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 large linearity range in each segment. The proposed range-segmented circuit is different from all segments constructed only by quadratic circuits or only by linear circuits. The proposed circuit was simulated using UMC 0.18 mu m 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 is between 69 and 150 MHz for input range from -63 to 198 mu A.