US2221015A - Periodic wave generator - Google Patents

Description

Nov. 12, 1940. J. c. wlLsoN PERIODIC WAVE GENERATOR 1 Filed Feb. 16, 1939 INVENTOR HN a w|\.so

ATTORNEY TAm A fem Patented Nov. 12, 1940 PATENT oFFlcE PERIoDTc WAVE GENERATOR John (l. Wilson, Bayside, N. Y1, `assignor to Hazeltine Corporation, a'corporation of Delaware Application February 16, 1939, serial No. 256,663

6 Claims. f (Cl. Z50-36) This invention relates to periodic wave generators and, while of general application, it is especially useful in the development of scanning fields of saw-tooth wave form in television systems.

Periodic waves having complex wave forms, such as saw-tooth and related forms, are useful for various purposes. In television systems, for example, at both transmitters and receivers, elec- 1,0; trostatic or electromagnetic fields of saw-tooth wave forms are utilized in scanning systems to deflect a beam, such as the cathode ray in a cathode-ray tube system, focused upon a target so as to cause the beam to scan successive fields' 15, or series of parallel lines on the target. `These fields are produced by applying periodic waves" oi the desired wave form to field-producing lelements. f

In general, it is required that generators of the type described be capable of developing waves of the precise desired wave form, in a television system of a form suitable to effect accurate linearity of trace and rapid retrace of the scanning beam. Moreover, it is highly desirable that these generators be readily adjustable for controlling separately the frequency and amplitudeV of the developed Waves. Further characteristics essential to such generators are simplicity of construction and dependability in operation.

,3.0 l It is an object of the present invention, therefore, to provide an improved generator for developing a periodic wave of complex wave form, such as a saw-tooth or related form.

It is a further object of the invention to provide a generator having one or more of the desirable characteristics and features referred to above. l

In accordance with the present invention, there is provided a periodic wave generator which comprises a seriesI circuit including inductance means,

a normally highly conductive conductance-controlling device and a source of operating voltage. The effective impedance of this circuit comprises substantially only inductancebut also 45 contains incidental undesired impedancesof other types. There is also provided means responsive to an electrical condition of the series circuit and including auxiliary impedance means having values related in a predetermined manner to 59 those of the undesired impedances for developing a control wave having a plurality of predetermined wave form components. The control wave is utilized by suitable means to so control the vconductance-controlling device as periodically `circuitwitli a conductance-controlling device,`

andsubstantiallyvto reduce its conductivity` for of operating voltage to adjust the amplitude of the periodic wave developed by the generator independently of other characteristics thereof. Suitable means are also preferably providedfor controllingthe operation of the control-wave-developing means toadjust `the frequency of the 101 f control Wave, thereby to adjust the period of the generated wave independentlyyof other characteristics thereof.

In a preferred embodiment of the invention,` auxiliary means responsiveto the operating conditions in the series circuit may be provided for developing a control effect. The eiiect is applied by suitable means to the conductance-controllingdevicev to aid in maintaining at leasta portion of the wave form of the generated pe-` 2Q riodic wave substantiallylinear. i l

The term normally 4highly conductive?" as applied to a vacuumtube Aor likeconductance-controllingdevice inthis application, is used-to refer to the characteristic of `such conductance-com" 2,5 trolling device, bywhich, in its static condition and not energizedby a iiuctuating signal, it is highly conductive and requires some signal cornponent to render it nonconductive or of low conductivity. e For a better understanding of the invention, together With other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the 3.5 appended claims, In the accompanying drawing, Fig. is a circuit diagram of a periodic wave generator embodying the present invention, While Fig. 2 is a group of curves illustrating the wave forms of various waves developed in the genera- 40 tor of Fig. l. ,i Referring now more particularly to Fig. 1 of the drawing, the generator illustrated comprises in-I ductance element l0, which may be a magnetic scanning element of ya television scanning sys- 45 tem through which it is desired to produce a current of saw-tooth Wave form, as shown,` or any suitable portion `of a load circuit.` The inductance element I0 is included in'a `mainseries preferably a vacuum tube Il which may be a triode,` as shown, or a multigrid tube, and a source of operating voltage. The source of` voltage includes a battery I2gor othersuitable `volt-f age supply means together with an adjustable denser 2l) and leak-resistor 2l.

series resistor I3 and a by-pass shunt condenser I4 of large value. To aid in controlling the linearity of the Wave developed by the generator, an adjustable resistor I5 of small value is also included in the series circuit. With this arrangement the effective series resistance of the series circuit at the operating Vfrequency is of a very low value. The effective impedance of the series circuit comprises substantially only the reactance of the inductance element I0, but incidentally includes undesired impedances of other types as Will be presently more fully explained.

