US2243524A - Oscillation generator - Google Patents

Description

May 27, 1941. H. B. DEAL ET AL 2,243,524

OSCILLATION GENERATOR Filed Oct. 29, 1938 IIKK I Ill vvvu vvvv INVENTORS HARMUN B. DEAL AND BY ARTWSEELEY M'MJ/L/ ATTORNEY.

Patented May 27, 194i err sass OSCILLATION GENERATOR Delaware Application Q'ctober 29, 1938, Serial No. 237,634

11 Claims.

This invention relates broadly to electron tube oscillator circuits, and particularly to an oscillator for producing oscillations of substantially constant frequency.

The primary object of the present invention is to provide an oscillator circuit which substantially eliminates the effect of variations inthe anode voltage supply upon the frequency of oscillations, due to change in apparent input capacity of the oscillator tube. More specifically,

frequency of the oscillator caused by variations in the anode voltage supply. In the preferred embodiments of the invention this space discharge path takes the form of another electron tube disposed in parallel relation to at least a portion of the tuned oscillatory circuit.

The theory underlying the present invention will now be given: It appears that the largest single factor affecting the frequency of the oscillator as, its operating potentials are varied is the chan e in input capacity with anode current. The total apparent input capacity of an electron tube is usually composed of three factors. First, the static capacity between the metallic electrode elements. This type of capacity is due to the physical geometry of the tube and is not affected by operating potentials. Secondly, the capacity due to the Miller effect. This second type of capacity is due to reactive currents flowing between the grid and a positive electrode element whose potential is varying at the same frequency-but 180 out of phase with that of the grid. Third, the so-called trans-it time input capacity which is due to the instantaneous unbalance between approaching and departing electrons in the vicinity of the grid. The present invention is believed to be concerned mainly with this last type of input capacity, i. e., that which is due to finite electron transit time, although it is'to' be distinctly understood that the inventionisnot to be limited by any theory advanced for the results achieved.

If the input capacity of a typical tube is measured between grid and all other elements Icy-passed together, it will be found that the input capacity depends to some extent upon the amount and the electron velocity of the space current passing through the grid. As an illustration, the input capacity of an R. C. A. 605 vacuum tube with 200 volts on its anode will increase as the grid potential is decreased from cut-off toward zero value. This increase is very nearly proportional to the anode current up to 10 m. a. (8.5 volts bias) at which point it amounts to about 1.0 ,u f. As the grid bias is decreased further, the anode current continues to rise, but the capacity curve levels 01f, showing a capacity saturation characteristic. It also appears that as the grid is made positive, the input capacity may actually decrease, but this is extremely diflicult to measure in the presence of grid conductance.

Ordinarily, it would seem that an increase in plate voltage of an oscillator would tend to raise the input capacity and thus decrease the frequency. However, we have found the reverse to be true due to the saturation characteristic of the capacity curve. A tube with grid lea k bias and normal plate potentials will operate same but the tube operates with a greater portion of its cycle in region of less capacity. It will be understood, of course, that it is the integrated value over the cycle which determines the effect on frequency.

According to the present invention, any tendency on the part of the oscillator tube to have its input capacity change in one sense with change in anode voltage is off-set or compensated by another electron tube whose input capacity tends to change in an opposite sense with the same change in anode voltage. This compensation is accomplished by paralleling the inputcircuit of the oscillator electron tube Whose frequency increasesdue to a decrease in input capacity because of an increase in anode voltage, with a grid circuit of another vacuum tube having an opposite effect on input capacity with change in anode voltage.

The following is a detailed description of the invention in conjunction with drawing, wherein:

Fig. 1 and Fig. 2 show by way of illustration only, two embodiments of the invention as applied to a Hartley type of oscillator circuit;

Fig. 3 shows an embodiment of the invention as applied to an oscillator circuit having an inductively coupled feed-back circuit; and

Fig. 4 shows the invention as applied to a multigrid vacuum tube oscillator.

Referring to Fig. 1, there is shown an electron tube oscillator I for the generation of high frequency oscillations. The grid and anode electrodes of tube I are coupled to opposite terminals of a tuned oscillatory circuit comprising an inductor 2 and a parallel connected variable capacitor 3, while the cathode K is connected to an intermediate point on the inductor 2. A suitable grid-leak and condenser combination 4 supplies bias to the grid of the tube I, while a source of anode potential +13 supplies a positive polarizing potential to the anode of tube I through a radio frequency choke coil 5.

In order to eliminate or reduce the effect of variations in the anode voltage supply, +B, upon the frequency of oscillations, there is provided a compensating tube 6 whose grid-cathode or input capacity is disposed in parallel to a portion of the oscillatory circuit 2, 3; more specifically, across the low potential part of inductor 2 and in parallel relation to the anode-cathode capacity of the oscillator tube I. The anode of electron tube 6 is connected to the positive terminal of the source of anode supply +B, as shown, both anodes being by-passed to ground from a radio frequency standpoint. The negative bias on the grid of compensating tube 6 is adjusted by means of the cathode tap I on potentiometer 8.

