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

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.