微小容差检测系统中基准源的设计与应用

Design and Application of Reference Source in Tiny Capacitance Difference Detecting System

为进一步提高fF级微小容差数据采集系统精度,满足10^(-4)~1 Hz测量频带内μV级电路噪声测试需求,采用平均值电路形式的AD780基准源电路,替代原有采集系统中模数转换芯片AD7712的内部电压基准。仿真分析AD780基准源的频域噪声满足指标要求,实测对比AD780与AD7712内部电压基准的时域、频域噪声,以及2种基准源下系统的采集精度与频域本底噪声。实测结果表明:在AD780提供外部电压基准的条件下,指标频点处噪声分辨率为0.5μV/Hz^(1/2),对比内部基准条件下提高了3.34倍。该设计进一步提高了系统检测精度,为分析测试微小容差检测电路的低频噪声特性及提高电容传感分辨率提供了必要条件。

In order to further improve the accuracy of fF level capacitance difference detection data acquisition system and meet the demand ofμV level circuit noise in 10^(-4)~1 Hz measurement frequency band,the AD780 reference source circuit in the form of average circuit was adopted to replace the internal voltage reference of AD7712 in the original acquisition system.The frequency domain noise of AD780 reference source met the requirements of the index by simulation analysis,and the time and frequency domain noise of AD780 and AD7712 internal voltage reference were measured and compared,as well as the acquisition accuracy and frequency domain background noise of the system under the two reference sources.The measured results show that the noise resolution at the index frequency point is 0.5μV/Hz ^(1/2) under the condition AD780 provides external voltage reference,which is 3.34 times higher than that under the condition of internal reference.The design further improves the performance index of the system,and provides a necessary condition for analyzing and testing the low-frequency noise characteristics of the capacitance difference detection circuit and improving the resolution of capacitance sensing.