FPGA-Based Digital Lock-in Amplifier With High-Precision Automatic Frequency Tracking
Cheng Zhang, Huan Liu, Jian Ge, Haobin Dong
Abstract
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.