US1921476A - Relaxation oscillator and amplifier system - Google Patents

Description

Mg. 8, 1933., R. M. PAGE 6 namxnxon OSCILLATOR AND AMPLIFIER SYSTEM Filed July 1:5, 1929 2 She'ets-Sheet 1 Email- INVENTOR.

96, 61194, BY I 1 an ATTORNEY A .8, .1933. R. M. PAGE 1,921,476

RELAXATION OSCILLATOR AND AMPLIFIER SYSTEM Filed July 13, 1929 2 sheets-Shem 2 I VEN TOR.

ATTORNEY Patented Aug. 8, 1933 PATENT OFFICE 1.92;,410 RELAXATION OSCILLATOR AND Am SYSTEM Robert M. Page, Washington, D. 0. Application July 13, 1929. Serial No. 378,102

13 Claims.

My invention relates to relaxation oscillators and amplifiers of the thermionic tube tm.

One of the objects of my invention is to provide an improved oscillator system for producing alternating current energy.

Another object of my invention is to provide an improved amplifier of alternating current energy whereby subrnultiple frequencies may be Produced.

Still another object of my invention is to provide an improved oscillatory circuit arrangement employing thermionic tubes whereby the life of the tube employed is greatly increased.

A further object of my invention is to provide an oscillator system wherein the thermionic tube employed is prevented from operating at the saturation point.

A still further object of my invention is to provide a relaxation oscillator system wherein the efficiency of operation is greatly improved and wherein constancy of frequency may be maintained at all times.

A better understanding of my invention can be had from the specification following and from the accompanying drawings wherein:

Figure 1 shows a relaxation oscillator system of my invention wherein impedance elements are connected between the cathode and the inner grid and between the cathode and outer grid; Fig. 2 shows an impedance element connected between the cathode and outer grid, and a source of direct current potential connected between the cathode and inner grid with the negative terminal connected to the inner grid; Fig. 3 shows a circuit similar to that of Fig. 2 with the positive terminal of the source connected to the inner grid; Fig. 4 shows a circuit arrangement embodying my invention for frequency division or the generation of submultiples of an applied frequency where the frequency to be divided is applied to the inner grid; and Fig. 5 shows a modified form of circuitarrangement of my invention for frequency division or for the generation of submultiples of an applied frequency where the frequency to be divided is applied to the outer grid.

Many different types of oscillators and amplifiers are possible by employing thermionic tubes. The ordinary oscillator is that employing inductance and capacity where the input and output circuits are interconnected by inductance or capacity coupling. In such arrangements the oscillation constant is roughly the product of all capacity in the circuits and all inductance. Such arrangements have a number of disadvantages well known to those skilled in the art. H. Abraham and E. Bloch were perhaps the first to devise a system, which they called a multivibrateur which employed what was later called a relaxation circuit. The system was called multivibrateur because of the many higher harmonics of appreciable amplitude which were produced. Balthasar van der Pol, Jr., extended the work of Abraham. and Bloch and developed the mathematical solution of the circuit and method of operation. The system of Abraham and Bloch may be regarded as a two-stage resistance-capacity coupled amplifier where the output is coupled to the input. Balthasar van der Pol, Jr., devised a circuit employing a single thermionic tube having a cathode, anode and two grids. In developing this circuit it was found that the time constant was equal to the time of relaxation and approximately the product of the resistance and capacity of the circuit. For this reason the terms relaxation oscillator and relaxation circuit are employed. In the arrangement proposed by Balthasar van der Pol, Jr., the generated energy does not remain at constant frequency for any length of time, is destructive of the tube employed in that the tube is operated at saturation, slight changes in filament emission cause changes in impedance of tube and resulting changes in frequency of th generated energy and a number of other 35 effects contribute to the disadvantages of the system. In the relaxation oscillator and amplifier system of my invention the disadvantages encountered with systems heretofore employed are avoided.

The operation and the advantages of the re-= laxation oscillatorand amplifier of my invention may best be understood by referring to Fig. l of the accompanying drawings. In accordance with the scheme of my invention I employ a thermionic tube 1 which is of the type having a cathode 2, grids 3, 4 and 5 and anode 6. Cathode 2 is energized by battery 7 or any suitable source. Grid 3 is connected externally to cathode 2 by means of resistor 8. Resistor 8 provides the necessary bias for grid 3. Grid 4 is supplied with a potential of positive polarity with respect to cathode 2, this being provided by source 9 which is connected to grid 4 through resistor 10. Grid 5 is connected to cathode 2 through resistor 12 and is..capacitively coupled to grid 4 by means of condenser 13. Anode 6 is supplied with a potential of positive polarity with respect to cathode 2, this being obtained by means of source 11 and source 9. It is possible to operate the system without source 11, connecting the anode directly to source 9 although this will not give as satisfactory operation as will be obtained with source 11. In describing the operation of the system the grids 3, 4 and 5 will be referred to as inner grid, center grid and outer grid, respectively.

