US2044137A - Crystal controlled oscillator circuits - Google Patents

Description

June 16, 1936. H. TUNICK 2,044,137

CRYSTAL CONTROLLED OSCILLATOR 'CIRCU ITS Filed Feb, 6, 1932 3 Sheets-Sheet 1 T0 gm UTILIZATION CIRCUIT INVENTOR 38 HARRY TUNICK' ATTORNEY June 16,1936. H T N CK 2,044,137

CRYSTAL CONTROLLED OSCILLATOR CIRCUITS Filed Feb. 6, 1952 I 3 Sheets-Sheet 2 INVENTiOR 1 HARRY TUNICK BY Hi un M/ ATTORNEY June 16, 1936. H u c 2,044,137

CRYSTAL CONTROLLED OSCILLATOR CIRCUITS Filed Feb. 6, 1932 3'Sheets $heet 3 HARRYVTUN CK BY M ATTORNEY INVENTOR Patented June 16, 1936 Y iJlTED STATES PATENT OFFICE CRYSTAL CONTROLLED OSCILLATOR CIRCUITS Harry Tunick, Rye, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application February 6, 1932, Serial No. 591,365

3 Claims. (01. 250-36) Crystal controlled vacuum tube oscillators as for preventing undesired capacitive coupling benow known operate at fairly constant frequency. tween certain electrodes of a crystal controlled Ordinarily, these oscillators are coupled to some oscillator; and, load circuit as a result of which variations in load Figure 9 illustrates a regenerative system under 5 react back upon the oscillator causing variations crystal control wherein inductive feed back is in frequency. Accordingly, the principal object of utilized. my present invention is to provide crystal con- Figs. 5, 5a, 6, and 8 form the basis of my cotrolled vacuum tube oscillator circuits wherein the pending divisional application Serial No. 694,229, crystal is loaded as lightly as possible and wherefiled October 19, 1933.

19 by variations in load cannot cause appreciable Turning to Figure 1 I connect an electrome- 10 reaction upon the crystal. To do so, I associate chanical vibrator or piezo-electric crystal resothe crystal with an electron discharge device nator 2 between the control grid or cold control such that certain electrodes within the device togrid 4 adjacent cathode 6 and the cathode, which gether with the crystal, form a complete oscillatmay be of the D. C. heated type, the indirectly l5 ing circuit. Then, I couple another electrode to heated type or of the raw A. C. heated type. In the oscillating system, this coupling taking place series with the cold electrode or screen grid 8 only through the electron stream within the elecadjacent another cold electrode or anode I0, I tron discharge device. This coupling is of such connect an impedance I2, here shown in the form a nature that despite variations in load, there is of a parallel tuned circuit comprising an inducvery little efiect or reaction upon the crystal tance coil and a variable condenser connected in 20 whereby the system oscillates at a frequency parallel. In series with the plate or anode I0 is widely independent of load variations and of a another impedance here also in the form of a constancy heretofore unobtainable with known parallel tuned circuit [4. Proper control grid bias systems. for grid 4 is maintained by action of grid leak Turning to the accompanying drawings, which resistor l6 shunting the capacity formed by crystal 25 are given solely by way of illustration and in no 2 and its electrodes. way are limitative of my present invention. Output energy is derived from the impedance Figures 1 and 2 illustrate forms of my invention or parallel tuned circuit M as illustrated; The wherein the piezo-electric crystal or electrooutput may be utilized in any transmitting or mechanical vibrator is connected between a conreceiving circuit wherein oscillations of constant 30 trol electrode or grid and the cathode or filament frequency are necessary. of a vacuum tube or electron discharge device, Suitable screen grid and plate potentials are and wherein another grid acts as a plate or anobtained as shown by suitable taps I8, 20 to poode, and. wherein still another electrode, preftential source 22 which, though illustrated as a erably the usual anode or plate, acts as an output group of batteries, may of course be any other 35 electrode coupled solely by virtue of the electron source such as a potentiometer.

