Abstract:
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In recent years, Electrical Bioimpedance (EBI) methods have gained importance.
These methods are often based on obtaining impedance spectrum in the range of β-dispersion,
i.e. from a few kHz up to some MHz. To measure EBI a constant current is often injected and
the voltage across the tissue under study is recorded. Due to the performance of the current
source influences the performance of the entire system, in terms of frequency range, several
designs have been implemented and studied. In this paper the basic structure of a Voltage-
Controlled Current Source based on a single Op-Amp in inverter configuration with a floating
load, known as load-in-the-loop current source, is revisited and studied deeply. We focus on
the dependence of the output impedance with the circuit parameters, i.e. the feedback resistor
and the inverter-input resistor, and the Op-Amp main parameters, i.e. open loop gain, CMRR
and input impedance. After obtaining the experimental results, using modern Op-Amps, and
comparing to the theoretical and simulated ones, they confirm the design under study can be a
good solution for multi-frequency wideband EBI applications because of higher values of the
output impedance than 100kΩ at 1MHz are obtained. Furthermore, an enhancement of the
basic design, using a current conveyor as a first stage, is proposed, studied and implemented. |