For the purpose yof developing a control Wave for the generator, there is provided means responsive to an electrical condition of the series circuit and comprising a feed-back'or reversing vacuum tube I6 of the pentode type. The input circuit of the tube IS is vconnected across the load circuit of tube II by Way of a couplingimpedance I'I, which may comprise an adjustable condenser I'Ia, and an impedance I8 which may include an adjustable leak resistor I8a. shunted by a condenser I8b. 1

A complex load impedance I9 for the tube I6 f is connected between its anode and its source of operating potential, which may be the same as that of the tube II, as shown. This impedance may include, for example, a resistor lila, a parallel-connected resistor ISD and condenser i9c, and an inductance element Ild, connected in series in the-order named. '.The control grid of the tube II is effectively connected across the load impedance I9 by Way of a suitable coupling con- A negative-bias potential is applied to the-control grid of the tube Il by way of the resistor'ZI from a suitable source, for example, the battery I2', while screen` potential for tube i6 may be provided from a suitable sourcc indicated at -l-Sc. The impedance values of the elements of the impedance I9, are related in a predetermined rmanner to the impedances of the vmain series circuit so that the control -Wave developed bythe tube I6 is of the proper Wave form so to vcontrol the tube II as periodically to reduce its conductivity to a very low-value for a. small portion of each cycle, thereby tok develop a currentl Wave through the inductance elementy I0 of saw-toothwave form.

lSuitable equivalent circuit arrangements-may, of

course, be substituted for the impedances I5, I'I, I8, Yand I9. For'the purpose of synchronizing the operation of the generator, asynchronizing signalmay be applied to the control grid of the tube I6 from a terminal S;

The operation of the generator embodying the presentl invention, as just described, may be considered as starting at a point Where the conductivity of the tube 'il has just been established. Currentl rises through the Winding I0 and the internal resistance of 'the tube II. This current rise producesa voltage across the tube II and the resultant drop in its anode potential is applied by Way of the impedances I'I and I8 to the control grid of thetube I6. The tube I6 is thus cut oi during this portion of the cycle of operation, which corresponds to the trace period of the generated periodic current wave through the inductance element I0 Which is illustrated by the curve im yof Fig. 2, lthe traceportion being indicated at t. e

After a certain period, the rate of rise of current through the Winding I0 begins to decrease,

a pentode or tetrode type of tube is employed, so that anode potential of tube II, applied to the control grid of tube I6, increases positively. The latter tube begins to pass current, developing a voltage across its load circuit and the resultant drop in its anode potential is applied by way of condenser 20 and resistor 2l to the control grid of tube II, serving still further to reduce the current through this tube, Since this action is highly regenerative, the anodecurrent of the tube II is rapidly reducedv to a loW value. The period of'this rapid drop in anode current of the tube II through the inductance element I0 corresponds to the retrace period of the generated current Wave, which is indicated at 1 on the curve z'io of Fig. 2. The g-rid of the tube II remains negative, maintaining the conductivity of this tube at a low value, only during the short retrace period just described, after which the grid returns to its normal bias as determined by battery I2 so that the current again begins to rise through the inductance element I0 and tube I I and the cycle begins de novo.

