Analysis, Simulation, and Development of a Low-Cost Fully Active-Electrode Bioimpedance Measurement Module

A low-cost 1 kHz–400 kHz operating frequency fully-active electrode bioimpedance measurement module, based on Howland current source, is presented in this paper. It includes a buffered positive feedback implemented with operational amplifiers, as well an AD8421 instrumentation amplifier, for the differential voltage measurements. Each active module can be connected to others, assembling wearable array. From array, 2 electrodes selected driven from THS413 fully activating mirrored source. This work performs complete circuit analysis, verified MATLAB and SPICE simulations of source’s transconductance output impedance over range between MHz. Resistors’ tolerances, possible mismatches, amplifiers’ non-idealities are considered both analysis simulations. comparison study four amplifiers (ADA4622, OPA2210, AD8034, AD8672) additionally performed. The also hardware-implemented tested lab all measured load resistors 150 Ω, 660 1200 Ω. Measurements showed that, using AD8034 remains constant frequencies up 400 KHz Ω 250 load, while lower performance achieved other 3 amplifiers. Finally, transient measurements performed at bipolar aforementioned resistor values.