Hello everybody!
Need help!
We've founded a noise in signals, which lookes quite the same as quantization noise, but with extremely high amplitude. The picture below shows the original signal from ADS1292R without any filtering and transformation.
Then we tested all the parts of our device step-by-step and stated that problem is somewhere in ADS chip or SPI connection. Also we tried the internal test signals generator and result is absolutely the same.
As it's showed the noise in second channel is much stronger than in first and it's a stable behavior. Also the amplitude of test signals is changed as well as scale factor of ECG on the first picture, although the MATLAB scripts and other software wasn't changed.
And most interesting! This behavior is repeated on two devices with the same principial diagram, but absolutely different PCBs. So it cannot be a bug in the board.
We don't know khow long time ago it beginned, because usually filters "mask" this noise, thus don't know which actions or changes in design caused such a problem.
Does anybody observed something looking similiar as our situation? Any ideas what it could be?
Hope for your help!
Regards, Alex.
P.S. Principial diagrams are attached below
