US2294797A - Oscillator - Google Patents

Description

Sept. 1, 1942. A. L. NE'LSON OSCILLATOR Fiied Sept. 26, 1940 2 Sheets-Sheet l FIG. I

OSCILLATOR Filed Sept. 26, 1940 Z'Sheets-Sheet 2 T E45 IINVENTOR UR L. NELSON Patented Sept. 1, 1942 OSCILLATOR Arthur" L. Nelson, Fort Wayne, Ind., assignor to Farnsworth Television and Radio Corporation, a corporation of Delaware Application September 26, 1940, Serial No. 358,495

3 Claims. (Cl. 250-36) This invention relates to oscillator systems and more particularly to an oscillator system adapted to produce a plurality of signals of different phases.

Oscillator systems of the prior art are ordinarily of the type which produce a single output signal, or two output signals in phase opposition. In general, such oscillators are operated by feeding a portion of the output voltage of a signal-repeating means back into its input circuit. The feedback may take place either within the signal-repeating means itself or through an external path. Such oscillators, even those employing more than one signal-repeating means, are not adapted to supply a plurality of output voltages other than in phase opposition.

It is an object of the present invention, therefore, to provide an improved oscillator system which is capable of producing a plurality of output signals having desired phase relationships.

In accordance with the present invention, there is provided an oscillator system comprising a plurality of resonant circuits. Means including an external source of energy are also provided for translating energy from each of the resonant circuits to another of the circuits, and for energizing the latter in phase-shifted relationship to the first-mentioned one of the circuits. In this manner, signals are developed across the resonant circuits with predetermined difierent phases.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

Fig. 1 is a circuit diagram of an oscillator system in accordance with the present invention;

Fig. 2 is a vector diagram representing certain operating characteristics of the oscillator system of Fig. 1;

Fig. 3 is a circuit diagram of a modified form of oscillator system in accordance with the present invention; and

Fig. 4 is a vector diagram representing certain operating characteristics of the oscillator system of Fig. 3.

Referring now more particularly to Fig. 1, there is shown a system comprising a pair of electron discharge tubes I and 2. The tube l is provided with a cathode 3, a control grid 4, a screen grid 5 and an anode 6; while the tube 2 includes a cathode l, a control grid 8, a screen grid 9 and an anode H). The cathodes 3 and I are connected to ground through the resistors I l and I2, respectively, these resistors each being shunted by a by-pass condenser l3. For the purpose of applying a signal voltage to the con- I8, and are by-passed to ground by the condensers 18A.

- The anodes 6 and In of the tubes I and 2 are provided with a suitable positive potential, from the source indicated by B+, by way of choke coils l9.

A parallel resonant circuit, comprising an inductance element 20, and a condenser 2| in series with a resistor 22, is connected, by way of the blocking condenser 23, between the anode 6 and ground. A similar parallel resonant circuit comprising an inductance element 24 and a condenser 25 in series with a resistor 26 is connected, by way of a blocking condenser 21, between the anode l0 and ground.

The high-potential terminals of the resonant 3 0" circuits -2l-22 and 242526 are connected to the output terminals 28 and 29, respectively. The common output terminal 30 is grounded. The junction of the inductance element-{20 and the resistor 22 is connected by means of a lead 3| to a tap 32 on the inductance element Hi. The junction of the condenser and the resistor 26 is connected by means of a lead 33 to a tap 34 on the inductance element [4.

The operation of the device of Fig. 1 may be understood more readily by reference to the vector diagram of Fig. 2. Let the signal voltage which appears between the output terminals 28 and be represented by the vector E28, and the signal voltage which appears between the terminals 29 and 30 by the vector E19. The latter voltage leads the former voltage by The current which passes through the condenser 2| is represented by the vector I21, and this current leads the voltage E28 by 90. The current which passes through the inductance element 24 is represented by the vector I24, and this current lags the voltage E29 by 90. Due to the phase reversal of the tube l, the corresponding voltage on the control grid 4 of this tube, which is represented by the vector E4, must be in phase op-" position with the voltage E28. Likewise, the voltage on the control grid 3, represented by the vector E2, must be in phase opposition with the voltage E22, due to the phase reversal which takes place in the tube 2.