Normally the potential of the center grid 4 is equal to the potential supplied from source 9 minus the potential drop across resistor 10. The potential of outer grid 5 is equal to the cathode potential minus the potential drop across resistor 12. The condition therefore, is that the center grid 4 is positive with respect to cathode 2 and the outer grid 5 will be slightly negative with respect to cathode 2. Under this condition the anode current Ip will be of a low order, the negative polarity of outer grid 5 repelling the electrons emitted from cathode 2. Accordingly the grid current Ig will be of a relatively high order since center grid 4 is positive with respect to cathode 2. The total current delivered from the cathode to center grid 4 and anode 6 is nearly constant because center grid 4 and anode 6 are always positive relative to the cathode. In a tube having no inner grid the value of this total current is determined by the volume of emission of electrons from the cathode. In a tube having inner grid, the value of this total current is determined by the potential of the inner grid 3. In the system here disclosed the potential of the inner grid is maintained constant. Any increase in the current of eithercenter grid 4 or anode 6 is therefore accompanied by corresponding decrease in the current of the other. This follows from observed characteristic curves of such tubes, as is known to those familiar with the art. Assume that a small disturbance of I would be effected causing an increase in the anode current. This increase in the anode current will eiiect a decrease in the grid current Ig and accordingly a decrease in the potential drop across resistor 10, since the potential drop across resistor 10 is proportional to the current flowing through it, which current is here the current of the center grid 4. Since this potential drop is decreased it follows that the potential of center grid 4 will be increased to a higher value of positive polarity with respect to cathode 2. By electrostatic induction through condenser 13 the potential of outer grid 5 receives a positive impulse which causes an increase in the anode current I. There is then a corresponding increase in the potential of center grid 4 efiected by decreasing the potential drop across resistor 10. Ordinarily the increase in anode current Ip will continue to the saturation point of the tube, the potential of center grid 4 will be of a high positive value and maintain this value as long as Ip remains constant and outer grid 5 will have a corresponding high potential of positive value with respect to cathode 2.

The potential difference between the outer grid 5 and cathode 2 will cause a current to flow through resistor 12. This current may be well called the charging current for condenser 13 which current will decrease according to an exponential law as is well known to those skilled in the art. As this current decreases the drop across resistance 12 decreases and outer grid 5 approaches the potential of cathode 2. As the potential of outer grid 5 approaches the potential of cathode 2 the anodecurrent I1: is decreased. This decrease in the anode current Ip will effect an increase in the grid current I increase the potential drop across resistor 10 and decrease the potential of positive polarity of center grid 4. This decrease in polarity, by means of condenser 13. causes a current impulse of negative value to be impressed upon outer grid 5. This impulse further hastens the decrease in I and further decreases the potentials of grids 4 and 5. This continues until Ip has relaxed to zero and outer grid 5 is negative with respect to cathode 2. Center grid 4 now remains at a potential of constant value while the anode current 1;) remains zero. At this time outer grid 5 is caused to approach a potential equal to the potential of cathode 2 by virtue of the discharge of condenser 13 through resistors 12 and 10. When the potential of outer grid 5 approaches the potential of cathode 2, the anode current Ip will increase and the cycle will be repeated. From the above it will be seen that the time of relaxation or time constant may be expressed as ap proximately the product of the resistance in the circuit times the capacity.

Thus far the inner grid 3 has performed no part in the operation of the system, the operation being possible without the same. By referring again to the electrostatic induction, by virtue of condenser 13, to impress a positive impulse upon outer grid 5 it was previously pointed out that this caused an increase in the anode current Ip. It was further mentioned that this increase in I continued to the point of saturation of the tube. It is not to be desired to allow this condition to exist since operation at the saturation point is accompanied by reducing the life of the tube, inconstancy of frequency and many other disadvantages. In accordance with my invention I provide an inner grid 3 which prevents such disadvantages. Without the use of such means, the anode current Ip would only be limited by the saturation point of the tube employed. The inner grid 3 limits the electronic current and prevents operation on the saturation point of the tube. By impressing a potential of the proper value and polarity upon inner grid 3, the effective electronic emission of cathode 2 is controlled. By such means the electronic current from inner grid 3 will be substantially constant and minor irregularities in the initial liberation of electrons from cathode 2 will have substantially no effect on the operation of the system. It therefore follows that the impedance of the tube is unaffected by minor irregularities in electronic emission from cathode 2 and that the generated alternating current energy will be substantially of constant frequency. When the tube is operating at saturation all of the electronic emission from cathode 2 is utilized with the resulting effect that cathode 2 soon fails in electronic emission and the tube is destroyed. This is avoided by employing inner grid 3 in accordance with my invention.

