US3502937A - Electron beam image intensity control - Google Patents

Description

March 24, 1970 w. F. BADER ET AL.

ELECTRON BEAM IMAGE I NTENSITY CONTROL Filed Nov. 12, 1968 3 Sheets-Shedl 1 March 24, 1970 w. F, BADER ET AL 3,502,937

ELECTRON BEAM IMAGE INTENSITY CONTROL Filed Nov. 12, 1968 5 Sheets-Sheet 2 March 24, 1970 w. F. BADER ETAI- 3,502,937

ELECTRON BEAM IMAGE INTENSITY CONTROL Filed Nov. 12, 1968 3 Sheets-Sheer:l 5

Mfr of (HA/V55 f (5) United States Patent O 3,502,937 ELECTRON BEAM IMAGE INTENSITY CONTROL William F. Bader, Maplewood, and Arney Landy, Jr., Roseville, Minn., and Marvin J. Schmitz, North Hudson, Wis., assignors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Continuation-impart of application Ser. No. 676,860, Oct. 20, 1967. This application Nov. 12, 1968, Ser. No. 774,625

Int. Cl. H01j 29/74 U.S. Cl. 315-22 10 Claims ABSTRACT OF THE DISCLOSURE The intensity of an image produced by a pulsed electron beam being deflected in response to an input signal is controlled by varying the duration of the electron beam pulses in proportional response to the rate of change of the input signal amplitude. The electron beam pulse duration may be accordingly varied in order to provide an approximately uniform image intensity.

CROSS-REFERENCE This is a continuation-in-part of our copending application Ser. No. 676,860 for Electrocardiographic Recording System, led Oct. 20, 1967, now Patent No 3,434,151.

BACKGROUND OF THE INVENTION The present invention is related to means for controlling the intensity of an image produced by an electron beam being deflected at a variable rate in response to an input signal.

Image intensity may be dened as the effective brilliance of the time varying illumination sensed at a point distant from the source of illumination within a given time interval. It is the brilliance with which an image appears to the human eye, to photosensitive iilm, or to other such sensing means during a given time interval within which the image is exposed. The image intensity of a given portion of a waveform displayed on a cathode -ray tube is determined by the luminous intensity, the duration, and the cross-sectional area of the phosphor glow on the screen within that given waveform portion.

A problem frequently encountered in displaying Waveorms on a cathode ray tube is that of the variation of the image intensity associated with variations in the slope, i.e. the rate of change of the displayed waveform. For example, when displaying a Waveform having as a portion thereof a relatively high slope, the slope portion appears to be considerably dimmer than the remainder of the waveform. In the high slope portion, the image intensity is reduced because a larger area of phosphor must be scanned in a given time interval when there is a high rate of waveform change in contrast to a smaller area of phosphor which is scanned in the same given time interval when there is a lower rate of waveform change. This problem is compounded in applications wherein the waveform image is photographed on microlm. In some situations, the image i11- tensity varies over such a range that proper exposure for the brighter portion of the image display results in underexposure for the duller portions. Increasing the image intensity of the duller portion to give suicient exposure often results in overexposure of the brighter portion and may also result in burning the phosphor of the cathode ray tube.

In the prior art, image intensity has been controlled by either varying the cross-sectional area with which the electron beam impinges the electron sensitive medium or by varying the luminous intensity which is related to the energy with Iwhich the electrons impinge the electron sensitive medium.

In accordance with the prior art, cross-sectional area may be varied by varying the electron Ibeam current density. In an image observed on a cathore ray tube, the image source is within an area containing a multiple of phosphor particles. Thus, the greater the number of particles immediate to the image source which are illuminated, the greater the image intensity sensed from the image source. However, illuminating a greater number of particles by increasing the cross-sectional area of the electron beam results in an image of lower resolution. Thus, the prior art method of controlling image intensity by varying the cross-sectional area of electron beam impingement has the inherent disadvantage of providing a Waveform of varying resolution.

Also in accordance with the prior art, image intensity may be controlled, as stated above, by varying the luminous intensity which is related to the energy with which the electrons impinge the electron sensitive medium by varying the potential applied to accelerate the electron beam or `by varying the current density of the electron beam. One disadvantage of the acceleration potential control method is that acceleration potential variations change the deflection sensitivity of the electron beam. Also, such method requires high magnitude acceleration potential variations. The current density method of varying luminous intensity requires a focusing step to overcome the already discussed resolution problem incident to the current density method of varying cross-sectional area. Also as phosphor approaches its combustion point, its efliciency for increasing its luminous intensity in response to an increasing impinging electron current density recreases.

