US3676708A

US3676708A - Pulse generator for fast rise-time pulses

Info

Publication number: US3676708A
Application number: US825864A
Authority: US
Inventors: Kozo Uchida
Original assignee: IWASAKI TSUSHINKI ALKALA IWATS
Current assignee: IWASAKI TSUSHINKI ALKALA IWATS
Priority date: 1968-05-21
Filing date: 1969-05-19
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11
Also published as: NL6907726A; DE1925827C3; DE1925827A1; GB1275105A; DE1925827B2

Abstract

Disclosed herein is a pulse generator for producing repetitive uni-directional pulses or single signal-initiated uni-directional pulses by use of pulse generation means, in which output pulses each having an extremely short rise time can be obtained by applying the output pulses of the pulse generation means to a step recovery diode to render the diode non-conductive during such pulses; while the step recovery diode is otherwise maintained conductive, in the absence of a pulse from the pulse generation means, by flowing a forward dc current therethrough.

Description

United States Eatent Uchida July 1 1, 1972 54] PULSE GENERATOR FOR FAST RISE- 3,205,375 9/1965 Berry et a1. ..307/319 x TIME PULSES 3,309,532 3/1967 Frye ..307/28l X 3,369,131 2/1968 Stromer ..307/281 Inventor: K019 Uehldfl, Tokyo-t0, Japan 3,385,982 5/1968 Raillard et a1. .307/319 [73] Assigneez Iwasaki Tsushinki Kabushiki Kaisha alkala 3,076,902 2/1963 Van Duzer et al... ....307/281 X Iwatsu Electric Co. Tokyo) Japan 3,200,267 8/1965 Cubert ..307/319 X 3,391,286 7/1968 Casale et a] ....307/3l9 X [22] Filed: May 19, 1969 3,459,971 8/1969 King ..307/3 1 9 X 1211 A l. No.: 825,8 OTHER PUBLICATIONS Pub. 1, Step Recovery Diode by Wheeler in Solid State [30] Foreign Application Priority Data D i F b, 1963, ge 20- 2 l 22:; ii, 125:: Primary Examine,- $tan1ey Miller, JR y 1968 Japan. 43/34203 A1mrneyRobert E. Burns and Emmanuel J. Lobato May 21, 1968 Japan ..43/34204 [57] ABSTRACT [52] US. Cl ..307/263, 307/262, 307/268, Di l h i is a pulse generator for predueing repetitive 307/275, 307/281, 307/319 uni-directional pulses or single signal-initiated uni-directional 51 Int. Cl ..H03k 5/12, 1-103k 3/26 pulses y use of pulse generation means, in which Output p [58] Field of Search ..307/260, 262, 263, 268, 281, Ses each having an extremely short rise time can be Obtained 307/319 by applying the output pulses of the pulse generation means to a step recovery diode to render the diode non-conductive during such pulses; while the step recovery diode is otherwise [56] References cued maintained conductive, in the absence of a pulse from the UNITED STATES PATENTS pulse generation means, by flowing a forward dc current therethrough. 3,191,062 6/1965 Forge ..307/263 3,205,374 9/1965 Cajal et al.... ..307/263 6 Claims, 12 Drawing Figures P'A'TENTEDJUL H 1972 3, 676,708 sum 1 OF 5 minimum 1972 3676.708

SHEET 3 OF 5 522-1 EFCOVEKY DIST R/ BU TED CONSTANT CIRCUIT STEP EEZOVEE) 0/0 DE Fig. 6

PATENTEDJUL U 1912 SHEET 5 BF 5 0; 5r fiicokmy 0/005 PULSE GENERATOR FOR FAST RISE-TIME PULSES This invention relates to a pulse generator for producing repetitive uni-directional pulses or single signal-initiated unidirectional pulses.

In the case of digital control techniques, digital communication techniques and/or digital measurement techniques etc., uni-directional pulses, each having a short and constant rise time, are desirable to perform as desired operation in a highspeed and precise manner. However, the rise time of each pulse generated from conventional pulse generators deviates usually in accordance with a change of the pulse duration, or the repitition frequency thereof. Moreover the rise time of a generated pulse is usually extended in a shaping network employed to eliminate overshoot or sag (tilt) of the generated pulse. Accordingly, it is very difficult to generate repetitive uni-directional pulses or single signal-initiated unidirectional pulses each having a stable and short rise time without overshoot or sag.

