| Oil is one of the most important energy of our modern society. Oil exploration workers find the oil reservoir within reflected sound waves, and record the time of which sound waves reflected back. Then process the data and construct the image of underground rock system by using computer. Geophone is responsible for receiving and processing reflection waves which are generated by man-made seismic. Traditional geophone is only a sensor, but modern geophone is composed of a sensor and an A/D converter. Within micro-technology they are integrated in a chip which is called digital seismograph. The transmission of digital signal has high reliability and informative in a digital seismograph, and weak signal can be preserved as much as possible, as well as noise would be reduced.The resolution of A/D converter has great effort to seismograph, so high resolution, good dynamic range and stable performance of A/D converters in seismic exploration are required which is difficult to a normal Nyquist A/D converter.ΣΔA/D converter is popular because of outstanding behavior in the low-frequency and high-precision implement. By means of high-rate sampling, one-bit quantization, integrator noise shaping technology and digital filters,ΣΔADC is able to get high resolution, so it is widely used in the new generation of seismograph, and the most of major manufacturers focus on this technique gradually.The subject is theoretical study and application implementation of the high-precision digital geophone system support in the Shandong Province Natural Science Foundation. High-precision A/D converter bases on front-end MEMS accelerometer analog sensor which integrated with an A/D converter on a chip to form a self-intellectual property rights of high-precision digital seismic detector. The main jobs in this subject are:1. Modeling and analysis ofΣΔmodulatorIn accordance with the signal parameter which output by MEMS sensors of seismic detection, using MATLAB and Simulink to simulateΣΔmodulator in system-level. The main features ofΣΔmodulator are over sampling and noise shaping. By mathematical and simulation analysis, we can learn first-orderΣΔmodulator is very difficult to achieve high accuracy, while high order and cascadeΣΔmodulator can achieve high resolution.2. Analysis of non-idealities of switched capacitorΣΔmodulatorThere are many non-ideal factors in actual circuit. You can not figure accurately the mathematical modeling, except analyze and simulate any possible phenomenon in the circuit lever, such as finite amplifier gain and component mismatch. These non-ideal factors will result in nonlinearities and degrade the SNR, a high-level modeling method based on MATLAB is presented which could guide the circuit design ofΣΔmodulator.3. Circuits design ofΣΔModulatorΣΔA/D converter is the cascade of an analog modulator and a digital filter. Modulator circuit consists of integrator, comparator, D flip-flops and feedback. The difficulty lies in selecting appropriate bandwidth and speed of opamp, choosing suitable parameters of integrator, and the circuit stability problems. In digital section, where the system clock generation, digital filtering and down-sample data take place by using FPGA. In this paper, the second orderΣΔmodulator circuits design is presented and the performance can meet the needs.4. Explore parameter optimization method of cascade and interpolative loopΣΔmodulatorHigh-order and single-loopΣΔmodulator suffers from instability problems and considerable performance degradation compared to an ideal modulator. An alternative to circumvent instabilities while obtaining high-order shaping can be found in the cascade and interpolative loopΣΔmodulator. The problem is the coefficients design which is combinatorial optimization problems. The scheme adopts Simulated Annealing Algorithm to design parameters. |
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