Analog Integrated Current Drivers for Bioimpedance Applications: A Review <s> Introduction <s> A circuit for estimating the amplitude of small signals (in the range of microvolts to a few millivolts) developed initially for an electrical impedance tomography (EIT) data acquisition system is presented. The paper is focused on two points, the accurate demodulation of the difference of two sinewave signals and the common-mode correction of the measurement. The method is oriented for applications in measuring instruments, where a signal source (sinewave oscillator) is assumed to be incorporated. It uses a sample-and-hold circuit, suitably driven, as an amplitude demodulator. One of the advantages of this method is that the realization of the synchronous demodulator (or phase-sensitive detector) does not require a low-pass fitter at the output, resulting in a smaller settling time, that is, in higher speed of measurement. Finally, to improve the accuracy, a self-calibration technique has been developed. > <s> BIB001 </s> Analog Integrated Current Drivers for Bioimpedance Applications: A Review <s> Introduction <s> Electrical impedance tomography (EIT) is a relatively new imaging method that has evolved over the past 20 years. It has the potential to be of great value in clinical diagnosis; however, EIT is a technically difficult problem to solve in terms of developing hardware for data capture and the algorithms to reconstruct the images. This review looks at the development of EIT and how it has evolved. It focuses on its clinical applications, examining hardware for the collection of data and reconstruction algorithms to generate images. Finally, this review looks at future developments that are evolving from EIT. These new variations use mixed modalities that may produce interesting new clinical imaging tools. <s> BIB002
Bioimpedance measurement is defined as the study of biological tissue/cell in response to an alternating electric field, which can cover a frequency range from tens of Hz to several MHz   . The electrical properties of tissue/cell (conductive and dielectric properties) are characterized by frequency variable complex electrical bioimpedance providing important information about the tissue/cell physiology and pathology. In order to measure the bioimpedance, a current stimulus is required to be provided through a set of electrodes and measuring the corresponding potential via the same, or another, pair of electrodes. Depending on whether to measure the real and imaginary components of the impedance, as in electrical impedance spectroscopy (EIS), or to image the impedance, as in electrical impedance tomography (EIT), a synchronous detection method BIB001 , or finite element algorithms BIB002 , can be utilized respectively. To provide an accurate impedance measurement, the current injected into the tissue should have a constant and accurate amplitude throughout the required band of frequency. This imposes tight specifications on the design of the current driver. A current driver should have high output impedance with respect to load, so that all the current gets transferred to the load, and not shunted away. For example, an output impedance of 1 MΩ for a load of 1 kΩ will provide 0.1% accuracy of the output current. As the impedance is presented as real and imaginary or magnitude and phase values, it is of prime importance to have the minimum phase error at the output of the current driver. This is due to the fact that any phase variation at the output of the front end should be only due to the tissue under test, otherwise the phase errors between the driver and the measured potential cannot be distinguished from each other. It is appreciable to perform the impedance measurement up to 10 MHz range, as it can provide an insight to the nucleus of the cell  . This paper provides a review on multiple integrated current drivers, used mostly in EIS and EIT applications. They are configured in two groups of open loop and closed loop drivers. In each system, the transconductance and output impedance has been analyzed. The measurement results, in terms of