An object of this invention is to provide a pulse generator in which the above-mentioned defects of conventional generators have been eliminated and which generates repetitive unidirectional pulses, or single signal-initiated uni-directional pulses, each having a stable and short rise time.

The principle of this invention will be better understood from the following more detailed discussion taken in conjunction with the accompanying drawings, in which the same or equivalent parts are designated by the same reference numerals, characters and symbols, and in which:

FIG. 1 is a circuit diagram illustrating an embodiment of this invention for generating pulses of positive polarity;

FIGS. 2A and 2B are wave-form diagrams explanatory of the operation of the embodiment shown in FIG. 1;

FIG. 3 is a circuit diagram illustrating an embodiment of this invention for generating pulses of negative polarity;

FIG. 4 is a circuit diagram illustrating another embodiment of this invention for generating pulses of positive polarity;

FIG. 5 is a circuit diagram illustrating another embodiment of this invention for generating pulses of negative polarity;

FIG. 6 is a circuit diagram illustrating another embodiment of this invention for generating pulses of positive polarity;

FIGS. 7 A and 7B are wave-form diagrams explanatory of the operation ofthe embodiment shown in FIG. 6;

FIG. 8 is a circuit diagram illustrating another embodiment of this invention for generating pulses of negative polarity;

FIG. 9 is a circuit diagram illustrating another embodiment of this invention for generating pulses of positive polarity; and

FIG. 10 is a circuit diagram illustrating another embodiment of this invention for generating pulses of negative polarity.

With reference to FIG. I, an embodiment of this invention will be described. In this example, trigger pulses of positive polarity are applied through an input terminal I and a capacitorC Bleeder resistors R and R are connected in series between a negative terminal (-C) of a dc source and ground potential. The junction between the resistors R and R is connected, through a winding of a transformer T to the base of a transistor TR to apply a bias voltage thereto. The transistor TR,, the transformer T a diode D a resistor R (employed as a current limiter) and a capacitor C form a blocking oscillator. The output voltage of the blocking oscillator is derived from another winding of the transformer T, and amplified by a transistor TR A positive terminal (+8) and a negative terminal (-B) of a dc source are connected, directly, and through a series connection of a coil L and a resistor R to the collector and the emitter of the transistor TR respectively. Resistors R and R and a capacitor C are employed as current-adjusting means of the transistor TR The potential of the collector of the transistor TR is grounded through a capacitor C with respect to the alternating-current component thereof. The emitter of the transistor TR is connected to a shaping network comprising resistors R R and R and a capacitor C A step-recovery diode (i.e., snap-off diode or charge storage diode; hereinafter referred as S.R. diode) D is'connected across the output terminal of the shaping network and ground. The anode of a high-speed switching diode D is connected to the cathode of the S.R. diode D and the cathode of this diode D is connected to the center conductor of a coaxial output connector 2. A reference resistor R has a load impedance approximating 50 ohms.

When a positive trigger pulse is applied to the input terminal I, the transistor TR; of the blocking oscillator is turned from the OFF-state to the ON-state. This ON-state of the transistor TR; continues during a time determined by values of the capacitor C,, the resistors R R and R and the impedance of the winding of the transformer T and is thereafter turned to the OFF-state. In response to this change of state, a negative pulse is obtained at the collector of the transistor TR,. This pulse is applied, through a winding of the transformer T to the base-emitter path of the transistor TR so that the potential of the base of the transistor TRg becomes positive to cause; the transistor TR;- to be switched to its ON-state during the duration of this pulse. On the other hand, a direct current flows through the S.R. diode D the resistors R and R the coil L and the resistor R to an negative terminal (-8). Accordingly, the S.R. diode D assumes the ON-state during the non-conductive interval of the transistor TRg, and the potential of the cathode of the S.R. diode D is maintained at a voltage of about 0.8 volts. In response to the above-mentioned change of state of the transistor TR a positive pulse v is obtained at the emitter of the transistor TR The pulse rise time of this positive pulse v, is usually about 5 nano-seconds (5 X 10' seconds). This positive pulse v is applied to the S.R. diode D through the shaping network comprising the resistors R R and R and the capacitor C.,.

