Low-Voltage Linear OTAs Employing Multi-TANH Doublet and Exponential-Law Circuits

In this paper, new linearization technique for bipolar OTAs using exponential-law circuits is described. The core circuit of the proposed OTAs is the multi-TANH doublet. Two kinds of the OTAs have been designed. One has parallel configuration and the other is adaptively biasing configuration. The core circuit is combined with the SINH circuit for the parallel configuration or the COSH circuit as an adaptively biasing current source. In addition, two other designs of linear OTAs are proposed, and thus altogether four new linear OTAs are presented. Although these designs of the proposed OTAs are different, the theoretical normalized transconductances of the OTAs are expressed as the same function. The performance of the OTAs is compared with that of the multi-TANH circuits, which are known as conventional linear bipolar OTAs. The linear input voltage ranges of the OTAs are wider than that of the multi-TANH doublet and almost the same as that of the multi-TANH triplet. Furthermore, the power dissipated in the proposed OTAs is lower than that in the multi-TANH doublet and triplet. SPICE simulation shows that each OTA has different advantages.