FPGA-Based Digital Lock-in Amplifier With High-Precision Automatic Frequency Tracking

• Main Authors: Cheng Zhang, Huan Liu, Jian Ge, Haobin Dong
• Format: Article
• Language: English
• Published: IEEE 2020-01-01
• Series: IEEE Access
• Subjects: Automatic frequency tracking; digital lock-in amplifier; weak signal detection; DSP builder
• Online Access: https://ieeexplore.ieee.org/document/9129659/

Aiming to overcome the problem of the frequency error between the reference signal and the measured signal in an analog lock-in amplifier, this paper presented a digital lock-in amplifier (DLIA) with accurate frequency automatic tracking to improve its performance. In this paper, a modular design approach based on DSP Builder was employed to develop a quadrature vector type lock-in amplifier with automatic frequency tracking. A reference signal generator with high-frequency resolution and a digital filter with good performance were implemented. The performance of the design was tested by determining the linearity, the Q value, and the noise immunity of the DLIA. The experimental results showed that the proposed DLIA has good linearity and the Q value can reach up to 82. The relative errors of the signals with amplitudes greater than 10 mV were less than 1% when the equivalent input was a sine wave signal with a frequency of 1 kHz and an amplitude of 500 mV. When the superimposed noise was less than or equal to 400 mV, the relative error was less than 2% in the same condition. The proposed DLIA has higher precision and efficient noise immunity.