Oesophageal pressure (Pes) measurements are important in medical research and useful in clinical diagnosis. Measurements, however, are contaminated heavily by cardiac artifacts. The spectrum and waveform of the Pes signal is obtained from the oesophageal balloon. Adaptive finite impulse response (AFIR) filter and modified adaptive noise cancellation (MANC) methods are adopted to filter out cardiac beat interference. These results are compared. In the frequency domain, frequency variations and spectral overlap between the Pes components and cardiac beat signal components impact on the performance of the filter. From our experimental results on power strength, the fourth or higher harmonics did not have any significant effect on the filter performance. However, the second harmonics of these signals had a significant effect on the filtering result. Thus, in the design of AFIR filters, attention is needed to minimise these effects. In frequency analysis, these harmonics or overlapping frequencies do not affect MANC. MANC was the better method for eliminating cardiac beat artifact in Pes measurement. The dynamic compliance (Cdyn) was also used to evaluate the performance of MANC and AFIR. The standard deviation of Cdyn was less than 0.15 using MANC, compared with standard deviations as high as 0.57 for AFIR. We conclude that MANC performs better than AFIR.
In this paper, an innovative passive equalizer that is also able to filter common-mode noise is proposed, which is realized based on a via-conducted coplanar waveguide structure with resistive load (VCPW-R) formed on the ground plane. The proposed structure is low cost, compact and easily designed. Based on the analyses of the odd mode and even mode, a codesign flow is established, with which a set of design parameters are determined for 10 Gbps differential transmission and utilized in test-board fabrication. The effectiveness of the proposed structure is validated by the frequency-domain measurement result and time-domain simulation result of the test board.
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