US2007637A - Crystal controlled oscillator - Google Patents

Description

July 9, 1935. F. BYRNES V CRYSTAL CONTROLLED OSCILLATOR mama? Filed March 30, 1953 2 Sheets-Sheet 1 0 E 1. .7 w M\ 38 l l l l INVENTOR IRVING FRANCIS BYRNES BY 9% J ATTORNEY July 9, 1935. BYRNES 2,007,637

CRYSTAL CONTROLLED 050 I LLATOR Filed March 30, 1933 2 Sheets-Sheet 2 /2) l I k 6 40 R54 ///4 78 6 g 24 104 I 00 4 g 7g 210 z E 2% "umo 1 1 if ma 706? 1/2 1/8 INVENTOR IRVING FRANCIS BYRNES ATTORNEY Patented July 9, 1935 UNITED STATES:

CRYSTAL CONTROLLED oscILLA'roR Irving Francis Byrnes, Riverdale, N. Y., assignor to Radio Corporation of America, a. corporation of Delaware Application March30,19 3 3, Serial No. 663,435

7 '7 Claims. (01. 25036) controlled oscillation generators adapted for use in transmitters, receivers and frequency meas uring systems, and has particular reference to constant frequency oscillation generators for a use in aircraft.

Things much to be desired in, for example, oscillation generators for aircraft transmitters are, operation at a constant predetermined frequency, simplicity of construction, simplicity of adjustment, absence of critical settingsand freedom from undesired parasitic oscillations. Moreover, when crystal controlled oscillation generators are used, it is highly desirable to obtain a reasonably high power output in order to eliminate the weight and cost of subsequent amplifiers. When obtaining a high power output from a crystal controlled oscillator it is also desirable to prevent undue stress of the crystal, or, in other words, to obtain a high power output without having a large current flow through the crystal. I

To provide for these prime desiderata is, there'- fore, the principalobject of my present invention. In carrying it into effect I connect the serial combination of a-high. reactance and a piezo-electric crystal between a control or cold electrode and cathode of an electron discharge device whereby the high reactance prevents energization of the crystal which would otherwise occur due to the interelectrode capacity of the elements of the device or tube. In the alternative or in addition, I provide electrodes within the tube to eliminate, or assist in eliminating the undesired interelectrode feed back. For desired feed back purposes I couple the anode orv plate circuit to the control electrode or active side of the frequency controlling piezo-electric crystal, by means of a variable resistor whereby desired operation ensues, namely, excitation of the crystal in such a way as to give a reasonably high power output witha reasonable minimum of current flowing through the crystal.

Further understanding of my present inven tion may best be obtained by referring to the accompanying drawings although, of course, as required by law, it is defined with particularity in the appended claims.

Figure l of the drawings ilustrates in wiring diagram form a preferred modification of my present invention wherein undesired inter-eleccapacitorgfjor reducing interelectrode feed back is aided by the use of electrodes intermediate the control electrode and anode of the tube forming part of my oscillation generator;

Figure 3 illustrates, according to my present invention, a pushpull form of oscillation generator; and,

Figure 4 is a'wiring diagram of my present invention wherein the screen grid of a tube is used as the anode or plate.

A Referring in greater detail to the drawings and in particular to Figure 1, I have illustrated dia-- grammatically an electron discharge device having within an hermetically sealed container 2, a cathode 4, a cold control electrode or grid ii and an anode 8. The cathode 4 may, of course, be of then. C. energized type, or of the filamentary D. C. energized type as illustrated; it may be of the indirectly heated type, or it may be what is known as a cold cathode. The control elec-v trode or grid 6 is spaced from the anode i and is subjected to a unidirectional negative potential by the action of a grid leak resistor l0, which may be replaced by the serial combination of a choke coil and a source of negative biasing potential.

Between the control electrode 6 and cathode 4 there is connected a high impedance in the form of a small condenser [2 in series with the two electrode piezo-electric crystal M. The condenser 12, because of its small size, has a high capacitive reactance at the operating frequency of the-crystal, and prevents energization of the piezo-electric crystal I4 which would otherwise occur due to the interelement capacity existing between the anode 8 and the control electrode 6.

