US2179791A - Stabilized oscillation generator - Google Patents

Description

Nov. 14, 1939. w. E. KocK 2,179,791

STABILIZED OSCILLATION GENERATOR F'iled March 17, 1957 Patented Nov. 14, 1939 UNITED STATES STABILIZED OSCILLATION GENERATOR Winston E. Kock, Cincinnati, Ohio, assignor to The Baldwin Company, Cincinnati, Ohio Application March 17, 1937, Serial No. 131,422

10 Claims.

My invention. has reference to electric oscillation generators of the class in which gas-filled tubes containing electrodes are employed and which are commonly known as glow-discharge oscillators. More particularly, the invention refers to oscillators of this class, in which tubes containing three or more electrodes are used, and it pertains especially to means for improving the frequency stability of such oscillators.

Glow-discharge oscillators are convenient sources of electric oscillations. They do not, however, possess inherent frequency stability and the causes for variations in their frequencies can be conveniently classified as (1) changes in circuit parameters (2) supply voltage changes and (3) changes in tube characteristics, principally those in tube ignition potentials. It is possible to secure circuit parameters such as resistances, condensers and inductances of stable value with time, current and voltage, and hence the first cause can be eliminated. A satisfactory method for eliminating the effects of the second cause has been shown in my United States Patent No. 2,646,463, issued July '7, 1936, on an application filed December 6, 1933, whereby an inductance added properly, and as taught, to the circuit of a relaxation type glow-discharge oscillator renders the oscillation frequency substantially independent of supply voltage.

A method for reducing the effects of the third cause, namely, changes in tube characteristics, is shown in a co-pending application, No. 46,449, Patent No. 2,139,893, granted December 13, 1938, filed by me on October 23, 1935, for an Oscillation generator, wherein by inductively coupling the grid circuit of a three-electrode glow-discharge tube to the anode circuit, the grid is caused to stabilize tube characteristics, principally the ignition potential, and thus exerts a stabilizing effect on the oscillator frequency. The method shown therein is particularly applicable to an inductive three-electrode glow-discharge oscillator.

The objects of the present invention are to provide a frequency stabilizing means which is applicable to all types of three-electrode glowdischarge oscillators; which will minimize the effects of tube characteristics therein to a greater extent than has hitherto been disclosed; which is simple and durable; and which will permit of interchanging tubes of greatly varying characteristics, in such oscillators, without appreciably affecting the frequency thereof.

The manner in which these objects are attained, and the attainment of other objects which will be apparentto those skilled in the art on further reading of this specification, is shown "in the following detailed description and accompanying drawing to which reference will now be made.

In the drawing,

Figure 1 is the circuit diagram of an ordinary three-electrode relaxation type glow-discharge oscillator, drawn for 'purposes of comparison;

Figure 2 is the circuit diagram of Fig. 1 modified to include my invention in one exemplary application thereof; and

Figure 3 shows another exemplary application of the invention to an inductive three-electrode glow-discharge oscillator. 7

Referring now in greater detail to Figure 1, the arrangement and operation of the relaxation oscillator shown will be apparent to those skilled in the art. A brief description of it, however, will serve to point out the necessity for my invention and may be used in comparing oscillators of the class-embodying it with those not so equipped. Thus a tube T having therein a gas for electric discharge, an anode A, a grid G, and a thermionic cathode K (which may be heated in any Well-known way) is shunted from anode to cathode by a condenserC. A source of positive voltage +B, asreferred to the cathode K which may begrounded as shown, is connected to the anode A through a resistance R1. 30 The grid G is connected to a source of negative voltage -C, likewise referred to the cathode K, through a resistance R2. The operation of the oscillator is as follows. The condenser C charges through the resistance R1 until its voltage equals the ignition potential of the tube. The tube then ignites, rapidly discharges the condenser, extinguishes at a lower potential and the operation repeats. Oscillations of the relaxation type are thus produced, the frequency of which is determined by the circuit parameters R1 and C, the supply voltage +13 and the tube characteristics, principally the tube ignition potential. The function of the resistance R2 is to limit current in the grid circuit; without this resistance the grid, being at a different potential than either the anode or cathode, would draw a heavy current while the tube is in a state of ignition and its delicate structure possibly damaged thereby.

The use of a hot cathode in a glow-discharge tube is known to be advantageous. With its employment, however, a third electrode, a grid, must be added to the tube and biased negatively with respect to the cathode in order that the tube function in effecting glow-discharge oscillations,

'as is also well known.

In keeping with this, a heated cathode has been described for the oscillator of Figure 1; and the grid G and a source of negative voltage C included. By the addition of the grid and the negative voltage-applied thereto at least one advantage is obtained. For, by changing the value of this voltage the tube ignition potential (an important tube characteristic), and with it the oscillator frequency, can be conveniently changed or adjusted. It is well known, of course, that if the grid bias voltage is made less negative, the ignition potential is lowered, causing the frequency to be raised, and vice versa.

