Circuit generates a pulse of high interval stability with a complexity level considerably below systems of comparable stability. This circuit is being used as a linear frequency discriminator in the signal conditioner of the Apollo command module

Fisher, B.

English

NASA Technical Reports Server

November 1966	 Brief 66-10501 
NASA TECH BRIEF 
NASA Tech Briefs are issued to summarize specific innovations derived from the U. S. space 
program and to encourage their commercial application. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Electronic Circuit Delivers Pulse of High Interval Stability 
V V Sweep Generator 
I	 V 
Electronic 
Switch
crV 
____________	 aV
Signal 
Input Bistable 
Or Gate	
Mult,vibrator	 - -	
' rentuaI	 C
Amplifier 
Differentiator I
Supply Potential
Storage Capacitor I	
Charging Potential 
Output 
Signal  
The problem: 
In a number of electronic instrumentation systems, 
accurate counting of events per unit time requires a 
pulse of specified and highly stable interval. Such 
systems have been designed in the past but, generally, 
at a very high complexity level. 
The solution: 
A circuit that fundamentally depends, for its stabil-
ity, on the regularity of an energy storage-energy dissi-
pative time constant. This circuit generates a pulse of 
high interval stability with a complexity level consider-
ably below systems of comparable stability. 
How it's done: 
An input pulse of either random or predetermined 
period triggers the bistable multivibrator. With the 
multivibrator in the reset state, this pulse drives it to 
the set state and its true output drives the switch to 
the open or nonconducting state. This causes the ca-
pacitor terminal potential to increase toward the sup-
ply potential (V). The high gain and wide bandwidth 
differential amplifier now generates a single-ended 
output voltage in response to the capacitor instan-
taneous potential as well as to the fixed potential V, 
the algebraic difference between the two representing 
the amplifier input signal.
Assuming that the capacitor is allowed to charge in-
definitely, the differential amplifier output signal 
would appear as shown in the figure on the 'right. At 
the instant denoted T, the differential input signal 
changes relative polarity, that is, the attenuated po-
tential V is greater than the capacitor potential before 
time T, whereas after time T the converse is true. 
This in turn causes the amplifier output potential to 
rapidly reverse potential at T in a period dependent 
or the gain and bandwidth of the amplifier. 
The interval T is solely dependent on the supply 
potential Vif the capacitor 1 s initially 'charged Vc (0) 
so that proper circuit oftration depends on the capaci-
tor being fully discharged before each triggering event. 
This requirement effectively sets an upper limit to 
the frequency of operation, being related to the choice 
of capacitance of the RC time constant for a given 
application. 
Output of the differentiator resets the bistable 
multivibrator at a precise preselected instant and the 
output of the multivibrator drives the switch to the 
closed or conducting state to discharge the capacitor, 
which in time returns to its quiescent state. The cir-
cuit remains in the discharged state until the next 
input triggers the bistable multivibrator to repeat the 
events described above. 
-.	
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19660000499 2020-03-11T17:37:48+00:00Z
Notes:	 Patent status: 
1. This circuit is being used as a linear frequency	 Inquiries about obtaining rights for the commercial 
discriminator in the signal conditioner of the	 use of this invention may be made to NASA, Code 
Apollo comand module.
	
GP, Washington, D.C. 20546. 
2. Inquiries concerning this invention may be di- 	 Source: Benjamin Fisher 
rected to:
	
of North American Aviation, Inc. 
Technology Utilization Officer	 under contract to 
Manned Spacecraft Center 	 Manned Spacecraft Center 
Houston, Texas 77058	 (MSC-673)
Reference: B66-10501 
Brief 66-10501	 Category 01


Electronic circuit delivers pulse of high interval stability

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