The input capacity (i. e., grid-cathode capacity) of the oscillator tube I, it should be noted, is across the high potential part of inductor 2 (lower half of inductor 2, as shown in the drawing), while the input capacity of compensating tube 6 is across the low potential part of coil 2 (upper half of inductor 2 as shown in the drawing). Consequently, as the input capacity of one electron tube increases, the input capacity of the other electron tube will decrease, and the net result of the change in capacity across the entire inductor 2 will be less than that caused by the oscillator tube alone.

The adjustment of the negative bias on the grid of the compensating tube 6 by means of tap I enables the change of input capacity of the oscillator tube I with change in anode voltage to be counterbalanced by an opposite change in the input capacity of tube 6. By changing the degree of negative bias on the grid of tube 6, we can thus overcompensate or undercompensate for the changing input capacity of the oscillator tube,

provided that the total variation of input capacity of the compensating tube 6 can be made greater or less, respectively, than the changing input capacity of the oscillator tube.

In Fig. 2 the input capacity of the compensating tube 6 is connected across the entire oscillatory circuit 2, 3 instead of across only a portion of the oscillatory circuit as shown in Fig. 1. Consequently, in Fig. 2, there is required less of a change in the input capacity of the compensating tube 6 to off-set or counterbalance the change in the input capacity of the oscillator tube I. The input capacity of compensating tube 6 is here shown connected between the anode and grid of oscillator tube I.

In Fig. 3 there is shown another type of oscillator circuit which employs feed-back from. the anode of tube I. In this case the feed-back is produced by the inductive coupling between coils 2 and 9. In this figure it will be seen that the electrodes of compensating tube 6 are connected to corresponding electrodes of oscillator tube I.-

Fig. 4 shows an arrangement, by way of example, wherein the electrode structure of a multiple grid oscillator tube is employed with the electrode structure of a compensating tube for stabilizing the frequency of oscillations. In this circuit the electrode structure of the oscillator and the electrode structure of the compensating arrangement are located within the same envelope I I. The oscillator portion of the circuit includes a cathode K, first, second and third grids, G1, G2 and G3, respectively, and an anode A, While the compensating portion of the circuit includes cathode K, a grid G4 and an anode A1. We thus have a five electrode tube oscillator and a triode compensating tube. The oscillator is of the inductive feed-back, tuned anode type and includes an inductance 2', a parallel variable capacitor 3, a feed-back coil 9' coupled to inductance 2', and a grid leak and condenser combination 4. The grid G4 of the compensating portion of the tube is arranged in parallel to the oscillator circuit through a large coupling capacitor I2. A resistor I0 supplies direct current bias to the grid G4 without shorting the input capacity of the compensating triode portion.

What is claimed is:

1. The combination with an oscillating electron tube circuit including an electron tube containing a cathode, an anode, and an intermediate control grid, an oscillatory circuit coupled to said cathode, anode and grid, and a source of potential for maintaining said anode positive relative to said cathode, the frequency of said electron tube circuit tending to change with change in anode potential, of an electron space path located outside the space contained between said cathode and anode and coupled across at least a portion of said oscillatory circuit, said electron space path including an anode and a grid, a connection from said last anode to the same terminal of said source of potential to which said first anode is connected, and means for applying to the grid in said last space path a constant potential of such value that the frequency change tendency in said electron tube caused bya variation of said anode potential is effectively opposed by a change in the apparent capacity of said space path caused solely by said same variation in anode potential.

2. In combination, an electron discharge device oscillator having grid, anode and cathode electrodes, an oscillatory circuit coupled to said electrodes, another, electron discharge device having an anode, a grid and a cathode, a common source of anode potential for both of said devices, connections between corresponding grid and cathode electrodes of both of said electron discharge devices, means for biasing said devices sufficiently differently so that the. input capacity of one device varies with anode potential oppositely in sense compared to the variation in input capacity of the other device, due solely to the same change in anode potential, including means for applying a constant bias to the grid of said second device of such value as to control the magnitude of the change in input capacity of said second device.

3. In combination, a vacuum tube oscillator comprising a grid, an anode, and a cathode, a parallel tuned circuit of inductance and capacity having terminals connected across said grid and anode, a connection from said cathode to a point on said tuned circuit intermediate said terminals, and a non-oscillating vacuum tube also having grid, anode and cathode electrodes, a connection between the grids of saidtwo vacuum tubes, is

" connection from the cathode of said non-oscillating vacuum tube to the anode of said oscillator tube, a source of common anode potential for both said anodes, means for biasing said vacuum tubes sumciently differently so that the input capacity of one tube varies with anode potential oppositely in sense compared to the variation in input capacity of the other tube due solely to the same change in anode potential, said means including means for applying a constant and controllable bias to the grid of said non-oscillating tube which is independent of the frequency of said oscillator and of such value that the magnitude of the net change in capacity across said tuned circuit is less than that which would be produced by the change in input capacity of the oscillator tube alone with change in anode potential.

