Simulation of a current source with a Cole-Cole load for multi-frequency electrical impedance tomography

Area of Science:

• Electrical Engineering
• Biomedical Engineering
• Instrumentation

Background:

• Accurate current sources are crucial for Electrical Impedance Tomography (EIT) systems.
• Existing current sources face limitations at higher frequencies and with complex resistive loads.
• The Howland current source is a common topology, but improvements are needed for robust EIT hardware.

Purpose of the Study:

• To simulate and evaluate an improved Howland current source for EIT applications.
• To compare the performance of two operational amplifiers (THS4021 and OPA843) within the improved current source.
• To assess the current source's stability and output impedance across a range of frequencies and with a Cole-Cole load model.

Main Methods:

• Simulation of an improved Howland current source circuit.
• Modeling of a Cole-Cole impedance for realistic biological tissue representation.
• Comparative performance analysis of THS4021 and OPA843 operational amplifiers from 1 kHz to 1 MHz.
• Evaluation of output impedance and current stability.

Main Results:

• The THS4021 operational amplifier outperformed the OPA843 in the simulated improved Howland current source.
• The THS4021-based current source achieved an output impedance of 20 MΩ at 1 kHz and >320 kΩ at 1 MHz.
• A constant and stable output current of up to 4 mA was maintained across the tested frequencies and with the Cole-Cole load.

Conclusions:

• The improved Howland current source utilizing the THS4021 offers enhanced performance for EIT systems.
• This configuration provides a stable current output suitable for various biological tissue impedances.
• The simulation results support the use of the THS4021 for developing more accurate and reliable EIT hardware.