US2434439A - Oscilloscope amplifier - Google Patents

Description

H. w. G. SALINGER OSCILLOSCOPE AMPLIFIER Jan. `13, 194s.

Filed Feb, 15. 1945 HANS w G. SALINGER E m T its average value.

Patented Jan. 13, 1948 OSCILLOSCOPE AMPLIFIER Hans W. G. Salinger, Fort Wayne, Ind., assigner, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application February 15, 1945, Serial N o. 578,027

8 Claims.

This invention relates to cathode rayv oscilloscopes, and particularly to an oscilloscope ampliiler for amplifying an input signal to produce visual indications of the signal including its direct current component.

A conventional oscilloscope is usually provided with two pairs of deflecting plates or coils, one being connected to a sweep generator to periodically deflect the cathode ray beam across the screen of the oscilloscope, and the other to a signal source to trace; a pattern onv the screen which is representative of the input signal. In most cases the input signal does not have sufficient strength to effect deflection of the cathode ray beam which traces the pattern on the screen. Therefore, it is customary to provide a conventional vacuum tube amplifier for amplifying the input signal. However, amplifiers of this type do not pass the direct current component or the averagevalue of the signal to be amplified. This limits seriously the ield` of application of a cathode ray oscilloscope. Frequently, it is desirable to obtain visual indications of a signal including This is particular-ly true when it is desired to check the performance of television equipment by means of a cathode ray oscilloscope.

It has, for instance, been found that the response of a television picture signal generating tube of the light storage type is not directly proportional to the intensity of the light falling on the photosensitive cathode of the tube. When the light intensity increases, the signal output falls off. For investigating this phenomenon it is very desirable to utilize a cathode ray oscilloscope which will produce a visual indication of the signal output of the pickup tube including its direct current component.

Vacuum tube amplifiers are known which will pass direct current but they are difcult to adjust, are unstable, have a limited power output and their internal resistance depends upon the load.

It is an object of the present invention, therefore, to provide an amplifier for a cathode ray oscilloscope which will amplify an input signal to produce a visual indication on the screen of the oscilloscope which is representative of the input signal including the average value thereof.

In accordance with the present invention there is provided the combinationv of a cathode ray tube comprising a screen andv an electron gun for developing an electron beam and focusing'it upon the screen. A sweep generator is connected to a first pair of deflectorsV for deflecting the electron beam across the screen in a predetermined ldirection. An electron multiplier is provided which includes a plurality of secondary emissive multiplying stages and an electron source for supplying electrons to the rst multiplying stage. Further means are provided for controlling the ow of electrons through the multiplier in accordance with an input signal. Finally, means are provided for coupling the output of the multiplier to a second pair vof deflectors forming part of the cathode ray tube. Thus, the electron beam of the cathode ray tube is deflected across the screen to trace a pattern which is representative of the input signal and of its average value.

In accordance with a further feature of the invention the electron multiplier which includes a plurality of secondary emissive multiplying stages is associated with means for collecting the electrons from the last multiplying stage. Means are provided for coupling the electron collecting means and the last multiplier stage toa pair of deflectors to provide a push-pull connection. Hence, the pair of deflectors generates a symmetrical electronv deecting field which` prevents defocusing of the electron beam of the cathode ray tube.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawing, and its scope will be pointed ourl in the appended claims.

In the accompanying drawing:

Fig. 1 is a circuit diagram of a cathode ray oscilloscope and an associated electron multiplier embodying the present invention;

Fig. 2 is a curve representing a saw-tooth voltage wave referred to in explaining the operation of the invention; and

Fig. 3 is a circuit diagram similar to Fig. 1 and embodying a modification of the invention.

