US2292100A

US2292100A - Square wave generator

Info

Publication number: US2292100A
Application number: US354830A
Authority: US
Inventors: Warren H Bliss
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1940-08-30
Filing date: 1940-08-30
Publication date: 1942-08-04
Anticipated expiration: 1959-08-04

Description

Aug. 4, 1942.

BLISS S QUARE WAVE GENERATOR Filed so, '1940 Wig/ABLE FULL WAVE FREQUENCY 0.5C/LLATOR REfT/F/ER PHASE .SH/FTER FZ/u. WAVE RECTIFIER 2 Sheets-Sheet 1 our ur GAS'DISCHARG 15 755 UTILIZATION ems/um: DEV/CE OSCIHATOR f0 OUTPUT FROM /8 "RECTIFIER I6 I N VEN TOR.

WARREN H. BLISS A TTORNEY.

Aug. 4, 1942.

INPUT W. H. BLISS SQUARE WAVE GENERATOR Filed Aug. 50, 1940 sets-Sheet 2 INVENTOR. 1 EN H. BLISS Patented Aug. 4, 1942 UNITED STATES PATENT OFFICE SQUARE WAVE GENERATOR Warren H. Bliss, Maplewood, N. 1., assignor to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application August 30, 1940, Serial No. 354,830

6 Claims.

This invention relates to an improvement in generators for producing current or voltage variations of substantially square or rectangular wave form.

Frequently it is desirable to generate current or voltage variations of square or rectangular wave form of a predetermined frequency and it is also often desirable that the ratio of the positive to the negative half-cycles of the generated wave form be differentially adjustable. Wave forms of such shape are particularly useful in facsimile transmitting systems where a system using constant frequency variable dot transmission is employed. Furthermore, voltage variations of square or rectangular wave form are frequently desirable in television transmission, and in fact voltage or current variations of such wave form may be used in many respects where it is desired that the voltage of the wave form be cyclically increased to a predetermined value substantially instantaneously and remain at that value for a predetermined length of time.

A new and improved square or rectangular wave generator has therefore been developed which is simple and positive in operation and which employs a minimum amount of electrical apparatus. Furthermore, the generator as developed and as described herein is capable of producing oscillations of square or rectangular wave form of substantially any desired frequency, and it is also capable of regulation whereby the ratio of the positive and negative half cycles of the wave form may be differentially varied.

It is, therefore, one purpose of the present invention to provide a new and improved square or rectangular wave form generator by means of which current or voltage variations of square or rectangular wave form may be generated.

It is still another purpose of the present invention to provide a square or rectangular wave form generator in which definite control may be exercised over the ratio between the lengths of the'positive and the negative half-cycles of the wave forin generated.

Still another purpose of the present invention resides in the provision on. square or rectangular wave form generator in which the frequency of the wave form generated may be readily controlled.

Other advantages and purposes of the present invention will become more apparent to those skilled in the art from a reading of the following specification and claims, particularly when considered with the drawings, wherein like reference Figure 1 shows the elements of the present invention schematically in block diagram,

Figure 2 shows curves of potential variatifns which appear at the output terminals of varparticular desired frequency. The particular frequency oscillator used is not vital, and may be an ordinary source of 60-cycle power supply where low frequency waves are desired, or the oscillator may take the form of a well-known Hartley or Colpitts oscillator. Since the present invention is not concerned primarily with the particular oscillator used, the oscillator is not shown in detail. It is desirable, however, that the voltage variations of the oscillations produced by the oscillator vary substantially as a sine function or some closely similar voltage variation. The oscillations which are supplied by the frequency oscillator ID are fed to a phase shift device l2 which, through manual control, is capable of shifting the phase relationship of the voltage variation preferably from about zero to the oscillator.

