MINIMIZATION OF STRAY CAPACITANCES IN HOWLAND CURRENT SOURCE

D. Bouchaala, O. Kanoun, N. Derbel

Abstract

Stray capacitances, due to e. g. limitations of layout and the use of active circuit elements, lead to limitations of the performance of bioimpedance devices at higher frequencies. The effects of stray capacitances can be avoided by several methods, such as Generalized Impedance Converter (GIC), Negative Impedance Converter (NIC) or external compensating operational amplifier. <BR />In this work, the investigation of NIC and GIC for Howland current source shows that both methods are not suitable for multifrequency measurement system, because they need different adjustments of components for every frequency. The external compensation method is investigated with uncompensated and compensated operational amplifier. Simulation results show that the addition of compensation capacitor externally to the operational amplifier in Howland current source has good accuracy about 0.02 % at high frequencies up to 1MHz.

Keywords

stray capacitance, bioimpedance spectroscopy, voltage controlled current source, Howland topology, compensation capacitor

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IMEKO TC

TC13 - Measurements in Biology and Medicine

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