US2314916A - Circuit for the amplification and/or frequency-transformation of electrical oscillations of ultra high frequency - Google Patents

Description

March 1943- G. H. P. ALMA ET AL 2,314,916

CIRCUIT FOR THE AMPLIFICATION AND/OR FREQUENCY-TRANSFORMATION OF ELECTRICAL OSCILLATIONS OF ULTRA HIGH FREQUENCY Filed May 9, 1941 I Fig.1 PC9245 2 4; f5 or; I

INVENTORS GER/W7 H. R ALMA MAX/M/L/AA/V 0. STRUT? .5. BY 4mm v DER z/a Patented Mar. 30, 1943 CIRCUIT FOR THE AMPIJFIOATION AND/OR FREQUENCY-TRANSFORMATION OF ELEC- TRICAL OSCILLATIONS F ULTRA HIGH FREQUENCY Gerrit Hendrik Petr-us Alma, Maximiliaan Julius Otto Strntt, and Aidert van der- Ziel, Eindhoven,

Netherlands; vested in the Alien Property Custodian Application May 9, 1941, Serial No. 392,833

In the Netherlands June 12, 1940 18 Claims. (01. 179-471) This invention relates to a circuit arrangement for the amplification and/or frequency-transformation of electrical oscillations of ultra-high I frequency. and to a discharge tube adapted to be used in such a circuit. I

With ultra-high frequencies a virtual ohmic resistance of comparatively low value generally occurs intermediate the control grid and the cathode of a discharge tube. said resistance bringing about a considerable damping of the input circuit. The occurrence of this virtual ohmic resistance is principally to be attributed -to two causes. In the first place the inductances of the supply conductors to the various electrodes constitute rather appreciable impedances for ultra-high frequencies. High-frequency voltages occur across these impedances and give rise to currents through the capacities of the tube.

Thus, the alternating current of the cathode will generally bring about a voltage across the inductance of the cathode supply-conductor, which voltage leads 90 relatively to the alternating voltage of the control grid. This voltage brings about a current from the control grid to the cathode via the control grid-cathode capacity, which current is in phase with the alternating voltage of the control grid and may consequently be regarded as a result of an ohmic resistance existing between the control grid and the cathode. Similar currents flow from the control grid via the capacitiesof the tube to other electrodes. The resulting total damping of the input circuit is referred to as conductor damping.

It is known to decrease the conductor damping by using a tube whose cathode is provided with two separate supply conductors, one of these supply conductors being included in the input circuit and the other in the output circuit. In this case the voltage brought about by the output current across the cathode supply-conductor included in the output circuit is not active in the input circuit and consequently cannot bring about damping of the input circuit.

In the second place, with ultra-high frequencies the transit time of electrons is of the same order of magnitude as the cycle of the oscillations to be amplified, so that a. rather appreciable phase-displacement may occur between the electron current flowing through the apertures oi the control grid and the alternating voltage of the control grid. Due to this phase-displacement, an influence current flows from the control grid to the cathode, which current comprises a component which is in phase with the alternating voltage of the control grid and may therefore be regarded as a result of an ohmic resistance existing between the control grid and the cathode. The reciprocal value of this ohmic resistance is referred to as transit-time damping or electron damping.

I It has been found as will be explained hereinafter that the electron damping which occurs between the control grid and the cathode may be considerably reduced and under certain conditions be made even negative by the use of a circuit in which a grid of positive polarisation voltage is provided intermediate the control grid and the cathode.

For a better understanding oi the invention, reference will be had to the accompanying drawing in which Fig. l discloses a circuit which utilizes a tube having a space charge or suction grid whereby the electron damping occurring between control grid and cathode maybe reduced; Figs. 2 to 6 disclose various circuits which embody the invention of the present application and which are improvements over the circuit oi Fig. 1; Fig. 8 shows the manner oi converting the circuits of Figs. 2 to 8 to frequency-changing stages; and Fig. 7 shows a preferred form of construction and electrode arrangement of a discharge tube utilized in the circuit of Figs. 2 to 6.