The oscillations as derived directly from the frequency oscillator l0 and as also derived from the phase shifter l2, are supplied to two independent full-wave rectifiers l4 and It for supplying uni-directional pulsating current. The rectifiers do not include any filtering circuits for reasons which will be explained later. The outputs from the full-wave rectiflers are therefore pulsating uni-directional voltage variations of identical frequency and substantially identical wave form, the phase relationship of the pulsations being determined by the degree of phase shift introduced *bythe phase shifter l2. These pulsations from the full-wave -rectiflers H and it are then supplied to a gas discharge squarenr rectangular wave generator l8 from which oscillations of the desired wave form are derived.

characters reprwent like parts and wherein: 'The phase shifter I 2 is shown in detail in Figure 3 and at the input terminals 22 and 24 are impressed the oscillations as produced by the oscillator l8. These oscillations are induced in the secondary winding of the transformer 26 and across the secondary winding is placed a load resistance or impedance 28 in order that some loading will be present on the transformer. Also connected across the secondary of the transformer 26 is a series arrangement of a condenser 38 and resistance 32. In parallel with these elements is a second series arrangement of a resistance 34 and condenser 38. These resistances and condensers are connected as indicated in the figure, and the two resistances 32 and :34 are preferably of the same value and are preferably so arranged as to be simultaneously adjustable in value. The condensers 30 and 36 are also preferably of the same value, and may or may not be so arranged as to be simultaneously controlled as to their value.

An electron discharge tube 38 is also used which includes a cathode, a control electrode and an anode. The cathode of the discharge tube 38 is connected to ground or to the negative terminal of a source of anode potential by means of a resistance 48 which is by-passed by condenser 42. The control electrode or grid of the tube 38 is connected to the junction of the series-connected condenser 30 and resistance 32 while the junction point of the resistance 34 and condenser 36 is connected to ground. By reason of these connections there appears between the control electrode and the cathode of tube 38 a voltage variation of the same frequency as the impressed voltage variation, but the phase relationship of the potential applied between the control clectrade and the cathode with respect to the input voltage variation depends upon the value of the

resistances

32 and 84. The tube 38 operates primarily as an amplifier tube, since the adjustable phase alteration in the applied voltage variation is a result of the resistance-condenser combinations 38-32 and 34-38. By varying the value of the resistances 32 and 3d simultaneously, and

by equal amounts, the phase relationship of the voltage impressed upon the control electrode of the tube 38 with respect to the voltage variations impressed upon the

terminals

22 and 28 may be varied from substantially zero to 980 degrees. The voltage variations which are impressed upon the control electrode and the cathode of tube 38 are, therefore, present in the anode circuit of the tube 38 and by means of the transformer 88 these voltage variations are caused to appear at the

output terminals

48, 48 and 58 which are connected to the secondary of the transformer 44.

As stated above, the voltage variations as supplied directly by the oscillator i8 and by the phase shifter I2 are of the same identical frequency, but are displaced in phase relationship and these voltage variations are each separately rectified by full-wave rectifiers l4 and I8 respectively. Since the operation of the present invention does not depend upon the specific rectifier used, no particular details of this element are shown, since any conventional and practical fullwave rectifier may be used. Normally it would be desirable to use a rectifier similar to that used for supplying anode current to the tubes in a radio receiving set or a simple duo-diode: tube may be utilized to afford the desired rectification. The rectifier includes only the rectifier tube or the asymmetric unit which performs the function of rectifying the voltage variations, and no filter circuit is used so that the output from the rectifiers is somewhat cycloidal in wave form and amounts to a pulsating direct current or potential. Since the square or rectangular wave form generator (to be hereinafter described in detail) responds to changes in the potential or the pulsating wave form derived from the rectifiers, in order that the square wave generator may remain as stable as possible it is desired that the generator respond to the voltage variation at a. point where its rate of change is substantially the greatest. Since this is the case, the output from the rectifier is preferably derived from the negative terminal of the rectifier which would be the terminal 48 of the output transformer 44 shown in Figure 3 if a conventional electronic rectifier is used.

The wave forms of the various potential variations appearing in the system are shown in Figure 2, the wave form 5| representing the voltage variations as derived directly from the frequency oscillator l8. Associated with this wave form is shown a second wave form 52 of identical frequency, the wave form 52 being displaced in phase relationship with respect to the wave form 5!. This displacement, which is a result of the operation of the phase shifting device shown in Figure 3, is indicated by Figure 2 as being of the order of approximately degrees. The voltage variation represented at 5| is supplied to the full-wave rectifier l4, and the output from this rectifier is indicated by the curve or wave form 53 which, of course, includes pulsations of a frequency double the frequency of the impressed wave form 5|. The wave form shown at54 is the result of the full-wave rectification of the wave form shown at 52, and bears a phase relationship with respect to the pulsating wave form shown at 53 as determined by the phase relationship of the wave forms impressed on the rectifiers, The pulsating wave forms shown at 53 and 58 are impressed upon the square or rectangular wave form generator, and in response to these wave forms current or voltage variations of square or rectangular wave form is generated.

