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Abstract

A baseline wander filter (BWF) with linear phase response for an ECG signal measuring system includes two cascaded box car FIR filters to estimate the baseline wander. The cascaded box car filters form, in effect, a triangular FIR filter that generates a weighted sliding window average of the input samples to serve as the estimated baseline wander. The estimated baseline wander samples generated by the BWF are then subtracted from the corresponding input ECG samples. The boxcar filters can be designed to avoid multiplication by adding the samples and dividing the resulting sum by the number of coefficients. By choosing the number of coefficients as a power of two, binary division can be performed by shifting the bits of the resulting sum to the right. Accordingly, the present invention avoids the relatively large computational load of conventional FIR filter-based systems. The BWF can be implemented in software in which each boxcar filter uses an accumulator data structure that generates the sum of the previous N samples. When adding the next sample to the sum, it subtracts the Nth previous sample. The output sample of the BWF is equal to the value in the sum buffer, appropriately shifted.

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First Claim