stream within the tube to the oscillating system In operation, the screen grid 8 acts as a plate, formed by the control electrode cathode and and oscillations of constant frequency are genscreen grid and crystal; I erated in the oscillatory crystal controlled circuit Figure 3 is a wiring diagram of a modification comprising crystal 2, control grid 4, screen grid 8 40 somewhat similar to the arrangement shown in acting as. a plate, and tuned circuit !2. Ob- Figure 2 with the exception that the electrome- Viously, the current in this oscillatory circuit is chanical vibrator or piezo-electric crystal is conrelatively small whereby t e y a is Only nected between two grids of the electron disloaded very lightly. Moreover, inasmuch as the charge device oscillator; final output circuit, namely that to which the 45 Figure 4 is still another modification wherein plate or anode I0 is coupled, is only connected to the frequency controlling crystal is connected bethe oscillatory system formed by the crystal screen tween the screen grid or grid electrode adjacent grid and control grid by way of the electron the anode or plate and the cathode of an electron stream within the tube, it should be further clear discharge device; that variations in the ultimate load circuit have 50 Figures 5, 5a, 6 and 8 are modifications utilizing no appreciable reaction back upon the crystal as a plurality of electron discharge devices as part a result of which the system operates widely inof the primary oscillatory system; a dependent of load variations and at an extremely Figures 7 and 7a illustrate still other forms of constant frequency. my-present invention utilizing improved shielding That is, oscillations are'set up due to regenera- 55 tive action between the screen grid 8 and the control grid 4, capacitive feed back between the grids furnishing the correct exciting. energy for the piezo-electric crystal 2. However, should that interelement feed back be insufiicient it may be supplemented or augmented by the addition of a variable condenser 34 which, of course, being in shunt with the interelement capacity between the screen grid and control grid adds directly its value in capacity to that interelement capacity. Of course, if desired, other forms of inductive feed back may be used, as is evident to those skilled in the art.

Similar remarks are applicable to the arrangement illustrated in Figure 2, wherein the impedances l2, !4 of Figure 1 have been replaced by resistors 24, 26. If desired, simple choke coils or radio frequency currents may be used to replace the resistors, or, any combination of the impedances described may be used in the screen grid or plate circuits. For example, a choke coil may be placed in the screen grid circuit and a resistor in the plate circuit, or, a tuned circuit may be placed in the plate circuit and the resistor in a screen grid circuit, or, vice versa and so forth.

In Figure 2 also output energy is derived through blocking condenser 28 rather than from the inductive coupling illustrated in Figure l. The choke coil 30 and potential source 32, of course, replaces the biasing resistor 60 of Figure 1.

It is to be noted in connection with Figure 1 that any desired point may be grounded as a reference point. In Figure 1, as is customary, the filament or cathode has been shown grounded. However, that grounding point as well as the others illustrated may be removed and the circuit may be grounded if desired at either points X or Y.

In Figure 2 one point along the potential source has been illustrated grounded, and this grounding point is chosen, of course, to suit the conditions of operation.

Turning back to Figure 1 again, should it be desired to have a harmonic output, the circuit i4 is. tuned to some harmonic as a result of which energy of harmonic frequency will be built up by a frequency multiplication action in the output circuit I4.

Whereas in Figure 1 the crystal has been connected between the control grid and cathode, it is not necessary that the crystal or frequency controlling element or electromechanical vibrator be placed in that position alone. As shown in Figure 3 the crystal 2 is placed between the screen grid 8 and control grid 4 and in Figure 4 the crystal 2 is shown connected between the screen grid 8 and cathode 6.

In the arrangement shown in Figure 3, the output circuit I4 is tuned preferably to the fundamental of crystal 2 as is also the tunable circuit l2, which circuits may of course be replaced by any of the impedances or combination of impedances already adverted to. In addition, in the arrangement shown in Figure 3 the additional grid 36 may be employed to prevent undesired interelement feed back and thus insure operation under crystal control. This grid may be maintained preferably at some suitable positive potential and ground for radio frequency currents by action of by-passing condenser 38.

