US2284101A - Impulse generator - Google Patents

Description

May 26, 1942. 3. w. ROBINS 2,284,101

IMPULSE GENERATOR Filed Feb. 29, 1940 Fi e. 3. 1.9 I

W INPUT I ll I c 51 Q5 F1 G. 6. e

0 P l e I I 1 T IG. 007 1 07 I A 0 I t2 3 t7 Engentor Rolnns Patented May 26, 1942 T OFFICE IMPULSE GENERATOR Ben White Robins, Philadelphia, Pa., assignor to Radio Corporation of America,

Delaware a corporation of Application February 29, 1940,- Serial No. 321,547

2 Claims.

This invention relates to impulse generators and more particularly to an apparatus for converting electric waves into short electric impulses which have the same frequency as the original wave or a frequency related thereto in the ratio of small whole numbers.

Impulse generators have been utilized in the art to provide short impulses for use with certain types of frequency meters, to provide marking impulses in connection with cathode ray oscillographs, or as harmonic generators. An example of the first-named use is found, for example, in a copending application of R. C. Sanders, Serial No. 248,577, filed December 30, 1938, Patent No. 2,228,367, January 14, 1941. This Sanders application describes a frequency indicator in which short voltage impulses of uniform amplitude are derived from an alternating wave and applied to an impulse counter. The principal object of this invention is to provide an improved circuit for obtaining sharp impulses from an alternating voltage which are of uniform duration, which are independent of varia tions in the amplitude and wave shape of the applied alternating voltage, and which are of w the same frequency.

In accordance with a modification of this invention, a circuit is proposed by means of which modified to provide frequency division; and Figures 4 to 7 inclusive are curves illustrating the operation of this invention. Similar reference numerals refer to similar parts throughout the several figures of the drawing.

Referring to Fig. 1, a pair of terminals 9, II are connected between a source of alternating waves which is not shown, and an input transthe derived impulses may have a frequency less than the frequency of the applied alternating wave. Frequency dividers which accomplish the same result are known. Multivibrators and relaxation oscillators, for example, have commonly been used for this purpose. Such systems,

' however, are likely to have a free frequency at which they oscillate in the absence of a synchronizing voltage of sufficient amplitude to' maintain the control. fers in that the output voltage is a direct func-, tion of the frequency of the input voltage over a wide operating range. That is, the proposed circuit will not oscillate in the absence of a signal input. A further object of this invention is- Figure 3 is a circuit diagram of a wave converter The proposed system dif-' former I3 having a center-tapped secondary winding I 5. The center-tap of secondary I5 is connected to the cathode ll of a thermionic triode l9, and to one terminal of a capacitor 2|. One terminal of the secondary winding is connected to the grid 23 of thermionic tube 19 through a biasing battery 25, or its equivalent. and, optionally, through agrid current limiting resistor 21. The remaining secondary terminal is connected to the anode electrode 29 of a diode rectifier 3 I, the cathode 33 of which is connected to the remaining terminal of capacitor M, and to an output terminal 35. A second output terminal 31 is connected to the anode 39 of thermionic tube l9. A load resistor 4| is connected between output terminals 35 and 31.

The operation of the device illustrated in Fig. 1 will be explained in connection with Figs. 4 and 5. The voltage which is applied to the input terminals H and 9 is an alternating wave having any desired wave shape. 'The voltage which is induced across half of the secondary of transformer I3 is applied to capacitor 2| through the rectifier 3i. Consequently, charging current flows into the capacitor during each half of the applied alternating wave during which the anode 29 is positive with respect to its associated cathode 33. During the opposite half of the cycle, however, capacitor 2| retains its charge,

so far as rectifier 3| is concerned, since the anode 29 is then negative with respect to its associated cathode 33. It is to be noted, therefore, that one charging impulse is applied to capacitor 21 for each cycle of the applied alternating Wave. It is also to be noted that during the half cycle in which capacitor 2| receives a charge, the grid 23 of thermionic tube It! is biased to a negative potential with respect to its cathode. Battery 25 also applies a negative potential to the grid, and it will therefore be appreciated that substantially no anode current flowsv during the first half cycle of the applied voltage. During the successive half cycle, however, a positive pulse is applied between the cathode and grid electrodes of the tube. The positive pulse is of sufficient amplitude to overcome the negative bias supplied by the biasing battery 25. The tube then becomes conductive, and capacitor 2| discharges through the circuit including resistor 4| and the anode-cathode electron path of tube is.

The output voltage is the voltage drop across anode resistor 4|. Consequently, an impulse is applied to the output terminals 35, 31 each time capacitor 2| discharges through the resistor 4| and tube is. The length of each impulse may be determined by suitably selecting the time constant of the capacitor 2| and the total resistance in the discharging circuit.

This cycle of operation is illustrated in Figs. 4 and 5, to which reference is now made. Curve E represents the applied voltage which is assumed to be substantially sinusoidal, although the invention is not limited to the application of such a wave. The dotted line Ec is the voltage across capacitor 2|. This voltage increases from zero to maximum during each half cycle of the applied voltage in which the rectifier 3| is conductive. This half cycle is represented by that portion of curve E above the zero axis X-X. The voltage across the capacitor 2| remains substantially at its maximum value after the applied voltage has passed beyond its peak value. However, as the polarity of the applied wave reverses,

the negative bias on the grid of tube I9 is reduced, the tube becomes conductive, and the capacitor is rapidly discharged. This process is repeated during each successive cycle of the applied voltage. output impulses to the input voltage E and the voltage Ec across capacitor 2|. It is to be noted that the impulses correspond in time with the discharge of the capacitor.

