A typical Electroencephalography (EEG) acquisition system must include a lowpass filter (LPF) unit. According to the clinical applications, EEG signal have a conventional frequency range of 0.1-Hz to 70-Hz. The cutoff frequency for an LPF in EEG acquisition system should be in the same range.
Some analog, even more to say passive LPF input filtering is usually used to suppress possible high frequency interference, especially rectification (amplitude demodulation) of high frequency pulses - e.g. I guess everyone experienced effect of mobile phone causing audible interference in near sound equipment when responding to SMS or call.
If you are talking about the digitalization task, the filter prior the sampler is analog because you are handling an analog signal. You can use digital filter only after digitalization of course.
Generally speaking, an analog filter could have better characteristcs in terms of frequency response, but it is more sensible to temperatures for example and needs more effort to design it. Of course it involves electronics design skills and if you want to change the characteristics you have to change the components or fine tuning variable resistors, capcitors and so on.
With a digital filter you could design the filter (filter type, order, cut-off frequency and so on) simply by writing a software for example, because you are processing the EEG after sampling and digitalization, and there is need of signal processing skills. It is not depends directly on the external parameters such as temperature and it is programmable.
dear colleagues Abbas Thajeel Alsahlanee
IN addition to the previous answer i would like to address some points. The advantages of digital filter over analog filter come from the advantage of digital circuits over analog circuits such as: more robust to white noise and temperature changes. Moreover, digital filter can implemented by using software and it
doesn't need any extra component such as power supply, op amp and transistors. However, Digital filter is sensitive to clock frequency. so, it needs accurate clock signal generator.
Best regards
Dears
This article is about the digital filter, feel free to contact me
Conference Paper Convergence Rate For Low-Pass Infinite Impulse Response Digital Filter
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