Compact CMOS Wideband Instrumentation Amplifiers for Multi-Frequency Bioimpedance Measurement: A Design Procedure

Abstract

The design of an instrumentation amplifier (IA), based on indirect current feedback and suited to electrical bioimpedance spectroscopy, is presented. The IA consists of two transconductors and a summing stage, featuring a single-stage configuration process that allows the maximum achievable bandwidth to be extended. The transconductors are linearized by means of resistive source degeneration, whereas the use of super source followers allows a reduction in the values of the source degeneration resistors. This fact leads to a decrease in the overall noise and the silicon area, thus resulting in a compact implementation. A thorough analysis of the proposed solution, accompanied by a design procedure and verified by means of electrical simulations, is also provided. Two versions of the IA, i.e., a single-ended (SE) and a pseudo-differential (PD) structure, were designed and fabricated using 180 nm CMOS technology to operate with a 1.8 V supply. The experimental results, including a BW of 5.2 MHz/8.0 MHz, a CMRR higher than 72 dB/80 dB, a DC current consumption of 139.0 µA/219.3 µA and a silicon area equal to 0.0173 mm2 /0.0291 mm2 for the SE/PD implementation, validate the suitability of the approach.