US2269417A - Cathode-driven oscillator - Google Patents

Description

CATHODE-DRIVEN OS C ILLATOR Y @RAY G. 02055)/ ATTORNEY.

Jan. 6, 1942.

M. G. CROSBY CATHODE-DRIVEN OS C ILLATOR Filed May 13, 1959 3 Sheets-Sheet 2 A TTORNE Y.

Jan. 6, 1942.

M. G. CROSBY CATHODE-DRIVEN OS C ILLATOR Filed May 13, 1959 3 Sheets-Sheet 3 INVENTOR. MURRAYG. CROSBY Patented Jan. 6, 1942 CATHODE-DRIVEN OSCILLATOR Murray G. Crosby, Riverhead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 13, 1939, Serial No. l273,460

(Cl. 25o-36) 12 Claims.

The present invention relates to oscillators and, more particularly, to twin type oscillators requiring only a two-terminal oscillator coil.

An object of the present invention is the generation of an alternating current wave of substantially perfect wave form and of substantially constant amplitude over a wide band of frequencies.

Another object is the provision of a tunable oscillator giving an output of substantially perfect wave form.

Still another object is the provision of a tunable oscillator requiring no change in regeneration with tuning.

A further object of the present invention is the provision of a simple tunable oscillator which does not require tapped or multiple coils for regeneration.

Another object is the provision oi an oscillator which places a reduced load on the tuned circuit.

My invention includes, among its features, a pair of tubes connected so that the cathode circuit of one tube drives the cathode circuit of the other tube. A two-terminal tuned circuit is placed in the plate circuit of one tube and coupled to the grid circuit of the other tube. The remaining plate and grid circuits may be directly connected to opposing sides of the power supply source.

The oscillator of the present invention has advantages over other oscillators of the prior art, of which I am aware, in that only a two-terminal tuned circuitl is required and that the grid coupled to the tuned circuit is a class A grid which does not damp the tuned circuit so that stability and wave form are improved.

Further objects, features and advantages will appear from a reading of the following detailed description which is accompanied by drawings in which Figure 1 illustrates a circuit diagram of an embodiment of the present invention; Figure 2 illustrates a modification which is adapted to produce square waves; Figure 3 illustrates an adaption of the present invention to an oscillator and a harmonic generator; Figure` 4 illustrates a modification of Figure l utilizing linkcoupling circuits; Figure 5 illustrates a modification of Figure 3 utilizing crystal control; Figure 6 illustrates a further modification of Figure l; Figure 'l illustrates a modification of the present invention in which the cathode to ground capacity of the tubes is compensated; and Figure 8 shows how a pair of oscillators according to Figure 1 may be combined so that the wave 55 generated by one is modulated by the wave generated by the other.

In Figure 1 of the drawings I have shown a pair of triode tubes. or electron discharge structures T1 and T2 as being enclosed in the same envelope I. While I have shown the use of a twin triode it is to be distinctly understood that my invention is not limited thereto but that a pair of entirely separate and distinct tubes may be used. It should further be understood that I intend by the use of the term tubes to mean structures comprising a cathode electrode and an anode electrode within an evacuated space, and means for causing, influencing or otherwise controlling an electron stream between said electrodes regardless of whether the evacuated space is common to more than one electrode assembly or how it is maintained in an evacuated condition. Furthermore, the invention is not limited to the use of triode tubes since pentode or beam tubes may be used.' Different types of tubes such as the triode and a beam tube may be combined. A common cathode resistance 3 is utilized for the cathodes of the two tubes T1 and T2 so that the voltage which is applied to grid I2 of tube T1 is fed to the cathode circuit of tube T2. Utilizing the cathode circuit of tube T1 as an output circuit results in percent inverse feedback and the voltage applied to the grid I2 of tube T1 appears unamplifled on its cathode. Due to this high degree of inverse feedback the grid I2 of tube T1 may be swung over a wide range of voltage without drawing grid current so that the impedance presented to the tuned circuit, to be later described, by the grid is that of a negative biased or Class A grid which is very high. In order to produce sustained oscillations the feedback voltage fed from the tuned circuit 6, composed of inductance 'I and capacity 8, is fed through the grid I2 of tube T1 through blocking condenser 4. This feedback voltage must be fed back to the grid 22 of tube Tz with 180 degrees phase reversal in order to produce oscillations. 'Ihis is readily accomplished due to the fact that the common cathode resistance 3 effects such reversal. A positive voltage on the grid I2 of tube T1 causes more current to flow through the cathode resistor 3 and thereby makes both cathode II and cathode 2| more positive. The cathode 2I of tube T2 becoming more positive is equivalent to the grid 22 becoming more negative. Thus, a positive voltage change on the grid I2 of tube T1 is equivalent to a negative voltage change on grid 22 of tube T2 and the required 180 degree phase reversal is thus obtained. Tuned circuit 6 is tuned to the required frequency of oscillation. The output signal is taken from the moving arm of potentiometer 2 to ground. The amplitude of the output oscillations may be controlled by varying the position of the moving arm of potentiometer 2 along the resistance. If desired, additional amplitude control may be obtained when inserting a variable resistance at the point marked X in Figure 1.

