US2298673A - Double cathode electron discharge device and circuits - Google Patents

Description

Oct. 13, 1942. c. H. BROWN irrm.

DOUBLE CATHODE ELECTRON DISCHARGE DEVICE AND CIRCUITS Original Filed Oct. 28, 1935 2 Sheets-Sheet 1 AFJNPUT our/207 B SWM RR m f" T HA NS WE? NMW OUT/ 0 ATTORNEY oct.1s,1a42. c. H. BROWN HAL 2,29 1

DOUBLE CATHODE ELECTRON DISCHARGE DEVICE AND CIRCUITS Original Filed Oct. 28, 1935 2 Sheets-Sheet 2 INPUT MODULA TING VOLTAGE m l l OUTPUT AMPLITUDE LIMITER) INPUT SIGNAL NTENNA INVENTOR- CHARLES H. BROWN AND BY WA TER AN B .ROBERTS ATTORNEY V Patented Oct. 13, 1942 DOUBLE CATIIODE ELECTRON'DISCHARGE DEVICE AND CIRCUITS Charles H. Brown, Brooklyn, N. Y., and Walter van B. Robe rts, Princeton, N. 1., assignors to Radio Corporation of America, a corporation of Delaware Original application October 28, 1935, Serial No. 6,980, now Patent No. 2,121,087, dated June 21, 1938. Divided and this application August 25, 1936, Serial No. 97,722

12 Claims. (Cl. 179-1715) This invention is a division of our copending application Serial No. 46,98i), flied October 28, 1935, now United States Patent 2,121,067, granted June 21, 1938, and relates to cold cathode negative conductance devices functioning by means of secondary emission of electrons.

The present invention provides, among other things, an improved oscillator system employing an electron discharge device containing two cold cathodes oppositely disposed with respect to a central positive'charged anode in the form of a metal ring. The cathodes are treated, or designed to emit copious secondary electrons when bombarded by other electrons, and the resulting electrons are prevented from immediately striking the anode by a coil arrangement surrounding the device, which produces a guiding magnetic field perpendicular to the plane of the anode. In accordance with the invention, means are provided for modulating the amplitude, phase or frequency of the generated oscillations in a highly efficient manner, and for preventing reaction upon the frequency of the oscillations due to the load.

In the accompanying drawings:

Fig. 1 illustrates an oscillator circuit in accordance with the invention, whereby modulation is achieved, and output energy taken from the vacuum tube without reaction upon the frequency of the generated oscillations:

Figs. 2, -3, 4 and 5 illustrate various double resonance oscillator circuits of the invention having means for modulating the generated oscillations; and

Fig. 6 illustrates another oscillator embodiment of the invention.

Fig. 1 shows an oscillation generator system provided withmeans for modulating the amplitude of the generated oscillations, and an output circuit'which is electron coupled to the frequency determining elements whereby there is obviated any possibility of reaction by the load upon the frequency of the generated oscillations. Cathodes C, C are each provided withone or more perforations through which intermittent pulses of electrons flow to working anodes A",

ondary electrons as may be emitted from anodes A" caused by bombardment, from landing on screen grids SG. Modulation, if desired, may be effected by impression modulating voltages upon the suppressor grids G in parallel by means of an audio frequency signal applied to transformer T.

Fig. 2 illustrates a highly advantageous arrangement which requires much less power for modulating the oscillations produced in a double resonance system than other constructions. Here the collector anode A. which is in the form of a ring, is surrounded-by another ring G in I the form of a grid, the latter of which is maintained at a suitable negativepotential by a battery 3. The effective potential of anode A is thus reduced, and its effective value is altered by varying the potential of grid G by the application of a modulating voltage from dicated as being coupled to resonant circuit R to obtainenergy at a fundamental frequency, it will be appreciated that energy at double the fundamental frequency can be obtained by including in series with battery B a circuit tuned to such double frequency, and coupling the output to said last tuned circuit.

