Electronic filters are used in every biomagnetic measurement, whether intentionally or not. The inherent limitations of field sensors and amplifiers impose an upper limit on the frequency of their output signal, and in some cases a lower limit as well. In most applications the signal bandwidth is intentionally further restricted to avoid noise at frequencies that are quite different from those of the signal of interest. Electronic filtering is a subject that has been studied by electrical and communications engineers for many decades, and the behavior of common types of filters is well understood. In this chapter we shall outline the essential characteristics of analog filters and point out the inherent problems of filtering which can arise by an improper choice of a filter. This introduction is not intended as a guide for the design of electronic filters, but should serve the practical function of pointing out how the most popular types can be applied to best advantage.
KeywordsAmplitude Response Group Delay Stop Band Comb Filter Notch Frequency
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