US2492185A

US2492185A - Oscillator

Info

Publication number: US2492185A
Application number: US677656A
Authority: US
Inventors: Royden George Taylor
Original assignee: Standard Telephone and Cables PLC
Current assignee: STC PLC; Federal Telephone and Radio Corp
Priority date: 1946-06-19
Filing date: 1946-06-19
Publication date: 1949-12-27
Anticipated expiration: 1966-12-27
Also published as: BE476373A; NL132648B; CH266249A; ES180303A1

Description

G. T. ROYDEN Dec. 27, 1949 OSCILLATOR 2 Sheets-Sheet 1 Filed Jun 19, 1946 INVENTOR. GEORGEIROYDEN ATTORNEY.

- Dec. 27, 1949' G. T. ROYDEN OSCILLATOR Filed June 19, 1946 2 Sheets-Sheet 2 IN VEN TOR. GEORGE TROYDEN ATTORNEY.

PM. Dec. 21, 1949 UNITED STATE oscmnron seem Orange, N. 1., as-

Gcorge Taylor Borden,

signer to Federal Telephone and Bad! poration, New York, N. Y.,

Delaware Cora corporation of Application June 19, 1946, Serial No. 677,656

' 1c Claims.

This invention relates to an oscillator and particularly to an oscillator having a predetermined and controllable frequency variation with reference to a fixed mid-frequency. In many signaling systems, particularly where frequency modulation is present, it is necessary that an oscillator have a fixed calibrated frequency as the carrier from which frequency modulating deviations are provided. The simplest and most accurate means for calibrating frequency include piezo crystals. Such crystals have sharp resonance characteristics and, by themselves, cannot be frequency modulated over a wide range. The usual range of frequency deviation in a frequency modulated communication system is far greater than can be accommodated by any simple crystal circuit.

In accordance with the invention, two vacuum tube amplifiers have their outputs connected in parallel to form a system output. Between the high side of the output and tube inputs is connected a crystal containing circuit and phase adjusting means. The arrangement is such that, under normal conditions, the phases of the input potentials to the amplifiers are shifted in opposite directions with respect to the corresponding effective total anode current. Push-pull modulation ofv the amplifiers results in variations in amplification of the amplifiers. Thus, the phase relation between the potential inputs and combined plate currents of the amplifiers is varied in response to modulating potentials. In the absence of modulation, the crystal circuit provides a fixed frequency at which the oscillator system stabilizes itself. Of particular importance is a means for stabilizing the crystal circuit. This stabilization is due to the connection of the crystal in the circuit sothat only its series resonant properties are effective, the shunt capacitance of the crystal being neutralized by a parallel resonant circuit containing the crystal. In shunt to the crystal part of the circuit is an inductor of such a value that its inductive reactance at the mid-frequency is numerically equal but opposite in sign to the capacitive reactance of the shunt capacitance of the crystal and distributed capacitance of both inductor and crystal arm of the circuit. Thus. the effect of these capacitances on the oscillations are suppressed making far more stable operation. Thus, desirable operating characteristics for the system above and below crystal resonance is provided.

For a more complete explanation of the invencuit diagram of a modified form of the invention.

Referring to Figure 1, vacuum tube It has cathode connected by wires l2 and I3 to any suitable source of heating current, here shown as battery |4 merely by way of example. Vacuum tube III has control grid'li connected through grid resistor II to the cathode. Grid I6 is also connected through condenser |8 to junction l9. Vacuum tube III has accelerating electrode 2| connected to junction 22. Junction 22 is connected through blocking condenser 23 to cathode H by lead l2. The cathode is also connected to center tap 24 of any source of modulating potential, here shown astransformer secondary 26. Secondary 26 has one end terminal 21 connected to suppressor electrode 28 of vacuum tube Ill. Anode 33 of vacuum tube I0 is connected by a suitable lead to junction 3|.

