US2492767A - Oscillator - Google Patents

Description

Dec. 27, 1949 M. T. REYNOLDS 2,492,767

OSCILLATOR Filed Nov. 12, 1947 +2 NET vom-AGE or: SCREENED GFuD'e Inventor: Merl TR eyo lds,

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H i S Attcrey.

Patented Dec. 27, 1949 OSCILLATOR Y Meri T. Reynolds, Ballston Lake,N. Y., assigner to General Electric Co New York mpany, a corporation of Application November 12, 1947, Serial No. 785,261

9 Claims. (Cl. Z50-36) This invention relates to electronic circuits 5.1

obtaining negative transconductance and to electron discharge device oscillator circuits employing the phenomenon of negative transconductance.

A general object of the invention is to provide improved electron discharge device circuits obtaining negative transconductance.

, An object of the invention also is to provide an improved negative transconductance oscillator.

v A more specic object is to provide an osci1- lator of the negative transconductance type wherein the frequency determining tuned circuit has one terminal at ground potential. l

, -A further object is the provision of an oscillator comprising a small number of components which will provide stable sine-wave signals with low distortion over a wide range of frequencies.

An additional object is to provide an oscillator from which an output voltage of high intensity is obtainable without direct connection to the frequency determining elements.

It is also an object of the invention to provide an oscillator which will become inoperative to generate oscillations upon disconnection ofthe inductance included in the tuned circuit.

Another object is to provide a `negative translconductance oscillator in which the tuned circuit inductance has no tapped connection.

rIt is a further specific object of my invention to provide an improved negative transconduct-` ance oscillator operable over a wide band of frequencies, wherein one terminal of the parallel tuned circuit is maintained at direct current ground'potential, wherein the other terminal is connected to the third, or screened, gridrather than to the rst grid, the first grid being directly grounded, and wherein operation up to very high radio frequencies is practicable without the necessity of providing tuned lter circuits to lsolate'the screen grid from the low impedancev power supply.

The novel features which I believe-to be characteristic of my invention are set' forth with parcomponents and possessing additional advantages; and Fig. 3 is a group of curves explanatory of the operation of oscillators according to the invention.

' Referring now toFig. 1, I have shown a pentaf grid discharge device I comprising a grounded cathode 2, a rst grid 3, which is also grounded, a screen grid consisting of grid elements 4 and 5 disposed on opposite sides of a second control grid being the third grid from the cathode, which maybe referred to as the screened grid. Grounded suppressor grid 1, the fifth grid from the cathode, is arranged inside anode 8, the anode being directlyconnected to a source of positive B+ potential, such as the battery 9, the negative terminal of the source being grounded. The

impedance of the potential source is made low for the frequencies at which operation is desired by connecting a capacitor I0 of high capacity from B+ to ground.

A frequency determining parallel-tuned circuit comprising inductance II and condenser I2 is connected between control grid 6 and ground, and a feedback circuit including a series condenser I3 is arranged to feed back oscillatory energy from the screen grid 4 and 5 to the tuned circuit. vAs explained below the feedback through condenser I3 is in phase with the voltage appearing on control gridV 6. If the value of condenser I3 is made low, the oscillator output will very closely approach a true sine wave. Higher values, however, may be `desirable to insure strong oscillation Aover a wider range of supply voltage variations or over a wider range of frequencies. B+ supply for the screen grid is through a load resistor I4, across which the output signal is developed. f

A modification of the device is shown in Fig.2'

the secondfgrid 4 and fourth grid 5, comprising the screen grid, are connected to the B+ potential source, battery 9, through a load resistor I4, and 'the tuned circuit comprising inductance II and parallel capacitor I2 has; one terminal grounded and the yother connected through capacitor I3 to feed back energy4 to the screenedgrid' s.

The anode tains a lload resistor I8 across; which the oscil- 65 lating output voltage is developed. The resistor circuit inthe devicecf Fig. '2

may conveniently be arranged as a potentiometer, as shown, in order that the output voltage derived from the movable contact may be adjusted in intensity. A direct current blocking capacitor I1 may be connected in series with the output terminal in a known manner, if desired.

