Title:
Expander circuit for oscilloscopes
United States Patent 2368448


Abstract:
My invention relates to oscilloscopes and concerns particularly oscilloscopes of the type having a signal-tracing beam, such as cathode ray oscilloscopes, with means for deflecting the beam in a given plane in response to a signal wave to be examined in the oscilloscope and for deflecting the...



Inventors:
Cook, Ellsworth D.
Application Number:
US33836040A
Publication Date:
01/30/1945
Filing Date:
06/01/1940
Assignee:
GEN ELECTRIC
Primary Class:
Other Classes:
315/384, 315/395, 327/134, 327/136, 331/144, 331/153
International Classes:
A47B9/04; G01R13/32
View Patent Images:



Description:

My invention relates to oscilloscopes and concerns particularly oscilloscopes of the type having a signal-tracing beam, such as cathode ray oscilloscopes, with means for deflecting the beam in a given plane in response to a signal wave to be examined in the oscilloscope and for deflecting the beam in a transverse plane in response to a time-axis or "sweep" wave.

It is an object of my invention to provide methods and apparatus for expanding on the screen of the oscilloscope an image of a portion of the signal wave to be observed, and to select any desired portion of the signal wave for expansion.

It is a more specific object of my invention to provide methods and apparatus for modifying the shape of the "sweep" wave of the oscilloscope and to introduce a portion of greater steepness for expansion of the wave.

Other and further objects and advantages will become apparent as the description proceeds.

In carrying out my invention in its preferred form in connection with cathode ray oscilloscopes having deflection plates for electrostatic deflection of the beam, I provide a discharge tube circuit for producing a "sweep" wave for application to the "sweep" deflection plates of the oscilloscope and an off-setting wave for application to the signal-responsive deflection plates of the oscilloscope. The "sweep" wave has an amplitude-time graph which is made up of successive sloping linear segments and its shape is such that, during the greater portion of the cycle, the oscilloscope beam is swept at a speed producing a normal representation of the signal wave on the oscilloscope screen, but during a fraction of the cycle, the beam is swept at a greatly increased speed for the purpose of expanding a selected portion of the signal wave to be observed.

Such a "sweep" wave is made up in one exemplification of this invention by superimposing upon a normal triangular or so-called "saw tooth" wave, another wave having short steep portions to produce high "sweep" speed. For selecting the portion of the signal wave to be expanded, I provide a phase shifting circuit arranged to vary the phase relationship between the normal triangular wave and the high sweep-speed component. An off-setting wave which may be added to the usual vertical deflecting signal, serves to separate the expanded portion from the remainder of the wave on the oscilloscope screen in order to avoid confusion.

My invention will be understood more readily from the following detailed description when considered in connectiop, with the accompanying drawings and those/features of the invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. In the drawings Pig. 1 is a diagram representing a form of "sweep" wave which may be used in accordance with one embodiment of my invention. Figs. la and lb are graphs representing the components of the "sweep" wave of Fig. 1. Fig. 2 is a block diagram schematically representing the electrical circuits of a "sweep" wave generator and a cathode ray oscilloscope, forming one embodiment of my invention. Fig. 3 is a circuit diagram representing more in detail the same arrangement as that represented in Fig. 2 and including graphs of wave shapes in various parts of the circuit. Fig. 4 is a graph representing a modified form of "sweep" wave which may be used in accordance with a modified embodiment of my invention. Figs. 4a, 4b and 4c are graphs representing the components of the "sweep" wave shown in Fig. 4. Fig. 5 is a block diagram schematically representing the electrical circuits of a "sweep" wave generator and cathode ray oscilloscope which may be used when a "sweep" wave of the shape shown in Fig. 4 is desired. Fig. 6 is a graph representing an image which may be produced on the oscilloscope screen when examining a sine wave and expanding the central portion thereof by use of the method and apparatus represented in Figs. 1, 2 and 3. Fig. 7 is a graph representing the appearance which the sine wave would take if no portion thereof were expanded. Fig. 8 is a diagram corresponding to Fig. 6 representing the image obtained on the oscilloscope screen when the method and apparatus represented in Figs. 4 and 5 are employed, and Fig. 9 is a fragmentary circuit diagram repreSsenting more in detail certain portions of the circuit represented in Fig. 5. Like reference characters are utilized throughout the drawings to designate like parts.