Between the anode 8 and the cathode 4 there is connecteda circuit l6 having inductance and capacity. Theinductance is provided by the coil l8, connected intermediate its ends, through conductor 20 and by-passing condenser 22, to the cathode 4. The capacity of the circuit may be due to the distributed capacity of the-coil i8 alone orin combination with the capacity existing between the anode and cathode. This capacity may be augmented, if desired, by the addition of a variable tuning condenser 24.

.In order to establish a desired feed back, I have shown in Figure 1 a circuit having a variable resistor 26 connected between the anode or anode circuit andthe control electrode 6 and through the control electrode side or terminal of condenser i2 to the active electrode of the piezo-electric crystal l4. To prevent the application of unidirectional plate potential or anode potential on to the grid 6 of the tube, there is inserted in this coupling circuit comprising conductors 28, 36, a blocking condenser 32. Also, it will be noted that the coupling circuit or resistor 26 is connected to the lower end of coil I8 and hence the volt-' ages fed back tothe control electrode are in sub.-

stantial opposite phase relation to those existing upon the anode which, as apparent to those skilled in the art, is the correct condition for oscillation generation. This action will occur with a circuit as described at only a frequency corresponding to one of the natural modes of vibration of the piezo-electric crystal l4. 7

In the foregoing circuit no oscillations will be produced with the crystal removed and similarly, with the coupling resistor 26 removed, no oscillations will be produced. By removed I mean actual removal and consequent opening of the circuit 28 and 38, to show that there is not enough feed back through 12 to sustain oscillation. With resistor 26 shorted there will be excessive feed back and crystal may then not determine frequency of oscillations.

Output energy may be taken from the conductors 34 and fed directly to a radiating antenna (not shown). The energy fed into the antenna may be modulated by impressing, through the medium of an audio frequency transformer 36, audio frequency voltages upon the anode potential supply 38.

I have found that the circuit described in Figure 1 is easy to construct and requires no critical settings, and these features are highly desirable in apparatus for use in, for example, aircraft transmitters. As already pointed out, removal of the coupling resistor or the crystal stops oscillations. The crystal, therefore, is in full control of the oscillation frequency and this 'may readily be proved by changing the tuning of the output circuit I6 either by varying its inductance or by varying the tuning condenser 24; or, by changing the plate or filament voltage. Moreover, I have found that the current through the crystal is onehalf to one-quarter of that which flows in other circuits, which I am aware of, for a given output from the tube.

In the arrangement shown in Figure 2, action of the small condenser or the highly capacitive reactor [2 in preventing excitation of the crystal 1 4 due to interelectrode capacity of the tube 2 is aided by the addition of a screen grid 40 and/or a suppressor grid 42, the former of which is grounded for radio frequency currents by means of a by-passing condenser 44 and maintained at a suitable unidirectional positive potential by the action of voltage dropping resistor 46. It is to be clearly understood, however, that condenser I 2 may be entirely omitted if the suppressor 42 and/or screen grid 40 act to prevent feed back other than the desired feed back through resistor 26. The suppressor grid is grounded by the action of a by-passing condenser 48 and maintained at a suitable negative potential by means of conductor 50 tapped to potential biasing source 52 which may be used directly, if desired, in conjunction with resistor I0, to subject control electrode or grid 6 to a suitable negative potential. Also, in the arrangement shown in Figure 2, feed back may be accomplished by use of a coupling coil 54 grounded as shown and inductively coupled to inductance coil l8, although, if desired, electrostatically shielded therefrom through the medium of a grounded shield 56. In the event that coils I8 and 54 are mounted concentrically, shield 56 may be made concentric therewith and preferably in the form of a slitted, grounded metallic cylinder mounted between the coils.

