US2369953A - Oscillator circuit - Google Patents

Description

Feb. 20, 1945. 'R 1 DowNEY 2,369,953

OSCILLATOR CIRCUIT Filed Feb. 13, 1943 {ii- EFD 7g Y 1 Inventor: Y 50d@ 2 uw Reginald I D'owrwc-zg,

s Hi Attorney.

Patented Feb. 20, 1945 OSCILLATOR CIRCUIT Reginald L. Downey, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application February 13, 1943, Serial No. 475,731

4 Claims.l ,(Cl. Z50-36) This invention relates to oscillator circuits and more particularly to oscillator circuits employing piezo-electric crystals.

The power output of a crystal oscillator is limited by the permissible radio frequency crystal current. If the electron discharge devices associated with crystal oscillator circuits are operated in the region of maximum power output, the voltage driving the crystal may become too high because of feedback effect if the anode potential for any reason should become too high. As a result the crystal may be damaged.

It is, therefore, an object of my invention to provide new and improved means for regulating the anode voltage in a crystal oscillator in order to prevent the application of an excessive voltage across the crystal.

It is another object of my invention to provide means for maintaining substantially constant the output of an oscillator in order to maintain substantially constant the excitation of any succeeding amplifiers and the like.

In accordance with my invention there is provided in a crystal oscillator employing a discharge device of a type having at least two control electrodes, means for impressing a voltage on one of the control electrodes which is proportional to a rectified discharge device voltage, as the anode-to-cathode or the other control electrode-to-cathode voltage, in such a direction as to tend to maintain the first mentioned electrode at a potential which tends to oppose any change in the output of the oscillator. The regulating means is so arranged that increases in output tend to drive the first mentioned electrode more negative or from positive to negative depending upon the characteristics of the discharge device, and, conversely, decreases in the output voltage tend to cause the rst mentioned electrode potential to increase in the positive direction. In order to improve the sensitivity and accuracy of regulation, the regulating voltage may be amplified. y

Electron discharge devices of high power sensitivity, such as a pentode, have been used in crystal oscillators because for a given crystal voltage a higher power output is obtained than when a discharge device of the triode type or pentode type is used, for example. The gain in devices having at least two negative electrodes, such as the pentode, depends to a large extent'upon the bias of a suppressor electrode, the bias on the ordinary or regular control electrode being of relatively minor effect, because the suppressor electrode, while maintaining an average negative bias, is driven considerably positive during a portion of each cycle when Class C operation is employed. Therefore, my inventionis particularly applicable to electron discharge devices of the type having at least two control electrodes, both of which operate at an average negative bias, but one of which is driven positive during the peaks of each cycle and the second of which is maintained at a negative; or only very slightly positive potential at all times.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Figs. 1

to 'I inclusive illustrate different embodiments of the invention.

Referring to Fig. 1 of the drawing there is illustrated a crystal oscillator circuit including an electron discharge device I0 of the pentode type having an anode II, a cathode I2, a control electrode I3, a screen electrode III, and a suppressor electrode I5. A piezoelectric crystal I6 is connected between the control electrode I3 and the cathode I2 for radio frequency currents by means of a suitable capacitor I1. In order to bypass direct current around the crystal there is provided a radio frequency choke I8 in shunt with the crystal I6 of such a value that direct current is passed therethrough but radio frequency currents are caused to circulate through the crystal.

The oscillator circuit also includes a tuned anode circuit comprising a shunt connected variable capacitor I9 and an inductance 20 connected between the anode I I and the cathode I2 through a condenser 22 for radio frequency current. The tuned circuit' is also connected to a suitable source of direct current potential 2l, the negative terminal being grounded and also connected to the cathode I2 and the positive terminal being connected to one side of the condenser coil combination. The bypass condenser 22 provides a low impedance path for radio frequency. currents between the anode circuit and the cathode and comprises a substantially open circuit for direct currents.