The elements of the square wave generator are shown specifically in Figure l, and include gas discharge tubes 58 and 62. These gas discharge tubes may be of any type, but are preferably of the type generally known by the name thyra. tron. The gas discharge tubes each include a cathode, a control electrode and an anode. The cathode of the gas discharge tube 68 is connected to ground by way of resistance 6|, which is bypassed by condenser 84 and the anode of the tube 68 is connected to the positive terminal of a source of potential through a load resistance 68. The control electrode for the gas discharge tube 60 is connected to the input terminal 68 by way of a resistance 10 and -a source of biasing potential 12, and the terminal 68 is connected to ground through a grid resistance H. The potential variations as derived from the full-wave rectifier l4 are impressed upon the terminal 88 and accordingly control the potential of the control electrode of tube 88 with respect to its associated cathode.

The gas discharge tube 62 is also connected to ground by way of cathode resistor 16 which is bypassed by condenser 18, and the anode of the tube 62 is connected to the positive terminal of a source of potential by way of the load resistance 88. The control electrode of the gas discharge tube 62 is connected to input terminal 82 by way of the resistance 84 and the grid bias potential 86. A control electrode resistance 88 is also connected between the input terminal 82 and ground.

In order that the gas discharge tubes II and 62 may be made to operate alternately, their anodes are connected together by means of condenser 90 so that a change in the potential at one anode will accordingly affect the potential impressed upon the anode of the other tube. Therefore, if one of the gas tubes is conducting at any particular instant, and the control electrode oi the other gas tube is made sufllciently positive to permit a discharge through that tube, then the presence of current in the second tube, by reason of the condenser ll, will cause a cessation of current flow in the first tube, assuming, of course, that the control electrode of the first tube is at a potential below that required to initiate a discharge in that tube. Thyratrons," being gas discharge tubes, are responsive to the potential of the control electrode in that the control electrode may initiate a discharge in the tube, but after a discharge has been initiated the control electrode loses control and the discharge will be maintained until the anode potential is removed or reduced below a value capable of maintaining a sustained discharge. The amount of current which flows through the discharge tube is limited by the impedance of the tube plus the impedance of the cathode and anode load resistances.

Since the pulsating voltage variations shown at 53 and 54 in Figure 2, as derived from the fullwave rectifiers l4 and it, are impressed upon the terminals 68 and B2 of the circuit shown in Figure 4, the operation of the

gas discharge tubes

60 and 62 will depend upon the occurrence and presence of these impulses at the terminals 68 and 82. Each time a positive impulse is applied to the control electrode of one of the gas discharge tubes, that particular tube will become conducting, and the other tube will be made nonconducting. This is by reason of the inclusion of the condenser 90 as explained above, and furthermore, the control electrodes of the gas discharge tubes 50 and 62 are biased negative with respect to their associated cathodes by an amount determined by the size of the

potential sources

12 and 86. These potential sources are so adjusted and their values are so chosen that the control electrodes are negative with respect to their associated cathodes by an amount suflicient to require the pulsations represented at 53 and 54 to be of the order indicated by the dotted line shown on these curves. Accordingly, gas discharge tube 60 will become conducting only when the pulsating potential shown at the curve 53 increases to a value equal to or greater than that represented by the dotted line shown associated with the curve, and similarly, gas discharge tube 62 is made conducting only when the potential applied to its control electrode is of the order of that indicated by the dotted line associated with the curve 54.