When the positive pulse v is applied to the S.R. diode D which diode has a dc current flowing therethrough in the forward direction, the direction of the dc current is at first turned to the backward direction of the S.R. diode D without changing the conductive state thereof to the OFF-state. The S.R. diode D then turns to the OF F-state after the expiration of the storage time 1 of the S.R. diode D so that a positive pulse v is obtained at the cathode of the S.R. diode D at this time, as shown in FIG. 2A. The transition time t, of the S.R. diode D necessary to turn from the ON-state to the OFF-state is approximately lOO pico seconds (I00 X 10 seconds). This positive pulse v is applied to the coaxial output connector 2 through the high-speed switching diode D The fluctuated low voltage region of the positive pulse v is cut by the high-speed diode D so that a square pulse v having a pulse rise time approximating I00 pico-seconds is obtained at the coaxial output connector 2 as shown in FIG. 2B. This square pulse v rises fast from a potential level of substantially zero.

The storage time 1,, of the S.R. diode D is variable in accordance with changes of values of the resistors R R and R and the voltage of the negative terminal (-B), so as to vary the forward dc current of the S.R. diode D This storage time 1,, is determined so as to be equal to or longer than the pulse rise time t of the pulse v The amplitude of the output square pulse v is substantially equal to r,,/( r r r,,) times the voltage of the positive terminal (+B); where the values r r and r,; are respectively the resistances of the resistors R R and R Accordingly, the output square pulse having a relatively large amplitude can be obtained at the coaxial output connector 2.

The shaping network, comprising two series connected resistors R and R and a series connected capacitor C and resistor R connected in parallel with one of the resistors R and R serves as a current limiter for the transistor TR and the high-speed switching diode D in case a short circuit of the coaxial output connector 2, in addition to having the above mentioned pulse-form shaping function. Moreover, since the emitter of the pulse-amplifying transistor TR is directly coupled with the diodes D and D through a transfer impedance transmissible of a direct current, the storage time r of the transistor TRg and the pulse rise time of the output square pulse v;, are stably maintained even if the duration and/or the repetition frequency of the output square pulse v are/is varied.

In this example, a blocking oscillator synchronized with the external trigger pulses is employed. Of course, a blocking oscillator of non-synchronous type or another pulse generation means, such as multivibrator or a pulse generator using other active elements, may also be employed. Moreover, if desirable, the pulse amplifier using the transistor TR, may be eliminated, so that the output of the pulse generation means (e.g., the blocking oscillator) is applied to the S.R. diode D through the shaping network.

If negative output pulses are desirable, the embodiment shown in FIG. 1 can be modified as shown in FIG. 3. In this embodiment, the output of the transistor TR is derived from the collector thereof, and the forward directions of the diodes D, and D are directed in the reversed directions to those shown in FIG. 1. Since the construction and operation of this embodiment can be understood on reference to those shown in FIG. 1, details are omitted.

With reference to FIG. 4, another embodiment of this invention will be described for generating output pulses each having a relatively high amplitude. In this embodiment, the anode of a switching diode D, is connected to the junction of the cathode of S.R. diode D the anode of the switching diode D and the resistor R and the cathode of the switching diode.

D is connected to a positive terminal (+E) of a dc source. A capacitor C is employed to ground an alternating current passing through the diode D,. Other elements are arranged in the same connection as the embodiment shown in FIG. 1.

