A Non-Linear Feedback Current Driver with Automatic Phase Compensation for Bioimpedance Applications

Abstract

In a conventional sinewave current driver for electrical impedance spectroscopy, as the frequency is increased the input/output phase delay of the current driver increases due to limited bandwidth. The required maximum phase delays of < 4° mean that operation is limited to about 1/12 of the driver bandwidth. A new phase compensation scheme is presented to reduce the phase delay at higher frequencies and can extend the useful operating frequency range of a current driver. The system is capable of reducing the phase error due to the current driver by an appreciable level so that it can operate much nearer the pole frequency of the driver. An integrated circuit was fabricated in a 0.35-μ m CMOS process technology, which provides a phase error reduction from 22° to 3° at 3 MHz. Its core occupies a silicon area of 1.2 mm2. It operates from a ±2.5 V power supply and can deliver output currents up to 1.8 mAp-p at 3 MHz.