Optimal Parameter Design of DAC-Based Sinusoidal Signal Generators for Electrical Impedance Spectroscopy

This article provides parameter optimization processes of sinusoidal signal generators (SSGs) based on a digital-to-analog converter (DAC) for electrical impedance spectroscopy (EIS) applications. The SSG, which is the most power-hungry building block in EIS systems, generates a sinusoidal signal by using a DAC. To achieve high accuracy for the overall EIS system, high linearity is required for the sinusoidal signal. Thus, the SSG’s DAC is typically operated with a high oversampling ratio (OSR) and a large number of quantization levels ( ${L}_{\text {DAC}}$ ) at the expense of increased power consumption, large area, and high complexity. For efficient use of the power and area in the SSG, it is necessary to optimize the OSR, ${L}_{\text {DAC}}$ , and the order of the low-pass filter (LPF) ( ${N}_{\text {LPF}}$ ). In this article, optimal design parameters of SSGs, which can achieve highly accurate EIS systems with low complexity, are presented. First, the minimum OSR and ${N}_{\text {LPF}}$ for lowering the magnitude error to less than 0.1% are presented. Then, optimal quantization levels of finite-resolution DACs are found for sufficient accuracy and harmonic tones. In addition, the accuracy and harmonics of odd-number OSR cases are analyzed and compared with even-number OSR cases. According to the results, it is possible to design an SSG that only differs from the ideal sinusoidal signal by approximately 0.1% by using OSR $\leq32$ , ${N}_{\text {LPF}} \leq2$ , and ${L}_{\text {DAC}} \leq256$ .