Патент USA US2408684код для вставки
Oct. i, 1946. l -w. VAN B. ROBERTS t ' l. FREQUENCY-VARIABLE OSCILLATOR CIRCUIT Filed Feb. 4, 1945’ ' 2,408,684 Patented Oct. l, 1946 2,408,684 UNITED STATES PATENT OFFICE n 2,408,684 FREQUENCY-VARIABLE OSCILLATOR ` CIRCUIT - 'Walter'van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application February 4, 1943, Serial No. 474,646 1 'ClainL (Cl. Z50-36) . _ 1 My present invention rrelates lto frequency variable oscillator circuits,y and more especially to an voscillatorcircuit adapted to be shifted in frequency without amplitude change. v 2 electrode 5 and an anode, or plate; E. It will be understood that other electrodes could be uti lized between the cathode 2 and plate 6 -to ac complish additional functions, where desired. ‘One of the main objects of my present inven tion is to provide a single tube oscillator which may be frequency modulated without amplitude modulation of the oscillatory output energy. Amore specific object ofV this invention is to provide an oscillator circuit adapted to provide constant-amplitude oscillations, and the fre quencyn'o’f the oscillator circuit Vbeing determined by a :control potential applied to a control grid of the oscillator tube; the latter having separate phase shifter networks in separate connections . from the anode and screen electrodes to voltage points on the .tank circuit which are of opposite phase to that of a feedback grid", and the phase shifter networks providing opposite senses of In the present case cathode 2 is established at an invariable alternating potential, such as ground. The grid 3 is returned to ground through a radio frequency choke coil ‘I in series with a resistor 8. ' f ' .'I‘he Screen electrode/4 is returned to ground through a coil '9 and the` direct current source I0. In other Words, the Screen electrode 4 is connected, through coil 9, to the positiveter minal -of the direct currentsource I il, `and the negative terminal of the latter is grounded. The upper end of coil'9 is `connected through con denser II Ato a desired point on the'coil `I2 of the oscillatory tank circuit I3. The condenser I 4, which is arrangedin shunt with coil I2, tunes frequency shift. 20 the coil I2 to' a desired operating oscillatory fre . AStill other objects of my invention are to pro quency. The circuit 'I3 is the usual oscillator vide a single tubey oscillator capable .of frequency tank'circuit, ' deviation free of amplitude change, and `adapted The plate IiV isconnected to a desired point on for use in a frequency modulated oscillator ksys I2, which may be at a higher or >a lower tem or in an automatic frequency control (AFC) 25 ‘coil alternating potential than the point. on coil I2 circuit of al superheterodyne receiver. ' to which electrode d is connected bythe coily I5. The plate end of coil I5 is connected to ground through 'the‘condenser IG. The coil 9 and con ticularity in the appended claims; the invention denser are shown enclosed in a dotted square itself, however, ~as to both its organization and. 30 which isIIindicated as “Phase shifter.” Similarly, method of operation will best be understoodfby coil I5 and condenser I 6 are shown enclosed in reference to the following description, takenvin a dotted rectangle also -labelled “Phase shifter.” connection with the drawing,v in which I have _The phase shifters P1 and P2 are shown ter indicated diagrammatically several' circuit or minating at the coil I2 in an adjustable manner ganizations whereby my invention may be car-. 35 vto indicate thatv they may be -adjiïstably con ried intoeifect. ' nected to the tank coil. ` In' the drawing:v ’I‘he control ,grid 5 is shown connected to the Fig; 1 shows'a circuit employing the invention, negative terminal-“of a direct Vcurrent source 20, Figs. 2a and 2by show vector relations existing and the positive terminal of the latter may be in the oscillator circuit, ` . _ connected to av source of frequency control volt Fig. 3 schematically illustrates.theapplication age` 'Y This source of frequency control voltage Äo'f. the invention to an AFC system. may be either alternating current or direct cur The novel features which I believe to be char acteristic of my invention are set forth with par Referring, now, tothe accompanying drawing, 'wherein like reference characters in the different .figures designate Similar'circuit elements, there is shown in Fig. 1 an oscillator circuitwhich may r Vbe employed for any desired frequency band, rent. In-'the case of a frequency modulation transmitter, the sourceV of frequency control 45 voltage would be an audio frequency modulation source. However, in the case of AFC of a super heterodyne receivengthe source of frequency con~either in