US2380982A - Electronic commutation of currents - Google Patents

Description

Aug. 7, 1945. M|THELL 2,380,982

ELECTRONIC COMMUTATION OF CURRENTS Filed NOV. 12, 1942 PHASE SHIFT AT TORNE Y v 1940, comprising a and other electrodes arranged concentrically Patented Aug. 7; 1945 uNrrso s'r-Arss PATENT OFFICE mcraomo co Dorm Mitchell,

Bell Telephone mmrsrrou or Boundlrook', 8.1., signer to New York, N. Y., a museum of New York Application November 12, 1942, Serial No. ceases 50mins.

The present invention relates to the commutation or electrical currents for signaling or other purposes, including electronic or other type of commutation.

An object of the invention is to eliminate or reduce ripple -.or other distortion effects such as may be caused, in the case of an electronic commutator. by the fact that the moving electron beam has finite width. 1

Electronic' switching -or commutation is favored in some types ofjtransmission systems speed at which because of the almost unlimited the beam may be rotated.- This speed may exseed mam times overthe highest speed possible with mechanical commutators. A- drawpressed on a commutator with the result that amplitude variations n the commutated cur- .rents representing ripple and similar disturbances can be reduced in the process or convertcathode l2. The beam is caused to rotate by ing back to the amplitude pulses that are to be used for transmission.

Reference 'will now be made to the following detailed description and the accompanying drawing for a more complete understanding of the invention, together with itsvarious objects andfeatures.

The single figure of the drawing shows a schematic circuit diagram of a terminal of a an accelerating grid l4, shields ll, control grids ii, and a common anode il, the latter being in the form of a cylinder. The surroimding envelope is not shown. Positive voltage is applied to the accelerating grid 14, shields II and anode i'I from suitable taps on battery 20, the negative pole of which is shown grounded as is also the a rotating magnetic field generated in field coils two of which are shown at 2| and 22 supplied with alternating current of suitable frequency from generator 23. A phase shifter, such as a quarter phasenetwork 24, is connected in circuit with the field coil II to provide the necessary phaseshift'for generating the required rotating field.

As the beam Ii rotates it strikes the shields II in succession and these, shields have the effect of cutting-oil the electron current to the anode ll momentarily while the beam is incident upon them. Pulses oi' anode current are produced when the beam falls between two of the shields i5 and is allowed to strike the anode i1. During the time when such an output pulse is being generated, the strength of the beam and, therefore, the strength ofv the output pulse can be modulated by placing variable potentials on the control grids it. These control grids are shown connected in pairs with respective pairs connected to the output of individual frequency modulators 4, 5, 6, etc. If desired, individual grids may be connected to the frequency moduators instead of connecting the grids in pairs.

'l'he connection of the grids in pairs illustrates one way 'that a tube having a greater number of electrodes than the number of lines to be served may be used,'by connecting pairs or groups of multiplextelephone system embodying the invention in anillustrative form.

Referring to the drawing, a number of separate telephone lines shown as extending from individual microphones i, 2, 3, etc. are connected .4 through respective frequency modulators I, ll,

etc. to electrodes of an electron commutating tube II which has a rotating electron beam ii adapted to sweep over electrodes of the tube.

The tube It may be of the type disclosed in Skellett Patent 2,217,774, granted October 15, centrally located cathode 12 thereabout. These electrodes comprise, proceeding-in order from the cathode l2 outwardly,

the grids in common to any one line. The grids i6 receive an initial bias, usually negative, from common grid bias battery 25. v

A high frequency oscillator 26 is shown connected in common to all .of the frequency modulators so that the mean frequency of the frequency-modulated waves produced in the varius-frequency modulators is the same throughout; These frequency modulators may be reactanee control tubes of a type well known in the art, an example being disclosed in Patent 2,076,264 'to Chireix et al., granted April 6, 1937.

Another type of frequency modulator that may be used comprises a saturable core inductance and rectifier, this type being disclosed, for exple. in L. R, Wrathall, application Serial No.

354,357, filed August 2'7, 1940, which matured into Patent No. 2,311,796, February 2;, 194a.

2 s,s so,oss

Outputcurrentfromtheanodellpasses through the primary winding of output transformer ll and into a heterodynlng detector 20 supplied with" heterodyne oscillations from source it for stepping the frequency of the fref uency-modulated waves down to a convenient sent signals. use of frequency meme- .tion, however, as described, these smplitude'var-' iations are greatb reduced provided they are not or desired level. Detector 20 is followed by an" amplitude limiter it after which comea slope circuit ll, amplitude detector 38 and low-pass filter 34 leading to the outgoing transmission line SI.

