A Sub-0.1% THD Sinusoidal-Signal Generator for Impedance Measurement Using a Delta-Sigma-Modulated Look-Up Table

Many frequency-based electronic measurement applications require a sinusoidal stimulus with high linearity, such for accurate impedance measurement systems used in chemistry, biology, and physical sensing. In this work, we present a highly linear sinusoidal-signal generator (SSG) on chip for use in such impedance measurement systems. Building upon prior digital SSG approaches that use a digital multi-stage noise-shaping (MASH) modulator to achieve high linearity while using a small digital-to-analog converter (DAC), we introduce delta-sigma modulation directly to the look-up table, achieving similarly high linearity without requiring a MASH modulator in the signal chain, which adds both design complexity and in-band errors. A prototype integrated circuit was fabricated using 180 nm CMOS and measured while generating a 20 kHz, 140 mVpp sine wave. It achieves 0.088% THD through the 20th harmonic and 63.5 dB SFDR. The approach is highly digital in nature and therefore amenable to implementation using automated synthesis and place and route, which makes it a promising approach for future scalability in advanced CMOS process nodes.