Implementation of a Dual Howland Current Source for Biological Tissue Characterization

Abstract

Medical devices based on bioimpedance spectroscopy are widely used an have low costs compared to traditional diagnosis methods. Although, the most challenging part while designing a portable biomedical device is the design of the current source which requires a high output impedance over a wide frequency range in order to supply a constant output current for a certain range of load resistance. The Howland current source is one of the most popular topologies for voltage controlled current source. It is highly dependent on not only the operational amplifiers characteristics, but also the resistors values. This paper realizes a comparative analysis of the inverting dual Howland current source with three different cases of resistors configurations and three different operational amplifiers. The implementation is done based on the simulation results using the operational amplifier AD8021 with the resistor configuration R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> =R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> =30k Ω, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2a</sub> =0.5k Ω, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2b</sub> =3k Ω, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> = 3.5 kΩ.