A second vacuum tube 35 has cathode 36 connected to wires |2 and I3. While the cathodes of both tubes are shown as of the directly heated type, it is understood that indirectly heated cathodes may be used. Vacuum tube 35 has control grid 31 connected through grid resistor 38 to the cathode, this same grid also being connected through inductor 39 to junction l9. Vacuum tube 35 has accelerating electrode 40 connected to junction 22. Suppressor electrode 42 is connected to outer terminal 43 of transformer winding 26. Vacuum tube 35 has anode 45 connected by a suitable lead to junction 3|. nected to junction 46 of phase inverting circuit 41 comprising inductor 48, condenser 43, inductor 50 and condenser 5|, all connected in series with each other to form a generally parallel resonant circuit. Junction 52 between inductor 48 and condenser 49 is connected by wire 53 to the positive terminal of a suitable source of potential shown, for example, as battery 55. The negative terminal of this source of potential is connected by wire 56 to the cathode circuit. Wire 53 is also connected through dropping resistor 51 to grids 2| and 40 of the two vacuum tubes.

Inductors 43 and 5|! together with the coupling capacitor 49 and tuning capacitor 5| form a phase reversing network which may be tuned to resonance by movable core for example.

Between inductor 50 and condenser 5| is junction 6|. Between junction GI and junction I9 is connected 2. piezo crystal circuit consisting of crystal 62, including suitable mounting means, all

tion, reference will now be made to the-drawings wherein Figure 1 shows a circuit diagram of, one form of the invention, and Figure 2 shows a cirshunted by inductor 63. The output of the en-. tire system is taken from junction 3| :through blocking condenser 54 and cathodes while modu- Junction 3| is con- 50 of metal, such as iron lating input for the system may be provided by means of transformer primary 65 cooperating with secondary 26. Such modulating potentials may be at any suitable frequency. Thus, if audio frequencies are used, transformer 56 including primary 65 and secondary 26 may be of the iron core type. On the other hand, if frequencies are too high for the use of iron cores, then air core transformers or capacitance coupling may be used.

Referring to the crystal circuit, inductor 53 has such a value that at the operating frequency its reactance substantially balances not only the reactance due to the shunt capacitance of crystal 62 but also that due to the distributed capacitance of the crystal containing branch of the circuit as well as the distributed capacitance of inductor 63 itself. Thus, at the desired operating frequency in the absence of modulation, this shunt circuit presents a high impedance between junctions I9 and 6| so that only the series reactance elements of the crystal are effective. The circuit between junctions 46 and GI forms a phase reversing network which may be tuned to resonance by controlling the coupling between

inductors

48 and 50, such as by moving core 50. It is, of course, possible to effect this tuning by varying either or both of condensers 49 and 5|.

Capacitor I8 and inductor 39 are so proportioned with respect to resistors I1 and 38 that, at the operating frequency of the system, substantial phase shifting will occur. Thus, with respect to the potential at junction I9, the potential at grid 31 will be retarded in phase, while the potential at grid I6 will be advanced in phase. Therefore, a corresponding phase shift of the plate currents in tubes 35 and I will occur. Consequently, the potential of junction 3| with respect to line I2 will be determined by the vector sum of the plate currents in the two vacuum tubes.

The potential at junction 6| is 180 degrees out of phase with respect to the potential at junction 3|. The phase relations necessary for oscillation are therefore provided.

Resistors I I and 38 may be the usual grid resistors having a value of 100,000 ohms or more. The value of resistor 51 will depend upon the potential in line 53 due to B supply 55 and the bias potential to be maintained upon accelerating electrodes 2I and 40. Condenser 23 is provided for blocking purposes and otherwise should readily by-pass all frequencies.

It is evident that vacuum tube I0, in the absence of modulation, tends to behave like a capacitive reactance, while vacuum tube 35 tends to simulate an inductive reactance.

