US2472779A

US2472779A - Cathode-ray tube amplifier

Info

Publication number: US2472779A
Application number: US729022A
Authority: US
Inventors: Paul J Selgin
Original assignee: Farnsworth Research Corp
Current assignee: Farnsworth Research Corp
Priority date: 1947-02-17
Filing date: 1947-02-17
Publication date: 1949-06-07
Anticipated expiration: 1966-06-07

Description

June 7, 1949.

P. J. SELGIN 2,472,779

CATHODE-RAY TUBE AMPLIFIER Filed Feb. 17, 1947 SIGNAL SOURCE FIG.3

UTILIZATION CIRCUIT INVENTOR PAUL J. SELGIN WTORHEY Patented June 7, 949

UNITED STATES PATENT OFFICE CATHODE-RAY TUBE AMPLIFIER Application February 17, 1947, Serial No. 729,022

3 Claims.

This invention relates to amplifiers and particularly to multistage amplifiers of the type wherein a plurality of amplifying stages are con nected efi'ectively in cascade.

In signaling systems there are numerous cases where signal amplification must be efiected by employing a plurality of amplifying stages, de-

spite the fact that amplifier tubes capable of high gain or amplification have been made available. It is customary to couple a number of amplifying stages in cascade for the purpose of effecting a signal amplification having an order of magnitude approximately equal to the product of the individual amplifications capable of being effected in all of the stages. Usually grid-controlled vacuum tubes are employed in the various stages. The signal to be amplified is impressed upon the control circuit of the first stage and the amplified signal effects derived from the plate circuit. The amplified signal effects then are impressed by suitable coupling facilities upon the control grid circuit of the succeeding stage. The other cascaded amplifier stages are coupled together in a similar manner. The signal amplification is accomplished by conducting current through the tube and a load impedance device from a suitable source of current. For satisfactory operation most vacuum tubes require the impression upon the anode circuits of a voltage of few hundred volts, which is the voltage of the current source.

Where the signals to be amplified are of the alternating type, any type of coupling between the amplifier stages may be used. Preferably, however, the coupling usually is either capacitive or inductive. By reason of this preferred type of coupling, the control grid circuits of all of the amplifier stages may be operated at relatively low voltages relative to ground at which potential the cathode circuits of the tubes usually are operated. However, where the signals to be amplified are of relatively low frequency, commonly considered as direct current signals, inductive or capacitive couplings between stages are unsatisfactory for the reason that the relatively low frequency signals are not readily transmitted by such couplings. It, therefore, becomes necessary to employ direct, or conductive, couplings between the amplifier stages in order to pass the direct current signals. The vacuum tubes of the various stages of adirect current amplifier requirethe same voltages to be impressed between the'respective anodes and cathodes thereof. As a result, the control grid circuits of each of the cascaded amplifier stages, in addition to the first,

must be operated at increasingly higher voltages. Also, to maintain the proper anode-to-cathode voltage of these stages, the voltage of the space current supply therefor must be made increasingly greater. If a considerable number of such amplifier stages are required, there must be provided a space current source which is capable of furnishing voltages extending sometimes to several thousand volts.

It is an object of the present invention, therefore, to provide a multistage amplifier capable of operating with the various stages coupled to one another in cascade without the necessity of employing abnormally high operating voltages.

Another object of the invention is to provide a multistage signal amplifier, the various stages of which may be directly coupled in cascade and the input and output circuits of all of these stages being susceptible of operation at substantially the same potential.

Still another object of the invention is to provide a novel cathode ray deflection tube having a plurality of stages in each of which an electron beam is deflected and in which the output circuit electrodes of one stage may be directly coupled to the input circuit electrodes of a succeeding stage for energization purposes.

A further object of the invention is to provide a novel cathode ray tube of the deflection type wherein a plurality of electron beams are individually deflected over respective target electrodes and in which the target electrodes of one stage are directly coupled by a novel structure, providing a load circuit, to the deflecting electrodes of a succeeding stage.

