US2203519A - Periodic wave generator - Google Patents

Description

June 4, 1940. M, cAwElN 2,203,519

PERIODIC WAVE GENERATOR 7 Filed Oct. 7, 193'! LJ/IO l2 l3 l4 l5 CARRIER VIDEO- CATHODE 0 T FREQUENCY RAY Z'ifiii? DETEC OR AMPLIFIER TUBE O Q 1 n 0 e l6 |--o a svncnnomzme FRAME F I SIGNAL FREQUENCY lG. SEPARATOR GENERATOR 29 OUTER Gflafl VOLTAGE VOLTAGE INVENTOR M DISON CAWEI TIME-- B W z ATTORNEY UNITED STATES PATENT OFFlCE,

2,203,519 PEBIODIO WAVE GENERATOR ,Ma'dison Cawein, Manhasset, N. Y., assignor to" p Hazeltine Corporation, a corporation of Dela- I ware Application October 7, 1 93'7, Serial No. 1 7,710

Claims.

""This invention relates to the generation of system in which a generator of the character periodic waves having complex forms, suchas saw-tooth and related forms, and more particularly, to television systems including means for generating and utilizing such waves for effecting scanning. l

In certain television systems according to present practice, including both transmittersand receivers, a beam, such as the cathode ray in a,

cathode-ray tube systemQis focused on a target and, by means of electrostatic or electromagnetic fields of saw-toothwaveform, is deflected to scan series of parallel lineson the target. The image to be transmitted is usually focused on the target of thetransmitter and the transmitting apparatus including this targetis such that the re quired signalis developed. The scanning action at the receiver is synchronized with that at the transmitter and the receiving apparatus including its target is such that the scanningis efiective to reproduce the scene on the target. scanning wave generators are required, therefore, at both television transmitters and receivers and it'is essential that these generators be capable of developing waves of the proper wave form to effect accurate linearity of trace and rapid retrace of-the scanning beam. Moreover, it is highly desirable that these generators be relatively simple in construction and dependable in operation l ,1 I

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

It is a 'further object to provide a television described is employed to provide a scanning wave.

In accordance with the present invention, there is provided a generator which comprises a single vacuum tube having a cathode, an anode and a plurality of gridsincluding inner and outer grids disposed between the cathode and anode and having relatively sharp upper and lower space current cutoff characteristics with respect to the potential on the outer grid. A loadresistor is connected between the inner'grid andthe cathode and a resistance reactance network is provided, coupling the inner and outer grids and having a phase shift ofless than 90 degrees and preferably as nearly zeroas practicable. An

impedance network is also effectively connected in thecathode-anodecircuit andis proportioned to have a time constant of, a predetermined value greaterthan and functionally related tolthe pe- 555; riod of the wave to bs generated. Means are further provided for applying operating potentials to the electrodes of the tube and for maintaining the inner gridat a substantially higher unidirectional potential than the outer grid.

,In a preferred embodiment of the invention, the resistance-reactance network between the inner and outer grids includesa condenser cone nected directly betweenthese grids and a resistor connected between the outer grid and cathode. Preferably, anl auxiliary or additional biasing grid is disposed adjacent the cathode and maintained at a negative potential with respect thereto to maintain the total space current substantially constant and to ensure that the operation of the tube is non-critical with respect to the potentials of the other electrodes. There may be provided also means for applyinga synchronizing signal to the last-mentioned grid to maintain the generator in, synchronism with any desired control wave; The output impedance network may comprise a resistor and condenser in parallel having a time-constant related tojthe period of the wave to be generated. For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection ,with the accompanying drawing and itsqscope'wi'll be pointed out in the appended claims. l

In the accompanying drawing, Fig. 1 is a cire cuit diagram; partially schemati of a complete television receiving system including a scanning wave generator embodying the present invention; Fig. 2 is a graph representing certain static characteristics of the single tube included in generator of Fig. 1; while Figs. 3 and 4*are curves representing voltage and current waves developed at various points in the generator of Fig. 1 during operation, to aid in the understanding of the invention. i

Referring now more particularly to Fig. 1 of thedrawing, the system there illustrated comprises a television receiver, which may be of either i synchronization and connected to scanning elements or coils of the cathode-ray tube I5 in a conventional manner. The generators l6 and Il are similar and are constructed in'accordance with the present invention, only the generator I! being shown in detail and hereinafter further described. The apparatus shown in schematic form, excepting the generator I6, is preferably conventional in construction and operation.