The screen electrode is connected to a suitable tap on the source of potential 2|. In order to keep radio frequency currents out of the power supply or source of potential 2|, and yet permit the flow of direct current in the screen electrode through the interelectrode capacities is insuill- 4 cient for stable oscillations.' an external condenser may be connected as shown by the' dotted lines.

In order to maintain substantially constant the output voltage in the circuit of Fig. l, there is provided means for causing the suppressor electrode to have such a potential that any changes in output are opposed and a substantially constant output obtained. For this purpose, the suppressor electrode is adjustablyconnected to the resistor 26, which may be ofthe potentiometer type, and which is connected between the grounded cathode |2 and the cathode side of the crystal I6. With these connections there is impressed across resistor 26 the rectified control electrode potential. The suppressor electrode is grounded for radio frequency currents by means of a suitable capacitor 21.

When the discharge device I0 isconducting, there is a voltage drop across the resistance 26, the upper end being at a negative potential with respect to the cathode. Therefore the suppressor l electrode is connected to a point on the resistance which is negative with respectl to the. cathode. The amount of the negative potential depends upon the amount of current owing .through the resistance and the suppressor electrode has impressed thereon a negative potential with respect to the cathode which is proportional to or determined by the radio frequency control electrode voltage. If for any reason the voltage of the con trol electrode circuit is increased, the output ofl the oscillator tends to increase. .The increased current flow causes an increased drop. in the resistance 26. Therefore, a more negative voltage is applied to the suppressor electrode which opposes the more positive control electrode voltage.

As a result the output voltage tends to remain constant. Similarly, if the control electrodevoltage drops, a less negative voltage is applied to the suppressor electrode which'tends to permit more current to flow through the tube and, again, maintain relatively constant the output. A stable operating point is reached, as determined by the initial adjustment of the connection between the suppressor electrode and the resistance 26, and the amount of the regulating voltage supplied or fed back to the suppressor electrode under these conditions tends to regulate the oscillator ouput voltage despite changes inoutput loading and despite changes in the activity of crystals used in the oscillator circuit. There is'also exercised a regulating effect tending to protect extremely active crystals against excessive ra'dio frequency crystal currents. l A

In some applications, as when the oscillator circuit employsrelatively large power tubes, it may be desirable to provide amplification ofthe regulating voltage potential in order to obtain the desired operation. In Fig'. 2 there is illustrated a -circuit employing directI current -a-mplify-ing means. rEhe oscillator'circuit is generally-simi Aground and the anode of discharge device 3|.

lar to that shown in Fig. 1 and the same numerals are used to designate parts which correspond to those of Fig. l. Separate sources of potential, such as batteries, are illustrated for convenience of illustration. Single or separate sources may be employed, if desired.

The amplifier comprises a pair of discharge devices 30 and 3|. The discharge device 30 has an anode 32, a cathode 33, and a, control electrode 34. The discharge device 3| includes an anode 35, a cathode 3G, and a control electrode 31. A part of the voltage drop appearing on the` resistor 26 is applied between the cathode 33 and the control electrode 34. In series with the control electrode there is provided a biasing voltage, such as a battery 34a of potential suitable for Class A oper ation. An increase of current through resistor 26 which accompanies an increase in output causes electrode 34 to become more negative. Accordingly, the anode-to-cathode voltage 0f device 3|! increases. The output of the discharge device 3U is impressed across a resistance 39, a suitable source of anode potential 3B being connected between the upper end of the resistor and the anode. Under the conditions assumed'the flow of current through resistance 39 increases.