In cathode ray oscilloscopes, it is customary to provide "sweep" wave generators which "sweep" the beam in a direction transverse to that in which the beam is deflected by the variations in magnitude of the signal to be examined in order that the time relationship of the variations in magnitude of the signal wave may be ascertained. If a relatively faithful representation of the signal wave is desired, means are provided for sweeping the beam forward at a uniform rate of speed and afterwards quickly returning the beam. to the starting point. The rate of movement of the beamn during the forward "sweep" may be represented by the rising or advancing portion 11 of the wave shown in Fig. la. The portion 12 of the wave shown in Fig. la may represent the quick return of the beam during which period the beam may be blanked out to avoid confusion. In the case of oscilloscopes having electrostatic deflection plates, the wave of Fig. la may represent the voltage applied to the horizontal plates, or in the case of oscilloscopes having magnetic deflecting coils, the wave of Fig. la may represent the current flowing in the horizontal deflection coils. Throughout the description and claims the term "wave" as applied to the deflection producing force of the oscilloscope signifies a voltage wave in the case of oscilloscopes have electrostatic deflection plates and signifies a current wave in the case of oscilloscopes having electromagnetic deflection coils. The horizontal and vertical amplifiers may be arranged to convert voltage waves into current waves of corresponding shape when deflection coils instead of plates are used. It will be understood that in order to make the signal wave appear to stand still when the cathode ray beam is rapidly swept across the screen in response to successive repetitions of the signal wave, the "sweep" wave must have the same frequency as the fundamental of the signal wave to be examined or some sub-multiple thereof and must be synchronized therewith. Although I have described my invention in connection with cathode ray oscilloscopes in which the wave-tracing beam is a bundle of cathode rays or a stream of electrons, my invention is not limited thereto and the term "beam" in the description and claims signifies any suitable deflectable means for tracing a wave on a screen or on a sensitized surface.

I have found that any desired portion of the signal wave may be expanded for the sake of more convenient inspection on the oscilloscope screen by modifying the shape of the "sweep" wave to include relatively short portions of increased steepness. For example, as shown in Fig. 1, the forward portion of the "sweep" wave is broken into three linear segments 13, 14 and 15, the portions 13 and 15 having the same slope and the portion 14 having a greater slope for the purpose of increasing the speed of "sweep" of the oscilloscope beam and thereby expanding the portion of the signal wave occurring during the 60 interval represented by the portion'14. The return or fly-back portion of the wave is represented by the segment 16 which is shown dotted to indicate that the beam may be blanked out during the return. I produce a wave of the shape shown in Fig. 1 by combining two triangular waves, such as the waves shown in Figs. la and lb. It will be observed that the wave shown in Fig. la has an advancing portion I I which is relatively long or may be said to have a relatively great pulse width in comparison with the return portion 12. The wave shown in Fig. lb, on the other hand, has an advancing portion 17 which is relatively short and steep in comparison with the return portion 18. It will be seen from an examination of the graphs that the wave of Pig. 1 is a resultant of the waves of Figs. la and Ib. In the case of cathode ray oscilloscopes having electrostatic deflection plates, I accomplish this resolution by applying voltage waves, such as shown in Figs. Ia and lb in an addition or "mixing" circuit.

The fundamental component of the "sweep" wave illustrated and described has a relatively quick return sweep or retrace portion compared with the forward sweep portion. However, my invention is not limited thereto and does not exclude, for example, having the forward and retrace portions of the "sweep" wave substantially equal in time duration so that the input signal wave may be fed through some form of electronic switch, such as that illustrated in United States Patent 2,089,430, Roys and Mayer, for instance, for showing two separate and independent functions on the screen, and either one or both of these functions having sectional wave expansion.

Waves such as those illustrated in Figs. la and lb may be produced and combined to form the wave of Fig. 1 by means of apparatus, such as that represented in Figs. 2 and 3. The signal to be observed is assumed to be applied as a voltage, by suitable direct or indirect coupling, e. g., conductors 7, to a pair of synchronizing terminals 8 and 9, the latter of which is shown as being grounded. A cathode ray oscilloscope of the electrostatic beam deflection type is illustrated having horizontal deflection-producing plates 14, vertical deflection-producing plates 15, a beam intensity control electrode or grid 16, a cathode 17, a fluorescent screen 18, an anode, not shown, and possibly other auxiliary electrodes, not shown, in accordance with well known standard types of oscilloscopes.

The general arrangement of the "sweep" wave generator is shown in Fig. 2 in which the various elements of the circuit are represented by rectangles and the electrical relationship between the elements is indicated by means of connecting lines and arrows. The input signal, which it is desired to observe upon the oscilloscope screen is represented by the arrow 19. A synchronizing amplifier 20 is provided to which an impulse derived from the signal 19 may be applied for sufficient amplification to control the phase of the "sweep" wave. A rectangular wave generator 21 is provided which is subject to synchronization with the signal amplified by the synchronizing amplifier 20 and a saw tooth wave generator 22 is provided for converting an output of the rectangular wave generator 21 into a triangular wave to form the principal component of the "sweep" wave, as illustrated in Fig. la.

For producing the component of the "sweep" wave effecting the expansion, there are provided a relatively short-pulse rectangular wave generator 23 and a saw tooth wave generator 24 associated therewith. For combining the two wave components from the saw tooth wave generators 22 and 24, an addition, or mixing, circuit 25 is provided, the output of which is supplied to the horizontal deflection plates 14, preferably through a horizontal amplifier, not shown.

Although single ended output is shown for the deflection circuit, it is understood that push-pull operation is possible.

For enabling any portion of the signal wave to be selected for expansion, phase shifting equipment is provided including an actual phase shifter 26 and a wave shaping circuit 27 which is interposed between the rectangular wave generator 21 and the phase shifter 26 to convert the generated wave into a wave shape sufficiently sinusoidal for successful operation in a relatively simple phase shifter circuit.