Assume now that suppressor electrode 28 of vacuum tube I0 has its potential increased positively with respect to cathode I I. The amplification of tube I0 will, therefore, be increased and result in increased plate current. Conversely, the potential of suppressor electrode 42 of amplifier 35 will be decreased and the amplification of this tube will be decreased. With no modulating potentials, the tubes may be adjusted to have equal amplification and equal plate currents although these plate currents are displaced in phase with respect to each other. With push-pull modulating potentials on

electrodes

28 and 42, the vector sum of the two plate currents will be displaced in phase as compared to the vector sum of the plate currents without modulating potentials. The absolute magnitude of the vector sum will remain generally constant with various phase changes.

In order to maintain the entire system in oscillation, it is necessary that the sum of all phase shifts around a complete oscillating circuit including vacuum tubes be an integral number of 360 electrical degrees. Since the effective phase 5 shifts through vacuum tubes I0 and are varied by modulation, it follows that the frequency of the entire circuit will shift accordingly. Thus, in the example previously given where electrode 28 has its potential raised above cathode II and electrode 42 has its potential dropped toward cathode 36, the resulting effect on the entire system will be to raise the oscillating frequency.

The reverse will happen if the potential of electrode 42 goes up and the potential of electrode 28 15 goes down. It will be understood that the frequency of oscillation of the entire system will be high in comparison to the frequency of modulation at

electrodes

28 and 42 respectively.

Inasmuch as the network between junctions and 6| is used to produce a phase shift of 180 degrees or any odd number of such shifts, it follows that other phase reversing means such as vacuum tubes may be utilized. It is also clear that the amplification of tubes I0 and 35 may be varied in other manners. Thus, injection of the modulating potentials at cathode or anode or the grid nearest to the cathode are all well known and may be utilized. It is also possible to apply the modulating potentials to any two electrodes, such as anode and grid, instead of the usual cathode and other electrode arrangement. The output of the system may be alternatively taken from junction 8| or junction I9 or coupled to

inductors

48 or 50, or other well known manner and may be fed to frequency multipliers for operation in suitable frequency bands.

Referring now to Figure 2, a modified arrangement is shown wherein vacuum tube 10 has cathode ll connected to lead I2. Tube 10 has anode 13 connected to junction I4 in linev I5. Line 15 is connected through blocking condenser I6 to junction 11. Junction I1 has crystal I8 and crystal containing circuit including crystal holder connected between it and junction I9. Inductor 80 is shunted around the crystal by connecting the same to junction 11 and I9. It is understood that inductor 80 substantially neutralizes the shunt capacitance of crystal 18, the distributed capacitance of the crystal containing branch of the circuit and the distributed capacitance of inductor 80 at the frequency of oscillation. Junction 19 is connected through inductor 82 to junction 83. Junction 83 is connected by lead 84 to control grid 85 of vacuum tube 10. Vacuum tube I0 has accelerating electrode 86 connected to junction 81 and thence through resistor 88 to a suitable source of B plus potential.

Vacuum tube 90 has cathode 9| connected to lead I2, this lead being connected to the negative terminal of the B supply. Tube 90 has control grid 92 connected by wire 93 through inductor 94 to junction 83. Wire 93 is connected to wire 12 through grid resistor 96.

Vacuum tube 90 has accelerating electrode 91 connected to junction 81. Between junction 81 and line 12 is by-pass condenser 98. Vacuum tube 90 has anode 99 connected to junction I00 on lead 15. From junction I00, an output circuit through blocking condenser I 0| is provided.

Between junction I00 and B plus is choke I02.

Vacuum tubes I0 and 90 have suppressor electrodes I03 and I04 respectively connected to the outer terminals of transformer secondary I05. Winding I05 has center tap. I06 connected to the cathode circuit. Secondary Il5 has associated therewith primary I81 for providing modulatin potentials. The inductance of-the inductor 82 may be adjusted by iron core H0. The inductance of inductor 94 may similarly be adjurted by an iron core.

Shown in dotted lines are capacitances H I and 2 between the cathodes of the tubes and the opposite sides .of inductor 94. In practice, the input capacitance of

control grids

85 and 92 to ground will usually suffice and function as capacitors at the places indicated.

