US3151271A

US3151271A - Electronic switch display in chopped operation of oscilloscopes

Info

Publication number: US3151271A
Application number: US86071A
Authority: US
Inventors: Maron Meyer
Original assignee: Fairchild Camera and Instrument Corp
Current assignee: Fairchild Semiconductor Corp
Priority date: 1961-01-31
Filing date: 1961-01-31
Publication date: 1964-09-29
Anticipated expiration: 1981-09-29

Description

Sept. 29, 1964 M. MARON ELECTRONIC SWITCH DISPLAY IN CHOPPED OPERATION OF OSCILLOSCOPES Filed Jan. 51, 1961 9m omm mwoml mwmim 1 En ENVENTOR Meyer Moron -g aflgd-o a'fi ATTOR'NIEIYS United States Patent ELECTRON C SWITCH DISPLAY 1N (SHOkPED OPERATlON OF OSfiiLLOSCOPES Meyer Maren, East Paterson, N..l., assignor to Fairchild Qamera and instrument Corporation, Syosset, N.Y., a corporation of Delaware Filed Jan. 31, 1901, Ser. No. 86,071

'7 Claims. (til. 315-23) This invention is directed to chopped or rapidly switched operation of time sharing oscilloscopes arranged to view two independent displays on the same viewing screen. When one of the displays is at a very low frequency the usual alternate presentations of the two displays by time sharing switches is apt to cause flicker in the presentations. This is particularly objectionable when one of the displays is an electrical wave which requires an appreciable fraction of a second for its completion, and when the other display is a dot presentation for direct readout measurement of the electrical Wave, as described in a copending application by Bernard L. Hegeman, entitled Direct Readout System for Oscilloscopes, Serial No. 34,124, filed June 6, 1960.

Chopped operation is not new as regards oscilloscopes equipped with time sharing electronic switches for a single electron beam. It has been usual in such operation to provide a free running multivibrator to generate substantially rectangular or square waves for operation of the electronic switches at a relatively high frequency, say at several thousand cycles. Separation of two independent displays may be provided as described in a copending patent application by Fred L. Katzmann, entitled Time Sharing Oscilloscope, Serial No. 55,014, assigned to the same assignee as the instant application.

In chopped operation the high frequency electronic switches alternately present small portions of each of the independent displays at two separated positions on the viewing screen. One defect in such a chopping operation has been the appearance of switching excursion transients between the separated waves. When the chopping frequency is very high relative to the frequency of the displayed waves, the displays may be considered as being made up of a great number of alternately presented dots which blend into two apparently continuous traces, one of each of the separated displays. As the beam switches back and forth between the two displays a great number of faint vertical lines appears on the display screen between the two separated traces. These are caused by the switching excursion transients of the beam as it shuttles rapidly back'and forth between the separated displays.

The defect in appearance of the display is due to a faint but apparent smear between the displays. My invention avoids this defect of smearing between the separate displays without the use of blanking signals derived (by costly circuits) from the switching wave transients themselves.

It is, therefore, an object of my invention to provide simplified circuitry for chopped operation of an oscilloscope in which two separated independent displays appear clearly and sharply against a uniform dark background.

It is another object of my invention to derive a high frequency electronic switching wave from a blanking wave so that the switching excursion transients occur within the blanking interval.

It is still another object of my invention to prevent a smeared display between two independent displays produced by chopped operation.

It is a still further object of my invention to provide direct readout dots for quantitative measurements without objectionable flicker or smear when measuring a low frequency display.

Other objects will be understood by those skilled in the art after consideration of the description and annexed drawings, in which,

FIGURE 1 illustrates a prior art presentation of two separated independent displays in chopped operation;

FIGURE 2 illustrates a presentation according to this invention; and

FIGURE 3 is a schematic circuit of a preferred embodiment of this invention.

Referring to FIGURE 1, a prior art display screen is depicted in which two independent displays 101, 102 are shown in separated relationship, as normally produced by the technique well known as chopping. Segments 104, of each display are produced by switching alternately from one display to the other at a high rate. Switching excursion transients 103 occur on each switching operation between display portions such as 104 to 106 and 106 to 108. Thus, switching results in a shaded or smeared area between the displays.

