Design and Optimization of a High Linearity On-Chip Sinusoidal Current Generator for Bioimpedance Measurements Using Direct Digital Synthesis

This paper presents an optimization methodology to enhance the linearity of direct digital synthesis (DDS)-based on-chip sinusoidal current generators (SCGs) for bioimpedance measurements. After a detailed analysis of the origin of harmonics and their impact on measurement accuracy in conventional DDS-based SCGs, three different harmonic cancellation schemes are proposed. These are designed to decrease the harmonics in various applications with differing hardware requirements, significantly improving the precision and efficiency of DDS-based SCGs. The approach was implemented in a DDS-based SCG in 65 nm CMOS technology. Both simulations and measurements demonstrate a marked improvement in linearity with a figure-of-merit at least 9.4 times better than prior work. Although tailored for bioimpedance applications, the approach is also suitable for other low power, high linearity sinusoidal signal generators.