CompanyName: Rensselaer Polytechnic Institute
Broadband High Precision Current Source Design Solutions and Limitations
To achieve maximum distinguishability , 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.