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ADPD 105 input configurations

Question asked by simonhart on Mar 16, 2017
Latest reply on Mar 20, 2017 by simonhart

Currently we are working on a project using the ADPD105 optical sensor to measure heart rate and SpO2 values. We designed our own board including the ADPD105 photometric front end combined with two external LEDs and two photodiodes.
Now we are trying to receive an accurate signal out of the front end, and thus some questions regarding the settings of ADPD105 arose. 

1.       If two channels are connected to each photodiode, we can detect differences in the absolute value between the channels for the same photodiode. We assumed if no individual setting is applied for the channels, the values should be the same. In some cases for instance channel 1 is constant zero and channel 2 shows an accurate signal, though they are connected to the same photodiode. So do we miss any special setting in normal operation mode?
2.       If only one single channel is connected to each photodiode (low photodiode currents), we expect to get no values out of the other channels. However, if we change the offset values of the unused channels, we are able to gather a signal on these channels. So is it mandatory to power down the unused channels?
3.       Nevertheless sometimes we are able to get a PPG signal, but in some cases the signal itself is very noisy. Are there any other recommendations to optimize the signal quality especially the AC amount of the pleth signal besides the mentioned methods in the datasheet?