US1943471A - Dynatron circuit - Google Patents

Description

Jan. 16, 1934. P. o. FARNHAM 1,943,471

DYNATRON CIRCUIT Filed Jan. 15, 1932 Patented Jan. 16, 1934 UNITED STATES PATENT ()FFICE DYNATRON CIRCUIT Paul 0. Farnham, Boonton, N. J., assignor to Radio Frequency Laboratories, Incorporated, Boonton, N. .L, a corporation of New Jersey This invention relates to dynatron circuits and particularly to methods of and circuits for obtaining. regenerative amplification.

My copending' application, Ser. No. 563,635, filed SeptemberlS, 1931, describes and claims the method of reflecting a negative capacity into the input circuit of a dynatron, through a capacitive coupling between plate and control grid, by the use ofa plate circuit load which is a resistive impedance for the signal frequencies. According to the present invention, a negative resistance is reflected into the input circuit of a dynatron, through capacitive coupling between the input and output circuits by providing a plate circuit load which is capacitive at the radio frequencies.

Objects of the invention are to provide novel methods of andcircuit arrangements for obtaining regeneration in networks including a tube that is operated as a dynatron, that is, is so energized that it has a negative plate impedance. Further objects are to provide methods of and circuit arrangements for obtaining substantially constant regeneration over a band of radio frequencies. These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing,in which V Fig. 1 is a schematic diagram illustrative of the invention, and

Figs. 2 and 3 are circuit diagrams of embodi- Z9. and the output or plate circuit has a loan Zb, the circuits being coupled by asmall capacity Cm.

The tube 1 may be of the known screen grid type in which the capacity between control grid and plate is of such low magnitude as to prevent a retroactive flow of current from the output to the input circuit.

With the tube 1 operating as a dynatron, the

effect of the coupling capacity Cm is to reflect a negative resistance into the tube input circuit so long as the signal frequencies impressed upon the input circuit fall within the range for which the plate load Zb is a capacitive impedance.

In the dynatron detector shown in Fig. 2, the

input circuit of tube 1 may comprise an inductance 2 and adjustable condenser 3 for tuning the circuit to resonance at a desired signal frequency. The control grid is coupled to the plate by a small condenser Cm which is preferably capable of adjustment but which is not varied during normal operation of the dynatron detector. The capacity C1 of about 15 micromicrofarads represents the inherent capacity between the tube elements, plate and screen. To make the plate load capacitive for signal frequencies, the composite impedance L, C is arranged betweenthe plate and the resistance 4, and a capacity C2 from the junction of L C and 4 to ground, the values of these impedances being so related that the effective impedance of this composite load is capacitive over all or a desired part of the tuning range of the input circuit.

For frequencies of from 550 to 1500 kilocycles, values which satisfy this condition may be:

Resistance 4=100,000 ohms Capacity C: 10 micromicrofarads Capacity C2 100 micromicrofarads Inductance L=5 millihenries.

With this circuit arrangement, the eifective capacity of the plate circuit load for radio frequencies varies with frequency in such a way that the feedback current through the constant capacity Cmmay be made to increase when the input circuit is tuned to the low frequency end of its range. In this way, a falling off of input tuned circuit impedance at lower frequencies rather large capacity, 8, across 4, the external circuit from plate to cathode may be made capacitive for the entire range of signal frequencies. By choosing the values of capacity 5, choke 6, and capacity 8 so that this circuit approaches resonance at the low frequency end of the range, sufficient increase in feedback current through Cmmay be obtained to give a substantially constant eilect upon the input circuit when used over the entire radio frequency range.

While the invention provides a simple means for obtaining constant regeneration over a frequency band, it will be apparent that the regeneration may be automatically varied as a function of the frequency by substituting, for the L, C impedance of Fig. 2, a composite impedance having an effective capacity which varies with frequency in any desired manner.

The resistance 4 is shown as an illustration of resistance coupling for the modulation frequency although it will be understood that a choke or transformer designed to provide coupling for transferring the modulation frequency output to the succeeding tube may be used in place of resistance coupling.

While I have described my invention in connection with a tetrode comprising two grids and a plate, it will be understood that any form of multiple-electrode tube, energized in the requisite fashion to reduce negative resistance effects in an internal circuit between one electrode and the emitter, may be used in applying the principles of my invention. In the appended claims as in the foregoing specification, I employ certain terms, designating the individual electrodes, in accordance with the following definitions:

Cathode. An electrode thermionic space-current.