In accordance with this invention there is provided a multistage signal amplifier of which each stage consists of a cathode ray deflection device. In this type of amplifier, advantage is taken of the fact that once an electron beam is given the required acceleration to project it against a target electrode, the means for deflecting the beam over the target electrode may be operated at approximately the same average voltage as the average voltage impressed upon the target electrode. In such a case the average voltage impressed upon the deflecting and target electrode systems may be no greater than the voltage required to eifect the desired acceleration of the beam. Accordingly, the number of such stages may be coupled together in cascade by a direct connection of the target electrode of one stage to the deflecting electrodes of a succeeding stage. In this manner the electron beams of the succeeding stages may be deflected by systems which are energized from the target electrode system of a preceding stage. The signals to be amplified are directly coupled to the deflecting electrodes of the first stage and the amplified signals are derived from the target electrodes of the last amplifier stage. As many stages of amplification as required may be coupled together in cascade in the manner described without the necessity of progressively increasing the voltages required for operation of the amplifier.

Further, in accordance with the invention, all of the amplifying stages may be incorporated in a single evacuated envelope. The various stages may be separated from one another by suitable shielding barrier plates. Each stage includes an electrode structure for producing an electron beam, a target electrode system for the beam and a deflecting system for deflecting the beam over the target electrode.

In a preferred form of the invention, the target -electrode system consists of a pair of electrodes symmetrically located relative to the undeflected path of the beam and the deflecting system consists of a pair of plate electrodes suitably located on opposite sides of the beam to produce the required electrostatic deflecting field. The target electrodes of one stage are coupled to the deflecting electrodes of a succeeding stage by means of a pair of conductors terminating respectively at the target electrodes and the deflecting electrodes. These conductors are carried through the barrier plate between the two stages. For this purpose the plate is provided with two openings, in each of which is inserted a lead-through bushing in the form of carbon particles suitably held together by a binding material. The conductors are inserted in holes formed substantially through the centers of the lead-through bushings. In this manner the bushings provide a resistive connection between the coupling conductors and the barrier plate which may be connected to a source of voltage. The lead-through bushings comprise a load for the target electrodes so that signal representative voltages may be developed at the target electrodes in accordance with the magnitude of the beam deflection. This voltage thus provides the deflecting voltage for the succeeding stage. If desired, the signal voltage may be impressed upon the first pair of deflecting electrodes and the amplified signal voltage may be derived from the last pair of target electrodes in a similar manner utilizing resistive lead-through bushings.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the accompanying drawing:

Fig. 1 is an elevational view, partly in section, of a cathode ray tube embodying the invention as a four stage amplifier;

Fig. 2 is a transverse sectional view of the tube taken on the line 22 of Fig. 1, and;

Fig. 3 is a schematic representation of a four stage cathode ray tube amplifier illustrating the coupling between stages, the input and output circuits and the auxiliary power supply connection for the device.

Having reference now particularly to Figs. 1 and 2 of the drawing, the structure of the cathode ray tube consists of an evacuated envelope within which are mounted the tube electrodes forming the four stage amplifier. Thetu-be is separated generally into four substantially equal horizontal compartments by means of five metallic barrier plates l2, I3, l4, l5 and IS. The electron beams for all of the amplifier stages are formed from the electron emission produced by an elongated cathode I! which extends vertically through suitable openings formed in all of the barrier plates. Within each of the compartments formed by these plates, the electron emission from the cathode is partially focused into an electron beam by means of electron repelling electrodes l8, 19, 2| and 22, respectively. The cathode l1 and the repelling electrodes are all electrically insulated from the barrier plates and from one another. The electron emission in the various compartments of the tube is accelerated and completely focused into a beam by accelerating

electrodes

23, 24, 25 and 26, respectively, located in front of the cathode. These accelerating anodes each are provided with small apertures such as the aperture 21 of the anode 24 (shown in Fig. 2'). In front of the anodes in each of the tube compartments there are located four pairs of deflecting

electrodes

28, 29, 3| and 32, respectively. At the other end of the

compartments target electrodes

33, 34, and 38 respectively are mounted substantially at right angles to the path of the electron beam. If desired, there may be located between the electrodes of each pair of target electrodes a secondary electron emission inhibiting electrode such as 31, 38, 39 and 4|, respectively.

The first stage pair of target electrodes 33 are connected respectively by a, pair of conductors 42 to the deflecting plates 29 of the second stage. These conductors are imbedded in beads or leadthrough bushings 43 which are mounted in suitable holes in the barrier plate I3. These leadthrough bushings may be of substantially any desired type having resistance between the embedded conductors and the plate in which they are mounted. Finely granulated particles of carbon, held together by any well known binder, are suitable for the bushings. In like manner the target electrodes 34 are connected by a pair of conductors 44 through resistive lead-through bushings 45 to the third stage deflecting electrodes 3|. Also, the third stage target electrodes 35 are connected by a ,pair of conductors 45 through resistive lead-through bushings 4] to the fourth stage deflecting electrodes 32.

