Optimized Design of Phase Self-Correcting Lock-in Amplifier

The output of a single-phase lock-in amplifier (LIA) is sensitive to the phase difference between the input and reference signals, which can significantly reduce detection sensitivity. This article proposes a simple, field-programmable gate array (FPGA)-based, phase self-correcting LIA (PSC-LIA) to address this issue. The PSC-LIA employs a phase segment estimation (PSE) function to determine the phase difference and a proportional-integral (PI) controller to generate a corrective phase control signal. A phase-adjustable square wave generator (P-A SWG), offering a phase adjustment range of$-\pi $to$\pi $, provides the reference signal. To simplify the design of the low-pass filter (LPF), a dedicated low-order high-pass filter (HPF) preprocesses the input signal. Simulations and experimental results validate the effectiveness of the proposed PSC-LIA. Furthermore, its efficacy in extracting error signals is evaluated by integrating it into a laser frequency stabilization system. The results demonstrate that the PSC-LIA exhibits excellent performance, a fast response time, and adaptability to a variety of applications.