Referring now more particularly to Fig. 1 of the drawing there is provided a cathode ray oscilloscope l having an evacuated envelope 2 and an electron gun 3 disposed therein. Electron gun 3 comprises cathode 4, which may be indirectly heated as shown, control grid 5, first anode 6 and second anode 1. Electron gun 3 serves for developing an electron beam, directing and focusing it upon luminescent screen 8, usually referred to as a fluorescent screen and arranged on the inner surface of envelope 2 opposite gun 3. A pair of deecting plates 9, IIJ is provided for deflecting the electron beam across screen 8 in accordance' with an input signal. A second pair of deecting plates Il, l I is provided in envelope 2 and arranged at right angles with respect to plates' 9, i8.

' input terminals 4I.

For the purpose f deflecting the electron beam periodically across screen 8 deecting plates I I are connected to sweep generator I2.

Electron multiplier I is provided for amplifying an input signal which is then connected across deflecting plates 9, I0 for deflecting the electron beam at right angles to the periodical deflection of the beam effected by sweep generator` I2 and dei'lecting plates Il. Electron multiplier I5 comprises cathode I6, which may be indirectly heated as shown, and control grid I1 for controlling the number of electrons directed into rst multiplier stage I8. Electron multiplier I5 comprises further multiplier stages 29, 2|, 22, 23 and 24 and electron collector 25.

For the purpose of supplying operating potentials to the electrodes of cathode ray oscilloscope I as well as to the multiplier stages of electron multiplier I5 there is provided a common source such, for example, as battery 26 connected across voltage divider 21 and having its negative terminal grounded. Leads 28 and 3i! connect catho'de 4 of oscilloscope I and cathode I6 of multiplier I5, respectively, to a tap on potentiometer 21 to keep them at a potential that is slightly positive against ground. Grid 5 of oscilloscope I is connected to ground as shown, while grid I1 of multiplier I5 is connected through lead 3I and resistor 32 to potentiometer 21 for keeping it at a potential that is negative against that of cathode I6. Multiplier stages I8, 2B, 2I, 22, 23 and 24 are connected to potentiometer 21 in such a manner that each multiplier stage is kept at a higher positive potential than the preceding stage.

First anode 6 of oscilloscope I is connected to potentiometer 21 through lead 33 and is maintained at a potential which is positive against cathode 4. Second anode 1 is kept at a potential which may be considerably more positive than that of anode 6 by means of lead 34 connected to potentiometer 21. Leads 35 connecting deflecting plates II to sweep generator I2 are shunted by resistor 36 having a center tap connected to lead 34. Lower deflecting plate 9 is also connected to lead 34, while upper delecting plate ID is connected throughlead 31 to electron collector 25. Electron collector 25 is supplied with positive potential through leads 34, 38 and load resistor 40 which may be adjustable as shown. The input signal is applied across terminals 4 I, 4I, one being connected to ground and the other one to lead 3I connected to control grid I1.

The operation of oscilloscope I is conventional and, therefore, n0 detailed explanation is necessary here. The electron beam developed by gun 3 and focused on screen 8 is deiiected in two directions at right angles to each other in accordance with the signal applied to deflecting plates 9, I0 and in accordance with periodically recurring voltages developed by sweep generator I2 to provide a time base for the input signal.

Cathode I6 of electron multiplier` I5 serves as an electron source, and the primary electrons provided thereby are attracted by rst multiplier stage I8 where they liberate secondary electrons which in turn impinge upon multiplier stage 20. In this manner the primary electron now is multiplied in successive multiplier stages and finally collected by electron collector 25. The number of primary electrons impinging upon rst multiplier stage I8 is controlled by control grid I1 in accordance with the input signal connected across Electron multiplier I5 amplies the input signal including any direct current component or the average value thereof.