SUMMARY OF THE INVENTION The present invention provides for controlling the intensity of an image produced by a deected electron beam impinging an electron sensitive medium in pulses by varying the duration of the pulses of electron beam impingement upon the electron sensitive medium in proportional response to the sensed rate of change of the electron beam deilection.

Briefly, the invention comprises means which senses the rate of change of the amplitude of the input signal to which beam deection is responsive, and means which varies the duration of pulsed electron beam impingements upon the electron sensitive medium in proportional response to the magnitude of the sensed rate of change. This duration may be varied between minimum and maximum durations in proportion to the sensed rate of change in order to maintain an approximately uniform image intensity. The proportional relationship may ybe linear or non-linear.

In a system wherein a pulsed electron beam is deflected in response to a multiplexed plurality of input signals, the duration of each pulse is synchronized to be in response to the rate of change of the amplitude of the input signal deecting that pulse.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is a schematic diagram in block form showing a preferred embodiment of the present invention connected to a cathode ray tube circuit.

FIGURE 2 is a schematic diagram in block form showing a modified specific preferred embodiment of the present invention in combination with a circuit for time share multiplexing a plurality of input signals;

FIGURE 3 is a schematic diagram of a typical differentiator circuit which may be used in practicing the present invention shown in FIGURES 1 and 2;

FIGURE 4 is a schematic diagram of a typical intensity modulator circuit which may be used in practicing the present invention shown in FIGURES l and 2;

FIGURE 5 is a graphical representation of the Waveforms of the various clocked control signals, the rate of change magnitude signal, and the modulated signal within the intensity modulator circuit of FIGURE 4 and also of the timing signal at the critical sensing junction within this circuit; and

FIGURE 6 is a schematic diagram of a typical unblanking amplifier circuit which may be used in practicing the present invention shown in FIGURES l and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the preferred embodiment, the input voltage signal to which electron beam deflection is responsive is fed through a diferentiator circuit to obtain a signal proportional to the slope or the rate of change of the waveform. The differentiated or rate of change signal is fed to an intensity modulator circuit which first recties the rate of change signal to provide a signal of uniform polarity. The intensity modulator circuit, which also receives signals from a clock, produces a modulated signal having pulse durations proportionally responsive to the magnitude of the rate of change. The modulated signal is fed to an unblanking amplifier circuit which in response to the modulated signal applies a potential to the grid of the electron gun to control the on-time or duration of the electron beam pulses.

Referring first to FIGURE 1, a waveform is displayed on the face of a cathode ray tube 10 in response to an input signal on line 12 being supplied through a vertical deflection amplifier circuit 14 to the vertical deflection portion of the cathode ray tube circuit 16. The sweep signal for the waveform is supplied to the horizontal portion of the cathode ray tube circuit 16 from a sweep generator 18. An unblanking amplifier 20 is connected to the cathode ray tube circuit 16 to control the on-time or duration of the electron beam pulses by applying a control signal to the grid of the cathode ray tube 10 for intervals responsive to the modulated signal received from the intensity modulator circuit 22. The intensity modulator circuit 22 produces a series of pulses at periodically clocked intervals and of varying duration in response to a differentiated or rate of change signal received from a differentiator circuit 24 which indicates the time rate of change of the amplitude of the input signal on line 12. The period of the clocked intervals is in response to clocking signals from clock 26.

Retracing the operation of the electron beam image intensity control circuit of this invention, the input signal on line 12, which controls the vertical deflection of the electron beam produced image, is fed into a differentiator circuit 24, which indicates the rate of change of the amplitude of the input signal at line 28. The rate of change signal on line 28 is then fed into an intensity modulator circuit 22, which also receives clocked control signals from clock 26. The intensity modulator circuit 22 produces a modulated signal on line 30. The modulated signal is made up of a series of periodically occurring pulses of varying duration. The period between the beginning of each pulse is in response to the clocked control signals from clock 26. The duration of each pulse is in response to the magnitude of the rate of change signal received on line 28 from diferentiator circuit 24. The modulated signal is fed into an unblanking amplifier 20 which produces a control signal on line 32 to the grid of the cathode ray tube 10. The magnitude of the control signal is predetermined to be suflicient to turn on the electron gun. The duration of the control signal is in response to the duration of the pulses of the modulated signal received on line 30. Thus, the electron gun of the cathode ray tube 10 is turned on during each periodic interval only for a duration responsive to the rate of change of the input signal which deflects the electron beam during that periodic interval.