In the arrangement shown in Figure 4 the crystal 2 is placed between the screen grid 8 and ground by action of by-passing condenser 38 for oscillatory energy generated, namely, that at a frequency corresponding to the natural frequency of the crystal 2. Preferably, in the circuit of the control grid 4 there is placed a parallel tuned circuit 40 which may of course be replaced by any other impedance such as a resistance 42 shown in the plate circuit of the electron discharge device I.

The crystal 2 is shunted by an impedance here shown by a choke coil 44 although it may be an ordinary resistor unilaterally conductive for the application of suitable biasing potential or polarizing potential to the screen grid 8.

In general, the remarks given in connection with Figures 1 and 2 apply with equal force to the arrangements shown in Figures 3 and 4 as for example the substitution of one form of impedance for another, or, as regards the grounding of various points on the oscillatory system.

My present invention is not limited to single tube arrangements but is also susceptible to multitube oscillator schemes. Thus, in Figure 5 I have shown the crystal 2 connected between the control grids 4 of .a pair of electron discharge device oscillators l, 3. As in Figure 1 grid bias is accomplished by means of resistors I6 which, however, may be replaced by such biasing means is indicated in Figure 2. The oscillatory system of Figure 5 as in Figure 1, is formed by the screen grid 8, control grids 4, cathodes 6 and crystal 2.

The anodes H! are coupled through the electron streams within the tubes to the oscillatory system as a result of which there is concomitant to the system shown in Figure 5 all of the advantages ascribed to the systems shown in Figures l and 2. Also, in Figure 5 irnpedances, preferably in the form of tunable circuits l2, 14, are connected between the screen grids and anodes respectively. To prevent spurious oscillation generation due, for example, to the inherent capacity 1 between the crystal electrodes, neutralizing condensers 4B, 48 areprovided. These are suitably adjusted so that without the crystal in circuit the system fails to oscillate. However, it will be found that when the crystal is placed into circuit the circuit will go into oscillation at a frequency corresponding to that of a natural frequency of the crystal.

Circuit I4 is tuned to the fundamental frequency of the crystal, or, should odd harmonics be desired it should be tuned to some odd harmonic of the crystal 2 because of its pushpull relation with respect to the anodes of the devices. Should it be desired to obtain even harmonics the anodes ID as shown in Figure 5a should be connected in parallel and the tunable circuit 14 connected in series with the parallel connection, the circuit l4 being tuned to some even harmonic. Thus, as indicated, either odd harmonic or even harmonic energy may be built up in the output circuit l4 which, of course, is only coupled by virtue of the electron streams within the tubes to the crystal oscillating system.

As shown in Figure 6 the tuned circuit l2 and crystal 2 may be reversed in position, the circuit I2 being preferably tuned to a natural oscillating frequency. The circuit l2 as shown in Figure 6, may of course be replaced by a resistance or inductance. The crystal 2 is shunted in the arrangement shown in Figure 6 by a resistor 50 allowing polarizing potentials to pass unidirectionally to the screen grids of the electron discharge devices I, 3. By way of example, the output circuit I4 is coupled inductively to the input of a frequency multiplier modulator circuit diagrammaticallyindicated at 52 supplied with modulating potentials from a suitable source 54. Modulated output from the arrangement 52 is fed to some power amplifying device indicated at 56 and in turn transmitted either by wire line or preferably through the air by electromagnetic waves by the action of antenna 58.

