US2900502A - Sawtooth voltage generator - Google Patents

Description

Aug. 18, 1959 R. L. KUEHN ETAL 2,900,502 SAWTOOTH VOLTAGE GENERATOR Filed May 21, 1956 C2 R3 R2 2 I Rudolph L. Kuehn Robert K. Seigle INVENTORS ATTORNEY and) SAWTOOTH VOLTAGE GENERATOR Rudolph L. Kuehn and Robert K. S eigle, Pasadena, Calif.,

assignors, by mesne assignments, to Hymac Corporation, Los Angeles, Calif., a corporation of California Application May 21, 1956, Serial No. 586,287 6 Claims. 01. 250-27 The present invention relates generally to sweep generators and more particularly to a sawtooth voltage generator capable of both synchronized astable and triggered monostable operation.

The internal sweep generator of an oscilloscope, for example, can be either astable (free-running) and synchrom'zed by various generated signals, or it can be monostable (one-shot) and be triggered by incoming signals. The latter mode of operation is highly desirable since it insures positive synchronization with little tendency to jitter and is exclusively used in the analysis of transient and pulse phenomena.

During the fly-back interval of an oscilloscope sweep cycle, the fluorescent electron beam spot produces a return trace on the cathode ray tube screen. This return trace does not contribute to the analysis of the waveform or pattern being examined but only serves to clutter the screen. It is desirable to blank out the return trace that exists prior to each retrace sweep.

It is an object of this invention to provide a sawtooth voltage generator which is capable of both recurrent, free-running operation and triggered monostable operation.

Another object of the invention is to provide a sawtooth voltage generator which can be easily synchro nized in recurrent (free-running) operation.

Another object of this invention is to provide a sweep generator for Oscilloscopes, for example, which provides blanking of the return trace.

A further object of this invention is to provide a sawtooth generator which is simple of construction and is readily useful as a sweep generator for oscilloscopes, for example.

The foregoing and other objects are preferably accomplished, briefly, by providing two electronic tubes connected to form a modified cathode coupled multivibrator having an input connection to one tube for accepting synchronizing and trigger signals, and a storage capacitor connected to the other tube for control of the latter tube and to provide an output signal therefrom. Another output signal is obtained from the latter tube to provide a suitable blanking signal for oscilloscopes, for example. Means connectable to the storage capacitor provide triggered monostable operation of the multivibrator.

The invention possesses other objects and features, some of which together with the foregoing, will'be set forth in the following description of a preferred embodiment of the invention, and the invention will be more fully understood by reference to the following accompanying drawings, in which: 7

Figure 1 is a schematic wiring diagram of a preferred embodiment of the invention.

Figure 2 is a drawing showing a series of three curves of the voltage waveforms which can be applied to and occur at different points of the circuit.

A preferred embodiment of the invention is shown in Figure 1 of the accompanying drawings. Two

ite States Patent electronic tubes V1 and V2 are connected to form a modified cathode coupled multivibrator. The tube V1 is preferably a pentode and V2 can be a triode as illustrated. In actual practice, these two tubes are usually combined in a single envelope and are readily available on the market as such.

The cathodes of V1 and V2 are connected together to ground through cathode resistor R1. The control grid and anode of V2 are respectively connected to a source B+ of positive potential through resistors R2 and R3. Similarly, the screen grid and anode of V1 are connected to this same source B+ through resistors R4 and R5, respectively. The control grid of V1 is connected to the anode of V2 through a resistor R6 and to ground through resistor R7. Likewise, the control grid of V2 is also connected to ground, but through a capacitor C1. The control grid of V2 can be connected to the anode of V1 by a small capacitor C2 to provide neutralization of high frequency components in the synchronizing waveform and thus prevent cross coupling to the sweep sawtooth.

A diode D having its cathode connected to another source +B1 of positive voltage can be connected by switch S to the control grid of V2 and capacitor C1 as shown. The anode of V2 is connected to a first output terminal 1, and a second output terminal 2 is obtained at the common junction of resistor R2 and capacitor C1. An input terminal 3 is connected to the screen grid of V1. Negative voltage impulses can be applied to this input circuit for synchronization or triggering of the generator.