The present invention is, of course, usable with any apparatus in which an image is produced by deflecting an electron beam and not merely with a cathode ray tube. For example, the invention could also be used with an electron beam recorder.

The present invention is especially suitable for use in combination with a circuit which provides an electron beam deflection signal in response to a multiplexed plurality of input signals. An embodiment of such a combination is shown in FIGURE 2 and is described in some detail in our copending application cited above wherein a multiplex system for recording simultaneous electrocardiographic signals is set forth.

When the electron gun responds to a multiplexedly produced deflection signal, it is turned on for distinct intervals for each segment of the multiplexed signal. These distinct pulses are readily controlled by means of an unblanking amplifier which controls the grid potential to periodically turn the electron gun on and off to provide blank intervals in the image during the times in which the multiplexing circuitry is being switched between different segments of the disparate input signals. The present invention provides synchronized image intcnsity control for the multiplexed image producing system by controlling the on-time or duration of the electron beam pulse for each multiplexedly produced segment in accordance with the sensed rate of change of the amplitude of the input signal which deects the electron beam for the corresponding segment.

In FIGURE 2, the waveform displayed on the face of cathode ray tube 10 is in response to a plurality of input signals on lines 34 which are multiplexed by signal mu1tiplexer 36, summed in summing amplifier 38 with reference signals from reference multiplexer 40 to produce a composite time division output signal on line 42 which is supplied through vertical deflection amplifier circuit 14 to the vertical deflection portion of the cathode ray tube circuit 16. The sweep signal for the waveform is supplied to the horizontal portion of the cathode ray tube circuit 16 from a sweep generator 18. The on-time or duration of the electron beam is controlled through unblanking amplifier 20. The signals which control the unblanking amplifier 20 are produced in the following manner. The rate of change of the amplitude of each of the plurality of input signals on lines 34 are sensed by a multichannel differentiator circuit 44 which produces a plurality of rate of change signals on lines 46. The plurality of rate of change signals are multiplexed by intensity multiplexer circuit 48 and fed to intensity modulator circuit 22 on line 50. The intensity modulator circuit 22 also receives clocked control signals from multiphase clock 52. The multiphase clock 52 produces a plurality of disparate clocked control signals having a predetermined frequency but different preselected phases. The clocked control signals are used for controlling the operation of the signal multiplexer 36, the reference multiplexer 40, the intensity multiplexer circuit 48 and the intensity modulator circuit 22 and for synchronizing their operations with each other. The intensity modulator circuit 22 produces a modulated signal on line 30, which signal is made up of a series of periodically occurring pulses of varying duration. The period between the beginning of each pulse is in response to the clocking signals from multiphase clock 52. The duration of each pulse is -responsive to the magnitude of the rate of change signal segment received on line 50 during the interval corresponding to that particular rate of change signal segment. The modulated signal is fed on line 30 into unblanking amplifier 20. The modulated signal received on line 30 by the unblanking amplifier 20 determines the duration over which a control signal is fed over line 32 to the grid of the cathode ray tube 10 for controlling the on-time or duration of the electron gun. The magnitude of the control signal 011 line 32 is predetermined to be sufficient to turn on the electron gun. Thus, the electron gun of the cathode ray tube is turned on during each interval corresponding to each multiplexed signal segment only for a duration responsive to the rate of change of the amplitude of the particular input signal which is deecting the electron beam during that corresponding interval.

FIGURE 3 illustrates a typical differentiator circuit which may be used in practicing the present invention. The input signal on line 12, which is directed to the vertical deection amplifier circuit 14 on line 54, is fed into the differentiator comprising capacitor 56 and resistor 58 through an emitter follower circuit comprising NPN transistor 60| and resistor 62. The bias values of |5 .6 volts at the collector of transistor 60 and of 5.6 volts at the open terminal of resistor 62 are the bias values used in one typical embodiment of this invention. Other bias values used in a compatible typical embodiment of this invention are indicated in FIGURES 3-6 Without further comment. Identitication of and component values for the various circuit elements shown in the circuits of FIGURES 3', 4, and 6 are given hereinafter following the description of FIGURE 6. The emitter-follower circuit (60 and 62) provides a low impedance source to the diiferentiator (56 and 58) and serves to isolate the diiferentiator (56 and 58) from lines 12 and 54 so that the input signal appearing on lines 12 and 54 will be unaffected Iby the operation of differentiator (56 and 58) Resistor 64 limits the current through capacitor 56. Operational amplifier 66 maintains junction 68 of diferentiator (56 and 58) at near zero potential in order to provide true differentiation. Capacitors 70' and 72 are selected to predetermine the bandwidth of frequency response of operational amplifier 66. The output of the differentiator circuit appears on line 28.