The signal 19 to be observed, is applied to the vertical deflection plates 15, preferably through a vertical amplifier 28, and in order to off-set the expanded portion of the wave from the remainder of the wave, the vertical amplifier 28 is preferably arranged as an addition circuit so that it will add to the input signal, a rectangular wave synchronized with the expansion pulse derived from the short-pulse rectangular wave generator 23. It is of course understood that operation is possible without the addition of this off-setting pulse to the vertical amplifier 28.

The amplifiers, rectangular wave generators, and addition circuits may consist of standard types of circuits employing electronic discharge devices, such as vacuum tubes, a suitable form of tube circuits being shown more in detail by way of example in Fig. 3.

Fjr blanking out the cathode ray beam during the return sweep, a blocking stage 29 may be provided.

The synchronizing amplifier 20 may comprise a triode vacuum tube 30 having an anode 31, a control electrode 32 and a cathode 33. Since in the arrangement shown the various vacuum tube stages are resistance-capacity coupled, a resistor 34 is shown in the anode lead of the tube 30.

For negative feed-back or stabilization, a biasing resistor 35 may be connected in the cathode lead without the by-pass condenser 36, but where the additional gain is helpful, the condenser 36 is employed. The control electrode 32 is excited by a portion of the input signal to be observed applied through a coupling condenser 36 and a volume control potentiometer 37.

The rectangular wave generator 21 may be in the form of a generator or multi-vibrator stage 38 and a "clipper" stage 39. The particular form of multi-vibrator stage shown as 38 consists of a pair of triodes or triode units 40 and 41 including anodes 42 and 43, control electrodes or grids 44 and 45, and cathodes 46 and 47, respectively. The triodes 40 and 41 also have resistors in the anode leads and the anodes are cross connected to the control electrodes or grids by means of coupling condensers 48 and 49. It is therefore essentially a resistance capacitycoupled amplifier with its output coupled back to its input. Grid leak resistors 50 and 51 are connected from the grids to an adjustable tap 52 of a potentiometer 53 which is connected across the plate voltage source for the tubes.

For permitting adjustment of the fundamental frequency of the wave produced by the multivibrator 38. to approximately that preferred for the given input signal 19, the position of the tap 52 on the potentiometer 53 is made adjustable. Preferably a by-pass condenser 54 is connected between the tap 52 on the ground point of the system. For synchronizing the wave produced by the multi-vibrator 38, a tie-in is made through a coupling condenser 55 between the anode 31 of the synchronizing amplifier 20 and a suitable point in the multi-vibrator circuit 38, for example, a point on the grid leak 50 which is connected to the control electrode 44 of the triode 40.

For converting the steep-sided peaked loops of the wave produced by the multi-vibrator 36 into rectangular pulses a "clipper" stage 39 is provided having electron tubes 56 and 57 of such a design that the wave loops applied to them by the multi-vibrator 38 exceed the cut-off points of the tubes 56 and 57. The tube 56 includes an anode 58, a control electrode 59, and a cathode 60, and the tube 57 includes corresponding electrodes 61, 62 and 63, respectively. The control electrode or grid 59 is coupled to the anode 43 of the multi-vibrator stage 38 through a coupling condenser 84, the grid 62 in turn being coupled through the coupling condenser 65 to the anode 58 of the tube 56.

The triangular wave generator 22 may take the well-known form of a resistor 88 and a condenser 87 connected in series across the plate circuit of the clipper tube 57. The condenser 67 is on the cathode side of the series combination and the common terminal 68 and the ground bus serve as the output terminals across which the triangular wave appears.

The addition circuit 25 includes suitable means for additively combining two waves which may take the form of a mixer tube 69, such as a tetrode, for example, having an anode 10, a secondary control electrode or screen 71, a primary control electrode or grid 72 and a cathode 73.

The control electrode 71 is positively polarized if it is of the screen grid type. A connection is made between the output point 68 of the triangular wave generator 22 and one of the control electrodes of the tube 69 through a coupling condenser 74, and if desired, through an injector amplifier, not shown. The mixer or horizontal amplifier 25 may also include one or more stages of vacuum tube amplification, such as the tube 75, for example. Although I have by way of .illustration described the use of a mixer tube for combining two voltage waves, it will be underso stood that my invention is not limited thereto and does not exclude, e. g., applying one wave directly in a grid circuit and the other across a cathode resistor of an electron tube.

The blanking stage 29 may take the form of a triode 76 having an anode 77, a control electrode 78 and a cathode 79. The anode 77 serving as the output terminal of the blanking stage 29 is connected to the control electrode or grid 16 of the oscilloscope tube 13. The grid 78 of the tube 76 is connected to a source of a wave having positive potential impulses during the periods of the return sweep of the "sweep" wave, for example, to the anode 58 of the clipper tube 56 in the clipper stage 39. Blanking may also be ac4" complished by connecting the oscilloscope grid 16 directly to the anode 61 of the final "clipper" stage of the rectangular wave generator 21, omitting the blanking tube 16.

