US1830642A - Piezo electric crystal controlled oscillating system - Google Patents

Description

Nov; 3, 1931. A. CROSSLEY 1,330,642

PIEZO ELECTRIC CRYSTAL CONTROLLED OSCILLATING SYSTEM Original Filed June 11, 1928 a 9 7 7 m y wmm wa l f a W glwuentow Patented Nov. 3, 1931 UNITED STATES PATENT OFFICE ALFRED CROSSLEY, OF SOUTH HAVEN, MICHIGAN, ASBIGNOR, BY HESNE ASSIGNMENTS, TO FEDERAL TELEGRAPH COMPANY, A CORPORATION OF CALIFORNIA PIEZO ELECTRIC CRYSTAL CONTROLLED OSCILLATING SYSTEM Application filed 'J'une 11, 1928, Serial in. 284,571. Renewed October a, mo.

My invention relates broadly to circuits for the generation of electrical oscillations and more particularly to a piezo electric crystal controlled oscillator system.

One of the objects of my invention is to provide a circuit arrangement for sustaining the electrical oscillations of piezo electric crystal elements ground for any selected frequency characteristic with maximum efiiciency.

Another object of my invention is to provide a circuit arrangement for sustaining the natural oscillations of a piezo electric crystal element independently of inherent characteristics of the electron tube employed in the oscillator circuit.

Still another object of my invention is to provide a piezo electric crystal osci ator sysem wherein the inherent interelectrode capacity of the electron tube system associated with the piezo electric crystal oscillator is compensated and oscillations sustained at the natural frequency of the piezo electric crystal independently of the characteristics of the electron tube.

My invention will be more fully understood from the following specification by reference to the accompanying drawings wherein:

Figure 1 is a diagrammatic illustration of the circuit arrangement of my invention showing a series feed crystal oscillator circuit; Fig. 2 shows an oscillator circuit embodying the principles of my invention for a parallel feed system instead of the series feed system of Fig. 1; Fig. 3 shows a modified circuit arrangement for an oscillator embodying the principles of my invention in which a system of double feed back is employed; and Fig. 4 illustrates the application of my invention to a push-pull type of oscillator system.

In the conventional piezo electric crystal cont-rolled electron tube oscillating system the feedback means for obtaining the oscillation condition of the electron t'ibe circuit is the capacity present between the grid and plate electrodes of the three electrode electron tube. This capacity .is fixed by virtue of the permanent structure of the electron tube and its component parts, and the only means for obtaining greater grid voltage excitation is by resort to higher plate voltage or by the ineflicient method of varying the amount of I, inductance in the plate circuit. For any given tube there is a definite frequency at which the circuit will oscillate at a maximum efiiciency and any variation in frequency above or below this value will be accompanied by a reduced efficiency. 7

By reason of the inherent characteristics of the three electrode electron tube withits fixed feedback properties, maximum efliciency for fixed plate voltage is only obtainable at one particular frequency. The circuit arrangement of my invention-provides means to overcome the limitations of the three electrode tube circuit, and for this purpose I employ a four electrode vacuum tube with special means for varying the feedback relation to obtain maximum efiiciency.

The drawings show the special means employed for securing efficient operation of the piezo electric crystal controlled oscillator system. In Fig. 1 a variable capacity designated at 12 is used, while in Fig. 3 a combination of inductive and capacitive coupling is employed. The capacitive coupling in Figs.

1, 2 and 4 for the optimum efliciency condition should be decreased as the frequency is increased. Practice has shown that the capacity variation in the range from 2000 to 5000 kilocycles is from 25 to 4 micromicrofarads for optimum oscillation efficiency condition. The combination of inductive and capacitive feedback shown in Fig. 3 provides means for adjusting the feedback to a definite value by arranging the phase of the inductive feedback to be 180 out of hase with capacitive feedback, but of sma ler value. The two feedback voltages add up algebraically, with the result that the total voltage is less than the voltage due to the capacitive feedback. The reverse inductive feedback acts as a limiting means and is desirable in certain cases where surges or stray magnetic feedback .are present.