Since the system of Fig. 1, as thus far described, is, in general, Well understood in the art, a detailed explanation of its operation is deemed unnecessary. Briefly, however, vision-modulated carrier waves are intercepted by the antenna I 6-H and selectively amplified in the carrier amplifier l2. heterodyne type the signals are impressed upon an oscillator-modulator in the amplifier I2, where they are converted to an intermediate-frequency signal and further selectively amplified. The

amplified signal from the amplifier I2 is delivered u to the synchronizing signal separator 34, wherein the synchronizing signals are separated from the video signals and the frame and line impulses are also separated, the latter being thereupon delivered to the control elements of the generators l6 and H, respectively. The intensity of the electron beam or ray of the cathode-ray tube I5 is thus modulated or controlled in accordance with the video-frequency voltages impressed on a control grid of the tube, in the usual manner. The saw-tooth current scanning waves developed by the generators i5 and H are controlled by the synchronizing voltageimpulses supplied from the video-frequency amplifier I l and are utilized in a conventional manner to produce magnetic fields of saw-tooth wave form to deflect the ray of the-cathode-ray tube l5 vertically and horizontally, so as to trace successive fields or framesof parallel lines on the target of the tube, thereby to reproduce the transmitted image.

Referring now more particularly to the portion of the system of Fig. 1 which embodies the present invention, the generator I! comprises a vacuum tube I3, preferably of the pentode type and having a cathode, an anode, and a plurality of grids including inner and outer grids disposed between the cathode and anode and having relatively sharp upper and lower space-current cutoff characteristics with respect to the outer grid.

The tube 53 comprises first, second, and third grids disposed between the cathode andanode in the order named. The second and third grids may be-screen and suppressor grids, respectively, and hereinafter are referred to for convenience as the inner and outer grids, respectively, and the first'or control grid as an auxiliary or biasing adjacent the cathode. The first or auxiliary grid is connected to the cathode by way of a resistor l 9 and battery 2|] and serves to maintain substantially constant the total space-current of Where the receiver is of the superstated above.

sistance-reactance network'which may comprise acondenser 24 connected directly between these two grids, a resistor 23 and suitable source of negative biasing potential, for example battery 3 I, connected between the third grid and cathode, as shown, and the resistor 2|.

actance network has a time-constant of the de sired predetermined value, related to the period of the saw-tooth wave to begenerated, and has a phaseshift which is less than preferably approaching zero. The inner or second grid is maintained at a higher unidirectional potential than the outer or third grid, by the battery An impedance network, for example a sawtooth wave-forming circuit, is included in the anode circuit of the tube and preferably comprises a load resistor 25 and condenser 26, cffectively connected in parallel between the anode and cathode, as shown, and having a time consant related to, that is, of the same order of magnitude as, the period of the wave to be generated. Operating potential may. be supplied to the anode by way of the, resistor 25 from a suitable sourceior example a point on the battery 22. The potential of this point controls the peak output of the generator. A resistance 32, 'of suitable value, is preferably inserted in the cathode circuit for the purpose of stabilizing the operation of the relaxation oscillator and making the circuit constantsand biases less critical. The first grid is coupled to the separator-34 by way of condenser 33 to receive the line-synchronizing impulses therefrom.

An output tube 2'! isv preferably provided for the generator ll comprising a pentode having its input circuit coupled to the output circuit of the tube it, by way of a coupling condenser 28, and

itsanode circuit coupled to the line-scanning coils of the cathode-ray tube 15, by way of a coupling condenser 28. Operating potentials may be supplied to the screen and anode of the tube 27 from suitable sources indicated at +Sc and +3, respectively, thelatter being supplied by way of a suitable blocking resistor 30.