During the retrace period, the condenser I'Ia is charged by the ow of grid current of tube I6 and such current as flows through resistor Ia and condenser I8b. At the end of the retrace period, which is the termination of the positive pulse from tube Il, the charge on condenser I'Ia is, in part, transferred to condenser |82) and changes to opposite polarity, that is, with its upper terminal, connected to the grid of tube I6, negative. The rate of change of the potential ron the grid of .tube I6 during the following trace period is then determined by the time constant Y of R and C representing, respectively, the Values of the resistor IBa and condenser I8b. This rate of change of grid potential, in turn, determines the periodicity of the control wave developed by tube I I and, hence, the frequency of the current Wave through the inductance I0. Thus, after the rst cycle, the periodicity of the generator is controlled by the time constant of the impedance I8, or by the application of synchronizing pulses,

and is independent of the saturation characteristics of tube Ilf The periodicity of the generated wave thus may be `readily adjusted, independently of the other characteristics thereof, by adjustment of thef resistor I8a. Moreover, by

the application of a synchronizing Wave to the control grid of the tube I6, so that synchronizing pulses are applied positively thereto just prior to the time that the tube I6 Would commence .to conduct, the generator may be readily synchronized. It is to be noted that during the normal operation of the generator, While the leading edge of a synchronizing pulse applied to the tube I6 determines the start of the retrace period, the reaching of cutoff by the tube II,` effecting a negative pulse on the grid of the tube Iii, de-

complex grid impedance I8, to differentiate the f negative pulses so that the amplitudes of the pulses as applied to the control grid of -tube I6 are effectively increased.

The amplitude of the generated Wave may be readily controlled and its linearity maintained by means of the arrangement for applying the operating voltage to the tubes II and I6, including the elements I3 and I4. These elements are so proportioned as to have a time constant which is Very large compared to the period of the generated wave, thereby ensuring a steady potential at the upper end of the resistor I3 throughout a cycle `of operation; that is, condenser I4 bypasses the alternating components of the total battery current drawn by tubes II and I6. Since the rate of rise in current through the winding I0 is substantially equal to E/L, where L is the inductance of element I0 and E the elfective operating potential, the Wave form of the current through the winding lil is substantially linear and adjustment of the operating voltage, by adjustment of the resistor I3, serves to adjust the amplitude of the wave developed by the generator independently of other characteristics thereof, particularly its wave form and periodicity. This circuit is essentially different from various generators of the relaxation type heretofore devised, wherein an adjustable resistor is included in series with the inductance element through which it is desired to produce a saw-tooth current wave in order to adjust the periodicity of the generated wave, since such resistors always cause the wave form of the current to be decidedly exponential in addition to aifecting its periodicity.

However, even in the series circuit of the generator of the present invention, there are undesired incidental impedances of other types. In order, therefore, to procure a current of the desired wave form through the inductance Ill, the values of elements I9a, I9b, |90, and I9d of the impedance I9 are related in a predetermined manner to those of the various incidental series circuit impedances.

If a current of saw-tooth wave form is to flew through inductance I0, considering it as a pure inductance, and if tube II had no internal resistance, a voltage wave of rectangular-pulse form, such as shown by curve |911 of Fig. 2, would appear thereacrossand it would only be necessary to apply a similar pulse voltage wave to the control grid of tube II. However, the tube Il does have appreciable internal resistance and the current therethroughfollows approximately the Wave form of its input voltage. Further, the incidental undesired impedances in the anode circuit of the tube II include not only this resistance of the tube I itself but also its shunt capacitance, indicated by the dotted-line condenser C in Fig. l, as Well as the inherent resistance and capacitance of the winding itself. By proper transformation of circuit constants, this main series circuit can be reduced to a simple electrical equivalent of resistance and capacitance in parallel with inductance lll.

Since the flow of a current wave o1' sawtooth wave form through the inductance Ill results in a voltage wave of rectangular-pulse wave form thereacross and, since this voltage appears also across the equivalent parallel incidental resistance and capacitance, there results a current of rectangular-pulse Wave form through the incidental resistance and a current oi' double-pulse wave form through the incidental capacitance. The total output current wave of tube II, therefore, is a complex current wave which is the resultant of the rectangular-pulse, the saw-tooth, and the double-pulse wave form current components. It is essential, therefore, that the control voltage wave applied to the grid of the tube II, which is developed across the load circuit of the tube I6, be of a corresponding complex wave form and include components corresponding with each of these wave form components. The elements I9a, I9b, I9c, and I9`d of the cornplex impedance I9, therefore, are so proportioned relative to the undesired incidental `impedances of the` main series circuit that such a control wave is developed across the impedance I9. In` general, the `impedance of i the unit I9 is the inverse of that of the equivalent parallelimpedance circuit; that is, in the impedance unit I9gthere areincludedimpedance elements corresponding to impedance elements of the equivalent parallel-impedance circuit and so related thereto that the product of the resultant impedances of the two circuits is a constant with respect to frequency. This relation requires that each reactance in the one circuit be represented by a reactance in the other circuit of opposite type and changed in position from shunt to series or vice versa, and the resistanc-e of the one circuit be represented by a conductance and similarly changed in position.

