US3027517A

US3027517A - Blocking oscillator system

Info

Publication number: US3027517A
Application number: US756379A
Authority: US
Inventors: Arthur K Drake; Douglas O Cochrane
Original assignee: Edgerton Germeshausen and Grier Inc
Current assignee: PerkinElmer Inc
Priority date: 1958-08-21
Filing date: 1958-08-21
Publication date: 1962-03-27
Anticipated expiration: 1979-03-27

Description

A. K. DRAKE ET AL BLOCKING OSCILLATOR SYSTEM Filed Aug. 21, 1958 \WNEW R M r mam s m? WW M 1/.V 0 KM w w A 2 r m fin V. B

March 27, 1962 United States Patent Ofiice 3,027,517 Patented Mar. 27, 1962 3,027,517 BLOCKING OSCHLLATOR SYSTEM Arthur K. Drake, Braintree, and Douglas 0. Cochrane,

Dorchester, Mass., assignors to Edgerton Germeshausen and Grier, Inc., Boston, Mass, a corporation of Massachusetts Filed Aug. 21, 1958, Ser. No. 756,379 6 Claims. (Cl. 328242) The present invention relates to blocking oscillator systems and, more particularly, to those employing electron tubes as the relay element of the oscillator.

Numerous types of blocking oscillators for generating electric impulses have been proposed throughout the years, employing electron-tube relays connected with time-constant-controlled networks and an input circuit-tooutput circuit transformer, as described, for example, in United States Letters Patent No. 2,677,788, issued May 4, 1954, to Kenneth J. Germeshausen. -It has been found that, for purposes later explained, the transformer, with its inherent restriction upon high-frequency response, can be eliminated and improved operation can be obtained if an electron tube embodying a secondary electron-emitting electrode is employed in a novel oscillator circuit. An object of the present invention, therefore, is to provide a new and improved blocking oscillator system embodying such an electron tube having a secondary electron-emitting electrode.

A further object is to provide a new and improved oscillator that need not employ a transformer.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

In summary, the present invention relates to the employment of the above-mentioned type of electron tube having an internal secondary electron-emitting electrode and provided with input and output circuits. A network, such as a capacitance-resistance circuit, is connected with the input and output circuits for controlling the operation of the blocking-oscillator tube. Means is provided for biasing the secondary electron-emitting electrode to cause it to emit secondary electrons upon the impingement thereupon of electrons in the tube during the operation of the same, and a further circuit connection is provided to the secondary electron-emitting electrode for coupling therefrom an output impulse produced by the operation of the tube. Preferred circuit details are hereinafter set forth.

The invention will now be described in connection with the accompanying drawing, the single FIGURE of which is a schematic circuit illustrating the invention in preferred form.

Referring to the drawing, the electron tube 1 is shown embodying a cathode electrode 3 as a primary-emitting source of electrons, a control-grid electrode 5, a screengrid electrode 7, a grounded beam-forming electrode 9, and an anode-electrode 11, together with a secondary electron-emitting dynode electrode 13 preferably disposed near the anode 11. The tube 1 may be of the type EFP60 and is connected into a blocking-oscillator circuit, generally indicated by the numeral 2. The anode 11 is connected through an anode load resistor 19 to the positive terminal B-lof a source of anode potential, the negative B terminal of which is preferably grounded, as shown, and is connected through a cathode resistor 15 to the cathode electrode 3. The term ground, as used herein, is intended to connote not only actual ealthing, but also any reference potential, such as chassis potential and the like. The screen-grid electrode 7 is connected to a source of positive potential B'-}- which may be of the same order of magnitude as the anode potential B+, and is decoupled to ground through a capacitor 17.