The means just described, for altering the oscillator frequency, will not function per se, however, as means for maintaining the frequency at a substantially constant value, that is, as a frequency stabilizing means. For, changes in tube ignition potential, and thus in oscillator frequency, may occur even though the grid bias voltage be held constant. Such changes, which may be conveniently called inherent variations, may be due, for example, to tube aging (absorptionor emission of gas by the electrodes), to changes in the physical alignment of the electrodes, or to diiferences in ignition potential from tube to tube. It is known, of-course, that tubes, as commercially available today, even when purchased to the same specifications, may have ignition potentials differing by 10 to 20 volts per tube, and thus do not permit interchanging tubes in an oscillator without adjustment of its frequency.

Thus it is seen that some means must be devised for stabilizing the frequency of. a glow-discharge oscillator against inherent variations in the tube ignition potential and that this means preferably should be applicable to glow-discharge oscillators irrespective of type. In the practice of my invention, whereby I have provided a practical such means, I make the frequency of oscillation substantially independent of the tube ignition potential by controlling this potential in such a way that, in spite of inherent variations in it, the tube will discharge as soon as the condenser has charged to a given value. In this way the frequency is made to depend only upon the charging characteristic of the condenser and to be sub stantially independent of any factors which do not aifect this characteristic. (The charging characteristic, 1. e., the time-charge equation, of the condenser C in Figure 1 depends on the values of +B, R1 and C.) I accomplish the objects of my invention by varying the grid bias in accordance with the amount of charge on the condenser, as will now be more specifically described.

My invention of frequency stabilizing means is exemplarily shown in Figure 2, wherein like indices represent like parts, of the same functions and arrangements as those in Figure 1. Additionally, however, a resistance R3 connects the grid G to the condenser C (and to the anode A and the lower voltage end of the resistance R1). With the resistance R3 inserted, it is desirable that the negative voltage -C be of greater negative value than it would be without R3, and that both R3 and R2 be large with respect to R1, to make the frequency rather independent of the values of R3 and R2, and to counteract the tendency of the source of positive voltage +3 to place the grid at a positive, and undesired, voltage. If, for example, R1 has a value of one megohm, then I have found it best to make R3 and R2 about 1.5 megohms each. A desirable value for C is about 80 volts negative, and. for +B about 250 volts positive. These values are illustrative, but not restrictive, and for further illustration, if the condenser C now be given a value of .003 microfarad, the oscillator in Figure 2 will operate at a frequency of the order of 700 cycles per second, stabilized according to my invention. It will be understood, of course, that the frequency of the oscillations produced by the means illustrated in Figure 2 will vary as the values of R1 and C are changed; thus the values given above are exemplary only.

It is to be noted that a positive and undesired potential for the grid G, might be indicated in Figure 2 if one considers only the circuit through R1, R3 and R2, from +3 to C, with the values given above. However this does not occur in practice, for it is necessary to take into account the control circuit containing the capacity C, and the fact that the tube is in a condition of oscillation. At the instant when a discharge is completed, the anode potential of the tube will be very low, substantially all of the voltage drop from the source +B occurring across the resistance R1. At this instant the grid G will be biased strongly negatively. As then a charge builds up across the condenser C, the condenser voltage (and the anode voltage) will be increased, and therefore, owing to the resistance R3, there will occur a diminution in the negative bias on the grid G. However, the tube will discharge again before the grid swings positive.

Now it will be seen that the negative bias upon the grid G is directly dependent upon the charge on the condenser C at any given instant. Moreover by my invention the condenser charges to i a desired amount. For, if the condenser be imagined to have charged above this amount the negative grid bias would have been reduced, the ignition potential thus lowered and the condenser would have been discharged by the tube. Conversely, if the condenser be charged to below the desired amount, the negative grid bias is of increased value, thus raising the ignition potential and permitting the condenser to charge further. In this way the frequency of oscillation of the system becomes substantially independent of any inherent variation of the ignition potential of the tube and thus is dependent only on the charging characteristic of the condenser.

A step further toward complete stability in an oscillator. of this type can be taken in accordance with the disclosure of Figure 3. As has been indicated, I have succeeded in making the frequency of oscillation substantially independent of tube characteristics by the organization shown in Fig. 2. This leaves the frequency dependent upon the values of +3, R1, and C. Of these, R1 and C can be made substantially fixed and constant, leaving the greatest source of frequency instability variations in the voltage value of +3 In order to counteract this, as shown in Figure 3, (where like indicia have been given to like parts) I insert an inductance L in the control circuit containing the capacity C. The system thus operates substantially in accordance with the teachings of my Patent No. 2,046,463, as an inductively stabilized glow-discharge oscillator with the additional advantage of independence of variations in tube characteristics, produced by controlling the ignition potential of the tube in accordance with the attainment of the desired charge upon the condenser C.

