US2202376A - Cathode ray tube detector circuits - Google Patents

Description

' C. W. HANSELL CATHODE RAY TUBE DETECTOR CIRCUITS May 2 s, 1940.

Filed lay 2a, 1938 s Shoots-Sheet 2 qmiiumw EEEE w New INVENTOR.

cues/v0 .HANSEL-L ATTORNEY.

Patented May 28, 1940 NITED "STATES CATHODE RAY TUBE DETECTOR CIRCUITS Clarence W. Hansell, Port Jefierson, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application Ma zs, 1938, Serial No. 210,588

. 1 Claims. (cram-27) The present invention relates generally to novel and improved detector circuits employing a cathode ray type of electron tube wherein an electron stream is shifted between a plurality .of electrodesshield is provided between the anodes to which is attached an accelerating grid structure in the path of the electrons which is maintained at a positive potential relative to the cathode. In the operation of this type of tube, practically all of the electron stream will be focussed upon the center of the accelerating grid, in the absence of a deflecting field, and no electron current will flow to the anodes. However, upon the occurrence of a deflecting field, such as may be produced by a radio frequency signal, the electron stream will oscillate back and forth across the center or bridge of the accelerating grid and a portion of the electron stream will pass through the grid to the anodes. With relatively appreciable high fre quency deflecting potentials, most of the. electron stream will strike the anodes. For intermediate values of applied radio frequency deflecting potentials, the distribution of the electron current between the grid and anodes will vary more or less in proportion to the strength of the applied radio frequency current, and if the tube is properly designed the distribution or variation in electron flow to the grid and anodes will reproduce any amplitude modulation which may be present in the applied radio frequency current. For a more detailed description of such a tube, reference is made to my United States Patent No. 2,066,037, granted December 29, 1936.

The present invention has for one of its objects to employ this particular type of cathode ray tube as a detector of amplitude modulated waves, or as a detector of phase or frequency modulated waves; by connecting to the tube suitable electrical circuits for converting phase or frequency modulated waves into amplitude modulated waves.

An advantage of the present invention resides in my ability to obtain very great sensitivity in detector circuits employing the foregoing type ofcathode ray tube.

' A better understanding of the invention may be had by referring to the following description which is accompanied by drawings, wherein:

Fig. 1 shows, very diagrammatically, the es,- I

sential elements of the cathode ray tube employed in my improved detector circuits;

Figs. 2, 3 and 4 illustrate, diagrammatically three diiferent circuit arrangements employing the cathode ray'tube for detecting modulated signals;

Fig. 5 shows a complete tuned radio frequency receiver, all of whose stages are composed of cathode ray tubes; and r Fig; 6 illustrates the application of the preferred cathode ray tube to all stages of a superheterodyne typeof receiver.

Referring to Fig. 1 in more detail, there is shown the preferred type 01' structure for the cathode ray tube. The essential elements of this tube are a cathode electron emitting element K, a pair of deflector electrodes D, D which also serve as electron focussing elements, a pair of cupshaped an odes A, A symmetrically positioned with respect to the cathode, and an accelerating grid G supported at its center by a cylindrical shield S and rod P. The envelope of the tube, not shown, is evacuated and maybe of glass or of metal with suitable insulation for connections. The electrons-emitted by cathode K will be drawn over to the grid and anodes by virtue of suitable'positive potentials applied to these electrodes, as.

to D, D, such as may becaused by radio frequency input signals, will shift the electron beam to one side or the other of the shield S, thus enabling the electrons to pass through the grid and to impinge upon the internal portion of the cupshaped anodes A,- A. By arranging the anode tube operation is overcome.

Figs. 2, 3 and 4 illustrate how the tube of Fig. 1 may be usedfin detector circuits. The input circuit for eachtube of these figures comprises a parallel tuned circuit ll, connected across the deflector electrodes D, D. The detected modulation output from the tube is-passedon to a suitable utilization circuit l2. The deflector electrodes D, D are maintained at a suitablenegative biasing potential and the accelerating grid G and In'the-operation of Figs. 2, 3 and 4, the modulated radio frequency signal waves from a suitable line I!) are applied to the tuned circuit,

to produce a change in the distribution of the electron flow to the anodes A, A and the grid G. If no signal arrives over line "I, all the electron current preferably flows to the center of the grid structure.

Referring to Fig. 2 in particular, with no radio frequency signal input, the electrons of the tube will strike the grid G and produce a direct current flow in primary winding l, which is in series with the connection to the anodes. Winding I is coupled to secondary winding 5 of the output transformer. When radio frequency signal energy flows in the input circuit, however, the

electrons are divided between the anodes A, A and there is obtained a direct current component in connections 2 and 3, respectively extending to the accelerating grid and the two anodes. The high frequency components of current in the output of the tube is short-circulted to ground by bypass condensers 4 and/or by the capacity of the tube, its transformer and connections. The variation in the direct current in the winding l is the modulation frequency component which is the desired detected output. If the carrier alone is in the input circuit, i. e., without modulation, the distribution of electron flow in the tube should normally be about one-half to the grid G and one-half to the two anodes. This condition is obtained by the adjustment of the ampliseries with the connection to the accelerating grid.

G. Because of this change, the polarity of the alternating current output in the primary I of the transformer in Fig, 3 is reversed from thatof Fig. 2. This reversal of polarity, obtainable by taking the modulation frequency output from either the grid or the anodes, is a very great convenience provided by the tube of Fig. 1 which can be used to advantage in many other types of circuits than those shown.

