US2968766A - Pulse-sharpening circuit - Google Patents

Description

1961 l. HOROWITZ 2,968,766

PULSE-SHARPENING CIRCUIT Filed Oct. 51, 1956 T /III 45+ m C P r7 m,

INVENTOR. IRVING HOROWI TZ Z5 WM ATTORNEYS United States Patent PULSE-SHARPEN IN G CIRCUIT Irving Horowitz, Eatontown, N..I., assignor to Blonder Tongue Laboratories, Westfield, NJ., a partnership Filed Oct. 31, 1956, Ser. No. 619,475

7 Claims. (Cl. 328-223) The present invention relates to pulse-sharpening circuits, and, more particularly, to circuits for steepening relatively sloping step-function voltage signals and the like.

Many types of pulse-sharpening circuits have been proposed for solving the numerous problems relating to the utilization of voltage impulses. In connection with television pick-up tubes, for example, there are instances where sharp voltage signals are intended to be generated, but the signals are generated, instead, with relatively sloping characteristics. While the invention will hereinafter be described as particularly applied to such television systems, it is to be understood that it is of much broader utility, being adaptable for use, also, where other types of voltage waveforms are to be modified. Returning to such television systems, the finite size of the electron stream associated with the television pick-up tube produces what is termed aperture distortion. Were the electron stream a point source, a sharp transition Would be produced as the stream scans from, for example, a dark area to a light area, producing a steep step-function signal waveform. The finite size of the electron stream, however, produces a less sharp transition, giving .rise to a somewhat broader, rounded and more sloping voltage waveform. The signal available at the television receiver does not, therefore, permit reproduction of the original dark-area-light-area sharp contrast, but gives rise to a grey transition region.

Several techniques have been proposed for overcoming this aperture distortion. As an illustration, successive stages of pulse-shaping circuits have been provided to convert a generally sloping characteristic into a rather steep waveform with the aid of compensatory voltage Waveforms that are combined in the successive stages to produce a resultant sharp step function. Unfortunately, however, these circuits require more than one electrontube stage and they are not provided with simple means for adjusting the size and dimensions of the compensatory waveforms.

The purpose of the present invention, accordingly, is to provide a new and improved compensating circuit of the above-described character that may employ but a single electron-tube stage and that shall be adapttd to permit easy adjustment of the compensatory waveforms.

A further object is to provide a new and improved pulse-steepening circuit.

In summary, the present invention resides in the utilization of preferably a single electron-tube stage having an input and an output circuit. Means is provided for applying the input voltage of relatively sloping characteristic to the input circuit, and means is disposed in the output circuit for producing resulting oscillations which are to serve as compensatory waveforms. Further means maintained at floating potential with respect to the output circuit is provided for generating further oscillations corresponding to the oscillations generated in the output circuit. The floating-potential further generating means is, in turn, connected in circuit with a point of the input Fatented Jan. 17, 1961 circuit at which a voltage similar to the original sloping input voltage is developed, thereby to combine the said similar voltage and the further oscillations into a resultant voltage having the desired relatively steep characteristic. Preferred constructional details are explained hereinafter.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawing the single figure of which is a schematic circuit diagram illustrating the invention in preferred form.

An electron tube 1, shown for purposes of illustration as of the tetrode variety, is provided with an anode or plate electrode 3, a cathode electrode 5, a control-grid electrode 7 and a screen-grid electrode 9. The controlgrid electrode 7 is connected to a terminal 11 of the input circuit of the tube 1 and the cathode 5 is connected through a cathode load resistor 13 to the other input terminal 15 of the input circuit. The terminal 15 may be grounded, as illustrated, and may be connected to the negative terminal B- of the anode or plate supply voltage source (B+) (B) for the tube 1. The positive anode or plate-voltage supply terminal 3+ is connected in the output circuit of the tube 1 and through a primary winding P of a transformer T to the anode or plate 3 of the tube 1. The screen-grid electrode 9 is also connected to the B+ terminal by a conductor 17.

The before-described relatively sloping characteristic resulting, in the illustrative case of the television pick-up tube, from aperture distortion as the finite-size electron beam scans successively positioned dark and light areas, is represented by the relatively sloping or inclined waveform I having rounded upper and lower edges I and I". Substantially the same or similar waveform, though somewhat broadened out, is produced at II across the cathodeload resistor 13, which is shunted by a bypass condenser 19. When the downwardly or negatively sloping waveform I is applied to the input circuit 117, 15-5 of the tube 1, the tube current reduces abruptly. This sets the inductance winding P and the parallel combination of the output capacitance 25 of the tube 1 and the load or input capacitance 24 of the next stage, not shown, into ringing or shock-exciting oscillation, as shown at III. These ringing oscillations in the output circuit of the tube 1 comprise a first positively varying pulse 111 followed by a negatively-going pulse III and successive smalleramplitude trailing pulses. Other types of ringing circuits, including differentiating circuits, that can produce similar positive and negative pulses III and III" may, of course, be employed. It will be observed that the oscillation III occurs at the rounded onset I of the input voltage I, and the negative-going peak III" occurs in the region where the waveform I is gradually sloping downward. The negative impulse III is, of course, a very much steeper downwardly falling impulse as a result of the relatively high frequency of the shock-excited oscillations of the output winding P.