the kilocycle (kc.) or megacycle' (mc.) trol voltage would be the direct Vcurrent voltage ranges. The oscillator tube is of the pentode output of the usual discriminator-rectifier net type. Of course, the oscillator is not limited to 50 `anys'peciiic type of electron discharge tube. `It is>> suíñcient for the purposes of the present in vention that the tube I include a cathode or electron emission electrode 2, a first control grid ¿3, apositive screen electrode 4, _a _third controI- work. _ - f y y v The plate E is maintained at a positive poten ytial relative to ground by means of a direct cur- ' rent source 2l whose negative terminal is grounded, while its positive terminal is adjust ably connected to a desired point on coil I2. The 2,408,684 3 frequency control voltage substantially equal volt grid 3 is connected to the low potential side of tank circuit I3 through a direct current blocking ages are induced in the tank circuit I3 by the screen and plate currents I2 and I1. In this way condenser 22, and coil 23 is illustrated as the a frequency modulated oscillator is provided output link to the subsequent utilizing circuit. whose frequency is caused to deviate both above C11 It Will be realized that Fig. 1 shows a Hartley and below the frequency prevailing in the absence type oscillator circuit, wherein grid 3 functions of frequency control voltage. » as the oscillator grid. The oscillator tube has Where the present invention is employed in a two output electrodes, viz., the positive screen electrode ¿i and the positive plate 6. The screen transmitter of frequency modulated carrier wave 4 and plate 5 are connected to the tank circuit at different points on the other side of the ground tap from the grid 3. As the grid 3 varies in po tential, both the screen current and plate current will be produced across tank circuit I3 frequency energy, then electrode 5 of Fig. 1 will be connected to a source of audio modulation energy, and there modulated oscillations having a mean frequency of a predetermined value. The frequency devia tion will depend/upon the relations between the vary in the same sense. The plate current is in dicated by the reference character I1. rt win be Seen that the voltages introduced by the plate and screen currents respectively in the tank cir cuit I3 both assist in maintaining oscillation. The screen and plate currents are introduced into " voltages e1 and e2, and will be dependent upon the requirements of the system. It is to be under stood that the present invention may also be Y the tank circuit preferably at such points that the voltages induced by the two currents are equal. However, the current I1 passes through the phase shifter Pi. This slightly retards its phase. The screen current I2 passes through the employed in connection with’phase modulated energy, and the generic term “angle modulated” is to be understood as applying to either of fre quency or phase modulated carrier wave energy. In Fig. 3, I have shown schematically a super heterodyne receiver wherein the present inven tion is utilized for AFC purposes. Since those second phase shifter P2, thereby slightly advanc 25 skilled in the art are fully acquainted with the ing its phase. Accordingly, the voltages induced constructional details of a superheterodyne re in the tank circuit by these two currents may be represented .vectorially as in Fig. 2a. Referring to Fig. 2a, the vectors e1 and e2 cor respond to the voltages induced in the tank cir 30 cuit I3 by the plate current and screen current respectively. The sum of these two vectors, which is the equivalent total voltage in the tank circuit, is shown by the dotted arrow designated e1 plus e2. This total voltage is preferably 180° out of phase with the voltage on grid 3 when the fre quency is at its mean value, i. e. in the absence of modulating voltage. So far, no mention has been made of the con trol grid 5. The action of this grid is to control the distribution of the total space current of tube I between the screen and plate electrodes 4 and ceiver, it is not necessary to show such details. Generally, received modulated carrier wave en ergy is applied to a converter, or ñrst detector, designated by numeral 3D. The output of the lat ter, which is at an intermediate frequency (I. F.) , is fed to an I. F. amplifier 3l. A second detector 32 demodulates the amplified I. F. energy. The local oscillator, which feeds its energy to the con verter circuit, is provided by the tube I. The circuits of the tube I are precisely the same as shown in Fig. 1. The difference resides in the fact that the tank circuit I3 is tuned to a fre q-uency which differs from the frequency of the modulated carrier applied to the converter input circuit by a frequency value equal to the operat ing I. F. value. 