US2408261A - Pulse generator - Google Patents

Description

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Patented Sept. 24, 1943 PULSWE GENERATOR Louis L. Lakatos, Bela-Cynwyd, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application January 21, 1944, Serial No. 519,100

' r 8Claims- (01. 178-44) This invention relates to pulse generators;

Pulses of electrical energy of short duration are used fo keying transmitters of radio frequency energy, for blanking indications'for'the synchro- 1 ization of signals in television apparatus, in the sweep circuits of oscilloscopes, and have many other applications. In many applications it is desirable that such pulses should have a fixed phasic relation to the wave derived.

Prior art pulse generators having these features have used gas tubes, multivibrators, relaxation oscillators and the like; such devices are comparatively expensive and need complicated circuits and substantial power supplies for their proper operation.

It is, therefore, the primary object of this invention to provide an improved method of, and apparatus for,- generating pulses of electrical energy of short duration and having a fixed phasic relation to the Wave from which they are derived.

A further object of the invention is the provision of improved apparatus for generating pulses of the character described, in which a comparatively simple circuit and comparatively inexpensive and compact apparatus are used- For the attainment of these objects, the invention makes use of the'abrupt reversal in direction of the transfer characteristic existing between two electrodes of an electron tube when the potentials'of the electrodes are properly chosen. A periodic wave is applied to one of the electrodes and as the potential of that electrode, under control of the applied wave, passes through the region in which such a reversal occurs, a pulse of electrical energy appears across an impedance in the circuit which includes the other electrode.

The invention will now be described with ref-- erence to the accompanying drawing, in which:

Figure 1 is a circuit diagram of apparatus suit-' able for carrying out the invention,

Figure 2 is a graph representing the transfer characteristic existing between two of the electrodes of the tube shown in Figure 1,

Figure 3 is a circuit diagram of an alternative connection of the apparatus shown in Figure 1,

Figs. 4A and 4B illustrate the relation of the input and output signals of the device of Fig. 1.

Referring to Fig. 1, a tube 2, which may be of RCA type 6SL'7GT or GSN'ZGT, and having a cathode 4, an anode 6and a control-electrode or grid 8, is connected as follows: An impedance Ill, which may be a resistor ofthe value of-20,000 ohms,-is' connected between anode and ground.

from which they are:

A resistor l2 (which may have a value of 1,000 ohms) in the cathode circuit serves to limit the current which flows in th grid circuit, as hereinafter explained. The anode is not connected to any source of potential and is maintained at the samepotential as the cathode. Since, however, the cathode is made of an electron-emissiv substance and the anode is not, the difference of potential between cathode and anode (sometimes called contact potential) may establish a weak anode current. This potential difference may amount to half a volt. The grid is normally maintained at substantially the same potential as the cathode. In the apparatus thus far described, it may be said that electrons are emitted by the cathode, and since the grid has neither a retarding nor an accelerating effect upon such electrons, some of them reach the anode and, thus, current flows through the impedance 10 in the anode circuit.

A periodic wave is now applied between the grid and the grounded end of the resistor l2. The wave or signal may be obtained from any source thereof, as from the oscillator l4, and may if desired be amplified as by the amplifier IS. Thesignal may be sinusoidal in form; sine wave in- P t signals at frequencies varying from 200 cycles'per second up to 20 kilocycles per second, and of" magnitudes varying between 20 to volts R. M, 5., have been used with the apparatus described ior the generation of pulses. I

During the vnegativehalf cycle of the signal wave, the applied signal puts a negative potential on the grid, which prevents electrons emitted by the cathode from reaching the anode; and,

therefore, during this half cycle no current flows in the anode circuit at all. This effect, however, diminishes as the signal approaches its zero axis, and whenthe grid is at-zero signal potential with respect to the cathode, a weak current may flow in the anode circuit because of contact potential.

During the positive half of the signal cycle, the grid maybe regarded as possessing a sufficiently positive charge to attract all or nearly all of the electrons which are emitted by the cathode. This causes current to flow in the grid circuit and, again, prevents any current at all from the grid is substantially the same as that of the cathode that current flows at all in the anode circult, anda pulse of energy appears across the impedance 13 in the anode circuit, as in Fig. 4B. The greater the frequency of the input signal, the shorter is the duration of the pulse.

Signals in the form of square waves may be used for the production of short pulses. Since the sides of square waves cross the zero axis in a very short space of time, a particularly short pulse is produced.

Whatever periodic waves are used for the input signals, th pulse in the output circuit of the tube will occur twice for each input signal cycle,

as the signal crosses its zero axis. It isat this point that the rate of change of a sine wa'v'e'is greatest. It is to be observed, therefore, that, the. pulse is not only of extremely shortxduration-butr is also in constant phase with respect to the input signal cycle.

