US2408061A - Stable pulse generator - Google Patents

Description

Sept. 24, 1946. w D. o. GRIEG STABLE PULSE GENERATOR Filed Dec. 20, 1941 17/6 VOLMGE' DOA/ALP a 6/?76'6' Patented Sept. 24, 1946 2,408,061 STABLE PULSE GENERATOR Donald D. Grieg,

New York, N. Y., assignor to Federal Telephone and Radio corporation of Delaware Corporation, a

Application December 20, 1941, Serial No. 423,862

2 Claims. (Cl. 250'36) This invention relates to improved means for the generation of short impulses of relatively high energy and periodically recurrent.

It is an object of the invention to provide relatively simple means for the generation of impulse energy.

Another object is to provide an improved stabilized impulse generator wherein it is not necessary to synchronize the generator to an external frequency standard.

A further ebject is to provide an improved impulse generator wherein the impulse frequency is independent of load or supply-voltage variations.

It is also an object to provide an improved impulse generator wherein the impulse width is constant over a range of supply voltage or load conditions.

A still further object is to provide an improved impulse generator wherein the impulse recurrence frequency may be varied and the width of impulses at the same time maintained constant in spite of such frequency variation.

Other objects and further features of novelty and invention will hereinafter be pointed out or will become apparent from a reading of the following specification in conjunction with the drawing included herewith. In said drawing, Fig. 1 is a schematic diagram of a circuit incorporating features of the invention, and Fig. 2 illustrates graphically the progressive treatment of wave forms in the circuit of Fig. 1.

Broadly speaking, the invention contemplates the generation of impulse energy by applying regularly recurrent current surges across an inductance whereby correspondingly recurrent damped oscillations are set up in the circuit of the inductance. Appropriate shaping means thereafter serve to remove all of such oscillations but the first current surge thereof.

Specifically, and in accordance with the preferred form shown in Fig. 1, an oscillator feeds an electron-coupled device to supply the regularly recurrent current surges. In the form shown, the circuit of this oscillator includes a vacuum tube T1 of known form having a cathode, control grid, screen grid, suppressor grid, and anode. The oscillatory circuit further comprises the parallel impedance combination of an inductance L1, a variable capacitance C1, and another capacitance C2. The frequency of oscillation of this circuit is largely determined by the magnitudes of elements L1, C1 and C2, and this frequency may be defined as In operation the oscillator functions with the screen grid, control grid, and. cathode circuits 2 of tube T1 to produce a sinusoidally varying voltage of the form shown in Fig. 2a.

The remaining elements of tube T1 preferably form an amplifier for amplifying portions of the voltage generated by the abovedescribed oscillator. Preferably, in accordance with the invention, the suppressor grid of tube T1, which forms an effective control grid for the amplifier, is biassed below cutoff so that class C operation of the amplifier results. It will be clear that the output of tube T1 will then comprise a series of current surges or pulses, the duration of which is determined by the degree to which the amplifier portion of tube T1 is operated class C, that is, the magnitude of negative bias applied to the suppressor grid across the used portion of resistance Rs. Preferably, this bias is relatively great so that only very short current surges are derived in the output of tube T1. These current surges may be of the form shown in Fig. 2b.

In accordance with features of the invention,

the output of tube T1 is applied directly across an inductance L2. Now, when the above-mentioned short pulses of current fiow through inductance L2, voltage surges of high value may appear thereacross, as will be clear. Inasmuch as there is unavoidably some capacity associated with inductance L2 and its associated circuit, the nature of the voltage pulses appearing across L2 will be damped oscillations, as shown for example, in Fig. 2c.

Now, in order to obtain relatively high voltage pulses of short duration from these damped oscillations, I propose to use appropriate shaping means for eliminating all of the voltage variations but the initial surge associated with these pulses. Several methods for so shaping the output appearing across inductance L2 will naturally occur to those skilled in the art. For example, it would be possible to shunt inductance L2 with resistance, thereby increasing the damping and further reducing any effect of the undesired voltage variations. The objection to this method is that the. initial pulse is likewise considerably reduced in amplitude, and at the same time its width at the base is substantially broadened due to the effect of such a shunt resistor on the time constant of the damped oscillation circuit.

