US2546027A - Neutralized crystal oscillator - Google Patents

Description

March 20, 1951 R. L. DOWNEY NEUTRALIZED CRYSTAL OSCILLATOR Filed ma 28, 1949 Inventor:

Wn w. m t d H 6 Patented Mar. 20, 1951 NEUTBALIZED CRYSTAL OSCILLATOR Reginald L.-Downey, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application May 28, 1949, Serial No. 95,901

6 Claims.

My invention relates to oscillation generators and more particularly to such generators in which the frequency is controlled by a piezoelectric crystal.

One type of such generator employs a pair of electron discharge devices and a circuit connection in which oscillations are supplied from the output of one of the devices through the other device to the cathode of the first device. A piezoelectric crystal is included in this connection to control the oscillations supplied through it and hence the frequency of oscillations generated.

One of the objects of my invention is to provide such a generator capable of operation over an extremely broad range of frequencies and in which the frequency of oscillations may be controlled at any frequency in the range by the crystal in said connection.

Commonly such crystals are mounted between the electrodes of a crystal holder, or they may be provided with electrodes plated upon the opposite surfaces of the crystal as described, for example, in Baldwin Patent No. 2,412,030, assigned to the same assignee as the present invention. The latter arrangement is commonly employed in the case of crystals operating at natural frequencies which are harmonics of a fundamental frequency of the crystal.

One of the objects of my invention is to provide such an oscillation generator in which the capacity between such electrodes is prevented from sustaining oscillations, if the crystal becomes inoperative or is removed from the holder.

A further object of my invention is to provide means to neutralize the capacity between the electrodes of such a crystal.

The novel features which I believe to be characteristic in my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure illustrates an embodiment of my invention.

Referring to the drawing, I have shown therein a pair of electron discharge devices I and 2. The discharge device I has a cathode 3, a control electrode 4 and an anode 5, while the discharge device 2 has a cathode 6, a control electrode I and an anode 8. The two-cathodes 3 and 6 are connected to ground through respective cathode load resistances 9 and I andthe cathodes are connected together by means of a piezoelectric crystal II. This piezoelectric crystal may be of any of the usual types but frequently is one of the harmonic mode type such as is described in the above mentioned Baldwin patent. Such crystals are commonly mounted between electrodes 23 in a suitable holder or are provided with electrodes which are plated upon the surface of the crystal. They operate at extremely high frequencies including frequencies which are harmonics of the fundamental frequency of the crystal.

Operating potential for the oscillator is supplied by a battery I Z to the anodes 5 and 8 of the two discharge devices through resistances I3 and M, respectively. The anode circuit of discharge device I also includes a tuned circuit I5 which is resonant at the frequency of oscillations to be produced.

Oscillations generated in this circuit I5 are supplied through a coupling condenser I6 to the control electrode 1 of the discharge device 2. This control electrode I is connected to ground through a grid resistor I! and also through bypass condenser I8.

Oscillations supplied through this coupling condenser I6 to grid 1 excite the latter discharge device and are reproduced thereby in the same phase upon resistance It connected between the cathode and ground. These oscillations are then fed backthrough the crystal II to the cathode 3 of discharge device I whereby they excite the latter discharge device to produce oscillations in the circuit I5. Such oscillations may be supplied to any desired load circuit, not shown, which may be coupled in any conventional manner, either inductively, capacitively, or both, to the circuit I5.

It is my desire to provide such a crystal oscillator which will operate at any frequency'between 20 and '70 megacycles dependent, of course, upon the operating frequency of the crystal and the tuning of the circuit I5. It is :also desired that in the event the crystal I I becomes inoperative, as due to cracks or other imperfections therein, or in the event it be removed from the holder, any tendency of the system to continue generating oscillations be prevented. Sometimes it occurs, especially at the higher frequencies in the range, that due to capacity between the electrodes of the crystal (that is, the inherent capacity 2% represented in dashed outline between the platings on the crystal surface, or between the electrodes of the holder in which the crystal is mounted), the system continues to gencrate oscillations even if the crystal becomes inoperative or is removed from the socket.