FIGURE 4 illustrates a typical intensity modulator circuit Which may be used in practicing the present invention. The differentiated signal which represents the rate of change of the amplitude of the input signal is fed on line 28 through an isolation circuit comprising NPN transistor 74, variable impedance compensation network 76, and resistor 78 to and through coupling capacitor 80 to full wave rectifier 82. The variable impedance compensation network 76 minimizes the distortion at junction 84 of the signal on line 28 due to the effect of coupling capacitor 80. Isolation circuit (74,76, 78) also incidentally acts as an analog inverter reversing the polarity of the signal at collector junction 84 from that received on line 28. Isolation circuit (74, 76, 78) is provided for the purpose of isolating coupling capacitor `80 from line 28 so that the differentiated or rate of change signal will be unaected by the ope-ration of the modulator circuit of FIGURE 4. Resistors 86 and 88 are biasing resistors for NPN transistor 74. Resistors 90, 92, 94, and 96 and capacitor 98 in combination with NPN transistor 99 of variable impedance compensation network 76 are selected to be so responsive to frequency 'changes that the signal at the collector junction 84 responds at approximately the same rate as the differentiated or rate of change signal on line 28, although it is of reverse polarity. Rectifier 82, comprising NPN transistors 100 and 102, PNP transistors 104 and 106, and biasing resistors 108-118, rectiiies the rate of change signal at emitte-r junction 120 and provides on line 122 a rate of change magnitude signal representative of the magnitude of the dilferentiated or rate of change signal.

When a positive going signal is present at emitter junction 120, transistor 104 conducts the positive going signal to the base ,of transistor 102 which causes transistor 102 to conduct a negative going signal to the base of transistor 106 which causes transistor 106 to conduct to line 122 a positive signal proportional to the magnitude of the signal at emitter junction 120.

When a negative going signal is present at emitter junction 120, transistor 100 conducts the negative going signal to the base of transistor 106 which causes transistor 106 to conduct to line 122 a positive signal proportional to the magnitude of the signal at emitter junction 120. When 6 there is no signal at emitter junction 120, transistors 106 do not conduct and no signal is conducted to line 122 thereby indicating a zero rate of change of the amplitude of the input signal on line 12.

The rate of change magnitude signal on line 122 in combination with 30 kHz. clocked control signals received on lines 124, 126, and 128, from either clock 26 of FIG- URE 1 or multiphase clock 52 of FIGURE 2, produces a modulated signal on line 30. Clocked signals providing reset and set control are received on lines 126 and 128 respectively.

Because of propagation delay in the reset signal on line 126, a clocking signal is provided on line 124 to assure blanking during the intervals between segments in the multiplexing operation described with reference to FIGURE 2.

Gates 130 and 132 are connected to provide a resetset flip-Hop. Gate 134, binary inverters 136, 138, and and capacitor 142 are connected to provide a delay one-shot 143. Gates 130 and 132 deliver or maintain a PLUS pulse at their respective outputs when any one of their respective input terminals receive a ZERO pulse. Gate 134 delivers or maintains a ZERO pulse only when both of its input terminals receive PLUS pulses. Other circuit components include voltage dividing resistors 144 and 146, biasing resistor 148, modulation adjusting resistors and 152, diodes 154, 156, and 158, NPN transistors and 162, PNP transistor 164, binary inverter 166, and timing capacitor 168.

To explain the operation of this typical intensity modulator circuit, reference is made to FIGURE 5 which shows the waveforms of the rate of change magnitude signal on line 122, the clocking signal on line 124, the reset signal on line 126, the set signal on line 128, the modulated signal on line 30, and the timing signal at junction 170.

