Lock-In Amplifier for Sensor Application Using Second Order Harmonic Frequency With Automatic Background Phase Calibration

An integrated lock-in amplifier (LIA) with automatic phase tuning and second-order harmonic frequency extraction is presented in this paper. The automatic phase alignment loop implemented in the proposed single-channel LIA can directly align the phases of an input signal with a reference signal. Furthermore, the proposed LIA system also includes an enhanced signal detection method in which the $2^{\text {nd}}$ harmonics of the carrier frequency ( $\omega _{\textit {ref}}$ ) is applied. As opposed to conventional LIA, this method reduces flicker noise and input offset effects that limit the signal-to-noise ratio (SNR). In terms of signal power detection, the proposed single-channel LIA architecture does not require phase synchronization between input and reference signals. The circuit is designed for a reference frequency of 100 Hz, suitable for biomedical applications. The LIA is Implemented using 0.18- $\mu \text{m}$ CMOS technology with a single power supply voltage of 1.8 V. The system consumes 360 $\mu \text{W}$ at an operating frequency of 100 Hz and presents a high input sensitivity dynamic range for a detection bandwidth of 50 Hz and a FOM of 116 dB.