6 respectively. If the plate voltage is chosen suffi The grid 5 has applied to it the AFC voltage ciently low, it is known that a negative potential output of the discriminator-rectifier network 40. .4. on grid 5 will cause more and more of the total The discriminator-rectiñer is schematically repre space current to flow in the screen circuit and sented, since those skilled in the art are fully ac less and less in the plate circuit. Although the quainted with the circuits thereof. It is fed with total space current itself is not affected by grid 5, I. F. energy, and the network 40 functions to pro Fig. 2b shows the result of making grid 5 less nega 50 vide a direct current voltage whose polarity and tive than normal. In this case the plate current magnitude are functions respectively of the di is increased above normal, while the screen cur rection and extent of frequency deviation of the rent is reduced ’below normal. Accordingly, the I. F. energy relative to the predetermined oper resultant of the two voltages e1 and e2 induced ating I. F. value. The AFC voltage output of net in the tank circuit is of a slightly different phase 55 work 4o is applied through the negative biasing than in the normal case illustrated in Fig. 2a), battery 20 to the control grid 5. The discrim It will be noted that the magnitude of the re inator-rectiñer 40 may be constructed, for ex sultant voltage in the case of Fig. 2b is substan ample, in the manner disclosed and claimed by tially unaltered so that the amplitude of oscilla S. W. Seeley in his U. S. Patent No. 2,121,103, tions is not changed. 60 granted Jun@ 21, 1938. The AFC circuit func However, it is well known that a phase shift tions to change the bias of grid 5 in such a in any part of the feedback mechanism of an manner that the frequency of tank circuit I3 will oscillator circuit will produce a frequency change. be shifted to an extent such as‘to maintain the Hence, under the conditions shown in Fig. 2b, I. F. energy output of converter 30 close to the the frequencies will be different from the fre predetermined I. F. Value. It is not believed quencies prevailing in the normal, or mean, con necessary to describe the functioning of the in dition depicted in Fig. 2a.. Conversely, making vention in connection with this utilization there the grid 5 more negative than normal will cause of. Those skilled in the art will fully appreciate an opposite phase shift in the resultant feedback the advantages of an AFC system wherein the to the tank circuit and opposite deviation of oscillator circuit does not utilize an auxiliary re the oscillator frequency from normal. actance tube system across the tank circuit, and It is further pointed out that the relative supwherein the oscillator frequency may be directly ply voltages for the screen Il and plate 6 are pref shifted without appreciable change in the oscilla erably so chosen, together with the tapping points tion amplitude. f of the separate connections from the screen and While I have indicated and described several plate on the tank circuit, that in the absence 0f 75 2,408,684 5 6 systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without departing from the scope of my invention, as set forth in the appended claim. v 5 one end of said coil, a direct current connection from the anode to a point on the coil which is lo cated on the opposite side of said predetermined intermediate point, a connection from the second grid to a point on the coil on the same side of Asaid intermediate point as the anode point, re spective phase Shifters in said anode and second grid connections for providing phase shifts of What I claim is: In an oscillator circuit comprising an electron opposite senses in the anode and second grid cur discharge tube having at least a cathode, an anode 10 rents ñowing through the connections, said con and at; least three successive grids in the space nections to said coil Ibeing chosen to produce equal current flowing from the cathode to the anode, a voltages inl said tank circuit from said phase coil and condenser connected in parallel to pro~ ~ shifted currents, means for applying a negative vide a tank circuit tuned to a predetermined os biasing voltage to the third grid adjacent the cillatory frequency, a source of direct current 15 anode, and means for varying the voltage of the voltage, means connecting a predetermined in third grid to vary the frequency of the tank cirJ termediate point on said coil to a positive poten~ cuit but Without amplitude variation. tial point of said source, a high frequency connec tion from the ñrst grid adjacent said cathode to WALTER VAN B. ROBERTS.