The operation of the oscillators of Fig. 1 and Fig. 2 may be best explained with reference to Fig. 3. As shown by the curves of Fig. 3, which are labeled to indicate current (I) or voltage (E) for the elements of tube I, an increase in the potential of the third grid 6, along the abscissa of the chart, produces a decrease in the current, curve 14,5, to the interconnected second and fourth grids 4 and 5, and a resultant increase in the potential thereon, curve E45, because of the lower current through resistor I 4, if the discharge device I is biased to operate at approximately the operating point indicated on the chart by a vertical dashed line. The increase in potential of grids 4 and 5 occurs simultaneously with the increase in potential of the third or screened grid 6 and provides an energy feedback to grid 6 through capacitor I3. The energy thus fed back is suicient to overcome the circuit losses, and oscillations thus occur which are at the resonant frequency of the tank circuit I I, I2. It will be understood that the resonant frequency will be affected by the inherent capacitance of the circuit elements, which is effectively in parallel with capacitor I2, as well as to a small extent by the inherent inductance of the circuit.

The anode 8 of the discharge device in Fig. 2 is provided with a load resistor IB connected in series to the source 9 of positive operating potential. The resistor may conveniently comprise a potentiometer resistance provided with a variable tap as shown to select a desired value of output voltage for furnishing to external apparatus through capacitor I'I. The device of Fig. 2 exhibits an anode voltage curve such as Ea in Fig. 3, whereas, of course, the anode voltage of the device of Fig. 1 is constant and would appear on the chart as a horizontal straight line.

An oscillator according to either of Figs. 1 or 2 of the drawings has wide frequency range and stability characteristics which particularly adapt them to use in devices for determining the inductance or capacitance of elements which may be inserted' in the tuned circuit II, I2.

For instance. if the value of the inductance of element II is unknown, but the capacitance of condenser I2 is available from a calibrated dial or otherwise, the condenser I2 may be adjusted until the frequency of the oscillator coincides with that of an external standard oscillator. The resonant frequency of the tuned circuit Il, I2 and the value of the capacitance I2 being both known, the inductance of element I I is readily calculated.

For such use of the oscillator, it will be obviously desirable that taps on the inductance in the tuned circuit should be unnecessary, that'one end of the inductance should be grounded for both direct currents and alternating currents, that the oscillator should be inoperative if there is no inductance element in the circuit, that there should be no substantial change under varying output load conditions, that the oscillator should be stable, relatively unaffected by supply voltage variations, and that it should provide oscillations over a very wide bandol frequencies.

Thev oscillator according to thisinvention successfully meets all of these criteria, is simple in construction, is composed of ordinary commer- 4 cially available components, and the values of the components are not critical, except, of course, that for accurate results, it may be necessary to provide accurate calibration of the values of inductance II or capacitor l2 if the value of one of these two elements is known and is to be determined as outlined above.

While I have shown only certain preferred embodiments of my invention by way of illustration, many modifications will occur to those skilled in the art and I therefore wish to have it understood that I intend, in the appended claims, to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electron discharge device oscillator system obtaining negativey transconductance, comprising a vacuum tube having therein a cathode, a i-lrst grid, a screened grid, a screen grid and an anode, a screen grid-to-cathode circuit comprising a source of direct current operating potential, a load resistor extending from said screen grid to a first point in said circuit which is positive with respect to said cathode, a parallel tuned tank circuit connected between said screened grid and a second point in said circuit which is negative with respect to said iirst point, a feedback coupling from said screen grid to said screened grid, a connection for said rst grid to said circuit for maintaining said'first grid at a potential negative with respect to said first point, and means for energizing said anod Y 2. An oscillator comprising a tuned circuit with two terminals, an electron discharge device with an anode, a cathode, a control grid and an anode grid, said anode grid comprising two sec tions respectively disposed on opposite sides of said control grid, said grids being disposed between said anode and said cathode, means for establishing a potential gradient between said anode and said cathode such that an increase Vin control grid potential causes an increase in anode grid potential, and means to feed back to said control grid without substantial phase shift changes in said anode grid potential, said tuned circuit being connected in a control-grid-'to Acathode circuit.

