US2409577A - Synchronized blocking oscillator - Google Patents

Description

Oct.. 15, 19461 L. E. `McrsoN, JR 2,409,577

SYNCHRONIZED BLOCKING OSCILLATOR Filed Dec. 3. 1943 BY WV ATTORNEY Patented Oct. 15, 1946 SYNCHRONIZED BLOCKING OSCILLATOR Leslie E. Matson, Jr., Merchantville, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application December 3, 1943, Serial No. 512,681

Claims.

l This invention relates to oscillation generators, and more particularly to an oscillator which blocks itself automatically, and is provided with means for control of the intervals during which it intermittently oscillates, and also for synchronization of the first of a series of oscillation trains or pulses with a suitable external signal.

There are many uses for apparatus of the type to Which this invention relates. One requirement in some of the applications involved is that there shall be made available apparatus for producing a succession of periodically recurrent oscillation trains; that is, trains of equal duration and equally spaced apart in time. Another requirement is that the rst train in such a group shall be synchronized with the leading edge of a square Wave impulse of relatively low frequency. Blocking oscillators are, therefore, capable of improvement in accordance with the disclosure of this application so that each train of oscillations shall consist of a uniform number of cycles (usually one cycle), and the initiation of the first of a group of trains of oscillations is so controlled as to be precisely synchronized with a particular phase of the applied rectangular wave.

It is an object of my invention to provide a blocking oscillator of vnovel type wherein the periods of oscillation are controlled by an external source of rectangular Waves.

It is a further object to provide a blocking oscillator wherein the leading edge of a square wave and the trailing edge thereof shall serve to initiate and to stop respectively the generation of oscillations.

Still another object of my invention is to provide a blocking oscillator having a pentode tube in which the cathode, first grid, and anode are included in the oscillatory circuit, the second grid being arranged to function as a screen and the third grid being used to initiate and to stop the oscillations in dependence upon the keying of an externally derived control potential.

Another object of my invention is similar to that set forth in the preceding paragraph but with the added feature that an auxiliary tube is provided for varying the control potential applied to the third grid of the oscillator tube.

The forego-ing and other objects and advantages of my invention will be made clear from the description to follow. This description is accompanied by a drawing, the sole figure of which shows a preferred circuit diagram of apparatus units which are combined for carrying out the invention.

Referring to the drawing, I show therein a discharge tube I which is preferably of the pentode type having a cathode 2, an anode 3, a control grid 4, a second grid 5, and a suppressor grid 6. The cathode 2 is grounded and is Valso connected to the grid E through a resistor 1. The input circuit of the oscillator proper includes a grid leak resistor 8 connecting grid 4 to ground. Feedback means are coupled to this circuit and include a transformer 9, the primary I6 of which is in the output circuit of the oscillator, while the secondary'V II is coupled to the grid 4 across capacitor I2. Anode potential is supplied to the anode 3 across the transformer primary I0, be-

ing delivered by a direct current source I3. This source also supplies screen grid potential to the grid 5 across resistor I4. The usual by-pass condenser I5 is provided, one terminal of which is connected to the screen grid 5 while the other terminal is grounded. Any suitable utilization device may be coupled to the oscillator at the terminals labelled output, Where one of these terminals is coupled to the anode 3 across capacitor IE. The output may, however, be taken at any of several other points.

If the suppressor grid 5 is maintained at cathode or ground potential, tube I generates intermittently blocked oscillations by virtue of a feedback circuit through transformer S, the oscillatory electrodes being the cathode, the anode, and the control grid, as is conventional. If, however, a negative potential is applied to the suppressor grid with respect to the cathode 2, then the oscillations are stopped. In order to supply this negative potential, an auxiliary control tube I'I is provided. This tube may, if desired, be of the triode type having a cathode I8, an anode I9, and a control grid 20. A cathode resistor 2l is here shown, this element being preferably used to avoid tube saturation.

An independent direct current source applies a negative potential to the cathode I8 through resistor 2|, the positive terminal of this source being grounded. The input circuit for tube il includes a grid leak resistor 23 connected between the grid 2l] and the negative terminal of the source 22. Grid 20 is also arranged to be fed with control potentials across capacitor 24. These control potentials develop a suitable voltage drop across the resistor 23. Input terminals 25, one of which is grounded, may be used for applying suitable control potentials. These potentials are preferably of the rectangular or square wave type in order that the leading and 3 trailing edges of the wave may be sharply defined.

In the operation of my invention, it will be seen that the square wave input constitutes a gate voltage which controls the space path impedance in the tube I'I. When this tube is blocked by a negative potential on the grid 20, then the anode I9 stands at ground potential since there is no voltage drop across the resistor 'I under these conditions. When, however, tube I1 is rendered conductive, it draws current by virtue of the negative potential applied to its cathode I8 from the source 22. The current traversing resistor 'i developsl a voltage drop which thereupon renders the suppressor grid 6 strongly negative. Hence, the tube I is biased to cut-oil and the oscillations instantly cease.