The tube may be operated at all times below the point of saturation and the electronic emission from cathode 2 maintained at a substantially constant and low value as desired.

Fig. 2 of the accompanying drawings shows a means for supplying the necessary biasing potential to inner grid 3. The source 14 may be connected either with the positive polarity to inner grid 3 or with the negative polarity to inner grid 3 with respect to cathode 2. This alternative polarity is not necessary with a given thermionic tube but varies with the difierent types of tubes employed. Certain thermionic tubes of foreign manufacture require that a positive potential be applied to the inner grid 3 with respect to cathode 2; the majority of tubes however, req'uire a potential of negative polarity with respect to the polarity of cathode 2 as shown in Fig. 2. The generated alternating current energy may be coupled from the oscillator and amplifier system by connecting to resistors 10 or 12. When it is desired toemploy the arrangement as an amplifier similar coupling may be employed.

In the conventional oscillator of the inductancecapacity type, in the multivibrator, and in threeelectrode tube relaxation oscillators with transformer feed-back, the total emission current of any single tube involved follows the cyclic variation of the output electromotive force. The Van der Pol circuit differs from all these in that the total emission current is essentially constant throughout the cycle. The frequency of the oscillation in this circuit, however, is highly sensitive to the value of this emission current. The frequency instability in the Van der Pol circuit is therefore due to the fact that the electron emission of the cathode varies during operation due to changes in the cathode from various causes, known to the art, even though all operating voltages are maintained at constant values. An object of my invention is to eliminate or reduce as far as possible the effect of changes in the emitting cathode on total electron current, that- From this it follows that under certain condi-.

tions the potential with respect to the cathode of inner grid 3 may be positive, negative, or zero, the characteristics of the tube determining which gives best results. It will be seen that the resulting electron current may be either greater than or less than it would be without the inner grid. depending upon the type of tube employed. It is reasonable to assume that, other things being equal, a tube which required a positive bias forv best frequency stability would be less suited to this circuit than one which required a negative bias due to considerations of circuit efficiency and tube life. If the most constant emission current is obtained with a negative potential on the inner grid, the the advantages of greater operating efficiency and longer tube life follow as secondary consequences. This is the condition normally to be expected from most tubes. Under practical operating conditions with the type of circuit here described and the tubes ordinarily available in the United States, a negative bias on the inner grid gives best results.

When it is desired to provide constant frequency energy of a frequency value equal to a submultiple of the exciting source, the exciting source may be coupled to either inner grid 3, center grid 4 or outer grid 5 and the system will oscillate at a submultiple frequency of the applied frequency. By means of varying the capacity of condenser 13, or the resistance of resistors 10 or 12 the frequency of the generated energy may be divided into frequencies of submultiple value as desired.

Fig. 4 shows a circuit similar to that of Fig. 1 wherein an exciting source 15 of a frequency of which a submultiple isdesired is coupled to the circuit of the inner grid. Fig. 5 shows a circuit similar to that of Fig. 2 wherein exciting source 15 of a frequency of which a submultiple is desired is coupled to the circuit of the outer grid. These circuits shown in Fig. 4 and Fig. 5 are tion.

intended only for the purposes of illustration, and not as limitations on the broad features of my invention. I

Some of the advantages obtained in accordance with the relaxation oscillator and ampliiier system of my invention are:

The generated energy is maintained at substantially'constant frequency.

Prevents operating the thermionic tube at the point of saturation.

Makes possible longer operation of the thermionic tube and prevents change in frequency characteristics which usually follows after a few hours use.

Avoids necessity of precisely maintaining uniform electron emission of cathode.

I realize that many modifications of my invention are possible and it is to be understood that the embodiments of my invention are not to be restricted by the foregoing specification or by the accompanying drawings but only by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A relaxation oscillator system for generat- -ing electrical oscillations comprising in combination a thermionic tube having a cathode, an anode, an inner grid, a central grid and an outer grid, a circuit arrangement including impedance elements interconnecting said cathode, anode and said central grid and outer grid for the generation of said oscillations and means for supplying a source of biasing potential to said inner grid electrode to prevent said tube from operating at the point of saturation.