Referring first to Fig. l the discharge tube l is shown to comprise a cathode 2, a control grid 3, a screen grid 4 and an anode 5. Intermediate the control grid 3 and the cathode 2 there is connected an input impedance 8 and between the anode 5 and the cathode 2 an output impedance I. Further, the tube comprises a grid 8 between the control grid 3 and the cathode 2, said grid being connected to the cathode 2 via a condenser 9, which practically constitutes a short-circuit for the frequency of the oscillations to be amplified and having a positive polarisation voltage supplied to it via a resistance it. Such a positive grid intermediate the control grid and the cathode is usually indicated as spacecharge grid or suction grid. The electron damping produced between the control grid 3 and the cathode 2 is considerably less than with a tube without a suction grid and may be even negative with a correct choice oi the polarisation voltages of the electrodes.

The occurrence of negative electron damping between the control grid and the cathode in a discharge tube comprising a suction grid may probably be explained as follows. When the control grid 3 has a great negative bias, all the electrons passed by the suction grid 8 will reverse their direction in the vicinity of the control grid and flow again to the suction grid. The electrons which reverse their direction constitute a space-charge in the vicinity of the control grid, inducing an equal positive image charge on the control grid. If, now, the control grid is made less negative, part of the electrons will be passed by the control grid. Consequently, the said space charge is reduced, resulting also in a decrease of th positive image-charge accumulated in the control grid so that there is a range of biasses of the control grid within which the charge of the control grid becomes less positive when the bias is made more positive. In other words. in this range the control grid has a negative capacity relatively to the cathode. In this case an alternating voltage set up between the control grid and the cathode will bring about a current from the control grid to the cathode whlch'lags 90 relatively to the said alternating voltage. This current is transferred by the electrons flowing from the cathode to the space charge. Now, with ultra-high frequencies .the transit-time of these electrons is of the same order of magnitude as the cycle of the oscillations to be amplified. The transfer of the said current will consequently be efi'ected with an appreciable time-lag, which means that the current will lag more than 90 relatively to the alternating voltag of the control grid and consequently comprise a component which is in anti-phase with the alternating voltage of the control grid This component may be regarded as a result of a negative ohmic resistance produced between the control grid and the cathode.

Due to the small or negative electron damping, the resulting input damping in a discharge tube having a suction grid is considerably smaller than in the usual discharge tubes so that it is particularly adapted for the amplification of oscillations of ultra-high frequency.

The invention has for its purpose further to decrease the input damping in a circuit arrangement for the amplification and/or the frequencytransformation of electric oscillations of ultrahigh frequency. in which use is made of a discharge tube having a suction grid.

According to the invention, this object is achieved by providing the suction grid with two separate supply conductors, the suction grid being connected for high-frequency via one of these supply conductors to the control grid and via the other supply conductor to the output electrode.

The invention is based on recognition of the fact that in a discharge tube having a suction grid the conductor damping produced between the control grid and the cathode is principally brought about by the inductance of the supply conductor to the suction grid. This may be explained as follows by reference to Fig. 1.

The electron current emitted by the cathode 2 is always exclusively determined by the voltage of the suction grid I. Since the suction grid is connected for high frequency via a minimum impedance to the cathode, the cathode current, if taken ro ghly, will be constant. This constant electron current is divided by the control grid 3 into two parts, viz. one part which flows through the apertures of the control grid to the anode 5 and another part which inverses its direction and is collected by the suction grid. If the control rid 3 is made less negative, the electron current to the anode will increase, whereas the electron current to the suction grid decreases by the same value. If, on the other hand, the control grid is made more negative the electron current which fiows to the anode decreases, where as the electron current which flows to the suction grid increases by the same value. If an alternating voltage is set up at the control grid, alternating currents of equal value but of opposite phase will consequently flow in the anode circuit and in the circuit of the suction grid. In the part of the cathode lead which is common to the anode circuit and the circuit of the suction grid these two alternating currents neutralise each other so that no alternating current flows in this part of the cathode lead. Consequently, the alternating current of the anode does not flow from the cathode to the anode, as in the usual discharge tubes, but i from the suction grid to-the anode. In other words, the suction grid has taken over the function of the cathode for alternating currents of the frequency to be amplified.

