US2117101A - Oscillator - Google Patents

Description

ay 10, 1938. o. M. OWSLEY OSCILLATOR Filed June 29, 1935 til Patented May 10, 1938 UNITED STATES PATENT OFF! C E OSCILLATOR tion of Delaware Application June 29, 1935, SerialNo. 29,026

9 Claims.

"This invention relates to electron tube oscillators, particularly to oscillators operating on raw alternating current, .andhas special refer- -enceto grid biasing arrangements for oscillators -of this general type.

Oscillators of the type described are useful in producing modulated voltages for aligning receiver equipment, calibrating frequency meters, and similar work where frequencies must be accurately and conveniently determined. They are also useful as radio beacons and for other purposes where an output of characteristic tone is required.

An object of the invention is to provide a. novel and useful grid biasing arrangement for raw alternating current oscillators.

Another object of this invention is to maintain a negative potential on the grid of an electron tube generator, operated on raw alternating current, throughoutthe entire A. C. cycle.

A more specific object of the invention is to obtain a negative potential for the grid of a raw A. C. oscillator by a combination of two independently operating biases, to wit: self-bias by means of plate current drop in a cathode resistor during the positive plate current cycle and an alternating current voltage of negative polarity bymeans of a potential drop across an impedance, such as a transformer winding, and applied through a grid resistor, during the negative half cycle of plate current.

Another and important object of the present invention is to ensure optimum performance of a piezo-electric oscillator energized by raw a1- ternating current.

In order to make the invention more clearly understood there are shown in the accompanying drawing means for carrying the same into practical efiect, without limiting the improvements in their useful application tothe particular embodiments, which, for purposes of explaining the inventive c0ncept, have been madethe subject of illustration.

Figure l is a circuit diagram of an electron tube oscillator, conveniently of the Hartley type, adapted to be energized by raw alternating current, and shows a grid biasing arrangement within the present invention.

Fig. 2 illustrates diagrammatically the grid biasing arrangement of the invention as applied to a piezo-electric oscillator energized with al ternating current.

Referring now to 'Fig. 1, the particular form of oscillator which has been selected for illustration isa modified form of what is known as the Hartley circuit. This oscillator comprises an electron discharge tube I, preferably but notnecessarily of the high vacuum thermionic type, having the usual grid, or control electrode 2 and a plate electrode fi. The tube is also provided with a preferably indirectly heated cathode 4 having afilamentary heaterB. The-tube and its associated circuits are adapted to be energized with "raw alternating current supplied from a convenient source of, say, 110-120 volts-50450 cycles. The plate 5 is connected through a plate coupling coilrfi and lead I to one terminal 8 of the primary winding Tp of a transformer T which bridges the leads AC. from the'alternating current source, not shown. The filament 3 is energized by ourrentinduced in the secondary winding Ts of the transformer T.

The grid is connected by means of lead I 2, condenser l3, grid coupling coil l4, and a short lead l2b toone terminal IU of the secondary winding TS, and by short lead [2a to the terminal 9 of the primary winding Tp opposite that (8) to which the plate lead I is connected.

Plate coil 6 and grid coil M are in energy transfer relation and are shunted by a variable condenser 15 which is provided for adjusting the frequency of the oscillations generated by the tube I.

Inaccordance with the invention, two sources Ofgrid biasing potential are provided. One of these, a grid resistor R1 is connected between the grid 2 andone terminal ll of the transformer secondary winding Ts across which one of the discrete biasing potentials is actually developed. The other grid biasingpotential is developed by a self-bias resistor R2, shown shunted by a condenser Cz'WhiChlS of suitable value to pass radio frequency oscillations of the generated frequency. Resistor "R2 is connected as by l2b to the terminal IU of the transformer winding Ts opposite that (ll) to which the grid resistorRi is connected. The transformer windings Tp-Ts are relatively so poled that the grid '2 "is prevented from'going positive irrespective of the instantaneous polarity of the alternating current applied, from the A. C. source, to the .anode 5.

From the foregoing it will be apparent that the objectstof'the' invention are simply achieved by'a'pplying to 'thegridz an alternating current *VoItagein-phaSe with: that supplied to the plate 5 and adjusting the self-bias resistor R2 to such a value that "the negative bias generated thereby on the positive plate cycle exceeds the effective positive :bias developed .at that instant across TS R1 by an amount to ensure proper operation of the device. Thus on the positive anode onehalf cycle the grid is negative by the amount that the biasing voltage generated by R2 exceeds the alternating current grid potential, and on the negative anode one-half cycle the grid automatically becomes negative by the amount of bias developed across transformer secondary winding Ts.

One advantage of the dual biasing arrangement, of the present invention, over single, socalled grid leak biasing systems, is that the effects of grid loading (caused by zero or positive bias on the negative plate swing) is substantially obviated, the device starts oscillating more readily at the beginning of each positive plate swing ensuring a substantially purely sinusoidal wave form; further, the efiiciency of the device generally is increased.