The control electrode 31 of the discharge device 3| is biased by a suitable source of potential 40 of a value to compensate for the voltage drop in the resistor 39. Under the condition assumed the flow of current through resistance 38 increases, causing a more negative potential on electrode 31. The resulting increased output voltage from device 3| is impressed across the resistance 4| The increased voltage drop across Vthe resistance 4| is applied to the suppressor electrode in series with a suitable source of potential 42 of sufficient value to compensate for the drop across the resistance 4|, the positive terminal of the source 42 being connected to the suppresor electrode through a suitable radio fre quency choke 43 which is provided to prevent radio frequency currents from flowing through the source of supply. A decrease in oscillator output results in a less negative potential on the suppressor electrode.

Changes in voltagev across the resistance 28 are thus amplified in a two-stage amplifier and applied to the suppressor electrode in a direction to regulate the output and crystal voltages in the 4same manner as discussed above.

In Fig. 3 there is shown a variation of the amplifying circuit of Fig. 2 in which a discharge device IUb of the tetrode type is used and voltage dividers substituted for the separate sources of potential.

A voltage divider comprising a resistance 10 is connected across a suitable source of potential 1l, the negative terminal of which is grounded. A second resistance 12 is connected between The cathodes ofthe discharge devices and the resistors 39 and 4| are adjustably connected to suitable points on the resistor 10. The anode of discharge device lllb is connected to the positive terminal of the source 1|. The screen electrode 13 is connected to a suitable point on resistance 12. The operation of the circuit of Fig. 3 is the same as that of Fig. 2 with one exception. In the circuit of Fig. 2, there is used a pentode type discharge device which employs two control electrodes normally at negative potential'. The screen electrode of the tetrode type device illustrated in Fig. 3 under normal vconditions is at a positive potential, but output regulation may be obtained by properly choosing the point'of connections of the screen electrode 13 to the resistor 12 so that the potential of the screen electrode may be either negative or positive.

Fig. 4 is illustrative of a different type of amplifying device. In this embodiment of my invention the amplifying means comprises a radio frequency amplier including an electron discharge device 45, a tuned anode circuit 46 and rectifying means such as a diode 4l for converting the radio frequency output to direct current. The discharge device 45 may be of the screen electrode type including an anode 48, a cathode 49, a control electrode 50 and a screen electrode 5I. The radio frequency potential of the control electrode I3 of the oscillator. I0 is applied to the control electrode 50 which is connected to the cathode through a grid leak resistor 52. The screen electrode 5I is connected to thepositive terminal of a suitable source of potential 53, the negative terminal being grounded. In order to ground the screen electrode for radio frequency currents and prevent such currents from flowing through the source, a suitable bypass condenser ,Y 54 is connected across the source of potential.' One side of the tunable anode circuit 46 is connected to the anode and the other side is connected through a suitable source of potential 55 to the cathode and ground. The output of the,1 'amplier is impressed across resistance 56 by /means of a suitable coupling condenser 51. The

anode of the diode 41 is connected to the upper end of the resistor and to the coupling condenser 51 and the cathode of the diode is grounded and l.. also connected to the lower end of the resistance. With these connections direct current flows up- Wardly through the resistor on the positive alternations of the radio frequency voltage applied to the rectifier. Therefore, the upper end of the resistor is negative with respect to ground and accordingly a negative potential with respect to the potential of the cathode I2 of the discharge device ID is applied to the suppressor electrode I5. Regulation takes place in the same manner as that described in connection with Fig. 1.

In Fig. 5 there is illustrated a different embodiment of my invention in which rectified anode current rather thanl rectiiied control electrode current is employed to effect the desired shown, the upper end of the resistance is negative and therefore increases in oscillatoroutput voltage to cause a-fmore negative potential to be applied to the suppressor electrode which tends to oppose the increase in output voltage.

In Fig. 6 there is illustrated an embodiment of my invention in which the oscillator discharge device Illa comprises a pentode and a diode within a single envelope.

Inl order -to apply the correct potential to the suppressor for regulationpurposes there are provided series connected resistors -Ba and 60h between the suppressor electrode I5 and the cathode 63 of the diode portion. A point between the resistors is connected to the anode B2 of the diode `resistor 60D is applied to the suppressor grid through the resistor 60a.