By impressing voice currents upon transformer 58, modulator tube 60 will cause varying currents to flow through inductive reactor 62, which, if desired may be a resistor, and hence the out.-

put of the system shown in Figure 2 will be modulated in accordance with the signal or voice currents impressed upon transformer 58. The modulated output of oscillator 2 may then be fed into a power amplifier 64 and radiated by a suitable antenna 66.

In the event of operation at exceedingly high frequencies, the inductance of the leads to the screen and suppressor grids may be insufficient to prevent their maintenance at ground potential. In that case condensers 44, 48 may be reduced in value so as to series resonate with the leads thereby maintaining the suppressor and screen grids at ground potential.

My present invention is not limited to single tube oscillators; for, as shown in Figure 3 my invention may be applied to a pushpull arrangement of, for example, screen grid tubes 2, 10. The crystal M in this case is blocked off from the control grids 6, 12 by small condensers l2,

'14 having relatively high capacity reactance.

These condensers prevent oscillation generation due to interelectrode feed back and this form of feed back may be reduced to a still lesser value by means of screen grids 40, 18, grounded by by-passing condenser 44 and maintained at a suitable operating potential by means of tap 18 connected to the anode source 80. The plates 8, 82 of the tubes are connected in phase opposition by means of an inductance coil 94 which may be so chosen as to have a suitable resonant period with its own distributed capacity. Or, if desired, a tuning condenser may be variably connected across the entire coil or any portion thereof. This statement, of course, applies equally well to the other arrangements such as shown in Figure 1, wherein, for example, condenser 24 may not only be connected in the position. shown, but may be connected across the lower half of coil l8 or across a lower and upper portion of coil [8, or if desired, across the complete coil.

Turning back to Figure 3, desired feed back may be accomplished by the use of solely variable resistor 26 and blocking condenser 32 connected between grid 6 and a point on coil 94 below the intermediate plate tapping point 88. Preferably, however, I provide a symmetrical arrangement of feed back circuits and as shown, to do so, a variable resistor 90 and blocking condenser 92 forming a circuit connected between a point 84 on coil 94 above tapping point 88 and to grid 12 of tube 10, are provided. The grids are subjected to a suitable operating potential by the action of grid leak resistors Ill, 96.

Output energy may be fed to a modulator 98 and then to a power amplifier and/or frequency multipliers I whose output may then be fed into ratio frequency transmission lines or preferably into a radiating antenna I82. If desired, the frequency multipliers may be placed ahead of the modulator.

In Figure 4 I have shown an arrangement wherein the various features of my present invention may be utilized in an oscillation generator wherein the screen grid 40 is used as a plate. Since the connections are similar to the arrangement shown in Figure 1, no detailed remarks concerning this circuit need be given. However, it may be pointed out that the anode 8 is coupled to the oscillatory system formed of the con trol grid 6, screen grid 40, cathode 4, the crystal, and the other necessary elements of the oscillatory circuit, only by way of the electron stream within the tube 2. The anode or output circuit of tube 2 may be in the form of a tunable circuit IM which may be tuned to some harmonic of the crystal M if desired. Moreover, harmonic production in the tunable circuit I04 may be facilitated by varying the relative poten-- tials on the plate 8 and screen grid lil bysuitable adjustment of taps I66, H38 respectively on source Hi3. Output energy from the output circuit I04 may be fed to a first detector l E2 to which is also fed, from amplifier H 5, radiant energy collected upon antenna H6. The output of the first detector H2 may then be fed after suitable amplification, if desired, to a second detector Hi5 whose output after audio frequency amplification may be fed to a translating device such as ear phones are.

Also, in the arrangement shown in Figure 4, output energy may be taken and utilized in any desired way from the screen grid tunable circuit formed of coil l8 and tunable circuit E i which, of course, may be placed across any portion of the coil it. Thus, for example, the output of coil [8 and tunable circuit 24 may be inductively fed into suitable circuits to control the frequency of oscillation of a transmitter whereas simultaneously output energy from circuit we may be used to control as shown a receiving circuit or vice versa. In addition, circuit ltd may obviously be replaced by a simple coil or by a resistor from which output energy may be taken in ways well known to the art.

