Design And Implementation Of Circuit For Magnetotelluric Data Acquisition With Low Noise And Low Power Consumption

The magnetotelluric method is one of the geophysical methods to study the geologicalstructure, its field source is the natural alternating electromagnetic field. When the alternatingelectromagnetic field is propagating in the stratum, due to the skin effect, the signals withdifferent cycles have different penetration depth. Magnetotelluric signal is a very weak naturalsignal with amplitude of only μV level, but its frequency range can reach to10^-510³Hz.At the same time the collected magnetotelluric signal consists of five components, namely thetwo orthogonal electro signals of Ex, Ey and the three mutual orthogonal magnetic signals ofHx, Hy, Hz. These require the magnetotelluric signal acquisition system with properties ofhigh sensitivity, wide band and multi-channel simultaneous measurement. In addition, for theacquisition of low frequency signals, it takes a long time to complete the acquisition, and thenatural noise and artificial noise are inevitable in the process of collection. These require theacquisition system with properties of low noise and low power consumption to meet thedemand of long time field work.This paper is as a part of the development of magnetotelluric detecting instrument in the“Wireless Electromagnetism （WEM）” project which is jointly proposed by ChinaShipbuilding Industry Corporation, China Seismological Bureau and Chinese Academy ofScience, designs a low noise and low power consumption printed circuit board of dataacquisition and processing with properties of high sensitivity, wide band and multi-channel.The paper first briefly introduces the design approach of low noise and low powerconsumption, the principle of Σ Δ A/D conversion technology and the hardware designand software design precept of magnetotelluric detecting instrument. And then detailedlyexpounds the design process of the data acquisition and processing circuit which is designedbased on the high-precision and high-resolution Σ Δ A/D convertor ADS1278. The circuitsinclude the input protection and signal attenuation circuit, the low-pass filter circuit, theprogrammable amplifier circuit, the voltage level conversion circuit, the A/D sampling circuit,the digital isolation circuit and the power supply circuit. Finally, the paper presents the systemperformance testing method of magnetotelluric detecting instrument, the test results show thatthe technical indicators are meeting the design requirements.