The wave-shaping circuit 27 may take any suitable form. For the sake of example, I have shown a low pass filter network consisting of a tapped inductance 81, adjustable condensers 82 connected between ground and the adjustable taps of the inductance 81, and a condenser 83 connectS5 ed in series with the inductance 8 for isolating the (+B) voltage from the circuit. The adjustable features show one way to permit the passage of waves of the frequency corresponding to the output of the rectangular wave generator 21. The cO wave-shaping circuit 27 converts a square wave into a substantially sinusoidal wave which may be handled by the phase shifter 26.

The phase shifter 26 may be of the simple rheostat and condenser type comprising a cona5 denser 84 in series with a rheostat 85 connected across the output of the wave-shaping circuit 27, preferably through the interposition of a transformer 86 and a polarity reversing switch 87, for extending the range of the phase shifter from 180 to 360 degrees. The center point of the secondary winding of the transformer 86 is grounded.

The short-pulse rectangular wave generator 23 may be of the same type as the rectangular wave generator 21 differing therefrom, however, in that the resistance ratio between the grid leak resistors 80 and 89 is made such as to produce the desired ratio between the lengths of the positive and negative pulses of the generator 22, making the positive pulses shorter than those produced by the rectangular wave generator 21.

The saw tooth wave generator 24 may also take the form of a resistor and condenser connected in series across the output of the rectangular wave generator 23, with a common terminal to which is connected an output lead 90 in which the short pulse triangular wave appears. The. lead 90 is connected to the remaining control electrode 72 of the mixer tube 69, preferably through a coupling condenser 91.

The vertical deflection amplifier 28 may also take the form of a vacuum tube amplifier including one or more stages of vacuum tubes, the initial stage, for example, comprising a mixer tube 92 having electrodes performing the same functions as the electrodes of the mixer tube 69, previously mentioned. In the particular form shown, it may include a control electrode 93 and control electrode or grid 94. One of the control electrodes, for example, the electrode 93, is tied through a coupling condenser 95 to a suitable point in the short-pulse rectangular wave generator 23 at which a short positive pulse appears. In the arrangement illustrated this connection is made to the output terminal of the generator 23. The remaining control electrode 94 is connected through a coupling condenser 96 to the terminal II at which the input signal 19 appears. If further amplification of the rectangular wave output short-pulse generator 23 is required for off-setting the expanded portion of the signal wave, an injector amplifier (not shown) may be itnerposed in the connection from the short pulse rectangular wave generator 23 to the control electrode of the tube 92. It will be understood that the output of the vertical amplifier 28 is connected to the deflection plates 15 of the tube for producing the signalrepresenting deflection of the cathode ray beam.

It will be further understood that a suitable source of power for energizing the heaters and plate circuits of the vacuum tube is provided, the positive terminal of the plate source being represented at 97. Other conventional elements of the circuit, such as anode resistors, rippleabsorbing filter condensers, grid leak resistors, decoupling circuits, and the like are to be used, as will be understood by those skilled in the art.

In the tube 92 it may be desirable to ground the screen 93 with respect to radio frequency, while permitting its potential to rise sufficiently with respect to sweep frequency by interposing a condenser 92' in series with a resistance between the screen 93 and ground. If the four-electrode tube 92 is of the screen-grid type the screen 93 8 must be polarized by a positive potential source 93'.

The principle of operation of the apparatus is indicated by the sample curves shown in Fig. 3 below each of the elements thereof to indicate 6 the type of voltage wave appearing at the output terminals of the corresponding element. The signal to be observed applied at the Input terminals II and 12 may, of course, have any wave shape which is, however, assumed to be recur- 7 ring in order that the traces on the screen 18 of the oscilloscope tube 13 may be superimposed.

The wave shape corresponding to the input wave 19 is amplified by the synchronizing amplifier 20 and energizes the control electrode 44 of the 7 multi-vibrator 38 whenever the polarity of the amplified wave applied thereto becomes sufficiently positive to permit the grid 44 to reach a predetermined value of potential which will 6 initiate conduction in tube 40. This shifts the current in the multi-vibrator circuit to the tube 40 at a predetermined point in each cycle, or if so desired in each group of cycles, of the input wave, thus synchronizing the output of the multivibrator 38 with the signal to be observed. Since the control electrodes and anodes of the multivibrator 38 are cross connected and condensers and resistors are interposed in the grid circuits, energization of one tube shifts the current away from the other tube by abruptly depressing its anode potential. However, the resistors 50 and 51 permit gradual discharge of the condensers 48 and 49 corresponding to the exponential portions of the wave 98, and when the potentials have been readjusted to a certain point, the tube which has been non-conducting fires abruptly shifting the current away from the other tube.

The abrupt shifts in current are represented by the vertical portions of the wave 98.

The magnitudes of the positive and negative loops of the wave 98 are such as to depress the grid potentials of the "clipper" tubes 56 and 57 alternatively to cut off so that the output of the clipper circuit 39 is in the form of a rectangular wave 99 having pulse lengths corresponding to the pulse lengths in the wave 98, but with flat tops.