Voltage variations representative of the ampliiied input signal are developed across load resistor 40 and, thus, the voltage supplied to deecting plates 9, I0 varies in accordance with the input signal to effect a corresponding deflection of the electron beam. In this manner a pattern is traced on screen 8 with the frequency of sweep generator I2 providing a time base to give a visual indication representative of the amplie'd signal. It should be noted that deflecting plates 9, I0 and Il, II have the same mean potential as second anode 1, as will be seen from an inspection of the drawing.

supposing the input signal is a saw-tooth Voltage wave such as illustrated in Figure 2 at 42. When an oscilloscope with a conventional amplifier is used for visuallyreproducing voltage Wave 42, it is not possible to distinguish whether the zero or reference potential is represented by dotted line 43 or by full line 44. However, since the oscilloscope amplier of the invention will pass the average value of the input signal it is now possible to distinguish Whether the zero potential of voltage wave 42 is at 43 or at 44,

Referring now to Fig. 3 in which like components are designated by the same reference numerals as were use-d in Fig. 1, it will be seen that cathode ray oscilloscope I and multiplier I5 are identical with the structure shown in Fig. l. The main difference between the circuit of Fig. 3 and the circuit of Fig.' 1 is that deiiecting plates 9, I0 are now connected in push-pull fashion across electron collector 25 and the last electron multiplier stage 24. To this end multiplier stage 24 is connected to a tap of potentiometer 21 through lead 45 and load resistor 46. Deflecting plate 9 is connected to a variable tap of resistor 46 through lead 41 and battery 48 having its positive terminal connected to deecting plate 9. Electron collector 25 is maintained at a potential that is positive with respect to that of multiplier stage 24 through lead 50 and load resistor 5I. Deiiecting plate I0 is connected through lead 52 to a variable tap of load resistor 5I and, thus, to electron collector-25. Shunt resistor 36, connected across leads 35, is connected through a center tap to second anode 1 in the same manner as explained in connection with Eig. 1.

The signal polarity obtained from the electron collector of a multiplier is opposite from that obtained from the last stage of the multiplier. This is so because the last multiplier stage is an electron source, while the collector is an electron sink. Thus, by connecting deflecting plates 9 and I Il to multiplier stage 24 and electron collector 25, respectively, a push-pull connection is obtained. Hence, the lines of force generated by the electric field produced by the signal connected to deflecting plates 9 and I0 are symmetrical, and the symmetrical deecting field prevents defocusing of the electron beam. Battery 48 is provided for maintaining both deflecting plates 9 and II] at the same mean potential, which is that supplied by lead 50 connected to potentiometer 21 and to second anode 1. The electron beam may be cenr'to each other.

l placed by deect-ing #to aeiect deiiection of the electron beam in two directions at right angles Oscilloscope "I mayalso be rused with two different input signals Whiehwmay -be connected vto deflectin-g plates vil, "Hl and Il, I l, in which case both input signals may be amplified .by electron multipliers. Inthis case sweep genvmbrainer 12 can-'be dispensed'with. It Wllfalsoibe Vobvious that anytype ofvoltagecontrolledfelectron `multipliermay be used "for A`amplifyingthe input signal connected to deflecting plates 9, lil.

While there has been described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modiiications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. The combination of a cathode ray tube comprising a target, means for developing an electron beam of substantially constant intensity and focusing it upon said target, a pair of deiiectors for deflecting said beam, an electron multiplier including a plurality of secondary emissive multiplying stages, an electron source for supplying electrons to the rst of said multiplying stages, means for controlling the flow of electrons through said multiplier in accordance with an input signal, and means for coupling the output of said multiplier to said pair of deiiectors, thereby to obtain an indication representative of said input signal and of its average value.

2. The combination of a cathode ray tube comprising a screen, an electron gun for developing an electron beam of substantially constant intensity and focusing it upon said screen, a first pair of deiiectors, a sweep generator connected to said iirst pair of deflectors for deecting said electron beam across said screen in a predetermined direction, a second pair of defiectors for deecting said beam, an electron multiplier including a plurality of secondary emissive multiplying stages, an electron source for supplying electrons to the rst of said multiplying stages, means for controlling the iiow of electrons through said multiplier in accordance with an input signal, and means for coupling the output of said multiplier to said second pair of deflectors, thereby to produce a visual indication representative of said input signal and of its average value.

