A 0.05%–0.08% THD, 762.9 Hz–10 MHz direct digital frequency synthesizer using a reconfigurable DAC for electrochemical impedance spectroscopy measurements

Abstract

SummaryA wide‐range direct digital frequency synthesizer (DDS) is considered an essential component that is used in measuring electrochemical impedance spectroscopy (EIS). Since it depends on exciting the electrochemical sensor by a pure sine wave, total harmonic distortion (THD) is considered a challenging specification for an accurate EIS measurement. This paper introduces a complete system and circuit designs of a wide range DDS with a comprehensive system model using MATLAB environment. In addition, it presents the usage of a reconfigurable digital‐to‐analog converter (DAC) on the circuit level that is used either as a 4‐bit delta‐sigma ( ) DAC or an 8‐bit binary‐weighted DAC for both low‐ and high‐frequency ranges, respectively. The designed DDS generates an output frequency range from 762.933 Hz to 10 MHz using a physical 8‐bit DAC. The circuits are simulated using 0.18 μm CMOS technology. The designed DDS system achieves THD less than 0.05% with superior free dynamic range (SFDR) 66 dBc for low‐frequency range and 0.08% with SFDR 62 dBc for high‐frequency range. The DDS circuits occupy an area of 400 × 800 μm. The whole system consumes a 2.5 mW power consumption from a 1.8 V supply.