The amplitude of the modulated signal on line 30 is a relatively constant +5 volts and is representative of a PLUS control pulse. Zero volts amplitude is representative of a ZERO pulse. The leading edge of the modulated signal on line 30 occurs periodically at a frequency of 30 kHz. The duration of the modulated signal is dependent on the time it takes to build up a potential at timing junction across timing capacitor 168 of sufficient magnitude to overcome the positive bias provided at the gate of transistor 164 by the rate of change magnitude signal on line 122, so as to cause transistor 164 to conduct. Transistor 164 then conducts a positive going signal to the gate of transistor 162 which conducts a ZERO pulse to gate 132 which results in termination of the PLUS pulse on line 30.

A modulation cycle commences at time a with a new PLUS clocking pulse on line 124, a PLUS reset pulse on line 126 which begins to change to a ZERO pulse, and a continuing PLUS set pulse on line 128. This cornbination of control pulses produces either a new or a continuing ZERO pulse at junction 172 as well as on line 30. A ZERO pulse at junction 172 is led through binary inverter 166 to the base of transistor 160 causing transistor 160 to conduct a signal having a potential slightly less than the on-bias potential of transistor 164 to the emitter of transistor 164 thereby turning olf transistor 164, which in turn turns olf transistor 162 which removes the ZERO pulse on line 174 to gate 132.

The delay one-shot 143 produces a ZERO pulse of sufficient duration to maintain a ZERO pulse on line 175 until after the propagation delayed reset signal on line 126 becomes a ZERO pulse, at approximately 0.5 microsecond after time a.

At time b, the reset signal on line 126 becomes a PLUS pulse and the set signal on line 128 becomes a ZERO pulse. This combination of pulses provides a PLUS pulse at junction 172 and on line 30. The PLUS pulse at junction 172 is fed through binary inverter 166 to turn off transistor 160 thereby enabling a potential to build up across timing capacitor 168. When the potential at timing junction 170 is greater than the potential at the base of transistor 164 (which latter potential is proportional to the rate of change magnitude signal on line 122) by an amount sutiicient to turn on transistor 164 through diode 154, transistor 164 conducts, thereby causing transistor 162 to conduct a ZERO pulse on line 174 to gate 132, which results in a PLUS pulse from gate 132.

At time c, the set signal on line 128 becomes a PLUS pulse. Thereafter, gate 130 will provide a PLUS pulse at junction 172 and line 30 only so long as gate 132 continues to deliver a ZERO pulse to gate 130. Thus, when at any time after time c there is a ZERO pulse on line 174, gate 130 will cease to deliver a PLUS pulse to junction 172 and line 30. If the potential at timing junction 170 has not built up sufficiently to result in the delivery of a ZERO pulse on line 174 before the beginning of the next modulation cycle, the clocking pulse on line 124 at time a will operate to provide a ZERO pulse at junction 172 and line 30 at time a.

The interval between times b and c is selected to provide for the modulated pulse having a minimum duration of 2 to 4 microseconds in the event the rate of change magnitude is zero, so that an image produced by a horizontally swept but nonvertically deflected electron beam will have a minimum intensity. The propagation delayed reset signal on line 126 provides a ZERO pulse on line 17S before the ZERO pulse provided on line 175 by the delay one-shot is completed and thereby assures blanking during the interval a to b between segments in the multiplexing application described with reference to FIGURE 2.

Diode 154 protects transistor 164 from reverse bias conduction. inasmuch as the voltage drop across diode 154 and across the emitter to base of transistor 164 is about 0.7 volt for each, two diodes 156 and 158 are connected between transistor 160 and zero volt potential to maintain a minimum potential of 1.4 volts at timing junction 170 so that the time for charging capacitor 168 to sufficiently initiate conduction of transistor 164 will be proportional to the potential at the base of transistor 164. To provide a linear proportionality, resistors 150 and 152 are selected so that capacitor 168 is charged during the relatively linear portion of its exponential charging curve. By varying these resistors, a non-linear relationship could also be obtained whenever desired.

In FIGURE 5 there is shown representations of modulated signals having varying durations dependent upon the rate of change magnitude signal for situations wherein the rate of change magnitude signal is (l) zero or less than 1.4 volts, (2) greater than 1.4 volts but not so great that transistor 164 does not conduct before completion of the modulation cycle at time a, and (3) so much greater than 1.4 volts that transistor 164 does not conduct prior to completion of the modulation cycle at time a.