3. The combination of a cathode ray tube comprising a screen, an electron gun for developing an electron beam of substantially constant intensity and focusing it upon said screen, a pair of deectors for deflecting said beam, an electron multiplier including a plurality of secondary emissive multiplying stages, an electron source for supplying electrons to the first of said multiplying stages, means for controlling the ow of electrons through said multiplying stages in accordance with an input signal, means for collecting the electrons from the last one of said multiplying stages, and means for coupling said collecting means to said pair of deilectors, thereby to obtain an indication representative of said input signal and of its average value,

4. The combination of a cathode ray tube comprising a luminescent screen, an electron gun for developing an electron beam of substantially constant intensity and focusing it upon said screen, a, first pair of deectors, a sweep generator connected to said rst pair of defiectors for deflectfsaaiclrelectronibearn -across said screen vltr-aupredeterminedidirection,..a second pair of delectors f-lor rdeilecting ,saidl-beam, an electron multiplier including .a plurality of Asecondary ,emissive 3 multiplying stages, means for ksupplying operating voltages `:to stages, an Velectron source 'for Asuppl'yfingfelectrons tothe-rst of said multiplying wstages, .means *for controlling the flow of elec- :ftronsfthroughsaid multiplier in accordance with .anLinputsignaLz mea-ns'for collecting the electrons from the last one of said multiplyingstageaand means forcouplingvsaid collecting means to said second pair of deflectors, thereby to trace a pattern on said screen representative of said input Asignal and of its average value.

5. The combination of a cathode ray tube comprising a screen, an electron gun for developing an electron beam and focusing it upon said screen, a pair of deflectors for deecting said beam, an electron multiplier including a plurality of secondary emissive multiplying stages, means for supplying progressively increasing operating voltages to said stages, an electron source for supplying electrons to the rst of said multiplying stages, means for controlling the iiow of electrons through said multiplier in accordance with an input signal, means for collecting the electrons from the last one of said multiplying stages, and means for coupling said collecting means and said last multiplier stage to said deiiectors, thereby to obtain an indication representative of said input signal and of its average value.

6. The combination of a cathode ray tube comprising a luminescent screen, an electron gun for developing an electron beam and focusing it upon said screen, a first pair of deiiectors, a sweep generator connected to said first pair of deilectors for deiiecting said electron beam across said screen in a predetermined direction, a second pair of deflectors for deecting said beam, an electron multiplier including a plurality of secondary emissive multiplying stages, means for supplying progressively increasing operating voltages to said stages, an electron source for supplying electrons to the iirst of said multiplying stages, means for controlling the iioW of electrons through said multiplier in accordance with an input signal, means for collecting the electrons from the last one of said multiplying stages, means for coupling said collecting means and said last multiplier stage individually to each one of said second pair of deflectors, and means for adjusting the normal and undeflected position of said electron beam on said screen, thereby to trace a pattern on said screen representative of said input signal and of its average value.

7. The method of producing a visual indication of an input signal on the target of a cathode ray tube, said method comprising developing an electron beam and focusing it on said target, generating a flow of electrons, multiplying said eleotron flow, controlling the intensity of said electron flow in accordance with said input signal, and deflecting said electron beam across said target in accordance with said multiplied electron iiow representative of the instantaneous and average values ofsaid input signal.

8. The method of producing a visual indication of an input signal on the luminescent screen of a cathode ray tube, said method comprising developing an electron beam and focusing it on said screen, deecting said electron beam periodically across said screen in a predetermined direction, generating a flow of electrons, multiplying said 7 8 electron ow by secondary electron emission, controlling the intensity of said electron flow in ac- REFERENCES CITED cordance with said input signal, collecting the The following references are of record in the multiplied electrons, deriving an output signal me 0f this patenti from the collected electron flow representative of 5 UNITED STATES PATENTS said input signal and of its average value, and delecting said electron beam in a direction sub- Number Name Date stantiauy at right angles to said predetermined 2157,529 DreWell et al May 9. 1939 direction across said screen in accordance with 2,131,720 Barthelemy s NOV. 28, 1939 said output signal, thereby to trace a pattern on 10 2,372,450 Rajchman et al. MaI'- 27J 1945 said screen.

HANS W. G. SALINGER.

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