A Current‐mode Logarithmic Function Circuit

Abstract

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.

A new CMOS logarithmic current generator

“…All other realizations found in the literature have at least one of the following drawbacks: absence of low voltage operation capability [1,3,5], limited dynamic range [1,3,6], employment of BJT transistors [1,5,6], does not enjoy current-mode [1,3,4,6], cannot realize a true logarithmic function circuit where the ratio is larger or smaller than unity [1,6,7], temperature dependent [1,5], relatively high power consumption [6,7], no gain controllability [1,3,6], to some extent linearity error is high [3,6,7], uses passive elements, i.e. resistors [1,5,6], and finally design complexity [6,7].…”

“…Many approaches to the design of logarithmic circuits have been reported in the literature [1][2][3][4][5][6][7] and the references cited therein. The authors did not find references to a CMOS current-mode logarithmic circuit in the open literature except for the one reported in [2].…”