A Phase Error Correction System for Bioimpedance Measurement Circuits

Abstract

Bioimpedance sensing is widely used across a spectrum of biomedical applications. Among the different system architectures for measuring tissue impedance, synchronous detection or demodulation (SD) stands out for its lock-in amplifier utilising in-phase (I) and quadrature (Q) demodulation signals to derive real and imaginary impedance components. Typically, the current injected into the tissue is controlled by a voltage-controlled current source (VCCS). However, the VCCS can introduce phase shifts leading to discrepancies in real/imaginary outputs, especially at the highest end of the operating frequency bandwidth. Such discrepancies can significantly impact diagnostic accuracy in applications reliant on precise tissue phase profiling, such as cancer and neuromuscular evaluations. In the present work, we propose an automatic phase error compensation stage for bioimpedance measurement systems to minimise this systematic error. Our experimental findings demonstrated a considerable reduction in phase error, with the Phase Error Compensated Synchronous Detection (PECSD) system exhibiting a maximum phase error of 2° (≤5% error) compared with the uncompensated SD system where error exceeded 20%. The improvements made by our proposed SD system hold great potential for enhancing the accuracy of impedance measurements, particularly in clinical diagnosis and disease detection.

Keywords

• bioelectrical impedance
• bioimpedance
• synchronous demodulation
• synchronous detection
• phase error
• PECSD