Other Parts Discussed in Thread: ADS1299
Hi,
I came across this thread regarding the anti-aliasing filter design for delta-sigma ADCs. It suggests to choose the differential filter’s 3-dB cutoff frequency, fC-DIFF, such that it is 10x to 100x lower compared to fMOD.
In the PDK, clearly the board is equipped with anti aliasing filters of 6.8kHz.
fMOD of ADS1299 = fCLK/2 = 2.048MHz/2 = 1.024MHz
Thus the range for the anti-aliasing filter is given by:
10.24kHz < fLP <102.4kHz
Here are my questions :
- Why the value for low-pass filter was chosen to be lower than the suggested minimum value in the guideline?
- Currently I am ahering below guidelines when designing the anti-aliasing filter, please let me know if I am missing something ?
-
fLP >> sampling rate configuration of ADS1299
- fLP shall be at least 10 times the bandwidth of interest
- fLP shall be higher than the 3-dB frequency of the ADS1299 configuration(from Table 1-4)
-
We are interested in detecting R-peaks of fetal QRSs reliably by choosing these values.
Thanks,