More particularly, the control voltage Wave includes first, a primary saw-tooth wave form component, such .as is illustrated by the curve eiscof Fig. 2, which produces the desired saw-tooth current wave in the main series circuit including inductance Ill. This wave is developed across or derived from the pulse current through condenser I9c. To compensate for the resistive components ofthe main series circuit, that is, to `develop a rectangular-pulse current wave through the undesired equivalent parallel resistance, a rectangular-pulse voltage Wave form component, such as illustrated by the curve eige Yof Fig.` 2, is derived from the pulse current through resistor I9a. For compensating for the capacitance components' of the main seriesv circuit, that is,to develop a `double-pulse current through the `equivalent parallel capacitance, a voltage component of oppositely-poled doublepulse wave form, ,such as is illustrated by the curve else, is derived `from the pulse current through inductance element I9d. The composite control voltageA wave developed across the im.- pedance I9 is thus of the complex wave form generally illustrated by the curve eis of Fig. 2 and includes the rectangular-pulse, the sawtooth, and the oppositely-poled double-pulse wave form components, each so related to, or`

corresponding to, an impedance of the main series circuit `that the effects of the undesired parallel equivalent impedance components thereof` are` compensated and a current of pure sawtooth wave form is caused to pass through the inductance I9.

The above` explanation presupposes that the tube II has an infinite internal resistance, that is, no internal conductance-` However, the internal resistance of` this tube is a nite quantity and its internal seriesconductance `is appreciable and must also be compensated. For this purpose the paralle1 resistor I9b is included in the circuit I9 and constitutes the negative reciprocal of the series conductance of the tube II, serving to so modify the control wave as to compensate for this-undesired internal conductance of the tube. l i i In certain cases where the compensation is inexact, due to the decrease in the rate of rise of current through the inductance IIJ during the latter part ofthe trace portion of the cycle, the linearity of the current wave tends to be distorted during the trace period. To compensate for this distortion, the negative feed-back resistor I5 is provided. This resistor is adjusted to a suitable relatively small value so that its im- .pedance is not Comparable with that of the insii ductance Il) and, therefore, itl does not contribute signiiicantly to the curvature 'of the current rise therethrough. However, during this current rise a voltage is developed across the resistor I5 and is applied, together With that developed across the impedance IS, to the control grid of the tube Il and is of such polarity thai it constitutes a negative feedback; that is, it introduces degeneration Which tends to cancel the distortion caused bythe decrease in Vthe rate of current rise through the Winding lil in a conventional manner. While this causes the total amplitude of the generated Wave to be less than ii otherwise would be, it improves its linearity more than in proportion to this reduction in amplitude. Thus, the dotted portion of the curve im of Fig. 2 shows the wave form which the current through the Winding ID Would have in the absence of the resistor l5, the distorted portion being indicated at d.

While the inductance l, disposed between the terminals indicated at X--X in the drawing, may, as stated, constitute a scanning element of a television scanning system, it Will be appreciated that the currents and voltages developed by the generator may be utilized in various other manners. For example, scanning elements may be inductively coupled to the winding IU, or the rectangular-pulse voltage appearing across this element or the saw-tooth voltage appearing across the tube ll may be readily utilized.

While there have been described what are at present considered to be the preferred embodiments of this invention, it Will be obvious to those skilled in the art that various changes and modications may be made therein Without departing from the invention, and it is, therefore, aimed in the appended claims to cover-all such changes and modications as fall Within the true spirit and scope of the invention.