In FIGURE 2 the same two displays 101, 102 are depicted according to my invention as they appear on a display screen 200 with a uniformly dark (unshaded) background 203. Elimination of the prior art transients 103 is achieved by the circuitry shown in FIGURE 3.

In this preferred embodiment of my circuit, electronic switch 330 has two pairs of push-

pull input terminals

301, 303 and 302, 304 to which display waves 101 and 102 are applied, respectively. Out-of-

phase switching waves

321, 322 are generated at a high frequency j (which may be, for example, 100,000 cycles per second), in a well known bistable inultivibrator circuit 340.

These switching waves are applied through diodes 307, 308 to the cathodes of push-pull pairs of

tubes

305, 306, respectively, to make them alternately conductive. Thus, when a portion 104 of potential wave 101 is amplified by 305 and applied to the

input conductors

318 and 319 of the vertical paraphase amplifier 317, a synchronous corresponding portion 105 of wave 102 is cut off and does not appear at the input to 317. Immediately succeeding portions of 101, 102, such as 104, 106, are amplified alternately in 317 and applied to the vertical deflecting plates V, V'. A portion of

switch waves

321, 322 is applied to grids 310, 311 of trace separator tubes 309.

Thus, when the negative excursion of switch wave 321 switches display wave 101 to the plates V, V input conductor 318 is positive with respect to 319 and V is positive with respect to V. This will produce display 101 near the top of display screen 200. Similarly, display 102 will be produced near the bottom of 200, and the two are separated. The amount of separation is adjustable by means of potentiometer unicontrol 315.

The multivibrator 350 is arranged to generate a narrow negative pulse wave 320 at a free running frequency of 2 f which may be, for example, 200,000 cycles per second. The duration t of a pulse 370 is made slightly longer than the time required for the switching transient 103 of

square waves

321 and 322. The wave 320 is used to start the switching action of the flip-flop generator 340 by means of a capacitor 314 connected to the junction of the cathodes of diodes 312 and 313. For example, t is made equal to 1.5 microseconds when 103 endures for only 1.3 microseconds, that is, t begins with the switching action and before switching is complete and ends after the switching is completed.

The output wave 320 serves two purposes: to synchronize the switch wave generator 340, and to blank out the switching transients which occur due to chopped operation. In order to accomplish this latter result, the blanking wave 320 is applied to the control grid 325 of cathode ray tube 331, through the blanking pulse diode 328 and cathode follower 329. A brightening pulse diode 326 may be used to control the intensity of beam 323 between the blanking pulses 320 by means of the brights3 ness adjusting potentiometer 327 which controls the positive potential on the grid of cathode follower 329, and thus the value of potential applied to the intensity control grid 325. Horizontal sweep waves are applied to the H-deflection plates H and H in any conventional manner, as from a sweep generator 316.

A low cost circuit has been described which utilizes a free running multivibrator 350 to synchronize the switch wave generator 346 and at the same time to turn off the electron beam 323 during the switching operation.

This low cost circuit is extremely useful in an oscilloscope adapted for direct readout measurements using dot producing waves alternately with a display wave as described in the copending Hegeman application above mentioned.

When two completely independent displays, such as an electrical waveform and readout dots for measuring this waveform, are presented alternately at a very low frequency of a few cycles per second or a fraction of a cycle per second, chopped operation is desirable to prevent a slow blinking of the dots and flicker of the waveform.

Normally, when chopped operation of such low frequency displays is utilized, the double switching transients which occur between the displayed waveform and the dots, due to rapid switching in both the vertical and horizontal dimensions, produce fan-shaped hazy areas centered on each dot and extending to all parts of the displayed waveform. In fact, the background of the entire pattern being displayed has so much unwanted transient hash extending in all directions that the dots are practically useless for the purpose of reading out quantitative information about the waveform.

By the use of my invention the dots and the displayed waveform appear on the displayed pattern with sharp, clean separation. In this case, the H sweep generator 316 will include a high frequency switch such as the H switch 350 of FIGURE 3 of the Hegeman application.