The resistance of the resistor 66 in the triangular wave generator 22 is relatively great in relation to the capacitance of the condenser 67 so that the charging current of the condenser 67 is determined substantially constant during the forward "sweep" part of the cycle. Since the ratio of the grid leak resistors 50 and 51 of the multivibrator 38 is made such as to cause the positive pulse of the output voltage wave as shown at 98 to be longer than the negative pulse, the rectangular output voltage wave 99 has long positive pulses and short negative pulses causing a relatively small, long continued, positive charging current in the condenser 67 and a relatively large, negative or discharging current of short duration in the condenser 67. The condenser potential accordingly rises gradually and falls more rapidly as represented by the triangular wave 100, which is the wave shown in Fig. la.

In a similar manner, the short-pulse rectangular wave generator 23 produces an intermediate irregular wave 101, and a rectangular wave 102 with short positive voltage pulses and long negative voltage pulses resulting in the triangular voltage wave 103 with short rapid ascending portions and longer descending portions, as 10 shown in larger scale in Fig. lb. It will be understood that any difference in ratio of lengths of the positive and negative pulses in the generators 21 and 23, as well as any turning over of the waves as shown at 98 and 101, is accom15 plished by a corresponding difference in the ratios of the grid-leak resistors, as well as an interchange of position of these resistors in the two multivibrator circuits.

The triangular waves 100 and 103 are com'0 bined in the mixer circuit 25, and the phase relationship of the wave 103 with respect to the wave 100 may be varied by adjustment of the rheostat 85 in the phase shifter 26. The waveshaper 27 converts the wave 99 into a substan' tially sinusoidal wave 99a which may be shifted in phase without distortion by a variable resistorcondenser- circuit.

Waves similar to wave 99 but reversed in polarity by being drawn from the clipper tube 56 of the clipper stage 39 are reversed again in a polarity by the blanking amplifier 71 so that the potential of the oscilloscope grid I6 is depressed to cut-off during the negative pulses of the wave 99 corresponding to the descending portion of the wave 100, shown at 12 in Fig. la, lf and at I in Fig. 1. The image on the oscilloscope screen is accordingly produced only during the forward sweep. Short positive pulses of the wave 102 obtained from the short-pulse generator 23 and combined with the signal in the vertical amplifier 28, off-set the portion of the signal wave occurring during the positive pulses of the wave 102. At the same time the oscilloscope beam is being swept with increased rapidity across the screen as represented by the portion 17 of Fig. lb and the portion 14 of the curve in Fig. 1. Accordingly the wave as depicted on the screen 18 is expanded during this interval of time with respect to those portions of wave corresponding to the portions 13 and 15 of the "sweep" wave shown in Fig. 1.

The image of the wave as it appears on the oscilloscope screen with the center portion of the sine wave expanded is shown in Fig. 6. The sine wave impulse signal represented in Fig. 7 has its center portion 04 expanded and the end portions 105 compressed to form the wave of Pig. 6 and the corresponding portions are represented by the same reference numerals primed. The expanded portion 104' is, however, offset from the remainder of the wave to produce the segment 106 to avoid confusion, in the case of irregular wave shapes. If the phase shifter 26 had been set to bring the fast sweep portion of the "sweep" wave to a different position with relation to the remainder of the wave a different portion of the input signal would, of course, have been expanded.

While the action has been shown for a single sine wave, it is apparent that it may also be applied to more complicated input waves and that it is 4 not restricted to a single cycle representation on the screen I8.

I have described and illustrated the use of the multi-vibrator circuit with clippers and the saw tooth or integrating circuit for producing a triangular sweep wave, because such a combination circuit is particularly well adapted for working in the high frequency limit of the sweep circuits.

My invention, however, is not limited to the spe- 5 cific arrangement illustrated and obviously does not exclude the use of a gas discharge tube to create the necessary triangular or saw tooth wave.

In accordance with the modified embodiment of my invention, I expand any desired portion of the wave without compressing the remainder of the wave, and I expand a selected portion the full length of the time axis of the entire signal wave. This I accomplish, by producing a sweep wave of the form represented in Fig. 4 having gradually ascending forward sweep portions III and 1 2 of the same slope for producing the normal representation of the signal wave and having a short steep portion 113 variable in phase relationship with respect to the rest of the wave for producing rapid sweep of the beam for expansion.

The sweep wave also includes a portion 114 of a negative slope for returning the beam. The lowest and highest points of the portion 13S of the sweep wave are substantially even with the low- iT est point of the portion 11 and the highest point of the portion 112 so that during the portion 113 of the sweep wave, the beam is swept horizontally through the entire length of its time axis. A wave shape such as shown in Pig. 4 may be produced by combining a short negative pulse rectangular wave as shown in Fig. 4a, a short-pulse steep rising triangular wave as shown in Fig. 4b, and a normal saw-tooth "sweep" wave as shown in Fig. 4c. The waves 4a and 4b are locked together but are adjustable as a unit in phase relationship with respect to the component of the wave shown in Pig. 4c. The wave of Fig. 4b has its slow return portion blanked out in a manr!., which will be described more in detail hereinafter.