The alternating current flowing from the suction grid to the anode brings about a high-frequency voltage across the inductance of the connection lead between the suction grid and the point II in which the anode circuit and the circuit of the suction grid come together. This voltage supplies a current through the series-connection of the input impedance 8 and the control grid-suction grid capacity indicated by I! in the figure, which current leads approximately relatively to the said voltage and is consequently in phase with the alternating voltage of the control grid. The current may be regarded to be brought about by an ohmic resistance existing between the control grid and the suction grid and bringing about damping of the input impedance 8. Now, th invention consists in that this conductor damping is suppressed by the use of a suction grid having two separate supply conductors so that the voltage brought about by the output alternating current across the supply conductor to the suction grid is no longer active in the input circuit.

Referring now to the circuit arrangement shown in Fig. 2 which embodies one form of the present invention the suction grid 8 is provided with two separate supply conductors I3 and I4.

The suction grid is connected via the supply conductor II and the input impedance 6 to the control grid 3 and via the other supply conductor H and the output impedance 1 to the anode 5. The alternating current or the anode does now produce a voltage across the inductance of the supply conductor H. but this voltage is not active in the circuit constituted by the input impedance 8 and the control grid-suction grid capacity and consequently cannot lead to damping of the input circuit.

The suction grid 8 is connected for high-frequency via a minimum impedance to the cathode.

In the circuit shown in Fig. 2 this connection ismade via the supply conductor l3 from which the suction grid is also connected to the control grid.

On the other hand, in the circuit shown in Fig. 3 the suction grid is connected to the cathode via the supply conductor 14 via which the suction grid is connected to the anode. The latter circuit is in general preferable and this on the ground of the following considerations.

'The cathode 2 is preferably earthed, that is to say connected to the chassis of the amplifier. The extremity of the output impedance 1 which is connected to the anode generally has a rather considerable capacity relatively t the chassis, which capacity is indicated by IS in Figs. 2 and 3. Consequently, a component of the alternating current of the anode will fiow from the suction grid via the connection of the suction grid and the cathode and via the chassis and the capacity 15 to the anode. In the circuit shown in Fig. 2 this component fiows via the supply conductor [3 and may then lead to damping of the input circuit. This inconvenience could be eliminated only by electrostatically screening the circuit 1 relatively to the chassis. On the other hand, in

the circuit shown in Fig. 3 the component of the anode current in question flows via the supply conductor l4 so that no damping of the input circuit can occur and screeningof the circuit 1 is redundant. These considerations are particularly of importance with cascade circuits since in these circuits the capacity i8 is also determined by the input circuit of the following stage so that this capacity cannot be completely eliminated even by screening the circuit 1. Consequently, in cascade circuits the suction grid in each stage will preferably be connected via the supply conductor H to the cathode.

In the circuits shown in Figs. 2 and 3 the screen grid 4 is connected via the supply conductor M to the suction grid. Consequently, the voltage brought about across the supply conductor is by the alternating current of the screen grid cannot cause damping of the input circuit. In addition, the advantage is obtained that the voltage set up across the supply conductor i8 gives rise to a current via the conductor IS, the input impedance 6 and the control grid-screen grid capacity, which current is in anti-phase with the alternating voltage of the control grid and consequentLv brings about a reduction of the damping of the input circuit.

If the discharge tube comprises a secondaryemission electrode, a similar damping-reduction action may be obtained by connecting the secondary-emission electrode for high-frequency to the suction grid via that supply conductor via which the suction grid is connected to the control grid. This case is represented in Fig. 4.

In the circuit according to Fig. 4 use is made of =supply conductor is to the suction grid. The current of the secondary-emission electrode brings about a high-frequency voltage across the supply conductor l3 which voltage produces a current through the input impedance and the control grid-suction grid capacity. Due to the fact that the current of the secondary-emission electrode is in anti-phase with the alternating voltage of the control grid oi the said current flowing through the control grid-sucticn-grid capacity will also be in anti-phase with the alternating voltage or the control grid and consequently exert a damping-reducing action on the input circult.

