US2452337A - Circuit arrangement for the amplification, frequency-transformation, or production of ultra high frequency oscillations - Google Patents

Description

1948- M. J. o. STRUTT ET AL 2,452,337

cmcurr ARRANGEMENT FOR THE AMPLIFICA'I'ION, FREQUENCY-TRANSFORMATION on PRODUCTION OF ULTRA HIGH FREQUENCY OSCILLATIONS Filed May 21, 1943 2 Sheets-Sheet 1 Mir/mum Juuw- 077v Jrearr Q0?- b ew flee 4,

Oct 26, 1943- M. J. o. STRUTT ET AL 2,452,337

cmcum ARRANGEMENT FOR THE AMPLIFIOA'I'ION, FREQUENCY-TRANSFORMATION 0R PRODUCTION OF ULTRA nmn FREQUENCY oscnmnons Filed May 21, 1943 I 2 Shasta-Sheet 2 MAY/114.140 Jun/us 0770 57207 1- Patented Oct. 26, 1948 UNll'ED STATES PATENT OFFICE CIRCUIT ARRANGEMENT FOR THE AMPLIFI- CATION, FREQUENCY-TRANSFORMATION, OR PRODUCTION OF ULTRA HIGH FRE- QUENCY OSCILLATIONS Maximlliaan Julius Otto Strutt and Aldert van der Ziel, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company,

Hartford, Conn., as trustee Application May 21, 1943, Serial No. 487,978 In the Netherlands August 20, 1941 Section 1} Public Law 690, August 8, 1946 Patent expires August 20, 1961 3 Claims. (Cl: 250-27) being connected between the cathode and the first grid having a negative potential or cathode potential, o cation at ultra-high frequencies the attempts The properties of tubes for amplifying and genhave n q n y to be ted to as high an crating oscillations at ultra-high-frequencles are put sta e a d utual co duct ce as greatly different from those at lower frequencies. possible I More particularly in amplifying ultra-high fre- Recently various DIODOSaIs have been made to quencies the fact has to be taken into account redlwe e put damp g of amplifying tubes. that avirtual ohmic resistance is set up between Thus. for instance, the l damping c n be rethe control grid and the cathode, which resistance duced y making use of a tube having two cathexerts a strong damping on the input circuit. p y Conductors, one of which is inserted The presence of this virtual ohmic resistance is in the input circuit, W reas the other is intermainly due to two causes. posed in the output circuit. Another expedient Primarily the comparatively great transit time to reduce the lead damping o sts in the use of of the electrons will involve a phase displacement p y ng tubes compri i two p -D 00 between the alternating control grid'voltage and nected amplifying systems whose cathodes are the alternating current passing through the aperconnected by s short a lead as P ssible. tures of the control grid, which phase-displace- A further improvem nt of he inp t pi merit involves the production of an influence curs p le by taking Vario s s essentially rent to the control grid. This influence current amounting o back-Coupling, r instance y has a component which is in phase with the sorting an additional inductance in the screenalternating control-grid voltage and may be congrid lead. strued as resulting from a virtual ohmic resist- In many cases, however, these steps o no y ld ance available between the control grid and the the d d eff t. aus t y ami mutual cathode, The reciprocal value of this resistconductance Of the discharge tube highly declines ance is called transit-time damping or electron t u i r qu s a d is usually much dampjng j 7 lower than the static'mutual conductance.

Secondly the natural inductances of the supply as The present invention purports to provide a conductors to the various electrodes will exhibit circuit by means of which the input damp of a considerable impedance in regard to the osci1-' the discharge tube can be highly decreased or even lations to be amplified. so that high-frequency rendered negative and/or y means of which the voltages are set up across these supply conductors, decreasein dynamic mutual conductance can be which voltages give rise to currents passing 4o materially reduced. through the natural tube capacities and being in According to the invention the second grid in phase with the alternating control grid voltage. a circuit of the kind referred to has a positive The damping of the input circuit thus caused may potential, whereas the next electrode has a negabe called lead damping. tive potential, the construction and the voltages At not t o h frequencies both the electron of the electrodes being so chosen that the elecdamping and the lead damping are about propo trons, at least for the greater part, perform an tional to the square of the frequency of the osciloscillatory movement in the path between the lations to be transmitted. At ultra-high frefirst grid and the electrode next to the second quencies the input damping resulting from both grid and pass several times through the secondgrid, the frequency of this oscillatory movement of these components is usually so strong that the impedance of the resonant circuit inserted in the signal control grid circuit is high relatively to the input resistance of the tube. Therefore, the output impedance of a stage in cascaded circuits is practically solely determined by the input resistance of the next stage, so that the attainable amplification per stage substantially corresponds to the product of mutual conductance and input resistance. In order to obtain sufllcient amplifiassassv being such that a decrease in input damping and/or an increase of the dynamic mutual conwhere 1: may represent any whole-number.

