Unitary vs. Resistive Feedback in CMOS Two-Stage Indirect Current Feedback Instrumentation Amplifiers

Two approaches to establish the feedback loop in a two-stage CMOS indirect current feedback (ICF) instrumentation amplifier (IA), i.e., unitary feedback (UF) and resistive feedback (RF), are compared in this paper. To this end, the transistor level implementation of the IA has been enhanced. Super source followers have been used to build the input and output transconductors required in the ICF approach. Besides, the IA has been provided with a class-AB output stage in order to handle with low resistive loads. The proposed IA has been designed in 180-nm standard CMOS technology to operate with a 1.8-V supply. Simulation results show that RF allows external programmability and leads to a more accurate value of the IA voltage gain, whereas UF provides a superior response in terms of noise, thus leading to better noise efficiency factor and similar dynamic range metrics.