Connected to the input circuit comprising the cathode 3 and control electrode 5 of the electron tube 1 is a source of impulses, schematically illustrated by the coaxial input terminals 4 and 6, the latter of which is shown grounded. In the vent that the oscillator tube 1 is to be externally triggered, the terminals 4 and 6 may be connected to a pulse generator or other impulse source, no shown. It will be evident from the description hereinafter contained, however, that the oscillator may also, if desired, be freerunning, as described in the said Letters Patent. A diode 8 is shown connected from the input terminal 4 to ground, in order to insure that only input signals of the desired polarity are applied through the grid-resistor 10, to the control-electrode 5. A shunt-connected input grid resistor 12 is connected between the input terminal 4 and the input terminal 6, through the ground. The cathode 3 of the tube 1 may be positively biased by connection through respective resistors R and 14 to a positive biasing potential source Connected between the anode 11 and the cathode 3, is the blocking oscillator network comprising one of a plurality of condensers C C C C C or C any one which may be selected by the rotation of a switch S, for a purpose later-described. In the drawing, the anode 11 is shown connected by conductor 16 through the switch S to capacitor C and thence, by conductor 18, to the right-hand terminals of the before-mentioned resistor R and diode D The anode is also connect-ed to the right hand terminals of resistor R and diode D through capacitor C which serves as a by-pass for switch S. The resistance of resistor R is, of course, very large as compared to the almost resistance-free connection through diode D for signals of the proper polarity and, therefore, the feedback circuit for the blocking oscillator is from the anode 11 by way of the parallel paths comprising connector 16, switch S, the capacitor C to C selected by switch S and connector 13 on the one hand, and capacitor O; on the other, through diode D to the cathode 3. A similar feedback circuit could be employed between the dynode 13 and the control grid 5. Diode D is connected in parallel with resistor R and is subject to a reverse bias substantially equal to the cathode bias of tube 1 across resistor R. The time duration of the blocking oscillator pulse is determined by the level of the anode current in relation to the capacity of the selected capacitance, C to C and C together with the circuit parameters including the resistan-ces of R. 14. 15 and 19.

The tube 1 is preferably operated substantially Class A, being normally conducting. All the voltages and currents are stabilized. The anode current in this condition is approximately one milliampere or more. This is preferable in order to operate tube 1 at a high mutual conductance level and thereby utilize the increased amplification factor of tube 1. Capacitor C and one of the capacitors C to C as selected by switch S, are charged to a potential substantially equal to the difference between anode potential derived from B+ through resistor 19 and the potential at the right hand terminal of diode D When a trigger pulse is fed to control grid 5, tube 1 starts to amplify and the electrons emitted by the cathode 3 are directed to secondary-olectron-emitting electrode 13. Upon the impingment of primary electrons, a greater number of secondary electrons are emitted which flow to anode 11. Tube 1 acts as an amplifier with a rapid increase in anode current and a correspondingly rapid voltage drop across resistor 19 which together produce a negative pulse which is fed back to the right hand terminal of diode D where it not only overcomes the reverse bias and passes through diode D thereby making the cathode 3 more negative with respect to the grid 5, but also opposes the source of the cathode bias to decrease that bias,

thereby increasing the mutual conductance of the tube which in turn produces an increase in anode current. Gnly an insignificant pant of the feed-back pulse passes through resistor R because, as previously mentioned, the resistance of R is very large in comparison with that of diode D When the reverse bias of diode D is overcome, diode D acts substantially as a closed switch providing a direct connection for the feed-back pulse from the anode 11 to the cathode 3, by-passing resistor R. The rapid potential drop at anode 11 causes a. rapid discharge, or decrease in potential, of the aforementioned charge on the capacitors in the feed-back circuit. The time-duration of the blocking oscillator pulse is controlled by the time required for the capacitors to decrease in potential to the new potential level between the said points and by the other circuit parameters previously mentioned. When the charge on the said capacitors decreases to this level, there is no longer a negative pulse suflicient to overcome the reverse bias of diode D so this reverse bias again takes control and the output pulse ends. Regeneration is thereafter prevented by the reverse bias across diode D until tube 1 is triggered anew and the entire process is repeated.

During the flow of electrons from the cathode 3 to the anode 11, electrons will strike the secondary electronemitting electrode 13. The electrode 13 is connected through'resistor 20 to a positive bias potential source that renders the electrode 13 adaptable to emit secondary electrons upon the impingement of primary electrons thereupon. The secondary electrons thus emitted from the secondary electron-emitting electrode 13 will then be directed to the adjacent anode 11. There will thus result at the secondary electrode 13 an impulse corresponding to the electron flow within the tube 1, which, in accordance with the present invention, is coupled-out therefrom by the coupling capacitor C to a pair of load circuits.

The first load circuit is shown fed from the capacitor C to a common point P and then through a coupling capacitor C" and a resistor 22, to, for example, the com trol grid of a cathode-ray tube, not shown, as for the purpose of intensifying the same or cutting the same off in synchronism with the pulses produced by the blocking oscillator tube 1. The second load circuit connected to the coupling capacitor C is the cathode follower stage 21, the control-grid electrode 23 of which is connected to the point P through a resistor 45. The cathode 25 of the tube 21 is provided with a cathode load 27, the lower terminal of which is grounded at D and the upper terminal of which connects through a further coupling capacitor C' to a pair of output terminals 4', 6. The outputterminals 4', 6' may be fed, for example, to the sweep circuit of the cathode-ray tube, not shown, in order synchronously to trigger the same. The anode or plate 29 of the cathode-follower tube 21 is shown decoupled to ground through a capacitor 31 and connected through an anode load 33 to the source of positive potential D+.