What is claimed is:

l. A periodic Wave generator comprising, a series circuit including inductance means, a normally highly conductive conductance-controlling device and a source of operating voltage, the effective impedance of said circuit comprising substantially only inductance but incidental undesired impedances of other types, means responsive to an electrical condition of said circuit and including auxiliary impedance means having values related in a predetermined manner to said undesired impedances for developing a control Wave having a plurality of predetermined Wave form components, means for utilizing said control Wave to so control said device as periodically substantially to reduce its conductivity for only a small fraction of each cycle, thereby to develop a current of saw-tooth Wave form through said inductance means, means for adjusting said source to adjust the amplitude of said operating voltage thereby to adjust the amplitude ofthe generated periodic wave independently of other characteristics thereof, and means for adjusting said control-Wave-developing means to adjust the frequency of said control Wave thereby to adjust the period ofthe generated wave independently of other characteristics thereof.

2. A periodic Wave generator comprising, a

. series circuit including inductance means, a normally highly conductive conductance-controlling device and a source of operating voltage including an adjustable resistor and a condenser in parallel, having a time constant very large compared to the period of the generated wave, the 'effective impedance of said series circuit comprising substantially only inductance, means responsive to an electrical condition of said circuit for developing a -control Wave, means for utilizing said control Wave so to control said device as periodically substantially to reduce its conductivity for only a small fraction-of each cycle, thereby to develop current of saw-tooth Wave form through said inductancemeans, and means for adjusting said voltage-source resistor to adjust the amplitude of said operating voltage, thereby to adjust the amplitude of said current Wave independently of other characteristics thereof.

3. A periodic Wave generator comprising, a series circuit including inductance means, a normally highly conductive conductance-controlling device and a source of operating voltage, the efiective impedance of said series circuit comprising substantially only inductance, means responsive to an electrical condition of said circuit for developing a control Wave, means having a unidirectional transconductance for so applying said control wave to said device as periodically substantially to reduce its conductivity for only a small fraction of each cycle, thereby to develop current of saw-tooth wave form through said inductance means, and means for adjusting the time constant of said control-wave-developing means to adjust the period of the generated periodic Wave independently of other characteristics thereof.

4. A periodic Wave generator comprising, a series circuit including inductance means, a normally highly conductive conductance-controlling device and a source of operating voltage, the eiiective impedance of said series circuit `comprising substantially only inductance, a control circuit comprising a vacuum-tube repeater having an adjustable time-constant input circuit and an output circuit for developing a control wave, means for deriving a voltage from said series circuit and applying it to said input circuit, means coupling said output circuit to said device for applying said control wave thereto so to control said device as periodically substantially to reduce its conductivity for only a small fraction of each cycle, thereby to develop a current of saw-tooth Wave form through said inductance means, and means for adjusting the time constant of said input circuit to adjust the frequency of said control Wave, thereby to adjust the period of the generated periodic wave independently ci other characteristics thereof.

5. A periodic Wave generator comprising, a series circuit including inductance means, a normally highly conductive conductance-controlling device and a source of operating voltage, the effective impedance of said series circuit comprising substantially only inductance, a control circuit comprising a vacuum-tube repeater having an input circuit including an adjustable gridleak resistor shunted by a condenser and an output circuit for developing a control Wave, means for deriving a voltage from said series circuit and applying it to said input circuit, means coupling said output circuit to said controlling device for applying said control wave thereto so to control said device as periodically substantially to reduce its conductivity for only a small fraction of each cycle, thereby to develop a current of saw-tooth Wave form through said inductance means, and means for adjusting said input circuit resistor to adjust the frequency ofI said control Wave, thereby to adjust the period of the generated periodic 6. A periodic Wave generator comprising, a series circuit including inductance means, a normally highly conductive conductance-controlling kdevice and a source of operating voltage, the

eiective impedance of said circuit comprising substantially only inductance, means responsive to an electrical condition of said circuit for de-4 veloping a control Wave; means for utilizing said -control Wave so to control said device as periodically substantially to reduce its conductivity vfor only a small fraction of each cycle, thereby to develop a current of saw-tooth Wave form through said inductance means, and means for adjusting the amplitude of said operating voltage to adjust the amplitude of said current Wave independently of other characteristics thereof.

JOHN c. WILSON.

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