Jwu-E CHEN, Chih-Jen CHENG, Kuo-Jen LIN

Design of a range-segmented CMOS current-mode exponential circuit

A CMOS current-mode exponential circuit is designed by plugging candidate circuits into a Taylor’s approximation circuit to make a multiple-segment circuit. The selection of candidate circuits is dependent on a largelinearity range in each segment. The proposed range-segmented circuit is different from all segments constructed only byquadratic circuits or only by linear circuits. The proposed circuit was simulated using UMC 0.18 µm CMOS technology.The output linearity of the circuit is 56.7 dB for gain error less than 0.5 dB, and the –3 dB bandwidth of the circuit isbetween 69 and 150 MHz for input range from –63 to 198 µA.

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