Plate I3 of tube T1 is directly connected to a source of plate potential marked +B. The grid 22 of tube T2 is directly grounded since the input to this tube takes place through the cathode resistor 3. By-pass condenser is provided between the positive terminal of the source of plate potential and ground.

In Figure 2 I have shown how the circuit of my invention may be connected as a multi-vibrator to give a square wave form. This type of multi-vibrator has the advantage that its output wave form is square without damped peaks on the tops of each half cycle as is characteristic of conventional multi-vibrators, of which I am aware. In this circuit resistances 26, 25 and condenser 24 control the frequency of oscillation. but resistance 25 may be held at a fixed value so that the frequency of oscillation is determined by the value of resistance26 and the capacity of condenser 24. -The grid 22 of tube Ta is conveniently available for the application of locking voltage by connecting the moving arm of potentiometer 28 to the grid 22. The desired locking voltage is applied tol terminals 21,`21 at the ends of the potentiometer 24. The locking voltage may be a source of oscillations having a frequency which is a harmonic or a subharmonic of the desired frequency of oscillations of the multi-vibrator. The square wave output from the multi-vibrator appears across resistance 29 and -is coupled to output terminals 3|, 3| by means of condenser 30. The amplitude of the output wave may be controlled by varying the position of the movable arm along resistance 29.

In Figure 3 I have shown how the circuit according to my invention may be adapted to a combined oscillator and harmonic generator. Tuned circuit 6 oscillates at the fundamental frequency in the same way as described with reference to Figure 1. The desired harmonie frequency is taken from tuned circuit 36, composed of inductance 31 and capacity 36. Tuned circuit 36 is tuned to the desired harmonic frequency. It should be noted that the presence of this tuned circuit in the plate circuit of tube T1 does not eiect the operation at the fundamental frequency because of the fact that the impedance of 36 at a submultiple of its frequency will be very low. A high harmonic output is avallable from tuned circuit 36 because the grid of tube Ti is driven by the fundamental oscillation circuit 6 over the full range of the fundamental oscillations.

In Figure 4 I have shown a modification of the circuit shown in FigureV 1 utilizing a linkcoupling circuit instead of a capacity coupling circuit. Tuned circuit 46 has been substituted for the resistance 2 of Figure 1. This tuned circuit comprises an inductance 41 and capacity 46, either or both of which may be variablevso that the circuit is tuned to the same frequency as tuned circuit 6. In a variable inductive relation to inductance 1 and to inductance 41 are small coils 49, 49. The two coils 49, 49, are connected together by leads 50. The circuit shown in Figure 4 has improved stability over the circui eviously shown due to the greater selectivity obtainable by means of the coupled tuned circuits.

A further modification of the form 0f the invention shown in Figure 3 is shown in Figure 5. The harmonic generator circuit of Figure 3 is arranged so that the fundamental circuit is crystal controlled. Piezo-crystal 68 takes the place of the fundamental tuned circuit 6. A radio frequency choke B1 passes the necessary direct current to the plate of tube Tn. The harmonic output is taken from tuned circuit 36 tuned to the desired harmonic in the same way as described with reference to Figure 3.

