Song Sixuan, Chen Kai
School of Geophysics and Information Technology, China University of Geosciences, Beijing 100083, China.
Key Laboratory of Intraplate Volcanoes and Earthquakes, Ministry of Education, Beijing 100083, China.
Sensors (Basel). 2024 Mar 17;24(6):1920. doi: 10.3390/s24061920.
The seafloor E-field signal is extremely weak and difficult to measured, even with a high signal-to-noise ratio. The preamplifier for electrodes is a key technology for ocean-bottom electromagnetic receivers. In this study, a chopper amplifier was proposed and developed to measure the seafloor E-field signal in the nanovolt to millivolt range at significantly low frequencies. It included a modulator, transformer, AC amplifier, high-impedance (hi-Z) module, demodulator, low-pass filter, and chopper clock generator. The injected charge in complementary metal-oxide semiconductor (CMOS) switches that form the modulator is the main source of 1/ noise. Combined with the principles of peak filtering and dead bands, a hi-Z module was designed to effectively reduce low-frequency noise. The chopper amplifier achieved an ultralow voltage noise of 0.6 nV/rt (Hz) at 1 Hz and 1.2 nV/rt (Hz) at 0.001 Hz. The corner frequency was less than 100 mHz, and there were few 1/ noises in the effective observation frequency band used for detecting electric fields. Each component is described with relevant tradeoffs that realize low noise in the low-frequency range. The amplifier was compact, measuring Ø 68 mm × H 12 mm, and had a low power consumption of approximately 23 mW (two channels). The fixed gain was 1500 with an input voltage range of 2.7 mV. The chopper amplifiers demonstrated stable performance in offshore geophysical prospecting applications.
海底电场信号极其微弱，即便具有高信噪比也很难测量。电极前置放大器是海底电磁接收器的一项关键技术。在本研究中，提出并开发了一种斩波放大器，用于在显著低频下测量纳伏至毫伏范围内的海底电场信号。它包括一个调制器、变压器、交流放大器、高阻抗（高阻）模块、解调器、低通滤波器和斩波时钟发生器。构成调制器的互补金属氧化物半导体（CMOS）开关中的注入电荷是1/f噪声的主要来源。结合峰值滤波和死区原理，设计了一个高阻模块以有效降低低频噪声。该斩波放大器在1Hz时实现了0.6nV/√Hz的超低电压噪声，在0.001Hz时为1.2nV/√Hz。转折频率小于100mHz，并且在用于检测电场的有效观测频段内几乎没有1/f噪声。描述了每个组件为在低频范围内实现低噪声所做的相关权衡。该放大器结构紧凑，尺寸为Ø68mm×H12mm，并且功耗低，约为23mW（两个通道）。固定增益为1500，输入电压范围为2.7mV。这些斩波放大器在海上地球物理勘探应用中表现出稳定的性能。