The invention will be more fully explained by reference to the accompanying drawing in which Fig. 1 depicts input damping and conductance curves of a tube which does not utilize the present invention; Fig. 2 discloses a circuit utilizing an hexode and embodying the basic principle of the invention; Fig. 3 shows input damping and conductance curves of a tube embodying the invention; Fig. 4 shows an embodiment of the invention utilizing a tetrode in an amplifier circuit; Fig. 5 shows an embodiment utilizing a tetrode in an oscillator circuit; Fig. 6 shows a modification of the circuit shown in Fig. 5 utilizing an hexode; Fig. shows an embodiment of the invention utilizing a push-pull tube and circuit; and Fig. 8 is a modified form of tube structure that may be used in the circuit of Fig. 7.

In Fig. 1 the curve I represents the variation of the input damping as a function of the frequency of the oscillations to be transmitted. if the invention the positive grid and are reflected again by control rid.

In this case the input circuit may be undamped to such a degree that not only the electrons and the lead damping. but, also the damping of the circuit itself is compensated so that the resulting damping becomes negative.

Fig. 2 of the drawing. by means of which the principle underlying the invention will be more fully explained, represents a hexode I which is connected as an amplifier and comprises a cathode l, a signal control grid 2. a positive grid 3, a negative grid 4, a positive grid 5 and an anode I which last-mentioned electrode also has a positive potential. Between the cathode I and the signal control grid 2 is connected a circuit 0 which is tuned to the frequency of the oscillations to be amplified and to which are supplied the oscillations to be amplified, the amplified oscillations being taken from a resonant circuit interposed in the anode circuit. With suitable values of the feed voltages a part of the electrons on the way from the cathode l to the anode 8 will be so strongly braked, due to the negative potential of the grid 4, as to reverse their direction. In the proximity of the signal control grid 2 the electrons reverse their direction again by the action of the electric field of the grid I. whereupon the same phenomenon is repeated in the neighborhood of the grid 4. This is schematically represented by the wave line I. The time T required by the electrons for covering the path between the grids l and 2 forth and back depends on the construction of the tube and in addition on the direct current voltages of'the electrodes.

It now appears that the damping or undamping brought about by the discharge tube on the is not used. From this curve it appears that with an increase in frequency the input damping initially increases slowly and then in an ever increasing way and that at very high frequencies. after having attained its maximum value. it decreases again comparatively swiftly at A and finally acquires even negative values on the right of point B. The curve 11 represents the ratio between the dynamic mutual conductance S and the static mutual conductance So as a function of the frequency. It appears that the dynamic mutual conductance swiftly decreases with an increase in frequency. Hence, the decreasing or even negative input damping in the region on the right of frequency A can not be utilized in practice, since the dynamic mutual conductance is too small in this region. Therefore, the frequency range to which the invention is primarily related lies in the rising branch of curve I, for instance between the frequencies designated D and A, which lies in the range of the centimeter and decimeter waves.

The invention is based on the recognition that it is possible to cause a flow of influence current to the signal control grid, which has a component which is in phase-opposition to the control-grid voltage and consequently involves undamping of the input circuit by causing the electronic stream to reverse its direction after it has traversed the signal control grid and bringing it again in the correct phase into the vicinity of the signal control grid. This may be effected by providing that the signal control grid is followed by a positive grid and a negative electrode and by biasing these electrodes in such manner'that the electrons pass through the meshes of the positive grid, are refiected by the negative electrode, traverse 83 -11! input circuit depends not only on the frequency I but also on the transit time T.