The said damping-reducing efiects may, it desired, be further increased by artificially increasing the screen grid-control-grid capacity or the control grid-suction-grid capacity by connecting an additional condenser in parallel, or by providing additional inductances in series with the supply conductors of the suction grid. Of the latter case an example is given in the circuit shown in Fig. 5.

In the circuit shown in Fig. additional impedances Z1 and Z: are provided in series with the supply conductors i3 and I4 for the suction grid. To obtain a greater damping reduction of the input circuit, these impedances are generally made in the form of inductances. With the amplification of very high frequencies, during which considerable phase-displacements of the anode current or oi the current oi the secondary-emission electrode may occur due to the finite transit time of the electrons, these phase-displacements may, however, be taken into account with the choice of the impedances Z1 and Z: with a view to obtaining the phase, required for the desired damping reduction, of the voltages which occur across these impedances and the supply conductors of the suction grid connected in series therewith. It is evident that the use of the impedance Z2 is only effective if the current of one or more positive electrodes fiows through the supply conductor is, that is to say. for example in the case that the tube has a secondary-emission electrode.

Fig. 6 shows a circuit according to the invention in which an additional control-grid ILconnected via a circuit ll to the cathode, is provided between the suction grid 8 and the cathode I. This circuit may be used in two manners and this either as a frequency-changing stage or for obtaining double amplification. When used a a frequency-changing stage in a superheterodyne receiver the circuit H has supplied to it the oscillations is locally generated while in the circuit 6 are produced the received oscfllations. Due to the presence of two separate supply conductors tor the grid 8, the circuit 0 is damped to a considerably 1w extent than in the mixing circuits hitherto used. The circuit 1 is in this case tuned to the desired intermediate-frequency J1.

It the circuit in question is used to obtain double amplification the circuits l,.l and II are amplified voltage of frequency I- being produced across the circuit 1.

The circuits shown in Figs. 2. 3, 4 and I may be adapted as frequency-changing stages, as shown in Fig. 8 by including an impedance II in the circuit at the control grid 8 in series with the circuit a, via which impedance there are imthe oscillations locally generated by a source 2i, and by tuning the circuit 1 to the desired intermediate-frequency.

Fig. 7 shows a cross-section through the electrode system oi a discharge tube which is adapted to be used in the circuits shown in Figs. 2 and 3. This tube comprises a directly-heated cathode 2. a control grid 3, a screen grid 4 and an anode 5. Between the control grid 3 and the cathode 2 is provided a suction grid I constituted by four rods placed in parallel with the cathode. Further, the space enclosed by the control grid is divided into two parts by a certain number of rods is which are preferably given a negative potential relatively to the cathode and which prevent electrons which inverse their direction in the vicinity of the control grid from propagating to the other side of the cathode. According to the invention, the suction grid 0 is provided with two separate supply conductors; as .is indicated diagrammatically bythe dottedi lines is and I4.

We claim:

1. A circuit for the transmission of electrical oscillations of ultra-high frequency, which comprises a discharge tube provided with at least a cathode, a control grid and an output electrode, a suction grid having a positive bias being provided intermediate the control grid and the cathode, in which circuit the suction grid is provided with two separate supply conductors, the suction rid being connected for high-frequency via one of these supply conductors to the control grid and via the other supply conductor to the output electrode.

2. A circuit as claimed in claim 1, in which the biasses of the electrodes are so chosen that a negative electron damping occurs between the control grid and the cathode.

3. A circuit as claimed in claim 1, in which the suction grid is connected to the cathode via the supply conductor, via which the suction grid is connected to the anode.

4. A circuit as claimed in claim 1, wherein the discharge tube comprises also a screen grid, the screen grid being connected to the suction grid via the supply conductor, via which the suction grid is connected to the anode.

5. A circuit as claimed in claim 1, wherein the discharge tube comprises also a secondary-emission electrode, the secondary-emission electrode being connected to the suction grid via the supply conductor, via which the suction grid is connected to the control grid.