Another pushpull modification is illustrated in Figure 8 wherein the crystal 2 is provided with two pairs of electrodes 68, 62. These electrodes are connected to the control grids 4 and screen grids 8, as indicated, of electron discharge devices I, 3. To prevent capacitive coupling between the leads to the crystal electrodes, shielding 64 grounded at point I8 or several points is provided. Polarizing potential is applied to the screen grids through shunting resistor I4, and, biasing potential is applied to the control grids to the shunting choke 16. In this arrangement, the screen grids act as plates in the crystal controlled oscillating system, and the plates or anodes I8 of the electron discharge devices I, 3 are coupled to the frequency control oscillating system formed by the crystal, screen grids, cathodes and control grids only by virtue of the electron streams within the tubes. Oscillations are set up by virtue of the fact that variations in screen grid voltages at a natural frequency of the crystal are fed to the crystal 2 which in turn generates voltages which are applied to the electrodes 62 in such phase that the electron streams are varied to cause continuous oscillation generation at a very constant frequency.

The shielding of the electrodes of the crystal is highly desirable and essential, and, may be applied to other forms of oscillator not within the general broad scope of this invention. Such an arrangement is shown in Figure 7a wherein the crystal 2 is provided with three electrodes 88, which is grounded, 82 connected to the plate I8 of electron discharge device I, and 84 connected to the control grid 4 of electron discharge device I. Feed back from the plate through electrode 82 causes oscillation of the crystal 2 which in turn, places controlling voltages upon the control electrode 4 through crystal electrode 84. It is clear, therefore, that it is highly desirable that there be no capacity coupling between the electrodes 82, 84, and to prevent such coupling I provide in a fashion quite similar to that shown in Figure 8, grounded shielding 64 grounded at point 18. Further, to prevent interelectrode feed back, a screen grid 8' is here provided which, of course, does not function in the same manner as that given in the other arrangements of my invention heretofore described herein. Here, the screen grid 8' acts merely as a capacity element to prevent feed back from the plate I 8 to control grid 4.

Also, as shown in Figure 7a, the screen grid 8' is grounded to the shielding 85 through the bypassing condenser 83. That is to say, the shielding 85 is connected to the ground connection 89 for the lower electrode 88. Condenser 8! serves to prevent the application of unidirectional plate potential from electrode 82 while allowing free feedback of radio frequency potentials from the plate to the electrode 82.

As applied to an arrangement involving the general principles of my present invention, the crystal and its associated shielded electrode system of Figure 7a. is given in Figure '7 proper. Here the crystal 2 with its electrodes 88, 82, 84 are connected between the screen grid 8, control grid 4, and cathode 6 of electron discharge device I. This electron discharge device has in addition another grid or space charge grid such as is also illustrated in the arrangement shown in Figure 6, which is maintained by the action of potential source 86 at a small positive potential for providing a relatively uniform electron emitting surface. The action of the oscillating system of Figure '7 comprising the screen grid 8, control grid 4 and space charge grid 5, is similar to that'given in Figure 7a. To prevent interelectrode feed back between screen grid 8 and control grid 4, a screening grid 8' is provided grounded for radio frequency currents by the action of by-passing condenser 88 and polarized from the plate or anode source by a suitable connection thereto including preferably a resistor 98 of such a value to cause a desired voltage difference between the grid 8' and the anode I8.

While referring to Figure 1, reference was made to the fact that inductive feed back might be used rather than capacitive feed back for required regeneration for sustained oscillations. Such an inductive feed back system is illustrated in Figure 9. Within electron discharge device I I have illustrated an anode or plate I88, a cold electrode or screen grid adjacent the anode I82 and a control grid I84 adjacent the cathode I86. The screen grid I82, control grid I84 and cathode I86 are associated with piezo-electric crystal 2 so as to form a complete oscillatory circuit, feed back to the control grid or input circuit taking place by way of transformer I88 having as indicated shielded primary and secondary coils to prevent capacity feed back therebetween. By virtue of the inductive coupling between the primary and secondary of transformer I88, the secondary of which is shown tuned by means of a variable condenser I I8, it being understood that the primary may equally as well be tuned by a similar condenser if desired, or, if desired the secondary may be left untuned and the primary tuned, required regenerative feed back is established. To compensate for the interelectrode capacity of the electrodes of the crystal 2, a neutralizing condenser H2 is provided, the input circuit comprising the secondary of transformer I88 being connected at some intermediate point such as I I '4 to the cathode I86. For grid bias a grid leak resistor H6 is provided, and, to further prevent generation of spurious oscillations or parasitic oscillations, a low impedance in the form of a condenser I I8 is shown connected in shunt with the grid I84 and cathode I86.