Fig. 3 illustrates another method by which the strength of oscillations may be modulated. As in Fig. 2, the battery voltage of B is adjusted not to a-point of maximum oscillation strength, but to a point such that a change in voltage in one sense will increase the oscillation strength, and in the opposite sense decrease it. The input modulating voltage, backed up by as much power as necessary, is then impressed in series with battery B. 1

In Fig. '4 is shown a still difierent method of modulating the oscillations produced by the double resonance oscillator wherein the modulating signal from the input is passed through a coil CL which forms part or all the field coil M. Since the strength of oscillation depends upon the magnetic field, a modulation of the magnetic field produces a modulation of the generated oscillations. If desired, there may be employed a separate coilsurrounding envelope E and coil M, which may be employed for modulating the oscillations produced, instead of or in conjunction with the modulating circuit illustrated in Fig. 4.

Fig. 5 is another embodiment of the invention and shows a double resonance oscillator adapted to be modulated in phase or frequency. This is accomplished by coupling the resonant circuit R to the input of an electron discharge device T1 whose effective input capacity between terminals XX is varied in accordance with signals as described in United States Patent No. 1,917,394, granted July 11, 1933, to Walter van B. Roberts. Since there is an interelectrode capacity between the anode and grid of electron discharge device T1, the input impedance across the terminals X-X is capacitive in nature and will be found to vary with variation of the load impedance across the anode and cathode of T1. This operation is briefly as follows: The effective input capacity of T1 across terminals X-X varies in accordance with the load resistance of the anode circuit (of Ti). and the resistance of the tube T2 used as load resistance for tube T1 is varied in accordance with the signals. Output energy from the double resonance oscillator may be taken in any of the ways shown in the previous figures, and may be passed through an amplitude limiter, if desired, and power amplifier, to any type of utilization circuit, such as an antenna, as indicated in the drawings.

Fig. 6 shows a double resonance oscillator wherein th left hand electrode C is not used as a cathode. A separate source of potential BB maintains electrode C negative at all times so that electrons from cathode 0' do not reach it. Electrode C' is then the cathode and in conjunction with tuned circuit R", located between C and anode A, maintains oscillations. The negative potential applied to C from battery BB, however, influences the frequency of electron oscillation, and consequently adjustments of electron frequency may be made by varying the bias of C rather than by varying the voltage of the anode battery B. It will be appreciated that in this figure the electrons can be made to oscillate over a portion of the distance between C and C rather than the entire distance between these two electrodes merely by adjusting the negative potential on C. With such an arrangement the production of harmonic frequencies will be intensified due to the fact that there will be approximately linear acceleration and deceleration in the space between the anode A and cathode C' but with much larger deceleration near the electrode C, thus producing hoth odd and even harmonics. An input circuit may be used for impressing modulating potentials upon electrode 0, as shown. Such a modulating arrangement has the advantage of modulating the oscillations without drawing appreciable power from the modulation source, as described in connection with Fig. 2. Battery BB may, of course, be replaced by any suitable source of voltage for eifecting the required bias effect on electrode C.

It should be understood that the systems of Figs. 1 to 5, inclusive, can be stabilized as to frequency of the generated oscillationsmerely by replacing the resonant circuit R shown in any of the figures by a mechanical resonator such as a piezo-electric crystal, a line a half wave long, or a magneto-striction rod, in accordance with the teachings of our copendlng application, supra. It is also to be understood that in all the figures output energy of a fundamental frequency orodd harmonic may be obtained by coupling the load to resonant circuit R, or its equivalent, while output energy of an even harmonic may be obtained by coupling the load to a suitably tuned resonant circuit placed in series with the anode connection.

