Design of a multi-frequency bio-impedance spectroscopy system analog front-end and digital back-end with on-chip implementation

In this paper, the design of a Bio-Impedance Spectroscopy system is presented. The system consists of a Direct Digital Synthesis Sine-Wave Generator (DDS-SWG), an Analog Front-End (AFE), an Analog-Digital Converter (ADC), and a Digital Back-End implemented using a Field Programmable Gate Array (FPGA). The FPGA also drives the ADC, the DDS-SWG, and the LCD. The AFE consists of a high output impedance Load-In-Loop Current Source (LL-CS) and a set of High Common-Mode Rejection Ratio (CMRR) Instrumentation Amplifiers (IA). It uses a simple and straightforward impedance extraction algorithm using just division and constant multiplication. The CMOS implementation of the AFE using the TSMC 0.35um 2P4M is also presented. The system forms part of a platform that aims to predict a urolithiasis (urinary stone) event.