The values of these elements are such that this resistance-re resent the inner grid and anode currents, respecand lower space-current cutofi characteristics with respect to the outer or third grid voltage, as Moreover, this characteristic is stable for all operating conditions and is not criticallyaffected by variations in heater current or changes in the bias voltage of the auxiliary or first grid. It is to be noted that these characteristics are'not present'in tubesof other types which have heretofore been proposed for use in complex wave form generators, such as tetrodes including only two grids.

Due to the coupling between the inner and" outer grids the cathode and inner and outer grids form a type of oscillator which is well known in the art, the inner grid acting as an anode. Such a circuit tends to oscillate .at a relatively high natural frequency, determined primarily by its distributed inductance and capacitance, so that'the potentials of the inner and outer cuit constants and operating potentials of the various electrodes, another fractional cycle of the natural oscillation ensues and the anode blocks again, this process continuing periodically.

From another standpoint, the operation of the generator may be explained by reference to Figs. 3 and 4. The curves of Figs. 3 and 4 represent the forms of the voltageor current waves developed at difierentpoints in the generator, the abscissae representing time. Curves C, D and E of Fig. 3 represent the voltages on the inner grid,

the anode, and the outergrid, respectively, while curves F and G of Fig. 4 represent current to the inner grid and the anode, respectively.

, The operation may beflconsidered as starting at a point where the heater current has just been switched on, proper operating potentials having previously been applied to the electrodes of the generator tube. Under these conditions, electron space-current flows from the cathode toward the anode. Part of this current flows to the inner grid, increasing as shown at 1 of curve F and causing a voltage drop across resistor 2 I, so that the inner grid voltage gradually decreases, as

shown by the portion of the curve C. This voltage being impressed on the outer grid by way of condenser, the voltage of this grid follows that of the inner grid; that is, it decreases as indicated bythe portion :21 of. thecurve E. The drop in voltage on the outer grid serves to decrease the current flow to the anode resulting in an increased current flow to the inner grid,

since the total space current is maintained sub stantially constant. Hence, there resultsa furthervoltage drop across resistor 2| which, when the cathode current has built up to a sufiicient value, in effect regenerates the operation during this part of the cycle, as indicated at 02 and c2. This partof the cycle may be considered as a highefrequency transient occurring at the natural resonant frequency of the circuit which is determined by the distributed inductance and capacitance and which, as indicated by the steepness of the slopes of the portions 02 and c2 of the curves mentioned, is very high.

When the outer grid voltage has decreased to a point where the anode current is entirely cut off, the voltage across condenser 24, which previously was charged, as represented by the difierence between the inner and outer ,grid voltages, curves Cand E, begins to discharge gradually through resistors 23 and 2|, in series, as indicated by the portion es of the curve E. That is, the outer grid voltage rises exponentially during this part of the cycle as the potential difference across the condenser 24 falls. During this part ofthe cycle, the

anode voltage gradually rises as indicated [by the portion d1 of the curve D.. During this portion of the cycle, the anode voltage becomes relatively high and, when the outer grid and anode voltages reach the relative values indicated at point X of curves A and B of Fig. 2, and similarly indicated at pointX, Fig. 3, the anode current again starts to flow, the current flow to the inner grid is reduced, as indicated at f4, resulting in an.

. reaches the condition where the curve B represents the plate current, and that on the outer grid reaches the values indicated by the point Y of the curves A1, B1 of Fig. 2 and Fig. 3. At this point, the anode current, as indicated at 91, and the inner and outer grid voltages reach their maximum values, and the inner grid current, indicated at is, is reduced to a minimum. The condenser 26 then discharges in approximately exponential fashion through the anode-cathode circuit of the tube with the result that the anode voltage falls rapidly, as indicated at (15, to a low value. This decrease in anode voltage causes a decrease in anode current, thus releasinga portion of the total space current to the second grid and thereby causing its potential to fall, as indicated at ca. This initial fall in potential is effective to lower' the potentialof the third grid by virtue of the condenser 24, with a consequent regenerated decrease in the second and third grid voltages, at the resonant frequency of the circuit, as indicated at es and cs. The anode current decreases along the characteristic B1, due to the relatively low anode voltage and, when the anode current has been reduced to zero, as indicated at the point Z, Figs. 2 and 4, the cycle begins de novo. The negative peaks of the voltage on the outer grid, curve E, are sufiicient to carry the tube well below the cutoff point X on the characteristic B.

