The AHA standard recommends usage of both analog and digital filter in ECG signal extraction. Why are the two set of filters required? Particularly, what is the role of a digital filter?
Hi Sudhanshu Janwadkar ,
if the amplitude of the analog signal exceeds the input range of the analog-to-digital-converter (ADC) due to noise and coupling to the power lines (16.6/50/60 Hz) or if its spectrum exceeds the limit set by the Nyquist theorem, the ADC would deliver artefacts which cannot be removed in the following signal chain. Therefore, in front of the ADC usually an analog filter is needed. Disadvantages of analog filters: In many cases, resistors and capacitors with narrow tolerances (and high prices) have to be used; increasing complexity takes increasing space ("real estate") on the PCB.
Even in the absence of artefacts, the resulting digital signal might still contain unwanted components. Removing these often requires rather complex filters. Those filters, implemented as digital filters, can take some computing power but the advantages of digital filters are that their characteristics are exactly reproducible, and that changes are just a matter of software.
Jagtap S.K., Uplane M.D. (2013) Digital Filter Approach for ECG in Signal Processing. In: Kumar M. A., R. S., Kumar T. (eds) Proceedings of International Conference on Advances in Computing. Advances in Intelligent Systems and Computing, vol 174. Springer, New Delhi
DOI: https://doi.org/10.1007/978-81-322-0740-5_131
I hope you find your answer here.
The analog filter filters the primary signal, while the digital filter filters the final signal, and the best type of digital filters is the IIR because it contains a feedback that helps filter the signals better. You can check out this research paper explaining the importance of digital filter for signal processing applications.
https://www.researchgate.net/publication/353571111_Convergence_Rate_For_Low-Pass_Infinite_Impulse_Response_Digital_Filter