Square-Signal-Based Algorithm for Analog Lock-In Amplifiers

Dual-phase lock-in amplifiers (LIAs) are designed to extract information (amplitude and phase) from signals buried in high noise levels. In spite of their popularity, their use has been traditionally limited to input sinusoidal waves with symmetric power supplies. This paper presents an algorithm that enables single-supply analog LIAs to properly process input square waves. Formed by linear equations, its computational implementation is much simpler than that of the traditional sinusoidal algorithm. Moreover, applied to battery-operated microcontrolled systems where square signals can be generated by the embedded microcontroller, it presents intrinsic advantages such as simplicity, versatility, and reduction in power and size. Experimental results validate the proposed algorithm, confirming its enormous possibilities in sensing applications.