A dc analog input can be used to produce an integrator with high dynamic range or a position servo with inherent stability. This is done by a switching system using digital-to-analog converters and an electronic switch to obtain the desired outputs

Matty, T. C.

English

NASA Technical Reports Server

Negative VoltagE 
Sensitive Trigger 
(Schmitt Trigger) 
Forward-Reverse 
Binary Counter 
Binary Data Lines 
HODigital-to-Analog Converter No. 2 put 
E2 
Input 
Integrating 
E1Amplifier 
C
FElectronic Switch I	 to Quench I Capacitor Charge 
June 1964	 Brief 64-10064 
NASA TECH BRIEF 
This NASA Tech Brief is issued by the Technology Utilization Division to acquaint industry 
with the technical content of an innovation derived from the NASA space program. 
Digital Logic Elements Provide Additional Functions from Analog Input 
Digital-to-Analog 
Converter No. 1 
Positive Voltage 
Sensitive Trigge
	 Binary Data Lines 
(Schmitt Trigger
The problem: To develop a system that can use a 
d c. analog input to produce an integrator with high 
dynamic range or a d.c, position servo with good 
inherent stability. 
The solution: A system in which appropriate 
switching utilizes digital-to-analog converters and an 
electronic switch to provide the desired outputs. 
How it's done: With digital-to-analog converter 
No. 1 in the system and the electronic switch 
disconnected, the system can be made to function as 
a d c position servo. Feedback of the output voltage 
of converter No. I will tend to cancel the input con-
trol voltage at the integrating amplifier summing point. 
With the d c input to the amplifier at other than 
zero, the integrating capacitor will charge either posi-
tive or negative. When the trigger voltage is reached,
the counter will count up or down depending on the 
polarity of the charge. As the counter changes its 
register, the output of converter No. 1 will also 
charge a value corresponding to one least-significant 
bit. Thus the difference input at the amplifier summing 
point is reduced by this amount. As the point is ap-
proached where the input and feedback voltages are 
equal, the charging action will slow almost to a stop. 
The output from converter No. 1, changing in steps, 
will never produce an exact null condition and the 
charge on the capacitor will oscillate around the true 
null state, thus eliminating drift, an inherent problem 
in conventional analog equipment. 
With converter No. 1 feedback circuit open and the 
electronic switch connected, the system can be used as 
an integrator with a dynamic range of 4,000 to I. 
(continued overleat) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States Govern-
ment. nor NASA, nor any person acting on behalf of NASA: A. Makes 
any warranty or representation, express or implied, with respect to the 
accuracy, completeness, or usefulness of the information contained in
this document, or that the use of any information, apparatus, method, 
or process disclosed in this document may not infringe privately-owned 
rights; or B. Assumes any liabilities with respect to the use of, or for 
damages resulting from the use of, any information, apparatus, method, 
or process disclosed in this document.
https://ntrs.nasa.gov/search.jsp?R=19640000021 2020-03-11T17:06:43+00:00Z
When a d.c input is applied at E 1 , the amplifier 
integrating capacitor charges at a rate proportional to 
the applied voltage. When a specific voltage level is 
reached, the appropriate voltage-sensitive trigger 
produces an output that steps the forward-reverse 
binary counter and simultaneously causes the elec-
tronic switch to quench the charge on the integrating 
capacitor. This action is repeated as long as an input 
is applied at E 1 and converter No. 2 registers the 
value of the time-integrated voltage. With some 
functional voltage input applied at E 2, the output at 
E. will be the product of E 2 and the time-integrated 
voltage at E 1 . In this system, if the counter is 
capable of registering 1,023 bits, the overall accuracy 
of the system approaches 0.1 percent. Larger registers 
would afford even greater accuracy. 
Notes: 
1. In the latter configuration, the system could be 
used as a multiplier in an analog computer, al-
though response time utilizing the present integrat-
ing capacitor circuit is relatively slow, being in the 
vicinity of 1 second. Response time of one milli-
second may be possible using solid state circuitry. 
2. For further information about this innovation 
inquiries may be directed to: 
Technology Utilization Officer 
Manned Spacecraft Center 
P.O. Box 1537 
Houston, Texas 77001 
Reference: B64-10064 
Patent status: NASA encourages the immediate 
commercial use of this invention. It is owned by 
NASA and inquiries about obtaining royalty-free 
rights for its commercial use may be made to NASA 
Headquarters, Washington, D.C. 20546. 
Source: McDonnell Aircraft Corporation 
under contract to

Manned Spacecraft Center (MSC-64) 
Brief 64-10064


Digital logic elements provide additional functions from analog input

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