Solid state device generates fixed width output pulses from variable width input pulses in the nanosecond range. The circuit produces pulse repetition rates in the megacycle range and exhibits low power drain

Garrahan, N. M.

English

NASA Technical Reports Server

Input 
Variable	 J 
W —
	 Output 1 
M
Output 2 Li 
11	
Output  
2	 Diodes Inverted t 
October 1965	 Brief 65-10310 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical information, Springfield, Virginia, 22151. 
Threshold Detector Produces Narrow Pulses at High Repetition Rates 
—3 Volts
The problem: To generate fixed-duration output 
pulses in the nanosecond range at input pulse repeti-
tion rates up to 5 megacycles whenever the input pulse 
amplitude is greater than a fixed threshold level. Prior 
art required gating and differentiating to produce trig-
ger pulses to drive monostable or blocking oscillators. 
Such circuitry is complex, consumes a relatively large 
amount of power, and does not readily lend itself to 
use with high repetition rate inputs. 
The solution: A solid-state device consisting of two 
tunnel diodes back-to-back in parallel with an induc-
tance driven by a constant-current generator. Input 
pulses of variable width in the nanosecond range yield 
output pulses of fixed width. The circuit produces 
pulse repetition rates in the megacycle range and ex-
hibits low power drain.
How it's done: Stages Qi and Q2, together with 
tunnel diodes D 1 and D2, form a threshold detector 
circuit in which the voltage across D 1 switches to its 
high-voltage state and produces output pulse W when-
ever the input exceeds the threshold level. Diode D2 
remains in its tow-voltage state and presents avery low 
impedance. Current through inductance L, starting at 
zero due to its initial high impedance, will increase 
with time, thereby decreasing current flow through D1 
and D2 Voltage across D 1 will decrease to near zero 
and D 1 will switch to its low-voltage state at a point 
in time when most of the current is flowing through L, 
which presents such low impedance that the output 
voltage will be approximately zero for the remainder 
of the input pulse. As the input pulse reaches zero, 
current through L now flows through Di and D2 in 
(continued overleaf) 
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the opposite direction causing D2 to switch to its 
high-voltage state and produce output pulse M as Di 
remains in its low-voltage state. Threshold level in D1 
and D2 is set by adjusting R1 and R2. The value of L 
determines output pulse width. The circuit configura-
tion shown yielded 50 nanosecond pulses for an induc-
tance of 56 microhenries. 
Notes: 
1. All possible combinations of output pulse polarity 
relative to pulse input polarity are available by ar-
rangement of Di and D2 and the input polarity. 
2. Because the output pulses occur at the rise and/or 
fall times of the input pulses, the circuit is useful as 
a zero-crossing detector.
Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland, 20771 
Reference: B65-10310 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about ob-
taining rights for its commercial use may be made to 
NASA, Code AGP, Washington, D.C., 20546. 
Source: Norman M. Garrahan 
(GSFC-383) 
Brief 65-10310	 Category 01


Threshold detector produces narrow pulses at high repetition rates

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