The dual biasing arrangement of the invention is especially useful in starting and maintaining the generation of oscillations when used in connection with piezo-electric controlled oscillators energized by raw alternating current. This is so because a piezo electric element itself requires appreciable time to start oscillations, i. e., it is not instantaneous in its operation. This reluctance or time lag is a property of the element per se and can be varied only to a small degree in the cutting of the element.

With 60 cycle power on the plate of the associated circuit there is only 1/120th of a second available in which to build up positive oscillations. With usual biasing arrangements, from the instant of zero plate voltage and during the negative half cycle, there is zero bias on the tube and high grid currents result. This results in grid loading which must be overcome before the crystal can again start oscillating. By the time circuit conditions become normal, i. e., are in an electrical condition to permit vibration of the crystal, so much time (of the 1/ 120th second plate pulse) has been consumed that the crystal does not have sufficient time to start oscillating before the plate voltage again falls to zero or some low voltage at which the circuit will not oscillate.

The above and other disadvantages inherent with existing A. C. actuated crystal controlled oscillators are substantially obviated by the grid biasing arrangement of the present invention.

To convert the circuit of Fig. 1 into a crystal v controlled oscillator it is merely necessary to insert a crystal having the desired frequency characteristics and suitably mounted, in the grid circuit. Such an arrangement is shown in Fig. 2, which, with the exception of the addition of the crystal and a novel frequency change-over device, is similar in all respects to that illustrated in Fig. 1 and above described.

While the invention is not to be limited by the employment of a crystal of particular frequency response characteristic, it has been found, especially, when the oscillator is to be used for frequency calibration purposes, that there are certain definite advantages in employing a crystal cut in accordance with the principles set forth in copending application Serial No. 29,000 to Charles Baldwin and Samuel Bokovoy, filed June 29, 1935, Patent No. 2,073,046, granted March 9, 1937. Such crystals are cut to oscillate at but two fundamental frequencies, one of the frequencies bearing a multiple or other predetermined useful relation to the other. Thus, in Fig. 2 the crystal P may be assumed to be capable of oscillating at a Y-mode frequency of 100 kilocycles per second and an X-mode frequency of 1000 kilocycles per second. The crystal is interposed between two electrode plates 33-3300 and, one of which, 33, is connected to the grid 22 of tube 2| and the other electrode 330. is connected through a coil L21 to the filament at a point 30 on one side of the secondary winding T5 of the transformer T. There are two plate coils, L22 and L23 which are adapted to be selectively coupled to coil L21 as by a switch S1. The mode or frequency at which the crystal P oscillates is determined by the constants of the tuned circuit with which it is associated, thus, for 100 K. C. oscillation switch S1 is thrown to form a tuned circuit including condenser C22, coil L22 and all of L21. For 1000 K. C. oscillation switch S1 is thrown in the opposite direction and a circuit tuned to 1000 K. C. is formed by the combination of inductances L23 and a portion of L21, shunted by capacitor C25. The necessary connection between L23 and L21 is provided by condenser C24, though it may be constituted by the low impedance of the A. C. line. L22 and C23 now contribute little to the constant of this tuned circuit because of the extremely high impedance of these two units when in series.

As in Fig. 1, one of the dual biasing arrangements of the present invention comprises the transformer secondary winding Ts, to which grid resistor R21 is connected. The other grid biasing potential is developed by a self bias resistor R22, across which is shunted a condenser C22 of suitable value to pass radio frequency oscillations of the generated frequency. Resistor R22 is connected as by lead 32b to the terminal of the transformer secondary winding opposite that (3|) to which the grid resistor R21 is connected. As set forth in connection With Fig. 1, the transformer windings are relatively so poled that the grid 22 is always maintained at a potential of a sign and intensity to ensure optimum performance. Appropriate values to achieve the hereinafter described operating characteristics are designated upon the circuit diagram. With circuit constants of the values indicated, operation of the device is characterized by a high degree of overloading and distortion whereby a substantial series of harmonics, particularly useful for calibration purposes, is obtained. Thus, assuming that the dial of a radio receiver is to be aligned, switch S1 is thrown to form a tuned circuit including capacitor C25, all of inductance L23 and a portion of L21, whereby the crystal P will oscillate at its X-mode fundamental frequency, i. e. 1000 K. C. The radio receiver is then tuned approximately to this frequency and, when the A. C. note is heard in the speaker, the dial is calibrated at that particular setting. If the switch is then thrown to its other position the note will still be heard but it will be that produced by the tenth harmonic of the 100 K. C. Y-mode fundamental frequency of the crystal. The receiver dial is then slowly rotated and the note will fade only to reappear again at a dial setting corresponding to a frequency 100 K. C. from the note first heard. It is thus possible to calibrate the dial exactly, as each multiple frequency is picked up by the receiver.

