US2244261A - Superregenerative amplifier - Google Patents

Description

June 3, 1941. K. RATH SUPERREGENERATIVE AMPLIFIER Original Filed July 18, 1936 INVJENTOR. a-rl 8191' ATTORNEY.

Patented June 3, 1941 SUPERREGENERATIV E AMPLIFIER Karl Rath, New York, N. Y., assignor to Radio Patents Corporation, a corporation of New York Original application July 18, 1936, Serial No. 91,328. Divided and this application February 10, 1939, Serial No. 255,586.

1 Claim.

This application is a division of my co-pending application, Serial No. 91,328, filed July 18, 1936.

In the above application there is described a regenerative system wherein amplified output energy is applied or fed back upon an input circuit purely electronically by the provision of a pair of electron discharge paths arranged in parallel relationship and connected with the input and feedback circuit, respectively. An advantage of such an arrangement is the fact that both the main amplifier currents and the feedback currents may be adjusted as to amplitude, frequency, phase, etc., in a most accurate manner substantially independently of each other, thereby enabling any desired modification of the main amplifier current by regenerative or degenerative feedback and improving the efiiciency and stability of regeneration.

An object of the present invention is to employ this principle in a super-regenerative amplifier wherein the regenerative action is controlled or stabilized by means of an interrupting or quenching signal applied to the main amplifier circuit through pure electron coupling.

Another object is to provide a highly stabilized and efiicient super-regenerative amplifier which can be adjusted easily to suit any special requirements as to degree of regeneration, permissible distortion and other operating conditions.

A further object is the provision of a superregenerative amplifier in which regenerative or feedback potentials are applied to react upon an input signal in such a manner that the degree of amplification and the quenching effect can be regulated entirely independent of each other.

A more specific object is to provide a superregenerative amplifying circuit for radio frequency signals wherein the same tube not only serves as a regenerative amplifier, but also to impose a periodic quenching efiect upon the amplifier or load circuit to render the resultant effective resistance in the latter periodically negative and positive at a rate above the highest modulating frequency of the signals being amplified.

These and further objects and aspects of the invention will become more apparent from the following description taken with reference to the accompanying drawing forming part of this specification and wherein:

Figure 1 shows a super-regenerative amplifying Figure 2 shows a multi-function amplifying tube for use in a circuit according to Figure 1.

As is well known, the degree of regeneration in super-regenerative amplifiers is adjusted to a point where the efiective resistance of a tuned circuit (load circuit) becomes negative, whereby normally the circuit would become an oscillator and generate self-sustained oscillations. This latter condition is prevented by the provision of an auxiliary interrupting or quenching device adapted to change the effective resistance of the circuit alternately from a positive to a negative value at a rate above the frequency of the modulating signal impressed upon the radio frequency signals being amplified; that is, above audibility in the case of signals modulated according to variations of sound such as speech or music. In this manner, the amplifier while providing considerable amplification due to the high degree of regeneration is prevented from causing excessive distortion and building up steady selfexcited oscillations.

In super-regenerative systems heretofore known, great difficulties have been experienced in maintaining a constant and stable quenching effect free from reaction upon the signalling cir- 'cuits, as well as in regulating or adjusting the degree of amplification and the quenching or interrupting frequency to suit existing requirements and to ensure stable operating conditions. These disadvantages are substantially overcome by the system proposed by the invention wherein the quenching or interrupting potential is applied to the main amplifier or load circuit through pure electron coupling.

Referring to the drawing, Figure 1, there is showna composite amplifying tube H3 comprising a common anode II for a pair of electron discharge paths produced by means of separate cathodes l2, l3 arranged in cooperative relation with the anode l l. The left-hand section of the tube comprising the cathode I 2 and anode H serves as an ordinary amplifier such as a triode amplifier as shown and for this purpose has a control grid l4 placed in the discharge path. This section of the tube serves for the amplification of a radio frequency signal impressed upon its grid-cathode path through an input coupling transformer having a primary winding l5 and a secondary winding IS, the latter being shunted by a tuning condenser I1. Item I8 is a resistance inserted in the cathode to ground lead and shunted by a decoupling condenser l9 to provide suitable steady biasing potential for the grid I4 in accordance with a well known practice.

The amplified output signals are impressed upon a further tuned circuit inserted in the anode circuit and comprised of an inductance 2B shunted by a condenser 2|. From the circuit 20, 2i the signals may be fed to a further amplifying stage or to a detector through the secondary coupling coil 22 or in any other suitable manner.

There is further provided a feedback or reaction coil 3| in the anode circuit disposed in inductive coupling relation with the input induct-- ance IS in such a manner as to impress a portion of the output signal energy upon the'received energy in the input circuit in cophasal relation with the latter and in such a manner as to. normally overcompensate the in-phase component or ohmic resistance of the circuit. As a result, the path between cathode I2 and anode H becomes a negative resistance shunted across the output or load circuit 28, 2| and compensating the ohmic or loss resistance of the latter. The design and adjustment of the circuit is such as to normally render the total eifective resistance of the circuit 20, 2| negative. This would result in the building up and generation of sustained oscillations at the natural tuning frequency of the circuit. In order to prevent this condition, there is provided further a periodically variable impedance in the form of an electron path arranged in shunt to the main amplifying path between the cathode l2 and anode II and comprising the cathode l3 and anode II and means for periodically varying the alternating current impedance of this path at a rate above audibility in the case of receiving signals modulated in accordance with sound wave variations.

