Qu Shao-Bo, Robert Olivier, Lognonné Philippe, Zhou Ze-Bing, Yang Shan-Qing
Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, CNRS, F-75013 Paris, France.
MOE Key Laboratory of Fundamental Physical Quantities Measurement, School of Physics, Huazhong University of Science and Technology, Wuhan 430074, People's Republic of China.
Rev Sci Instrum. 2015 Mar;86(3):034708. doi: 10.1063/1.4914890.
Low frequency 1/f noise is one of the key limiting factors of high precision measurement instruments. In this paper, digital correlated double sampling is implemented to reduce the offset and low frequency 1/f noise of a data acquisition system with 24-bit sigma delta (Σ-Δ) analog to digital converter (ADC). The input voltage is modulated by cross-coupled switches, which are synchronized to the sampling clock, and converted into digital signal by ADC. By using a proper switch frequency, the unwanted parasitic signal frequencies generated by the switches are avoided. The noise elimination processing is made through the principle of digital correlated double sampling, which is equivalent to a time shifted subtraction for the sampled voltage. The low frequency 1/f noise spectrum density of the data acquisition system is reduced to be flat down to the measurement frequency lower limit, which is about 0.0001 Hz in this paper. The noise spectrum density is eliminated by more than 60 dB at 0.0001 Hz, with a residual noise floor of (9 ± 2) nV/Hz(1/2) which is limited by the intrinsic white noise floor of the ADC above its corner frequency.
低频1/f噪声是高精度测量仪器的关键限制因素之一。本文采用数字相关双采样技术，以降低具有24位sigma-delta（Σ-Δ）模数转换器（ADC）的数据采集系统的失调和低频1/f噪声。输入电压由与采样时钟同步的交叉耦合开关进行调制，并由ADC转换为数字信号。通过使用适当的开关频率，避免了开关产生的不需要的寄生信号频率。噪声消除处理是通过数字相关双采样原理进行的，这相当于对采样电压进行时移减法。数据采集系统的低频1/f噪声谱密度降低到平坦状态，直至测量频率下限，本文中该下限约为0.0001Hz。在0.0001Hz时，噪声谱密度消除超过60dB，剩余本底噪声为（9±2）nV/Hz(1/2)，这受到ADC在其转折频率以上的固有白噪声本底的限制。