In this embodiment, if it is assumed that the voltage of the positive terminal (+B) is 40 volts, a total resistance of the resistors R and R is 50 ohms and the resistance r of the load resistor R, terminating the coaxial output connector 2 is 50 ohms, a square, pulse of 20 volts will be obtained at the cathode of the S.R. diode D and at the coaxial output connector in a case where the forward resistances of the transistor TR and of the diode D are negligible. In this case, if it is assumed that the maximum allowable inverse voltage (inverse breakdown voltage) V of the S.R. diode D is 20 volts, the diode D can withstand the voltage (20 volts) of the output pulse. However, if the load resistor R connected to the coaxial output connector 2 is removed, in a case where the diode D, is not used, an inverse voltage of 40 volts will be applied across the S.R. diode D with the result that S.R. diode D will be broken down since the maximum inverse allowable voltage V 25 volts) is less than the applied inverse voltage (40 volts). To avoid this breakdown, a dc voltage of 22 volts is applied to the cathode of the diode D, from the positive terminal (+E). Accordingly, if it is assumed that the voltage drop of the diode D in the forward direction is equal to a voltage 0.8 volts, the terminal voltage of the S.R. diode D is limited to the voltage 22.8 volts since the diode D switches to the ON-state when the voltage of the cathode of the S.R. diode D exceeds the voltage 22.8 volts. As mentioned above, even if the coaxial output connector 2 becomes an open circuit without the load resistance (R,,), the S.R. diode will not be broken down since the applied voltage of 22.8 volts is less than the breakdown voltage V,, (25 volts). In the case where the load resistance of ohms is connected to the coaxial output connector 2, the diode D, assumes the OFF-state since the maximum voltage of the output pulse is equal to 20 volts. If the voltage applied from the positive terminal (+E) is determined at an appropriate value, the S.R. diode D will not be broken down in the case of the open circuit of the coaxial output connector 2, even if the voltage of the output pulse obtained at the coaxial output connector 2 with the load resistance of 50 ohms approximates the breakdown voltage V (25 volts). In a case where the diode D,, the capacitor C and the positive dc source connected to the positive terminal (+E) are not used, the voltage of the positive terminal (+B) must be less than the breakdown voltage V (25 volts) to avoid the breakdown of the S.R. diode D at the open circuit of the coaxial output connector 2. Accordingly, the maximum voltage of the output pulse obtained at the coaxial output connector 2 with the load resistance of 50 ohms will be less than a voltage 12.5 volts.

If negative output pulses are desirable, the embodiment shown in FIG. 4 can be modified as shown in FIG. 5 in accordance with the same modification condition as described with reference to the embodiments shown in FIGS. 1 and 3. Since this embodiment of FIG. 5 will be readily understood from the embodiments shown in FIGS. 3 and 4, details are omitted.

The inverse breakdown voltage of the S.R. diode D, decreases generally in accordance with the decrease of the rise time 1,. However, output pulses each having a very short rise time and a relatively large amplitude can be obtained by the embodiments shown in FIGS. 4 and 5.

With reference to FIG. 6, another embodiment of this invention, modified from the embodiment of FIG. 1 and suitable to improve further the wave form of the output pulse, will be described. In this embodiment, a distributed constant circuit 3 is inserted between the shaping circuit (comprising the capacitor C, and the resistors R-,, R and R and the S.R. diode D,. Other elements are arranged in the same connection as the embodiment of FIG. 1.

In this embodiment, if the output pulse, obtained at the coaxial output connector 2 terminated with a load resistance, has a wave form v shown in FIG. 7A, which is formed by a sharp rise part 4, and a gentle rise part 5 succeeding to the sharp rise part 4 and reaching a constant level part 6, this wave form v can be shaped as a wave form v by the shaping circuit.

In general, the shorter the rise time of the output pulse, the more overshoot or sag (tilt) 7 it will have, as shown in FIG. 7B. To eliminate this overshoot or sag including higher frequency components, the distributed constant circuit 3 is employed. The pulse rise time of the pulse obtained from the pulse amplifier (TR may be usually about 5 nano-seconds. While the distributed constant circuit 3 does not substantially affect such a pulse, the output pulse reshaped so as to have a very short rise time by the S.R. diode D is affected by the distributed constant circuit 3. Accordingly, the overshoot or sag 7 on the output pulse v can be eliminated or reduced by adjusting the characteristic impedance of the distributed constant circuit 3 at frequencies suitable to eliminate respective concavities and convexities. If the interval of the overshoot or sag is relatively long, the delay time of the distributed constant circuit 3 will be long.

