Analysis and Application of a Buffered Feedback Path Improved Howland Current Source in BioImpedance Measurements

Bioimpedance measurement and its applications for health monitoring have received interest during the last decade. A bioimpedance measurement device may consist of different blocks depending on the application it is employed in, although a main and vital block in the system is the current injection block. The improved Howland circuit, and its variants, is a classic and most common used architecture for the current injection block. This paper provides a thorough analysis for a variant which is the improved Howland current source with a buffered feedback path and it will investigate the limitations for the mentioned topology. In particular, we derive equations for various factors that can impact the performance of the circuit. A complete analysis for noise and non-idealities of the components in the circuit, that can degrade the performance, is provided. The experimental results of the circuit, manufactured on a printed circuit board (PCB), are presented. The final aim here is to provide information by the analysis and the experimental results to investigate the limitations of the circuit. These limitations can be useful for the designs in which the mentioned circuit is selected as the current source in a BI measurement device.