Also, this interelectrode capacity 24 may permit oscillations at other than the desired crystal frequency when circuit I5 is incorrectly adjusted. In accordance with my invention, this is effectively prevented even at the highest frequencies in the operatingsrangeby the use of condenser connected between the cathode 3 and the anode circuit of device 2. Resistances I4 and 2| are included in this anode circuit and are so proportioned relative to the capacitance of condenser 20 that oscillations supplied through the condenser to cathode 3 and to the electrode of the crystal adjacent cathode 3 neutralize oscillations supplied through the capacity 24 between the crystal electrodes. Since oscillations with respect to ground appearing upon the resistances l4 and 2| are of opposite phase to those plied to an input of low impedance'and' in phase withthe amplifier output, which is supplied through thecondens'er 15 to device 2. Device 2 acts 'as "an amplifier with a low impedance output which is supplied from resistance It] to the crystal II, this voltage being in phase with that supplied to grid 1. At the same time, it acts as a phase inverter to supply oscillations of opposite phase through condenser!!! to efiect' the desired neutralization.

While I have shown a particular embodiment of my inventionfit will, of course, be understood that I do not Wish to be limited thereto since dil ferent modifications may be made without'departing from'the' spirit and scope of my invention, and I contemplate by the appended claims to cover any such modifications as fallwithiri'the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A crystal oscillator comprising a pair of electron discharge devices,-each having an anode, a cathode, and a control electrode, a piezoelectric erystalpmeans impressing anode operating potentials on each 'of said devices through respective anode and cathode load impedances, means couplin the anode of one of said devices to the control electrode of the other, 'means' regeneratively coupling the cathode of said other discharge device through said piezoelectric crystal" tiveanode and cathode load impedances, means coupling the anode of one of said devices to the control electrode of the other, means regeneratively coupling the cathode of said other discharge device through said piezoelectric crystal to the cathode of said one discharge device so as to excite oscillations in said one device at the natural frequency of said crystal, and a condenser connected betweentheano'deof 'said'other device and the cathode of said one device, said condenser bein proportioned to neutralize the capacity across said crystal at a desired frequency.-

3. A crystal oscillator comprising a pair of electron discharge devices, each having an anode, a cathode, and a; control electrode, means coupling the anode of one of said devices to the control electrode of the other, a pair of resistances, each resistance being connected between ground and a respective one of said cathodes, means impressing anode operating potentials on eachof said devices through respective anode impedances, 'means comprising a piezoelectric crystal connected between said cathodes for" regeneratively coupling said devices for the generation of oscillations, and a condenser connected between the anode of said other device and the cathode of said one device having capacity of such value as to supply oscillations to said cathode equal in magnitude to the oscillations supplied through the connections to said crystal when said crystal is inoperative;

4. The combination in a crystal oscillator of a pair of electron discharge devices, each having an anode, "a cathode, and a :control 'electrode, means coupling the anode of one 'of said devices to the control electrode of theoth'er, a pairof V resistances, each resistance being connected between ground and a'respective' one of said cathodes, means impressing anode operating potentials on each of said devices through respective anode impedancea means comprising a crystal 5i holder' having opposite electrodes con nected to said cathodes respectively and adapted to hold a piezoelectric crystal, said crystal regeneratively coupling said devices for'the generation of oscillations and having a natural frequency equal to the frequency of oscillations to be produced, and a condenser connected between the anode of saidother device and the electrode of said holder remote from said other device to supply oscillations to said last mentioned electrode equal to that supplied by capacity between said electrodes when said crystal is removed from'said holder.

5. The combination in a crystal oscillator of a pair of electron discharge devices, each having an input circuit and an output circuit, means coupling the output circuit of one of said devices-to the input of said other device and means coupling the output of said other device to the input ofsaid first device, thereby 'to support the generation -of oscillations, said lastmeans'. including a path comprising a piezoelectric crystal through which said oscillations are trans-- mitted, electrodes on either side of said crystal, and a neutralizing circuit extending from one electrode of said crystal to a point on one of said input and output circuits where oscillations appear having phase opposite to the phase of oscillations supplied through to said one electrode the capacity between saidelectrodes, said circuit being proportioned to prevent generation of oscillations due to said capacity between said electrodes.

6. A crystal -oscillator' circuit comprising first e and second electron discharge devices in cascade, said first device having a grounded grid input circuit and an output circuit tuned to a desired oscillation frequency, said second device having a grid circuit coupled to said output circuit and an anode circuit, said anode circuit including separate anode and cathode load impedances arranged to have oscillations of opposite phase developed thereon, a regenerative feedback connection between the cathodes of said devices for sustainin oscillations, said connection including a piezoelectric crystal and its holder electrodes, said crystal being series resonant at said desired frequency, said electrodes also having substantial capacity therebetween tending 15 ,4 9,842

to sustain spurious oscillations, and a degenerative feedback connection for neutralizing said spurious oscillations comprising a capacity connected between a point on said anode impedance and the cathode of said first device.

REGINALD L. DOWNEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,439,890 Hings Apr. 20, 1948 Royden Jan. 25, 1949

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