In accordance with thejinvention, however, I propose to employ thermionic damping means shunted across inductance L2 in order to remove the undesired voltage variations following the initial pulse. In the form shown, a diode T2 is connected across inductance L2, and a resistor R3 is preferably in series therewith to reduce the effect of the plate-cathode capacitance of the diode. The operation of such a connection will be readily apparent. Assuming the initial pulse across inductance Le to be positive, the cathode may be controllable in any dicated by the arrow traversing this element.

3 of diode T2 will be positive with respect to the plate thereof. No current will then flow through the diode, and the diode shunting efiect will be negligible. During the negative cycle of oscillation immediately following the initial pulse, diode T2 will be conductive, thus effectively shunting inductance L2. The removal of a voltage surge across inductance L2 in this manner immediately removes any cause for ,further and lesser voltage variations, It follows, therefore, that only single pulses corresponding to the initial surge of voltage across inductance L2 will appear across inductance L2 when diode T2 is connectedas shown. It is to be noted that in the preferred form of eliminating the undesired voltage surges, the amplitude of the initial surge is not noticeably affected, and successive lesser surges are completely eliminated.

Inasmuch as the width of pulse generated in the above manner depends upon the damped oscillation frequency, any desired control over such width (within limits, of course) may be effected by varying a circuit constant within the damped oscillation circuit. For example, inductance L2 known manner as in- Appropriate output may be derived from the above-described circuit by well known means. In

the form shown, a socalled cathode follower amplifier circuit is employed. This amplifier circuit includes a vacuum tube device T3, and the output pulses may be obtained therefrom in a load P1 across a low magnitude resistor R4 in the cathode, circuit of tube T3. In the form shown, a coupling condenser C3 in the input circuit of tube T3 is preferably made small in order to reduce the shunting effect of the input to tube T3, and a grid resistor R2 is also small in order not to increase the width of pulses due to the abovenoted undesirable damping effect of excessive resistance.

It will be noted in connection with the pulse generator described that since the pulse frequency isdetermined solely by the sinusoidal oscillator frequency, the frequency of pulse output may be varied by appropriate control of the oscillator, as by varying condenser C1, for example. The amplifier and oscillator sections of tube T1 are isolated from each other with the exception of a coupling by the electron stream in this tube. It follows that the pulse generator will have the desirable feature that variation in load output may not affect the pulse frequency. Furthermore, in accordance with well known methods, the oscillator may be made to supply a frequency substantially independent of supply voltage by proper adjustment of the cathode tap on inductacne L1 and adjustment of the screen grid voltage by posignal.

modifications may be made fully within the scope thereof. For example, if it is not desired to have a flexible variation of impulse frequencies, a crystal oscillator may be employedinstead of the oscillator described. Such an oscillator would, of course, furnish a permanently reliable and stable pulse frequency,

Furthermore, time modulation of the pulses generated bythe circuit described may be obtainedby the relatively simple expedient of varying some circuit constant in the damped oscillation circuit in accordance with an intelligence ,Such modulation may be effected in a relatively simple manner, say by varying the inductance of L2 in accordance with the intelligence signaL as will :be clear.

What I claim is: V 1. Pulse'generator comprising, in combination, a vacuum tube having control elements including an anode, a cathode and a grid, and a high internal plate resistance characteristic, a tank circuit, means interconnecting said tank circuit with elements of said vacuum tube to produce oscillations therein, an output circuit connected between the anode and cathode of said tube, means biasing an element of said vacuum tube to sucha value as to produce periodically recurrent currentsurges in said output circuit, a tun able inductive reactor serially connected in said output circuit, said reactor having a resistance value relatively small compared with the internal resistance of said tube, a um-directional rectifier connected in shunt with said inductive reactor,

tentiometer R1. For any fixed value of control A means deriving induced voltage pulses from said reactor when said current surges from said vacuum tube are impressed thereon, and means to produce the maximum voltage pulses possible from the time duration of the applied current surges, comprising means varying the bias of the vacuum tube element and means varying the tuning of saidreactor.

2. The combination according to claim 1, in whichsaid vacuum tube includes a suppressor grid, and said biasing means includes means for on said suppressor grid.

varying the bias DONALD D. GRIEG.

shown, it is to be understood that many

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