In explaining the operation of the square or rectangular generator, it will be assumed that gas discharge tube 60 is conducting, and that tube 62 is in a non-conducting condition. A positive impulse applied to the terminal 82 and to the control electrode of the discharge tube 62 will .cause the tube 62 to become conducting and by reason of the condenser 90. the tube 60 will simultaneously be rendered non-conductive since in the meantime the potential of the control electrode of tube 60 has been reduced to a value below that which will initiate a discharge in tube 60. Tube 62 will then continue to conduct current until tube 60 is again rendered conductive as a result of a positive impulse being applied to terminal 68. This alternate operation of the

gas discharge tubes

60 and 62 continues so long as alternate positive impulses are applied to their respective control electrode terminals, and the circuits associated with the

gas discharge tubes

60 and 62 are so arranged that the tubes will not, of their own accord, oscillate as a relaxing generator in the absence of positive driving impulses.

During the time that the one or the other of the two gas discharge tubes are in a conducting condition, there is, of course, a certain amount of cathodic current present in the cathode resistor of that tube. The presence of this current will produce a certain voltage drop across the cathode resistor, and this voltage drop will have a value dependent upon the intensity of the current flowing through the resistor. Furthermore, in the absence of current in the cathode resistor, there will be no potential drop thereacross, and no voltage will appear at the output terminals of the square wave form generator. The output wave form may be derived from across either of the two cathode resistors 6| or 18, since these two resistors carry current alternately and the only difference between the wave form which is developed across the one resistance or the other lies in the fact that they are of opposite polarity. As stated above, however, either cathode resistor may be used as the element from which the desired wave form is derived.

The wave form of the voltage variation appearing across resistance SI of tube 60 is indicated at 55 in Figure 2, and the wave form of the voltage variation appearing across the resistance 16 of tube 62 is indicated at 56 in Figure 2. Since, in Figure 2, the phase displacement of the voltage variation 52 is displaced approximately degrees with respect to the voltage variation shown at 5|, then the positive and negative half cycles of the waves shown at 55 and 55 will be substantially equal. If. however, it is desired that the positive or negative half cycle of either of the waves shown at 55 or 56 be increased or decreased, it is only necessary to alter the phase displacement of the wave form which is supplied to the rectifier [6 which is accomplished through a simultaneous adjustment of the

resistors

32 and 34 of the phase shifter. Since the phase shifter is capable of introducing a change in the phase relationship of from substantially zero to substantially degrees, then the positive or negative half cycle of the produced wave form may be decreased to substantially zero or'may be increased to occupy substantially the entire cycle of the wave alternation.

The intensity of the produced voltage variation of square or rectangular wave form depends upon the intensity of the current passed by the

gas discharge tubes

60 and 62, and upon th size of their cathode resistors. If this voltage variation is insufficient for the Purposes for which they are generated, they may be intensified by applying themto an amplifier 20 as indicated in Figure 1. Such amplification is, under certain circumstances, unnecessary.

The frequency of the generated wave form may be controlled by altering the frequency of the generated wave form as produced by the frequency oscillator ill. The adjustment of this oscillator depends upon the type oscillator used, and since oscillators in which the frequency may be controlled are well known in the art, no specific oscillator is shown.

From the above it may be seen that a new and improved system has been devised for producing oscillations of square or rectangular wave form, and furthermore it will be seen that the system as devised is simple in operation and includes a small number of components. Furthermore, in view of the use of gas discharge tubes which offer very low impedance to the flow of current therethrough, the amount of current passed by the tube is limited primarily by the resistances connected in circuit therewith, and since these resistances remain fixed in value, the amplitude of the wave form generated remains substantially constant. Furthermore, since gas discharge tubes are used which build up their maximum current output substantially instantaneously, the change from the positive to the negative half cycle of the generated square wave is substantially instantaneous.

It is to be understood that although a more or less specific form of phase shifter is shown and described in this application, it is not necessary that such phase shifter be used since various other phase shifters could as well be substituted for the one shown.

Various other alterations and modifications may be made in the present invention .without departing from the spirit and scope thereof, and

it is desired that any and all such modifications be considered within the purview of the present invention except as limited by the hereinafter appended claims.

