Widely deployed conventional moving-coil geophones lack the responses needed at low frequencies for detecting long-period seismic waves, and rely heavily on the A/D conversion chips for data acquisition. This work reports on a digital low-frequency geophone based on the PID force balancing technique and a single loop 4th-order sigma-delta modulator. The system is studied by Simulink modeling and is designed to satisfy demanding bandwidth and stability requirements. In addition, the hardware implementation adopts a readout interface for a geophone that consists of two parts: the analog part picks off the coil voltage while driving a control balancing force; and the digital part performs a real-time time DF integrators filtering in an FPGA for high-order noise shaping. The experimental results confirm the design concept of the proposed digital geophone. The balancing loop extends the low-frequency response of a commercial 4.5 Hz geophone down to 0.16 Hz. Within a 200 Hz bandwidth, the sigma-delta modulator achieves an equivalent acceleration noise floor of 4.3 ng/√Hz @ 1.0 Hz and shapes the in-band quantization noise to a level below other noises in the system. This investigation shows its potential to detect low-frequency seismic waves for efficient and high precision deep Earth exploration and hazard predictions.

部署广泛的常规动圈地震检波器缺乏低频检测长周期地震波所需的响应，并且严重依赖A / D转换芯片进行数据采集。这项工作报告了基于PID力平衡技术和单回路4阶sigma-delta调制器的数字低频检波器。该系统通过Simulink建模进行研究，旨在满足苛刻的带宽和稳定性要求。此外，硬件实现采用了地震检波器的读出接口，该接口包括两部分：模拟部分在驱动控制平衡力的同时拾取线圈电压；数字部分在FPGA中执行实时DF积分器滤波，以进行高阶噪声整形。实验结果证实了所提出的数字地震检波器的设计概念。平衡环路将商用4.5 Hz地震检波器的低频响应扩展至0.16 Hz。在200 Hz带宽内，sigma-delta调制器在1.0 Hz时达到4.3 ng /√Hz的等效加速本底，并将带内量化噪声整形为低于系统中其他噪声的水平。这项调查显示了其探测低频地震波的潜力，以进行高效，高精度的深层地球勘探和灾害预测。0 Hz，将带内量化噪声整形为低于系统中其他噪声的水平。这项调查显示了其探测低频地震波的潜力，以进行高效，高精度的深层地球勘探和灾害预测。0 Hz，将带内量化噪声整形为低于系统中其他噪声的水平。这项调查显示了其探测低频地震波的潜力，以进行高效，高精度的深层地球勘探和灾害预测。