US2051936A - Oscillation generator - Google Patents

Description

5, 1936. A. M. BRAATEN 2,051,936

OSCILLATION GENERATOR.

Filed May :5, 1935 INVENTOR ARTHUR M. BRAATEN ATTORNEY wherein,

.potential to the tube oscillator; and,

UNITED STATES PATENT OFFICE OSCILLATION GENERATOR Arthur M. Braaten, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 3, 1933, Serial No. 669,269

5 Claims.

This invention relates to the vacuum tube oscillator art and deals more specifically with a piezo-electric controlled, negative resistance oscillator.

Heretofore it has been the practice to use a three or four-element vacuum tube operating on the dynatron principle to supply oscillations of fairly constant stability. The output of such an oscillator, having a high harmonic content, has been used to provide a series of harmonic frequencies in frequency meters, or wherever such an output was desired. However, one disadvantage which limits the usefulness of such oscillators is that the frequency of oscillation depends to a great extent upon the supply voltages and the output loading. To improve the frequency stability of such systems and to provide a better means of obtaining harmonic outputs of the desired order arevprincipal objects of my present invention. A further object of my invention is to provide a greater degree of. frequency stability .for an oscillator operating on the dynatron principle, and to provide an efficient and more satisfactory method for making use of the output of such an oscillator. g

A further objectofmy present invention is to provide a dynatron oscillator circuit together with an arrangement or circuit in which power output may be derived therefrom without effecting the frequency of operation of the dynatron oscillator.

My invention is described in greater detail in connection with the accompanying drawing Figure 1 illustrates a preferred form of my invention wherein a piezo-electric crystal is utilizedto control the frequency of a dynatron oscillator and whereinthe oscillator is rendered substantially immune to load reaction.

Figure 2 is a modification of the arrangement .shown in Figure 1;

Figures 3 and 4. are further modifications of f the arrangement shown in Figure 1 wherein different circuits are provided for supplying plate Figures 5 and 6 are still further alternative arrangements for reducing still further the effects of load reaction upon my improved oscillation generator.

Referring to Figure 1, V.T. is a six-element vacuum tube of the heater type. The cathode 2 and one side of the heater 4 are connected to ground. The inner, or control, grid 6 is connected to ground through a fixed resistor R. Across R is connected the piezo-electric element Q. C. The middle, or screen grid 8 is connected to a source of positive potential, with respect to the cathode 2. The anode, or plate It! is connected to a potential positive with respect to the screen grid 8. In the plate circuit is connected 5 a tuning circuit L2C2., Connected between the outer, or suppressor, grid I2 and at a potential positive with respect to the cathode and negative with respect to the screen grid is a tuning circuit L1C1. Variable condenser C is connected be- 10 tweenvthe suppressor and control grids. The heater is energized by the usual battery l4. 7

The operation of, the system of Figure 1 is as follows:

Suppose the elements Q. 0., 0, L101 and L2C2 to be omitted from the circuit. With certain positive fixed potentials on the screen grid and the plate, if the potential on the suppressor grid is varied, a region will be found wherein the device acts as a true negative resistance. That is, an '20 appliedpotential will set up a current in the Wrong direction. This is due to secondary emission from the suppressor grid. A device with such a negative resistance characteristic may be made to produce sustained oscillations. If the tuned element L1C1 be adjusted so that its effective resistance is equal tothe negative resistance of the suppressor grid circuit, the total resistance of that circuit will be zero, and the device will produce sustained oscillations. In certain types 30 of tubes the negative resistance may be of such a high value that it is impossible tomake the .device. oscillate. In such a case, the addition of a capacity C of suitable value between the control grid and the suppressor grid will have the 35 effect of lowering the negative resistance, so that the device will oscillate. If a crystal oscillator is connected between control grid and cathode of this device and the element L1C1 tuned to the natural resonant frequency of the crystal, the 40 frequency of oscillation of the system will be maintained at the frequency at which the crystal is oscillating. Small changes in'the values of L1 or C1, or other circuit constants, *will have negligible effect on the frequency of the system, 45 and a degree of stability against voltage supply variations will be obtained which is unattainable without the crystal control element. If now the element LzC'z is connected inthe plate circuitof the device, this output circuit may be tuned to the fundamental oscillation frequency or any of its harmonics. Tuning of this circuit will have a minimum effecton the oscillator frequency. It will thus be seen that in this device there is incorporated an oscillator of substantially constant frequency and. a means for readily obtaining any desired harmonic of the fundamental in the output, without the use of additional frequency multiplying stages.

