A small, low-power, high-speed, 8-bit analog-to-digital converter using silicon chip integrated circuits is suitable for use in airborne test data systems. The successive approximation method of analog-to-digital conversion is used to generate the digital output

Dunn, R. D.

Fullerton, D. H.

English

NASA Technical Reports Server

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January 1968
	 Brief 68-10016 
NASA TECH BRIEF	 1 
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
Small, Low Power Analog-to-Digital Converter 
The problem: 
To design a small, low-power, high-speed analog-
to-digital converter that would be suitable for use in 
an airborne test data system. 
The solution: 
An 8-bit analog-to-digital converter using silicon 
chip integrated circuits. The output bit rate is I MHz 
and the maximum conversion rate is 125 kHz. The 
digital output quantum is 20 millivolts, and the maxi-
mum full scale output is 5.100 volts. Total power con-
sumption is less than 840 milliwatts. The successive 
approximation method of analog-to-digital conver-
sion is used to generate the digital output. Overall
volume of the converter, packaged in tour potted 
modules, is approximately 2 cubic inches. 
Operation of the converter is summarized in con-

junction with the block diagram. A start conversion 
pulse resets the control logic, counter, and ladder 
control register, which consists of 8 dc flip-flops and 
associated "dump" and reset logic. The most signifi-

cant bit (bit I) flip-flop in the ladder control register 
is set (by a specific output from the decoder) to
switch the most significant current from the current 
ladder to the comparator summing line. At 750 nano-

seconds after the end of the start conversion pulse, 
the bit I current is compared with the current derived 
from the analog input. If the summed ladder current 
(cnhinued Overleal) 
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.
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is smaller than the analog current, the bif is retained; 
if it is larger, a dump pulse is generated to reset the 
appropriate control register flip-flop. When the flip-
flop resets, it switches the corresponding ladder 
current off the summing line. At the end of the bit 
time (1 microsecond), the counter advances I count. 
This advance switches in the next smaller bit, the 
comparison is made after a 750 nanosecond settling 
time, and the bit is then either accepted or rejected. 
This procedure is repeated until all 8 bits have been 
compared. The control logic then resets register bits 
2 through 8 and holds the counter in bit time zero 
until thenext start conversion pulse is received. Simul- 
taneously with each comparison, the output flip-flop 
is set if the bit is accepted and reset if the bit is 
rejected, generating the digital output.
Notes:	 - 
I. The converter can be used in any digital system in 
which it is necessary to convert an analog voltage 
into a serial digital signal and 8-bit accuracy is 
acceptable, such as in automated production or 
process control systems. With further development, 
the converter could be improved to operate at a 
higher speed and with greater accuracy. 
2. Inquiries concerning this converter may be di-
rected to:
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: B68-10016 
Patent status: 
No patent action is contemplated by NASA. 
Source: D. H. Fullerton and R. D. Dunn 
of The Boeing Company 
under contract to 
Marshall Space Flight Center 
(M FS- 13954) 
Brief 68-10016	 Category 01


Small, low power analog-to-digital converter

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