Operation of the circuit can be described with reference to Figure 2 which illustrates the voltage waveforms e e and e that appear on terminals 1, 2 and 3, respectively. Curves 1a, 2a and 311 respectively depict the waveforms of e 2 and e;;. In recurrent or free-running operation, the switch S is open as shown, and V1 can be considered initially conducting because of a positive grid voltage across resistor R7. The accompanying cathode current produces a voltage drop across resistor R1 sufficient to bias V2 to cutoff. At the same time, capacitor C1 begins to charge toward B+ voltage through resistor R2. This is illustrated by the initial rising portion a of the center curve 2a of Figure 2. When this voltage across C1, which furnishes grid voltage to V2, reaches the proper point, corresponding to the conduction level of V2 as indicated by the broken line of curve 2a, V2 conducts.

The flow of V2 plate current through R3 produces a potential drop at terminal 1, and at the control grid of V1. R6 and R7 are so proportioned that this voltage drop at the grid cuts off V1. Conduction through V2 discharges the voltage across C1, as represented at b in the middle curve of Figure 2. The plate voltage at terminal 1 is low during the discharge interval of C1 (see curve 1a, Figure 2). When the voltage across C1 has dropped to a sufliciently low value such that the voltage on the grid of V1 due to plate voltage rise in V2 now permits V1 to conduct, and since the voltage across C1 is now also below the value for conduction through V2, the cycle has been completed. Conduction of V1 and cutofi of V2 will again allow capacitor C2 to start charging toward B-lvoltage through resistor R2, repeating the cycle. This recurrent operation will continue as long as the circuit is energized.

In oscilloscope work, for example, it usually is desirable to synchronize the sweep generator with an externally applied signal by means of a trigger impulse. A negative impulse voltage as shown in the lower curve 3a can be applied to terminal 3 and thence to the screen grid of V1 as a synchronizing signal and functions to cut off conduction in V1, and simultaneously lower the cathode potential of V2. Capacitor C1 has been charging toward B+ during the time that V1 was conducting, raising the grid potential of V2. This action, together with the drop in cathode potential of V2 causes V2 to conduct.

Plate current flow of V2 through its load resistor R3 produces a sharp voltage drop at the anode of V2 and terminal 1, as shown at c in curve 1a. This occurs at the time the negative trigger impulse is applied to V1. This sharp voltage drop is of course transmitted to the control grid of V1, cutting off V1. Since V1 is no longer conducting, the voltage drop across resistor R1 is smaller so that grid current flows in V2, discharging capacitor C1. the middle curve of Figure 2, and by the rising portion d of the upper curve la. When C1 has discharged 'to a sufficiently low voltage and the voltage drop across R1 biases V2 to cutoff, the plate voltage of V2 increases rapidly when V1 conducts as indicated at f in curve 1a and the capacitor C1 begins to charge toward B+, repeating the cycle.

Thus, a sawtooth voltage is produced on terminal 2,

as illustrated by the curve 2a of Figure 2. This can be used, for example, as the sweep voltage in an oscillo scope. At the same time, terminal 1 can be capacitively coupled to the control grid of the cathode ray tube such that fiyback blanking is provided by the voltage drop sections shown in the upper curve 1a. The negative trigger impulses of the lower curve 3a are strictly synchronizing signals used with recurrent operation, as described above.

For triggered monostable operation, switch S is closed, connecting a voltage +31 to capacitor C1 through the diode D such that the voltage on capacitor C1 cannot rise to the point of conduction in V2 because as the voltage on the plate side of the diode D exceeds that on the cathode, conduction through D takes place. Thus, the grid potential of V2 is held just below its critical point. When a negative trigger voltage of sufiicient amplitude is now applied to the screen grid of V1, V1 will cease conducting and the voltage drop across resistor R1 becomes zero. Then V2 will conduct because the grid to cathode potential now biases the grid of V2 strongly positive. Conduction of V2 discharges capacitor C1 rapidly.

After capacitor C1 discharges, V2 ceases to conduct and V1 begins conduction, and capacitor C1 immediately begins charging toward B+ through resistor R2 forming a sawtooth waveform up to the constant limiting voltage permitted by diode D. The operation is very similar to that of recurrent operation as depicted in Figure 2 except that the sawtooth tops of curve 2a are fiat. If negative trigger signals (like the negative impulses of curve 311, for example) are provided every time as soon as capacitor C2 reaches the constant limiting voltage permitted by diode D, the waveforms for triggered monostable operation will be identical to those of Figure 2.

