Email: rossa@rpi.edu

CompanyName: Rensselaer Polytechnic Institute

Country: USA

Abstract Title:
Broadband High Precision Current Source Design Solutions and Limitations

Abstract

To achieve maximum distinguishability [1], that is, to detect the
smallest inhomogeneity at the greatest distance from the electrodes,
multiple current sources must be designed to apply the desired optimal
patterns of currents. A factor limiting the precision of a broadband
current source is its finite output impedance, which is dominated by
input and stray capacitances. Current shunted away from the load and
into the output impedance degrades the precision of that source.

We have simulated current sources that are capable of producing an
output impedance corresponding to 11 bits of precision from 100 Hz to
100 kHz. Our design goal is to measure loads with at least 16 bits of
precision. This requires 16-bit or higher current sources, which
translates to an output impedance in the tens of megohms. To accomplish
this, two types of current source compensation have been designed and
simulated, each possessing distinct advantages and disadvantages. These
compensation techniques have produced simulated current sources with
output impedances in the hundreds of megohms from 100 Hz to 100 kHz.

References:
1. Isaacson, D. Distinguishability of Conductivities by Electric
Current Computed Tomography. IEEE Trans Med Imaging MI-5 (2): 92-95,
1986.