In Figure 6 I have shown an alternative method of coupling the cathodes of the two tubes I Ti and 'Iz together. In this figure the cathodes have separate resistors 63 and 64 coupled together by condenser 65. This form of construction enables individual adjustment of the cathode resistors so that different biases may be placed in the two tubes. In some cases condenser 65 may be replaced by a resistor which serves the same purpose and provides an additional adjustmeni-l on the degree of feedback of the oscillator. By making 65 of a high reactance compared to the resistance 64 a feedback is obtained which increases as the frequency is increased. With 65 replaced by an inductance the feedback increases as the frequency is decreased. This helps to maintain a constant output as the oscillator is tuned over a wide range.

vAt Aultra-high frequencies the circuits, as previously described, may present the disadvantage that the cathode to ground capacity of the two cathodes presents a reactance which may be small compared to the common cathode resistance at these higher frequencies. However, for normal values of cathode resistance the cathode reactance is not comparable to the cathode resistance until a frequency of about 10 megacycles is reached. This disadvantage is not serious since the capacity may be neutralized by inserting, as shown in Figure 7, an inductance 66 in series with a cathode resistor 3. By this means the capacity to ground of the cathodes may be tuned out in the same manner that television video amplifiers are equalized. Such equalization allows oscillation at the higher frequencies and improves the stability by limiting the phase shift due to capacity reactance across the cathode resistance. This phase shift otherwise causes the feedback to be different than exactly degrees and would impair the stability for the higher frequencies. With the cathode to ground capacity of the tubes compensated for there is no difficulty in making the oscillator, according to the present invention, oscillate at frequencies higher than 34 megacycles.

In Figure 8 I have shown a pair of oscillators as previously shown in Figure l and described with reference to that figure. However, the upper oscillator utilizing tuned circuit 6 is designed to oscillate at radio frequencies and the lower oscillator having its output resistance 2 connected in series with grid 22 of the upper oscillator is designed to oscillate at audio frequencies. This is accomplished by including in tuned circuit 6' an inductance 1' of high reactance and/or a large condenser 8'. The inductance 1 may conveniently be iron core choke such as used for impedance coupling in an audio frequency amplifier. The circuit shown in Figure 8 is of particular advantage for testing radio sets and other service work since the radio frequency oscillator may be tuned over a wide range of radio frequencies, depending on the constants of tuned circuit 6 and the radio frequencies may be either modulated or unmodulated as desired. The percentage modulation may be varied within a wide range by adjustment of potentiometer 2'. The output radio frequencies, if modulated by the lower oscillator, may be modulated by any audio frequency within the audible range by a proper proportioning of the constants of tuned circuit 6'. Furthermore, any audio frequency within the audible range is also directly available at the terminals 9', l0'.

By using a circuit as shown in Figure 6 for radio service work, not only may the radio frequency circuits of a radio receiver be aligned and checked but the audio response characteristics may be observed.

While I have shown and particularly described :several embodiments of my invention, it is to be distinctly understood that my invention is not limited thereto but that modifications within the scope of my invention may be made.

I claim:

l. An oscillator comprising a pair of electron discharge structures each having an anode, a cathode and a grid, a frequency determining circuit coupled to the anode of one of said structures and the grid of the other of said structures, means for effectively maintaining the remaining ones of said anodes and grids at a fixed reference potential, and impedance means connected between said cathodes and a point of zero reference potential for coupling said cathodes together.

2. An oscillator comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a frequency determining circuit coupled to the anode of one of said tubes and the grid of the other of said tubes, means for coupling said cathodes together comprising a common impedance connected from said cathodes to ground, an impedance connected from said separately mentioned grid to ground and an output circuit coupled to said last-mentioned impedance, said cathode coupling means serving to cause said cathodes to vary in potentials with respect to ground in like sense whereby said grids are effectively varied in potential in phase opposition.

3. An oscillator comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a resonant circuit coupled to the anode of one of said tubes, means for coupling the grid of the other of said tubes to said resonant circuit, means for effectively maintaining the remaining ones of said anodes and grids at a xed reference potential, and means connected between said cathodes and a point of zero reference potential for coupling said cathodes together.