A strip transmission line or a distributed constant line can be employed as the distributed constant circuit 3. For example, if a concavity occurs, on a wave shown in FIG. 78, at a time delayed by t nano-seconds after the rise position 8, an exact position along the distributed constant circuit 3 corresponding to the concavity, can be readily detected. In other words, if a small metal rod contacts a portion of the distributed constant circuit 3, fluctuations occuring at a portion of the output pulse v corresponding to the contact portion can be observed on a display device, such as a cathode-ray oscilloscope, and the above detection will be easily performed. In general, the position of the concavity or convexity corresponds to a position on the distributed constant circuit 3 affecting a delay time t/2 measured from the diodes D and D Accordingly, the concavity or the convexity can be eliminated by connecting a line having a length corresponding to the duration of the concavity or convexity to this detected position of the distributed constant circuit 3, or by connecting the line through a resistor to the detected position if the amplitude of the concavity is relatively small.

The distributed constant circuit 3 can serve further to make the pulse rise time of the output pulse shorter. That is, an output pulse having a shorter rise time has a great amount of higher harmonic frequencies of the fundamental frequency component of the output pulse, and, therefore, the characteristic impedance of the distributed constant circuit 3 is made higher for the higher harmonic frequencies, so that the greater part of the higher harmonic frequencies can reach the output coaxial connector 2. In this case, the characteristic impedance of a portion of the distributed constant circuit 3 corresponding to the rise time or to a time, slightly longer than the rise time, is made higher. This is performed by the use of a smaller size line at this portion of the distributed constant circuit 3.

The above-mentioned merits cannot be obtained by inserting a distributed constant circuit between the SR. diode D and the coaxial output connector 2, since a short rise time of a pulse reshaped by the SR. diode D will be extended at the distributed constant circuit.

If negative output pulses are desirable, the embodiment shown in FIG. 6 can be modified as shown in FIG. 8 in accordance with the same modification condition as described with reference to the embodiments shown in FIGS. 1 and 3. Since this embodiment of FIG. 8 will be readily understood from the embodiments shown in FIGS. 3 and 6, details are omitted.

The above-mentioned embodiments shown in FIGS. 6 and 8 may be provided, respectively as shown in FIGS. 9 and 10, with the switching diode D and a capacitor C each connected to the positive terminal (+E) or the negative terminal (E) of a dc source to improve the inverse breakdown voltage of the SR. diode D Operations of these embodiments shown in FIGS. 9 and 10 can be readily understood on reference to the aforementioned embodiments.

What I claim is:

l. A pulse generator for producing unidirectional pulses comprising: pulse generation means having on output conductor,

a transfer impedance circuit transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulse generation means, said transfer impedance including first and second series connected resistors having respective first leads connected together and respective second leads coupled respectively to said input and output conductors, and including a series connected combination of capacitor and a third resistor, said series connected combination being connected in parallel with one of said first and second resistors,

a step recovery diode one electrode of which is grounded and the other electrode of which is connected to the output conductor of the transfer impedance circuit,

a switching diode one electrode of which is connected to the output conductor of the transfer impedance circuit and another electrode of which is connected directly to a pulse generator output terminal,

means for causing a forward dc current to flow through the step recovery diode in the absence of a pulse from the pulse generation means,

whereby output pulses each having an extremely short rise time can be obtained at the output terminal as a result of the non-conduction and conduction, respectively, of the step recovery diode and the switching diode output pulse of the pulse generation means.

2. A pulse generator according to claim 1 further comprising an auxiliary switching diode having one electrode connected to the other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source means for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode.

3. A pulse generator according to claim 1, further comprising distributed constant circuit means inSerted between the transfer impedance circuit and the said other electrode of the step recovery diode to improve the wave form of the output pulses.

4. A pulse generator according to claim 3, further comprising an auxiliary switching diode having one electrode connected to said other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode.

