海洋电磁信号超低噪声同步采集系统设计

Design of ultra-low noise synchronous acquisition system for marine electromagnetic signal

针对海洋电磁采集系统的低频超低噪声信号采集和高精度时钟同步,文中设计一种基于“ARM+FPGA”的海洋电磁信号低噪声同步采集系统(LNS-MEM)。针对低频微弱电场信号的采集需求,设计“低噪声斩波放大+低噪声A/D转换”的信号采集电路;针对电磁采集系统的高精度分布式同步需求,设计“GPS授时+高精度温度补偿时钟”的时钟同步方法。系统主控采用“低功耗ARM+FPGA”方案,低功耗ARM负责系统任务管理,FPGA实现多通道信号同步采集。最后,开展实验室和海洋环境测试。测试结果表明,电场前置放大通道为一个低通滤波通道,通带增益为61 dB,-3 dB上限截止频率约为100 Hz,电场通道本底噪声为3nV√Hz@1Hz,时钟同步误差小于1.5 ms/d,海洋CSEM勘探的有效探测范围可达7.5 km,可以满足海洋电磁探测的需求。

In allusion to the low-frequency ultra-low noise signal acquisition and high-precision clock synchronization of marine electromagnetic acquisition system,an"ARM+FPGA"based low noise synchronous acquisition system for marine electromagnetic signal(LNS-MEM)is designed.The signal acquisition circuit of"low-noise chopper amplification+low-noise A/D conversion"is designed to meet the acquisition demand of low-frequency weak electric field signals.According to the demand of high-precision distributed synchronization of electromagnetic acquisition system,the clock synchronization method of"GPS time service+high-precision temperature compensation clock"is designed.The scheme of"low power consumption ARM+FPGA"is applied to the main controller of the system,in which the low power ARM is responsible for the task management of the system,and the FPGA is used to realize the synchronous acquisition of multi-channel signals.Laboratory and marine environment tests were carried out.The testing results show that the electric field pre-amplification channel is a low-pass filtering channel,the passband gain is 61 dB,the upper cut-off frequency of-3 dB is about 100 Hz,and the background noise of the electric field channel is 3nV√Hz@1Hz,the clock synchronization error is less than 1.5 ms/d,and the effective detection range of marine CSEM exploration can reach 7.5 km,which can meet the needs of marine electromagnetic detection.