The anode or output circuit I28 is shown in the form of a parallel tuned circuit although it may be replaced by a simple inductance coil or a resistor if desired. The output circuit, of course, is only coupled to the oscillating circuit by virtue of the electron stream within the tube I. As before, the output circuit I28 is tuned to a fundamental, although if desired it may be tuned to a harmonic of a natural frequency of the crystal 2.

Screen grid potential is obtained from the anode source through resistor I22. It is not necessary that the coupling between the primary and secondary be coupled regeneratively, for, it will be found that even with reversed coupling suitable tuning of the parallel tuned input circuit will give the correct condition for voltages applied to the control grid I84, for desired oscillation generation under crystal control.

To still further reduce reaction of the load circuit upon the oscillation circuit, input to the load circuit may be to some low impedance point. Then variations in the load will produce only very small fluctuations, or feed back, or reaction, due to the fact that because of the chosen tapping points the oscillator faces a very low impedance. Thus, in Figure 1, for this purpose, the tapping point W should be moved along acoil to some low impedance point such as Q or, in Figure 3, tapping point W should be moved to some point along the coil of the tunable circuit M as Q.

Similar remarks are applicable to the other figures such as Figure '7. In the arrangement such as shown in Figure 6, both tapping points W from each of the plates are moved to sym metrical low impedance points Q on the output circuit M, the points Q being symmetrical about the voltage nodal point.

Various modifications of my present invention may of course be made as will be apparent from even a casual reading of the specification. Accordingly, I do not intend to be limited by the exact modifications illustrated and described, but my invention should be given the full scope indicated by the breadth of the appended claims.

Having thus described my invention, what I claim is:

1. oscillatory apparatus comprising an electron discharge device having an anode, a cathode, a control grid and a screen grid, a piezo-electric crystal, 'an electrode for said crystal connected to said cathode, an electrode for said crystal connected to said control grid, and another electrode for said crystal connected to said screen grid, means for preventing capacitive coupling between the electrodes for said crystal and between the connections for said crystal and between said screen grid and control grid, said system as so far described setting up oscillations corresponding in frequency to a natural frequency of said piezo-electric crystal, and means comprising an anode of said electron discharge device for deriving oscilatory energy from said system, said anode being coupled to said system only through said electron stream within said electron discharge device.

2. An oscillation generator comprising an electron discharge device having an anode, a cathode, a control grid, a screen grid and a grid inter- -mediate said control grid and screen grid, 2. piezo-electric crystal, an electrode for said crystal connected to said cathode, an electrode for said crystal connected to said control grid, another electrode for said crystal connected to said screen grid, means including an alternating current path from said intermediate grid to ground for preventing capacitive coupling between said control electrode and screen grid, means for grounding said cathode, means for preventing capacitive coupling between the electrodes for said piezo-electric crystal connected to said control grid and said screen grid, means for impressing upon said control grid and cathode such relative potentials that oscillations corresponding to the natural frequency of said piezoelectric crystal are set up, a parallel tuned circuit connected between said anode and cathode, and means for tuning said circuit to a frequency higher than and harmonically related to the frequency of oscillation of said crystal.

3. An oscillation generator comprising an electron tube having a cathode, a space charge grid, a control grid, a shielding grid, a screen grid, and an anode, said grids being arranged between the cathode and the anode in the order named, a piezo-electric device having at least three electrodes of which one electrode is in circuit with the cathode of said tube and two other electrodes of the plaza-electric device are respectively in circuit with said control grid and said screen grid, an output circuit including said anode, and shielding means interposed throughout between the circuit connections from the electrodes of said piezo-electric device to said tube electrodes.

HARRY TUNICK.

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