The Research And Design Of Low Noise Pre-amplifier Of TEM Receiver

Time domain electromagnetic method (TEM) has been widely used in not only the exploration of mineral resources such as metal, oil and geothermal energy and so on, but also engineering, bedrock and searching for groundwater, as well as disaster prevention. In addition to prospecting, TEM has important using value in environmental aspects such as regional agro-ecological, investigation of water salinity and so forth. Particularly, searching for water with AEM will have profound social meaning to national conditions of shortage of water resources and uneven distribution.Low-noise preamplifier has been studied in detail in this paper. It focuses on analyzing noise model of single operational amplifier circuit and dual-differential operational amplifier circuit, and single op-amp circuit is simulated and tested in order to grasp the impact of each component on the circuit performance. Thereby dual-differential operational amplifier circuit is designed. After simulation, the actual welding circuit is debugged, and finally PCB is made.The work of the full text is summarized as follows:1.Study the basic principles of the transient electromagnetic method and its signal characteristics. Transmitter sends first field to the underground by using non-grounding line (the loop, magnetic dipole source), and in the first field interval, the receiver measures time-varying induced electromagnetic field (second field) which is generated by the underground media, thereby detecting the location of underground non-uniform body, and estimating its size and conductive properties. Transient electromagnetic signal has large dynamic range and broadband. When the first field and second field exist at the same time, early signal of the first field has large amplitude and rapid attenuation, terminal signal of the second field has small amplitude and slowly decay.2.Analyze noise model of single operational amplifier circuit and dual-differential operational amplifier circuit, and provide basis for theoretical calculations of noise. In regard to dual-differential operational amplifier circuit, total output noise consists of six items: the amplified voltage noise generated by the two in-phase terminal of operational amplifiers, the amplified voltage noise generated by the current noise of in-phase terminal of operational amplifiers flowing through the source impedance, the amplified source impedance thermal noise, the amplified gain resistor thermal noise, feedback resistor thermal noise, and voltage noise generated by current noise of inverse terminal of operational amplifier flowing through the feedback resistor.3.Simulate and test single operational amplifier circuit. Research the impact of each component on the performance of the circuit, in order to provide the basis for further circuit design. As for the same circuit, when the magnitude of the input signal is different, its bandwidth is different. Filter capacitor can not only smooth the gain changes, but also reduce the bandwidth. Compensation capacitor has the role of limiting bandwidth.4 . Dual-differential operational amplifier circuit is made of two parallel operational amplifier. High input impedance is its character. Differential-mode input signal and common-mode input signal are sent into the same phase side of the two operational amplifier. Therefore, the differential input impedance is large. The balance and symmetry structure of the circuit make the two common-mode amplifier gain, offset and drift errors with the role of offsetting.5.The power of low-noise amplifier is based on a voltage regulator circuit made of L7908CV, L7808CV device.