The detecting fetal heart sound plays an important role in monitoring fetal.The major frequency range of the fetal heart sound focus on 60

1

80 Hz.Before sampling the fetal heart sound

it is need to design filter circuit to percolate the syntonic of 50 Hz power frequency and the noise of the matrix.The filter fircuit uses chip OPA2277.A double-T frame trap filter which contains a positive feedback is designed percolate syntonic of power frequency.Base on Butterworth function a high-pass and a low-pass filter is designed to percolate the noise of matrix.Simulation of the frequency response characteristic by the software Multisim indicate that the filter could percolate the power frequency and the noise of matrix.