Li Gang, Zhou Mei, He Feng, Lin Ling
School of Precision Instrument and Opto-Electronics Engineering, Tianjin University, Tianjin 300072, People's Republic of China.
Rev Sci Instrum. 2011 Sep;82(9):095106. doi: 10.1063/1.3633943.
Because of a large amount of arithmetic in the standard digital lock-in detection, a high performance processor is needed to implement the algorithm in real time. This paper presents a novel algorithm that integrates oversampling and high-speed lock-in detection. The algorithm sets the sampling frequency as a whole-number multiple of four of the input signal frequency, and then uses the common downsampling technology to lower the sampling frequency to four times of the input signal frequency. It could effectively remove the noise interference and improve the detection accuracy. After that the phase sensitive detector is implemented. It simply does the addition and subtraction on four points in the period of same phase and replaces almost all the multiplication operations to speed up digital lock-in detection calculation substantially. Furthermore, the correction factor is introduced to improve the calculation accuracy of the amplitude, and an error caused by the algorithm in theory can be eliminated completely. The results of the simulation and actual experiments show that the novel algorithm combining digital lock-in detection and oversampling not only has the high precision, but also has the unprecedented speed. In our work, the new algorithm is suitable for the real-time weak signal detection in the general microprocessor not just digital signal processor.
由于标准数字锁相检测中存在大量运算，需要高性能处理器才能实时实现该算法。本文提出了一种将过采样与高速锁相检测相结合的新算法。该算法将采样频率设置为输入信号频率的四倍的整数倍，然后使用常见的下采样技术将采样频率降低到输入信号频率的四倍。它可以有效去除噪声干扰并提高检测精度。之后实现相敏检波器。它只需在同相周期内的四个点上进行加减法运算，几乎取代了所有乘法运算，从而大幅加快数字锁相检测计算速度。此外，引入校正因子以提高幅度的计算精度，理论上该算法引起的误差可完全消除。仿真和实际实验结果表明，将数字锁相检测与过采样相结合的新算法不仅具有高精度，而且具有前所未有的速度。在我们的工作中，新算法适用于普通微处理器而非数字信号处理器中的实时微弱信号检测。
