Hybrid Filtering Techniques for Lock-In Measurements

This application brief discusses the use of hybrid filtering techniques in lock-in measurements, focusing on the comparison between Finite Impulse Response (FIR) and Infinite Impulse Response (IIR) filters. It outlines the challenges faced when measuring AC signals in the presence of significant noise and explains how lock-in amplifiers can enhance sensitivity by mixing the measured signal with a reference signal. The document details the advantages of FIR filters, including faster settling times and better harmonic rejection when compared to traditional IIR filters. It also presents a hybrid filter approach that combines both FIR and IIR filters, allowing for improved signal-to-noise ratios and reduced measurement times. The brief includes specific examples of settling times for various filter configurations and the impact of these filters on measurement precision. Additionally, it addresses the Allan deviation as a method for analyzing measurement stability and the effects of environmental noise on measurement accuracy.