In sequence (l), the rate of change magnitude signal is zero volts. Thus, transistor 164 conducts and causes a ZERO pulse on line 174 from immediately following time b. Nevertheless the potential at timing signal junction 170 meaninglessly builds up until time c when the pulse on line 30 becomes zero due to the set signal on line 128 becoming a PLUS pulse. The duration of the modulated signal on line 30 when the rate of change magnitude signal is zero volts or less than 1.4 volts lasts from time b to time c and is solely dependent on the predetermined duration of the ZERO pulse of the set signal on line 128.

In sequence (2), the rate of change magnitude signal is quantity e, which is higher than 1.4 volts. The timing signal must reach 1.4+e volts at junction 170 in order for transistor 164 to conduct and thereby causes a ZERO pulse on line 174. Inasmuch as the timing signal reaches a potential suicient to cause transistor 164 to conduct at time d which is after time c, when the set signal on line 128 becomes a PLUS pulse, the modulated signal on line 30 becomes a ZERO pulse at time d. The modulated signal PLUS pulse lasts from time b to time d and is dependent on the potential of the rate of change magnitude signal on line 122.

In sequence (3), the rate of change magnitude rises at such a rate to quantity f which is so much higher than 1.4 volts that the timing signal cannot reach a potential sufficient to cause transistor 164 to conduct prior to time a when the clocking signal on line 124 causes the modu lated signal on line 30 to become a ZERO pulse, which results in turning on transistor so as to return the po tential of the timing signal at junction to 1.4 volts. The modulated signal PLUS pulse thus lasts from time b to time a and is responsive to the potential of the rate of change magnitude signal on line 122.

The interval between times b and a is selected to provide for the modulated pulse having a maximum duration of approximately 30 microseconds. It is therefore seen that the duration of each electron beam pulse is controlled to vary between prescribed minimum and maximum durations in proportion to the rate of change of the input signal amplitude.

Referring to FIGURE 6, a typical unblanking amplifier which may be used with the present invention will be described. The modulated signal is received on line 30 and led through binary inverter 176 and lead network comprising capacitor 178 and resistors 180 and 182 to NPN transistor 184. A positive going signal at the base of transistor 184 turns on transistor 184 and in turn turns off NPN transistor 186 which results in the removal of the 100 volt control signal from line 32. Line 32 is connected to the grid of the electron gun of cathode ray tube 10. Thus, removal of the control signal from line 32 blanks cathode ray tube 10.

Therefore, a PLUS pulse modulating signal on line 30 being inverted by binary inverter 176 to become a ZERO pulse on line 188 causes the cathode ray tube 10 to be unblanked, whereas a ZERO pulse modulation signal on line 30 causes the cathode ray tube 10 to be blanked.

Capacitor 190 is an integrating capacitor which damps the switching of the binary inverter 176. Resistor 192 provides a lower input impedance on line 188. Lead network comprising capacitor 178 and resistors 180 and 182 is included to reduce the switching time of the unblanking amplifier in response to the modulated signal on line 30. Resistors 194 and 196 are biasing resistors for transistor 186.

It is to be understood that the differentiator circuit, intensity modulation circuit, and unblanking amplifier circuit described herein With reference to FIGURES 3, 4, and 6 are merely typical circuits of their particular species which may be used in practicing the present invention, and that various other circuits of their species may also be used in practicing the present invention by combining them in accordance with the teachings of the present invention.

The present invention can, in fact, be practiced without the inclusion of a typical diiferentiator circuit. For example, a sample-hold method of sensing the rate of change of input signal amplitude could be utilized. Means for separately sampling the magnitude of the input signal at successive measured instants and measuring the difference in magnitudes provide `a measure of the rate of change during the measured interval between instants. First sampling means sense the magnitude of the input signal at time a and transfer the magnitude signal to holding means which delay the magnitude signal to time b. At time b, second sampling means sense the magnitude of the input signal. The signals from the holding means and the second sampling means are fed to a differential amplifier which indicates the change in the input signal from time a to time b and thereby provides the slope or rate of change of input signal amplitude. The interval between times a and b may be in nanoseconds.

The intensity multiplexer circuit 48 may be of the same type of multiplexer used as signal multiplexer 36 and reference multiplexer 40 as described in our hereinbefore referred to copending application and its operation is synchronized with theirs by the signals from the multiphase clock 52.

