US1756130A - Oscillation generator - Google Patents

Description

- April 29, 1930. s, OHL 1,756,130

050 ILLATION GENERATOR Filed Aug. 14, 1925 INVENTOR ATI'ORNEY Patented Apr. 29, 1930 uNiTEo I STATES PATENT OFFICE memes; o'HLjor jnEw YoEx, N. Y., ASSIGNOR "110 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A. CORPORATION or NEW YORK OSCILLATION' GENERATOR This linventionrelates to oscillation generconstant thefrequency of oscillations.

It: has: been known that'piezo-electric devices' nay be employed to control the frequencyof oscillations generated by space discharge tube oscillators. The piezoelectric device's so'u'sedfor controlling the frequency ofthe oscillators were crystals cut from quartz; and it was found that such crystals responded to anumber of frequencies With varying degrees ofactivity. There is usually one natural frequency atwhich the crystal gives its greatest response. Generally, however; oscillators which'have piezo-electric devices associated therewith for controlling the frequency ofthe oscillations are usually operated at the frequency at which the piezoelectric device gives its greatest response.

Inthe past" it'has. been customary to cut these piezo electric crystals used inoscillation generators-from quartz so that the dimension inthe 'fdirection ofthe axis of vibration of the'crystal is small as compared to the other dimensions. It ha'sbeen found that crystals so out have a number of "frequencies, which arenot'i'in the same neighborhood, to which they respond in a very large degree. Maximunr eificieiicy has been 'obtained when the oscillation generator was operated at a frequency which corresponded to the natural frequency of the crystal-for thegreatest response piezG-electric controlled oscillation generato-rs'has been thefailure of the piez'o-electric crystal to start-in operation without the aid of an initial mechanical jar. Another difliculty has been the failure to maintain the crystal inoperationafter being started. Because of these. difficulties the'application of piezo-electrio devices hasbeen-limited.

.Itis' an object of the present invention to control within'narr'ow limits the frequency of oscillations generated by an oscillator controlle'd b-y aupiezo-electric device. Another object of this invention is to provide means for starting the pie zo-electric device in vibration .withoutithe aid of any external mechan- Or ie of thechief difiiculties in the use of- Application filed August 14, 1925. Serial No. 50,336.

ical forces. Another object ofthe invention is to provide means for keeping the piezoelectric devices in vibration after being started, and it. is a further object to employ the capacity between the electrodes of a space discharge tube for coupling the input and output circuits of the tube in which such a piezo-electric device is present.

Acircuit arrangement for producing these results is shown in the accompanying drawing, which comprises a circuit electrically tuned to give oscillations of the desired frequency. 1 is a space discharge tube working onthe thermionic principle, including a cathodc2; an anode 3, and an input or grid electrode 4. The grid 4 is connected to one terminal of the piezo-electric device 5, while the other terminal of the piezoelectric device is connected to one terminal of an inductance 6. The cathode 2 is heated to incandescence by means of a battery 7. A source of potential 8 supplies space current to the anode 3 through the inductance 9. A condenser 10 is connected across the terminals of the source of-potential 8 in order to form a path of low impedance for alternating currents. A resistance 11 is connected between the grid electrode 4 and the cathode 2 in order to maintain the grid electrode at a suitable negative potential with respect to the cathode. A condenser 12, shown in dotted lines, represents the inherent capacity between the grid electrode 4 and the anode 8, including the capacity of the leads connected thereto. It is this capacity between the grid electrode 4 and the anode 3 which produces a reaction of the'plate circuit on the grid circuit in order to produce sustained oscillations.

The piezo-electric device 5 comprises conductive plates 13 adjacent to the opposite sides of thecrystal. Thecrystal is prefer- I ably disk-shaped, cut from quartz along one jected toan' electrostatic field a physical deformation occurs along the axis of the crystal. The signs of the charges produced in the first case depend upon the character of the stress, that is, whether tension or compression, Whereas in the second case the physical deformation due to the action of the electrostaticc field depends upon the direction of the field.

If'the stress changes from com;

pression to tension, or vice versa, the signs of the'electric' chargesfonthe faces of the crystal are reversed, whereas 1f the electrostatic field is alternately reversed tliecrystal undergoes alternately contraction and elongation in the direction of the axis. In other words,the crystal vibrates in an electrostatic the charge isalternately re-.

in the provision of means for starting the piezoelectric device in vibrationv atone of its natural frequencies without the aidfof any mechanical ar or other external force.

This means comprises an inductance for feeding some of-the energy in the plate circuit back to the grid circuit, and therefore pro;

vidcs for the production of a varying potential on the. terminals ofthe piezoelectric I has a maximum impedance is'slightly less device. Thus the potential on the terminals of the pieZo-electric device is gradually built up to assist in starting it in vibration. This advantage constitutes a. material improvement over any of the crystal-controlled oscillators known heretofore.