Certain applications of this invention require the successive short impulses to have constant amplitudes. In the embodiment of this invention described above, this may be accomplished by regulating the amplitude of the applied alternating wave in any conventional manner. It will be appreciated, however, that variations in the amplitude of the applied wave will cause like variations in the amplitude of the output impulses.

Fig. 2 is the circuit diagram of a modification whereby the amplitudes of the successive im pulses are maintained at a constant value in the presence of variations in the amplitude of the applied alternating wave. In such case, the voltage regulation referred to abovewill not be required.

Referring to Fig. 2, and considering that portion of the circuit between the input and terminals 35 and 31, input terminals 9 and II are connected to the primary of an input transformer l3, as before. Separate secondary windings 43 and 45 are provided. The first secondary winding 43 is connected to a thermionic tube I8 as described in connection with Fig. 1. The second secondary winding 45 is connected between the grid 41 and the cathode 49 of a second thermionic tube Cathode 49 is also connected to the junction of resistor 4| and capacitor 2| and to terminal 35. The anode electrode 53 is connected to the positive terminal of a battery 55 the negative terminal of which is connected to the cathode ll of the first thermionic tube l9.

During alternate half cycles of the applied, alternating voltage, grid 41 becomes positive with respect to its associated cathode 49, and the anode-cathode impedance of the tube is reduced sufliciently to permit substantially the full voltage of the battery 55 to be impressed across capacitor 2|. During intermediate half cycles of the applied alternating voltage, a negative po tential is applied to the grid 41, and capacitor 2| is unable to discharge through the charging circuit. However, as in the preceding illustration, first tube I! becomes conductive during the intermediate half cycles and causes "capacitor 2| to discharge through resistor 4| and tube It. It will be appreciated that the voltage which is utilized to charge capacitor 2| is limited to a constant value somewhat less than the value of battery 55, so that the total charge, and consequently the amplitudes of the impulses developed Fig. 5 shows the relation of the across resistor 4| are independent of the amplitude of the applied alternating voltage.

As noted above, the embodiments of this invention illustrated in Fig. 1 and the portion of Fig. 2 so far described produce short voltage pulses which recur at the frequency of the applied alternating wave. The embodiment of this invention illustrated in the remaining portion of Fig. 2 provides a simplified system for selecting every second, third, fourth, or nth impulse, as desired. The terminals 25, 31 of the anode load resistor 4| are connected to a second capacitor 51 through a resistor 59 and a rectifier 6|. A gas tube 53 and a resistor 55 are serially connected across'the second capacitor 51. Output terminals 35 and 40 are connected across resistor 65.

Periodically repeated pulses of the type illustrated in Fig; 5 are produced across resistor 4| in the manner described above. Assuming that these impulses have such a polarity that the anode of rectifier 6| is made positive with respect to its associated cathode, a charging current will -flow through resistor 55 into capacitor 5'! dining each of the successive pulses. The time constant of the charging circuit, however, is selected at such a value that the voltage across capacitor 51 does not reach the peakamplitude of the applied pulses during any one impulse. The voltage across capacitor 51, therefore, increases to successively higher values upon the application of successive impulses as indicated in Fig. 6.

- Impulse a, for example, charges capacitor 51 to a voltage el, impulse b increases the voltage across the capacitor to the value e2. After a number of successive charging impulses have been applied the voltage across the capacitor, which is likewise impressed across gas tube 53, reaches or exceeds the breakdown voltage for the tube 53, and a large current flows through the tube and resistor 55, discharging the capacitor and producing an output impulse as indicated in Fig. 7.

In case the ultimate voltage across capacitor 51 is less or greater than the breakdown voltage of the gas tube 63, the operating point, that is the' frequency division, may be suitably established by including a small biasing battery" .6] in series with the control. circuit of the gas tube. The polarity of this bias battery will be determined by the voltage ultimately built up across the capacitor and the normal breakdown voltage of the tube. 0n the other hand the opgals will become apparent to those skilled in the For example, the thermionic tubes illustrated in Figs. 1 to 3 may be included within a single envelope, or may be replaced by grid-controlled as tubes which. are well known in the art. Likewise, the gas tube 63 illustrated in Fig. 3 may be a grid-controlled tube if desired. In case it is desired to provide current pulses rather than voltage pulses, the output resistors may be replaced by a load device through which the current will flow to discharge the capacitor.

I claim as my invention:

1. A wave converter comprising an input circuit for connection to an alterating wave source, a capacitor, means coupled to said input circuit for applying a unidirectional charging current of constant amplitude to said capacitor once for each cycle of said alternating wave, means also coupled to said input circuit and controlled by said alternating wave for discharging said capacitor through an impedance once for each cycle of said alternating wave, a rectifier, a resistor and a second capacitor serially connected across said impedance ior applying a unipotential charging impulse to said second capacitor for each cycle of said alternating wave, the voltage across said second capacitor being increased by each successive impulse, and means for discharging said second capacitor, said means being operated only after said voltage has reached a predetermined amplitude.

2. A wave converter comprising an input circuit for connection to a source of alternating voltage, a capacitor, means coupled to said input circuit for applying a unidirectional charging current of constant amplitude to said capacitor once-for each cycle of said alternating voltage, means also coupled to said input circuit and controlled by said alternating voltage for discharging said capacitor through an impedance once for each cycle of said alternating voltage, a unidirectional conductor and a second capacitor serially connected across said impedance for applying a unipotential charging impulse to said second capacitor for each cycle of said alternating voltage, and means for discharging said second capacitor after a predetermined number of charging impulses have been applied to said second capacitor:

BEN WHITE ROBINS.

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