Referring to the drawings in more detail, reference character 1 designates a piezo electric crystal and holder, the crystal being com mooted series with the radio frequency I the plate battery-'6 with the intermediate volt :age contact-or which holds the shielding s 'd 1 6jat;a definite voltage. The inductance condenser "8 connected series with :ammeterit) complete the phase adjustin cirzcui-t. "Elihe iby-pass condensers l01=and '11 uncetion in bypassing the radio frequency current aroundthe plate :and shielding'gid volt- :age sources. The condenser '12 is the means;

for varying the feedback to obtain maximumoscillation efiiciency. Y a

The'four-electrode electron tube dhas four elements: The cathode 17 the control "grid 18 thefshielding I 'd 16 and the plate 19. The shielding gzrid l control 18 and the plate 19 and functions as an electrostatic shield, thus reducing the capacity between control .grid 18 and plate' 19 to a :small fraction of its normal value. This negligible value of capacity between control grid and plate electrode practically eliminates any tendency for feedback in the tubeand therefore makes this-tube ideally suited for use in m, piezo electric crystal os cillating system w erein I introduce a definite controlling feedback means in the form of the condenser 1'2 shown in the drawings. For best operation of this system it is necessary to provide a variable contactor 15 for the positive voltage source to the shielding grid 16 in order that a definite voltage be applied to this grid. Unless a voltage within tencentof the required amount is applied to the shielding grid 16 the circuit will not oscillate at maximum efiiciency,. 'It is also necessary to adjust the feedback condenser to-a value which produces maximum oscillation efficiency without obtaining a dangerous value of current through the crystal.

In Fig. 4 I'have shown a push-pull oscillator system having a piezo electric control circuit, with means for eliminating the effects of tube ca acity and enabling oscillations to be sustained in the push-pull circuit which are independent of the characteristics of the tube system. The controlling grid 18 and plate 19 of electron tube l-lare'interconnected by means of variable condenser 12. The control grid 18" and plate electrode 19' of electron tube 4' are interconnected by means of condenser 12'. The shielding grid 16 of tube 4 is shown at 16 connected to adjustable contactor 15 with battery 6. The

6 is positioned between the Vari- Battery 3 is provided common to the input circuits of each of the tubes 4 and 4" and choke coil'2 is provided in the input circuit of tube 4, while choke coil .2 is positioned in the input circuit ofitubedt.

The piezo electric crystal oscillator :sys-

item of imy;-invention has been found to :be

extremely-*efiicient in its operation for sustaining oscillations in accordance wIi-thfithe natural f-requencyof the piezoelectric crystal element at an amplitude greater than that which it is possib eto obtain in "a tube :system which is :beingforced to oscillate :at the natural frequency of the piezo electric crysztalelement by virtue of the normal tendency of the tube system to oscillate at an amplitude determined by the capacity characteristicsof the electron tube system.

' The potential on the shielding grid is hired from the source in the output system to that value at'which the grid-plate capacity effects of the tube system are substantially elimimatted, and oscillations ma be sustained entirely by virtue of the ar'ti cial feedback due to the condenser 12 or the inductance 14.

The inductive feed-back'can be reversed and made to add to the capacitive feedback whereby thecrystal will oscillate better if a minimum capacitive and a maximum inductive feedback is employed.

One of the advantages arising .out of my invention is derived from the use of the four electrode or shielded grid tube which has substantially no capacitance between control grid and plate and the use of either external capacity or inductance o" proper values to obtain maximum efliciency or output from a given crystal controlled system. 7

While I have described my invention in certain preferred embodiments, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than those imposed by the scope of the appended claims.

at I claim as new and desire to secure by Letters Patent of the United States is as follows 1. In a piezo electric crystal oscillator system, an electron tube having a cathode, a control grid and a plate, a shielding grid interposed between said control grid and said plate, a piezo electric crystal element con- 2. In a piezo electric crystal controlled oscillator system an electron tube including a cathode, a plate, a control grid and a shielding grid, a piezo electric crystal element,

connections between opposite faces of said element, said control gridand said cathode, an oscillatory circuit, connections between said oscillatory circuit, said cathode and said plate, a high potential source connected in circuit with said plate, and a connection between a selected point on said high potential source and said shielding grid for substanti ally eliminating the capacity effects between the plate and grid of said electron tube and sustaining in said oscillatory system oscillations of a frequency corresponding to the natural frequency of said piezo electric crystal element. a

3. In a piezo electric crystal control oscillator system, an electron tube including a heated cathode, a control grid and a plate, a shielding grid interposed between said grid and said plate, an input circuit including a piezo electric crystal element connected between said control grid and said cathode, an

output circuit including a high potential source connected between said plate electrode and said'cathode, an oscillatory system connected to said output circuit, a connection between a point on said highpotential source and said shielding grid for substantially eliminating the capacity effects of said electron tube, and means connected between said control grid and said plate for facilitating the transfer of energy between said input and output circuits whereby said piezo electric crystal element sustains oscillations in said oscillatory system at the natural frequency of said piezo electric crystal element.

