A novel CMOS current mode fully differential tanh (x) implementation

This paper presents a novel topology that implements an accurate approximation to the tanh (x) function. This approximation works in current mode and uses transistors in the subthreshold region of operation minimising power consumption and occupied area. Moreover, it has been designed with fully differential and balanced topologies so that the external influences, offset and distortion of even order are reduced. The proposed topology is thoroughly explained and it is analysed taking the body effect into account. Some modifications are applied in order to immunise it from the body effect, and simulated results for an implementation on a 0.35 mum AMI CMOS technology are presented.