Implementation of I/Q Demodulation Technique for Phase-Sensitive Detection in Educational Laboratories
Abstract
Accurate measurement of phase and amplitude differences between input and output signals is essential in characterizing dynamic behaviour in electrochemical and optical instrumentation systems. In this study, an In-phase and Quadrature (I/Q) demodulation technique is implemented as a method for extracting both phase shift and amplitude ratio under noisy signal conditions. The system demodulates the measured signal using two orthogonal reference signals at 0° (in-phase) and 90° (quadrature), enabling the extraction of real-time phase and amplitude information. The analog front-end consists of a phase-sensitive detector and a low-pass filter to suppress high-frequency components. The filtered outputs are digitized using a high-resolution ADC after appropriate level shifting. Experimental results demonstrate that the proposed system achieves reliable signal recovery with good tolerance to noise up to 20 dB. Beyond this threshold, the recovered signals exhibit substantial deviations, resulting in unacceptable errors in amplitude and phase estimation. Furthermore, validation through EIS measurements shows that the system is able to reproduce Nyquist responses in good agreement with theoretical predictions. In addition to its measurement capability, the developed system also supports laboratory-based learning by providing a practical framework for understanding AC circuits, spectral impedance analysis, and complex-number data processing.