Another advantage of the present invention lies in the provision of means for insuring the continuity of the vibration after started. This means comprises, the connection of a source of electromotive force, which may be the source employed for. supplying V herein means any body or substance capable the plate circuit with the necessary: space:cur-

rent, across the terminals ofthe piezo-electric This insures the continulty of the device.

' action of the piezof-electric device after it is source of potential 8 and inductance 9 may,

if; desired, be considered the output circuit,

and the circuit including grid electrode 4,

cathode 2, source o'fpotential 8, inductance 6 w and the. picnic-electric device 5 may be con;

sidered the input circuit. The input circuituand the output circuit are coupled through "the electrostatic capacity between the grid electrodev and the anode of the space discharge tube 1. The condenser 10 shunts the source of electromotivc force 8 for alternat- .in currents. Part ofthe energy in the out-i insurev its starting whenever ...Furthermore, the source 0f.potent1ali 8 is connected across the terminals of the piezofound lthat: a piezo-electric I his also constitutes a ma put circuit is fed back to the input circuit through the mutual inductance between windings 6 and 9. This energy so fed back tends to produce a variation in the potential across the piezo-electric device in order to required.

electric device 5, through the resistance 11 and tends to maintain'the continuity ofthe vibrations of the piezo-electric device after it is started. "The resistance 11' is used here instead of a battery to maintain the grid electrode at an appropriate negative potential with respect to the cathode. This means ofmaintaining the grid negative operates only when there is a convection current between the cathode and the grid electrode, that is, it tends, to main: tain the grid electrode negativewith respect to the cathode during that part of the cycle in which the grid electrode hasa positive charge impressed thereon. When the grid electrode becomes positive itattracts elec,-.

tronsiandthe currentflows through the resistance 11 During the! rest of the, cycle there is no fiow ofelectrons from the cathode to the grid electrode; A rectified current is therefore established through the resistance '11 and this therefore lowers the potential of the grid electrode with respect to the cathode. a

The frequency at which the output circuit than the natural frequency at which the piezo-electric device is vibrated. In one capable of producing a more stable oscillatory condition, The. piezo-electric device was started automatically invibration whenever required, and was maintained in vibrationcontinuously until the source of potential was disconnected. I M r The term. piezo-electric device as used of generating an electromotive force in response to a change'ln-pressure. I VVhlle this lnvention has been disclosed in one embodiment which is deemed. desirable,

ity is capable of embodiment in other and widely variedorganizations without departmg from the spirit and scope of the appended claims.

That is claimed is:

1, In an oscillator,a'three-electrode space discharge device, an inputcircuit connected to NHL arrangement actually operated under these CO11(il1l31011S,'1t was found that thesystem was two electrodes of said device, an output circuit connected to one of said electrodes and a third electrodemea'ns whereby said input and output circuits maybe capacitatively coupled to.

produce sustained oscillations, an inductance having a low distributed capacity,.a source of I potentia-L'ancl a piezo-electric' device as an element of said input circuit to govern the fre lations, a piezo-electric element associated with the input circuit having a natural frequency substantially the same as the frequency for which the output circuit has a high and predetermined impedance, and means for starting said piezo-electric ele ments in vibration and for maintaining the continuity of said vibrations after being started.

3. In an oscillation generator, a threeelectrode space discharge device having input and output circuits, said circuits being coupled by the natural capacity of their conductors in order that oscillations may be sustained, means for controlling the generation of said oscillations, said means comprising a piezo-electric oscillator arranged in said input circuit, said piezo-electric oscillator having substantial inductive reactance at some frequencies and substantially no reactance at other frequencies, and an inductive coupling between said input and output circuits for I supplying energy to said piezo-electric oscillator to start and continue said piezo-electric oscillator in vibration at the frequency at which it exhibits asubstantial inductive reactance.

4. Means for generating oscillations, comprising an electrical discharge tube having a cathode, an anode and an impedance-varying element, an inductance, a piezo-electric device, and a source of potential, part of said inductance being included in an output circuit along with said source of potential, said anode and said cathode, the rest of said inductance being included in an input circuit along with said piezo-electric device, said impedancevarying element and said cathode, said input and output circuits being coupled by the inherent capacity between said anode and said impedance-varying element, said inductance being arranged to feed energy from said output circuit back to said input circuit in order to insure the starting of said piezo-electric device, said piezo-electric device being also connected across said source of potential to render the action of said piezo-electric device continuous after being started.

5. Means for generating oscillations, comprising a space discharge tube having an anode, a cathode and a grid, an inductance, input and output circuits for said tube, each circuit including a part of said inductance, a

piezo-electric device and a source of potential, said inductance so coupling the input and output circuits as to set up a potential sufficient to start said piezo-electric device in vibration.

said source of potential being connected across the terminals of said piezo-electric device to render the vibration of said piezo-electric device continuous.

In testimony whereof, I have signed my name to this specification this 13th day of August, 1925.

RUSSELL S. OHL.

Images