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

Summary A 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.