Fig. 4 shows an arrangement in which the useful output is taken from both the anode and accelerating grid circuits. For this purpose there are employed two primary coil windings I and I which are arranged to cause the energy therein to addltively combine in the secondary winding 5 of the output transformer. In this case the direct current components of electron current through the two primary windings tend to balancego ut in so far as they tend to produce a steady state or unidirectional component of magnetization in the case of the transformer. Condenser 4', like condensers 4 in Figs. 2 and 3, serves to bypass to ground radio frequency components of current without at the same time allowing detected modulation output currents to' bev bypassed.

In the systems of Figs. 1 to 4, inclusive, if desired, there may be employed a magnetic field in a direction parallel to the center of the mean path of the electron stream to aid in focusing the electrons upon the center of the grid bridge, when there is no alternating current input. Such a magnetic field can be produced by a coil located externally of the envelope.

Fig. 5 shows my preferred type of cathode ray tube used to perform all the essential functieeof the stages of a complete tuned uni-controlled radio frequency receiver such as may be used for broadcast reception. The functions of the tubes are suitably labeled. The amplifiers are adjusted for maximum amplification. It should be noted that the cup-shaped anodes of the detector are short-circuited and by-passed to ground for radio frequency energy. In view of the detailed description of the operation of these tubes, given above, it is not deemed necessary to further amplify the same.

Fig. -6 illustrates the use of my preferred type of cathode ray tube in combination with a complete superheterodyne receiver. The cathode ray tubes are here used not only as detectors, but also as amplifiers (both radio frequency and audio) and as an oscillator.

It should be understood that the invention is not limited to the particular type of detector circuits illustrated and described, since various modifications in the detector circuits maybe made without departing from the spirit and scope of the invention.

What is claimed is:

1. A detector circuit comprising, in combination, an electron discharge device having a cathode for producing an electron stream, a pair of cup-shaped anodes symmetrically arranged relative to said cathode, a pair of deflecting electrodes intermediate said cathode and said anodes, and a grid structure adjacent said anodes and in the path of said electron stream for establishing an electric field, a direct connection between said anodes, an input circuit connected to said defiecting electrodes for applying modulated radio frequency waves thereto, an inductive output circuit directly connected to said anodes, and a low impedance connection for radio frequency energy between said anodes and ground, said connection including a by-pass condenser in shunt to said output circuit.

I 2. A detector circuit comprising, in combina-' tion, an electron discharge device having a cathode for producing an electron stream, a pair of cup-shaped anodes symmetrically arranged relative to said cathode, a pair of deflecting electrodes intermediate said cathode andsaid anodes, and a grid structure adjacent said anodes and in the path of said electron stream for establishing an electric field, a low impedance connection between said anodes, an input circuit connected to said deflecting electrodes for applying modulated waves thereto, an output circuit conductively coupled to said anodes, and a path of low impedance to high frequency energy from said anodes to a point of relatively fixedpotential, including a by-pass condenser in shunt to said output circuit for by-passing' high frequency components.

3. A detector circuit comprising, in combination, an electron discharge device having a. cathode for producing an electron stream, a pair of cup-shaped anodes symmetrically arranged relative to said cathode, a pair of deflecting electrodes intermediate said cathode and said anodes, and a grid structure adjacent said anodes and in the path of said electron stream for establishing anelectric field,an input circuit connected to said deflecting electrodes for applying modulated -waves thereto, a direct connection between said anodes, an output circuit comprising a coil connected between said anodes and a source of positive potential, and low impedance means connecting both sides of said coil to a point of fixed radio frequency potential.

4. A detector circuit comprising, in combination, an electron discharge device'having a cathode for producing an electron stream, a pair of cup-shaped anodes symmetrically arranged rela-' tive to said cathode, a pair of deflecting electrodes intermediate said cathode and said anodes, and agrid structure adjacent said anodes and in the path of said electron stream for establishing an electric field, an input circuit connected to said deflecting electrodes for applying modulated waves thereto, a direct connection between said anodes, an output circuit comprising a coil connected between the center of said grid structure and a source of positive potential, anda path of low impedance between said anodes and a point of fixed alternating current potential.

anodes, and an output circuit comprising a pair of coils one of which is connected between said anodes and a, source of positive potential while the other of which is connected between the 3 center of said grid structure and said source, said coils being arranged to cause the energies therein to additively combine in a utilization circuit coupled thereto.

6. An electron discharge device circuit comprising a cathode for producing an electron stream, a pain of cup-shaped anode electrode structures symmetrically arranged relative to 1 said cathode, a grid electrodestructure adjacent said anode structures and in the path of said electron stream for establishing an electric field,

a pair of deflecting electrodes-intermediate said cathode and said anode structures,a direct connection between said anode structures, an input circuit connected to said deflecting electrodes for applying radio frequency waves thereto, an inductive outputcircuit directly connected to said anode structures, and a low impedance connection for radio frequency energy connected between one of said electrode structures and ground, said connection including a by-pass condenser. I

'7. An electron discharge device circuit comprising a cathode for producing an electron stream, a pair of cup-shaped anode electrode structures symmetrically arranged relative ,to

said cathode, a grid electrode structure'adjacent said anode structuresand in the'path of said electron stream for establishing an electric field, a pair of deflecting electrodes intermediate said cathode and said anode structures, a direct connection between said anodestructures, an input circuit connected to said deflecting electrodes for applying radio frequency waves thereto, an outputcircuit including an inductance coil shunted by a condenser connected between said anode structures and the positiveterminal of a source of unidirectional potential, and a low impedance connection for radio frequency energy connected between one of said electrode structures and ground, said connection including a by-pass condenser.

' CLARENCE W. SELL.

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