The

switching terminals

380, 331 of generator 316 are supplied with

waves

321, 322 respectively, and the

terminals

382, 383 are supplied with calibrating wave 162 in order to switch the time base sweep wave 390 to plates H and H simultaneously as the displayed waveform 101 is switched to V and V, and to switch a dot producing sweep wave 102 (which is the rectangular calibrating wave) to H and H when it is switched to V and V' by the vertical switch 330. Thus, both the display and sweep waves are presented alternately in rapid, chopped operation to prevent flicker of the display or blinking of the dots in presentations of low frequency waveforms.

While I have described a preferred form of my invention and have described it in its application to the chopped display of two separate waveforms as well as to the chopped display of a single waveform together with calibrating index and readout dots therefor, it will be understood that other forms of the invention may be devised and other applications for the invention are entirely possible. Therefore, I wish to be limited not by the foregoing specification, but, on the contrary, solely by the claims granted to me.

What is claimed is:

1. In an oscilloscope having a cathode ray tube with a single electron beam and a fluorescent screen, means for presenting two electrical waveforms on separate portions of the tube screen comprising, in combination, means to deflect the electron beam in a first dimension to provide a time base for the waveforms, means to deflect the electron beam in a second dimension in accordance with the waveforms, means for generating a switching wave, means for controlling said second electron beam deflecting means to separate the waveform displays, means for applying said generated switching waves to said controlling means to position said beam in said separate tube screen portions alternately, said last-named means including means for combining each electrical waveform with a portion of said switch wave and means to cut off the electron beam during transition periods of said switching means to thereby assure that there will be no trace extending from one of said separated displays to the other.

2. In an oscilloscope having a cathode ray tube with a single electron beam and a fluorescent screen, means for presenting two electrical waveforms on separate portions of the tube screen comprising, in combination, means to deflect the electron beam in a first dimension to provide a time base for the waveforms, means to deflect the electron beam in a second dimension in accordance with the waveforms, means to generate blanking pulses, means for generating a switching wave, means for controlling said second electron beam deflecting means to separate the waveform displays, and means for applying said generated switching waves to said controlling means to position said beam in said separated tube screen portions alternately, said last-named means including means for combining each electrical waveform with a portion of said switch wave, said blanking pulses initiating operation of said switching means, said blanking pulses also cutting off the electron beam during transition periods of said switching means to thereby assure that there will be no trace extending from one of said separated displays to the other.

3. In an oscilloscope having a cathode ray tube with a single electron beam and a fluorescent screen, means for presenting two electrical waveforms on separate portions of the tube screen comprising, in combination, means to deflect the electron beam in a first dimension to provide a time base for the waveforms, said time base deflection recurring at a predetermined frequency, means to deflect the electron beam in a second dimension in accordance with the waveforms, means for generating a switching wave having a frequency greater than said time base recurrence frequency, means for controlling said second electron beam deflecting means to separate the waveform displays, means for applying said generated switching wave to said controlling means to position said beam in said separate tube screen portions alternately, said last-named means including means for combining each electrical waveform with a portion of said switch wave and means to cut off the electron beam during transition periods of said switching means to thereby assure that there will be no trace extending from one of said separated displays to the other.

4. In an oscilloscope having a cathode ray tube with a single electron beam and a fluorescent screen, means for presenting two electrical waveforms on separate portions of the tube screen comprising, in combination, means to deflect the electron beam in a first dimension, to provide a time base for the waveforms having a pre determined frequency of recurrence, means to deflect the beam in a second dimension in accordance with the waveforms, bistable means responsive to pulses for generating a square switching wave, said bistable means having a predetermined opera-ting time, means to generate pulses of a duration slightly greater than said operating time, said pulses recurring at a frequency greater than the frequency of recurrence of said time base, means applying said pulses to said bistable square-Wave switching means for controlling said first electron beam deflecting means to separate the waveform displays, means for applying said square switching wave to said controlling means to position the electron beam in said separate tube screw portions alternately, said last-named means including means for combining each electrical waveform with a portion of said switch wave, and means to cut off the electron beam during operating times of said bistable means.

