US2245718A

US2245718A - Oscillation generation

Info

Publication number: US2245718A
Application number: US249750A
Authority: US
Inventors: Walter Van B Roberts
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1939-01-07
Filing date: 1939-01-07
Publication date: 1941-06-17
Anticipated expiration: 1958-06-17

Description

June 17, 1941 w. VAN B. ROBERTS 2,245,718

OSCILLATION GEIIIERATION Filed Jan. 7, 1939 INVENTOR. W4L TER V N 5. ROBERTS A TTORNEY.

Patented June 17, 1941 STATES AT Waltcr'van Roberts, Princeton; N.' J l, .assignor 1 to RadioOorp'oration of America, 'a corporation of Delaware The present invention relates to an oscillator circuit of the type employing degeneration to improve its stability; I 4

The primary object of the invention isto simplif'y the stabilization of,v oscillation generator systems. In one embodiment of the invention the frequency of oscillation is stabilized, while in another embodiment both frequency and amplitude of oscillation are stabilized.

A better understanding of the invention may be had by referring to the following description, which is accompanied by a drawing wherein Figs. 1 and 2 show, by way of example only, two oscillation generation systems of the present invention, differing from one another only in the type of resistance used in the cathode lead.

Referring to the drawing, wherein like parts are represented by like reference characters, there is shown in each of Figs. 1 and 2 an oscillation generation system comprising an evacuated electron discharge device having a control grid G, a cathode K, a screen grid SG, and a plate P. Although a screen grid tube has been shown in the drawing, it should be understood that this is merely illustrative of any type of vacuum tube having a plurality of electrodes, the invention not being limited to a tetrode. In circuit with the cathode K between two points thereof, there is a pure resistive impedance R or R. In circuit with the grid G and plate P, there are, respectively, inductance coils Lg and Lt, both of which are coupled to the coil L of a parallel tuned oscillatory circuit 0. Coils Lg and 111) may be made of fine resistance wire, or have resistors connected in series with them in known fashion to prevent parasitic oscillation. It should be noted that connections extend from the grid circuit, plate circuit, screen grid circuit, and cathode circuit to a point of common radio frequency potential, such as ground. Fig. 2 differs from Fig. 1 only in the type of resistive impedance used in the cathode circuit, the resistor R being Application. January 7 1939,seriarNa-Mar so 2 Claims. (01. 250 -36) shown as an electrical light bulb whose alternating current resistance increases with increase in temperature.

An exposition of the theory and the operation of the invention follows: The pure resistive im- Where gm=the vtran'sconductance of the tubeand e =the vo-ltage'induced' in the grid circuit.

The conditionior oscillation of this :circuit may be derived as follows: e ='a'ttM1i ,1where 2' is the current in coil' La. i

1 The voltage "induced in the tank :circuit O=jwM2i while the voltage .drop in the tank circuit O=ir, where M1 is the mutual inductance between the grid coil Lg and the coil Lo of the oscillatory circuit O, and M2 is the mutual inductance between the plate coil Lip and the coil Lo of the oscillatory circuit 0.

For sustained oscillation, these two voltages must add to zero. Replacing i by its expression in terms of gm, R, w, M1 and i, this condition becomes 7 w M M 1 T Im If the left side of this equation is larger, the amplitude of oscillation will increase with time.

It will thus be seen that if R is large compared to 91. (or in other words, if Rgm is large compared to unity) the condition of oscillation is dependent only to a slight degree upon the value of 9111. The circuit is thus stabilized against the efieot of variation of electrode voltages, change of tubes, or any other factors which affect the value of mm.

As with any ordinary oscillator circuit however, when the condition for starting of oscillations is met, these oscillations will build up in amplitude until grid currentflows with a resulting increase in the effective value of the circuit resistance 1", or else the tube operates over such a wide range of its characteristic that the effective gm of the tube decreases. For either or both of these reasons, the amplitude comes to a limiting value. In order, however, to limit the amplitude to a value less than that which introduces the additional losses or the non-linear action mentioned above, the degenerative resistance R may be of the type whose alternating current resistance increases with increase in temperature, as indicated by the electric light bulb R of Fig. 2, so that as the amplitude of oscillations increases, its alternating current resistance value increases so that the amplitude of oscillations is maintained without further increase at a small value which does not introduce losses in the circuit or distortion in the tube. The introduction of such a resistance in other circuit arrangements for vastly different purposes is known and need not be further described.

While an electric light bulb has been mentioned and illustrated in Fig. 2, any other type of resistor may be used whose resistance increases with increase in oscillation amplitude.

While I have shown and described two specific forms of the invention, it will be understood that many modifications thereof will be readily apparent to one skilled in the art without losing the benefits of simplicity provided by the present invention. The essential conditions to be met are that plate circuit should be coupled to the oscillatory circuit and the oscillatory circuit in turn so coupled to the grid circuit as to produce a relatively large regenerative grid voltage which is in phase with the plate current at the resonant frequency, but out of phase therewith except at resonance, while at the same time the plate current produces a slightly smaller degenerative grid voltage which is independent of frequency.

What is claimed is:

1. In combination, in an oscillation generation system, an evacuated electron discharge device having control grid, cathode and plate electrodes, individual connections each including an inductance coil from said control grid and plate electrodes to a reference point, a parallel tuned oscillatory circuit having an inductance coll coupled to said coils in said grid and plate connections, and .a resistor having negligible shunt capacity connected between said cathode and said reference point, said resistor having a value as large as possible but which will not stop oscillations and being of such type that its resistance increases with increase in current flow therethrough.

2. In combination, in an oscillation generation system, an evacuated electron discharge device having control grid, cathode and plate electrodes, individual connections each including an inductance coil from said control grid and plate electrodes to a reference point, a parallel tuned oscillatory circuit having an inductance coil coupled to said coils in said grid and plate connections, and a resistor having negligible shunt capacity connected between said cathode and said reference point, the resistor being such that its value increases with current flow therethrough.

WALTER VAN B. ROBERTS.