Electronic amplifier contains matched pair of metal oxide semiconductor field effect transistor devices which have high input impedance and long-term stability. Thermistor in feedback loop provides temperature compensation for large drifts in the sensor

Stillman, G.

English

NASA Technical Reports Server

/dc 
April 1971	 Brief 71-10090 
NASA TECH BRIEF 
Manned Spacecraft Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a aubscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the. Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Polarographic Carbon Dioxide Transducer Amplifier 
The problem 
To devise a means of amplifying the output from 
a carbon dioxide sensor. The electronic amplifier 
must have long-term stability, high input impedance 
(greater than 1012 ohms) and a temperature co-
efficient which will compensate for large drifts in 
the CO 2 sensor.
ance and long-term stability. Temperature compensa-
tion is provided by a thermistor in a feedback 
loop. 
How it's done: 
Transistors Q 1 and Q 2, a matched pair of N-
channel, depletion mode, insulated-gate field-effect 
The solution:	 devices, form a differential input with a dc gain 
An electronic amplifier containing a matched pair 	 of 15V. Resistors R 1 and R2
 control the total 
of metal-oxide semiconductor field effect transistor	 emitter current; and resistors R 3
 and R4 , which 
(MOSFET) devices which have high input imped- 	 divide the total current between Q1 and Q2, de-
(conliiiued overleaf) 
Now
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Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States 	 will be free from privately owned -rights.
https://ntrs.nasa.gov/search.jsp?R=19710000089 2020-03-17T02:22:19+00:00Z
termine the total dc gain; and diodes CR 1
 and CR2 
protect the operational amplifier from excessive dif -
ferential voltages caused by turn-on transients, input 
transients, and output overloads. The voltage supply 
requirements for the circuit are 10.0 Vdc at 3.0 mA, 
and 8.0 Vdc at 2.0 mA. 
The overall temperature coefficient, referred to the 
input, is 12 AV/°K from 288°K to 308°K, and 
20 AV/°K from 273°K to 323°K. An important de-
sign feature of this circuit is the operation of the 
matched input transistors at or near the zero-
temperature coefficient point, resulting in superior 
temperature tracking.
Note: 
Requests for further information may be directed 
Technology Utilization Officer 
Manned Spacecraft Center, Code JM7 
Houston, Texas 77058 
Reference: TSP7 1-10090 
Patent status: 
No patent action is contemplated by NASA. 
Source: Gerald Stillman of

Beckman Instruments, Inc.

under contract to

Manned Spacecraft Center

(MSC-13728) 
Brief 71-10090 Category 02


Polarographic carbon dioxide transducer amplifier

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