4. In combination, a vacuum tube oscillator comprising a grid, an anode and a cathode, a parallel tuned circuit of inductance and capacity having terminals connected across said grid and anode, a connection from said cathode to a point on said tuned circuit intermediate the said terminals, and a non-oscillating vacuum tube also having grid, anode and cathode electrodes, a connection between the grids of said two vacuum tubes, a connection from the cathode of said non-oscillating vacuum tube to the anode of said oscillator tube, a source of common anode potential for both said anodes, means for biasing said vacuum tubes sumciently differently so that the input capacity of one tube varies with anode potential oppositely in sense compared to the variation in input capacity in the other tube, due solely to the same change in anode potential, including means for applying a constant bias to the grid of said non-oscillating tube which is independent of the frequency of said oscillator and of such value as to provide a change in input capacity across the grid and cathode of said nonoscillating tube of such a magnitude as to substantially compensate for any change in input capacity across the grid and cathode of the oscillator tube with a change in anode potential.

5. In combination, a vacuum tube oscillator comprising a grid, an anode and a cathode, a parallel tuned circuit of inductance and capacity having terminals connected across said grid and anode, a connection from said cathode to a point on said tuned circuit intermediate the said terminals, and a non-oscillating vacuum tube also having grid, anode and cathode electrodes, a connection from the grid of said non-oscillating tube to the cathode of said oscillator tube, a connection from the cathode of said non-oscillating tube to the anode of said oscillator tube, a source of common anode potential for both said anodes, means for biasing said vacuum tubes sufliciently difierently so that the input capacity of one tube varies with anode potential oppositely in sense compared to the variation in input capacity to the other tube, due solely to the same change in anode potential, including means for applying a bias to the grid of said non-oscillating tube which is independent of the frequency of said oscillator and of such value as to provide a change in input capacity across the grid and cathode of said non-oscillating tube of such magnitude as to substantially compensate for any change in input capacity across the grid and cathode of the oscillator tube with a change in anode potential.

6. The combination with an electron discharge device oscillator having grid, anode and cathode electrodes, a tuned oscillatory circuit coupled between said grid and cathode, a feed-back circuit inductively coupled to said tuned circuit and connected between said anode and cathode, and a non-oscillating vacuum tube having its grid, anode and cathode electrodes coupled to the corresponding electrodes of said oscillator device, there being a common source of anode potential for both anodes, means for biasing said oscillator and non-oscillating vacuum tube sufiicieiitly difierently so that the input capacity of said tubevaries with anode potential oppositely in sense compared to the variation in input capacity of said oscillator, due solely to the same change anode potential, including means for biasing the grid of said tube independently of the frequency of said oscillator and of such value as to control the magnitude of the change in input capacity of said non-oscillating tube to compensate for the change in input capacity of the oscillator with a change in anode potential.

7. In an oscillating electron tube circuit, the combination with an electron discharge device oscillator including a cathode, first, second and third grids, and an anode in the order named; an oscillatory circuit coupled between said anode and cathode; a feed-back circuit coupled between said first grid and cathode; a connection between said cathode and third grid; and means for maintaining said anode at a positive potential and said second grid at a less positive potential relative to said cathode; whereby oscillations are produced by said device whose frequency tends to change with change in anode potential; of an electron space path having therein anode and grid electrodes coupled to opposite terminals of said oscillatory circuit; and means for applying to the electrodes in said last space path such potentials that the frequency change tendency in said oscillator caused by a variation of said anode potential is opposed by a change in input capacity of said electron space path caused by said same variation in anode potential.

8. In combination, a vacuum tube oscillator, and another vacuum tube, each having a grid, an anode, and a cathode; an oscillatory circuit for said oscillator coupled to the electrodes thereof; a common source of anode potential for the anodes of both of said tubes; means for connecting the input capacity of said other vacuum tube across at least a portion of said oscillatory circuit; and means for biasing the grids of said vacuum tubes sufficiently differently so that the input capacity of said oscillator varies oppositely in sense compared to the variation in input of said resonant circuit, and means for biasing said devices sufiiciently diiferently so that the input capacity of one device varies with anode potential oppositely in sense compared to the variation in input capacity of the other device due solely to the same change in anode potential.

10. A high frequency oscillator system comprising a pair of electrode structures across each of which electrons flow, a common source of potential for an electrode in one of said structures and a corresponding electrode of the other structure, a resonant circuit coupled to the electrodes of one of said structures, means connecting the other structure in parallel to at least a portion of said resonant circuit, and biasing means to adjust the transit time of the electrons in one of said structures to produce variations of input capacity with variations in the potential of said source which are opposite to the variations of effective input capacity of the other structure due solely to the same variations in potential of said common source.

11. An oscillator system having a. frequency determining circuit, a pair of electrode structures, each comprising an anode, a cathode and a grid,

connections between corresponding electrodes of said structures for connecting said structures in parallel relation to each other, connections between said electrodes and saidfrequency determining" circuit, a source of polarizing potential having its positive terminal connected in common to the anodes of said structures, and means for biasing the grids of said structures difierently such that said structures operate on difierent portions of their respective grid characteristics and their input capacities vary in opposite sense with the same change in anode potential and independent of frequency.

HARMON B. DEAL. STUART W. SEELEY.

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