Study on Howland Circuits for Low Power Electrical Impedance Tomography Systems

According to the requirements of low power electrical impedance tomography systems, two configurations of the Howland current pump are studied in this article. The analytical expressions for performance features of the two configurations are derived and analysis is made. Then simulation on computer and experiment with a low power bio-impedance system are performed to evaluate the performances of the two configurations. The experimental results validate the derived expressions and analysis. It is shown that the buffered feedback configuration typically has better output impedance and voltage compliance performance than the standard configuration at low frequencies no more than around 100 kHz. Then several guidelines for designing a high-performance Howland circuit are presented for using in low power electrical impedance tomography systems.