A MODIFIED BESSEL FILTER FOR AMPLITUDE DEMODULATION OF RESPIRATORY ELECTROMYOGRAMS

We studied a device that is commonly used for amplitude demodulation o f respiratory muscle electromyograms (EMG). This device contains a rec tifier and a low-pass filter called a modified third-order Paynter fil ter. We characterized this filter and found that it has good transient characteristics that suit its task as an EMG demodulator, but it has poor high-frequency attenuation that passes interfering, higher freque ncy components to the output waveform. Therefore, we designed and cons tructed a new filter with transient characteristics that are comparabl e to those of the modified Paynter filter but with superior high-frequ ency attenuation. This new filter is a modified seventh-order Bessel f ilter. We also identified a simple technique to convert an existing mo dified Paynter filter back to an original Paynter filter. The original Paynter filter has a wider pass band than the modified Paynter filter but superior stop-band attenuation.