Dear Sir/Madam,
I purchased AFE4490SPO2EVM and tested its SNR. I have questions about this AFE's SNR performance.
I was looking for the SNR measurements in the datasheet, and it seems that SNR was presented as noise-free bits in AFE4490. By using the formulas of the noise-free bits page 10, it seems AFE4490 could reach 101.3dB or even 104.9dB, with 14.1 or 14.7 noise-free bits respectively. However, I could only get 98-100dB with AFE4490SPO2EVM (with 0.1-5Hz bandpass filter as the datasheet described). I am wondering where this difference comes from.
1. Were the measurements in the datasheet done with the DB9 finger clip sensor or some other on-board optics? That could explain the SNR difference.
2. What is the SNR definition here? Was it defined as the full channel SNR (both Tx and Rx) or the receiver channel only SNR?
Best,
I-Chun