On the design of very small transconductance OTAs with reduced input offset

Abstract

In this paper it will be demonstrated, from the theory and measurements, that series-parallel (SP) mirrors allow building current copiers with copy factors of thousands, without degrading mismatch or noise performance. SP current-division will be then employed to design OTAs ranging from a few pS to a few nS, with up to 1V linear range, consuming in the order of 100nW, and with a reduced area. An integrated 3.3s time-constant integrator will also be presented. One-by-one several design non-idealities will be revised: linearity, offset, noise, leakages; as well as layout techniques. A final analysis concludes that SP-association of transistors allows to build very efficient transconductors, for demanding applications in the field of implantable electronics among others.