The identification of and component values for the various elements shown in FIGURES 3, 4, and 6 are as follows:

Transistors 60-2N4124 106-2N4126 74-2N4124 160-2N4124 99-2N4124 162-2N4124 100-2N4124 164-2N4126 1022N4124 184-2N3499 104-2N4126 186-TRS4014LP 1 Rectifiers 154-1N9 14 156-1N914 8-1N9 14 Operational amplifiers:

66-Motorola Model MC1430 Gates:

130-DTL946 132-DTL962 134-DTL946 Binary inverters:

136-DTL946 166-DTL946 138-DTL946 176-DTL962 140-DTL946- Resistors:

58-33KQ 114-3.6KQ 62-1KQ 116-3.6KS2 64-3.3KQ 118-10KQ 7 8-3.6\KS2 144-1KS2 86-3.3KQ 14S-3.3K@ 88-2.4KS2 14S-4.7KQ 90'-47KS2 1504.7KQ 92-1800 152-10KS2 94-1KQ 180-4.7KQ 96-150KQ 182-1.5KQ 10S-3.6K9 192-1KQ 1103.3KQ 194-6\.8KQ 112-39KSZ 196-5K0 Capacitors:

56-.35pf. 142-470 pf. 70'-.005pf. 16S-.Olaf 72-820 pf. 17 8-100 pf. 80-120,uf. 190-120 pf. 98-100,u f.

In summary, a method and system for controlling the intensity of an image produced by a pulsed electron beam being deflected in response to an input signal has been described. The diiferentiator circuit 24 differentiates the input signal received on line 12 and applies a signal representative of the rate of change of the input signal amplitude to an intensity modulator circuit 22 on line 28. The intensity modulator circuit 22 is electrically connected to and controlled by clock 26. The intensity modulator circuit 22 is responsive to the rate of change signal for producing a modulated signal on line 30 which is of a duration proportionally responsive to the rate of change of the input signal amplitude as a function of time. The modulated signal is fed on line 30 to unblanking amplifier circuit which controls the duration or on-time of the electron beam in response to the duration of the modulated signal which is representative of the magnitude of the rate of change of input signal amplitude on line 28. Thus, the intensity of the image can be controlled to be substantially the same for both slow and fast rise times for deflection of the electron beam.

What is claimed is:

1. A method for controlling the intensity of an image produced by a pulsed electron beam being deflected in response to an input signal wherein the steps comprise sensing the rate of change of the input signal amplitude; and

controlling the durations of the electron beam pulses as a proportional function of the sensed rate of change of the input signal amplitude.

2. The method of claim 1 wherein the electron beam pulse durations are controlled in response to the rate of change of the input signal amplitude for maintaining an approximately uniform image intensity.

3. The method of claim 2 wherein the electron beam pulse duration is controlled between minimum and maximum finite durations in proportion to the rate of change of the input signal amplitude.

4. The method of claim 1 or 3 wherein the pulsed electron beam is deflected in response to a multiplexed plurality of input signals, a further step comprising synchronizing the duration of each electron beam pulse to be in response to the rate of change of the amplitude of the input signal deiiecting that pulse.

5. The method of claim 1 or 3 wherein the sensing step comprises differentiating the input signal.

6. The method of claim 1 or 3 wherein the controlling step is responsive to the sensed rate of change of input signal amplitude through a step comprising producing a modulated signal in response to the sensed rate of change of the input signal amplitude.

7. A circuit for controlling the intensity of an image produced by a pulse delectron beam deflected in response to an input signal, comprising means for sensing the rate of change of the input signal amplitude; and

means operatively coupled to the sensing means for controlling the durations of the electron 'beam pulses as a proportional function of the sensed rate of change of the input signal amplitude.

8. The circuit of claim 7 wherein the pulsed electron beam is deflected in response to a multiplexed plurality of input signals, further comprising means operatively coupled to the sensing means and to the control means for synchronizing the duration of each electron beam pulse to be in response to the rate of change of the amplitude of the input signal deflecting that pulse.

9. The circuit of claim 7 wherein the control means controls the electron beam pulse durations to maintain an approximately uniform image intensity.

10. The circuit of claim 7 or 9 wherein the control means is operatively coupled to the sensing means through a modulating means which provides a modulated signal to the control means in response to the sensed rate of change of the input signal amplitude.

References Cited UNITED STATES PATENTS 2,700,741 1/ 1955 Brown et al. 315-22 2,993,142 7/ 1961 Harvey 315-22 3,130,346 4/ 1964 Callick 315--22 RICHARD A. FARLEY, Primary Examiner T. H. TUBBESING, Assistant Examiner U.S. Cl. X.R. 315--30

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