AFE4490 Pulse Oximeter SPO2 Calculation

Hello,

Thank you for contacting us.

See link below for background information on PPG measurements and how to estimate SpO2 from PPG data.

http://www.ti.com/lit/ug/tidu124/tidu124.pdf

Ambient phases refers to external light that leaks into the receiver. The voltage measured at the ADC contains both the pleth component and the component resulting from the ambient light leakage. During high ambient light condition, measuring the ambient between LED phases and digitally subtracting the ambient component, the pleth signal can be extracted. Refer to Section 7 of the AFE4490 datasheet for a more elaborate explanation.

The timer module registers are tightly coupled to the sampling frequency or pulse repetition frequency i.e, in other words, when you want to change the sampling frequency, you may have to change all the timer module registers. For the device, the PRF is configured as end of pulse repetition period (reg addr: 0x1D). Refer to section 7.3 of the AFE4490 datasheet on the timer module and Table 2 for an example of the timing edges set for 500Hz PRF.

Hi again,

Thanks for your interesting but i could get any answer for my all questions.

I wat to learn which register will give the value of Red DC, Ir DC, Red AC, IR AC. I looked to the datasheets again and again but can not found them.

Also what is the K value for calculation which referst to Equation : %SpO2= K * R (K means Calibration constant)

I looked table 2 and section 7 but could not understand how will i calculate timing values for 200 Hz sampling frequency.

Finally i noticed that the init value for registers at the source code and Labview GUI are not the same. Which one I have to take reference value for my code.

Red and IR LEDs DC and AC values need to be calculated from the PPG data. The AFE does not provide those values directly. The AC component is the peak to peak of the PPG data and the DC component is the average of the PPG data. (refer to the article in the link that I sent out earlier)

The calibration constant  are derived empirically during in-vivo calibration by correlating the ratio calculated by the pulse oximeter against SaO₂ from arterial blood samples by an in vitro oximeter for a large group of subjects.

To calculate the timing values, you can use the AFE4490SPO2EVM GUI in simulation mode. In the Timing Controls tab under Device Configuration, set the Pulse Repetition Frequency to 200Hz and click Set. The timing values are automatically calculated for the specified frequency.

Use the init values from the LabVIEW GUI.

i am not able to open the link can you please help me on this.