2. In an oscillator system where the time constant is the time of relaxation in a thermionic tube circuit the combination of an auxiliary electrode adjacent to the cathode in said tube and means for applying to said auxiliary electrode a biasing potential with reference to said cathode for preventing the operation of said tube at the saturation point thereof.

3. In an oscillator system where the time constant is approximately the product of resistance and capacity in a thermionic tube circuit arrangement the combination of an auxiliary electrode adjacent to the cathode in said tube and means for applying to said auxiliary electrode a biasing potential with reference to said cathode for maintaining the operation of said tube below the point of saturation.

4. In a thermionic tube oscillator system employing a relaxation circuit the combination of an auxiliary electrode adjacent to the cathode in said tube and means for applying to said auxiliary electrode a biasing potential with reference to said cathode for maintaining the normal operation of said tube below the point of satura- 185 5. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a source of anode 14 potential connected between said anode and said source of central grid biasing potential, means for applying biasing potential between said outer grid and said cathode, means for applying biasing potential between said inner grid and said 6. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid and outer grid, a source of'central grid biasing potential connected between said central grid and said cathode, a source of anode potential connected between said anode and said source 01 central grid biasing potential, 9. resistance element connected between said outer grid and said cathode, a resistance element connected between said inner grid and said cathode, and a condenser connected between said outer grid and said central grid, whereby the emission of electrons from said cathode is maintained at a value below saturation.

'7. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, cen= tral grid and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a source of anode potential connected between said anode and said source of central grid biasing potential, means for biasing said outer grid with reference to said cathode, a source of inner grid biasing potential connected for applying to said inner grid a potential negative with reference to said cathode, and a condenser connected between said outer grid and said central grid, whereby the emission of electrons from said cathode is maintained at a point below saturation.

8. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a source of anode potential connected between said anode and said source of central grid biasing potential, means for biasing said outer grid with reference to said cathode, a source of inner grid biasing potential connected for applying to said inner grid a potential positive with reference to said cathode, and a con denser connected between said outer grid and said central grid, whereby the emission or else-- trons from said cathode is maintained at a point below saturation.

9. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid, and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a connection between said anode and said source of central grid biasing potential, means for applying biasing potential between said outer grid and said cathode, means for applying biasing potential between said inner grid and said cathode, and a condenser connected between said outer grid and said central grid, whereby the emission of electrons from said cathode is maintained at a value below saturation.

10. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid, and outer grid, a source of central grid bias ing potential connected between said central grid and said cathode, a source of anode potential connected between said anode and said source of central grid biasing potential, means for applying biasing potential between said outer grid and said cathode, and means for applying biasing potential between said inner grid and said cathode, a condenser connected between said outer grid and said central grid, whereby the emission o1 electrons from said cathode is maintained at a value below saturation.

11. In a relaxation oscillator system, an electron tube having cathode, anode, inner grid, central grid and outer grid, 2. source of central grid biasing potential connected between said central grid and said cathode, a connection between said anode and said source of central grid biasing potential, means for biasing said outer grid with reference to said cathode, a source 01 inner grid biasing potential connected for applying to said inner grid a potential negative with reference to said cathode, and a condenser connected between said outer grid and said central grid, whereby the emission of electrons from said cathode is maintained at a point below saturation.

12. In a system for generating constant irequency energy of a frequency value equal to a sub-multiple of the frequency of an exciting source, an exciting source of oscillations, an electron tube having cathode, anode, inner grid, central grid, and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a connection between said anode and said source of central grid biasing potential, means for applying biasing potential between said outer grid and said cathode, means for applying biasing potential between said inner grid and said cathode, a condenser connected between said outer grid and said central grid, and a connection between said exciting source and one of said grids.

13. In a system for generating constant frequency energy of a frequency value equal to a sub-multiple of the frequency of an exciting source, an exciting source of oscillatiom, an electron tube having cathode, anode, inner grid, sen tral grid, and outer grid, a source of central grid biasing potential connected between said central grid and said cathode, a connection between said anode and said source'of central grid biasing potential, means for applying biasing potential between said outer grid and said cathode, means for applying biasing potential between said inner grid and said cathode, a condenser connected between said outer grid and said central grid, and a connection between said exciting source and said inner grid.

ROBERT M. PAGE.

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