The signal of spo2 is unstabled using afe4400 and njl5501

hello:

     Sorry to bother you .

     I designed two boards according to TI"s  blood oxygen saturation. one board uses  transmission type sensor,while another uses  reflective sensor. The Schematic diagram and  program of the two boards are the same.

    Everytime I try to collect waveform by the board which use transmission type sensor, I can collect signal easily. The signal just like :

But when I try to collect waveform by the board which use reflective sensor, sometimes I can get the signal ,but more often than, I can't  get  the  signal. the signal just like:

The above three figure are got by the same configuration .So I think  njl 5501 is too sensitive   causing the  unstabled signal of spo2.  The strength of the finger and The distance of the finger with  sensor have an impact on the signal. But I don't know  how  to solve .Hope can get more information.  Thank you very  much .

                             xielinlin

                            2013.3.30