The wave represented in Fig. 4 may be produced by a "sweep" wave generator similar to that represented in Figs. 2 and 3 except for the modiflScation of certain elements and the addition of a few elements. As shown in Fig. 5, the modified form of "sweep" wave generator also includes a synchronizing amplifier 20, a rectangular wave generator 21, a saw tooth wave generator 22, a cathode beam return sweep cut-off stage 29, a wave shaping circuit 27, a phase shifter 26, a short-pulse rectangular wave generator 23, a saw tooth wave generator 24, and a vertical amplifier and mixer 28. The addition circuit or mixer 25 is replaced by a slightly modified element 25' which permits mixing or adding together three voltages instead of only two. For blanking out the return slope of the saw tooth wave output of the element 24, a blocking stage 116 may be interposed between the short pulse saw tooth generator 24 and the addition circuit 25' with a control connection from the short pulse rectangular wave generator 23. A further modification is a connection 11 for injecting into the addition circuit 25' a negative polarity short pulse rectangular wave derived from the rectangular wave generator 23. If desired, a square wave buffer stage 118 may be provided with its input connected to the rectangular wave generator 23 and with its output voltages leading through connections 117 and 119 to the addition circuit 25' and the addition or mixer circuit of the vertical amplifier 28, respectively.

The modified portions of the circuit represented in Fig. 5 are illustrated more in detail in Fig. 9.

The initial vacuum tube stage of the addition circuit 25' may comprise the vacuum tube 69' having three control electrodes 71, 120 and 72'. Although for the sake of simplicity in the drawing, I have shown a circuit for triple addition in a single tube, it will be understood that my invention does not exclude injection in two different stages instead of only in the first stage, and utilization in the two injection stages of tubes having two control electrodes, combining two voltages in the one stage by applying them to two of the control electrodes and adding the resultant to the third voltage in the next stage by applying the voltages in question to the control electrodes of the said stage. Alternately it may consist of three separate amplifier stages having separate input circuit for the respective voltages to be added and having a single output resistor circuit.

The particular form of addition circuit shown is not my invention and it will be understood by those skilled in the art that any modified form of addition or mixer circuit may be more convenient.

In the arrangement illustrated, the control electrode 11' of the tube 68', as in Fig. 3, is connected through a coupling condenser 74 to a long pulse triangular wave source, as in Figs. 2 and 3.

The control electrode 72' is connected through the coupling condenser 91 to a source of a modifled form of short-pulse triangular wave including the blocking stage 16. The added control electrode 120 is connected through a coupling condenser 121 to a source of negative polarity short-pulse rectangularwave voltage corre- 1 sponding to the wave 102 provided by the rectangular wave generator 23. The reversal in polarity may be obtained by drawing the voltage from the first stage of the buffer circuit I18, which may be, for example, a standard two-stage resistance coupled amplifier or buffer in which reversal of polarity takes place in each stage, as will be well understood by those skilled in the art. The form of wave applied to the control electrode 120-is represented by the curve 122, and the amplitude 2C is such that operation of mixer tube 69 is on the linear or amplifier part of its characteristic. The output of the buffer stage 118 is applied to the vertical amplifier 28 to off-set the expanded portion of the wave upwardly, as explained in connection with Figs. 2 and 3.

The blocking circuit 116 may take any suitable form which will pass the positive slope portions of the triangular wave 103 represented at I7 in Fig. lb, but will suppress the negative slope portion represented at 18 in Fig. lb, in response to rectangular pulses synchronized with the wave 103 wherein the portions 17 and 18 are consistent with Fig. Ib. The blocking circuit illustrated takes the form of a discharge tube 123 which may be a twin triode vacuum tube comprising two sets of electrodes, the first consisting of an anode 124, a control electrode or grid 125, a cathode 126, and the second set consisting of corresponding electrodes 127, 128 and 129, respectively. The left-hand element of the tube 123 is connected as a conventional resistance coupled amplifier with the triangular wave 103 from the saw tooth generator 24 applied through a coupling condenser 130 to the control electrode 125. The control electrode 128 of the right-hand element of the tube 123 is tied through a coupling condenser 131 to the output connection or anode 124. The right-hand anode 127, however, is so connected as to derive its potential through an anode resistor 132 from a source of rectangular wave voltage having long negative pulses and short positive pulses synchronized with the portions 18 and II of the triangular wave 103. If desired, such plate potential may be obtained from the rectangular wave generator 23. Alternatively a resistor in series with the cathode may be used and the proper rectangular wave applied across this resistor will permit conduction only during the short pulse period, during the long pulse period c0 the tube being driven past cut-off.

During the positive pulses of the rectangular wave 102 the tube 123 will act as a conventional two-stage resistance coupled amplifier causing the steep positive portion of the triangular wave to be reproduced as a corresponding wave portion 133 in a modified triangular wave 134, shown in larger scale in Fig. 4b. During the negative pulses of the wave 102, however, the anode 127 is without voltage and the potential accordingly falls to the uniform value represented by the horizontal line 135 in the curve 134.

