The filter circuit design and simulation of array induction logging tools

Array induction logging tools (AILT) is a new generation electric logging instrument with the advantages of high-precision, high-resolution and high-efficiency compared with the conventional resistivity logging instrument. The signal of the amplitude using the AILT is in the level of microvolt because it detects the stratum conductivity based on the principle of electromagnetic induction. In such condition as high-temperature and high-pressure, the small-signal is always drowned by noise, so the key of suppressing the noise in AILT are the preamplifier circuit and bandpass filter circuit. To decrease the noise from the preamplifier, we propose the method of bandpass filter based on the principle of differential amplifier and second band active filter with limitless gain and multipath negative feedback and simulate and optimize the circuit parameters using the Pspice 10.5. The result of simulation show such that the center frequency relative error of band filter less than 3.9% less than the relative error of routine instrument 5% and the signal modulator circuit is feasible and conform the validity of the bandpass filter circuit.