Detection circuit for measuring tiny differential capacitance

Abstract

A detection circuit for measuring micro differential capacitor comprises a frequency selection circuit, a phase-locked loop tracking circuit, a logic gating circuit and a low-pass filtering circuit, wherein the frequency selection circuit and the phase-locked loop tracking circuit are formed into resonance units; the resonance frequency of each resonance unit is determined by the capacity of a to-be-measured differential capacitor; and two sets of resonance units formed by the differential capacitor can realize frequency output in direct proportion to the capacity of the differential capacitor under the action of a back-end logic gating circuit and the low-pass filtering circuit. The detection circuit has high detection precision and output linearity, small temperature drift and strong anti-interference capacity; moreover, the detection circuit has simple circuit structure and is convenient for engineering and integrated circuit making. The detection circuit is suitable for the measurement based on micro differential capacitor sensitive mechanism in the fields of medical apparatus, security-monitoring detection, inertia device and fluid characteristics measurement.

Description

technical field [0001] The invention belongs to the technical field of precision measurement, and in particular relates to the application technology of micro-differential capacitance measurement, which is applicable to the measurement based on the micro-differential capacitance sensitive mechanism in the fields of medical equipment, security detection, inertial devices and fluid characteristic measurement. Background technique [0002] With the development of micro-electromechanical systems (MEMS) technology, micro-nano-sized sensors have been widely used in medical equipment, security detection, inertial devices, fluid characteristic measurement and other fields. Due to the size of MEMS sensors, the signals output by these sensors are extremely weak. A typical capacitive MEMS sensor output signal is 10 -15 fF magnitude. The current technical bottleneck that limits the development and application of microsensors is the accuracy and stability of signal detection. Sensors ...

AI Technical Summary

Problems solved by technology

Although the output signal is frequency information with strong anti-interference, the capacitor charging and discharging process directly related to the frequency is very sensitive to voltage, so the interference introduced by the charging and discharging process is difficult to overcome, and the conversion process of charging and discharging is controlled by the transistor, and the state switching There will be charge injection and charge feedthrough effects at the moment, which will seriously affect the detection accuracy; at the same time, due to the nonlinear characteristics of the capacitor charging and discharging process, the frequency of the output signal and the size of the capacitor to be measured present a serious nonlinearity, which requires a nonlinear Correction

[0004] Therefore, the above two detection methods are not suitable for the field of high-precision capacitance detection.

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