US2204428A - Electron multiplier - Google Patents

Description

June 11,1940. RMDLLER Er AL v 2,204,428

ELECTRON NULTIP LIER Filed D90. 4, 1936 Patented June 11, 1940 UNITED; STATES ELECTRON .Rolf Miiller, Berlin-Zehlendorf, and Fritz Below,

Klein Machnow Post Berlin-Zehlendorf, ,Ger-

many, assignors to the firm of Fernseh Aktien- Gesellschaft, Zehlendorf, near Berlin, Germany Application December 4, 1936, Serial No. 114,286

I In Germany January 31, 1936 7 er"; v I '4 Claims.

' In modulating a carrier frequency-with the aid of a photo-electric tubeit is generally required that the amplitude ofthe carrier frequency be odulated with respect to a given constant basic value. In some cases it is desired that this basic value bekept as small as possible, say even equal to Zero. 9 In order to attain this'endthe circuit of the irivention'is so arranged thata screening device adapted to screen off the carrier frequency is in- "terposed between the electrode to which the carrier frequency'is applied and the anode The carrier frequency is, for example, applied to an "electrode which isseparated from the anode by one or more secondarilyemitting electrodes constituted as screen electrodes. High frequency will therefore only be produced at the anode "when the photo cathode is illuminated, as long as (even in non-illuminated condition) a small capacity disposed between the first electrode carrying, the carrier frequency and the anode does not- 1 permit the high frequency to pass into the output circuit. This capacity however, in practice, is so greatly reduced by the screen arrangementthat it nolonger plays any part inmost instances. I Thisarrangement however would also have the drawback that low frequency would be produced "in'ithe output circuit in addition to the modulated carrier frequency. In order to prevent this, two similar electrode systems are incorporated into the photo-electric tube in accordance with the invention and these obtain their electrons from the'same photo cathode. The corresponding first electrodes of both systems are controlled in pushpull fashion from the carrier frequency generator through agency of a transformer. The result of this is that only one system is always in operathe corresponding half cycle is negatively biased to such an extent that no electron current can flow. The half wave trains of. the modulated united at the output into a complete wave train.

The low frequency produced within the tube isequal in phase with both halves and is accentuated.

55 The drawing illustrates embodiments of the tion. 'The electrode of the other system during high frequency originating from both systems are subject matter of the invention. Referring to the drawing: Fig. 1 represents a photo electric tube according to the invention. g Fig. 2 shows a photo electric tube containing two separate electrode systems. Fig. 3 is a circuit containing .a photo-electric tube according to Fig. 2.

The photo electric tube of photo cathode 2 and an electrode systemrcomprising grids 3, 4, 5, and anode 6. The "grids 4 and'5 and the anode 6 receive a potential from'a battery or adevice. connected to a power line which potential increases from grid to grid. -The carrier frequency generator is connected to grid 3. The grids 4 and 5 are constituted as screen gridsand have such a shape thatthe electrons do not find any free passage around grids 4 and 5. A special wall coating 1 may also beprovided for this purpose, connected with diaphragm-like rings and carrying about 20 volts with respect to the cathode! This wall coating at the same time serves to prevent negative wall charges. The electrodes 4 and 5' are either connected with the grids 4 and 5 or led outside by means of separate terminals. In this case it is preferable to give the electrodes 4' and 5' a more positive potential than the last accelerating electrode. The number of accelerating and retarding electrodes may be varied depending on the degree of amplification desired. Furthermore, according to the invention the screen arrangement is appli- ,.cable to tubes in which the electrodes are not formed of grid structures but rather as plates or partly as grids and partly as plates as illustrated in Fig. 2', or even as wires. The best type of screening can be determined after the electrodes have receivedtheir final shape commensurate with attaining'a s high a degree" of amplification aspossible.

The arrangement ,of Fig; 3 showsa photo electric tube I having two electrode systems. "The two grids 3 are controlled in push-pull fashion by a carrier frequency generator 9 through a transformer 8. The grids 4 and 5 are likewise formed as screen grids as shown in Fig. 1. They are attached to tap-off points of battery 16 and may also for example, have the shape shown in Fig.2 wherein a portion of the screen electrodes 4 and 5 are of solid plate construction. They are so shaped that the electrons cannot strike over from the cathode-facing high frequency carrying electrode to the anode 5. From anode 6 the currents are led through a transformer I0, a circuit H and to an amplifier ii. The modulated high fre- 5 Fig. 1 contains a I quency composed of two half-wave trains is obtained from transformer H] whereas the low frequency components are mutually suppressed. 4' and 5 have the same significance as in Fig. 1.

