My client want to evaluate the ADPD188GG for PPG solution.Do you have any ME portion design guide of ADI?
The primary mechanical consideration with your optical design using the ADPD188GG is going to be the thickness of the window placed above the module and the air gap between the window and the module. The graph below shows plots for ILP vs air gap for a couple different window thicknesses. ILP is what we call Internal Light Pollution and is a measure of light that is reflected directly back onto the PD from the LEDs without having first passed through tissue. This is expressed in CTR (current transfer ratio) in nA of PD current received per mA of LED current provided. The goal in the design is to keep the ILP to a level that is smaller than the smallest signal that you are trying to measure. As you can see in the plot, the thickness of the cover is not going to impact you as much as the air gap between the module and the cover. It also helps a great deal to use an anti-reflective coating, however, even without an AR coating the ILP is managed very well by the ADPD188 module design even at larger air gaps. It should be very easy in practice to keep the air gap to <1mm which will give very small amounts of reflected light from the cover.
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