The three wave forms represented in Figs. 4a, 40 and 4c and in the curves 122, 134, and 100 are combined in the addition circuit 26' to produce the wave form of Fig. 4, which is applied to the horizontal sweep-producing deflection plates 14 of the oscilloscope tube. Only the signal wave and the off-setting rectangular wave are combined in the vertical amplifier 28 for application to the vertical deflection plates 15 of the oscilloscope tube.

Referring again to Fig. 7, the portion 104 of the input signal wave which is selected for ex0 pansion and corresponding in width to the positive pulse width of the curves 102 and 103 is expanded and off-set to form the curve segment 136 shown in Fig. 8. This action results from the fact that the "sweep" wave shown in Fig. 4 rises along the steep portion 134 at a uniform rapid rate of speed from the minimum value of the "sweep" wave to the maximum value for producing the expansion. The "sweep" wave falls abruptly along the line 137 from the segment I I to zero or minimum before expansion starts.

Then again, after the expanded portion of the signal wave has been produced by the sweep wave portion 113, the "sweep" wave falls abruptly to the segment 112, i. e., to a value which it would have in case only a simple triangular wave, such as shown in Fig. 4c, were employed. The expanded segment 136 of Fig. 8 therefore has the full length of the time axis of the oscilloscope and is, in effect, cut out of the center of the Ssignal wave 105 by superposing the waves 122 and 134 of Figs. 4a and 4b, respectively, on the simple "sweep" wave 100 of Fg. 4c to produce the composite "sweep" wave of Fig. 4.

I have herein shown and particularly described certain embodiments of my invention and certain methods of operation embraced therein for the purpose of explaining its principle and showing its application but it will be obvious to those skilled in the art that many modifications and variations are possible and I aim, therefore, to cover all such modifications and variations as fall within the scope of my invention which' is defined in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is: 1. A wave-examining system comprising an oscilloscope having sweep and deflection signal circuits and a sweep wave generater comprising means for producing a rectangular wave, adjustable in frequency, means for synchronizing the rectangular wave with a signal to be observed, means for converting the rectangular wave into a triangular wave, means for producing a substantially sine wave synchronized with the rectangular wave, a phase shifter energized by the sine wave, means for producing a second rectangular wave of narrower pulse width than the first, a second means for converting said second rectangular wave into a second triangular wave, means for combining the two triangular waves and applying them in the sweep deflection circuit of the oscilloscope, and means for injecting a third rectangular wave synchronized with said second rectangular wave in the signal deflection circuit of the oscilloscope, whereby a portion of the signal wave to be observed is expanded and off-set with respect to the remainder of the wave.

2. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits and a beam controlling electrode, and said sweep wave generator comprising means for producing a triangular wave synchronized with a signal wave to be observed, said triangular wave having a relatively long advancing portion and a relatively short fly-back portion, a block-out stage synchronized with the triangular wave producer and having a coupling to the beam controlling electrode for blocking out the beam during the fly-back portion of the sweep wave, means for producing a second triangular wave having a relatively short advancing portion and a relatively long return portion, means for superimposing the two waves, and means for varying the phase relationship between the two triangular waves, whereby a resultant sweep wave is produced having a relatively steep portion which may be varied in relative position with respect to the remainder of the sweep wave to enable the expansion of any selected portion of a signal wave to be observed in the oscilloscope.

3. An oscilloscope sweep wave generator comprising in combination, means for producing a triangular wave synchronized with a signal wave to be observec', said triangular wave having a relatively long advancing portion and a relatively short fly-back portion, means for producing a second triangular wave having a relatively short advancing portion and a relatively long return portion, means for superimposing the two waves, and means for varying the phase relationship between the two triangular waves, whereby a resultant sweep wave is produced having a relatively steep portion which may be varied in relative position with respect to the remainder of the sweep wave to enable the expansion of any selected portion of a signal wave to be observed in the oscilloscope.

4. An oscilloscope sweep wave generator comprising in combination, means for producing a rectangular wave adjustable in frequency, means for synchronizing the rectangular wave with a signal wave to be observed, means for converting the rectangular wave into a triangular wave, means for producing a second rectangular wave, a sceond means for converting said latter rectangular wave into a second triangular wave with a relatively steep forward portion and a return portion, means for blocking out the return portion of the second triangular wave, and means for combining the two triangular waves and the second rectangular wave whereby a resultant sweep wave is produced having a relatively steep portion, represented by the forward portion of the second triangular wave, enabling the expansion of a portion of the signal wave to the length of the entire signal wave.

5. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits and a beam controlling electrode, and said sweep wave generator comprising in combination, means for producing a triangular wave with an advancing portion relatively long in comparison with the return portion, and a block-out stage having a coupling to the beam-controlling electrode for blocking out the beam of an oscilloscope during the return portion of the trianegular wave, means for producing a second triangulan wave with a shorter advancing portion than'.the first triangular wave and with the return portion blocked out, means for producing a rectangular wave with the same negative pulse twidth as said second-mentioned triangular wave, and means for combining the three-mentioned waves and applying them to the sweep deflection circuit .to produce a sweep wave with a portion thereof steeper than the remainder of the sweep wave to expand a portion of the signal wave to be observed, said steeper portion of the sweep wave having the same minimum and maximum heights as the minimm and maximum heights of the remainder of the sweep wave, whereby the expanded portion of the signal wave to be a observed is of the same length as the entire signal wave.

6. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits, and said sweep wave generator comprising in combination means for producing a sweep wave having an amplitude-time graph made up of substantially linear segments, including sloping segments, one of said sloping segments being steeper than the remainder of the sweep wave for the purpose of expanding a portion of a signal wave to be examined in the oscilloscope, means for applying the sweep wave to the sweep deflection circuit, means for synchronizing the sweep wave with the signal wave and varying the phase relationship between the signal wave and the steep portion of the sweep wave for the purpose of selecting the portion of the signal wave to be expanded, means for producing a rectangular wave synchronized with the steep portion of the signal wave, and means for injecting said rectangular wave in the signal deflection circuit of the oscilloscope for off-setting and separating the expanded portion of the signal wave from the remainder of the signal wave.

7. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits, and said sweep wave generator comprising a pair of synchronizing terminals with means for applying a voltage thereto corresponding to the signal wave to be examined in an oscilloscope, means coupled to said synchronizing terminals for producing a sweep wave made up of substantially linear segments, including sloping segments, said means including means for producing one of such sloping segments steeper than the remainder of the sweep wave for the purpose of expanding a selected portion of a signal wave to be observed in the oscilloscope, means for applying the sweep wave to the sweep deflection circuit of the oscilloscope and means for producing a rectangular wave synchronized with the steep portion of the sweep wave and injecting it in the signal deflection circuit for combination with the signal wave for the purpose of off-setting and separating the expanded portion of the signal wave from the remainder of the signal wave.

8. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits and a beam controlling electrode, and said sweep wave generator comprising in combination means for producing a sweep wave having an amplitude time graph made up of substantially linear segments, including sloping segments, one of said sloping segments being steeper than the remainder of the sweep wave for the purpose of expanding a portion of a signal wave to be examined in the oscilloscope, means for applying the sweep wave to the sweep deflection circuit, means for synchronizing the sweep wave with the signal wave, means for varying the phase relationship between the steeper portion of the sweep wave and the remainder of the wave for the purpose fo selecting the portion of the signal wave to be expanded, means for producing a rectangular wave synchronized with the steep portion of the sweep wave, and means for injecting said rectangular wave in the signal deflection circuit of the oscilloscope for off-setting and separating the expanded portion of the signal wave from the remainder of the signal wave.

9. In a cathode ray oscilloscope arranged for deflection of a wave-tracing beam in the directions of a sweep axis and a signal wave axis, transverse thereto, a sweep generator for producing a normal deflection along the sweep axis with alternate forward and return sweeps, means for increasing the velocity of the sweep deflection during a fraction of the time duration of the forward sweep to provide expansion of the wave, viewed in the oscilloscope, during said fraction of the forward sweep, and means for producing a substantially constant change in the deflection of the wave-tracing beam along the signal wave axis during said fraction of the forward sweep, for the purpose of separating the expanded portion of the wave from the remainder of the wave viewed in the oscilloscope.

10. Apparatus of the character set forth in claim 9 with means for varying the phase relationship between the increased velocity portion of the sweep and the remainder of the sweep.

11. In a cathode ray oscilloscope arranged for deflection of a wave-tracing beam in the directions of a sweep axis and a signal wave axis, transverse thereto, a sweep generator for producing a normal deflection along the sweep axis with alternate forward and return sweeps, means for increasing the velocity of the sweep deflection during a fraction of the time duration of the forward sweep for providing expansion of the wave, viewed in the oscilloscope, during the said fraction of the forward sweep, means for sufficiently changing the sweep deflection abruptly at the beginning or end of the said fraction of the forward sweep to retain the same sweep deflection outside said fraction of the forward sweep as would be obtained without said increase in sweep velocity, and means for changing by a substantially fixed amount the deflection of the wave-tracing beam along the signal wave axis during the increased velocity portion of the forward sweep for separating the expanded portion of the wave, viewed in the oscilloscope, from the remainder of the wave.

12. A wave-examining system comprising an oscilloscope and a sweep wave generator, said oscilloscope having sweep and signal deflection circuits, and said sweep wave generator comprising, in combination, means for producing a sweep wave with an amplitude time graph made .) up of substantially linear segments 'including sloping segments, means included therein for producing one of said wave segments with relatively steep slope in comparison with the remainer of the sweep wave for the purpose of expanding a portion of the signal wave to be examined in an oscillopscope, means for applying the sweep wave to the sweep deflection circuit, means for producing a rectangular wave synchronized with the steep-slope wave segment produced by said last-mentioned means, and means for injecting said rectangular wave in the signal deflection circuit of the oscilloscope for offsetting and separating the expanded portion of the signal wave from the remainder of the signal wave.

na ELLSWORTH D. COOK.