Weak capacitance change measuring circuit

Abstract

The invention provides a weak capacitance change measurement circuit, and particularly relates to the technical field of weak capacitance signal conversion and detection. The measurement circuit comprises a CV conversion circuit, an amplification circuit, an analog multiplier, a low-pass filter and a phase shift circuit, the CV conversion circuit converts the relative change rate of the capacitance value of a capacitance sensor into the amplitude change of a weak sinusoidal signal; the weak sinusoidal signal is amplified by an amplifying circuit; the amplitude of an output signal of the amplifying circuit is solved by an amplitude demodulation circuit consisting of the analog multiplier and the low-pass filter, and a direct-current useful signal in direct proportion to the relative changerate of the sensor capacitor is output through the low-pass filter; the phase shifter changes the phase difference between the reference signal of the amplitude demodulation circuit and the output signal of the amplification circuit, and the circuit sensitivity is improved.

Description

technical field [0001] The invention relates to a weak capacitance change measurement circuit, which is particularly suitable for detection of weak capacitance changes with relatively small basic capacitance (body capacitance or static capacitance) of a sensor, and belongs to the technical field of weak capacitance signal conversion and detection. Background technique [0002] The basic principle of a capacitive sensor is to convert a certain physical quantity such as displacement, area, dielectric, etc. into a capacitance, and then indirectly measure the desired physical quantity by measuring the capacitance. Capacitive sensors have a very wide variety of uses. Especially in the field of high-precision detection, capacitive sensors have an irreplaceable position. Capacitive sensors have the advantages of high sensitivity and fast response, but the measurement circuit is relatively complicated. In most cases, the capacitance of the capacitive sensor is relatively weak, and...

AI Technical Summary

Problems solved by technology

In this case, it is necessary to introduce a controller, and introduce a balance signal under the control of the program to balance the basic capacitance of the capacitive sensor to be measured, which introduces digital noise to a certain extent, reduces the accuracy of the measurement system, and also makes the system variable. more complicated

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