Inductor 82 is designed so that the phaseshift between crystal 18 and control grid 85 is less than 180 degrees. Inductor 94 on the other hand should provide a phase shift across it which is twice the difference between the previous phase shift and 180 degrees. Thus; as an example, if inductor 82 provides a phase shift of 120 degrees, then the phase shift provided by inductor 94 should be two times 183 degrees minus 120 degrees or 120 degrees.

It will be seen, therefore, that the invention provides two vacuum tube amplifiers having their output circuits connectedin parallel relation to form an output for the cntire system. Between the output and inputs of the two amplifiers, there is disposed suitable phase invertors and piezo crystal circuits for insuring a feedback of output energy to the tube inputs to maintain oscillation. By having the potentials at the inputs of the two tubes displaced in phase with respect to their respective anode potential, the amplifiers simulate reactances, the two having opposite signs. Push-pull modulation of the tube ampliflers results in effectively varying the magnitude of the simulated reactances. The crystal control circuit itself has suitable neutralization of shunt and distributed capacitances as to provide a crystal circuit of sharp resonance with generally symmetrical reactance properties on opposite sides of its series resonance frequency. a system is provided which will oscillate at high stability at crystal frequency or at a controlled deviation therefrom. The relationship. between modulating potential and deviation frequency is dependent upon circuit constants and, in general, can be made proportional whether the frequency deviation is above or What is claimed is:

1. An oscillating system comprising two vacuum tube amplifiers each having input and output circuits respectively, connections disposing said output circuits in parallel to form an output for the system, phase shifting means having output connections to said tube input circuits, at piezocrystal and phase reversing means, comprising a tuned circuit, in series between the input of said phase shifting means and the combined output of said tubes, said phase reversing means and phase shifting means providing a phase advance between the input potential and output current for one tube and a phase retardation between the input potential and output current for the other tube, and means for modulating said tubes in push-pull so that the amplification of said tubes are oppositely affected.

2. An oscillating system comprising two vacuum tube amplifiers each having input and output circuits respectively, connections disposing said output circuits in parallelto form an output for the system, phase shifting means having input and output connections, means connecting the outputs of said phase shifter to said tube input circuits, a piezo crystal circuit and phase reversing means in series grid and anode electrodes, means Thus below the crystal frequency.

phase shifter and the combined output of said tubes. said phase reversing means and phase shifting-means providing a phase advance between the input potential and output current for one tube and a phase retardation between the input potential and output current for the other tube, reactance means for neutralizing the shunt capacitance of the crystal, and means for modulating said tubes in push-pull so that the amplification of one tube is oppositely affected to that of the other tube.

3. An oscillating system comprising two vacuum tube amplifiers each having cathode, control for connecting said two anodes together to form an output terminal for the system, means for connecting said cathodes together to form the other output terminal, a phase shifter having an input terminal and two output terminals, means for connecting a phase shifter output terminal to a control grid respectively, a piezo crystal containing circuit and a separate tunable phase inverting circuit connected in series between the phase shifter input terminal and the system output terminal, means for tuning said inverter circuit to said crystal resonance frequency, an inductor connected across said crystal for neutralizing the shunt capacitance of said crystal and the distributed capacitance of said inductor, a source of modulating potential, and means for applying said modulating potential in push-pull relation to said two amplifiers to control their respective amplii'lcations. v

4. The system of claim 3 wherein each vacuum tube amplifier has an additional control electrode and wherein said modulating-potentials are impressed upon said, additional control electrodes.

5. An oscillating system comprising two vacuum tube amplifiers each having cathode, control grid and anode electrodes, means for connecting said cathodes and anodes together to form output terminals for the system, grid resistors'between said control grids and cathodes,

, a phase shifter having an input terminal and two output terminals, said phase shifter havi g a condenser in one branch and an inductor'in the other branch, means for connecting the outputs of said phase shifter to said control grids respectively, a piezo crystal containing circuit connected between said phase shifter input and a junction point, a resonant phase inverter circuit connected between said junction and the common anode output terminal, said resonant circuit being tunable over a range broad in comparison to the resonant frequency band of said crystal circuit, an inductor connected across the crystal, said inductor having such a value as to neutralize for the desired operating frequency the shunt capacitance of the crystal plus the distributed capacitance of the crystal circuit plus between the input of said the distributed capacitance ofthe inductor, a source of modulating potential and means for applying said potential to said two amplifiers in push-pull to affect the amplification of said amplifiers.