In Fig. '7 there is shown an embodiment of my invention which combines features of the circuits shown in Figs. 4 and 6. The depicted circuit comprises a radio frequency amplier for the control electrode voltage, the output of the amplier being rectified in the manner described in connection with Fig. 6` Thus the radio frequency control electrode voltage is applied to the control electrode 50a of the pentode portion of the electron discharge device 45a. The output of the pentode portion is applied to the diode portion through a coupling capacitor 68 and the negative voltage appearing across resistance 60h is applied to the suppressor` electrode I5 of the discharge device I0 through the resistor 60a.

In all embodiments of my invention the screen electrode is operated at groundradio frequency potential and the oscillatory circuits include the interelectrode capacity between the anode and control electrode or an external capacity between these points if necessary to make the circuit selfoscillatory. From the above description, it is evident that in the arrangements described the between the anode II and the cathode I3, anode S2 of the diode being connected to the cathode I3 of the oscillator discharge device I0. The cath.. ode of the diode is preferably connected to the anode II through a variable capacitor 64, the

purpose of which is to adjust the voltage applied 55 of the resistor 6U and a point between the recti- 70 er 6I and the condenser 64.

If the oscillator output increases, there will be an increased flow of current through the rectifier y and a correspondingly increased flow of current through the resistance 60. With the connections amplitude of oscillation can be reduced entirely to zero if necessary. This result will follow if the negative potential applied to the suppressor grid is sufli'cien-t to drive the discharge device to cutolf. Therefore, the amplitude of oscillation can be varied or compensated for over a range limited generally only by the sensitivity of the means for impressing the regulating voltage on the suppressor electrode and the effectiveness of the suppressor electrode in controlling the flow of electrons to the anode.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made Without departing from my invention in its broader aspects, and I therefore aim in the appended claims to cover all such changes and 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. A crystal oscillator comprising an electron discharge device having an anode, a cathode and a pair of control electrodes. a circuit including a a manner tending to oppose any change in said output voltage.

2. The combination, in a crystal oscillator, of an electron discharge device having an anode, a cathode, a control electrode` a screen electrode, and a suppressor electrode, a circuit including a piezoelectric crystal connected between said control electrode and said cathode, an oscillatory output circuit connected between said anode and said cathode, said screen electrode being operated at ground radio frequency potential, and means for maintaining substantially constant the output voltage of said output circuit, said means comprising means for amplifying the rectified current vin one of said circuits and for utilizing the amplied current to maintain said suppressor electrode at such a potential that the voltage of said output circuit tends to remain at a substantially constant value.

3. The combinatiom in a crystal oscillator, of

an electron discharge device having an ano'de, a.

trol electrode and said cathode, an oscillatory output circuit connected between said anode and said cathode, said screen electrode being operated at ground radio frequency potential, and means lfor maintaining substantially constant the output voltage of said output circuit, said means comprising means for applying a direct current potential to said suppressor electrode of such a direction as to oppose any change in the output voltage of said oscillator, said direct current voltage being determined by the amplitude of the rectied control electrode current.

4. The combination, in a crystal oscillator, of an electron discharge device having an anode, a cathode, a control electrode, a screen electrode, and a suppressor electrode, a circuit including a piezoelectric crystal connected between said control electrode and said cathode, an oscillatory output circuit connected between said anode and said cathode, said screen electrode being operated at ground radio frequency potential, and means for maintaining substantially constant the output voltage of said output circuit, said means comprising a resistor connected between said cathode and the cathode side of said piezoelectric crystal whereby rectified control electrode current flows through said resistor, and means for coupling said suppressor electrode to said resistor in such a manner that said suppressor electrode has applied thereto a potential which is determined by the amplitude of the rectified control electrode current, and which tends to oppose any changes in the voltage of said output circuit.

REGINALD L. DOWNEY.

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