Various modifications of the above described embodiments of the invention will suggest themselves to those skilled in the art. For instance, if it is desired to operate the oscillator at a plate voltage higher than that provided by a direct connection to the A. C. source, separate plate and filament transformer secondary windings may be employed, in which case one terminal of the plate winding is preferably tied to a corresponding terminal of the filament winding-due regard being had to the phasing of the several windings.

Polyphase current may, of course, be utilized, if desired.

Although certain specific ways and means for accomplishing the objects of the invention have been set forth, it will be understood that they have been given for purposes of explaining the inventive concept and should, therefore, not be construed as limitations to the scope of the invention.

What is claimed is:

1. In an oscillation generator, an electron discharge device having an anode, a cathode and a grid, a source of raw alternating current for said electrodes, and dual bias connections to said alternating current source for deriving therefrom a biasing voltage for maintaining saidgrid at all times with respect to said cathode irrespective of the instantaneous polarity of the alternating current supplied to said anode.

2. The invention as set forth in claim 1 further characterized in this,'that a piezo-electric element is provided intermediate said grid and cathode for controlling the frequency of the oscillations developed by said generator.

3. In an oscillation generator, an electron discharge device having a cathode, a grid and an anode, a source of raw alternating current for said electrodes, and means including a grid resistor and a transformer connected between said grid and cathode for deriving a negative biasing voltage from said alternating current source for maintaining said grid negative with respect to said cathode throughout the negative half cycle of the alternating current supplied to said anode.

4. In an oscillation generator, an electron discharge device having a heater type cathode, a filament for said cathode, a grid and an anode, a source of raw alternating current for said anode and said filament, and dual means operatively connected to said alternating current source and deriving a potential therefrom operative throughout both positive and negative cycles of said alternating current to prevent said grid from becoming positive with respect to said cathode.

5. In an oscillation generator, an electron discharge device having an anode, a cathode and a grid, a source of raw alternating current for said anode, two discrete sources. of biasing potential, and means determined by the instantaneous polarity of the alternating current applied to said anode for successively impressing said biasing potentials upon said grid to maintain it negative with respect to said cathode.

6. In an oscillation generator, an electron discharge device having an anode, a cathode and a grid, a source of raw alternating current for said anode, means for deriving discrete biasing potentials from said current source and for'successively applying the same to said grid to maintain it negative with respect to said cathode throughout the cycle of the alternating current applied to said anode.

'7. In an oscillation generator, an electron discharge device having a cathode, a heater for said cathode, a grid and an anode, a tunable circuit connected to said anode, a source of raw alternating current, a transformer having primary and secondary windings, circuit connections from said windings for impressing current from said source upon said heater and upon said anode through at least a portion of said tunable circuit, a self-bias resistor, a connection from said cathode through said resistor to one terminal of said secondary winding, a grid resister and a connection from said grid through said grid resistor to the other terminal of said secondary winding, said transformer secondary winding being relatively so poled that said grid is maintained negative with respect to said cathode throughout the cycle of the alternating current applied to said anode.

8. In an oscillation generator, an electron discharge device having a cathode, a heater for said cathode, a grid and an anode, a source of raw alternating current, a transformer having primary and secondary windings for impressing current from said source upon said heater and said anode, a grid circuit connection between said grid and said transformer primary and from said primary to one terminal of said secondary winding, a self-bias resistor, a connection from said cathode through said resistor to the terminal of said secondary winding to which said grid circuit is connected, a grid resistor, and a connection from said grid through said grid resistor to the other terminal of said secondary winding, said transformer windings being relatively so poled that said grid is prevented from going positive with respect to the cathode irrespective of the instantaneous polarity of the current applied to the anode from said source.

9. In an oscillation generator, an electron discharge device having a plate, a cathode and a grid, a source of raw alternating current for said plate, a circuit between said grid and said cathode, a piezo-electric element in said circuit, the electrical condition of said circuit during the brief period which includes the instant of zero plate current and the negative half cycle of said alternating plate current being normally such as to inhibit optimum performance of said piezoelectric element, and dual means for deriving a negative bias for said grid from said alternating current source and operative throughout said period to overcome said normal electrical condition of said circuit and including circuit connections for applying said bias between said cathode and grid to thereby negatively bias said grid throughout said brief period.

OLLIE M. OWSLEY.

CERTIFI GATE OF C ORRECTI ON Patent No. 2,117,101. May 10, 19

OLLIE M OWSLEYL It is-hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 21, claiml, after the word "grid" insert negative; and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of September, A. D. 1958.,

Henry Van Arsdale l) I Acting Commissioner 0f Patents.

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