US1776149A - Oscillation generator - Google Patents

Description

Sept. 16, 1930. R. s. DOME OSCILLATION GENERATOR Filed June 12, 1928 lTu/egco .Robert. .Dome

WW HxsAtto'hneg- Patented Sept, 16, 1930 I UNITED STATES PATENT I OFFICE ROBERT B. DOIIE, OI. SCH ENECTADY, NEW YORK, ASSIGIVOB TO GENERAL ELECTRIC commm'r, A coarona'rron or NEW YORK oscnim'rrou enumroa Application and .Tunp 12,

My invention relates to oscillation generators in which piezo-electric crystal elements are employed for the production of oscillations, these oscillations being amplified by an electron discharge device. I I Heretofore piezo-electric crystal elements have been employed in connection with electron discharge devices for the purpose of I producing oscillations of constant fre uency, these oscillations being amplified by t e discharge device and transmitted to a load circuit. In oscillation generators employing such crystal elements three element electron discharge devices, are customarily employed, 5 the crystal being connected between the control electrode and the cathode. To cause the crystal to maintain the production of oscillations' it is necessary that energy from the outppt, oranode, circuit of the discharge device sup lied to the grid circuit, and hence to the crygtal, this energy being represented by currents having the naturalfrequency of the crystal. In circuits of the prior art this feed back of ener to the crystal is more 1 com- :5 monly efi'ecte throu h the inherent capacity between the grid and anode; This capacity is of a fixed valueand is not readily subject to control by the operator. Frequently, and articularly in cases where devices having :0 'gb amplification ratio are employed, it is of a magnitude such that the energy supplied to the crystal circuit through this capaci is so great that the crystal is broken, that 1s, the oscillations of the crystal are of amplitude such that the mechanical elastic lim1t of the crystal is exceeded and rupture of the crystal results. Accordingly one of the purposes of my invention is to provide means whereby electron discharge devices having high amplification ratio may be employed and controlled by means of a piezo-electric crystal, thereby to produce a large amount of power in the output circuit and at the same time not supply enough power to the crystal to subject it to danger of rupturing. A further purpose of my invention is to provide means whereb the energy sup lied to the crystal from the output of the isicharge device having high 6 amplification is readily controllable.

1928. Serial 1T0. 284,758.

In carrying my invention into effect I employ a fourelement electron discharge device in which a screening grid is interposed between the anode and control gr1d. This screening grid is, as usual, maintained ata strong positive direct currentpotential and is connected to the cathode through a large by-pass condenser such that the high frequency potential of the screening grid is to the anode, or output circuit. By varying this external coupling, any desired amount of energy may be supplied to the crystal to maintain the production of oscillations.

' As is well-known four element discharge devices of the type indicated have high input impedance resulting capacity existing etween the grid and cathode as compared with three element devices of the same amplification ratio. Accordingly an equal amount of current flowing in the grid or crystal circuit will produce a greater alternating current potential upon the control grid of a four element device than would be obtainable in a three element device having an equal amplification ratio. Thus a be had from t e'four element device than could be had from the three element device havih the same am lification ratio, both devices fieing excited by means of crystals in which e ual exciting currents are caused to flow. e ratio, between these outputs have eater amount of power may,

from small inherent been found to be'about equal to the ratio between the input impedances of the two tubes. The effect of inherent ca acity between the anode and grid is su stantially eliminated and therefore the entire suppl of energy to the crystal is efiected throug the external couplm which may be adjusted to produce desired operation by the operator. e

- The novel featureswhich I belleveto be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure represents one embodiment thereof.

Referring to the drawing, 1 represents an electron discharge device havingan anode 2, a cathode 3, a control electrode 4 and a screening electrode 5, the latter electrode being interposed between the anode and control electrode. Between the anode and cathode is connected a suitable output circuit including the primary winding of a 1 transformer 6 and energy source 7. 8 represents a piezo-electric crystal element which may comprise a suitable quartz crystal which is placed between conducting plates, which plates are conventionally represented in the drawing, and maintained at a definite pressure in the usual manner. This crystal element is connected between the cathode and control electrode through a suitable coil 9 which is in inductive relation with one of the coils of transformer 6. While I have shown a coil 9, in the way of illustrating a suitable variable couplin tothe load circuit, it will be understood t at a resistance or capacitive coupling may also be used. 10- is the usual grid leak resistance which is connected between the control electrode and the cathode. A suitable biasing potential is supplied to the screening electrode 5 from the source of potential 7 through resistance 11. This electrode is maintained preferably at a positive potential with respect to the cathode but at a somewhat lower potential than the anode. The electrode 5 is also connected to the cathode through a condenser 12 which offers a low impedance to currents having the frequency of oscillations produced by the crystal 8.

It will be understood from the description given that the efiect of the screening electrode 5 is to reduce the effect of capacity between the control electrode 4 and the anode 2, thereb'y preventing any substantial transfer of energy from the anode to the control electrode through this capacity, the high frequency energy of the screening electrode being by-passed to the cathode by the condenser 12. The coil 9 provides external means whereby energy of the desired amount may be supplied to the grid circuit thereby to excite the crystal and to cause the maintenance of the oscillations. The coil 9 is variable with respect to the output circuit such that the amount of energy supplied to the crystal is variable and may be adjusted by the operator to a value such that oscilla tions are maintained without at the same time endangering the crystal or causing it to rupture. 1

While I have shown and described but one embodiment of my invention it will of course be understood that I do not wishto be limited thereto since modifications may be made without departing from the spirit and scope of my invention as set forth in the appended claims. I

What I claim as new and desire to secure by Letters Patent of the United States is 1. An oscillation generator comprising an electron discharge device having an anode, a cathode and a control element, the inherent capacity between said control element and said cathode being such as to provide a high input impedance, a piezo-electric crystal connected between said control element and cathode, a load circuit connected between said anode and cathode, means including a screening element between said anode and control element and a path of low impedance between said screening element and the cathode for I preventing energy from being supplied from said anode to said crystal through the discharge device, and means external of said device for supplying energy from the load circuit to the crystal to maintain the production of oscillations.

' 2. An oscillation generator comprising an electron discharge device having a relatively high input impedance, an anode, a cathode, a control element and a screening element interposed between said anode and control element whereby the effect of capacity between'said anode and control element is re duced, a connection between said control element and cathode including a piezo-electric crystal, a load circuit connected between the anode and cathode, and means external of said electron discharge device for supplying energy from said load circuit to said control element connection thereby to cause said crystal to produce oscillations.

3. In combination, an electron discharge device, having an anode, a cathode, a control element and a screening element interposed between the control element and anode, said device having a high amplification ratio and a high impedance between the control grid and cathode, a piezoelectric crystal connected between the control grid and the cathode, a load circuit connected between the anode and the cathode, a connection between the screening element and the cathode having low impedance to currents of the frequency at which said device is to operate, and variable means external of said device for supplying energy from the load circuit to the crystal in amounts suflicient to cause the crystal to produce and maintain the production of oscillations.

In witness whereof, I have hereunto set my hand this 8th daof June 1928.

' OBERT 'B. DOLE.

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