In this description of operation it should be emphasized that in usual practice the oscillatory state exists in ,a blocking oscillator during periodic intervals which are very brief compared with the intervals during which the oscillator is blocked. The ratio between oscillating times and blocking times depends, of course, upon the circuit constants. A train of oscillations, as herein referred to, consists of the single impulse or the plurality of impulses produced prior to each blocking period. Commonly, the blocking state is reached so suddenly that only a single cycle exists in each train. Under some circumstances, however, each train may comprise a plurality of cycles. The function of the externally derived rectangular wave is to periodically terminate the blocking periods. Thus it is possible to control the starting time for the first of a group of oscillatory trains in accordance with the steep wave front of a rectangular wave and to permit the oscillator to deliver a succession of trains comprised in that group during the persistence of a half cycle of said rectangular wave.

At the instant when a group of oscillation trains is again to be initiated in tube I, the trailing edge of the rectangular wave input to tube I'I blocks this tube so as to restore the ground potential to its anode IQ. Thereupon the suppressor grid S in tube I is brought back to ground potential and the generation of oscillations is resumed.

It will be noted that the degree of accuracy with which the oscillatory trains are synchronized with respect to an external source of rectangular waves depends upon the abruptness of transition between conductive and non-conductive states in the tube I'I. Hence by a carefully selected choice of circuit components, the control and synchronizing of oscillatory trains can be made as precise as is desired.

My invention is capable of modication in numerous ways without departing from the spirit and scope thereof. For example, it is not at all essential that the control potentials applied to the tube Il' shall be periodic. In certain applications, it is required that they shall be aperiodic, but that they, nevertheless, shall be enabled to initiate and to block the oscillatory trains generated by tube I regardless of their duration and of the duration of the blocking periods.

I claim:

1. In a device of the class described, an oscillation generator comprising a discharge tube having a cathode, an anode, and at least two grids, resonant circuit means connected to the Vcathode, anode, and rst grid for producing oscilla- 4 tions, and a keying circuit for at times blocking said oscillations, said keying circuit comprising a second discharge tube having at least a cathode, an anode and a control grid, the anode whereof is directly connected to a grid of the oscillator tube adjacent its anode, an input circuit connected between the cathode and control grid of said second discharge tube, and an output circuit for the second discharge tube including a direct current source the positive terminal of which is maintained at the cathode potential of the iirst said tube, a xed resistor being interposed between said positive terminal and the anode of the second discharge tube.

2. In combination two electron discharge tubes, each having a cathode, an anode, and one or more grids, input circuits and output circuits individual to each of said tubes, the input and output circuit of one of said tubes being so intercoupled as to cause that tube to generate periodic and discrete oscillatory trains, two sources of direct current, each individually constituting a means for supplying power to a respective one of said tubes, direct ground connections for the negative terminal of the source which supplies power to the oscillator tube and for the positive terminal of the source which supplies power to the other tube, a load impedance connected between ground and the anode of said other tube, a direct connection between that anode and a grid in the oscillator tube other than its oscillator grid, and means for so controlling the space path impedance in said other tube that, when conductive, it interrupts the periodicity of production of said oscillatory trains.

3. Apparatus for alternately initiating and interrupting trains of oscillations generated in a discharge tube which possesses oscillatory and suppressor electrodes, said suppressor electrode being iixedly connected through an ohmic resistance to the cathode of said tube, comprising a second discharge tube in which the space path impedance is varied by a rectangular wave input, this second tube having its anode resistively con- 1 nected to the cathode of the rst said tube, means for equalizing the bias potential of said suppressor electrode at all times with the anode potential in said second discharge tube, and means for shifting said anode potential from that of the cathode in the first said tube to a more negative potential whenever the oscillatory trains are to be blocked.

4. A control circuit comprising a vacuum tube to be controlled, said vacuum tube having an anode, a cathode, a control grid and at least one other grid, an input circuit connected between the control grid and cathode, said cathode being connected to ground, an output circuit connected between said anode and cathode, a resistor connected between said "other grid and the grounded cathode, a controlling vacuum tube having a plate, a control grid and a cathode, a cathode return circuit including a source of operating potential connected between the cathode f of the controllingtube and ground, the plate of said controlling tube being connected to said other grid in the first mentioned tube and the plate circuit including said resistor, and means for rendering said controlling tube alternately conductive and non-conductive thereby to negativeiy bias said other grid of the tube to be controlled during conductive periods of the controlling tube.

5. In combination, a blocking oscillator comprising a multi-grid discharge tube and means coupling its output to one of its grids for applying feedback potentials thereto, a keying control device directly connected between the cathode of said tube and a grid adjacent its anode, said device comprising a fixed impedance in the output circuit of a discharge tube the conductive and non-conductive states of which are controlled by an external source of rectangular Waves, independent sources of direct current in the respective output circuits of said tubes, and ground l0 connections for the cathode of the oscillator tube, the negative terminal of the source in the oscillator output circuit, and the positive terminal of the source in the output circuit of the tube in said keying control device, the negative terminal of the last mentioned source and the cathode of the tube in said keying device being interconnected through a cathode resistor.

LESLIE E. MATSON, JR.

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