In order to be able to compensate for variations in both systems, condensers l3, which may also, if desired, be replaced by resistances, may for example be connected into the output. By moving the contact terminal M at transformer ID the systems may be so compensated that the low frequencies are removed in an unobjectionable and complete manner. This displacement may for example also be effected by winding the primary coil in two halves so that these two halves may be varied separately or -in common in opposite direction as to their positional inductivity with respect to the secondary coil.

By means of a photo electric tube built in accordance with the invention the constant basic value of the modulated high frequency becomes extraordinarily small. In order to give it a definite desired value or in order to equalize capacity variations, variable neutralizing condensers l5 are preferably used. These are either cross connected or may also be applied direct between the first grid and the anode of one and the same electrode system.

The photo electric tube may also embody two push-pull connected electrode systems without the provision of screen electrodes. This is possible .in all cases in which compensation of the carrier frequency is not involved but rather a compensation of the modulation frequency.

We claim:

1. In combination, an electron discharge device comprising an envelope having therein a source of electrons, an anode, a control electrode disposed between said cathode and said anode and arranged to receive high-frequency potentials,

secondary electron emissive electrodes positioned substantially to enclose said anode to electrostatically shield said anode from said control electrode, at least two of said secondary electron emissive electrodes being disposed between the anode and control electrode, means for energizing said anode to a potential positive with respect to 'said'source of electrons, and means for energizing said secondary electron emissive electrodes to positive potentials having values intermediate that existing between said source of electrons and said anode.

In combination, a source of potentials of relatively high frequency, an evacuated envelope having therein a source of electrons, an anode, a control electrode disposed between said source of electrons and said anode, means for impressing high-frequency potentials from said first-mentioned source on said control electrode, and means for electrostatically shielding said anode from said control electrode while increasing by secondary electron emission the magnitude of the stream of electrons which flows from said source of electrons to said anode, said last-mentioned means including secondary electron emissive electrodes positioned substantially to enclose said anode, at least two of said secondary electron emissive electrodes being disposed between the anode and control electrode, means for energizing said anode to a potential positive with respect to said source of electrons, and means for energizing said emissive electrodes to positive potentials having values intermediate that existing between said cathode and said anode.

3. In combination, an evacuated envelope having therein a source of electrons, an anode, a control electrode positioned between said source and said anode, means for energizing said anode to a potential positive with respect to said source of electrons, means for impressing potentials of relatively .high' frequency on said control electrode to control the stream of electrons flowing from said source to said anode in accordance with said highdrequency potentials, and :means 'for electrostatically shielding said anode from said control electrode while increasing by secondary electron emission the magnitude of the stream which flows from said sourceto said anode, said last-mentioned means comprising secondary electron emissive electrodes positioned substantially to enclose said anode,at least two of said secondary electron emissive electrodes being disposed between the anode and control electrode, said secondary electron emissive electrodes being energized to positive potentials having values intermediate that between said cathode and said anode, a conductivewall coating'on said envelope in cooperative relation to said shielding electrodes to complete an enclosure for said anode, and means 'for maintaining said coating at a substantially fixed potential relative to said source of electrons.

4. An electron discharge device'comprising a source of electrons common to a plurality of output electrodes, a control electrode for each of said output electrodes, each of said outputelectrodes normally having an undesirable capacity with its control. electrode, and electron multiplying electrodes individual to each of said output electrodes for substantially enclosing each of said output electrodes in an electrostatic shield thereby to preclude flow of capacitive .current from each of said output electrodes to its controlelectrode, at least two of said electron multiplying electrodes being disposed between each output electrode and its associated'control electrode, said multiplying electrodes simultaneously increasing by electron emission the magnitude of the streamofelectrons which flows from said source to said output electrodes.

ROLF MoLLER. FRITZ BELOW.

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