6. The system of claim 5 wherein said resonant circuit includes a pair of inductors and wherein the tuning means comprise means for varying the value of said inductors and the coupling therebetween.

'7. An oscillating system comprising two vacuum tube amplifiers each having cathode, control grid, additional control grid and anode electrodes, means for connecting the cathodes and anodes respectively to provide common anode and cathode output terminals for the entire system, resistance means connected between the cathodes and grids, a condenser and an inductor connected in series between said two control grids and forming a phase shifter, a piece crystal containing circuit and phase inverter connected between the Junction 01' said condenser and inductor on the one hand and the junction 01' said two anodes on the other hand, said crystal containing circuit having an inductor for neutralizing the shunt capacitance of said crystal as well as the distributed capacitance of the crystal containing circuit, a source of modulating potential and means for applying said potential to said two additional control electrodes to vary the amplification or said tubes in an opposing sense.

8. An oscillating system comprising two vacuum tube amplifiers each having cathode, control grid and anode electrodes, means for connecting the cathodes and anodes respectively together to provide output terminals for the entire system, a crystal containing circuit and one inductor in series between the two anodes and control grid of one tube, a second inductor between the two control grids of both tubes, means for coupling said two inductors together, and means for applying modulating potentials to said tubes to vary the amplification thereof in opposing senses, said two inductors cooperating with input tube capacitances to provide phase shifting of potentials impressed upon said two control grids, the potentials of said two grids having respective phase advance and lag with reference to the respective combined anode currents and an additional inductor is shunted around said crystal, said inductor neutralizing the shunt and distributed capacitance of the crystal containing portion of the circuit.

9. An oscillating system comprising two vacum tubes each having cathodes, control grids and anodes respectively, means for connecting said cathodes together to form one output terminal for the system, means for connecting said anodes together to form another output terminal for the system, a blocking condenser, crystal containing circuit and inductor connected in series between the other output terminal of the system and one control grid, an additional inductor between said one control grid and the other control grid, resistance means connecting said control grids and cathode, said one inductor pro-' viding a phase shift less than degrees between the crystal and one control grid, said other inductor providing a phase shift substantially equal to two times the diil'erence between 180 degrees and the first-mentioned phase shift, and means for modulating said tubes to vary the amplification thereof in opposing senses.

10. The system of claim 9 wherein an inductive reactance is connected across the crystal containing circuit to neutralize the shunt and distributed capacitance 'of the crystal and crystal containing circuit.

11. The system of claim 9 wherein said two inductors have coupling therebetween and wherein means are provided for varying said coupling.

12. The system of claim 9 wherein mutual coupling between the two inductors are provided and wherein an inductor in shunt to the crystal is provided to neutralize the equivalent shunt capacitance of the crystal.

13. The system of claim 9 wherein each of said vacuum tubes has an additional control electrode and wherein said modulating potentials are impressed on said two additional control electrodes, the modulating difference in potential existing between said two additional control electrodes.

14. The system of claim 9 wherein an additional condenser is connected between cathode and control grid of each tube.

15. The system of claim 9 wherein an additional condenser is connected between cathode and control grid of each tube, and wherein an inductor in shunt to the crystal is provided to neutrallze the equivalent shunt capacitance of the crys- 16. An arrangement according to claim 1, further comprising means coupled in shunt with said crystal and tuned therewith whereby only the series reactance elements of the crystal are eflectlve in the associated circuits.

GEORGE TAYLOR ROYDEN.

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

UNITED STATES PATENTS Number Name Date 2,318,979 Usselman May 11, 1943 2,326,314 Usselman Aug. 10, 1943 2,440,621

Usselman Apr. 27, 1948