6. A circuit as claimed in claim 1, in which an impedance is provided in series with at least one of the supply conductors of the suction grid, said impedance being of such nature that a further damping-reduction of the input circuit is obtained.

7. A circuit as claimed in claim 1, in which a second control grid is provided between the suction grid and the cathode.

8. A circuit for the transmission of electrical oscillations of ultra-high frequency, comprising a discharge tube provided in. the order named with at least a cathode, a space charge grid, a signal control grid and an anode, two separate supply conductors connected to the space charge grid, means for connecting the space charge grid for high-frequency via one of said conductors to the signal control grid, and means for connecting the space charge grid for high-frequency via the other of said conductors to the anode. l

9. A circuit for the amplification of electrical oscillations of ultra-high frequency, comprising a discharge tube provided in the order named with at least a cathode, a space charge grid, a signal control grid and an anode, input and output circuits connected respectively to the signal control grid and to the anode, two separate supply conductors connected to the space charge grid, means for connecting the space charge grid for high-frequency via one of said conductors and the input circuit to the signal control grid, and means for connecting the space charge grid for high-frequency via the other-oi said conductors and the output circuit to the anode.

10. A circuit for the amplification of electrical oscillations of ultra-high frequency, comprising a discharge tube provided in the order named with at least a cathode, a space charge grid, a signal control grid and an anode, two separate supply conductors connected to the space charge grid, means for connecting the space charge grid for high-frequency via one of said conductors to the signal control grid, means for connecting the space charge and for high-frequency via the other of said conductors to the anode, and means .for connecting the space charge grid to the cathode via said other conductor.

11. A circuit as defined in claim 10 wherein the tube is provided with a screen grid, the latter being connected for high frequency to the space charge grid via the conductor which is connected to the anode and cathode.

12. A circuit as defined in claim 10 wherein the tube is provided with a. secondary-emission elec trode, the latter being connected for high ire: quency to the space charge grid via the conductor which is connected to the control grid.

13. A circuit as defined in claim 10 wherein the tube is provided with a screen grid and with a secondary-emission electrode, the former being connected for high frequency to the space charge grid via the conductor which is connected to the anode and cathode and the latter being connected for high frequency to the space charge grid via the conductor which is connected to the control grid.

14. A circuit as defined in claim 10 wherein an impedance is provided in series with at least one of the supply conductors of the space charge grid.

15. A circuit as defined in claim 10 wherein the tube is provided with a secondary-emission electrode, the latter being connected for high frequency to the space charge grid via the conductor which is connected to the control grid and wherein an impedance is connected in series with each supply conductor of the space charge grid.

16. A circuit for the amplification of electrical oscillations of ultra-high frequency, comprising a discharge tube provided in the order named with at least a cathode, a first signal control grid,

0. space charge grid, a second signal control grid and an anode, resonant circuits connected to both signal control grids and to the anode, two separate supply conductors connected to the space charge grid, means for connecting the space charge grid for high-frequency via one of said conductors to the second signal control grid, means for connecting the space charge grid for;

high-frequency via the other of said conductorsto the anode, and means for connecting the space charge grid to the cathode via said other conduc-. tor.

17. A circuit as defined in claim 16 wherein each of the three resonant circuits is tuned to the frequency of the oscillations to be amplified.

18. A circuit for the frequency-transformation of electrical oscillations of ultra-high frequency, comprising a discharge tube provided in the order named with at least a cathode, an oscillator grid, a space charge grid, a signal control grid and an anode, a circuit tuned to the frequency of a local oscillator connected to the oscillator grid, a circuit, tuned to the frequency of the received oscillations connected to the signal grid, a circuit tuned to the diiference frequency connected to the anode, two separate supply conductors connected to the space charge grid, means for connecting the space charge grid for highfrequency via one of said conductors and the tuned input circuit to the signal control grid, means for connecting the space charge grid for high-frequency via the other of said conductors and the tuned output circuit to the anode, and means for connecting the space charge grid to the cathode via said other conductor.

GERRIT HENDRIK PETRUS ALMA. MAXIMILIAAN JULIUS O'I'IO STRUTI. ALDERT VAN DER ZIEL.

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