In accordance with the present invention, a secondary winding S is tightly coupled to the primary winding P, as by forming the windings S and P as a pair of tightlycoupled bifilar transformer windings. There will therefore be generated in the secondary winding S oscillations corresponding to the oscillations III. The said generated oscillations in the secondary windings S, however, are maintained at floating potential with respect to the output circuit. The secondary winding S is, in turn, connected by a conductor 21 in series circuit with the upper end of the cathode load resistor 13, thus to add together the voltage corresponding to the waveform II and the voltage developed or generated in the secondary winding S that corresponds to the voltage HI appearing in the primary winding P. The sharply rising positive peak III thus adds to the initial rounded corner 11 providing a resultant square or sharp transition IV at the output load-circuit conductor 23. The steeply-falling oscillation III" serves to steepen the relatively sloping downward portions II and II of the waveform II, producing the square or rectangular steep resultant step-function waveform IV.

The utilization of the bifilar windings S and P, tightly coupled together, provides for a transformation with no intermediate phase-shift, the phase relations being either zero or one hundred eighty degrees. This is desirable in order that the position of the oscillations, corresponding to III and III may be fixed with respect to the rounded portions II and II" of the waveform 11, thereby accurately to eiiect the steepening compensation at the correct points of the waveform II. A simple adjustment of the width or period of the oscillation pulses III and III", moreover, is provided by a core C that is movable in and out of the preferably bifilar windings S and P. Amplitude control over the height of the peaks III and III", which is necessary to prevent too much compensation for the rounded edges II and II", may be simply efiiected through variation of the variable resistor R connected in parallel with the secondary winding S.

Modifications will appear to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. An electric system having, in combination, an electron device provided with input and output circuits, means for applying an input voltage of relatively sloping characteristic to the input circuit, means disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit, means having no complete-circuit electrical connection to the electron device and thus maintained at potential that may vary with respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, and means for connecting the variable-potential means in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic.

2. An electric system having, in combination, an electron device provided with input and output circuits, means for applying an input voltage of relatively sloping characteristic to the input circuit, inductance means disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit, means having no complete-circuit electrical connection to the electron device and thus coupled to the inductance means and maintained at potential that may vary with respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, and means for connecting the variable-potential means in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic.

3. An electric system having, in combination, an electron device provided with input and output circuits, means for applying an input voltage of relatively sloping characteristic to the input circuit, a first winding disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit, a second winding coupled to the first winding and having no complete-circuit electrical (connection to the electron device and thus maintained at potential that may vary With respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, and means for connecting the second winding in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic.

4. An electric system having, in combination, an electron device provided 7 with input and output circuits, means for applying an input voltage of relatively sloping characteristic to the input circuit, a first winding disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit a second winding coupled to the first winding and having no complete-circuit electrical connection to the electron device and thus maintained at potential that may vary with respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, means for connecting the second winding in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic, and a variably positioned core associated with the first and second windings for varying the period of the oscillations in order to control the steepness of the resultant voltage.

5. An electric system having, in combination, an electron device provided with input and output circuits, means 'for applying an input voltage of relatively sloping characteristic to the input circuit, a first winding disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit a second winding coupled to the first winding and having no complete-circuit electrical connection to the electron device and thus maintained at potential that may vary with respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, means for connecting the second winding in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic, and a variable impedance shunting the second winding for controlling the amplitude of the oscillations, thereby to control the shape of the resultant voltage.

6. An electric system having, in combination, an electron device provided with input and output circuits, means for applying an input voltage of relatively sloping characteristic to the input circuit, a first Winding disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit a second winding disposed in bifilar relation with the first winding and having no complete-circuit electrical connection to the electron device and thus maintained at potential that may vary with respect to the said output circuit for generating further oscillations corresponding to the first-named oscillations, and means for connecting the variable-potential means in series with the load circuit and in circuit with a point of the input circuit at which a voltage similar to the said input voltage is developed, thereby to combine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep characteristic.

7. An electric system having, in combination, an electron device provided with an input circuit having a cathode load, and an output circuit, means for applying an input voltage of relatively sloping characteristic to the input circuit, a first winding disposed in the output circuit for producing oscillations in response to the application of the said input voltage to the input circuit, a load circuit, a second winding coupled to the first winding 5 6 and having no complete-circuit electrical connection to References Cited in the file of this patent the electron device and thus maintained at pot ential that UNITED STATES PATENTS may vary with respect to the said output clrcult for gen erating further oscillations corresponding to the first- 2,409,909 Blrss May 1946 named oscillations, and means for connecting the second 5 2,493,517 APplegarth 1950 2,577,522 Hite et a1. Dec. 4, 1951 winding in series with the load circuit and in circuit with a point of the said cathode load at which a voltage simi- 2,597,038 y 20, 1952 lar to the said input voltage is developed, thereby to com- 2,341,705 Kuellsmel' et a1 y 1, 1958 bine the said similar voltage and the further oscillations to produce a resultant voltage of relatively steep char- 10 acteristic.

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