The current through the inductance element 20 and the resistor 22, which is represented by the vector I20, lags the voltage E28 by almost 90. Hence the voltage developed across the resistor 22, represented by the vector E22, is substantially in phase with the voltage Es necessary at the control grid 8 of the tube 2 to produce the desired output voltage. It is apparent, therefore, that since the voltage E22 is applied to the grid circuit of the tube 2 by means of the lead 3|, oscillation of the tube 2 occurs, thus developing the voltage E22 between the output terminals 29 and 30. The current flowing through the condenser 25 and the resistor 25 is represented by the vector I25, and leads the voltage E29 by almost 90. Therefore, the voltage drop across the resistor 25 due to the current I25, which is represented by the vector E26, is substantially in phase with the voltage E4 which must be applied to the control grid 4 of the tube to produce the desired output voltage. Since the voltage E26 is applied to the control grid 4 by means of the lead 33, this tube oscillates, resulting in the production of the voltage E28 between the output terminals 28 and 30.

The inductance elements I4 and I6, in cooperation with the taps 34 and 32, function as autotransformers to step up the relatively small feed-back voltages developed, respectively, across the resistors 26 and 22 so as to provide sufficient excitation of the control grids 4 and 8. In the absence of such means to step up the feed-back voltages, feed-back voltages of sufiicient magnitude to provide oscillation could be developed only by making the resistors 22 and 26 so large that the performance of the resonant circuits including them would be seriously afiected. No appreciable phase shift occurs due to the use of the taps 34 and 32, since the resonant circuits |4--|5 and |6-|1 are purely resistive at the frequency of oscillation to which they are tuned.

Referring now more particularly to Fig. 3, there are shown three electron discharge tubes 35, 36 and 31. The tube 35 has a cathode 38, a control grid 33, a screen grid 40, and an anode 4|. The tube 36 includes a cathode 42, a control grid 43, a screen grid 44, and an anode 45. The tube 31 has a cathode 46, a control grid 41, a screen grid 48, and an anode 49. The cathodes 38, 42, and 46 are connected to ground. For the purpose of applying a signal voltage to the control grid 39 of the tube 35, there is provided in the grid circuit a parallel resonant circuit comprising an inductance element 50 and a condenser Likewise, a parallel resonant circuit comprising an inductance element 52 and a condenser 53 is connected between the control grid 43 of the tube 36 and ground. Similarly, the input circuit of the tube 31 includes a parallel resonant circuit comprising an inductance element 54 and a condenser 55 connected between the control grid 41 and ground. The screen grids 40, 44 and 48 are provided with a suitable positive potential, from the source indicated by B-|-, through the resistors 55, and are by-passed to ground by the condensers 51.

The anodes 4|, 45 and 49 of the tubes 35, 36 and 31, respectively, are provided with a suitable positive potential from the source indicated by B+. A parallel resonant circuit comprising an inductance element 58 and a condenser 59 is connected in the anode circuit of the tube 35. The anode circuit of the tube 35 includes a parallel resonant circuit comprising the inductance element 60 and the condenser 6|, while the anode circuit of the tube 31 includes a parallel resonant circuit comprising the inductance element 62 and the condenser 63. The inductance coils 64, 65, and 66 are coupled, respectively, to the inductance elements 58, 66 and 62, and are connected, respectively, to the output terminals 61, 66and 69.

The coils 10, 1| and 12 are coupled, respectively, to the inductance elements 58, 60 and 62. The coil 10 is connected, through the phaseshifting means 13, between the tap 14 on the inductance element 52 and ground. The coil 1| is connected, through the phase-shifting means 13, between the tap 15 on the inductance element 54 and ground. The coil 12 is connected, through the phase-shifting means 13, between the tap 16 on the inductance element 50 and ground.

The operation of the device of Fig. 3 may be understood more readily by reference to the vector diagram of Fig. 4. Let the signal voltage which appears across the inductance element 58 be represented by the vector E58, and the signal voltage which appears across the inductance element 60 by the vector E60. The latter voltage leads the former voltage by Let the signal voltage which appears across the inductance element 62 be represented by the vector E62. This voltage leads the voltage E60 by 120. Due to the phase reversal occurring in the tube 35 the voltage required on the control grid 39 of this tube, which is represented by the vector E39, must be in phase opposition with the voltage E52. Likewise, the voltage necessary on the control grid 43, represented by the vector E42, must be in phase opposition with the voltage E50, due to the phase reversal which takes place in the tube 36. Similarly, the voltage necessary on the control grid 41, represented by the vector E41, must be in phase opposition with the voltage E62, due to the phase reversal occurring in the tube 31.