In the claims which follow the term anode is to be taken as not only including an anode such as plate 8 of Figure 1, but also is to be given a broader construction so as to include a. tube element such as screen grid ill of Figure 4.

Having thus described my invention, what I claim is:

1. A constant frequency oscillation generator comprising an electron discharge device having Within an hermetically sealed container an anode, a cathode, and a control electrode; a piezoelectric crystal connected between said control electrode and cathode; a reactor in series with said crystal and connected between said crystal and said control electrode for preventing eX- citation of said crystal due to interelectrode feed back; a circuit interconnecting said anode and cathode; and, another circuit coupling said anode circuit to the control electrode side of said reactor for causing energization of said crystal and hence oscillation generation at a frequency fixed by said crystal.

2. An oscillation generator comprising an electron discharge device having within an hermetically sealed container an anode, a cathode, and a control electrode; the series combination of a small condenser and a piezo-electric crystal connected between said, control electrode and cathode, one side of said small condenser being connected to said control electrode and the other side of said condenser being connected to said crystal, said small condenser acting to prevent excitation of said crystal by virtue of the interelectrode capacity of said device; and, a coupling circuit between the anode of said device and the control electrode side of said small condenser for causing desired energization of said crystal and hence the production of oscillations of said device at a frequency fixed by said crystal.

3. An oscillation generator comprising an electron discharge device having within an hermetically sealedcontainer an anode, a cathode, and

a control electrode, the serial combination of a small condenser and a piezo-electric crystal connected between said control electrode and cathode, one terminal of said small condenser being connected to said control electrode and the other to said crystal, a circuit interconnecting said anode and cathode; and, a circuit including a variable resistor for establishing feed back from said anode to the control electrode side of said small condenser whereby oscillations are set up at a frequency determined by said crystal.

4. An oscillation generator comprising a two electrode. piezo-electric crystal, an electron discharge device having Within an hermetically sealed container an anode, a cathode and a control electrode, the serial combination of a small condenser which is highly reactive at the operating frequency of the crystal and said two electrode piezo-electric crystal, connected between said control electrode and cathode, said small condenser having one side connected to the corn trol electrode and the other side to said crystal; a circuit having inductance and capacity connected between said anode and cathode, and,'a variable resistor coupled to the control electrode side of said small condenser and anode for establishing desired feed back whereby oscillations of a frequency determined by said crystal occur in said circuit having inductance and capacity.

5. An oscillation generator comprising a two electrode piezo-electric crystal, a vacuum tube having an anode a cathode and a control electrode, the series combination of a small condenser which is highly reactive at the operating frequency of the crystal and said two electrode piezo-electric crystal connected between said control electrode .and cathode said small condenser having one terminal connected to said control electrode and its other terminal to said crystal; a grid leak resistance connected between said control electrode and cathode, and, the series combination of a blocking condenser and a variable resistor connected between said anode and the control electrode side of said small condenser whereby feed back for causing oscillation generation at a frequency determined by said crystal, is established.

6. Apparatus as claimed in claim 5 wherein, for assisting said small condenser which is highly reactive at the operating frequency of the crystal for preventing excitation of said crystal due to interelectrode feed back, there is provided in addition an electrode between said control electrode and cathode, and means for maintaining said additional electrode at a suitable unidirectional potential.

7. A constant frequency oscillation generator comprising an electron discharge device having within an hermetically sealed container an anode, a cathode, and a control electrode; a piezo-electric crystal connected between said control electrode and cathode; a reactor in series with said crystal for preventing excitation of said crystal due to interelectrocle feed back said reactor being connected between said control electrode and said crystal; a circuit interconnecting said anode and cathode; and, another circuit including a resistor coupling said anode circuit to the grid side of said reactor for causing energization of said crystal and hence oscillation generation at a frequency fixed by said crystal.'

IRVING F. BYRNES.

Images