In the example illustrated, there is provided for this purpose a control grid 23 and a positively biased grid 24 placed in the discharge path between the cathode l3 and the anode H and having connected therewith an auto-oscillating system. The latter in the example shown comprises a tank circuit constituted by an induction coil 25 shunted by a tuning condenser 26. The tank circuit has its upper or high potential side connected to the grid 2@ through a con- 7;

denser 21, while its low potential end is connected to the grid '23 through a condenser '28. An intermediate point of the inductance 25 is connected to the cathode l3 and the grid 23 by-passed to cathode through a grid leak resistance 29. By means of an arrangement of this type, self-sustained oscillations will be maintained in the circuit 25, 26 at a frequency determined by the natural frequency of the circuit (quenching frequency) resulting in a periodic variation of the impedance of the electron path between the cathode t3 and the anode H. The grid leak 29 serves to provide proper biasing potential for the grid 23 by the Voltage drop therethrough due to direct grid current. The grid 24 is connected to the positive terminal of a suitable high tension source indicated by the plus sign through a choke coil 39 blocking the alternating potential from the supply circuit. In order to prevent mutual interference by stray electrons and the like between the two discharge paths a screen 32 is provided separating the tube into two halves or discharge sections.

As is understood, any other suitable means or oscillatory system maybe employed for effecting a variation of the electronic impedance path between the cathode l3 and anode l I.

As is seen from the foregoing, the effect of the periodic impedance variations of the discharge path between cathode l3 and anode H,

provided the circuit elements are properly designed and adjusted is to render the normally negative resistance of the path between the oathode l2 and the anode ll periodically positive at the rate of the oscillating or quenching frequency generated in the tank circuit 25, 26 in such a manner as to prevent undesirable distortion or building up of the oscillations in the output circuits 20, 21 to excessive amplitudes, while at the same time affording considerable amplification of the input signal energy during the negative resistance intervals. An advantage of a super-regenerative system of this type is the fact that the amplification and regeneration of the signal energy may be controlled in any desired manner substantially independently of the quenching frequency, thereby enabling an accurate adjustment of the separate circuit constants and, operating conditions and ensuring high efficiency and operational stability.

A further explanation of the function of the invention is given as follows; the grid 24 being at a high positive potential with respect to the cathode I3 acts as a decelerating means for electrons passing the meshes thereof, thereby producing a virtual cathode or concentrated space charge adjacent to the grid at the side of the anode H. This space charge fluctuates at the rate of the auxiliary and quenching frequency as determined by the control potential applied to the grid 23 and is equivalent to a charged conduct-or forming a condenser with the anode ll acting as the cooperating electrode. As a result, the electric charge on the anode varying in accordance with the frequency of the input signals is periodically accumulated on and released from the anode II in the rhythm of the auxiliary or quenching frequency to balance the space charge fluctuations near the grid 24, thereby reacting on both the amplitude and phase of the current through the feedback coil 3'! and resulting in a stabilization of the regenerative action and prevention of a continuous oscillating condition.

Referring to Figure 2, there is shown a multifunction discharge device especially suited for use in a circuit described. In the drawing, item 35 represents an evacuated vessel such as a glass bulb housing the electrode structure and mounted upon a base 33. The electrode structure comprises a common cathode sleeve 31 of oblong cylindrical shape surrounding a non-inductive heater winding 38. The latter is connected to a pair of prongs 355 and 40 mounted at the bottom of the base 38. The sleeve 31 is covered with separate adjacent coatings 4| and 42 of electron emitting material to form a pair of cathodes. The electron currents emitted by the latter are screened from each other by an insulating separator such as a mica disc 43 which also serves as a support for the electrodes as shown. The coatings 4! and d2 serve as the cathodes for the separate discharge sections, while the common cathode terminal formed by the sleeve connected to prong 44.

The tube includes furthermore a common cylindrical anode 45 concentrically surrounding both discharge sections co-extensive with the cathodes ll and 42. The lower discharge section serving for generating the local quenching oscillations. comprises a control grid 46 preferably of spiral shape concentrically surrounding the cathode ll and a positive or anode gride 4? consisting in the example shown of two or more single rods mounted between the grid 46 and the anode 45. It is understood that grid 41 may be of standard construction such as a suitably shaped wire mesh or net structure. The upper discharge section serving for amplifying the incoming signals comprises an input or control grid 48 connected in the example shown to a terminal cap 52 mounted at the top of the tube. The positive or anode grid 41 is connected to a separate prong 50 on the base 36. The anode 45 is connected to prong 49 and the grid 46 is connected to prong 5|. The electrodes may be mechanically mounted in any suitable manner such as by means of supporting rods sealed in the press at the lower and of the tube and partly serving as current conducting leads and by means of the mica separating disc 43 as shown.

As pointed out, separate tubes may be provided in place of composite tube constructed and connected in the manner described by the invention.

Although I have described the invention with reference to the embodiments shown in the drawing for illustration, it is understood that numerous modifications and variations suggest themselves coming within the broad scope and spirit of the invention as defined in the appended claim.

I claim:

In an amplifying circuit, the combination of a vacuum tube having a cathode, an anode, a control grid located between said anode and cathode adapted to control the electron current between one half only of said cathode and anode, an input circuit connected to said control grid and an output circuit connected to said anode, feedback means between said output and input circuits to'normally provide a negative resistance to signals impressed upon said tube, means for periodically varying the impedance of the electron path between the other half of said cathode and anode, and screening means between said electron paths between said first and second halves of said cathode and anode.

KARL RATH.

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