It will be understood that useful voltages may be derived from my organization from the feed circuit or the control circuit in any of the known ways. It will also be understood that a limiting resistor may be placed in the control circuit, if desired.

My invention may be applied in all devices where glow-discharge oscillators are used, for ample, in electrical musical instruments, cathode ray sweep circuits, inverter circuits, and the like.

I claim:

1. In an electrical oscillator, a glow-discharge tube having at least an anode, a cathode and a grid; an anode-to-cathode supply circuit containing a source of anode potential and a resistance; an anode-to-cathode control circuit containing a condenser; a grid-to-cathode circuit containing a resistance and a substantially constant source of potential; and a connection between said anode and said grid containing a resistance, said connection serving to control the negative bias of said grid in accordance with the value of a charge on said condenser.

2. A circuit as claimed in claim 1, wherein the value of the resistance in said connection is greater than the value of the resistance in said supply circuit.

3. In an electrical oscillator, a gaseous glowdischarge tube having at least a cathode, an anode, and a grid; a source of anode potential and a substantially constant source of grid potential, one terminal of each of said sources of potential being connected to the cathode of said tube; a connection between the other terminal of said source of grid potential and said grid including a limiting resistor; a connection between the other terminal of said source of anode potential and said anode including a limiting resistor; an anode-to-cathode control circuit for said tube, containing a capacity; and impedance means connected from said circuit, between said anode and said capacity, to said grid, whereby the building up of a potential on said anode will tend to decrease the negative bias of said grid.

4. In an electrical oscillator, a gaseous glowdischarge tube having at least a cathode, a grid and an anode; an anode-to-cathode feed circuit therefor; an anode-to-cathode control circuit therefor; a grid-to-cathode biasing circuit therefor, containing a substantially constant source of negative potential; and a connection between the anode of said tube and the grid thereof, said connection containing an impedance, whereby the anode potential of said tube is caused to modify the negative grid bias thereof.

5. In an electrical oscillator, a gaseous glowdischarge tube having at least a cathode, an anode and a grid; an anode-to-cathode control circuit comprising a capacity; an anode-to-cathode supply circuit containing a resistance and a source of positive anode potential; means for imposing upon said grid a direct negative bias afiecting the ignition potential of said tube; and means, distinct from the first said means, for diminishing the negative bias of said grid to cause the tube to ignite upon the attainment of a predetermined potential by said anode, said last mentioned means comprising a resistance of high value inserted between said anode and said grid.

6. In an electrical oscillator a gaseous glowdischarge tube having at least an anode, a cathode and a grid; a control circuit for said tube comprising at least a capacity connected between the anode and cathode; a supply circuit for said tube comprising a source of anode potential and a resistor; means for causing the frequency of oscillation of said oscillator to be substantially independent of variations in tube characteristics, comprising automatic means for controlling the ignition potential of said tube in accordance with the charging and discharging of said condenser irrespective of variations in the internal characteristics of said tube, said last mentioned means comprising a grid-to-cathode circuit containing a source of negative grid potential and a limiting resistor; and a connection between said grid and said anode comprising a resistor.

7. In an electrical oscillator a gaseous glowdischarge tube having at least an anode, a cathode and a grid; a control circuit for said tube comprising at least a capacity connected between the anode and cathode; a supply circuit for said tube comprising a source of anode potential and a resistor; and means for causing the frequency of oscillation of said oscillator to be substantially independent of variations in tube characteristics, comprising automatic means for controlling the ignition potential of said tube in accordance with the charging and discharging of said. condenser irrespective of Variations in the internal characteristics of said tube, said last mentioned means comprising a grid-to-cathode circuit containing a source of negative grid potential and a limiting resistor; and a connection between said grid circuit and said anode comprising a resistor, the value of said last mentioned resistor being large as compared with thevalue of the limiting resistor in the said supply circuit for said tube.

8. An oscillator as claimed in claim 6, having in the said control circuit an inductance of sufficient value in connection with the said capacity to provide a tuned control circuit having a frequency substantially independent of minor fluctuations in the value of said source of anode potential.

9. A method of operating an electrical oscillator of the glow discharge type having a feed circuit and a control circuit connected respectively with a glow-discharge tube of at least the three element type, which comprises normally biasing the grid of said tube by a source of substantially constant negative potential to increase the ignition potential thereof, and upon the attainment of a predetermined potential in said control circuit, rapidly diminishing the negative bias of said grid to the point where the tube discharges, whereby to make the frequency of oscillation independent of variations in tube characteristics.

10. In an oscillator, a glow discharge tube including therein an anode, a cathode and a grid; a source of positive potential for said anode; a resistance inserted in the connection from said source to said anode; a capacity connected from said anode to said cathode; a source of negative potential for said grid; a resistance inserted in the connection from said grid potential source to said grid; and a resistance connected from said grid to said anode-the two said potential sources being referred to the said cathode.

WINSTON E. KOCK.

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