Thus, there is provided a novel sawtooth voltage gen- This is illustrated by the dropping portion b of enumerated 'as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principles involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is, therefore, claimed in any of its forms or modifications within the legitimate-and valid'scope of the appended claims.

What is claimed is: v

l. A sawtooth voltage generator for both recurrent, free-running and triggered, monostable operation, comprising: a first electron tube including a cathode, a first control grid, a second control grid and an anode; a second electron tube including a cathode, control grid and anode; means for applying a positive potential to the second control grid of said first electron tube; an input connection to said second control grid for applying control signals thereto; an electrical storage element connecting the control grid of said second electron tube to a reference point of fixed potential; means for providing positive charging energy to said storage element; means connecting the anodes of said electron tubes to a source of positive potential; means connecting the cathodes of said electron tubes to said reference point for biasing said cathodes relative to said anodes; means for applying the anodepotential of said second electron tube proportionately to the first control grid of said first electron tube; means for maintaining the control grid of said second electron tube below a fixed predetermined potential to prevent conduction thereof in recurrent, free-running operation; switching means operable to connect said potential maintaining means to the control grid of said second electron tube; and an output connection to said storage element for obtaining a positive sawtooth output voltage, whereby said sawtooth voltage generator functions in recurrent, free-running operation when said switching means disconnects said potential maintaining means from the control grid of said second electron tube,

erator which is simple of construction and is capable of both recurrent and triggered operation. Blanking of a fiyback trace is readily and directly possible with this invention when employed as a sweep generator in an oscilloscope. The operation of the sawtooth voltage generator in recurrent (free-running) fashion can be synchronized by various suitable signals.

It should be noted that the trigger and synchronizing signals are not limited to the negative impulses illustrated but can comprise all forms of negative going signals. For example, the spikes (impulses) can obviously be replaced by short duration pulses for triggered operation and a sine wave can be employed as a synchronizing signal.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before and in triggered, monostable operation when said switching means connects said potential maintaining means to the control grid of said second electron tube.

2. Apparatus in accordance with claim 1 including, in addition, another storage element connected between the anode of said first electron tube and the control grid of said second electron tube for neutralization of high frequency components in the control signals applied to said input connection to said second control grid.

3. Apparatus in accordance with claim 1 including, in addition, another output connection to the anode of said second electron tube for providing a substantially square blanking wave therefrom.

4. A sawtooth voltage generator for both recurrent, free-running and triggered, monostable operation, comprising: a first electron tube including a cathode, con trol grid, screen grid and anode, a second electron tube including a cathode, control grid and anode; means for applying a positive potential to the screen grid of said first electron tube; an input connection to said screen grid for applying negative control signals thereto; a capacitor connecting the control grid of said second electron tube to a reference point of fixed potential; means for providing positive charging energy linearly to said capacitor; a cathode resistor connecting the cathodes of "said electron tubes to said'r'efere'nce point'for biasing said cathodes relativeto said anodes; plate resistors respec- 'tively connecting the anodes of said electron'tubes to a tube; undirectional rectifier means connected to another source of positive potential for maintaining the control grid of said second electron tube below a fixed predetermined potential to prevent conduction thereof in recurrent, free-running operation; switching means operable to connect said potential maintaining means to the control grid of said second electron tube; and an output connection to said capacitor for providing a positive sawtooth output voltage, whereby said sawtooth voltage gen erator functions in recurrent, free-running operation when said switching means disconnects said potential maintaining means from the control grid of said second electron tube, and in triggered, monostable operation when said switching means connects said potential maintaining means to the control grid of said second electron tube.

5. Apparatus in accordance with claim 4 including, in addition, a small capacitor connected between the anode of said first electron tube and the control grid of said second electron tube for neutralization of high frequency components in the control signals applied to said input connection to said screen grid.

6. Apparatus in accordance with claim 4 including, in addition, another output connection to the anode of said second electron tube for providing a substantially square blanking wave therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 2,265,290 Knick Dec. 9, 1941 2,548,953 Crown et al. Apr. 17, 1951 2,605,406 Bartelink et al. July 29, 1952 2,629,825 Eckert et al Feb. 24, 1954 2,688,696 Reeves Sept. 7, 1954 2,721,977 Rich Oct. 25, 1955

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