:In Fig. 3 the input damping of the tube as a function of the .product fl is represented by the curve 111, which holds in the case that in each instance 70% of the electrons approaching the grid 4 are so strongly braked as to reverse their direction. In Fig. 3, moreover, the curve I is plotted on the same scale, which illustrates the relation existing between the damping and the product f1 if there are no reciprocating electrons. In this case T is taken equal to double the value of the time required by the electrons for wandering from the grid 2 to the grid I. Consequently the curve I of Fig. 3 corresponds to the left part of the curve I in Fig. 1, but is plotted on a different scale. From Fig. 3 it appears that a decrease in damping occurs in the cross-hatched regions. These regions appear to lie about between the values and fI=n. where u. may be any whole number. From this it follows that a decreased input damping can be obtained by such a choice of the tube construction and of the feed voltages of the various electrodes that T lies between 5 1 used to make up entireLv or partly for the individual losses'of the input circuit. 4

However, in a circuit comprising a hexode, as shown in Fig. 2, the dynamic mutual conductance may be affected by the oscillatory movement of the electrons. According to the invention this unfavorable eflect on the dynamic mutual conductance can be reduced to a minimum if the moments at which the electrons approach the grid 4 in each instance after a complete oscillation are always in the correct phase-relation to the high frequency voltage on the signal control grid 2. This appears to be the case if the transit time of the electrons approximately corresponds to a multiple of the period of the oscillations to be amplified. i. e., if the product fl is awhole number. If this condition is satisfied the dynamic mutual conductance has again the value represented by the curve II in Fig.1.

Now there is a range of frequencies, in which the dynamic mutual conductance is not much lower than the value indicated by the curve 11 in Fig. 1 and in which a decreased input damping is obtained at the same time,.so that it is possible greatly to reduce the input damping, whilst the dynamic mutual conductance substantially conserves its initial value.

When replacing a hexode by a tetrode, in which the electrode most remote from the cathode and having a negative potential, is used asan output electrode a suitable choice of the biases of the electrodes even permits the obtainment of a dynamic mutual conductance S exceeding the static mutual conductance So which would be obtained with a normal positive voltage on the output electrode. This is clearly illustrated by the curve IV in Fig. 3. in which the course of the ratio S/So is indicated as a function of JT. If fT=1. consequently if the time required by the electrons for covering the path between the two negative electrodes forth and back, corresponds to one period of the oscillations to be amplified, a dynamic mutual conductance can be attained which is several times higher than the static mutual conductance.

Fig. 4 shows an embodimentof the invention making use of this principle. This figure represents a tetrode I comprising a cathode I I, a signal control grid l2, a positive grid i3 and a negative anode it, the latter being used as an output electrode. Between the control grid l2 and the cathode i I is connected a circuit l 5 which is tuned to the frequency of the oscillations to be amplified 6 1 in such manner that the damping of thiscircuit caused by the losses of its own is smaller than the negative damping exerted by the tube'on the circuit.

Fig. 5 represents an embodiment thereof, in whicha resonant circuit fl is connected between i the signal control grid 12 and the cathode ll of a tetrode III. which circuit may, for instance. consist of a coaxial-line whose external conductorisconnected to the cathode. The sources of direct the electrode II, as is schematically shown by the voltage B1 and Ba supply 'a positive and a negative voltage respectivelyto the electrodes l3 and II which are so chosen that the electrons perform an oscillatory movement between the grid l2 and line iii, the transit time T having such a value that amaximum undamping of the input circuit l5 occurs. From Fig. 3 it appears that the product f1 therefore has to be so chosen that it lies between V and 1;. If, moreover, care be taken that the which comprises a cathode 2|, a signal control grid '22ra positive screen grid 23, a negative grid 24, a positive screen grid and an output electrode 28, the latter having a positive potential. Between the control grid 22 and the cathode 2| is provided a circuit l5 which is tuned to the frequency of the oscillations to be generated, a similar circuit 21 is interposed in the anode'circuit. The voltages of the electrodes 22, 23 and 2 4 entirely correspond to those of the electrodes l2, I3 and it in the circuit shown in Fig. 5 so that oscillations are generated in the circuit i5. Alternating currents having the frequency determined by the circuit IE will appear in the anode circuit, as a result of which oscillations having this frequency,

can be taken from the circuit 21. The part of the hexode 20 which is constituted by the electrodes 26 and 26, acts as an amplifier in regard to the oscillations generated in the remaining part, since the electronic stream is controlled by the grid 22, so that the energy to be taken from the circuit 27 is larger than the energy produced in the circuit it. In .this circuit arrangement the circuits 2? and it are preferably coupled solely through the electronic stream. 1. e., neither capacitatively nor inductively, in order to avoid undesirable reaction and a source of potential B2 being connected to the external conductor. The positive grid Ills connected to the cathode through a condenser H. The feed voltages supplied by batteries B1 and B2 are so chosen that T lies between 1 and a if n is so chosen as to be unity then fT lies beeiiects. For this reason the cathode is also provided with two supply leads, one of which is inserted in the input circuit. whereas the other is included in the output circuit-thus avoiding coupling of the circuits l5 and 21 through the impedance of the cathode supply lead.