Control grid-An electrode so formed and emitting primary positioned in the tube that its potential with respect to the cathode governs the magnitude of 'the primary thermionic space-current leaving the vicinity of the cathode and available for collection by the remaining electrodes.

Screen-grid.An electrode positively polarized with respect to the cathode and which may serve to accelerate the primary thermionic space current and/or to provide a return path for secondary spacecurrents emitted by other electrodes.

Plate.-An electrode positively polarized with respect to the cathode, serving primarily as a collector of primary thermionic space-current and as an emitter of secondary space current. The plate may or may not serve as an output electrode. In the appended claims the term plate therefore designates an electrode which forms with the cathode, an internal tube circuit whose alternating-current resistance is negative within the operating range.

I claim:

1. Apparatus for producing a negative resistance effect between two terminals, comprising a vacuum tube and means for impressing on the elements thereof potentials effective to impart a negative plate resistance to said tube, a capacitive load in the plate circuit of said tube, a capacity coupling the plate and control grid of said tube, a connection from one of said terminals to the control grid of said tube, and a connection from the other terminal to the cathode of said tube.

2. In a vacuum tube circuit, a tube having the elements thereof subjected to energizing potentials eifective to impart a negative plate resistance to said tube, and means for establishing a negative resistance across an external circuit connected between the cathode and a grid element of said tube, said means comprising a plate load having a capacitive impedance at radio frequencies, and a capacitive coupling between the tube plate and the grid element.

3. In a detector, a tube subjected to energizing potentials effective to give said tube a negative plate resistance, a circuit tunable over a band of frequencies and connected between the input electrodes of said tube, an output circuit for said tube having a capacitive impedance for frequencies within said band, and a capacitive coupling between said input and output circuits.

4. In a detector for modulated signals, the combination with a tube having a negative internal plate-cathode resistance, an input circuit tunable over a band of radio frequencies for said tube, and an output circuit including an audio frequency load impedance, of means imparting to the output circuit a load impedance which is capacitive at radio frequencies, and a capactive coupling between the dynatron plate and control grid.

5. The invention as set forth in claim 4, wherein said means comprises a condenser connected between the plate and said audio frequency load impedance, a direct current path shunted across said condenser and a condenser connected across said audio frequency load impedance, said path having a high impedance at radio frequencies.

6. The invention as set forth in claim 4, wherein said means includes a capacitive impedance connected between the plate and cathode of said tube, a radio frequency inductance between the plate and said audio frequency load, and a condenser across said audio frequency load, said network of capacities and inductance presenting an eifective capacitive impedance to the plate cathode terminals of said tube over the band of radio frequency.

'7. The invention as set forth in claim 4, wherein the impedance of said radio frequency load impedance varies with frequency at such rate as to maintain a substantially constant regenerative effect upon the input circuit over its tuning range.

8. In a detector for modulated signals, the combination with a tube having a negative internal plate-cathode impedance, an input circuit tunable over a band of radio frequencies, and a capacitive coupling between the plate and control grid, of an output circuit for said tube said output circuit including an audio frequency load and means for producing a substantially constant regenerative effect through said capacity coupling as said input circuit is tuned over said band of radio frequencies.

9. The invention as set forth in claim 8,

wherein said means comprises a condenser be tween the plate and said audio frequency load,

between the plate and said audio frequency load and a condenser across said audio frequency load.

11. In a transmission system, the combination with a tube having a negative internal plate-cathode resistance, an input control-grid circuit tunable over a band of radio frequencies, and an output circuit connected to the plate and including an audio frequency load impedance, of means imparting to the output circuit, an impedance which is capacitive at radio frequencies, and a capacity coupling between the plate and control grid.

12. In the operation of an electron tube having a cathode, a control grid, an input circuit connected to said control grid, a screen grid,- and a plate, the method of introducing negaist with respect to the cathode that the internal circuit between said fourth electrode and said cathode exhibits a negative alternating current resistance, the method of introducing negative-resistance into the input circuit which comprises including in an external circuit between said fourth electrode and said cathode a load having a capacitive impedance at the operating frequencies, and capacitively coupling said fourth electrode to said control grid.

PAUL O; FARNHAM.

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