Connected between the point P and ground is a grid resistor 35 and a shunt or parallel-connected diode D The diode D insures that the electrical connection from the secondary electron-emitting electrode 13 of the tube 1 through the coupling capacitance C to the two load circuits represented by the grid of cathode-ray tube and the sweep circuit, respectively, does not assume an undesirable negative potential, by providing a shunt connection to ground in the event that such a potential should start to develop. It is also necessary, however, to insure that the grid of the cathode-ray tube is not driven too positive through the advent of an output pulse from the blocking oscillator of excessive magnitude. To prevent this result, the terminal P is also connected to the anode 24 of a further preferably triode electron tube 26, the control-grid electrode 28 of which is returned to the point P through a resistor 30. The cathode 32 of the tube 26 is connected to a source of positive potential E+ by a conductor 34, the value of E+ being selected to correspond to the predetermined maximum impulse voltage that it is desired to feed to the cathode-ray tube. A decoupling capacitor 36 is shown connected from the cathode 32 to ground. When, accordingly, the potential at the point P reaches the value of the predetermined voltage E+, the tube 26 will conduct and thus prevent the signal being fed out through coupling capacitor C" from exceeding the desired predetermined value.

Since different-length sweep voltages may be required, the switch S may communicate with any of the capacitors C C C C C and C of different values, as desired, thereby correspondingly to vary the duration of the resulting blocking-oscillator output pulse coupled out by the secondary electron-emitting electrode 13, as before described. Other types of load circuits besides cathoderay tubes may, of course, obviously be employed, also.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention, as defined in the appended claims.

What is claimed is:

l. A blocking oscillator system comprising:

an electron tube provided with input and output circuits, said tube having at least cathode, control and anode electrodes and a secondary-electron-emitting electrode;

means for biasing the tube to render the same normally conducting with all voltages and currents substantiah ly stabilized, said biasing means including a biasing potential applied to the cathode;

means for applying a trigger pulse to the input circuit to increase conduction in the tube thereby initiating the generation of a blocking oscillator impulse;

a feed-back network from the anode to the cathode for feeding back a signal to further increase conduction after the tube has been triggered; and

impedance means connected to the cathode and having a greater effective value when the cathode is under the control of the said cathode biasing potential than when it is under the control of the feed back signal from the anode;

said output circuit being connected to the secondaryelectron-emitting electrode for coupling out therefrom the blocking oscillator impulse.

2. A blocking oscillator system as claimed in claim 1 and in which the said input circuit is connected to said control electrode.

3. A blocking oscillator system as claimed in claim 2 and in which the said feed-back network is a capacitanceresistance network.

4. A blocking oscillator system as claimed in claim 3 and in which said resistancecap-acitance network is provided with a plurality of capacitance elements of ditferent values and a switch for selecting capacitance from said plurality and connecting the same into said network, the capacitance selected combining with the other elements of the network to control the time duration of the blocking oscillator impulse.

5. A blocking oscillator as claimed in claim 3 and in which the said impedance means comprises a diode and a resistor connected in parallel, said diode oriented in opposition to said cathode biasing potential but passes said feed-back signal when the biasing potential is overcome.

6. A blocking oscillator system as claimed in claim 5 and in which means are provided for controlling the polarity and maximum magnitude of the blocking oscillator impulse coupled out from said secondary-electron emitting electrode.

References Cited in the file of this patent UNITED STATES PATENTS 1,790,197 Brown Jan. 27, 1931 2,235,190 Alma Mar. 18, 1941 2,297,522 Zanarini Sept. 29, 1942 (Other references on following page} 5 UNITED STATES PATENTS Miller Dec. 11, 1945 Barnard et a1 Mar. 25, 1947 Levy Apr. 27, 1948 Van der Mark et a1 May 30, 1950 5 Toporeck Jan. 23, 1951 Glenn July 10, 1951 Wrenn Aug. 14, 1956 Purinton Aug. 5, 1958 OTHER REFERENCES Millrnan and Taub-Pulse and Digital Circuits, Mc- Knaus-s July 7, 1959 10 GraW-Hill Boo-k C0., Inc., 1956, page 128.