5. In a cathode ray oscilloscope having a cathode ray tube including a fluorescent screen, a single electron beam source and two deflection means for deflecting said electron beam across said screen in two directions; in combination; means for applying an electrical waveform to be analyzed to one deflection means and for simul- :5 taneously applying a second electrical timing wave to the other deflection means; means to produce a pair of phase related rectangular electrical Waves of the same frequency relative to one another; means to apply said rectangular electrical Waves one to each of said deflection means simultaneously; and electronic switching means for alternately applying portions of said electrical waveform and said timing wave and portions of said pairs of rectangular waves to said one deflection means whereby portions of a Waveform to be analyzed are displayed alternately on said screen with at least one of a pair of dots.

6. In a cathode ray oscilloscope having a cathode ray tube including a fluorescent screen, a single electron beam source and two deflection means for deflecting said electron beam across said screen in two directions; in combination; means for applying an electrical Waveform to be analyzed to one deflection means and for simultaneously applying a second electrical timing wave to the other deflection means; means to produce a pair of phase related rectangular electrical waves one to each of said deflection means simultaneously; means to control the intensity of the electron beam; means to apply a blanking signal of short duration and of much higher frequency than said rectangular waves to said intensity control means; means to generate a switching wave from said blanking signal, with switching transients synchronous with and shorter than said blanking duration; and electronic switching means operated by said switching wave for alternately applying portions of said electrical waveform and said timing wave and portions of said pairs of rectangular waves to said one deflection means whereby portions of a waveform to be analyzed are displayed *3 alternately on said screen with at least one of a pair of dots against a dark background.

7. In a cathode ray oscilloscope having a cathode ray tube including a fluorescent screen, a single electron beam source and two deflection means for deflecting said electron beam across said screen in two directions; in combination; means for applying a low frequency electrical Waveform to be analyzed to one deflection means and for simultaneously applying a second electrical timing Wave synchronized by said electrical waveform to the other deflection means; means to produce a pair of phase related rectangular electrical waves of the same frequency relative to one another and of higher frequency than said timing wave; means to apply said rectangular electrical waves one to each of said deflection means simultaneously; means to control the intensity of the electron beam; means to apply a blanking signal of short duration and of much higher frequency than said rectangular waves to said intensity control; means to generate a switching Wave from said blanking signal, with switching transients synchronous with and shorter than said blanking duration; and electronic switching means operated by said switching wave for alternately applying portions of said electrical waveform and said timing wave and portions of said pairs of rectangular waves to said one deflection means whereby portions of a waveform to be analyzed are displayed alternately on said screen with at least one of a pair of dots against a dark background.

References Cited in the file of this patent UNITED STATES PATENTS 2,706,265 Buehler Apr. 12, 1955 2,858,475 Blake Oct. 28, 1958 2,997,620 Katzmann Aug. 22, 1961

Claims

1. IN AN OSCILLOSCOPE HAVING A CATHODE RAY TUBE WITH A SINGLE ELECTRON BEAM AND A FLUORESCENT SCREEN, MEANS FOR PRESENTING TWO ELECTRICAL WAVEFORMS ON SEPARATE PORTIONS OF THE TUBE SCREEN COMPRISING, IN COMBINATION, MEANS TO DEFLECT THE ELECTRON BEAM IN A FIRST DIMENSION TO PROVIDE A TIME BASE FOR THE WAVEFORMS, MEANS TO DEFLECT THE ELECTRON BEAM IN A SECOND DIMENSION IN ACCORDANCE WITH THE WAVEFORMS, MEANS FOR GENERATING A SWITCHING WAVE, MEANS FOR CONTROLLING SAID SECOND ELECTRON BEAM DEFLECTING MEANS TO SEPARATE THE WAVEFORM DISPLAYS, MEANS FOR APPLYING SAID GENERATED SWITCHING WAVES TO SAID CONTROLLING MEANS TO POSITION SAID BEAM IN SAID SEPARATE TUBE SCREEN PORTIONS ALTERNATELY, SAID LAST-NAMED