A Wideband Low-Distortion CMOS Current Driver for Tissue Impedance Analysis

Bioimpedance measurements are performed in a variety of medical applications including cancer detection in tissue. Such applications require wideband (typically 1 MHz) accurate ac current drivers with high output impedance and low distortion. This paper presents an integrated current driver that fulfills these requirements. The circuit uses negative feedback to accurately set the output current amplitude into the load. It was fabricated in a 0.35-μm complementary metal-oxide-semiconductor (CMOS) process technology, occupies a core area of 0.4 mm
²
, and operates from ±2.5-V power supplies. For a maximum output current of 1 mAp-p, the measured total harmonic distortion is below 0.1%, and the variability of the output current with respect to the load is below 0.5% up to 800 kHz increasing to 0.86% at 1 MHz. The current driver was tested for the detection of cancer sites from postoperative human colon specimens. The circuit is intended for use in active electrode applications.