A new implementation for the logarithmic/exponential function generator

This paper presents two new approximations for the logarithmic and exponential functions. These approximations require only a square rooter function, a scalar function and a constant. Thus, the realization of these functions in current-mode is simple, straightforward and uses less number of MOSFETs. Simulation results obtained show that the logarithmic function can be obtained with relative root mean square (RRMS) error of 0.0755 over the normalized input range 0.001–1.0 while the exponential function can be obtained with RRMS error of 0.0489 over the normalized input range 0.01–3.0. Much less RRMS errors can be obtained for restricted normalized input values.