An impedance mismatching compensation based CM noise rejection method for capsule endoscope system

In this paper, common-mode noise (CMN) rejection method is presented. As is well known, CMN causes critical performance degradation in the wireless capsule endoscope (CE) system. The differential operation, a typical method for CMN rejection, can effectively remove CMN by subtracting two signals received by patch sensors. However, it cannot perfectly remove CMN when there is impedance mismatching between the two patch sensors. In order to overcome the impedance mismatching problem, therefore, we propose an impedance ratio estimation method and a mismatching compensation method. In the proposed method, the impedance ratio can be estimated by dividing two received signals. Then, we can compensate the impedance mismatching by weighting one of the received signals considering the estimated ratio, using analog amplifier and digital-to-analog converter (DAC). Also, we apply Lloyd-Max quantization algorithm for optimization of DAC output levels. Simulation results verified that the proposed method can effectively remove CMN even when there is impedance mismatching, thus it guarantees the superior quality of received signal.