ADPD4000 - HHb & HBO2 measurement


We are working on embedded NIRS sensor using ADPD4000 (or 4100 for futur use).

We decide to split measure for each LED wavelength: 

 - 550nm for heart rate measurement (HR, HR variability)

 - 660nm for HbO2, spO2 and breathing activity measures

 - 960nm for  HHb, spO2 and breathing activity measures

We are using ADPD4000Z eval board, we meet some difficulties concerning HHb and HBO2 measures.

Based on Beer-Lamber modifed law, we calculate Optical Density based on ΔOD(λ) = - Log(Io(λ) / Ii(λ)).

With ΔOD(λ) we can determinate ΔHbO2(λ) and ΔHHb(λ), thanks to molar attenuation coefficients, DPF and distance between LEDs and photodiode.

Few question about that:

 1 - How can we manage angular displacement of LEDs and photodiode ? On a first approach, we doesn't take this in consideration due to diffusion on tissue.

 2 - Do you have some experience about NIRS application ?

Thanks for your support,


  • 0
    •  Analog Employees 
    on May 10, 2021 6:56 PM

    Hi Benjamin,

    It sounds a very interesting project. What exactly do you plan to measure with this sensor, optical density or the SpO2? Where will you make the measurement?

    The Beer-Lamber Law is applicable where the light is defused through the tissue before detected by the detector. In most of the reflective HR/HRV and SpO2 application, only a small portion of the detected photons are from deep tissues  and doesn't meet the requirement by the Beer-Lamber Law.   

    Please refer comments below to your questions:

    1. Angular displacement of LEDs and photodiode (PD)

    It depends on the spacing between LEDs and PD(s). If the LED and PD are > 1 cm away from each other, probably there is no need for angular displacement. However, if they are close to each other, such as PD and green LED in the HR/HRV applications, a septum is needed to block the direct path from the LED to PD, as shown in the drawing below.


    2. NIRS application

    We provide support to our customers on HR/HRV and/or SpO2 applications. If your interest is NIRS application for optical density, we need to know more details of your application and discuss where we can support. We do provide support for applications where the light is heavily attenuated and a reference is needed, such as the fluorescence measurement.


    Glen B.