测量nV正弦电压的互功率谱方法

An Approach Using Cross Power Spectrum Estimator for Measurement of nV Sinusoidal Signal

本文提出了一种测量nV正弦电压的新方法——互谱估计法,克服了现有的LIA法存在的缺点,即测量系统中零漂及1/f噪声影响,进一步扩展了nV电压测量下限。文中首次对有限数据记录长度的周期图法互谱估计性能进行了详细分析。证明其期望值可排除噪声影响,是一种渐近无偏估计。与自谱估计的周期图法相同,本方法是非一致估计,特别是在被测正弦信号频率处的谱起伏更为严重,因而妨碍了nV正弦信号的准确测量,为此必需采用加窗的平均周期图法以减少谱起伏方差。文末给出对1nV正弦信号的测量结果,与实际信号值基本一致,说明互谱估计法对nV正弦电压测量是一种可行的方法。

In this paper, a new approach using cross power spectrum estimator for measurement of nV sinusoidal signal has been developed, Because of the zerodrift and 1/f noise in direct coupled amplifier, it is difficult to measure very weak signal by using lock-in amplifier (LIA).The theoretical analysis demonstrated that the expectation of cross power spectrum is non-coherent with the noise and zerodrift of amplifier,so that this method can ensure the accuracy measurement, even if the measured sinusoidal signal is very weak. Next,the periodogram performance of cross power spectrum based on the finite deta record length are discussed, we found that its variance is so much large at the frequency of measured sinusoidal signal that the accuracy measurement is unable.Hence the average periodogram using windowing proceduces and low noise preamplifier is necessary. Finally, the measured result of 1 nV sinusoidal signal is given which is in good agreement with the practical value, which means that this method is feasibility and accuracy for measurement of weak sinusoidal signal.