Moreover, in connection with the arrangement shown in Figure 1, if the output is taken from the plate circuit CzLz, load reaction will be substantially minimized and reduced to a negligible value thereby rendering the frequency of operation substantially independent thereof.

The circuit C1L1 is preferably tuned to a fundamental of the crystal Q. C. and the circuit C2L2 may be tuned to the same frequency or to a harmonic thereof. On the other hand the circuit C1L1 may be tuned to a harmonic of the crystal and circuit CzLz to the same harmonic, to a different harmonic, to a sub-harmonic, or to the fundamental.

Figure 2 illustrates a system quite similar to the one shown in connection with Figure l but in this case the condenser C of Figure 1 is omitted since it is assumed that the vacuum tube V. T. is of sufficiently low negative resistance to allow of oscillation generation. Also, in connection with Figure 2 by-passing condensers B. C. are provided to ground the lower ends of the tuned circuits CILI and C2112.

The arrangement shown in Figure 3 is similar to that shown in Figure 1 with the exception that the circuit C2L2 is blocked off from the direct current plate source P. S. by means of a blocking condenser 20. Plate potential is fed to the vacuum tube V. T. through the choke coil 22. In this manner a direct current component is kept from the tuned circuit CzLz of the vacuum tube V. T.

Figure 4 is similar to the arrangement shown in Figure 2 with the exception that the plate potential is fed through a resistor 22 and as in connection with Figure 3 the plate circuit CzLz is rendered immune from D. C. current flow by means of a blocking condenser 20.

The output circuit may be further isolated from the oscillating circuit as shown in Figure 5. Here the tuned circuit C1L1 is connected between the heated element 3 of the cathode and ground. Moreover, a suppressor grid I2 is grounded by means of a by-passing condenser 30 which, at very high frequencies may be chosen of a value to series resonate with the lead to the suppressor grid I0 so as to effectively maintain the suppressor at ground potential. Because of the circuit C1L1', the cathode 3 no longer operates at ground potential, but fluctuates at radio frequency potential. However, the suppressor grid I 2 is maintained at ground radio frequency potential by the action of by-passing condenser 30. This arrangement is advantageous since it more effectively isolates the oscillating circuit formed of the grids l2, 8, 6, cathode 3 and quartz crystal from the output circuit C2L2 and hence'rendering the oscillating circuit or frequency controlling circuit less liable to frequency'shift from changes in load reaction. The output energy, of course, is obtained by virtue of the electron stream within the tube impinging upon the anode l0 and in turn exciting the parallel tuned circuit C2L2 which may be tuned to the same frequency as the crystal or to some harmonic thereof. -The circuit ClLl may also be tuned to the same frequency as that of the crystal or to some harmonic thereof.

In the arrangement shown in Figure 6 a tuned circuit L303 is connected between the intermediate grid or screen grid 8 and the cathode 3, the circuit being completed by means of a radio frequency by-passing condenser 40. The intermediate grid 8 besides causing secondary emission from the suppressor grid I2 and hence dynatron action, acts as a plate for an oscillating system operating through regenerative action. This regenerative oscillating system is composed of the intermediate grid 8, the control grid 6 and the cathode 3. Condenser C is added only when there is insufficient capacity coupling between the grid 8 and control grid 6 to produce necessary feed back for sustained oscillation generation. Circuit C3L3 may be tuned to the fundamental of the quartz crystal or to some harmonic frequency thereof. Similarly circuit L1C1 may be tuned to the fundamental or to the same or different harmonic and likewise with the circuit L2C2. Output energy at the same or different frequencies may be taken as indicated from any one or more of the 'circuitsCiL1,-C3L3, or-CzLz simultaneously, or if desired only one of the circuits may be used'to supply oscillatory energy.

