One-stage, delay compensation amplifier, added to conventional univibrator circuitry time-synchronizes the trailing edge of the output pulse with the origin of the input pulse. The trailing edge is independent of the amplitude of the input pulse

Strauss, M. G.

English

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—5V 
May 1967
	
Brief 67-10130 
G dir,
	
AEC-NASA TECH BRIEF 
rES
AEC-NASA Tech Briefs describe innovations resulting from the research and development program 
of the U.S. AEC or from AEC-NASA interagency efforts. They are issued to encourage commercial 
application. Tech Briefs are published by NASA and may be purchased, at 15 cents each, from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Modified Univibrator Compensates for Output Timing Errors 
—12.5V	 —25V	 —12.5V —5V	 —5V
The problem: 
To design a univibrator circuit capable of time-syn-
chronizing the trailing edge of the output pulse with 
the origin of the input pulse. Conventional univibrator 
circuits are subject to output pulse timing errors pro-
duced by varying input pulse amplitudes. 
The solution: 
A simple, one-stage, delay compensation amplifier, 
added to the conventional univibrator circuitry so as 
to produce a univibrator output pulse whose trailing 
edge is independent of the amplitude of the input 
pulse.
How it's done: 
The timing circuit consists of conventional uni-
vibrator Qi and Q2, a spiker circuit, and one-stage 
compensation transistor amplifier Q. 
In the quiescent state, Q2 is conducting; Qi and 
Q3 are biased off. An input pulse is applied simul-
taneously to the spiker circuit and to the base of Q. 
The spiker applies a positive spike to the base of Q2, 
switching it off. When Q2 stops conducting, sufficient 
current flows to the base of Q  to bias it into the con-
duction region. Qi turns on and generates a positive-
going output pulse. Q2 is held in the cut-off state by 
(continued overleal) 
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the potential across capacitor Ci and remains biased 
off until Ci is sufficiently discharged. 
In a conventional univibrator, the discharge of Ci 
is governed by the current flowing through Ri. How-
ever, in the compensated univibrator, the discharge of 
Ci is governed by a discharge path through both Ri 
and R2. The potential existing at point A determines 
the discharge current through R2. 
An input pulse drives Q3 into a state of increasing 
conduction, causing the point A potential to increase 
from —22v to the clamp potential of —12.5v. This 
decreases the discharge current flowing through R2. 
From the time the clamp potential is reached to the 
end of the discharge, the discharge rate of Ci is 
nearly constant and slower than its initial discharge 
rate. For high amplitude input pulses, the threshold 
Of Q3 and the clamp potential are reached quickly. 
For low amplitude input pulses, the potential at 
point A increases less rapidly, and the nearly constant 
discharge rate is reached at a later time. Thus Ci 
discharges more rapidly for low amplitude input 
pulses than for high amplitude pulses, causing the 
compensated univibrator to turn off earlier for low 
amplitude input pulses than for high amplitude input 
pulses. 
Low amplitude inputs reach the triggering threshold 
Of Q2 later than high amplitude inputs, causing a 
delay in the occurrence of the leading edge of the out-
put pulse. The discharge control of Ci, however, 
compensates for this delay by producing narrow out-
put pulses for small inputs and wide output pulses for 
large inputs. This pulse width compensation effect 
causes the trailing edge of all output pulses to occur 
at the same time regardless of input pulse amplitude.
Notes: 
I. Manual adjustment of Ri determines the pulse 
delay time through Ci in the compensated cir-
cuit. 
2. This circuit can function with double RC-differ-
entiated input pulses and requires no delay-line 
wave shaping or zero crossing techniques. 
3. Resistor R3 and catching diode Di are added in 
the collector circuit of Q3 to enhance the compen-
sation for input pulses of high amplitude. 
4. Additional details are contained in: The Review of 
Scientific  Instruments, vol. 34, no. II, pp. 1248-
1253, November, 1963. 
5. Inquiries concerning this innovation may be di-
rected to:
Office of Industrial Cooperation 
Argonne National laboratory 
9700 South Cass Avenue 
Argonne, Illinois 60439 
Reference: B67-101 30 
Source: M. G. Strauss 
Electronics Division 
(ARG-85) 
Patent status: 
Inquiries about obtaining rights for commercial use 
of this innovation-may be made to: 
Mr. George H. Lee, Chief 
Chicago Patent Group 
U.S. Atomic Energy Commission 
Chicago Operations Office 
9800 South Cass Avenue 
Argonne, Illinois 60439 
Brief 67-10130	 Category 01


Modified univibrator compensates for output timing errors

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