Furthermore, the arrangements of the present invention may be used not only as generators of oscillations for transmitting or receiving purposes, but also as amplifiers, detectors, or electron multipliers. It is known that in a structure operating upon the principles underlying any of the figures, the anode current varies with the effective anode potential, passing through one or more maxima as the anode battery voltage is increased. If the anode battery voltage is adjusted to produce a maximum of anode current, then by the very definition of the word maximum" it is evident that a change of anode voltage in either sense will reduce the anode current. This applies whether the cathodes C, C are excited from an external source of high frequency voltage or are maintained at a fluctuating potential by self-oscillation. The structures shown in Figs. 2 and 6, for example, are particularly adapted to be used as detectors or amplifiers, inasmuch as the effective anode potential may be varied by varying the potential of a negatively biased electrode which does not draw current and hence'does not absorb power. In Fig. 2 the negatively biased electrode is grid G and in Fig. 6 it is electrode C. If signal voltages, such as modulated radio frequency of a frequency preferably relatively low compared to the frequency of excitation of the cathodes, are impressed upon the negatively biased element, the anode battery being adjusted for a maximum anode current, the average anode current will be reduced by an amount dependent upon the strength of the signal voltage. This produces a component of anode current which may be called the rectified current.

On the other hand, if the anode battery is adjusted not to a point of maximum anode current but to a point where anode current increases with increasing anode voltage, then signailing voltages impressed upon the negatively biased electrode will cause changes of anode current in the sense that the more negative the control element the less the anode current and vice versa. This is exactly what occurs in an ordinary vacuum tubes and hence the arrangement may be used as an amplifier in the same way as an ordinary tube. But, if the anode battery voltage is adjusted to a point where increasing voltage causes a decreased anode current, then the more negative the control element the larger the anode current, which state of affairs corresponds to an amplifier having a negative transconductance between the control grid and anode. A device having a negative transconductance is useful in producing oscillations and for other purposes known in the art, as well as for ordinary amplification.

Any of the circuits shown in the accompanying figures may be used for electron multiplication as follows: The oscillation or resonant circuit R may be replaced by a transformer secondary winding connected between the cathodes C, C having voltage induced in it by a high frequency current from an external source passing through a primary coil coupled thereto. It now the anode battery voltage is adjusted so that the electron time of flight between the cathodes C, C is not exactly equal to a half period of the exciting voltage, the secondary emission will not build up to any great extent from random electrons within the structure because the electron flow or oscillation will not long remain in step with the exciting voltage. However, if a beam of electrons is-admitted to the structure, for example, through a hole in.one of the cathodes, there will be a certain number of round trips between the cathodes, each with an increase in the number of electrons passing back and forth, so that the anode current will increase in proportion to the strength of the incoming beam of electrons. This action constitutes the effect desired of an electron multipler device. If instead of an output current proportional to the input electron stream, it is desired to have an output electron stream proportional to but greater than the input stream, a perforated electrode may be inserted in the tube to draw of! electrons through the hole therein to form an electron stream to be utilized for whatever purpose desired.

Fig. 6 can, with slight changes, be used either as a rectifier or as an amplifier. In Fig. 6, if radio frequency excitation is impressed on C' with a frequency related to the voltage B so that the battery current varies with battery voltage, then the battery current may be varied in accordance with signals impressed on the negative electrode C and power may be derived from the battery or anode lead circuit. If the adjustment is such as to make the anode current a maximum,

electrons at a ratio greater than unity when impacted, means for causing an electron cloud to oscillate between said surfaces to creat repeated multiplying impacts therewith, means for diverting a portion of said cloud into a space apart a from that bounded by said surfaces, and means there will be a rectifying action, but if the adjustment is such that anode current changes are in a sense corresponding to the change of potential of electrode C, there will be a true repeating or amplifying action and p the transconductance between C and the anode circuit will be positive or negative according to the selection.

of exciting frequency and battery voltage. An advantage of such an arrangement is that little or no power is required to vary the potential of electrode C in accordance with incoming signals.

Similar reasoning applies to the system of Fig. 2, which can also be used as an amplifier and rectifier and wherein input signals are applied to grid G instead of to electrode C of Fig. 6.

