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ADS1292: High-pass filter 3dB frequency, problem with 60601-2-47, frequency response test

user5198461
Prodigy 20 points
Part Number: ADS1292
Other Parts Discussed in Thread: ADS1298,

I am  currently developing medical holter with ADS1292IRSMT front end. I have problems with complying with "frequency response" test according to IEC 60601-2-47. The response to a 3mV 100ms rectangular pulse shall not show a baseline amplitude displacement more than 0,1mV and the slope sholud be less than 0,3mV/s. With fs=125Hz we achieved 0,8mV displacement and with fs=500Hz 2,1mV. From my calculations it looks like there is a high passs filter with 3dB frequency of 0.5Hz. In order to comply with IEC 60601-2-47 we should have a 3dB frequency at 0.05Hz not 0.5Hz.  I did not have problems with our other holters based on ADS1298. 

For me it looks like ADS1292 could comply requirements of 60601-2-27 (monitoring ECG) where they require 0,67Hz-40Hz badndwidth. For ambulatory recorders with diagnostics I cannot achieve small amplitude displacement after pulse.

What could cause a problem? 

Thank you in advance for your help. 

  • 0
    Prodigy 20 points

    Thank you for your support.
    We have already solved the problem. Our software department implemented 0.5dB 1st order IIR filter without reporting it. Hardware department had no idea about this filter and they assumed that this filter must be implemented inside ADS1292 (even if they cannot find any informations about it in datasheet) so they are trying to find it (maybe some parasitic capacitance, electrodes etc.) but from obvious reasons it was impossible as the filter was in the software.

  • 0 in reply to user5198461
    TI__Guru**** 168745 points
    Thanks for letting us know!