Circuit increases the range of a logarithmic current amplifier by combining a commercially available amplifier with a silicon epitaxial transistor. A temperature compensating network is provided for the transistor

Gilmour, G.

English

NASA Technical Reports Server

I )Ut 
August 1966	 Brief 66-10350 
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. 
Transistor Circuit Increases Range of Logarithmic Current Amplifier 
L-----------------I 
Temperature Compensating Network 
The problem: 
To design . a logarithmic current amplifier capable 
of operating throughout a range of 10- 12 to 10-2 
amperes. Amplification through this range can be ob-
tained by cascading amplifiers in incremental steps 
but this creates problems of physical volume, relia-
bility, calibration, and difficult operation. 
The solution: 
A circuit that provides logarithmic amplification of 
an input range from 10- 12 to 10-2 amperes by com-
bining a commercially available amplifier with a sili-
con epitaxial transistor.
How it's done: 
The principle of operation involves the placement 
of a logarithmic feedback element across the ampli-
fier. The circuit operates on the transfer function of 
the silicon epitaxial transistor, Qi in which the out-
put voltage is proportional to the log of the input cur-
rent. Resistors RI and R2 and the capacitor stabilize 
the circuit. That portion of the circuit within the 
dotted lines serves only to provide temperature com-
pensation for QI. Input impedance is 10 megohms and 
input signal strength is 10- 12 to 10-2 amperes. 
(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=19660000349 2020-03-11T17:41:18+00:00Z
Note: 
Inquiries concerning this innovation may be di-
rected to:
Technology Utilization Officer 
AEC-NASA Space Nuclear Propulsion 
Office 
U.S. Atomic Energy Commission 
Washington, D.C. 20545 
Reference: B66-10350
Patent status: 
No patent action is contemplated by NASA. 
Source: G. Gilmour

of Westinghouse Astronuclear Laboratory

under contract to

Space Nuclear Propulsion Office

(NU-0018) 
Brief 66-10350	 Category 01


Transistor circuit increases range of logarithmic current amplifier

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