Incidentally, it is to be pointed out that while oscillations are generated in L101 by virtue of dynatron action which involves secondary emission from suppressor grid l2, oscillations are generated in circuit LaCs by virtue of regenerative action or capacity feed back in the case shown. In the circuit CzLz oscillations are produced by virtue'of the coupling of that circuit to the other oscillating circuits C1L1 and 03L: through the medium of the electron stream within the vacuum tube V. T.

Considerable power may be obtained from the system contained in Figure 6 and is capable of functioning as a master oscillator of extremely high frequency'stability, as a buffer amplifier, and as a plurality of frequency multiplier stages, all at the same time.

Various minor changes may be made in all of the circuits which may be used for controlling the frequency of a transmitter for wave measurement purposes, or for example, for use in a superheterodyne type of radio receiver. Also, it should be understood that such circuits as L303 may be replaced by an inductance whose natural frequency is higher than that of a crystal, if it is desired to operate that portion of the circuit at the fundamental frequency of the crystal and the output energy may be taken from any one or more of the various circuits in any of the figures and used for different purposes if found desirable. Moreover, it will be readily apparentthat in place of the, six element heater type of tube,

' a non-heater type of tube may be employed in any one of the systems. Also, the present invention is not to be limited to any specific arrangement of supply voltages but optimum voltages will be chosen with a view to produce a negative resistance characteristic. The crystal may be of quartz or of any material exhibiting piezo-electric effects, or, may be replaced by an electrically tuned circuit, or by any magnetic mechanical resonator as will be apparent to those skilled in the art. Instead of a common ground connection, any common conductor such as a large piece of shielding may be used.

Having thus described my invention, what I claim is:

1. An oscillation generator comprising a vacuum tube having a cathode, a control grid, 2. screen grid, a suppressor grid and an anode, a high frequency frequency controlling circuitincluding a piezo-electric crystal connected between the control grid and cathode, a high frequency circuit connected between the suppressor grid and cathode, means for polarizing said suppressor and screen grids with unidirectional potential such that said vacuum tube has a negative resistance characteristic and continuous oscillations are set up in said circuit between said suppressor grid and said cathode, and a high frequency circuit connected between said anode and said cathode, said high frequency circuit being adapted to derive its excitation from the electron coupling action between said anode and said oscillatory system formed of said suppressor, screen and control grids, and cathode.

2. A vacuum tube oscillation generator comprising an electron discharge device having an anode, a cathode, a control grid, a screen grid, and a suppressor grid, a hi h frequency circuit connected between said control grid and cathode, a high frequency circuit connected between the screen grid and cathode, said control grid and screen grid being subjected to potentials such that oscillations are set up by virtue of regenerative coupling between said screen grid and control grid, 2, high frequency circuit connected between said suppressor grid and said cathode, means for polarizing said suppressor grid with respect to said screen grid and cathode as to cause oscillations to be set up in said circuit between said suppressor grid and cathode by virtue of dynatron action, and, a high frequency circuit connected between said anode and cathode, said anode being polarized such that oscillations are set up in said last mentioned.

circuit by virtue of the coupling of said anode to said other oscillating circuits by means of the electron stream within the vacuum tube.

3. Apparatus as claimed in the preceding claim wherein one of said high frequency circuits is in the form of a p-iezo-electric crystal.

4. An oscillation generator comprising a tube having an anode, a cathode, a first grid, 2. second grid, and a third grid, a frequency controlling circuit connected between the first grid and cathode, a high frequency circuit connected between the third grid and cathode, means for polarizing said third grid to a direct current potential with respect to said grid, means for polarizing said second grid to a positive potential with respect to said third grid and with respect to said cathode, whereby oscillations are set up in the circuit between said third grid and cathode by virtue of negative resistance action, means for polarizing said anode to a direct current potential with respect to said cathode, a high frequency circuit connected between said anode and cathode, and means for deriving oscillations from said last mentioned high frequency circuit, said oscillations being controlled in frequency by virtue of said frequency controlling circuit connected between said first grid and cathode;

5. Apparatus as claimed in claim 4 characterized by the fact that said frequency controlling circuit includes a piezo-electricorystal and being further characterized by the fact that at least one of said high frequency circuits is tuned.

ARTHUR M. BRAATEN.

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