In the operation of the system as shown in the drawing, speech waves from diflerent talkers produced in microphones I, I, 3, etc. effect frequency modulation oi waves supplied from the common oscillator 28 and the respective frequency-modulated waves are applied to indi-.

vidual pairs of control grids It. As the beam sumcient to shut oif'the spacecurrent completely. This is because the amplitude limiter II serves to wipe out such-chsngesin amplitude asareproducedbythetypeotvariationsmentioned. caused by movement of the radial beam across the tube electrodes. Further, it is to be noted that overlap produced .by the beam strikon two neighboring-grids at the same instant, which might result in cross-talk, is reduced since such effect will disappear as soon as a diflerence of 6 decibels or more in strength appearsbetween the two signals.

The invention is not to be construed as limited to the particular circuit arrangements that H rotates past the shields It and comes in between a pair of shields the strength of the beam is varied in accordance with the frequency-modulated wave on the respective grid It, setting up a corresponding frequency-modulated wave in the output transformer 28. These frequencymodulated waves occurring in spurts or pulses have variable frequencies representing signal modulations. Their frequencies are stepped down in the detector stage 2! and amplitude variations occurring in the pulse envelope are largely eliminated by the amplitude limiter circuit 3| which can be arranged to limit the maximum amplitude of the transmitted wave to as small a value as may be desired in accordance with well-known practice in the reception of frequency-modulated waves. The slope circuit 32 converts the frequency-modulated waves into waves of variable amplitude so that they are capable of detection in the amplitude detector 38. In this way a series of pulses comprising frequency-modulated waves are converted to a series of amplitude pulses or direct current pulses a varying in amplitude in accordance with the respective signal variations. Low-pass filter 34 ,may be provided to suppress undesired carrier components or other undesired amplitude peaks or variations representing distortion are largely eliminated; The transmitted pulses may, therefore, be received by any suitable type of time division multiplexreceiver, such as that shown in Fig. 12 of the Skellett patent, or in the patent referred to. It will be understood that the commutating means used to receive the messages from the transmitter shown. in the drawing must be operating in proper synchronism and phase with respect to the beam Ii.

As explained above, the beam H has a flnite width or thickness so that as the beam passes over the various electrodes .in the tube I I amhave been disclosed herein for illustrative purposes but the scope is define which follow.

What is claimed is: 1. In a signal commutating circuit, means to translate signals into frequency modulated waves, a rotary beam electronic commutator tube having beam modulating electrodes and an output circuit, meansto place the frequency-modu-' lated wave potentials on said electrodes in accordance with the signals to cause a frequency-' modulated wave to appear in saidoutput circuit whenever said beam sweeps past a beam modulating electrode, means to remove incidental amplitude variations from said frequency modulated waves appearing in said output circuit, and means in said output circuit for detecting said frequency-modulated waves.

2. In a signaling system, a plurality of signal input circuits, a rotary beam electronic commutator tube, having input electrodes arrang'ed'to exert successive controfion said beam, an' output .circuitfor said tube, means to translate signals in said input circuitsinto frequencymodulated waves and to impress the latter on respective control electrodes of said tube'whereby to set,

up frequency-modulated waves in said output circuit in successive times,-and means insaid v output 'circuit for removing incidental amplitude variations from said output wavesand thereafter converting said output waves into varying amplitude signal currents.

3; In a signal system, signal input circuits, a rotary beam electronic commutator having a beam adapted to move past a succession of control electrodes, a common anode and output circuit therefor, a source of high frequency oseillations, means to modulate the wave-length of a said high frequency oscillations by signals in said input circuits, means-to impress the modu-. lated oscillations on respective control electrodes whereby to produce in said output circuit wavelength modulated oscillations representing said signals in successive times, and means to convert said output oscillations into amplitude var-v iations including an amplitude limiter ahead of plitude changes will occur in thespace current depending to a considerable extent upon whether the plate hitsthebeam squarely or is partly cut oil by one of the shields It. In an ordinary amplitude modulated system in which,v for example, the speech signals are directly applied .to the grids It. these variations'inthe space current would. introduce components of noise into the the converting means. 1

4. In a rotary-beam electronic commutator having control electrodes for successivelymodulating the strength of the beam in its rotation and a common output circuit,"'means for reducing distortion of input waves arising from the fact that the beam has a width comparable to the width and spacing of said control electrodes comprising means for first converting inputcontrol waves to wave-length modulations of high frequency oscillation and means to impress the' latter on said control electrodes, and means in inthe claims said output circuit for removing amplitude variations from the wave-length modulated oscillations and converting said oscillations into varying amplitude currents.

5. In a, signal transmission system, sources of signal waves, means to frequency-modulate a high frequency wave in accordance with each signal, a common transmission path, a commutator for switching the frequency-modulated waves into said common transmission path in succession, means in said common path for suppressing amplitude variations in the waves in said path, and means in said common path to detect the frequency-modulated signals.

DOREN MITCHELL.

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