An 89.3% Current Efficiency, Sub 0.1% THD Current Driver for Electrical Impedance Tomography

Accurate electrical impedance tomography (EIT) measurements require a current driver with low total harmonic distortion (THD) and high output impedance. Conventional EIT current drivers attain good performance for these parameters but at the expense of low current efficiency. This Brief presents a differential current driver based on a current feedback structure with isolated common-mode feedback, achieving very low THD, high output impedance and high current efficiency. In addition, it uses current DACs to remove any dc offsets at the output nodes. The current driver was fabricated in a 65-nm CMOS technology with 3.3 V supply. Measured results demonstrate a THD of 0.05% and 0.1% at 80 kHz, for
$1\,\,{\mathrm{ mA}}_{\mathrm{ p-p}}$
and
$1.375\,\,\rm mA_{\mathrm{ p-p}}$
output current, respectively. The total current consumption is 1.54 mA, resulting in a maximum current efficiency of 89.3%. The measured output impedance is 1.023
$\text{M}\Omega $
at 500 kHz and 568
$\text{k}\Omega $
at 1 MHz.