I claim:

1. A generator for producing voltage variations of substantially rectangular wave form comprising a pair of gas discharge tubes each of which includes a cathode, a control electrode and an anode, means including a resistance for connecting each cathode to a point of fixed potential, a condenser connected between the anodes, and means for maintaining each of the control electrodes negative with respect to its associated cathode by an amount suilicient to prevent initiation of a discharge through the tubes, means ior impressing upon the control electrodes phase displaced positive impulses of identical frequency whereby the discharge tubes will be caused to be rendered alternately conductive whereby potential variations of substantially rectangular waveform may be produced across the cathode resistances of each discharge tube, and means for varying the phase relationship of the positive impulses which are applied to the control electrodes of the tubes.

2. A device for producing potential variations of substantially rectangular Wave form comprising means for generating an oscillation of substantially sine wave form and of a predetermined frequency, means for shifting the phase of the produced oscillation, means for rectifying the oscillations produced directly by said first named means and the oscillations from the phase shifting means whereby two series of impulse of identical frequency and of displaced phase relation ship may be produced, a pair of gas discharge tubes each including a cathode, a control electrode and an anode, means including a resistance for maintaining each anode positive with respect to its cathode, a condenser connected between the anodes of such tubes, and means for individually impressing the two series of impulses upon the control electrodes of said tubes whereby 75 potential variations of substantially rectangular wave form may be produced by said tubes.

3. A device for producing potential variations of substantially rectangular wave form comprising means for generating an oscillation of substantially sine wave form and of a predetermined frequency, controllable means for shifting the phase of the produced oscillation a predetermined amount, means for rectifying the oscillations produced directly by said first named means, means for rectifying the oscillations from the phase shifting means, whereby two series of impulses of identical frequency and of variable phase relationship may be produced, a pair of gas discharge tubes each including a cathode, a control electrode and an anode, means including a resistance for maintaining each anode positive with respect to its cathode, means for maintaining each control electrode negative with respect to its cathode, a condenser connected between the anodes of such tubes, and means for impressing the two series of impulses upon the control electrodes of said tubes individually whereby potential variations of substantially rectangular wave form may be produced by each 01 said tubes.

4. A device for producing potential variations of substantially rectangular wave form comprising an oscillation generator for producing an oscillation of substantially sine wave form and of a predetermined frequency, adjustable means for shifting the phase of the produced oscillation, means for rectifying the oscillations produced directly by the oscillation generator and th oscillations from the phase shifting means whereby two series of positive impulses of identical frequency and of variable phase relationship may be produced, a pair of gas discharge tubes each including a cathode, a control electrod and an anode, means including a resistance for maintaining each anode positive with respect to its cathode, a reactance device connected between the anodes of such tubes, and means for impressing the two series of positive impulses to the control electrodes of said tubes individually whereby potential variations of substantially rectangular wave form may be produced by said tubes.

5. A device for producing voltage variations of substantially rectangular wave form comprising a pair of gas discharge tubes each including a cathode, a control electrode and an anode, a source of potential having a positive and negative terminal, a resistance connected between the positive terminal of the source of potential and each of the anodes, a resistance connected between the negative terminal of the source of potential and each of the cathodes, a condenser connected between th anodes of each of the tubes, means for maintaining each of the c0ntrol electrodes negative with respect to their associated cathodes by an amount sulficient to prevent an electron flow through the tubes, means for individually impressin upon the control electrodes a series of positive impulse 01 identical frequency but displaced in "phase relationship, and means for varying the phase displacement of the impulses whereby the tubes may be rendered alternately conducting and whereby the tubes may be caused to produce voltage variations of substantially rectangular wave form.

6. A device for producing voltage variations of substantially rectangular wave form comprising a pair of gas discharge tubes each including a cathode, a control electrode and an anode, a

source of potential having a positive and negative terminal, an impedance connected between the positive terminal of the source of potential and each of the anodes, an impedance connected between the negative terminal 01 the source of potential and each 01' the cathodes, a reactance connected between the anodes of each of the tubes, means for normally maintaining each of the control electrodes negative with respect to the cathode associated therewith by an amount suflicient to prevent the initiation or an electron flow through the tubes, means for individually impressing upon the control electrodes a separate series of positive impulses of identical frequency but of displaced phase relationship whereb the tubes may be rendered alternately conducting to produce a voltage variation of substantially rectangulanwave form, and means for varying the phase displacement of the impulses of one of the series of impulses with respect to th im- 1 pulses of the other of the series of impulses.

WARREN H. BLISS.