' Synchronizing impulses are applied negatively from the separator 34 to the first grid of the tube I8, preferably at a point in the cycle 'just prior to the point X, Fig. 3, thereby to synchronize the operationof the generator with the corresponding apparatus of the transmitter. The synchronizing impulses serve to initiate the rapid decrease in the current to the inner grid an d hence the corresponding increase in the voltages on the inner and outer grids. The saw-tooth anode voltage shown by the curve D is impressed by way of the condenser 28 upon the control grid l of the tube 27, thereby producing a saw-tooth cur- Tube l8 Type-6B6 pentode amplifier Condenser 24 2,000 micro-microfarads Resistor 2| 25,000 ohms Resistor 23---- 0.1 megohm Condenser 26 500 micro-microfarads Resistor 25. 0.5 megohm Resistor l9 0.1 megohm Resistor 32 10,000 ohms (adjustable) Generated frequency 13,230 cycles While there has been hereinbefore described 4 what is at present considered to -be the preferred embodiment of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the invention and it is, therefore,-aimed in the appended claims to cover all such changes andrnodifications as .fall within the true spirit and scope of the invention.

.What is claimed is: A periodic wavegenerator comprising a va'cuumitube having a cathode, an anode and a plurality of grids including inner and outer grids disposed between said cathode and anode and having relativelysharp upper and lower. spacecurrent cutoii characteristics with respectto, said outer grid, a load resistor. coupled between said inner grid and said cathode, means coupling said grids comprising an impedance network having a phase shift of less than 99, an impedance network effectively connected between said cathode and anode and having a time constant of a predetermined value greater than and functionally related to the period of the wave to be generated, and means for applying operating poten" tials to theelectrodes of said tube and for maintaining saidinner grid at a higher unidirectional potential'than said outer grid.

A periodic ,wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner, outer and auxiliary grids disposed between said cathode and anode and having relatively sharp upper and lower space-current cutoff characteristics with respect to said outer grid, a loadresistor coupled between said inner grid and said cathode, means coupling said inner and outer grids comprising an impedance network having a phase shift of less than 96, an impedance network effectively connected betweensaid cathode and anode and having a time constant of a predetermined value greater than and functionally related to the period of the wave to be generated, and means ion applying operating potentials to the electrodes of said tube and for maintaining said auxiliary grid at a fixed unidirectional potential with respect to said cathode and said inner grid at a higher unidirectional potential than said outer grid.

v A periodic wave generator comprising a vaccum tube having a cathode, an anode and a plurality of grids including inner, outer and auxiliary grids disposed between said cathode and anode and having relatively sharp upper and lower spacemurrent cut oil characteristics with respect to said outer grid, a loadresistor coupled between said inner grid and said cathode, means coupling said innerand outer grids comprising an impedance network having a phaseshift of less than $0", an impedance network effectively connected between said cathode and anode and having a time constant of a predetermined value greater than and functionally related to the period oi the wave to be generated, and means for applying operating potentials to the electrodes of said tube and for maintaining said auxiliary grid at a fixed unidirectional potential with respect to said cathode and said inner grid at a higher unidirectional potential than said outer grid, and means for applying a synchronizing signal to said auxiliary grid.

4. A periodic wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner and outer grids disposed between said cathode and anode and having relatively sharp upper andlower spacecurrent cutoff characteristics with respect to said outer grid, a load resistor coupled between said inner grid and said cathode, means coupling said grids comprising an impedance network havin a phase shift of less than means for applying operating potentials to the electrodes of said tube and for maintaining said inner grid at a higher unidirectional potential than said outer grid, and a resistance-reactance network effectively connected between'said anode and cathode and having' a time constant of a predetermined value greater than and functionally related to the frequency of the wave to be generated.

5. A periodic wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner and outer grids disposed between said cathode and anode and having relatively sharp upper and lower spacecurrent cutoff characteristicswith respect to said outer grid, a load resistor coupled between said inner grid and said cathode, means coupling said grids comprising an impedance network having a phase shift of less than 90, means for applying operating potentials to the electrodes of said tube and for maintaining said inner grid at a higher unidirectional potential than said outer grid, and a resistor and condenser having a time constant of a predetermined value greater than and functionally related to the period of the wave to be generated effectively connected between said anode and cathode tointegrate the anode current of said tube, thereby to develop an output voltage wave thereacross of saw-tooth form.

