Significantly enhanced sensor signal detection method using harmonic frequency in lock-in amplifier

In this study, we present a significantly enhanced signal detection method using harmonic frequency in a lock-in amplifier (LIA). This method reduces the effect of flicker noise that limits the signal-to-noise ratio in a conventional DC-based LIA. Furthermore, it has a definite advantage that it is not necessary to match the phase between the input and the reference signals. To verify such merits, we constructed a hybrid LIA circuit and conducted experiments. The results demonstrated that the dynamic range improved by approximately 43 dB compared to a conventional DC-based LIA. Moreover, the harmonic LIA output is successfully obtained regardless of the phase difference.