US1836735A

US1836735A - Crystal oscillator

Info

Publication number: US1836735A
Application number: US466738A
Authority: US
Inventors: Edgar D Tillyer
Original assignee: American Optical Corp
Current assignee: American Optical Corp
Priority date: 1924-07-16
Filing date: 1930-07-09
Publication date: 1931-12-15
Anticipated expiration: 1948-12-15

Description

Dec. 1931. E. D. TILLYER ,836,735

CRYSTAL OSCILLATOR Original Filed July 16. 1924 avwemto'a attounq 1a to provide means whereb higlh I f Other obi Patented Dem-15, 1931 nssacmrsnr'rs, 1 assreuoaro Amman OPTICAL (DIP-ANY, F soumamen, IABS ACHUSETTS, L VOLUNTARY 'ASSOt'EI A.

- 'rroror nssacnusms cavern. 0 m

ori inal application and m, 10, ion, sum Io. mm. mvmea mam. a u auoii fled m a; ieao.

Serial IQ. 468,788.

The present invention relates on an improved form of crystal oscillator and has par-.

ticular reference to the production of a constant frequency electric oscillator.

An important object of the inventionis to provide anelectric oscillating circuit of constant frequency using a crystal grid contrel, or piezo electric properties -,of certain crystals.

'A furthenobject of the, invention is gerovide means whereby such a crystal will free to oscillate freely without-the presence of restraining friction. A stillifurther object of the invention is powers may be'drawn from the crysta wit out danger of fracturing or in otherwise ruining the crystal.

and advantages of the m- -v ention wi become apparent during'the a0 courseof the following description: 7

In the-drawings, wherein like numerals are employed to designate like parts'throughout the same,

Figure 1 is a diagrammatic view of a well known type of crystal and mounting therefor.

Figure 2 is a sectional view showing. one form of my invention, v and' Figure 3 is an elevation showing another form of my invention.

tals, suchas quartz, Rochelle salts and tourmaline have the uliar' property of be coming changed e ectrically w en they are compressed or stretched in certain directions. On the other hand they change their shape slightly when they are placed in field. Such crystals when vibrated mechanically will roduce an alternating voltage, and nature y, if they are placed in an alternat' electric field they will vibrate. Such are said to be of piezoelectric properties. a

If a wee of quartz is cut from a crystal arallel to its axis and is properly mounted m an-electric circuit as shown in the drawings, itmay-vibrate and cause the circuit to become an electric oscillator and thus a source of oscillations. If it 1 the an electricaldoes vibrate, the: vibrations are dependent upon "the form of influenced by external sources, as is wellknown;

Howe'ver, even if the crystal does vibrate well, when suflicient energy-is applied to really produce satisfactory oscillation for power control b the additional corona and In the drawings, wherein for the purposes of illustration .is'sh'ownthe preferred em:

purposes a corona appears,v .wherebythe cry'stal'is-locally stressed be- "yond its limit the crystal brea s'j down.

bodiment'of my invention the numeral 10' designates a crystal having piezo electricproperties: The crystal is shown vas being supported .between two metallic either in contact, touching very lightly, or just clearin the metal. Wire connections 12 are associatedwith' the plates 11, the-said plates usuallybeing brass.

plates 11,

whereusing the crystal asa grid control-in r101 tructures, namely,- first, the surface of t e c stal is in contact witha viscous medium un er-pressure and,second,thismedium permits'a brush disc urge to the crystal, producing local strains an much vgreater thansound in the air.

ocity' of sound within the crystal, which velocity is. In

other. words, we have a tremendous friction heating, thus 'causmg the fracture of a valuablecrystal as soon as any appreciable power is being. drawn; p from the circuit. Y

It' a llknown factthatoertainc sls we ry one in the direction A to B- and;

in the viscous medium air in. trying to impart this vibrationto the air surrounding the crystal. This energy is' all lost and in fact more than lost as the dampening may be sufficient at'alL',

Many attem ts have been made to over-. come. or to re uce the friction, such as for instance, curving the face BC of the crystal but while Anothergreat difliculty with the prior structures is that with high power use -a to prevent the crystalfrom vibrating this curved face has assisted, it has not eliminated the air viscosity.

There are two big difliculties encountered i .denser used for high frequenc oscillations,

inevitably producing a brea down under high power. 'With the crystal we cannot impregnate it with. wax as in the condenser because the 'wax stops the Vibration. Furthermore, we cannot add compressed air as is done in some high power air condensers, be-- cause the friction of ordinary air is unde- .sirable and the greater the pressure the greater the friction.

In accordance with my invention I remove the air friction by lowering the air pressure. A moderate reduction in pressure will accomplish this to a limited extent, but will. increase the corona discharge. However, if the air pressure is still further lowered the corona discharge will no longer pass between the plates and the crystal even if present. A still further reduction in the air pressure will stop all discharge and eliminate the air friction. Probably the best point of operation is where the discharge is stopped for the voltage used.

In Figures 2.-.and 3 is shown a crystal oscillator so arranged that it can readily be used as a grid oscillator control. The crystal 10 and plates 11 are mounted inbulb 13 in which'is formed either a complete or a partial vacuum. In Figure 3 the bulb is provided with a base 14 so that the bulb can easily be placed in or removed from a circuit easily and rapidly. By mounting the crystal and holder in a vacuum the corona cannot be present. Furthermore, the crystal is more stable, will stand much higher voltage and will vibrate much more freely because of the absence of air viscosity.

This application is a division of my prior application Serial-Number 726,289, filed July 16, 1924 entitled Crystal oscillator.

It is to be understood that the form of the invention herewith shown and described is to be taken as the preferred embodiment of the same and that various changes may be made in the shape, size and arrangement of parts without departing from the spirit of the invention or the scope of the subjoined claims.

I claim:

1. A piezo-electric crystal holder comprising in combination a hermetically sealed bulb and means within said bulb for securing a .piezo-electric crystal therein and establishing electrical connection therewith to said crystal through said bulb, while permitting the free vibration of said piezo-electric crystal with substantially no restriction, the space within said bulb being evacuated.

2. A piezo-electric oscillator having in combination a hermetically sealed bulb, a piezo-electric crystal therein, means within said bulb for mounting said crystal and establishing electrical connection therewith,

electrical connections extending through said bulb-to said mounting, the space within said bulb being evacuated.

3. A piezo-electric crystal holder comprising in combination a base plug, an evacuated bulb secured to said plug, means for supporting a piezoelectric crystal within said evacuated bulb, and means for establishing electrical connection with the said crystal from points on said plug which are exterior to said bulb.

4. A piezo-electric crystal holder comprising in combination a screw base plug, a glass evacuated housing secured to said plug, means for supporting a piezo-electric crystal within said housing, and means for establishing electrical connection with said crystal from points on said plug which are exterior to said housing. i

5. A piezo-electric crystal holder comprising a base plug having a stem, 8. housing enclosing the stem and supported by the plug, electric connections through the stem, a pair of separated plates one each being carried by one of said electric connections, and a piezo-electric crystal held between the plates.

6. A piezo-electric crystal holder comprising a closure, a pair of wires extending into the closure, a plate supported by each wire,

and a piezo-electric crystal held between the In testimony whereof I have signed my name to this specification.

EDGAR D. TILLYER.