6. A periodic wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner and outer grids disposed between said cathode and anode and having relatively sharp upper and lower spacecurrent cutofi characteristics with respect to said outer grid, a load resistor coupled between said inner grid and said cathode, a condenser and resistance means effectively in parallel therewith for generated periodic waves, said condenser and resistance means coupling said grids and having a phase shift of less than 90, an impedance network effectively connected between said cathode and anodeand having a time constant of a predetermined value greater than and functionally related to the period of the wave to be generated, and means for applying operating potentials to the electrodes of said tube and for maintaining said inner grid at a higher unidirectional poten--v tial than said outer grid.

7. A, periodicv wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner, outer and auxiliary grids disposed between said cathode and anode'and having relatively sharp upper and lower space-current cutoil characteristics with respect to said outer grid, a load resistor connected between said inner grid and said cathode, a condenser and resistance means effectively in parallel therewith for generated periodic waves, said condenser and'resistance means coupling said inner and outer grids and having a phase shift of less than 90, an impedance network efiecgrid at a fixed unidirectional potential relative to said cathode and said inner grid at a higher unidirectional potential than said outer grid.

shift of less than 90, a resistance-reactance network effectively connected between said anode and cathode and having a time constant of a predetermined value greater than and functionally related to the period ofthe wave to be generated, and means for applying operating potentials tothe electrodes of said tube and for maintaining said auxiliary grid. at a fixed unidirectional potential relative to saidcathode andsaid inner grid at a higher unidirectional potential than said outer grid.

e 9. A periodic wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner, outer and auxiliary grids disposed between said cathode and anode and having relatively sharp upper and lower space-current cutofi characteristics with respect to said outer grid, aload resistor connected between said inner grid and said cathode, a con denser and resistor couplingsaid inner and outer grids and having a phase shift of less than 90, and means for applying operating potentials to the electrodes of said tube and for maintaining said auxiliary grid at a fixedunidirectional potential relative to said cathode and said inner grid at a higher unidirectional potential than said outer grid, and a resistance-reactance network eifectively connected between said anode and cathode and having a time constant of a predetermined value greater than and functionally related to the period of the wave to be generated. l0. Aperiodic wave generator comprising a vacuum tube having a cathode, an anode and a plurality of grids including inner, outerv and auxiliary grids disposed between said cathode and anode and having relatively sharp upper and lower space-current cutoff characteristics with respect to said outer grid, a load resistor connected between said inner grid and said cathode,

a condenser and resistance means effectively in parallel therewith for generated periodic waves,

said condenser and resistance means coupling said inner and outer grids and having a phase shift of less than 90, and means for applying operating potentials to the electrodes of said tube and for maintaining said auxiliary grid at a fixed unidirectional potential relative to said cathode and said inner grid at a higher unidirectional potential'than said outer grid, means for apply ing a synchronizing signal to said auxiliarygrid, and a parallel-connected resistor and condenser effectively conneotedbetween said anode and cathode and having a time constant of a predetermined valuegreater than and functionally related to the period of the Wave to be generated,

thereby to develop an output voltage Wave thereacross of saw-tooth form.

11. A, relaxation oscillator comprising a vacuum tube having a cathode, a, control grid, a screen grid, a suppressor grid and an anode, a circuit between said cathode and said anode consistingof, a resistor and a source of voltage in series,

said source being so poled as to apply a positive voltage to said anode, a circuit between said cathode and said screen grid consisting of a resistor and a source of potential in series, said second source being so poled as to apply a positive voltage to said screen grid, a circuit between said cathode and saidsuppressor grid consisting of a resistor and a third source of potential, said third source being so poled as to apply a negative potential to said suppressor grid, a condenser connected between said screen grid and said suppressor grid, and a grid resistor connectedbetween said control grid and said cathode, thevoltage applied to said screen grid being substantially greater than the voltage applied to said anode.

MADISON CAWEIN.

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