Influence Analysis of Sensor's Nonlinearity on Output of Lock-in Amplifier

Abstract

Generally the lock-in amplifier (LIA) can be used to detect very weak signal. This is based on the fact that any signal with a different frequency from that of the LIA's reference signal will result in zero output. However, if the signal is measured by a sensor with some nonlinearity, the LIA indeed yields some mixed output that comes from the correlation between the measured signal and reference signal. This paper presents a theoretical analysis on the output of LIA. Furthermore, based on analysis results, a curve fitting method of measuring the sensor's dynamic and tiny nonlinearity is provided. Experimental results verify that it is a useful measurement method when the accuracy is focused on