Characteristics of the Howland current source for bioelectric impedance measurements systems

In the development of bioelectric impedance measuring systems, design of a stable current source with broad bandwidth and high output impedance is an important consideration. Howland circuit is a well known high performance, voltage controlled current source which can provide high output impedance as well as high frequency bandwidth. This paper presents a detailed study of Howland current source by considering the non-ideal characteristics of the components. Two different forms of Howland current source are compared and resulted relationship were evaluated by simulations. The results of this study facilitate the design of Howland circuit for bioelectric impedance measurement systems.