US2260545A - Oscillation generation - Google Patents

Description

Oct. 28, 1941. G. STARK 12,260,545

' OSCILLATION GENERATION Filed April 15, 1939 Syd T 4 Z i ATTORNEY.

Patented Oct. 28, 1941 OSCILLATION GENERATION Gottfried Stark, Berlin-Niederschoneweide, Germany, 'assignor to-General Electric Company, a

corporation of New York Application April 15, 1939, Serial No. 268,001 r In Germany May 20, .1938

. I 4 5 Claims. "It is known that elements-with a falling characteristic, such as the dynatron, can be used "iorproducing oscillations and, in connection with "normal positive reactances, for obtaining negative are'used, however, difliculties occur, since because of the non-linearity of the falling part of the characteristic, there o'ccur harmonics and combination tones in the controlled range, which may become very disturbing.

7 "While the non-linear products can be easily eliminated from'certain types of oscillation generators by the application of selective circuits, 'their'elimination in quadripoles for 'the transmission-of wide frequency bands creates serious difiicultiesj It is known that in order toattain this purposega non-linear resistance may 'be connectedwith the element having the non-linear falling characteristic-either in series or in parallel, in'such a way that the non-linear distortions of both elements will just offset each other. To this end it is necessary that the characteristics of both elements be accurately tuned with respect to each other, or, provision must be made for tuning them automatically with respect to each other. The realization of characteristics the curvatures of which are suficiently alike for the purpose in view is exceedingly difiicult to attain in practice, and can be brought about only by the utilization of many additional circuit elements.

This disadvantage of the known linearization or straightening methods is avoided by means of the present invention.

The object of the invention is to provide a dipole (i. e., a two-terminal network) with a falling characteristic, for instance a dynatron, which can be changed, as regards its absolute resistance value, by a controlling quantity (for instance control-grid potential), which will not influence the falling tendency of the characteristic. According to the invention, there is used for straightening the falling characteristic a connection between the output alternating current circuit and the controlling input circuit, which connection acts as a negative backcoupling.

The invention will now be discussed with reference to Figs. 1 to 4, which relate to a dynatron circuit that has been chosen as a typical embodiment. Fig. 1 illustrates a known type of dynatron circuit, while Fig. 3 illustrates a dynatron circuit in accordance with the present invention. Figs. '2 and 4 are graphical representations of the "operation of the circuits of Figs. 1 and 3, respectively.

I Fig. 1 shows a knowndynatron circuit. D is "the dynatron, with the cathode I, the anode 2, the screen grid 3, and the control grid 4'. The control grid receives by means of the battery B1 'a negative potential with respect to the cathode, while the screen grid "3 is positively biased with respect to the anode 2, the batteries B2 and Ba being of suitable potentials to meet this requirement. The discharge tube generates oscillations because of the secondary emissionfrom the anode. This secondary emission is of such in tensity that the tube possesses a negative transjconductance I characteristic. The cathode-toanode circuit usuallyincludes a direct current source 133 and *a load resistor T1. The utilization circuit may be connected to the terminals a, b "for deriving potentials developed across the load resistor n. The dynatron action of the circuit arrangement is equivalentto an oscillator having a "falling characteristic.

"This characteristic (which characterizes the dependence of the alternating current i, flowing 'in the anode circuit-of the dynatron, on an alternating potential u applied from the outside to "the-resistance T1) is represented in Fig. 2. 'Its falling part, say the controlling range between the points 0 and d, is not sufficiently straight, and as a result non-linear distortions are created. In order to decrease or eliminate these distortions, I have modified the known dynatron circuit according to the circuit shown in Fig. 3. In the anode circuit, another resistance in is connected in series with the resistance 11. This resistance T2 is by-passed by the primary winding of the transformer T, whose secondary winding is connected on the one side with the cathode of the tube and on the other side with the positive pole of battery B1. In this manner the anode alternating potential developed acrossthe resistance r: is degenerative in its back coupling action on the control grid.

Just as degenerative back-coupling in amplifier, circuits produces a straightening of the amplifier characteristic, so a straightening of the falling characteristic is attained in the dynatron by the back-coupling just described. Fig. 4 shows the straightened falling characteristic.

The circuit according to Fig. 3 permits difierent variants within the scope of the invention. For instance, the degenerative back-coupling need not be produced in the manner which has been repreany of electrodes and inductive means coupled across said last mentioned resistancefor inter-coupling said output and input circuits thereby to obtain a degenerative feed-back voltage to 'be applied to said control grid, said voltage being that which is developed across at least a portion of said load impedance, and being operative to improve the linearity of the negative resistance characteristic of said device.

2. A negative resistance circuit comprising an electron discharge device oscillator having an anode, a cathode, a control grid and a screen grid, means for applying a negative bias to said control grid and a positive bias to said screen grid and anode relative to said cathode, the positive bias on said screen grid being higher than that on said anode, the values of said biases being such that said oscillator functions by secondary emissive eifects'and produces a negative resist-l ance; across a resistance in its anode circuit, means for developing analternating current voltage across said resistance, and means for producdegenerative back-coupling comprising 7 a transformer coupled across a-portion of said revsistance insaid anode circuit and adapted to feed ,alternating current energy from said anode circuitto said control grid, wherebythe linearity of the falling characteristic of said device is improved. 1

'3. A negative resistance circuit comprising an electron discharge device oscillator having an anode, a cathode, a control grid and a screen grid, means for applying a negative bias to said control grid and a positive bias to said screen grid and anode relative to saidcathode, the- .positive bias on said screen grid being higher than that on said anode, the values of said biases being such that said oscillator functions by secondary emissive effects and produces a negative resistance across a resistance in its anode circuit, means for developing an alternating. current voltage across said resistance, and means for producing degenerative back-coupling comprising another resistance in series with said first resistance, a transformer having one winding connected across said other resistance and another winding coupled between said control grid and cathode, whereby the linearity of the falling characteristic of said device is improved.

4. A negative resistance circuit comprising an electron discharge device having an anode, a,

cathode and a control grid, means including said electron dischargedevice for producing secondary emission from said anode whereby a negative resistance characteristic appears therein, a pair of terminals in the anode circuitacross which said negative resistance is presented to a load connected therebetween, a resistance in series in said anode circuit, and means including atrans" former having one winding connected across said resistance and another winding coupled between said control gridand cathodefor producing a degenerative back-coupling action, whereby the linearity of the falling characteristic of said device is improved; 7

- 5. An oscillation generatorcomprising an electron discharge tubehaving a cathode,; an anode and a plurality of grids including acontrol grid and a screen grid,,r neans for producing adynatron action in saidtube, said means being constituted by a steady source of voltage applied more positively to the, screen grid than to the anode with respect to the cathode, a nonresonant input circuit connected between the cathoderand control grid, a load circuitconnected between the cathode andlanode, means for deriving a feed-back voltage from said load circuit, and means comprising a transformer having its primary connected in shunt with aportion of said load circuit and its secondary in said input circuit for applying; said feed-back voltage 'degeneratively to saidcontrol grid, whereby the falling characteristic of said discharge tube :is

rendered substantially linear over its working range. I GOTTFRIED STARK.

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