High-Purity and Wide-Range Signal Generator for Bioimpedance Spectroscopy

Abstract

This brief presents an integrated high-purity current signal generator (SG), part of a bioimpedance spectroscopy system that performs measurements in the frequency range from 1 kHz to 2 MHz, and it is able to measure bioimpedance values from 100 ${ \Omega }$ to 1 $\text{M}{ \Omega }$ . The SG is implemented in a 0.18- $ {\mu }\text{m}$ CMOS process, it is powered by a single 1.8 V voltage source, and occupies a total area of 1.62 mm2. It is able to generate single-frequency signals from 1 kHz to 2 MHz in 12 steps logarithmically spaced. High signal purity is achieved by using a second-order low-pass filter, with a bandwidth that can be programmed from 4 kHz to 8 MHz, in 12 points logarithmically spaced. The SG’s power consumption varies from 750 $ {\mu }\text{W}$ , at the lowest frequencies and gain, to 2.06 mW at the highest frequencies and gain. The output current levels can be modified from 130 nA up to 10 $ {\mu }\text{A}$ in five programmable steps (9.5 dB per step). The SG achieves a spurious-free dynamic range larger than 40 dB while covering almost three decades in frequency. Such performance enables measurements with errors below 1%, as it is required for accurate bioimpedance measurements in many medical applications.