The first stage deflecting electrodes 28 are energized by the impression thereon of a signal voltage. This may be accomplished by connecting to these electrodes a pair of conductors 48 which may be supported in the barrier plate 12 by lead-through resistive bushings 49. In like manner the target electrodes 35 of the fourth stage may be connected by a pair of conductors 5| which are suppported in lead-through resistive bushings 52 in the barrier plate IE to the output circuit.

The cathode I! may be heated either directly or indirectly in any manner known to those versed in the art, by suitably connecting

conductors

53 and 54 to a suitable power supply. In order that the cathode may be made a unipotential device, it is preferable to employ indirect heating thereof. The conductor 54 may be grounded so that the secondary electron emission inhibiting plates '31, 38, 39 and 4| may be connected thereto. The repelling electrodes 8, l9, 2| and 22 may be connected by a conductor 55 to a source of voltage which is of negative polarity with respect to'the cathode voltage. 'The barrier plates l2, l3, l4, l and IS, the accelerating

anodes

23, 24, 25 and 26 may be connected by a conductor 56 to a source of voltage which is of positive polarity relative to the cathode voltage.

Referring now to Fig. 3 of the drawing, there is shown the tube elements and associated circuit components in diagrammatic form. It will be understood that, while the cathode I1 is shown broken up among the various tube stages, the actual physical structure of the cathode is as described in conjunction with Fig. 1. Also, the resistive lead-through bushings for the coupling conductors between amplifying stages and to the external circuits are illustrated in Fig. 3 by conventional diagrammatic circuit symbols. The various tube electrodes are provided with suitable operating potentials by means of connections to a power supply such as shown herein by a battery 5?. The negative terminal of the battery is connected by the lead-in conductor 55 to the electron repelling electrodes I8, l9, 2| and 22 of the four amplifying stages. A somewhat more positive point of the battery is connected to the cathode H by means of the lead-in conductor 53. Also in this form of the invention the cathode is connected to ground by means of the conductor 54. Alternatively, instead of grounding the oathode the conductor 55 may be grounnded and, in that manner, the input and output circuits of the amplifier may be operated substantially at ground potential. In addition, the secondary electron

emission inhibiting electrodes

31, 38, 39 and 4! are shown connected to ground by the conductor 54. The positive terminal of the battery 5'! is connected by the lead-in conductor 56 to the interstage barrier plates l2, l3, l4, l5 and It and also to the accelerating

anodes

23, 24, 25 and 25.

A signal source 58 is shown connected by leadin conductors 38 to the terminals of the resistive bushings 49 and also to the first stage deflecting electrodes 28. The last stage target electrodes 36 are shown connected to the terminals of the resistive bushings 52 and also to a utilization apparatus or circuit 59 by means of the pair of lead-in conductors 5|.

Referring now to the operation of the device, it will be understood that in each of the four amplifying stages shown, there is produced an electron beam. In the first stage, for example, the electron emission from the cathode I1 is formed into a beam by means of the repelling electrode 18 and the accelerating anode 23. The beam passes between the deflecting electrodes 28 and is directed against the target electrodes 33. A signal voltage which is derived from the source 58 is impressed upon the resistive lead-through bushings d9. Effectively, the signal voltage is connected to the terminals of these two resistive units which are connected electrically in series. By reason of the structural arrangement of these resistive units, relative to the barrier plate I2, the efiective midpoint of the series circuit is coupled to the positive terminal of the battery 57. Thus, the average unidirectional voltage of the deflecting electrodes 28 is substantially equal to the potential of the positive battery terminal. The instantaneous voltages of the two deflecting electrodes varies in accordance with the impressed signal. Depending upon the instantaneous voltages impressed upon the deflecting electrodes 28, the electron beam of the first stage is deflected over the target electrodes 33. An upward deflection of the beam, for example, causes the impingement of more electrons on the upper electrode and fewer electrons upon the lower target electrode.

The connections of the target electrodes 33 by the conductors 42 to the resistive units 43 and the connection of these resistive units to the barrier plate is and hence to the positive terminal of the battery 5! impresses an average unidirectional voltage upon the target electrodes 33 which is substantially equal to the potential of the positive battery terminal. The variation of the respective numbers of electrons impinging upon the upper and lower target electrodes 33 as a result of the described beam deflection, develops instantaneous voltages across the resistive units 43 in accordance with the electron impingement of the target electrodes.

