Design and development of variable pulse width multiplie

Groom, N. J.

English

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U. S.  Patent No. t 3,473,050 
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NASA Patent Case No. t 
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ct. 14, 196 PI. J. GROOM 
VARIABLE PULSE WIDTH MULTIPLIER 4, 
Filed June 10, 1966 
PIG. 2 
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INVEhTOR 
NELSON J. GROOM 
3,473,050 
US. el. 307-26 
10 
A CT 
A device for producing an output pulse whose dura- 
tion is proportional to the duration of an input pulse. 
Means are provided for linearly discharging a fully charged 15 
capacitor throughout the duration of the input pulse. 
Thereafter the capacitor recharges to its fully charged 
state. Means are connected to the capacitor for producing 
a pulse beginning at the time the capacitor begins to dis- 
charge and ending at the time the capacitor becomes fully 20 
recharged. Means are provided for changing the discharge 
and recharge rates of the capacitor. 
The invention described herein was made by an em- 25 
ployee of the United States Government and may be 
manufactured and used by or for the Government for gov- 
ernmental purposes without the payment of any royalties 
thereon or therefor. 
multiplier and more specificallfr concerns a device for 
receiving input pulses and producing output pulses whose 
durations are proportional to the durations of the input 
pulses. 
the pulses in a train of pulse duration modulated pulses. 
For example, if these pulses are utilized in an electro- 
mechanical device, the device will be responsive to only 
those pulses having durations above a certain value. Pulses 
having durations below this certain value will not over- 40 
come the inertia of the mechanical system. Consequently, 
if the duration of each pulse is multiplied by some con- 
stant greater than one the pulses can be more effectively 
used in an electro-mechanical device. 
invention. There are many types of pulse stretchers; how- 
ever, these devices provide a constant output pulse re- 
gardless of the duration of the pulse being stretched. 
Therefore there is not proportionality between input and 
output pulses. Consequently, if these pulse stretchers are 50 
used to stretch pulse duration modulated pulses, the 
stretched pulses will no longer be pulse duration mod- 
ulated. 
It is therefore an object of this invention to provide 
a device for multiplying the durations of pulse duration 55 
modulated pulses by a constant greater than one. 
Another object of this invention is to increase the 
durations of pulse duration modulated pulses so that they 
can be more effectively used in ana electromechanical 
device. 60 
A further object of this invention is to provide a device 
for stretching pulses proportional to their durations. 
Other objects and advantages of this invention will fur- 
ther become apparent hereinafter and in the drawings in 
which: 65 
FIG. 1 is a schematic circuit drawing of a preferred 
embodiment of the invention; and 
FIG. 2 is a series of waveforms useful in explaining 
the operation of the circuit in FIG. 1. 
In describing the preferred embodiment of the invention 
illustrated in the drawings, specific terminology will be 
resorted to for the sake of clarity. However, it is not 
The invention relates generally to a pulse duration 30 
It is sometimes desirable to increase the durations of 35 
There is no pulse duration multiplier known by the 45 
intended to be limited to the specific terms so selected, 
and it is to be understood that each specific term includes 
all technical equivalents which operate in a similar man- 
ner to accomplish a similar purpose. 
Turning now to the specific embodiment of the inven- 
tion selected for illustration in the drawings, the numbm 
11 designates an NPN transistor. The base of transistor 
11 is connected through a resistor 12 to an input terminal 
13, and through a Zener diode 14 to ground. The emitter 
of transistor 11 is connected through a variable resistor 
15 to ground. The collector of transistor 11 is connected 
through a variable resistor 16 to a B+ power supply, 
through a capacitor 17 to ground, and directly to the base 
of an NPN transistor 18. The emitter of transistor'18 is 
connected through a Zener diode 19 to ground and di- 
rectly to the emitter of an NPN transistor 20. The collec- 
tor of transistor 18 is connected through a resistor 21 to 
the power supply and through the parallel combination of 
a resistor 22 and a capacitor 23 to the base of transistor 
20. The base of transistor 20 is also connected through 
a resistor 24 to ground. The collector of transistor 20 is 
connected through a resistor 25 and a resistor 26 to the 
power supply. The junction of resistors 25 and 26 is con- 
nected to the base of a PNP transistor 27. The emitter of 
transistor 27 is connected through a resistor 28 to- the 
power supply. The collector of transistor 27 is connected 
through a resistor 29 to ground, and directly to an output 
terminal 30. 
The pulse duration multiplier shown in FIG. 1 consists 
basically of four parts. These parts are: (1) the capacitor 
17; (2) a charge source consisting of variable resistor 16; 
( 3 )  a discharge source consisting of transistor 11, variable 
resistor 15 and Zener diode 14; and (4) a level detector 
consisting of transistors 18 and 20, and the associated 
circuitry. Transistor 27 merely serves as a switch to refer- 
ence the output to ground. The level detector is the well 
known Schmitt trigger circuit. 
The operation of the pulse duration multiplier shown 
in FIG. 1 will now be described while referring to the 
waveforms in FIG. 2. Under quiescent conditions tran- 
sistor 11 is not conducting and capacitor 17 is charged; 
through resistor 16 to a voltage determined by Zener 
diode 19. The resulting voltage across capacitor 17 puts 
a forward bias on the base-emitter diode of transistor 18 
causing it to conduct which in turn causes transistor 20 
to become nonconductive. Since transistor 20 is not con- 
ducting the base and emitter of transistor 27 are at the 
same potential, transistor 27 is not conducting and output 
terminal 30 is at ground potential. When a square wave 