What is claimed is:

1. In combination, an electron discharge device oscillator comprising an evacuated. envelope containing an anode and a pair of surfaces capable of emitting electrons on impact oppositely disposed with respect to said anode, each of said surfaces having an aperture therein, a plate collecting the electrons passing through the aperture of each surface, a grid between each plate and its nearest surface, a resonant circuit external to said envelope coupled between said surfaces, a source of energy connected to said anode and resonant circuit for maintaining said anode at a positive potential relative to said surfaces, means for producing an electricalfleld perpendicular to the plane of said anode, an output circuit coupled to said plates, and means for modulating the oscillations produced by said oscillator.

2. A system in accordance with claim 1, including a suppressor electrode between each grid and its nearest surface, means for maintaining said grids at a positive potential and said suppressor electrodes at a negative potential relative to said surfaces, a connection between said suppressor electrodes, said modulating means applying modulating potentials to said suppressor electrodes in parallel relation.

for absorbing power from said diverted portion within said space.

4. An electron multiplier comprising a pair of opposed surfaces capable of emitting secondary electrons at a ratio greater than unity when impacted, means for causing an electron cloud to oscillate between said surfaces to create repeated multiplying impacts therewith, means for dividing said cloud at the plane of one of said surfaces, means for abstracting one of the divided portions from the space bounded by said surfaces, and means for absorbing power from the abstracted portion.

5. An electron multiplier comprising a pair of opposed surfaces capable of emitting secondary electrons at a ratio greater thanunity when impacted, means for causing an electron cloud to oscillate between said surfaces to create repeated multiplying impacts therewith, means for dividing said cloud at the plane of one of said surfaces, means for abstracting one of the divided portions from the space bounded by said surfaces, means for absorbing power from the abstracted portion, and a work circuit for utilizing the power obtained.

6. In an electron multiplier wherein electrons are directed against a cathode surface to produce secondary emission therefrom, the method of power production comprising oscillating electrons against and away from said surface to produce an electron cloud augmented by secondary electrons at each impact therewith, abstracting from the cloud through apertures in said surface a definite proportion of the electrons therein, and absorbing the energy from the abstracted electrons.

7. In an electron multiplier structure wherein an electron cloud is oscillated against and away from a surface to produce secondary emission therefrom upon impact therewith, the method of abstracting power from said cloud which comprises feeding energy to said cloud and abstractingenergy from said cloud within diiferent spatial boundaries.

8. In an electron multiplier structure wherein an electron cloud is oscillated against and away from a surface to produce secondary emission therefrom upon impact therewith, the method of abstracting power from said cloud which comprises dividing said cloud at each impact feeding energy to one portion of said cloud to continue multiplication and abstracting useful energy from the other portion.

9. In an electron multiplier structure wherein an electron cloud is oscillated against and away from a surface to produce secondary emission therefrom upon impact therewith, the method of abstracting power from said cloud which comprises feeding energy to electrons traveling along one set of paths, changing the paths, and abstracting power from said electrons while in said changed paths.

10. In an electron multiplier structure wherein an electron cloud is oscillated against and away from a surface to produce secondary emission therefrom upon impact therewith, the method of abstracting power from said cloud which comprises feeding energy to electrons traveling along one set of paths, continuously diverting a portion oi said cloud into a different set of paths, and absorbing energy from said electrons while in said diflerent paths.

11. In an electron multiplier structure wherein an electron cloud is oscillated against and away 1mm a surface to produce secondary emission therefrom upon impact therewith. the method 0! abstracting power from said cloud which comprises feeding energy to said cloud to maintain oscillation of the cloud across a space in a predetermined path, shitting the oscillation to a different predetermined path, and absorbing power from the electrons in the latter path.

12. In combination, a pair of opposed electrodes capable of emitting secondary electrons at a ratio greater than unity. a second pair of opposed electrodes incapable of emitting secondary electrons, adjacent said iirst pair, means for feeding energy to electrons in the space between said ilrst pair of electrodes to produce electron multiplication by cyclical impact therewith. and means associated with said second pair of electrodes for absorbing power from said electrons.

CHARLES H. BROWN, WALTER VAR BROBERTS.

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