4. In a piezo electric crystal controlled oscillator system, an electron tube including a cathode, a plate, a controlling grid and a shielding grid, circuit connections from said controlling grid and said cathode to a piezo electric crystal element, an output circuit including said plate and cathode, an oscillatory system connected to said output circuit, and a source of potential in said output circuit, a tapped connection from an intermediate point on said source to said shielding grid, whereby oscillations of a frequency corresponding to the natural frequency of said piezo electric crystal element are sustained in said oscillatory system independent of the capacity effects of said electron tube.

5. In a piezo electric crystal controlled oscillator, a plurality of electron tubes each including a control grid, a shielding grid filament and plate electrodes, a piezo electric crystal element connected to each of said control grids, an oscillation circuit connected to each of said plate electrodes, and circuits con-. nected with said shielding gridelectrodes for sustaining in said oscillation circuit oscillations of a frequency corresponding to the natural frequency of said piezo electric crystal element independent of the frequencies system including the plate and filament electrodes of said tubes, a source of. potential common to said output system, a shielding grid interposed between the grid and plate electrodes of each of said tubes-and connected to a point along the potential source in said output system and a piezo electric crystal having its opposite faces connected to the grid electrodes of eachof said electron tubes.

7. A vacuum tube device comprisinga catliode, an anode, a control grid and a shield grid between said control grid and said anode, sources of potential for said electrodes, a variable capacity connected between said control grid and said anode, a piezo electric crystal connected with at least two of said else-@- trodes for controlling the frequency generated and a connection between said shield grid and the source of potential for saidano-(le.

8. The combination of a piezo electric 'element, a plurality ofspace dischargedevices each provided with a control grid, a shield grid, a. cathode, and an anode, said shield,

grid being interposed between said control grid and said anode, said control grids and i said cathodes being connected in a series cir cult containing said piezo electnc element,

a source of potential connection between said shield grids and said cathodes, said shield grids being thereby rendered positive with respect to said cathodes, and circuit connections between said anodes and said cathodes.

9. The combination of a piezo electric element comprising a plurality of terminals, a

plurality of space discharge devices each ineluding a control grid which is connected individually to one of'said terminals, said discharge devices each including, in addition to said control grid, a cathode, a shield grid, and an anode, said cathodes being interconnected, a source of der said shield grids positive with respect to said cathodes, and circuit connections between said anodes and said cathodes.

10. The combination of a piezo electric element comprising a plurality'of terminals, a plurality of space discharge devices each including a control rid, said control grids being connected indlviduall to different ones of said terminals, said devices each including, in addition to said control grids, a cathode, a shield grid, and an anode, an impedance element connected between said terminals, mean's interconnecting the cathodes of said devices with said impedance element at a point intermediate its connections to said terminals, a source of potential connected otential connected so as to renbetween said cathodesand said shield grids whereby said shield grids are renderedpositive with respect to said cathodes, and circuit connections between said anodes and said cathodes. v v

11. An electron tube device comprising a. cathode, an anode, a control electrode and a shield electrode disposed between said control'electrode' and said anode, sources of potential for certain of said electrodes, a piezo electric element connected in a circuit including said cathode-and another of said electrodes, and a capacity external to the electron tube connected to 'saidcontrol grid and said anode. e

12. An electron tube device having a control grid, a shield grid, a cathode and an anode, a piezo electric element in a circuit including said control grid and said cathodei a tuned CIIClllt' connected to said anode an said'cathode, a capacity external to said electron tube connected to said control grid and said anode, and a source of potential connected between said shield grid and said cathode.

13. In combination with an electron discharge device having a control grid, a shield grid, a cathode and an anode, circuits interconnecting said electrodes, a piezo electric element in the control grid circuit, means'includingsaid shield grid for reducing to a negligible amount thecapacity effect between said anode and sa-id control electrode, and means for feeding back a selected amount of energy from the anode circuit to the control grid circuit.

ALFRED CROSSLEY.

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