The phase-shifting means 13 are such as to produce a phase shift of 60. Hence the voltage applied to the tap 14, represented by the vector E14, lags the voltage E52 by 60, but is in phase with voltage E43, thus causing the tube 36 to oscillate and produce an output voltage at the terminals 68. Likewise, the voltage developed across the coil 1| has its phase shifted 60 by the phase-shifting means 13, so that the voltage at the tap 15, represented by the vector E75, lags the voltage E60 by 60". Since the voltage E75 is in phase with the voltage E47, oscillation of the tube 31 occurs, thus developing an output voltage at the terminals 69. Similarly, the voltage developed across the coil 12 has its phase shifted 60 due to the phase-shifting means 13 and is applied to the tap 16, the voltage at this tap being represented by the vector E76. This voltage lags the voltage E62 by 60, but is in phase with the voltage E22, thus causing the tube 35 to oscillate and produce an output voltage at the terminals 61. The inductance elements 50, 52, and 54, in cooperation, respectively, with the taps 16, 14, and 15, function as auto-transformers to step up the relatively small feed-back voltages produced, respectively, by the coils 10, 1|, and 12, so as to provide sufiicient excitation of the control grids 39, 43 and 41. Since the resonant circuits 50-5|, 52-53 and 54-55 are purely resistive at the frequency of oscillation at which they are tuned, they function effectively as a terminating resistance for each of the phase-shifting means 13.

Although the tubes are shown in Figs. 1 and 3 as tetrodes, it will be understood that triodes or pentodes may be employed with equal success. If triodes are used, neutralization means must be provided to prevent self-oscillation of the tubes due to their interelectric capacitance. Conventional means may be employed for heating the cathodes 3 and I of Fig. 1 and 38, 42 and 46 of Fig. 3, these means not being shown in the drawings to avoid unnecessary complication 7 thereof.

' means 13 of Fig. 3, which are shown at 1r networks, may be replaced by any other suitable arrangement. By so selecting the phase shifting means as to give a phase shift other than 60, the output voltages of the system may be made to have phase relationships difierent from the 120 relationship provided in the arrangement described.

Although the oscillator system here disclosed is applicable to any use where output signals of predetermined difierent phases are required, the arrangement in accordance with the present invention is especially suitable for use in connection with the frequency multiplier disclosed in my copending application Serial No. 314,480, filed January 18, 1940. The use of the present oscillator system to drive my earlier-disclosed frequency multiplier permits the elimination of the phase-shifting means normally employed in the latter device, thus simplifying its construction.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An oscillator system for developing a plurality of signals having different relative phases, comprising a plurality of resonant circuits each including resistance elements in one of its arms for developing a voltage in phase-shifted re1ationship to the voltage developed across said circuit, and a plurality of signal repeating means each coupled between one of said resistance elements of said circuits and another of said circuits for translating the voltage developed across said resistance element in each one of said circuits to another of said circuits and energizing the same in phase-shifted relationship to said one of said circuits, whereby signals are developed across said circuits with predetermined difierent phases.

2. An oscillator system for developing a plurality of signals having difierent relative phases, comprising first and second signal-repeating means, first and second input resonant circuits connected respectively to said signal-repeating means, first and second output resonant circuits connected respectively to said signal-repeating means and each including phase-shifting means, a connection between said first phase-shifting means and said second input circuit for energizing the same in phase-shifted relationship to said first output circuit, and a connection between said second phase-shifting means and said first input circuit for energizing the same in phase-shifted relationship to said second output circuit, whereby signals are developed across said output circuits with predetermined different phases.

3. An oscillator system for developing a plurality of signals having difierent relative phases, comprising first and second signal-repeating means, first and second input resonant circuits connected respectively to said signal-repeating means, first and second output resonant circuits connected respectively to said signal-repeating means and each including a resistor in one branch, a connection between the resistor in the inductive branch of said first output circuit and said second input circuit for energizing the same in phase-shifted relationship to said first output circuit, and a connection between the resistor in the capacitive branch of said second output circuit and said first input circuit for energizing the same in phase-shifted relationship to said second output circuit, whereby signals are developed across said output circuits with predetermined different phases.

ARTHUR L. NELSON.

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