4. An oscillator comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a resonant circuit coupled to the anode of one of said tubes, means for coupling the grid of the other of said tubes to said resonant circuit, means for effectively maintaining the remaining ones of said anodes and grids at a xed reference potential, and means for so coupling the cathodes of said tubes together that the effective potential of both cathodes varies in a like sense, said last mentioned means comprising a common impedance connected from said cathodes to saidl point of reference potential.

5. An oscillator comprising a. pair of thermionic discharge tubes each having an anode, a cathode and a grid, a source of anode potential, a resonant circuit connected between said source and the anode of one of said tubes. means for coupling the grid of the other of said tubes to said resonant circuit, a common impedance connecting the cathodes of said tubes to ground, means for connecting the remaining grid to ground, means for connecting the remaining anode to said source and an output circuit connected from said rst mentioned grid to ground.

6. An oscillator and frequency multiplier comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a means resonant to a fundamental frequency connected to the anode of one of said tubes, means for coupling the grid of the other of said tubes to said resonant means, impedance means connected between said 'cathodes and a point of zero reference potential for coupling the cathodes of said tubes together, a circuit resonant to the desired harmonic connected to the anode of the other of said tubes and an output circuit coupled to said second resonant circuit.

7. An oscillator and frequency multiplier comprising a pair of thermionic electron discharge structures each having an anode, a cathode and a grid, a source of anode potential, means resonant to a fundamental frequency connected between the anode of one of said structures and said source, means for coupling the grid of the other of said structures to said resonant means, means for coupling the cathodes of said structures together, said means comprising a common impedance connected from said cathodes to ground, a circuit resonant to the desired harmonic connected between the anode of the other of said structures and said source and an output circuit coupled to said resonant circuit.

8. An oscillator and frequency multiplier comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a crystal circuit resonant to a fundamental frequency coupled to the anode of one of said tubes, means for coupling the grid of thepther of said tubes to said crystal circuit, impedance means connected between said cathodes and a point of zero reference potential for coupling the cathodes of said tubes together, a second circuit resonant to the desired harmonic coupled to the anode of the other of said tubes and an output circuit coupled to said second resonant circuit.

9. An oscillator and frequency multiplier comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a. source of anode potential, means for connecting said source to the anode of one of said tubes, a crystal circuit resonant to a fundamental frequency coupled to said anode, means for coupling the grid of the other of said tubes to said crystal circuit, means for coupling the cathodes of said tubes together comprising a common impedance connected from said cathodes to ground, a second circuit resonant to the desired harmonic connected between the anode of the other of said tubes and said source and an output circuit coupled to said second resonant circuit.

10. An ultra high frequency oscillator comprising a pair of electron discharge structures each having an anode, a cathode and a grid, a frequency determining circuit coupled to the anode of one of said structures and the grid of the other of said structures, means for effectively maintaining the remaining ones of said anodes and grids at a fixed reference potential, means for so coupling said cathodes together that the effective potential of both cathodes varies in a like sense comprising a common impedance connected from said cathodes to said point o! reference potential, an impedance connected from said separately mentioned grid to xed reference potential and an output circuit coupled to said impedance, a portion of said common impedance being inductive whereby the capacity of said structures to said point of reference potential is neutralized.

ll. An oscillator comprising a pair of thermionic discharge tubes each having an anode, a cathode and a grid, a resonant circuit coupled to the anode of one of said tubes, means for coupling the grid of the other of said tubes to said resonant circuit, an impedance connected from each of said cathodes to ground, and means for coupling the cathodes of said tubes together, said last mentioned means comprising an impedance connected between said cathodes.

l2. An oscillator comprising a pair of electron discharge structures each having an anode, a cathode and a. grid, a source of anode potential, a resonant circuit connected between said source and the anode of one of said structures, an impedance connected from the grid of the other of said structures to ground, a condenser connecting said grid and said anode, a common impedance connecting the cathodes of said structures to ground, means for connecting the remaining grid to ground, means for connecting the remaining anode to said source and an output circuit coupled to said first mentioned impedance.

MURRAY G. CROSBY.

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