The pulses appear across the impedance ID in the anode circuit and may, if desired, beyampli-jfied (as by the amplifier I8) and used for keying a transmitter, or for suchother purpose as may be. required. Pulses 1'5 micro-seconds long and having a peak value of '15 volts before amplification have been produced by this method from input signalsat a frequency of200 cycles per second.

Each input cycle results in two pulses in the output circuit. It is often desired, however, to have but on pulse for each input cycle, and in that event the connection shown in Fig. 3 may be-used. I'wo channels 2D andTZZ are provided The negativ voltage blocks the amplifier during the occurrence of alternate pulses so that the output ofthe amp er consists of only one amplified pulse for each'cycleof the original input signal.

While the apparatus which has been described for -carrying out the invention has consisted of a triode in which both the anode and control electrode are held at the same potential asthe cathode, the invention is not intendedv to bev limited Within the to that specific form ofapparatus. scope of the appended claims, the invention includes any electronic device forthe production of' pulses of electrical energy of short. duration, in

which a transfer characteristic,.which reverses. in direction as shown by Figure 2, may. be produced I- claim as my invention:

1 In combination an electron tubehaving. a cathode and an anode and at leastone-other electrode located between said cathode andsaid an.-

ode, a circuit including a resistor connecting said cathode and anode externally of said tube said anode and electrode being maintained at such respective potentialswith respect to said cathode and to each other that current deriving: from the electron stream flows insaid circuit, but that onvariation in either direction of the potentialpf said; electrode with respect to the cathode said current is completely diverted from said circuit,

means for applying a signalof abruptly varying amplitude to said electrode, and means. for deriving from said circuit sharply defined-pulses of electrical energy.

2. In combination an electron tube having-a cathodeand an anode and at least one othepelec- 4. trode located between said cathode and said anode, a circuit including a resistor connecting said cathode and anode externally of said tube said anode and electrode being maintained at such respective potentials with respect to said cathode and to each other that current deriving from the electron stream flows in said circuit, but that on variationin cit-her direction of the potential of said. electrode with respect-to the cathode said current is completely diverted from said circuit, a sourc of periodic electrical energy, and connections between said source and said electrode for impressing the energy from said source on said electrode, whereby to generate in said circuit pulses of; electrical: energy having a fixed phasic relation to therepetition period of said energy.

3. In combination, an electron tube having a cathodeand an anode'and at least one other electrode-located between said cathode and said anode, a circuit including impedance connecting said anodeand cathode externally: of said tube said electrodela'nd anode having such respective potentials" witl'irespect to said cathode and to each other that on increase of the potential of said electrodewith respect to saidcathode above cut-off,v current, deriving from the electron streami'lows-insaid circuit, and on-further increase of said-potential in-thesame'directiomsaid current is completely diverted'to the-circuit which includes said electrode, means for producing; a periodic signal; of rapidly varying; amplitude, and means for impressing said signal upon said electrode:-

i; A: pulse generator comprising an electron tubet'havinga' cathode-zandfat leasttwojothefelectrodes so connected to said cathodeexterna'lly. of said tube as tolb'e substantially. at'c'ontact potential with respect thereto; on'e of said other electrodes being located between said cathode andv a.-

s'econ'da cf 'said other electrodes; connections for impressing-=- a periodically varying signal between one of said electrodes and saidcathode, and a utilization circuit; connecting the other of saidelectrodes to said-cathodeexternally'ofsaid tube.

5. A pulse generator comprising the combination of asource of periodic electric energy; an electron? tube having a' cathode and a control electrode andiarr an'ocieiso', conne'ctedto said cathode externally'ofisaid tube as to be substantially riodically: varying signal between-saidinputelece trode and said cathode, andla' uti-lization circuit.

connecting said outputelectrode a to said cathode externally of said tube.

"7. A pulse generator comprising an electron tube having acathode, an. anode, and a control electrode located betwcen said cathode and said anode, said anode andsaid control. electrode beingsoconnectedto, said cathode-externally of" said tu beastobe substantially at contact potential withxrespectthereto, connectionsforimpress: l ingg a: periodically varying signal between said controlelectrodefand said cathode, and a utilization circuit connecting said anode and said cathode externally of said tube.

8. In combination, a pulse generator comprising an electron tube having a cathode and an anode and at least, one other electrode located between said cathode and said anode, a circuit including impedance connecting said cathode and anode externally of said tube, said anode and electrode being maintained at such respective potentials with respect to said cathode and to each other that current deriving from the electron stream flows in said circuit but that on variation in either direction of the potential of said electrad with respect to said cathode, said current is completely diverted from said circuit, and connections for applying an abruptly varying signal between said electrode and said cathode, means connected in parallel with said pulse generator for aleringthe phase of said signal, an amplifier, and connections for applying the output of said pulse generator and of said phase-altering 10 means to said amplifier.

LOUIS L. LAKATOS.

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