Application And Research About Digital Demodulation In Differential Capacitance Sensor

Tiltmiter is one of the most important instruments which dedects the change in ground weak tilt and monitors the earthquake and solid tide.In geodesy,although crustal deformation is very small,differential capacitance sensor can detect it with high accuracy?high sensitivity?well stability?small size and so on.At present,the components used for the analog circuit whose debugging workload is very large and which has poor environmental adaptability and reliability in tiltmeter should satisfy the request of the high performance.In order to improve the reliability and reduce debugging workload,digitized transformation of analog circuit is necessary.Differential capacitance sensor is core part of the crustal deformation instrument which can detect faint ground tilt signal.First step for digitized transformation of the analog circuit is to realize digital demodulation.This paper introduces the working principle of the differential capacitance sensor and the characteristics of analog demodulation.Then it introduces three methods for implementing digital demodulation which including digital envelope demodulation and digital orthogonal demodulation and digital demodulation based on Goertzel algorithm.The principle of digital envelope demodulation similar to envelope demodulation is that the maximum value is taked out from every carrier.And the principle of digital orthogonal demodulation similar to orthogonal demodulation is that two signals from modulated signal multiplied by carrier and quadrature signal seek sum of squares and then extract its square root.This paper focuses on the study of digital demodulation based on Goertzel algorithm by which we can get spectrum at a particular point.Digital demodulation based on Goertzel algorithm iscompared with the other two methods with MATLAB simulation.