pulse, such as the one shown in FIG. 2(a) ,  is applied to 
input terminal 13, the leading edge of the pulse at a time 
t1 causes transistor 11 to start conducting. As soon as 
transistor 11 starts conducting, capacitor 17 begins to 
discharge through transistor 11 and resistor 15. The re- 
sulting voltage drop across resistor 15 is clamped to a 
voltage determined by Zener diode 14. Therefore the 
discharge of capacitor 17 is essentially linear. Zener diode 
19 in addition to its function as voltage limiter to capaci- 
tor 17, also determines the trip point of the level detector 
and provides essentially zero hysteresis. Therefore, as 
soon as the voltage across capacitor 17 starts decreasing 
at time tl, as shown in FIG.2(b), transistor 18 becomes 
nonconductive, and transistors 20 and 27 start conduct- 
ing. The resulting voltage drop across resistor 29 at out- 
put terminal 30 is shown at time tl in FIG. 2 ( c ) .  This is 
the leading edge of the output pulse. At the time fa, when 
the input pulse is terminated, transistor 11 becomes non- 
conductive and capacitor 17 is recharged through resistor 
16. When the voltage across capacitor 17 reaches the 
Zener voltage of Zener diode 19 at time tS, transistor 18 
again becomes conductive, transistors 20 and 27 become 
3,473,050 
noncondutive and the voltage at terminal 30 returns to 
ground potential to produce the trailing edge of the out- 
put pulse of FIG. 2(c). 
As can readily be seen from FIG. 2, the duration of the 
pulse at output terminal 30 (FIG. 2(c))  is directly pro- 
portional to the duration of the pulse at input terminal 
53 (FIG. 2(a)).  The multiplication factor is 
over a range of from 10 microseconds to 10 milliseconds, 
or three orders of magnitude of input pulse duration 
change. 
The advantage of this invention is that it provides a 
device for multiplying the durations of pulse duration 
modulated pulses by some constant greater than one. The 
invention is useful when pulse duration modulated pulses 
are applied to a control system that has a response time 
greater than the durations of the pulses. The invention 
t1- tz lo could also be used as a pulse duration modulator by 
This multiplication factor can be changed either by adding voltage control of the charge rate of capacitor 17. 
varying resistor 15 or by varying resistor 16. The value of A modulating voltage could then be applied to the charge 
resistor I5 determines the rate of discharge of capacitor control exerting any amount of modulation above the 
17 and thus determines the slope of waveform FIG. 2(b) input pulse duration. 
between the times tl and tz. The value of resistor 16 15 It is to be understood that the form of the invention 
determines the rate of charge of capacitor 164 and thus herewith shown and described is to be taken as a pre- 
determines the slope of waveform FIG. 2 ( b )  between the ferred embodiment. Various changes may be made in the 
times ta and t3. The linearity of the charge circuit is due shape, size and arrangement of parts, For example, equiv- 
to the fact that only a small almost linear portion of the alent elements may be substituted for those illustrated and 
charge curve of the capacitor 117 is utilized. An alternate 20 described herein, parts may be reversed, and certain fea- 
method would involve the use of a variable constant cur- tures of the invention may be utilized independently of 
rent charge source in place of variable resistor 16. How- the use of other features, all without departing from the 
ever, this would require at least one extra transistor and spirit or scope of the invention as defined in the following 
add to the complexity of the circuit. claims. 
What is claimed as new and desired to be secured by 
in the circuit in PIG. 1 and found to operate satisfac- Letters Patent of the United States is: 
tl-t3 
The following circuit component values have been used 25 
lo 30 
110 
23 
6.6 
3.3 
5.6 
1 
100 
4.7 35 
The multiplication factor was set at 50 with an input 
pulse duration of .1 millisecond. 
The multiplication factor can be varied from 1 to a 
maximum determined by the input pulse duration and 
pulse repetition rate by varying resistor 16. The pulse 65 
duration range over which the pulse duration multiplier 
will operate can be varied by changing resistor 115. This 
5. A pulse duration multiplier comprising: 
a first resistor and a capacitor connected in series be- 
tween a voltage source and ground; 
a pulse responsive gate with an input that is conductive 
while an input pulse is applied to it and is non- 
conductive while an input pulse is not applied to 
it; 
said gate connected in series with a second resistor 
between the junction of said first resistor and said 
capacitor and ground whereby while an input pulse 
is applied to said gate said capacitor discharges 
through said gate and said second resistor and while 
an input pulse is not applied to said gate said capaci- 
tor recharges through said first resistor; 
a Zener diode connected between the input of said gate 
and ground to insure that said capacitor discharges 
linearly; and 
means including a Schmitt trigger circuit connected to 
the junction between said first resistor and said ca- 
pacitor for producing an output pulse beginning at 
the time when said capacitor begins to discharge and 
ending at the time said capacitor is fully recharged 
whereby said output pulse begins at the beginning of 
an input pulse and has a duration proportional to 
the duration of said input pulse. 
References Cited 
UNITED STATES PATENTS 
3,152,267 10/1964 Clapper _ _ _ _ _ _ _ _ _ _ _ _  307-265 
3,346,743 1011967 Strenglein _ _ _ _ _ _ _ _  328-58 XR 
rangeis determined by the lowest pulse duration which 
will operate the pulse duration multiplier, the multiplica- 
tion factor, and the pulse remtition rate. For examule, 60 J- zAzwoRsKy~ Assistant Examiner 
ARTHUR GAUSS, primary exa in^^ 
the pulse dkation muitiplier will operate reliably down to 
10 microseconds with a multiplication factor of 50 and a 
pulse repetition rate of 2 per second and it will operate 
U.S. C1. X.R. 
328-58; 329-106; 332-9 


Variable pulse width multiplier Patent

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