Analysis of a single supply constant current source for bioimpedance measurements

Abstract

Constant current source is one of crucial components of every bioimpedance measurement device. Here we present an analysis of a single supply current source based on a modified Howland circuit. The analysis of track to track capacitances has been performed by finite element numerical device simulation and compared to measurements on developed PCB without soldered elements. Capacitances of the order of 1 pF were simulated/measured the largest being the voltage source to ground capacitance (3 pF). The measured transconductance bandwith was about 3 MHz at 100 Ω load and 100 kHz at 100 kΩ. Circuit analysis with Spice resulted in larger bandwidths compared to the measured ones.