基于紧耦合电感臂电桥的弱信号电容传感器检测电路设计

Design of weak signal capacitive sensor detection circuit based on a tightly coupled inductive bridge

电容传感器作为信号检测系统的感知部件,在进行信号测量时,由于信号的微弱和寄生电容的干扰,将难以实现信号的精准测量.为解决这一问题,针对当前最新的测试系统提出了改进方案:在C-V(电容-电压)转换电路中,用相互耦合的电感替换交流电桥的两个固定电阻臂,再用差动式接入的电容传感器替换另外两个电阻臂,如此便构成了改进后的紧耦合电感臂电桥.通过改变紧耦合电感臂电桥中两个电容传感器的微小变化量,对所提的CV转换电路在Multisim仿真软件中进行仿真实验,实验结果表明:检测电容的分辨率可以实现至飞法级别,检测灵敏度可以实现至49 mv/fF.相比改进前的方案优势具有较大的提高,与理论分析一致.这样,使用所提的弱信号检测方法在灵敏度、分辨率方面均高于改进前的检测方法,达到对较弱信号的检测.同时,一些降噪措施被提出用来抑制寄生电容的影响,进一步提高了所提电容传感器检测电路的性能.

As the sensing component of the signal detection system,the capacitive sensor is difficult to accurately measure the signal due to the weak signal and the interference of parasitic capacitance during signal measurement.In order to solve this problem,an improvement scheme is proposed for the latest test system:In the C-V(capacitance-voltage)conversion circuit,the two fixed resistance arms of the AC bridge are replaced with mutually coupled inductances,and the other two resistance arms are replaced with differentially connected capacitive sensors.By doing so,the tightly coupled inductive arm bridge is made.By changing the small changes of the two capacitive sensors in the tightly coupled inductive arm bridge,the proposed C-V conversion circuit is simulated in the Multisim simulation software.The experimental results show that:the resolution rate of the detection capacitance can be achieved to the Femto level,and the detection sensitivity can be achieved to 49mv/fF.Compared with the scheme before the improvement,the advantages of the scheme have been greatly improved,which are consistent with the theoretical analysis.In this way,the sensitivity and resolution of the proposed weak signal detection method are higher than these of the detection method before the improvement,and the detection of weaker signals can be achieved.At the same time,some noise reduction measures are proposed to suppress the influence of parasitic capacitance,which further improves the performance of the proposed capacitive sensor detection circuit.