube having an input circuit and having an output circuit coupled to said primary, and means for impressing a voltage upon said input circuit which has two main components, one of said components having a saw-tooth wave form, and the other of said components having a wave form which is an integral of said saw-tooth component, said means including a network which comprises a reactive element and a resistive element.

3. The invention according to claim 2 characterized in that said network comprises a condenser and a resistor in series.

4. The invention according to claim 2 chara terized in that said network comprisesan inductance coil and a resistor in series.

- 5. The invention according to claim 1 characterized in that N is approximately equal to where N equals the ratio of transformer secondary turns to transformer primary turns, Ls equals the inductance of the transformer secondary, Rp equals the plate impedance of the electric discharge tube, and T equals the period of the sawtooth voltage.

6. In a cathode ray tube deflecting circuit for impressing a saw-tooth voltage upon a pair of deflecting plates, a pair of deflecting plates, a transformer having a primary and a secondary, said secondary being coupled across said plates and having so few turns that its distributed capacity has a negligible effect upon the action of said deflecting circuit, said primary having fewer turns than said secondary to provide a step-up ratio whereby the impedance of said primary is so low that the transformer draws appreciable exciting current, an electric discharge tube having an input circuit and having an output circuit coupled to said primary, and means for supplying a voltageto said input circuit which has only two main components, one of said components being a saw-tooth component and the other of said components being an integral of said sawtooth component, the relative magnitudes of said integral component and said saw-tooth component being such as to impress a substantially pure saw-tooth wave across said primary.

7. The invention according to claim 6 characterized in that the peak value of [the saw-tooth component is approximately equal to the peak value of the integral component.

' 8.' The invention according to claim 6 characterized in that N isapproximately equal to FIT,

. where N equals the ratio of secondary turns to primary turns, Ls equals the inductance of the" secondary, Rp equals the plate impedance of the p electric discharge tube, and T equals the period of the saw-tooth voltage, and. further characterized in that the peak value of said saw-tooth component is approximately equal to thepeak value of said integral component.

ARTHUR W. VANCE.

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