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Active and Passive Electronic Components
Volume 27 (2004), Issue 3, Pages 183-187

A Current-mode Logarithmic Function Circuit

King Fahd University of Petroleum and Minerals, Box 203, Dhahran 31261, Saudi Arabia

Received 18 October 2003; Revised 14 November 2003

Copyright © 2004 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A new current-mode analog circuit configuration that implements the function ln (x/y) is proposed. The circuit uses bipolar transistors and resistors and is suitable for integration. In the proposed circuit the ratio (x/y) can be larger or smaller than unity. Simulation results are included.