5. A pulse generator having an output terminal for producing uni-directional pulses comprising: pulse generation means having an output conductor,

transfer impedance circuit means transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulse generation means for shaping the form of pulses produced by said pulse generation means, and for protecting said pulse generation means against excessive loads,

a step recovery diode one electrode of which is grounded and the other electrode of which is connected to the output conductor of the transfer impedance circuit means,

a switching diode one electrode of which is connected to the output conductor of the transfer impedance circuit means and another electrode of which is connected directly to said pulse generator output terminal,

distributed constant circuit means inserted between the transfer impedance circuit means and the said other electrode of the step recovery diode to improve the wave form of the output pulses, and an auxiliary switching diode having one electrode connected to the other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source means for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode,

whereby output pulses each having an extremely short rise time can be obtained at the output terminal as a result of the non-conduction and conduction, respectively, of the step recovery diode and the switching diode in response to an output pulse of the pulse generation means.

6. A pulse generator having an output terminal for producing uni-directional pulses comprising: pulse generation means having an output conductor,

transfer impedance circuit means transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulses generation means for shaping the form of pulses produced by said pulse generation means, and for protecting said pulse generation means against excessive loads,

means for causing a forward dc current to flow through the step recovery diode in the absence of a pulse from the pulse generation means, and

an auxiliary switching diode having one electrode connected to said other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode,

Claims

1. A pulse generator for producing unidirectional pulses comprising: pulse generation means having on output conductor, a transfer impedance circuit transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulse generation means, said transfer impedance including first and second series connected resistors having respective first leads connected together and respective second leads coupled respectively to said input and output conductors, and including a series connected combination of capacitor and a third resistor, said series connected combination being connected in parallel with one of said first and second resistors, a step recovery diode one electrode of which is grounded and the other electrode of which is connected to the output conductor of the transfer impedance circuit, a switching diode one electrode of which is connected to the output conductor of the transfer impedance circuit and another electrode of which is connected directly to a pulse generator output terminal, means for causing a forward dc current to flow through the step recovery diode in the absence of a pulse from the pulse generation means, whereby output pulses each having an extremely short rise time can be obtained at the output terminal as a result of the nonconduction and conduction, respectively, of the step recovery diode and the switching diode output pulse of the pulse generation means.

5. A pulse generator having an output terminal for producing uni-directional pulses comprising: pulse generation means having an output conductor, transfer impedance circuit means transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulse generation means for shaping the form of pulses produced by said pulse generation means, and for protecting said pulse generation means against excessive loads, a step recovery diode one electrode of which is grounded and the other electrode of which is connected to the output conductor of the transfer impedance circuit means, a switching diode one electrode of which is connected to the output conductor of the transfer impedance circuit means and another electrode of which is connected directly to said pulse generator output terminal, means for causing a forward dc current to flow through the step recovery diode in the absence of a pulse from the pulse generation means, distributed constant circuit means inserted between the transfer impedance circuit means and the said other electrode of the step recovery diode to improve the wave form of the output pulses, and an auxiliary switching diode having one electrode connected to the other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source means for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode, whereby output pulses each having an extremely short rise time can be obtained at the output terminal as a result of the non-conduction and conduction, respectively, of the step recovery diode and the switching diode in response to an output pulse of the pulse generation means.

6. A pulse generator having an output terminal for producing uni-directional pulses comprising: pulse generation means having an output conductor, transfer impedance circuit means transmissible of a dc current and having an input conductor and an output conductor, said input conductor being connected to the output of the pulses generation means for shaping the form of pulses produced by said pulse generation means, and for protecting said pulse generation means against excessive loads, a step recovery diode one electrode of which is grounded and the other electrode of which is connected to the output conductor of the transfer impedance circuit means, a switching diode one electrode of which is connected to the output conductor of the transfer impedance circuit means and another electrode of which is connected directly to said pulse generator output terminal, means for causing a forward dc current to flow through the step recovery diode in the absence of a pulse from the pulse generation means, and an auxiliary switching diode having one electrode connected to said other electrode of the step recovery diode, said auxiliary switching diode having another electrode, and a dc source for applying a dc voltage less than the inverse breakdown voltage of the step recovery diode to said other switching diode electrode, whereby output pulses each having an extremely short rise time can be obtained at tHe output terminal as a result of the non-conduction and conduction, respectively, of the step recovery diode and the switching diode in response to an output pulse of the pulse generation means.