Furthermore, in order to prevent undesirable damping, the electrodes 28, 24 and 25 should be connected in the most suitable way to the cathode in regard to high frequencies, which may be effected in the manner well known to the art by the use of capacitors 33, '34 and as shown in Fig. 6, or which may be effected by means of suitable Lecher systems or coaxial lines.

In order to decrease the lead damping it is also possible to make use of a push-pull circuit. Fig.

'7 represents an embodiment thereof, in which use is made of a double hexode system 30, whose'two halves have a common cathode 2|, and which comprises two signal control grids 22 and 22' alleges? which are symmetrically arranged with respect to the cathode. The'auxiiiary electrodes 22, 22, 2|, 24' and 28, 2! have cathode potential in regard to high frequencies, which may be e'fiected in the manner known to the art by means of capacitors 33, 33, 3|, 34', SI and II as shown in Fig, 7. This can be achieved also by uniting in each instance two corresponding electrodes of the two systems, for instance 23 and 21, into one electrode including the two control grids 22 and 22' and by connecting a point of symmetry of this electrode to the cathode through a conductor whose electric length amounts to a whole number of half wave lengths. This position of the electrodes is represented in plan view'in Fig. 8. With a suitable choice of the feed voltages an oscillatory movement of the electrons occurs between the electrodes 22, 24 and 22', 24' respectively, which oscillatory movement is such that the tube exerts a negative damping on the input circuit iii. If the natural damping of the circuit i is smaller than this negative damping osciliations will be produced in the circuit II as a result of which high frequency voltages are set up at the electrodes 22 and 22'. These voltages are amplified by the tube so that amplified energy can be taken from the output circuit 21.

We claim:

1. A circuit arrangement for the translation of ultra-high-frequency oscillations comprising a discharge tube which successively contains a cathode, a signal control grid, a first positive grid, a negative grid, 9. second positive grid and an anode, a resonant input circuit tuned to the frequency of the oscillations and connected between said cathode and said control grid, an output load circuit connected to said anode, said control grid having a negative potential or cathode potential, and all grids except the control grid being at cathode potential with respect to radio frequencics, said grids and anode being so constructed and arranged and the direct current voltages applied thereto being so chosen that the electrons, at least for the greater part, perform an oscillatory movement through said first positive grid and within a region defined by said control grid and said negative grid, the electrons passing several times through said first positive grid and the frequency of this oscillatory movement being so related to the operating frequency of the circuit that a decrease in input damping and an increase in dynamic mutual conductance is obtained.

2. A circuit arrangement for the translation of ultra-high-irequency oscillations comprising a discharge tube which successively contains a cathode, a signal control grid, a first positive grid, a negative grid, a second positive grid and an anode, a resonant input circuit tuned to the frequency of the oscillations and connected between said cathode and said control grid, anoutput load circuit connected to said anode, said control grid having a negative potential or cathode potential, said anode having a positive potential and all grids except the control grid being at cathode potential with respect to radio frequencies, said grids and anode being so constructed and arranged and the direct current voltages applied thereto being so chosen that the electrons, at least for the greater part, perform an oscillatory movement through said first positive grid and within a region defined a by said control grid and said negative grid, the electrons passing several times through said first positive grid and the frequency of this oscillatory movementbelng so related to the operating frequency of the circuit that a decrease in input damping and an increase in dynamic mutual conductance is obtained.

- 3. A circuit arrangement for the translation of ultra-high-frequency oscillations comprising a discharge tube system comprising a cathode and in the order named, two signal control grids, two first positive grids, two negative grids, two secand positive grids, and two anodes, a resonant input circuit tuned to the frequency of the oscillations and coupled to said control grids, an output load circuit interconnecting said anodes, said control grids being atnegative potential or at cathode potential, and all grids except the control grids being at cathode potential with respect to radio frequencies, said grids and anodes being so constructed and arranged and the direct current voltages applied thereto being so chosen that cathode electrons, at least for the greater part,

. perform oscillatory movements through said first positive grids and within the regions defined by the control grids and the said negative grids, the electrons passing several times through the said first positive grids and the frequency of these oscillatory movements being so related to the operating frequency of the circuit that a decrease in input damping and an increase in dynamic mutual conductance is obtained.

MAXIMILIAAN JULIUS OTTO STRUTT. ALBERT VAN nan ZIEL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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