3. In an oscillator with two output terminals and including a resonant circuit, an electron discharge device with an anode, a cathode and ve grids between said cathode and anode, the first and fifth of said grids from said cathode being connected to a point at ground potential, one of said terminals being connected to said ground point, the other of said terminals being connected' to the second and fourth of. said grids, said in-` terconnected second and fourth grids being conan nected through a load impedance to a source of positive potential, regenerative feedback coupling from said second and fourth grids to the' third of said grids, means for providing operating potentials to saidcathode and said anode,

: and means for biasing said third grid to a po tential relatively negative with respect to said interconnected second and fourth grids.

4. An oscillator comprising a tuned circuit, an

electron discharge device with an anode, a cath` v g ,ode, a control grid and an anode grid, saidanode grid comprising two sections respectively 'dis-A posedfon opposite sides of said control grid, said grids being disposed Vbetween said anode and said cathode, means for establishing a potential gradient between said anodel and said cathode such!y that an increase in control grid potential causes 5 an increase in anode grid potential, means to feed back to said control grid without substantial phase shift changes in said anode grid potential, said tuned circuit being connected in a control-grid-to-cathode circuit, and output means associated with said anode.

5. In a negative transconductance oscillator including a resonant circuit, an electron discharge device with an anode, a cathode and at least four grids between said cathode and anode, means for supplying a relatively large positive operating potential to said anode with respect to the potential of said cathode, means maintaining not more than relatively small respective biasing potentials from the second and' fourth grids to said cathode, said last means comprising said resonant circuit in series with said second grid. means interconnecting and maintaining the first and third grids at a more positive potential than any of the other grids in said device and less positive than said anode, an inphase feedback circuit from said interconnected rst and third grids to said second grid to sustain oscillation in said resonant circuit.

6. An electronic oscillator comprising an electron discharge device with an anode, a cathode, a control electrode, a screen electrode in two connected portions arranged respectively on opposite sides of said control electrode to screen said control electrode toward said anode and toward said cathode, and a grid adjacent said anode, said anode being connected to a point in a source of potential positive with respect to said cathode, means comprising a series impedance connecting said screen electrode to a point of said source of potential not more positive than the point of connection for said anode, said grid being maintained at a potential negative with respect to the potential of said screen electrode to form with said anode a virtual cathode for said screen electrode, means comprising another impedance for biasing said control electrode negative with respect to said screen electrode, means forming a resonant circuit with one of said impedances, and means for feeding back in-phase energy from said screen electrode to said control electrode.

'1. An electronic circuit obtaining negative transconductance comprising an electron discharge device with an anode, a cathode and five grids, said grids being arranged in sequence from said cathode to said anode, means maintaining the first and fifth of said grids substantially at a xed reference potential, means providing a positive operating potential to said anode, means maintaining said cathode at a potential less positive than the cut-oir potential established by the potential of said 'rst grid, means for providing a positive operating potential to the second and fourth of said grids together through a load impedance, means for biasing the third of said grids to a potential substantially the same as that of said rst grid and for applying a signal to said third grid whereby said signal produces a corresponding 'in-phase signal across said load impedance.

8. A circuit obtaining negative transconductance comprising an electron discharge device with an anode, a cathode, and five grids in sequence between said cathode and said anode, means providing positive operating potentials to said anode and through an impedance to the second and fourth of said grids, said second and fourth grids being interconnected, means for biasing the first grid with respect to said cathode to a potential within the operating range of said device, means for biasing the third and fifth grids to substantially the potential of said first grid, and means to provide a signal to said third grid whereby a corresponding signal in phase with the signal on said third grid appears on said second and fourth grids.

9. A negative resistance comprising an electron discharge device with an anode, a cathode and at least four grids, means providing a positive operating potential to said anode with respect to said cathode, two of said grids comprising a screen grid, another of said grids comprising a control grid and being disposed between said last mentioned two grids thereby to be screened from said anode and from said cathode, the fourth of said grids being disposed between said screen grid and said anode, means comprising an impedance in series with said screen grid providing an operating potential to said screen grid not more positive than said anode potential, means for biasing said fourth grid negative with respect to said screen grid, means for biasing said control grid negative with respect to said screen grid, and a capacitor connected to feed back in-phase energy from said screen grid to said control grid.

MERL T. REYNOLDS.

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

UNITED STATES PATENTS Number Name Date 1,943,302 Dow Jan. 16, 1934 2,119,357 Schalkwijk May 31, 1938 2,230,097 Whitaker Jan. 28, 1941

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