Evolution of Lock-In Amplifier as Portable Sensor Interface Platform: A Review

The phase-sensitive detection (PSD), popularly referred to as lock-in amplifier (LIA) has been around for quite a long time. Lock-in amplifier has been quite a versatile measurement instrument for extracting low-level signals buried in noise. In the recent past, the importance of LIA has been realized as a sensor interfacing platform and a number of portable implementations targeting sensing applications have been reported. This review surveys LIA design, implementation and application as portable sensor interfaces. The paper put forward a brief history of phase-sensitive detection leading up to the state-of-the-art implementation in various fields of application. Different designs and implementation techniques for LIA have been categorized and introduced as per the design topologies. The main category being analog, digital, FPGA and CMOS integrated design. Finally, the application of LIA in resistive, capacitive, impedance, optical and Nano-bio sensors is categorized and investigated in detail.