The varying voltages developed in the resistive units 43 are impressed upon the deflecting electrodes '29 of the second amplifying stage. These voltages, in general, are of greater magnitudes than the signal voltages impressed upon the first stage deflecting electrodes 28 by reason of the amplifying characteristic of the first stage, Consequently, the deflection of the electron beam of the second stage will be greater than the defiection of the first stage beam. The voltage variations also will be in accordance with the signals derived from the source 58. Under the influence of these increased voltages, the electron beam of the second stage will cause a greater variation in the numbers of electrons impinging upon the target electrodes 35. The signal representative voltages developed in the resistive units 45 as a result will be of greater magnitudes than those developed in the output circuit of the first stage. The impression of these amplified signal voltages upon the deflecting electrodes 3! of the third stage causes a still greater deflection of the beam of this stage over the target electrodes 35 and an even greater signal representative voltage thus is developed in the resistive units 41 for impression upon the deflecting electrodes 32 of the fourth and final stage. A maximum deflection of the electron beam of the last stage is, therefore, effected over the target electrodes 36. Accordingly, the signal representative voltage developed in the output circuit resistive units 52 is of a considerably increased magnitude, relative to the signal voltage derived from the source 58. The magnified signal voltage developed in the resistive units 52 is impressed upon the utilization circuit 59.

It is seen that, by virtue of the novel structure of the cathode ray tube and the circuit arrangement of its components, the input circuits of all of the amplifier stages and the output circuits thereof may be operated at substantially the same average unidirectional voltage. It, therefore, is necessary to provide a power supply for the operation of such a device which is required to have no greater voltage output capacity than is required for the operation of a single stage. In this manner many of the difficulties encountered in operating multistage direct current amplifiers are avoided. Also, a device of the character described is susceptible of such construction that a number of amplifying stages may be included in a single envelope as illustrated and described herein. In such a case there are required no more lead-in conductors to the device than are required for the operation of a single amplifying stage. This simplifies the manufacture of such a device. Also there is effected the advantage of minimizing capacity between conact/awe ductors and between the conductors and ground. This same advantage is also secured by the relative simplicity of the tube structure wherein the number of components is maintained at a minimum. Obviously, the invention is not limited to the use of the specific type of lead-through bushings disclosed herein. Other types of coupling and load resistors are contemplated as coming within the purview of the invention. For example, conventional resistor units, mounted either internally or externally of the tube may be used without departing from the invention.

Furthermore, it is not necessary, in order to practice the invention, to have all of the amplifier stages in the one envelope. Groups of stages may be provided with separate envelopes or, i'fdes'ired, each stage may be contained within an individual envelope.

While there has been described what is cousincred, at present, the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is aimed, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

'1. A cathode ray tube comprising, an evacuated envelope, means for producing a plurality of electron beams, a pair of deflecting plates and a pair of target electrodes for each of said beams, a plurality of pairs of resistors mounted in said envelope, there being one pair of said resistors for each of said beams, and conductors coupling respective pairs of said resistors to the target electrodes for one of said beams and to the deflecting electrodes for another one of said beams.

2. A cathode ray tube comprising, an evacuated envelope, a plurality of spaced parallel plates mounted in said-envelope and dividing said tube into apluralityrof compartments, an electron gun, apair of deflecting electrodes and a pair of target electrodes in each of said compartments, a pair of resistive bushings mounted in openings in each of said Plates and in good electrical contact with said plates, and conductors extending through said bushings and in good electrical contact therewith connecting the respective target electrodes of one compartment to the deflecting electrodes of an adjacent compartment.

3. A cathode ray tube comprising, means for producing a plurality of parallel electron beams, a plurality of barrier plates located between said beams and dividing said tube into a plurality of compartmentsone for each of said beams, a pair ordefiecting plates and a pair of target electrodes located respectively in each of said compartments, means including resistive bushings mounted in said barrier plates for coupling respectively the target electrodes of each of said stages, except the lastto the deflecting electrodes of all of said stages, except the first, means for energizing the deflecting electrodes of said first stage according to signal effects and means for deriving from the target electrodes-of said last stage amplified signal elfects.

PAUL J. SELGIN.

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

UNIT-ED STATES PATENTS Number Name Date 1,990,733 Helntz Feb. 12, 1935 2,064,469 'Haeff Dec. 15, 1936 2,205,071 Skellett June 18, 1940 2,214,729 Hickok Sept. 17, 1940 2,262,406 Rath Nov. 11, 1941